Systems and methods for hybrid respiratory therapy

Abstract

A breathing assistance apparatus comprising a flow generator for providing a flow of gases to be delivered to a patient via a patient interface for respiratory therapy. The breathing assistance apparatus determining a target pressure for the flow of gases delivered to the patient and controlling the flow rate of the flow of gases output by the flow generator to deliver the flow of gases to the patient at substantially the target pressure.

Description

[0001] SYSTEMS AND METHODS FOR HYBRID RESPIRATORY THERAPY

[0002] FIELD OF THE DISCLOSURE

[0003] The present disclosure relates to methods and systems for providing a hybrid respiratory therapy to a patient. In particular, the present disclosure relates to controlling one or more operating parameters during use of a breathing assistance apparatus by a patient, to provide a hybrid respiratory therapy.

[0004] BACKGROUND

[0005] Breathing assistance apparatuses are used in various environments such as hospital, medical facility, residential care, or home environments to deliver a flow of gases to users or patients. A breathing assistance apparatus may be used to deliver supplementary oxygen or other gases with a flow of gases, and / or a humidification apparatus to deliver heated and humidified gases. A breathing assistance apparatus may allow adjustment and control over characteristics of the gases flow, including flow rate, pressure, and gases concentration.

[0006] SUMMARY

[0007] This international application claims priority to and incorporates by reference in its entirety U.S. Provisional Patent Application No. 63 / 734,437, filed 16 December 2024, and U.S. Provisional Patent Application No. 63 / 898,815, filed 14 October 2025.

[0008] In a first aspect, the present disclosure provides for a breathing assistance apparatus configured to provide a flow of gases to be delivered to a patient via a patient interface for respiratory therapy, comprising: a flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases; and a controller configured to: receive a user-specified therapy value, receive data indicative or representative of the flow rate of the flow of gases output by the flow generator from one or more flow sensors, receive data indicative or representative of a pressure of the flow of gases output by the flow generator from one or more pressure sensors, determine a target pressure for the flow of gases delivered to the patient via the patient interface, wherein the target pressure is based at least in part on: the user-specified therapy value, the data indicative or representative of the flow rate of the flow of gases output by the flow generator, and the data indicative or representative of the pressure of the flow of gases output by the flow generator, and control the flow rate of the flow of gases output by the flow generator to deliver the flow of gases to the patient via the patient interface at substantially the target pressure.

[0009] In a configuration, the flow generator is configured to be coupled to a supply conduit at a first end, and wherein the supply conduit is configured to convey the flow of gases output by the flow generator.

[0010] In a configuration, the supply conduit is configured to be coupled to the patient interface at a second end, and wherein the patient interface is configured to receive the flow of gases from the supply conduit and deliver the flow of gases to the patient. In a configuration, the patient interface is an unsealed patient interface.

[0011] In a configuration, the unsealed patient interface is a non-sealing nasal cannula.

[0012] In a configuration, the non-sealing nasal cannula is configured to cause an asymmetrical flow of gases at the patient's nares.

[0013] In a configuration, the target pressure is sufficient to keep the airways of the patient open when delivered to the airways of the patient. The target pressure may be between about 3cmH2O and about 8 cmH20.

[0014] In a configuration, the flow of gases delivered to the patient at substantially the target pressure further provides a level of leak flow out of the patient interface. The level of leak flow may be sufficient to substantially clear exhaled CO2 from the airways of the patient.

[0015] In a configuration, the non-sealing nasal cannula comprises a first prong and a second prong, and wherein at least one of the first prong and the second prong is sized to maintain a sufficient gap between the outer surface of the prong and a patient's skin to avoid sealing a gas path between the non-sealing nasal cannula and the patient.

[0016] In a configuration, the first prong has a larger inner cross-sectional area in a direction transverse to gases flow through the first prong than a corresponding inner cross-sectional area of the second prong in a direction transverse to gases flow through the second prong.

[0017] In a configuration, at least the first prong is made of an elastomeric material that enables the first prong to deform and set its shape in use in response to temperature and contact with the patient's naris.

[0018] In a configuration, the first prong is configured to deform and set its shape in use to substantially match the internal shape of the patient's naris.

[0019] In a configuration, the user-specified therapy value relates to a target for one or more parameters of the flow of gases at or about the patient interface.

[0020] In a configuration, the user-specified therapy value is a target average flow rate.

[0021] In a configuration, the target average flow rate is a target for an average of the leak flow rate of the flow of gases out of the patient interface over a set period of time.

[0022] In a configuration, the delivery of the flow of gases to the patient at substantially the target pressure maintains the flow of gases leaking from the patient interface at substantially the target average flow rate.

[0023] In a configuration, the controller is configured to implement a first control loop and a second control loop, and wherein the first control loop comprises a first method, and the second control loop comprises a second method, and wherein the second control loop takes as input one or more outputs from the first control loop. In a configuration, in the first control loop the controller is configured to determine and output the target pressure for the flow of gases delivered to the patient.

[0024] In a configuration, in the first control loop the controller is configured to determine the target pressure for the flow of gases delivered to the patient based at least in part on: the user-specified therapy value, the data indicative or representative of the flow rate of the flow of gases output by the flow generator, and the data indicative or representative of the pressure of the flow of gases output by the flow generator.

[0025] In a configuration, the data indicative or representative of the flow rate of the flow of gases output by the flow generator comprises at least data indicative or representative of the average flow rate of the flow of gases output by the flow generator.

[0026] In a configuration, the data indicative or representative of the pressure of the flow of gases output by the flow generator comprises at least data indicative or representative of the average pressure of the flow of gases output by the flow generator.

[0027] In a configuration, the flow generator comprises a blower, and the control of the flow generator to output the flow of gases at one or more flow rates by the controller comprises controlling the motor speed of the blower.

[0028] In a configuration, the motor speed of the blower is controlled to output the flow of gases at one or more flow rates to deliver the flow of gases to the patient via the patient interface at substantially the target pressure.

[0029] In a configuration, the breathing assistance apparatus or respiratory therapy system further comprises one or more motor speed sensors configured to provide data indicative or representative of the motor speed of the blower.

[0030] In a configuration, in the second control loop the controller is configured to determine a target motor speed for the blower based at least in part on the determined target pressure of the flow of gases delivered to the patient.

[0031] In a configuration, the second control loop is configured to determine the target motor speed for the blower based further on data indicative or representative of the motor speed of the blower.

[0032] In a configuration, the second control loop is configured to determine the target motor speed for the blower based further on data indicative or representative of the pressure of the flow of gases delivered to the patient.

[0033] In a configuration, the data indicative or representative of the pressure of the flow of gases delivered to the patient comprises at least data indicative or representative of the average pressure of the flow of gases delivered to the patient.

[0034] In a configuration, the data indicative or representative of the pressure of the flow of gases delivered to the patient is an estimation of the pressure of the flow of gases delivered to the patient. In a configuration, the controller is configured to determine the target motor speed for the blower using a proportional-integral-derivative controller which takes as input at least: the determined target pressure of the flow of gases delivered to the patient, the data indicative or representative of the motor speed of the blower, and the data indicative or representative of the pressure of the flow of gases delivered to the patient.

[0035] In a configuration, the controller is configured to determine the target motor speed for the blower using a non-linear model which takes as input at least: the determined target pressure of the flow of gases delivered to the patient, the data indicative or representative of the motor speed of the blower, and the data indicative or representative of the pressure of the flow of gases delivered to the patient.

[0036] In a configuration, the non-linear model represents a relationship between the target pressure of the flow of gases delivered to the patient and the measured data indicative or representative of the pressure of the flow of gases delivered to the patient.

[0037] In a configuration, the controller is configured to control the motor speed of the blower based on the target motor speed.

[0038] In a configuration, the controller is configured to control the motor speed of the blower to meet the target motor speed.

[0039] In a configuration, the controller is configured to estimate the pressure of the flow of gases delivered to the patient based at least in part on: the data indicative or representative of the pressure of the flow of gases output by the flow generator, the data indicative or representative of the flow rate of the flow of gases output by the flow generator, and one or more flow resistance constants.

[0040] In a configuration, the one or more flow resistance constants are based on at least the patient interface.

[0041] In a configuration, the one or more flow resistance constants are user-specified.

[0042] In a configuration, the breathing assistance apparatus further comprises a housing, and wherein the flow generator is located within the breathing assistance apparatus housing.

[0043] In a configuration, the breathing assistance apparatus further comprises the one or more flow sensors, and wherein the one or more flow sensors are located within the breathing assistance apparatus housing.

[0044] In a configuration, the one or more flow sensors are positioned at an outlet of the flow generator.

[0045] In a configuration, the one or more flow sensors comprise ultrasonic transducers.

[0046] In a configuration, the breathing assistance apparatus further comprises the one or more pressure sensors, and wherein the one or more pressure sensors are located within the breathing assistance apparatus housing.

[0047] In a configuration, the one or more pressure sensors are positioned at an outlet of the flow generator. In a configuration, the breathing assistance apparatus further comprises a user interface comprising a display and one or more input devices.

[0048] In a configuration, the display is configured to display one or more parameters of the flow of gases.

[0049] In a configuration, the one or more parameters of the flow of gases comprise one or more of: the flow rate of the flow of gases output by the flow generator, and the pressure of the flow of gases delivered to the patient.

[0050] In a configuration, the one or more input devices are configured to receive input from a user, wherein the input from the user comprises at least a user-specified therapy value.

[0051] In a configuration, the breathing assistance apparatus further comprises a humidifier configured to heat and humidify the flow of gases output by the flow generator.

[0052] In a configuration, the target pressure is a target minimum pressure for the flow of gases delivered to the patient via the patient interface.

[0053] In a configuration, the controller is configured to determine the target flow rate for the blower based at least in part on the determined target minimum pressure of the flow of gases delivered to the patient, and to control the flow generator to output the flow of gases at the target flow rate to deliver the flow of gases to the patient via the patient interface at or above the target minimum pressure.

[0054] In a configuration, the controller is configured to determine a target flow rate for the blower based at least in part on the determined target pressure of the flow of gases delivered to the patient, and a set minimum flow rate.

[0055] In a configuration, the controller is configured to control the flow generator to output the flow of gases at the target flow rate to deliver the flow of gases to the patient via the patient interface at or above the target pressure.

[0056] In a second aspect, the present disclosure provides for a respiratory therapy system for delivering a flow of gases to a patient for respiratory therapy, comprising: a breathing assistance apparatus comprising at least a flow generator, the flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases; a supply conduit coupled at a first end to the flow generator and configured to convey the flow of gases output by the flow generator; a patient interface coupled to a second end of the supply conduit and configured to receive the flow of gases from the supply conduit and deliver the flow of gases to the patient; and a controller configured to: receive a user-specified therapy value, receive data indicative or representative of the flow rate of the flow of gases output by the flow generator from one or more flow sensors, receive data indicative or representative of the pressure of the flow of gases output by the flow generator from one or more pressure sensors, determine a target pressure for the flow of gases delivered to the patient, wherein the target pressure is based at least in part on: the user-specified therapy value, the data indicative or representative of the flow rate of the flow of gases output by the flow generator, and the data indicative or representative of the pressure of the flow of gases output by the flow generator, and control the flow rate of the flow of gases output by the flow generator to deliver the flow of gases to the patient at substantially the target pressure.

[0057] In a third aspect, the present disclosure provides for a breathing assistance apparatus configured to provide a flow of gases to be delivered to a patient via a patient interface for respiratory therapy, comprising: a flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases; and a controller configured to: receive a user-specified therapy value, receive data indicative or representative of the flow rate of the flow of gases output by the flow generator from one or more flow sensors, receive data indicative or representative of a pressure of the flow of gases output by the flow generator from one or more pressure sensors, determine a target pressure for the flow of gases delivered to the patient via the patient interface, wherein the target pressure is based at least in part on: the user-specified therapy value, the data indicative or representative of the flow rate of the flow of gases output by the flow generator, the data indicative or representative of the pressure of the flow of gases output by the flow generator, and determine a target flow rate for the blower based at least in part on the determined target pressure of the flow of gases delivered to the patient, and a set minimum flow rate, and control the flow generator to output the flow of gases at the target flow rate to deliver the flow of gases to the patient via the patient interface at or above the target pressure.

[0058] The second aspect and the third aspect may comprise any one or more of the features of the first aspect described above.

[0059] In a fourth aspect, the present disclosure provides for a respiratory therapy system for delivering a flow of gases to a patient for respiratory therapy, comprising: a breathing assistance apparatus comprising at least a flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases; a supply conduit coupled at a first end to the flow generator and configured to convey the flow of gases output by the flow generator; a patient interface coupled to a second end of the supply conduit and configured to receive the flow of gases from the supply conduit and deliver the flow of gases to the patient, wherein the patient interface is a non-sealing nasal cannula configured to cause an asymmetrical flow of gases at the patient's nares; and a controller configured to: determine a target pressure for the flow of gases delivered to the patient via the patient interface, and control the flow rate of the flow of gases output by the flow generator to deliver and maintain the pressure of the flow of gases delivered to the patient at substantially the target pressure.

[0060] In a configuration, the controller is further configured to: receive a user-specified therapy value, receive data indicative or representative of the flow rate of the flow of gases output by the flow generator from one or more flow sensors, and receive data indicative or representative of the pressure of the flow of gases output by the flow generator from one or more pressure sensors. In a configuration, the controller is configured to determine the target pressure based at least in part on: the user-specified therapy value, the data indicative or representative of the flow rate of the flow of gases output by the flow generator, and the data indicative or representative of the pressure of the flow of gases output by the flow generator.

[0061] The fourth aspect may comprise any one or more of the features of the first aspect, or the second aspect, or the third aspect described above.

[0062] In a fifth aspect, the present disclosure provides for a breathing assistance apparatus configured to provide a flow of gases to be delivered to a patient via a patient interface for respiratory therapy, wherein the patient interface is a non-sealing nasal cannula configured to cause an asymmetrical flow of gases at the patient's nares, and the breathing assistance apparatus comprising: a flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases; and a controller configured to: determine a target pressure for the flow of gases delivered to the patient via the patient interface, and control the flow rate of the flow of gases output by the flow generator to deliver and maintain the pressure of the flow of gases delivered to the patient at substantially the target pressure.

[0063] In a sixth aspect, the present disclosure provides for a method for controlling the pressure of a flow of gases delivered to a patient for respiratory therapy, the method comprising: controlling a flow generator to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases, and wherein the flow of gases output by the flow generator is configured to be delivered to the patient via a patient interface, wherein the patient interface is a non-sealing nasal cannula configured to cause an asymmetrical flow of gases at the patient's nares; determining a target pressure for the flow of gases delivered to the patient via the patient interface, and controlling the flow rate of the flow of gases output by the flow generator to deliver and maintain the pressure of the flow of gases delivered to the patient at substantially the target pressure.

[0064] The fifth aspect and the sixth aspect may comprise any one or more of the features of the first aspect, the second aspect, the third aspect, or the fourth aspect described above.

[0065] In a seventh aspect, the present disclosure provides for a respiratory therapy system for delivering a flow of gases to a patient for respiratory therapy, comprising: a breathing assistance apparatus comprising at least a flow generator, the flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases; a supply conduit coupled at a first end to the flow generator and configured to convey the flow of gases output by the flow generator; a patient interface coupled to a second end of the supply conduit and configured to receive the flow of gases from the supply conduit and deliver the flow of gases to the patient; and a controller configured to: receive a user-specified therapy value, receive data indicative or representative of the flow rate of the flow of gases output by the flow generator from one or more flow sensors, receive data indicative or representative of a pressure of the flow of gases output by the flow generator from one or more pressure sensors, determine a target minimum pressure for the flow of gases delivered to the patient via the patient interface, wherein the target minimum pressure is based at least in part on: the user-specified therapy value, the data indicative or representative of the flow rate of the flow of gases output by the flow generator, the data indicative or representative of the pressure of the flow of gases output by the flow generator, and determine a target flow rate for the blower based at least in part on the determined target minimum pressure of the flow of gases delivered to the patient, and control the flow generator to output the flow of gases at the target flow rate to deliver the flow of gases to the patient via the patient interface at or above the target minimum pressure.

[0066] In an eighth aspect, the present disclosure provides for a breathing assistance apparatus configured to provide a flow of gases to be delivered to a patient via a patient interface for respiratory therapy, comprising: a flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases; and a controller configured to: receive a user-specified therapy value, receive data indicative or representative of the flow rate of the flow of gases output by the flow generator from one or more flow sensors, receive data indicative or representative of a pressure of the flow of gases output by the flow generator from one or more pressure sensors, determine a target minimum pressure for the flow of gases delivered to the patient via the patient interface, wherein the target minimum pressure is based at least in part on: the user- specified therapy value, the data indicative or representative of the flow rate of the flow of gases output by the flow generator, the data indicative or representative of the pressure of the flow of gases output by the flow generator, and determine a target flow rate for the blower based at least in part on the determined target minimum pressure of the flow of gases delivered to the patient, and control the flow generator to output the flow of gases at the target flow rate to deliver the flow of gases to the patient via the patient interface at or above the target minimum pressure.

[0067] In a ninth aspect, the present disclosure provides for a method for controlling the pressure of a flow of gases delivered to a patient for respiratory therapy, the method comprising: controlling a flow generator to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases, and wherein the flow of gases output by the flow generator is configured to be delivered to the patient via a patient interface; receiving a user-specified therapy value, receiving data indicative or representative of the flow rate of the flow of gases output by the flow generator from one or more flow sensors, receiving data indicative or representative of a pressure of the flow of gases output by the flow generator from one or more pressure sensors, determining a target minimum pressure for the flow of gases delivered to the patient via the patient interface, wherein the target minimum pressure is based at least in part on: the user-specified therapy value, the data indicative or representative of the flow rate of the flow of gases output by the flow generator, the data indicative or representative of the pressure of the flow of gases output by the flow generator, and determining a target flow rate for the blower based at least in part on the determined target minimum pressure of the flow of gases delivered to the patient, and control the flow generator to output the flow of gases at the target flow rate to deliver the flow of gases to the patient via the patient interface at or above the target minimum pressure.

[0068] The seventh aspect, the eighth aspect, and the ninth aspect may comprise any one or more of the features of the first aspect, or second aspect, or third aspect described above.

[0069] In a tenth aspect, the present disclosure provides a breathing assistance apparatus configured to provide a flow of gases to be delivered to a patient via a patient interface for respiratory therapy, comprising: a flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases; and a controller configured to: receive a user-specified therapy value, receive data indicative or representative of the flow rate of the flow of gases output by the flow generator from one or more flow sensors, receive data indicative or representative of a pressure of the flow of gases output by the flow generator from one or more pressure sensors, determine a target pressure for the flow of gases delivered to the patient via the patient interface, wherein the target pressure is based at least in part on: the user-specified therapy value, the data indicative or representative of the flow rate of the flow of gases output by the flow generator, the data indicative or representative of the pressure of the flow of gases output by the flow generator, and determine a target flow rate for the blower based at least in part on the determined target pressure of the flow of gases delivered to the patient, and a set minimum flow rate, and control the flow generator to output the flow of gases at the target flow rate to deliver the flow of gases to the patient via the patient interface at or above the target pressure.

[0070] In an eleventh aspect, the present disclosure provides for a breathing assistance apparatus configured to provide a flow of gases to be delivered to a patient via a patient interface for respiratory therapy, comprising: a flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases; and a controller configured to: receive a user-specified therapy value, receive data indicative or representative of the flow rate of the flow of gases output by the flow generator from one or more flow sensors, receive data indicative or representative of a pressure of the flow of gases output by the flow generator from one or more pressure sensors, determine a target pressure for the flow of gases delivered to the patient via the patient interface, wherein the target pressure is based at least in part on: the user-specified therapy value, the data indicative or representative of the flow rate of the flow of gases output by the flow generator, the data indicative or representative of the pressure of the flow of gases output by the flow generator, and determine a target flow rate for the blower based at least in part on the determined target pressure of the flow of gases delivered to the patient, and a set minimum flow rate, and control the flow generator to output the flow of gases at the target flow rate to deliver the flow of gases to the patient via the patient interface at or above the target pressure.

[0071] In a twelfth aspect, the present disclosure provides for a method for controlling the pressure of a flow of gases delivered to a patient for respiratory therapy, the method comprising: controlling a flow generator to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases, and wherein the flow of gases output by the flow generator is configured to be delivered to the patient via a patient interface; receiving a user-specified therapy value, receiving data indicative or representative of the flow rate of the flow of gases output by the flow generator from one or more flow sensors, receiving data indicative or representative of a pressure of the flow of gases output by the flow generator from one or more pressure sensors, determining a target pressure for the flow of gases delivered to the patient via the patient interface, wherein the target pressure is based at least in part on: the user-specified therapy value, the data indicative or representative of the flow rate of the flow of gases output by the flow generator, the data indicative or representative of the pressure of the flow of gases output by the flow generator, and determining a target flow rate for the blower based at least in part on the determined target pressure of the flow of gases delivered to the patient, and a set minimum flow rate, and controlling the flow generator to output the flow of gases at the target flow rate to deliver the flow of gases to the patient via the patient interface at or above the target pressure.

[0072] The tenth aspect, the eleventh aspect, and the twelfth aspect may comprise any one or more of the features of the first aspect, or second aspect, or third aspect described above.

[0073] In a thirteenth aspect, the present disclosure provides for a breathing assistance apparatus configured to provide a flow of gases to be delivered to a patient via a patient interface for respiratory therapy, comprising: a flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases; and a controller configured to: receive a minimum flow parameter representing a minimum allowable parameter relating to the flow of gases, receive data indicative or representative of a flow rate of the flow of gases, receive or estimate data indicative or representative of a pressure at or near the patient's nares, determine a target pressure for the flow of gases delivered to the patient, wherein the target pressure is based at least in part on: the data indicative or representative of the flow rate of the flow of gases, the data indicative or representative of the pressure at or near the patient's nares, and the minimum flow parameter, and control the flow rate of the flow of gases output by the flow generator to deliver the flow of gases to the patient at substantially the target pressure.

[0074] In a configuration, the minimum flow parameter is a floor flow rate representing a minimum allowable flow rate for the flow of gases.

[0075] In a configuration, the minimum flow parameter is a floor pressure representing a minimum allowable pressure for the flow of gases.

[0076] In a configuration, the controller is further configured to receive data indicative or representative of a pressure of the flow of gases output by the flow generator.

[0077] In a configuration, the controller is configured to estimate the data indicative or representative of a pressure at or near the patient's nares based at least in part on the data indicative or representative of the flow rate of the flow of gases, and the data indicative or representative of the pressure of the flow of gases output by the flow generator.

[0078] In a configuration, the controller is further configured to estimate a flow rate of the patient’s breathing based at least in part on the received or estimated data indicative or representative of a pressure at or near the patient’s nares and the data indicative or representative of the flow rate of the flow of gases.

[0079] In a configuration, the controller is configured to determine the target pressure at or near the patient's nares based on the estimated flow rate of the patient’s breathing.

[0080] In a configuration, the controller is further configured to determine a target flow rate for the flow of gases output by the flow generator based on the determined target pressure for the flow of gases delivered to the patient. In some configurations, the target flow rate is no lower than the floor flow rate.

[0081] In a configuration, the target pressure is sufficient to keep the airways of the patient open when delivered to the airways of the patient. The target pressure may be between about 3cmH2O and about 8 cmH20.

[0082] In a configuration, the flow of gases delivered to the patient at substantially the target pressure further provides a level of leak flow out of the patient interface. The level of leak flow may be sufficient to substantially clear exhaled CO2 from the airways of the patient.

[0083] In a configuration, the controller is further configured to receive or estimate one or more nasal resistance parameters, each nasal resistance parameter representative or indicative of the pneumatic resistance between one or both prongs of the nasal cannula and the one or both corresponding nares of the patient.

[0084] In a configuration, the controller is further configured to estimate the pressure of the flow of gases at or near the patient's nares based at least in part on: the data indicative or representative of the flow rate of the flow of gases, the data indicative or representative of the pressure of the flow of gases, and one or more estimated nasal resistance parameters.

[0085] In a configuration, the controller is further configured to receive or estimate one or more flow resistance constants, each representative or indicative of the pneumatic resistance of one or more portions of the flow path between an outlet of the flow generator and a patient interface.

[0086] In a configuration, the controller is further configured to estimate the pressure of the flow of gases at or near the patient's nares based at least in part on: the data indicative or representative of the flow rate of the flow of gases, the data indicative or representative of the pressure of the flow of gases, and the one or more flow resistance constants.

[0087] In a configuration, subsequent to the step of estimating the pressure of the flow of gases at or near the patient's nares, the controller is further configured to perform a comparison of an estimated nasal resistance parameter with an expected value. In a configuration, the controller is configured to perform the comparison after an inspiratory phase of the patient's breath cycle. In a configuration, the controller is configured to perform the comparison after providing a maximum or peak flow rate of the flow of gases.

[0088] In a configuration, the controller is further configured to revise the nasal resistance parameter based on a determined deviation between the estimated nasal resistance parameter and the expected value.

[0089] In a configuration, the controller is further configured to determine a deviation between the estimated nasal resistance parameter and the expected value based on a comparison of any one or more of a: flow rate, pressure, or a parameter of the flow of the patient’s breathing with an expected value indicating a deviation from the expected value.

[0090] In a configuration, the parameter of the flow of the patient’s breathing is a peak inspiratory flow rate, a minute ventilation, or a variance metric of the flow rate of the patient’s breathing.

[0091] In a configuration, the controller is further configured to update the estimated nasal resistance parameter based on the determined deviation based on a comparison.

[0092] In a configuration, the flow generator is configured to be coupled to a supply conduit at a first end, and wherein the supply conduit is configured to convey the flow of gases output by the flow generator.

[0093] In a configuration, the supply conduit is configured to be coupled to the patient interface at a second end, and wherein the patient interface is configured to receive the flow of gases from the supply conduit and deliver the flow of gases to the patient

[0094] In a configuration, the patient interface is an unsealed patient interface. In a configuration, the unsealed patient interface is a non-sealing nasal cannula. In a configuration, the non-sealing nasal cannula is configured to cause an asymmetrical flow of gases at or near the patient's nares.

[0095] In a configuration, the non-sealing nasal cannula comprises a first prong and a second prong, and wherein at least one of the first prong and the second prong is sized to maintain a sufficient gap between the outer surface of the prong and a patient's skin to avoid sealing a gas path between the non-sealing nasal cannula and the patient.

[0096] In a configuration, the first prong has a larger inner cross-sectional area in a direction transverse to gases flow through the first prong than a corresponding inner cross-sectional area of the second prong in a direction transverse to gases flow through the second prong.

[0097] In a configuration, at least the first prong is made of an elastomeric material that enables the first prong to deform and set its shape in use in response to temperature and contact with the patient's naris.

[0098] In a configuration, the first prong is configured to deform and set its shape in use to substantially match the internal shape of the patient's naris. In a configuration, the non-sealing nasal cannula is configured to cause a substantially symmetrical flow of gases at or near the patient's nares.

[0099] In a configuration, the non-sealing nasal cannula comprises a first prong and a second prong, and wherein the inner cross-sectional area in a direction transverse to gases flow through the first prong is substantially equal to the corresponding inner cross-sectional area of the second prong.

[0100] In a configuration, the minimum flow parameter is received as user input.

[0101] In a configuration, the data indicative or representative of the flow rate of the flow of gases is indicative or representative of an instantaneous flow rate of the flow of gases.

[0102] In a configuration, the data indicative or representative of the flow rate of the flow of gases is indicative or representative of an average flow rate of the flow of gases.

[0103] In a configuration, the data indicative or representative of the pressure of the flow of gases is indicative or representative of an instantaneous pressure of the flow of gases.

[0104] In a configuration, the data indicative or representative of the pressure of the flow of gases is indicative or representative of an average pressure of the flow of gases.

[0105] In a configuration, the data indicative or representative of the pressure at or near the patient's nares is an instantaneous pressure at or near the patient's nares.

[0106] In a configuration, the controller is configured to implement a first control loop and a second control loop, and wherein the first control loop comprises a first method, and the second control loop comprises a second method, and wherein the second control loop takes as input one or more outputs from the first control loop.

[0107] In a configuration, in the first control loop the controller is configured to determine and output the target pressure for the flow of gases delivered to the patient.

[0108] In a configuration, in the first control loop the controller is configured to determine the target pressure for the flow of gases delivered to the patient based at least in part on: the data indicative or representative of the flow rate of the flow of gases, the data indicative or representative of the pressure at or near the patient's nares, and the minimum flow parameter.

[0109] In a configuration, the second control loop is configured to determine a target flow rate for the flow of gases output by the flow generator.

[0110] In a configuration, the second control loop is configured to determine a target flow rate for the flow of gases output by the flow generator based at least in part on: the determined target pressure for the flow of gases delivered to the patient.

[0111] In a configuration, the flow generator comprises a blower, and the control of the flow rate of the flow of gases output by the flow generator comprises controlling the motor speed of the blower. In a configuration, the motor speed of the blower is controlled to output the flow of gases to deliver the flow of gases to the patient via the patient interface at substantially the target pressure.

[0112] In a configuration, the breathing assistance apparatus or respiratory therapy system further comprises one or more motor speed sensors configured to provide data indicative or representative of the motor speed of the blower.

[0113] In a configuration, the controller is configured to determine a target motor speed for the blower based at least in part on the determined target pressure of the flow of gases delivered to the patient.

[0114] In a configuration, the controller is configured to determine the target motor speed for the blower based further on data indicative or representative of the motor speed of the blower.

[0115] In a configuration, the controller is configured to determine the target motor speed for the blower based further on data indicative or representative of the pressure of the flow of gases delivered to the patient.

[0116] In a configuration, the breathing assistance apparatus further comprises one or more flow sensors, the one or more flow sensors configured to provide data indicative or representative of the flow rate of the flow of gases, and wherein the one or more flow sensors are located within the breathing assistance apparatus housing. In a configuration, the one or more flow sensors are positioned at an outlet of the flow generator. In a configuration, the one or more flow sensors comprise ultrasonic transducers.

[0117] In a configuration, the breathing assistance apparatus further comprises the one or more pressure sensors, wherein the one or more pressure sensors are configured to provide data indicative or representative of a pressure of the flow of gases and wherein the one or more pressure sensors are located within the breathing assistance apparatus housing. In a configuration, the one or more pressure sensors are positioned at an outlet of the flow generator.

[0118] In a configuration, the breathing assistance apparatus further comprises a user interface comprising a display and one or more input devices.

[0119] In a configuration, the display is configured to display one or more parameters of the flow of gases, and wherein the one or more parameters of the flow of gases comprise one or more of the flow rate of the flow of gases output by the flow generator, and the pressure of the flow of gases delivered to the patient.

[0120] In a configuration, the one or more input devices are configured to receive input from a user, wherein the input from the user comprises at least the minimum flow parameter.

[0121] In a configuration, the breathing assistance apparatus further comprises a humidifier configured to heat and humidify the flow of gases output by the flow generator.

[0122] In a fourteenth aspect, the present disclosure provides for a breathing assistance apparatus configured to provide a flow of gases to be delivered to a patient via a patient interface for respiratory therapy, comprising: a flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases; and a controller configured to: receive a floor flow rate representing a minimum allowable flow rate for the flow of gases, receive data indicative or representative of a flow rate of the flow of gases, receive or estimate data indicative or representative of a pressure at or near the patient's nares, determine a target pressure for the flow of gases delivered to the patient, wherein the target pressure is based at least in part on: the data indicative or representative of the flow rate of the flow of gases, the data indicative or representative of the pressure at or near the patient's nares, and the floor flow rate, and control the flow rate of the flow of gases output by the flow generator to deliver the flow of gases to the patient at substantially the target pressure.

[0123] In a configuration, the controller is further configured to receive data indicative or representative of a pressure of the flow of gases output by the flow generator.

[0124] In a configuration, the controller is configured to estimate the data indicative or representative of a pressure at or near the patient's nares based at least in part on the data indicative or representative of the flow rate of the flow of gases, and the data indicative or representative of the pressure of the flow of gases output by the flow generator.

[0125] In a configuration, the controller is further configured to estimate a flow rate of the patient’s breathing based at least in part on the received or estimated data indicative or representative of a pressure at or near the patient’s nares and the data indicative or representative of the flow rate of the flow of gases.

[0126] In a configuration, the controller is configured to determine the target pressure at or near the patient's nares based on the estimated flow rate of the patient’s breathing.

[0127] In a configuration, the controller is further configured to determine a target flow rate for the flow of gases output by the flow generator based on the determined target pressure for the flow of gases delivered to the patient, wherein the target flow rate is no lower than the floor flow rate.

[0128] The fourteenth aspect may comprise any one or more of the features of the thirteenth aspect described above.

[0129] In a fifteenth aspect, the present disclosure provides for a breathing assistance apparatus configured to provide a flow of gases to be delivered to a patient via a patient interface for respiratory therapy, comprising: a flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases; and a controller configured to: receive a floor flow rate representing a minimum allowable flow rate for the flow of gases, receive data indicative or representative of a flow rate of the flow of gases, receive data indicative or representative of a pressure of the flow of gases, estimate a pressure of the flow of gases at or near the patient's nares based at least in part on the data indicative or representative of the flow rate of the flow of gases and the data indicative or representative of the pressure of the flow of gases, estimate a flow rate of the patient’s breathing based at least in part on the estimated pressure of the flow of gases at or near the patient's nares and the data indicative or representative of the flow rate of the flow of gases, determine a target pressure for the flow of gases delivered to the patient based at least in part on the estimated flow rate of the patient’s breathing, determine a target flow rate for the flow of gases output by the flow generator based on the determined target pressure for the flow of gases delivered to the patient, wherein the target flow rate is no lower than the floor flow rate, and control the flow rate of the flow of gases output by the flow generator based on the target flow rate.

[0130] In a configuration, the controller is configured to control the flow rate of the flow of gases output by the flow generator to deliver the flow of gases to the patient at substantially the target pressure.

[0131] The fifteenth aspect may comprise any one or more of the features of the thirteenth aspect described above.

[0132] In a sixteenth aspect, the present disclosure provides for a breathing assistance apparatus configured to provide a flow of gases to be delivered to a patient via a patient interface for respiratory therapy, comprising: a flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases; and a controller configured to: receive a floor pressure representing a minimum allowable pressure for the flow of gases, receive data indicative or representative of a flow rate of the flow of gases, receive or estimate data indicative or representative of a pressure at or near the patient's nares, determine a target pressure for the flow of gases delivered to the patient, wherein the target pressure is based at least in part on: the data indicative or representative of the flow rate of the flow of gases, the data indicative or representative of the pressure at or near the patient's nares, and the floor pressure, and control the flow rate of the flow of gases output by the flow generator to deliver the flow of gases to the patient at substantially the target pressure.

[0133] The sixteenth aspect may comprise any one or more of the features of the thirteenth aspect described above.

[0134] In a seventeenth aspect, the present disclosure provides for a respiratory therapy system for delivering a flow of gases to a patient for respiratory therapy, comprising: a breathing assistance apparatus comprising at least a flow generator, the flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases; a supply conduit coupled at a first end to the flow generator and configured to convey the flow of gases output by the flow generator; a patient interface coupled to a second end of the supply conduit and configured to receive the flow of gases from the supply conduit and deliver the flow of gases to the patient; and a controller configured to: receive a minimum flow parameter representing a minimum allowable parameter relating to the flow of gases, receive data indicative or representative of a flow rate of the flow of gases, receive or estimate data indicative or representative of a pressure at or near the patient's nares, determine a target pressure for the flow of gases delivered to the patient, wherein the target pressure is based at least in part on: the data indicative or representative of the flow rate of the flow of gases, the data indicative or representative of the pressure at or near the patient's nares, and the minimum flow parameter, and control the flow rate of the flow of gases output by the flow generator to deliver the flow of gases to the patient at substantially the target pressure.

[0135] The seventeenth aspect may comprise any one or more of the features of the thirteenth aspect described above.

[0136] In an eighteenth aspect, the present disclosure provides for a respiratory therapy system for delivering a flow of gases to a patient for respiratory therapy, comprising: a breathing assistance apparatus comprising at least a flow generator, the flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases; a supply conduit coupled at a first end to the flow generator and configured to convey the flow of gases output by the flow generator; a patient interface coupled to a second end of the supply conduit and configured to receive the flow of gases from the supply conduit and deliver the flow of gases to the patient; and a controller configured to: receive a floor flow rate representing a minimum allowable flow rate for the flow of gases, receive data indicative or representative of a flow rate of the flow of gases, receive data indicative or representative of a pressure of the flow of gases, estimate a pressure of the flow of gases at or near the patient's nares based at least in part on the data indicative or representative of the flow rate of the flow of gases and the data indicative or representative of the pressure of the flow of gases, estimate a flow rate of the patient’s breathing based at least in part on the estimated pressure of the flow of gases at or near the patient's nares and the data indicative or representative of the flow rate of the flow of gases, determine a target pressure for the flow of gases delivered to the patient based at least in part on the estimated flow rate of the patient’s breathing, determine a target flow rate for the flow of gases output by the flow generator based on the determined target pressure for the flow of gases delivered to the patient, wherein the target flow rate is no lower than the floor flow rate, and control the flow rate of the flow of gases output by the flow generator based on the target flow rate.

[0137] The eighteenth aspect may comprise any one or more of the features of the thirteenth aspect described above.

[0138] In a nineteenth aspect, the present disclosure provides for a method for controlling the pressure of a flow of gases delivered to a patient for respiratory therapy, the method comprising: controlling a flow generator to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases, and wherein the flow of gases output by the flow generator is configured to be delivered to the patient via a patient interface; receive a minimum flow parameter representing a minimum allowable parameter relating to the flow of gases, receiving data indicative or representative of a flow rate of the flow of gases, receiving or estimate data indicative or representative of a pressure at or near the patient's nares, determining a target pressure for the flow of gases delivered to the patient, wherein the target pressure is based at least in part on: the data indicative or representative of the flow rate of the flow of gases, the data indicative or representative of the pressure at or near the patient's nares, and the minimum flow parameter, and controlling the flow rate of the flow of gases output by the flow generator to deliver the flow of gases to the patient at substantially the target pressure.

[0139] The nineteenth aspect may comprise any one or more of the features of the thirteenth aspect described above.

[0140] In a twentieth aspect, the present disclosure provides for a method for controlling the pressure of a flow of gases delivered to a patient for respiratory therapy, the method comprising: controlling a flow generator to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases, and wherein the flow of gases output by the flow generator is configured to be delivered to the patient via a patient interface; receiving a floor flow rate representing a minimum allowable flow rate for the flow of gases, receiving data indicative or representative of a flow rate of the flow of gases, receiving data indicative or representative of a pressure of the flow of gases, estimating a pressure of the flow of gases at or near the patient's nares based at least in part on the data indicative or representative of the flow rate of the flow of gases and the data indicative or representative of the pressure of the flow of gases, estimating a flow rate of the patient’s breathing based at least in part on the estimated pressure of the flow of gases at or near the patient's nares and the data indicative or representative of the flow rate of the flow of gases, determining a target pressure for the flow of gases delivered to the patient based at least in part on the estimated flow rate of the patient’s breathing, determining a target flow rate for the flow of gases output by the flow generator based on the determined target pressure for the flow of gases delivered to the patient, wherein the target flow rate is no lower than the floor flow rate, and controlling the flow rate of the flow of gases output by the flow generator based on the target flow rate.

[0141] The twentieth aspect may comprise any one or more of the features of the thirteenth aspect described above.

[0142] In a twenty first aspect, the present disclosure provides for a breathing assistance apparatus configured to provide a flow of gases to be delivered to a patient via a patient interface for respiratory therapy, comprising: a flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases; and a controller configured to: receive data indicative or representative of a flow rate of the flow of gases, receive data indicative or representative of a pressure of the flow of gases, receive or estimate one or more nasal resistance parameters, each nasal resistance parameter representative or indicative of the pneumatic resistance between one or both prongs of the nasal cannula and the one or both corresponding nares of the patient, estimate a pressure of the flow of gases at or near the patient's nares based at least in part on the data indicative or representative of the flow rate of the flow of gases and the data indicative or representative of the pressure of the flow of gases, and the one or more estimated nasal resistance parameters, compare the one or more estimated nasal resistance parameters with a corresponding expected value, and update the estimated nasal resistance parameter based on the comparison, and control the flow rate of the flow of gases output by the flow generator to deliver the flow of gases to the patient at substantially the target pressure.

[0143] The twenty first aspect may comprise any one or more of the features of the thirteenth aspect described above.

[0144] In a twenty second aspect, the present disclosure provides for a breathing assistance apparatus configured to provide a flow of gases to be delivered to a patient via a patient interface for respiratory therapy, comprising: a flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases; the flow generator configured to be coupled to a supply conduit at a first end, and the supply conduit configured to convey the flow of gases be coupled to the patient interface at a second end, the supply conduit configured to convey the flow of gases output by the flow generator to the patient interface, and the patient interface configured to deliver the flow of gases to the patient; wherein the patient interface is a non-sealing nasal cannula configured to cause an asymmetrical flow of gases at or near the patient's nares; and a controller configured to: receive a minimum flow parameter representing a minimum allowable parameter relating to the flow of gases, receive data indicative or representative of a flow rate of the flow of gases, receive or estimate data indicative or representative of a pressure at or near the patient's nares, determine a target pressure for the flow of gases delivered to the patient, wherein the target pressure is based at least in part on: the data indicative or representative of the flow rate of the flow of gases, the data indicative or representative of the pressure at or near the patient's nares, and the minimum flow parameter, and control the flow rate of the flow of gases output by the flow generator to deliver the flow of gases to the patient at substantially the target pressure.

[0145] In a configuration, the non-sealing nasal cannula comprises a first prong and a second prong, and wherein at least one of the first prong and the second prong is sized to maintain a sufficient gap between the outer surface of the prong and a patient's skin to avoid sealing a gas path between the non-sealing nasal cannula and the patient.

[0146] In a configuration, the first prong has a larger inner cross-sectional area in a direction transverse to gases flow through the first prong than a corresponding inner cross-sectional area of the second prong in a direction transverse to gases flow through the second prong.

[0147] In a configuration, at least the first prong is made of an elastomeric material that enables the first prong to deform and set its shape in use in response to temperature and contact with the patient's naris.

[0148] In a configuration, the first prong is configured to deform and set its shape in use to substantially match the internal shape of the patient's naris.

[0149] The twenty second aspect may comprise any one or more of the features of the thirteenth aspect described above. Where used in the foregoing statements the term “has” shall be construed non-exclusively, to mean that a named feature is present but that the presence of other features is not excluded unless the context requires otherwise.

[0150] The term "axis" as used in this specification means the axis of revolution about which a line or a plane may be revolved to form a symmetrical shape. For example, a line revolved around an axis of revolution will form a surface, while a plane revolved around an axis of revolution will form a solid.

[0151] As used herein the term “and / or” means “and” or “or”, or both.

[0152] As used herein “(s)” following a noun means the plural and / or singular forms of the noun.

[0153] For the purposes of this specification, the term “plastic” shall be construed to mean a general term for a wide range of synthetic or semisynthetic polymerization products and generally consisting of a hydrocarbon-based polymer.

[0154] For the purpose of this specification, where method steps are described in sequence, the sequence does not necessarily mean that the steps are to be chronologically ordered in that sequence, unless there is no other logical manner of interpreting the sequence.

[0155] The term “comprising” as used in the specification and claims means “consisting at least in part of.” When interpreting each statement in this specification that includes the term “comprising,” features other than that or those prefaced by the term may also be present. Related terms “comprise” and “comprises” are to be interpreted in the same manner.

[0156] This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

[0157] To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting.

[0158] Other aspects of the invention may become apparent from the following description which is given by way of example only and with reference to the accompanying drawings.

[0159] BRIEF DESCRIPTION OF THE DRAWINGS

[0160] Preferred embodiments will be described by way of example only and with reference to the drawings, in which: Figure 1 shows schematically a respiratory therapy system configured to provide a respiratory therapy to a patient.

[0161] Figure 2 shows schematically a control system for the respiratory therapy system of Figure 1.

[0162] Figure 3 shows a perspective view of an example breathing assistance apparatus.

[0163] Figure 4 shows a side view of the example breathing assistance apparatus of Figure 3.

[0164] Figure 5 shows a top view of the example breathing assistance apparatus of Figure 3.

[0165] Figure 6 shows an underside view of the example breathing assistance apparatus of Figure 3.

[0166] Figure 7 shows a perspective underside view of the example breathing assistance apparatus of Figure 3.

[0167] Figure 8 is a front left perspective view of an exemplary configuration patent interface of the present disclosure comprising a nasal interface with asymmetrical nasal delivery elements.

[0168] Figure 9 is a front right perspective view of the patient interface.

[0169] Figure 10 is a front left exploded perspective view of the patient interface.

[0170] Figure 11 shows a nasal interface of the present disclosure, where Figure 11(a) is a top view, Figure 11(b) is a front view, and Figure 11(c) is a bottom view.

[0171] Figure 12 shows a front sectional view of a nasal interface of the present disclosure inserted into the nares of a user.

[0172] Figure 13 shows a rear view of a small size nasal interface of the present disclosure.

[0173] Figure 14 shows a rear view of a medium size nasal interface of the present disclosure.

[0174] Figure 15 shows a rear view of a large size nasal interface of the present disclosure.

[0175] Figures 16 to 18 show flow charts of different variations of a control method according to the present disclosure.

[0176] Figure 19 shows a flow chart of a control method according to a first embodiment the present disclosure.

[0177] Figure 20 shows a flow chart of a control method according to a second embodiment the present disclosure.

[0178] Figures 21 and 22 show example graphs showing how various flows and pressures vary over the course of several breathing cycles of the patient according to the control method of the first embodiment the present disclosure.

[0179] Figure 23 shows a series of example graphs showing how various flows and pressures vary over the course of several breathing cycles of the patient according to the control method of the second embodiment the present disclosure. DETAILED DESCRIPTION

[0180] Although certain examples are described below, those of skill in the art will appreciate that the disclosure extends beyond the specifically disclosed examples and / or uses and obvious modifications and equivalents thereof. Thus, it is intended that the scope of the disclosure herein disclosed should not be limited by any particular examples described below.

[0181] A schematic representation of an example respiratory therapy system 1 is provided by FIG. 1. The respiratory therapy system 1 may comprise at least a breathing assistance apparatus 10, supply conduit 20, and patient interface 30. Other modules or elements may be present in the system. Hereinafter, the apparatus comprising a flow generator 11 and a humidifier 12 will be referred to as a ‘breathing assistance apparatus’, whereas the system comprising the flow generator 11, humidifier 12, supply conduit 20, and patient interface 30 will be referred to as a ‘respiratory therapy system’, but these terms should not be considered limiting. The respiratory therapy system 1 may omit the patient interface 30 in some circumstances. In some other circumstances, the humidifier 12 may be omitted from the breathing assistance apparatus 10.

[0182] An exemplary breathing assistance apparatus will now be described, with reference to FIGS. 1-7.

[0183] A breathing assistance apparatus 10 can be configured or operable to provide one or more respiratory therapies via the supply conduit 20 and the patient interface 30.

[0184] The respiratory therapy may be a flow based respiratory therapy, such as high flow therapy (HFT), or a pressure based respiratory therapy, such as continuous positive airway pressure (CPAP), or, as will be explained, it may be a hybrid respiratory therapy that combines aspects of a flow based respiratory therapy with aspects of a pressure based respiratory therapy.

[0185] It will be appreciated that the components, methods, and processes described herein may be applied to other breathing assistance apparatuses and / or to other modes of operation and / or modes of therapy delivered by such apparatuses. For example, the breathing assistance apparatus 10 may additionally or alternatively be configured or operable to provide other flow-based therapies or other pressure-based therapies such as bi-level positive airway pressure (bi-level) therapy. In some examples, when providing such other therapies, the patient interface used may be a sealing interface, such as nasal pillows, a nasal mask, under-nose mask, or full-face mask.

[0186] 1. Breathing Assistance Apparatus

[0187] 1.3. Flow Path

[0188] The breathing assistance apparatus 10 may be an integrated apparatus comprising a plurality of key components in a single housing, or a discrete component-based arrangement where the key components are separate but connected together. With reference to FIG. 1, the breathing assistance apparatus 10 comprises at least a flow generator 11 and a humidifier 12. With reference to FIGS. 3-7, in some configurations, the flow generator 11 and humidifier 12 are part of an integrated breathing assistance apparatus 10, sharing a common housing 16. In other configurations, the breathing assistance apparatus 10 could be a modular arrangement of discrete components, with the flow generator 11 and humidifier 12 being separate modules that can be connected together.

[0189] The breathing assistance apparatus 10 comprises an inlet module 110 for providing a gas or gases such as air, oxygen (O2), air blended with oxygen, or a mix of air and / or oxygen and one or more other supplemental gases to the flow generator 11. The inlet module 110 may comprise one or more inlets for receiving flows of (or drawing in) ambient and / or pressurised air, oxygen, and / or other gases. For example, with reference to FIG. 1, in some embodiments the inlet module 110 may comprise an ambient air inlet 1101, low-pressure gas inlet 1102, and / or high-pressure gas inlet 1103. A greater or lesser number of inlets may be provided in other embodiments. Some or all of the inlets may comprise connectors (such ports, terminals, couplers, and the like) for establishing fluid or pneumatic connections to the sources of said gases. The inlet module 110 may be considered to form part of the flow generator 11, the breathing assistance apparatus 10, or it may be a separate, modular component, depending on the context.

[0190] With reference to FIG. 1, a fdter or multiple filters may be provided as part of the inlet module 110, at or immediately downstream of the ambient air intake 1101 , the low-pressure gas inlet 1102, and / or the high- pressure gas inlet 1103. There may be a single filter 1106 positioned at the inlet or inlets to blower 1111 to filter particulates and pathogens carried with the incoming gases before they reach the blower 1111. Additionally, or alternatively, there may be individual filters positioned at each of the inlets or intakes

[0191] 1101, 1102, 1103. In an exemplary embodiment, a filter 1104 is provided between the high-pressure gas inlet 1103, at or upstream of the proportional valve 1105, in addition to a filter 1106 positioned at the inlet or inlets to the blower 1111, downstream of the proportional valve 1105 and the intake 1101 and inlet

[0192] 1102.

[0193] According to the above and depending on the configuration (some components may be optional), the respiratory therapy system 1 can include a combination of components or modules selected from the following:

[0194] • a flow generator 11, comprising an inlet module 110, comprising one or more gas source inlets and their respective connectors (if applicable), a filter or filter module 1106, and a blower / sensor module 111,

[0195] • non-retum valve 112,

[0196] • a humidifier 12 for humidifying the gases flow,

[0197] • a supply conduit 20, and / or

[0198] • a patient interface 30. The respiratory therapy system 1 and breathing assistance apparatus 10 will now be described in more detail.

[0199] The gas sources connected to the inlet module 110 or inlets of the inlet module may include an in-wall (‘piped’) supply of supplementary gas (e.g., oxygen) or mixture of gases, a tank of said supplementary gases, and / or a gas flow source such as an oxygen concentrator. The aforementioned gas sources may provide the respective gas or gases at low or high pressures and / or low or high flow rates. In some configurations, one or more of the gas sources may include a shut-off valve and / or regulator or other flow or pressure control means which may be manually adjustable by a user. For example, one of the gas sources may be pressurised gas cylinder connected to the high-pressure gas inlet 1103 via a regulator and shut-off valve.

[0200] The flow generator 11 comprises a blower / sensor module 111 that least comprises a blower 1111 that controls flows delivered to a patient via the supply conduit 20 and patient interface 30. The blower 1111 may be a centrifugal blower, comprising at least a motor and impeller or fan that is driver by the motor. Other types of blowers may be employed, such as axial blowers. The flow rate and / or pressure of flows of gases being output by the flow generator 11 can be controlled by varying the output of the blower 1111, for example by varying the rotational speed of the motor driving the impeller or fan. The flow generator may be configured to provide flows of gases at high flow rates. Examples of high flow rates are provided later.

[0201] The blower / sensor module 111 may further comprise a sensor module 1112. With reference to FIG. 1, in some embodiments the sensor module 1112 may be positioned ‘after’ or downstream of the blower 1111 (i.e., an inlet of the sensor module 1112 may be fluidically / pneumatically connected to the outlet of the blower 1111) but may instead be positioned upstream of the blower in other embodiments. The sensor module 1112 may be located prior to humidifier 12.

[0202] One or more sensors (for example, Hall Effect sensors) may be used to measure a motor speed of the blower motor.

[0203] Positioning sensors (e.g., flow rate, pressure, oxygen fraction, and / or other types of sensors in the sensor module 1112) downstream of the blower 1111 can increase accuracy of measurements, such as the measurement of fractional gas concentrations, including oxygen fraction, over systems that position the sensors upstream of the blower and / or a mixer. Positioning these sensors at a location further along the flow pathway, after the flow of gases has been more mixed (and may therefore be more homogeneous), may yield more consistent and / or repeatable measurements.

[0204] In some embodiments of the breathing assistance apparatus 10, a non-retum valve (NRV) 112 may be located downstream of the blower 1111 or blower / sensor module 111 but prior to the flow generator outlet 113 and / or the inlet to humidification chamber 120. The NRV 112 may be positioned within the flow generator outlet 113. The non-retum valve 112 may serve to prevent any backflow of gases, aerosols, and / or liquids into the flow generator 11 via the humidifier 12. During the provision of respiratory therapy, some flows of gases expired by patients may travel down the supply conduit 20, back into the humidifier 12 and potentially reaching the flow generator or displacing other gases that then travel into the humidifier and / or flow generator; these flows of gases may carry pathogens which could contaminate the flow generator. In addition, the flows of gases may transport significant quantities of water vapour (especially if returning via the humidifier 12) which, overtime, may damage the internal hardware of the flow generator if backflow is allowed to occur. Hence, a non-retum valve may be included in the breathing assistance apparatus.

[0205] 1.2. Patient Interface

[0206] The patient interface 30 may be an unsealed or non-sealing interface such as a nasal cannula. The term ‘non-sealing’ as used when referring to patient respiratory interfaces may be defined as a patient interface having elements that do not completely seal a respiratory passage of the user from the outside environment. For example, in the context of a nasal cannula prong, a non-sealing nasal cannula prong may ideally occlude 80% or less of a user’s naris. Conversely, a sealing patient respiratory interface may be a full or under-nose face mask, or nasal masks and nasal pillows, where the nares of a patient are completely sealed off from the outside environment, in contrast to non-sealing nasal prongs which allow for some movement of gases between the outside environment and the nasal passageways. Non-sealing patient interfaces may help to prevent barotrauma effects (e.g., tissue damage to the airways and / or lungs due to differences in pressure relative to standard atmospheric pressure).

[0207] The patient respiratory interface 30 may instead be a tracheostomy interface or any other suitable type of patient interface, depending on the type of therapy being provided and / or the patient’s needs.

[0208] In the present disclosure, the patient interface 30 may be a non-sealing nasal cannula. In some examples, the non-sealing nasal cannula may be configured to cause an asymmetrical flow of gases at the patient's nares, as will be explained.

[0209] In examples, a humidifier 12 may be provided between the flow generator 11 and the apparatus outlet 13 and / or supply conduit 20 to humidify the flow of gases being output by the flow generator 11. Humidification is particularly useful when providing respiratory therapies having high flows (where high flow rates of otherwise dry gases are delivered to the patient’s airways) as it improves the tolerability and comfortability of the therapy. Increasing the humidity of the gases to or closer to the natural levels in a healthy patient’s airways (e.g., 37°C dew point) may help to maintain the condition of the airways, reducing or preventing drying-out or other effects which may cause discomfort and adverse health outcomes. In some configurations the humidifier 12 may be optional, in which case the breathing assistance apparatus 10 may provide non-humidified gases from the flow generator 11 to the patient.

[0210] The humidifier 12 may be a heated humidifier, wherein the humidifier comprises at least one heating element. The humidifier 12 may be a heated pass-over humidifier. A heated pass-over humidifier typically comprises at least a heater plate 121, a heating element 122 arranged and configured to heat the heater plate 121, and a humidification chamber 120 comprising a heat-conductive base that is in close contact with the heater plate 121 when in use. The humidification chamber 120 will be at least partially filled with water when in use; the heat-conductive base will transfer heat from the heater plate to the water, thereby causing controlled evaporation of the water to increase the humidity of a gases flow travelling through the chamber.

[0211] 1.3. Sensors

[0212] Various sensors configured to detect or measure properties or parameters of the respiratory therapy system 1 and / or the flow of gases may be disposed at one or more locations throughout the apparatus and / or system.

[0213] In an exemplary embodiment of the respiratory therapy system 1, at least the following sensors may be provided:

[0214] • Sensor 1107 at the ambient air inlet 1101 (e.g., a pressure, flow, temperature, and / or humidity (relative and / or absolute) sensor);

[0215] • Sensor 1108 at or optionally downstream of the high-pressure gas inlet 1103 (e.g., a pressure and / or a flow sensor);

[0216] • Sensor 1109 downstream of the proportional valve 1105 (e.g., a pressure and / or a flow sensor);

[0217] • Sensor 1113 at the blower 1111, optionally proximal to the stator windings of the motor driving the blower (e.g., a temperature and / or a motor speed sensor);

[0218] • Sensor 123 at the heating element 122, or proximal to the heater plate 121 (e.g., a temperature sensor);

[0219] • Sensor 130 downstream of the apparatus outlet 13 (e.g., a temperature sensor);

[0220] • Sensor 21 at a patient end of the supply conduit 20 (e.g., a temperature sensor).

[0221] Sensors 1107, 1108, 1109, 1113, 123, 130, and / or 21 may comprise multiple sensors. The multiple sensors may be part of a single package or separate, discrete sensors, or a combination of integrated sensor modules and discrete components.

[0222] Additional sensors may be provided as part of or within the sensor module 1112. The sensor module 1112 may be configured and arranged to measure properties of the gases flow travelling from the blower 1111 through to flow generator outlet 113 and beyond. For example, the sensor module may comprise a sensor or sensors to detect the flow rate, oxygen concentration fraction (FdCf). pressure, temperature, and / or humidity of the flow of gases.

[0223] In addition to the sensors described above, various other sensors may be provided in and throughout the respiratory therapy system 1. The sensors may be configured to detect, measure, and / or determine flow rate, pressure, temperature, humidity (e.g., relative and / or absolute humidity), oxygen concentration / fraction, and / or motor speed of the blower. Other sensors can be placed throughout the system and / or at, on or near the patient — for example, a pulse oximetry sensor may be attached to the patient and coupled to the controller 14 via a pulse oximeter. Alternatively, or additionally, sensors from which the above parameters can be derived could be used.

[0224] 1.4. Controller

[0225] Some or all of the sensors listed above may be electrically and / or communicatively connected to a controller 14, as mentioned above. The connection may be direct or indirect — e.g., via signal conditioning circuits, driver circuits, another controller, and / or other types of circuit. The connection(s) may be wired or wireless.

[0226] The controller 14 may be a microprocessor, a microcontroller, a programmable logic device (such as a CPLD or FPGA), a digital signal processor (DSP), an application-specific integrated circuit (ASIC), or other suitable form of device, and may not necessarily be implemented in a single monolithic integrated circuit (IC) but may include additional discrete electrical and / or electronic components. The controller 14 may comprise a single device or multiple devices and components. For example, the controller 14 may comprise multiple microprocessors or microcontrollers. Overall, it will be appreciated by persons of skill in the art that various types of devices and components may be employed as or in controllers such as controller 14.

[0227] The controller can include programming instructions for detection of input conditions and control of output conditions. The programming instructions can be stored in memory of or associated with the controller 14. The programming instructions can correspond to the methods, processes and functions described herein. The programming instructions can be executed by one or more processors of the controller 14. The programming instructions can be implemented in C, C++, Java, or any other suitable programming languages or combinations thereof. Some or all of the portions of the programming instructions can be implemented in application specific circuitry such as ASICs and FPGAs.

[0228] In some configurations, the outputs from at least some or all of the sensors described above are sent to the controller 14 to assist the control of the respiratory therapy system 1 and its constituent components or modules (e.g., the blower 1111, heating element 122, supply conduit 20, display and input / output (I / O) 142, and other modules). The controller 14 may be coupled to at least one or more of: the proportional valve 1105, blower 1111, humidifier heating element 122, and / or the heated breathing tube of supply conduit 20. In some configurations, the controller 14 controls at least these and other parts of the respiratory therapy system 1 as described herein. ‘Control’ as referred to herein may involve direct control of components (i.e., by signals output from the controller 14) or control via signal conditioning circuits, drivers / driving circuits (such as MOSFET gate drivers or motor drivers, for example).

[0229] In some examples, the controller can operate the blower 1111 and / or the proportional valve 1105 to provide a flow of gas at a desired flow rate. The controller 14 may also receive user input from a user interface aspect of the display and I / O 142. The user input may include a target flow rate, pressure, oxygen fraction (i.e., FdO2 (fraction of delivered oxygen) or FiO2 (fraction of inspired oxygen)), therapy mode (high flow therapy, CPAP, etc.), alarm thresholds, and / or other parameters. The user can be a patient, healthcare professional, or others.

[0230] The controller 14 may output information to a display and I / O peripheral 142. The display and I / O peripheral 142 can display warnings and / or other alerts. The display and I / O peripheral 142 can be configured to display characteristics of sensed gases in real time or otherwise. The controller 14 can also receive user inputs via a user interface aspect of the display and I / O peripheral 142. The user interface can include virtual and / or physical button(s) and / or dial(s). The user interface can comprise a touch- sensitive screen.

[0231] 1.5. Wireless Communications

[0232] The breathing assistance apparatus 10 may include one or more communications modules 141 which can enable data communications with one or more external devices or servers over a data or communication link or data network, whether wired, wireless or a combination thereof. In one configuration, for example, the breathing assistance apparatus 10 can include a wireless data transmitter, receiver, and / or transceiver to enable the controller 14 to send and receive data signals in a wireless manner to / from external devices, including sensors (e.g., sensors affixed to a patient), patient monitoring systems, mobile phones or other devices, and / or remote servers. In one example, the one or more communications modules 141 may comprise cellular (e.g., 3G, 4G, and / or 5G), Bluetooth, and / or Wi-Fi modules. The one or more communications modules 141 may comprise a singular module configured to perform communication using cellular, Bluetooth, and Wi-Fi technologies and protocols.

[0233] The one or more communications modules 141 can deliver data to a remote patient management system (for example, implemented or located on a remote server) and / or enable remote control of the breathing assistance apparatus 10 or respiratory therapy system 1. The remote patient management system may comprise a single server, multiple servers, or multiple computing devices implemented in a cloud computing network. The communication may be two-way (bidirectional) communication between the breathing assistance apparatus 10 and the remote patient management system, and / or another remote system.

[0234] The one or more communications modules may allow the controller 14 to wirelessly send information to another local device such as, for example, a user or patient’s mobile phone, tablet, smartwatch, etc. The breathing assistance apparatus 10 may additionally, or alternatively, comprise a Near Field Communication (NFC) module to allow for local data transfer and / or data communication. In some examples, the breathing assistance apparatus 10 may transmit data over a wired or wireless connection to the local user or patient device, for example via USB, Wi-Fi, Bluetooth, or NFC, and the user or patient device may then wirelessly transmit data to a remote server, such as the remote patient management system (for example, via the Internet).

[0235] As mentioned above, estimated, measured, or determined respiratory parameters that are generated or received by the breathing assistance apparatus 10 may be transmitted via the one or more communications modules 141 to a remote server. In addition, usage information and selected therapy parameters may also be transmitted. Therapy parameters e.g., flow rate, humidity level and other respiratory parameters such as respiratory rate, occurrences of apnoeas, pulse oximetry data (e.g., SpCT). may be transmitted together. In some examples, the breathing assistance apparatus 10 or the user or patient device may generate an index (for example, a respiratory oxygenation (ROX) index) that contains, comprises, or is based on therapy parameters e.g., patient SpCh, device FdCh or FiCF. flow rate, humidity level, and other determined or estimated respiratory parameters, and is transmitted by the breathing assistance apparatus 10 or the user or patient device to a remote server.

[0236] The remote patient management system may be implemented on a single server or a network of servers or a cloud computing system or other suitable architecture for operating a remote patient management system. The remote patient management system may further include memory for storing received data and various software applications or services that can be executed to perform multiple functions. Then, for example, the remote patient management system may communicate information or instructions to the breathing assistance apparatus 10 at least in part dependent on the data received. For example, the nature of the data received may trigger the remote server (or a software application running on the remote server) to communicate an alert, alarm, or notification to the breathing assistance apparatus 10. The remote patient management system may further store the received data for access by an authorized party such as a clinician, or the patient, or another authorized party. The remote patient management system may further be configured to generate reports in response to a request from an authorized party, and respiratory or selected therapy parameters may be included in the generated reports. The reports may comprise other data or patient breathing or respiratory parameters, e.g., respiratory rate, SpCX. and / or parameters such as flow rate(s), pressure(s), temperature(s), and / or humidity level(s).

[0237] 1.6. Control System

[0238] FIG. 2 illustrates a block diagram 300 of an example control system 310 (which can be implemented on, by, or at least partially on or by the controller 14 (and any other controllers or circuits described herein)) that can detect patient and / or system conditions and control operation of the respiratory therapy system 1, including any gases source (s). The control system 310 can determine and generate the output control signals 322-326 based on one or more received inputs 311-321. The inputs 311-321 can correspond to sensor measurements received automatically by the controller 14 and / or user inputs. The control system 310 can receive, including but not limited to, pressure sensor(s) input(s) 311, temperature sensor(s) input(s) 312, flow rate sensor(s) input(s) 313, motor speed sensor(s) input(s) 31, gas fraction / concentration sensor(s) input(s) 315, humidity sensor(s) input(s) 316, pulse oximetry sensor(s) input(s) 317 (for example, SpCh and / or heart rate), stored or user parameter(s) input(s) 318, duty cycle or pulse width modulation (PWM) input(s) 319, voltage(s) input(s) 320, current(s) input(s) 3211.

[0239] / . 7. Breathing Assistance Apparatus Housing With reference to FIGS. 3-7, the breathing assistance apparatus 10 can include a main housing 16. The housing 16 may house the inlet module 110, blower / sensor module 111, and the heater plate 121 and heating element 122 of the humidifier 12. The controller 14, communications modules 141, display and I / O 142, and peripheral ports 143 may also be positioned within or on the main housing 16. As mentioned above, the humidifier 12 may, in some embodiments, be a separate module with its own housing and therefore not enclosed by the main housing 16 of the breathing assistance apparatus 10.

[0240] The main housing 16 has a main housing upper chassis 161 and a main housing lower chassis 162. The main housing upper chassis 161 has a peripheral side wall 1611. The peripheral wall defines a humidifier or humidification chamber bay dock, compartment, or bay 1612 for receipt of the removable humidification chamber 120. The removable humidification chamber 120 contains a suitable liquid for humidifying gases that can be delivered to a patient, such as water. A floor portion of the humidification chamber dock 1613 (not shown) can have a recess to receive a heater arrangement such as a heater plate 121 or other suitable heating arrangements(s) for heating liquid in the humidification chamber 120 during a humidification process.

[0241] The breathing assistance apparatus 10 comprises an arrangement to enable the blower to deliver air, oxygen (or alternative auxiliary gases), or a suitable mixture thereof to the humidification chamber 120 and thereby to the patient. This arrangement can include an air inlet 1101 in the peripheral side wall 1611 of the lower chassis 162 of the housing 16. Additionally, or alternatively, the air inlet 1101 may be positioned in an underside wall 1615 of the housing 16.

[0242] A filter cartridge can be positioned adj acent the air inlet 1101 internally in the main housing and in communication with the blower 1111 to deliver filtered air and / or oxygen to the blower 1111 via an inlet port in the motor / sensor module 111. The filter cartridge can include a filter 1106 configured to remove particulates (e.g., dust) and / or pathogens (e.g., viruses or bacteria) from the gases flow. The apparatus 10 can include a separate oxygen inlet port 1103 positioned adjacent one side of the housing 16 or at a rear end thereof, the oxygen port 1103 being for receipt of oxygen from an oxygen source such as a tank or source of piped oxygen. The oxygen inlet port 1103 may be in fluid communication with a valve 1105. The valve 1105 can suitably be a solenoid valve that enables electronic control of the amount of oxygen that is added to the gases flow that is delivered to the humidification chamber 300.

[0243] With reference to FIGS. 3-5, an apparatus outlet port 13 can include a removably-connected (removable) L-shaped elbow 131. The removable elbow 131 can include a patient outlet port 1311 for coupling to the supply conduit 20 to deliver a flow of gases to a patient interface. The inlet to the removable elbow 131 may extend at least substantially along the longitudinal axis 60 while the outlet of the removable elbow 131 (i.e., the patient outlet port 1311) may extend at least substantially along a vertical axis 62. In other words, the patient outlet port 1311 may extend upwardly from the main housing upper chassis 161 of the breathing assistance apparatus 10 main housing 16. The flow generator outlet port 113, gases inlet and gases outlet ports 124, 125 of the humidifier 12 (or the inlet and outlet ports of the manifold 126), apparatus outlet port 13, and patient outlet port 1311 each or all can have soft seals such as O-ring seals or T-seals to provide a sealed gases passageway between the flow generator 11, the humidification chamber 120, and the supply conduit 20.

[0244] The main housing upper chassis 161 can comprise a shroud portion 1614 (hereinafter ‘shroud’). With reference to FIGS. 3-4, the shroud 1614 can protrude outwardly from the main upper housing chassis 161, such that it may extend at least partially over the flow generator outlet 113 and the inlet to the elbow 131.

[0245] The main housing upper chassis 161 may further comprise the display and I / O 142 mentioned previously. The display and I / O 142 can include a user interface which may comprise a display screen and input devices such as mechanical buttons or dials, a touch screen (e.g., a touch-sensitive LCD or LED screen), a combination of a touch screen and mechanical buttons or dials, or the like. In one configuration, the user interface of the display and I / O 142 may comprise a separate display and / or touch screen that is not permanently integrated with the breathing assistance apparatus housing 16 but may be communicatively connected to the apparatus in a wired or wireless fashion. The breathing assistance 10 may comprise a docking element for securing the separate display screen to.

[0246] With reference to FIGS. 3-5, the breathing assistance apparatus 10 may at least comprise a display screen 1420 that may be part of the display and I / O 142 (i.e., it may be aforementioned display screen or touch- sensitive screen). With reference to FIGS. 3-5, the display screen 1420 can protrude from the housing 16, for example, in an angled fashion. The angle of the display screen relative to a plane defined by the surface of the main housing upper chassis 161 may help to improve visibility and / or usability of the screen for users. For example, an angled display screen may be more easily view from a distance than a complete flat screen provided in the main housing upper chassis 161.

[0247] 1.8. Humidification

[0248] With continued reference to FIG. 1, a supply conduit 20 can be coupled to an apparatus outlet 13 formed in or as part of the housing 16 of the breathing assistance apparatus 10 at one end, and to a patient interface 30, such as a non-sealing interface (for example, a non-sealing nasal cannula) at another end.

[0249] The gases flow generated by the flow generator 11 may be humidified before being delivered to the patient via the supply conduit 20 and the patient respiratory interface 30, as explained previously. The controller 14 can control the flow generator 11 to generate a gases flow of a desired flow rate, and / or one or more valves (such as proportional valve 1105) to control the mixing of air and oxygen and / or other supplemental gases by the blower 1111. The controller 14 can control a heating element 122 in or associated with the humidifier 12, if present, to heat the gases flow to a desired temperature that achieves a desired level of temperature and / or humidity for delivery to the patient. The supply conduit 20 may be a heated conduit, comprising one or more conductors (i.e., heating elements) embedded within the walls of the supply conduit, which may be supplied with electrical current in order to heat the internal passageway(s) of the conduit. Alternatively, the heating element(s) may be attached to the interior surface of the supply conduit 20, or even float within the interior of conduit. The power supplied to the heating elements can be controlled by the controller 14.

[0250] The humidifier 12 of the apparatus is configured to increase the humidity of the gases flow by introducing water vapour to gases passing through the humidification chamber 120. Various humidifier configurations may be employed. In one configuration, the humidifier 12 can comprise a removable humidification chamber 120 that is configured to contain one or more liquids. For example, the humidifier 12 may be configured to allow the humidification chamber 120 to be partially or entirely removed or disconnected from the flow path and / or breathing assistance apparatus 10. The humidification chamber may be removed for refilling, cleaning, replacement and / or repair. With reference to at least FIGS. 3-5, in one configuration, the humidification chamber may be received and retained by or within a dock, compartment, or bay 1612 of the breathing assistance apparatus 10 or may otherwise couple onto or within the housing 16 of the breathing assistance apparatus 10.

[0251] With continued reference to at least FIGS. 3-5, the humidification chamber 120 of the humidifier 12 comprises at least a gases inlet 124 and a gases outlet 125 to enable connection to the gases flow path of the breathing assistance apparatus 10, optionally via a gases manifold 126 that connects between the flow generator outlet 113 and humidifier gases inlet 121, and the humidifier gases outlet 124 and apparatus outlet 13. For example, the flow of gases from the outlet 113 of the flow generator 11 is received into the humidification chamber via its gases inlet and exits the chamber via its gases outlet, after being heated and / or humidified.

[0252] The humidification chamber 120 may be configured to contain a volume of liquid, typically water. In operation, the liquid in the humidification chamber is controllably heated by one or more heaters (e.g., heater plate 121) or heating elements (e.g., heating element 122 of the heater plate 121) associated with the humidifier 12 to generate water vapour and thereby increase the humidity of the gases flowing through the chamber 120.

[0253] In one configuration, the humidifier 12 is a heated pass-over humidifier. In another configuration, the humidifier may be a non-heated (i.e., cold) pass-over humidifier. In another configuration, the humidifier may be a non-pass-over humidifier.

[0254] As will be discussed, the breathing assistance apparatus 10 of the present disclosure may be considered a breathing assistance apparatus which is capable of delivering a hybrid respiratory therapy. The hybrid respiratory therapy may incorporate aspects of a flow-based therapy (such as high flow therapy) and a pressure-based therapy (such as CPAP therapy).

[0255] 1.9. Pres sure -Based Therapy

[0256] Pressure-based therapy as discussed herein is intended to be given its typical ordinary meaning, as understood by a person of skill in the art, which generally refers to a respiratory therapy system or breathing assistance apparatus delivering a flow of gas to a patient at a therapeutic pressure above atmospheric pressure. The delivery of the flow of gas to a patient at a therapeutic pressure above atmospheric pressure may reduce the frequency and / or duration of apnoeas, hypopneas, and / or flow limitations. A constriction of the airway, otherwise known as an obstructive apnoea or a hypopnoea (collectively referred to as obstructive sleep apnoea or OSA), can occur when the muscles that normally keep the airway open in a patient relax during slumber to the extent that the airway is constrained or completely closed off, a phenomenon often manifesting itself in the form of snoring. When this occurs for a significant period of time, the patient's brain typically recognizes the threat of hypoxia and partially wakes the patient in order to open the airway so that normal breathing may resume. The patient may be unaware of these occurrences, which may occur as many as several hundred times per session of sleep.

[0257] This therapy may be delivered by using a breathing assistance apparatus to propel a pressurized stream of air through a supply conduit to a patient through a patient interface or mask located on the face of the patient. The stream of air may be heated to near body temperature. The stream of air may be humidified. The humidification may be performed by forcing the stream of air to travel through a humidifier containing water and a heater for heating the water. In such a system the heater encourages the evaporation of the water, which in turn partially or fully imbues the stream of air with moisture and / or heat. This moisture and / or heat may help to ameliorate discomfort that may arise from the use of a nonhumidified pressure-based therapy.

[0258] In respiratory therapy methods involving administration of pressurized respiratory gases to treat obstructive sleep apnoea, it is known to use constant positive airway pressure (CPAP) therapy, in which the pressure delivered over the course of a therapy session remains constant. In some situations, bi-level PAP therapy may be used. Bi-level PAP therapy may refer to a pressure-based therapy in which a breathing assistance apparatus may be used to deliver a first pressure at or around a detection of an inhalation of a patient (e.g., an inhalation positive airway pressure or IPAP) and deliver a second pressure at or around a detection of an exhalation of the patient (e.g., an exhalation positive airway pressure or EPAP). CPAP and Bi-level PAP are both examples of pressure-based therapies. To improve patient comfort, the second pressure may be lower than the first pressure, reducing the resistance during exhalation. In some situations, the breathing assistance apparatus may reduce the pressure delivered from a therapeutic level to a sub-therapeutic level upon determination of a wakeful state of the patient and increase the pressure delivered from a sub-therapeutic level to a therapeutic level upon determination of an asleep state of the patient.

[0259] A minimum pressure is typically required to be delivered to a patient’s airways in order to provide the therapeutic benefits of a pressure-based therapy, such as opening the patient’s airways so that normal breathing can occur. This minimum pressure is typically between about 3 and about 4 cmEEO. As such, the range of pressures commonly delivered in a pressure-based therapy are between about 4 cmEEO and about 25 cmEEO. In some examples, the range of pressures delivered may be between about 4 cmEEO and about 20 cmEEO. In some examples, the range of pressures delivered may be between about 4 cml O and about 15 cmlLO. In some examples, the range of pressures delivered may be between about 4 cml O and about 10 cnftLO. In some examples, the range of pressures delivered may be between about 6 cmfbO and about 15 cmFbO. In some examples, the range of pressures delivered may be between about 4 cmlLO and about 8 cmlLO. In many cases, the minimum and / or maximum pressures delivered in a pressure -based respiratory therapy are prescribed by a medical professional, and the apparatus is likewise configured by the professional or a medical device dealer.

[0260] 1.10. High Flow Therapy

[0261] High flow therapy as discussed herein is intended to be given its typical ordinary meaning, as understood by a person of skill in the art, which generally refers to a respiratory therapy system delivering a targeted flow of humidified respiratory gases via an intentionally unsealed or non-sealing patient interface with flow rates generally intended to meet or exceed the inspiratory demand of a user. High flow therapy is typically provided at desired flow rates high enough to meet or exceed a patient’s inspiratory demand. The flow rate provided is ideally sufficient such that ambient gases are not entrained as the patient inspires. Typical patient interfaces used for high flow therapy include, but are not limited to, a nonsealing nasal cannula or a tracheal patient interface. Typical flow rates for adults often range from, but are not limited to, about fifteen litres per minute to about sixty litres per minute or greater. Typical flow rates for paediatric users (such as neonates, infants and children) often range from, but are not limited to, about one litre per minute per kilogram of user weight to about three litres per minute per kilogram of user weight or greater.

[0262] High flow therapy can also optionally involve delivery of gas mixture compositions including supplemental oxygen and / or administration of therapeutic medicaments.

[0263] High flow therapy is often referred to as nasal high flow (NHF), humidified high flow nasal cannula (HHFNC), high flow nasal oxygen (HFNO), high flow therapy (HFT), or tracheal high flow (THF), among other common names. For example, in some configurations, for an adult patient ‘high flow therapy’ may refer to the delivery of gases to a patient at a flow rate of greater than or equal to about 10 litres per minute (10 L / min), such as between about 10 L / min and about 500 L / min, or between about 15 L / min and about 95 L / min, or between about 20 L / min and about 90 L / min, or between about 25 L / min and about 85 L / min, or between about 30 L / min and about 80 L / min, or between about 35 L / min and about 75 L / min, or between about 40 L / min and about 70 L / min, or between about 45 L / min and about 65 L / min, or between about 50 L / min and about 60 L / min.

[0264] In some configurations, for a neonatal, infant, or child patient ‘high flow therapy’ may refer to the delivery of gases to a patient at a flow rate of greater than 1 L / min, such as between about 1 L / min and about 25 L / min, or between about 2 L / min and about 25 L / min, or between about 2 L / min and about 5 L / min, or between about 5 L / min and about 25 L / min, or between about 5 L / min and about 10 L / min, or between about 10 L / min and about 25 L / min, or between about 10 L / min and about 20 L / min, or between about 10 L / min and 15 L / min, or between about 20 L / min and 25 L / min. A high flow therapy apparatus with an adult patient, a neonatal, infant, or child patient, may deliver gases to the patient at a flow rate of between about 1 L / min and about 500 L / min, or at a flow rate in any of the sub-ranges outlined above.

[0265] High flow therapy can be effective in meeting or exceeding the patient's inspiratory demand, increasing oxygenation of the patient and / or reducing their work of breathing. Additionally, high flow therapy may generate a flushing effect in the nasopharynx such that the anatomical dead space of the upper airways is flushed by the high incoming gases flow. The flushing effect can create a reservoir of fresh gas available of each and every breath, while minimizing re-breathing of carbon dioxide, nitrogen, etc. High flow therapy can also increase expiratory time of the patient due to pressure provided during expiration. This in turn reduces the respiratory rate of the patient.

[0266] 1.11. Ultrasonic Sensing System Details

[0267] The second type of sensor can comprise an acoustic sensor assembly. Acoustic sensors including acoustic transmitters and / or receivers can be used to measure times of flight of acoustic signals to determine gases velocity and / or composition. In one ultrasonic sensing (including ultrasonic transmitters and / or receivers) topology, a driver causes a first sensor, such as an ultrasonic transducer, to produce an ultrasonic pulse in a first direction. A second sensor, such as a second ultrasonic transducer, receives this pulse and provides a measurement of the time of flight of the pulse between the first and second ultrasonic transducers. Using this time-of-flight measurement, the speed of sound of the gases flow between the ultrasonic transducers can be calculated by a processor or controller of the respiratory therapy system. The second sensor can transmit and the first sensor can receive a pulse in a second direction opposite the first direction to provide a second measurement of the time of flight, allowing characteristics of the gases flow, such as a flow rate or velocity, to be determined. In another acoustic sensing topology, acoustic pulses transmitted by an acoustic transmitter, such as an ultrasonic transducer, can be received by acoustic receivers, such as microphones.

[0268] In one example configuration, a flow rate sensor or sensors, or sensor assembly, may be located in the main apparatus housing before or after the humidifier 52 (if present). For example, the flow rate sensor may be arranged or configured in the main apparatus housing to sense the flow rate of the gases in the flow path at a location between the flow generator 50B and humidifier 52, or a location in the flow path after the humidifier. In another example configuration, the apparatus may comprise any combination of the mentioned one or more flow rate sensor or sensor assembly configurations or locations. For example, the apparatus may comprise any combination of one or more flow rate sensors or sensor assemblies in any one or more locations along the gases flow path, whether in the main apparatus housing, supply conduit 16, and / or patient interface 51.

[0269] 2. Patient interface

[0270] 2.1. Unsealed nasal cannula

[0271] As discussed above in relation to FIG. 1, patient interfaces 30 can be used in respiratory therapy systems 1 for delivering of flow of gases to the airways of a patient. The patient interfaces may comprise nasal interfaces that can be used to deliver a flow of gases to a patient. The nasal interfaces may comprise nasal delivery elements, such as nasal prongs (and may optionally comprise nasal pillows). The nasal delivery elements may be intended to substantially seal or partially occlude one or both of the nasal passages, or may not be required to seal at the nose, to deliver the respiratory therapy. A nasal prong can be inserted into the nose of a patient to deliver the required respiratory therapy. Nasal prongs typically refer to nasal delivery elements designed to not seal or to only partially occlude the nasal passages. However, some larger prongs might substantially occlude the nasal passages. When one or more of the nasal delivery elements comprises a nasal pillow, the nasal delivery elements are designed to substantially seal at the nose.

[0272] The present disclosure relates to a non-sealing respiratory therapy that delivers relatively high flow to the patient through a patient interface, such as a nasal interface. A nasal interface as herein described may refer to, but is not limited to, a nasal cannula.

[0273] Disclosed is a system and apparatus to deliver gases to a patient through a nasal cannula or nasal interface. In examples, the patient interface is an asymmetric nasal interface or may comprise asymmetric nasal delivery elements. An asymmetric interface or asymmetric nasal delivery elements, as described herein, refers to an interface where the nasal delivery elements differ in size such as internal and / or external transverse dimensions or diameters, and / or internal and / or external cross-sectional areas. The external cross-sectional area is the cross-sectional area bounded by the outer wall of the nasal delivery element. For non-circular cross-sections, the references herein to a diameter may be interpreted as a transverse dimension (in the non-circular cross section). In some configurations, references herein to a diameter include but are not limited to a hydraulic parameter.

[0274] An asymmetric nasal interface may have any one or more of the features and functionality described in PCT publication no. WO 2022 / 229909 Al. The contents of that specification are incorporated herein in their entirety by way of reference.

[0275] When the system of the present disclosure is used with an asymmetric nasal interface, an asymmetrical flow of gases can be delivered through the interface to both nares or to either naris of the patient. Asymmetrical flow as described herein refers to a flow that differs within the interface or within the nose or within the interface and the nose. In this way, a different flow may be delivered by each nasal delivery element, or the flow may differ between inspiration and expiration, or the delivered flow may differ in a combination of the above ways. An asymmetrical flow may also include partial unidirectional flow, where flow occurs into one nostril and out of the other nostril.

[0276] Delivery of asymmetrical flow may improve clearance of dead space in the upper airways of the patient, decrease peak expiratory pressure, increase safety of the therapy, particularly for children and infants, and reduce resistance to flow in the interface. An asymmetric nasal interface and / or nasal delivery elements as described herein includes interfaces or systems configured to produce such asymmetrical flow through asymmetric nasal delivery elements or otherwise. The pressure generated by the flow of gases delivered to the patient depends at least in part on the flow through the nasal interface, the size of the nasal delivery elements and / or nares of the patient, and the breathing cycle of the patient. If flow, leak, or a combination of flow and leak, is asymmetrical through the nasal interface, the flow through the nose may become asymmetrical during breathing. Partial or total unidirectional flow may be types of asymmetrical flow. Partial or total unidirectional flow may provide improved clearance of anatomical dead space as the air is continuously flushed from the upper airways. Partial unidirectional flow may be more comfortable than total unidirectional flow. Total unidirectional flow as described herein includes flow entering one naris via a first nasal delivery element and exiting via the other naris via a second nasal delivery element or venting to the atmosphere, due to the absence of a second nasal delivery element, for example. Partial unidirectional flow as described herein includes flow that may enter the nose via both nares and leave the nose from one naris, flow that may enter the nose through one naris and leave the nose via both nares, or different proportions of flow that may enter the nose through both nares and different proportions of flow that may leave the nose through both nares, and may be flow that may enter the nose via both nares and leave the nose from one or both nares and / or optionally via the mouth.

[0277] Delivery of a flow of gases through an asymmetric nasal interface can involve using an interface in which the nasal delivery elements are of different size, e.g. different length and / or internal diameter or cross- sectional area and / or external diameter or cross-sectional area. Particularly for children or infants, nasal delivery elements will have a small internal diameter and thus higher resistance to gas flow. By using nasal delivery elements that are different lengths, each nasal delivery element may have a different internal diameter (e.g., minimum internal diameter or area). A longer nasal delivery element that has a smaller internal diameter may have a higher resistance to gas flow; a shorter nasal delivery element that has a larger internal diameter (e.g., larger minimum internal diameter), may have a lower resistance to gas flow at the interface. A lower resistance to flow allows a desired flow to be achieved using lower backpressure, or a lower motor speed of the flow generator, or a combination of the two.

[0278] Expiratory pressure is dependent on the combined cross-sectional area of the two nasal delivery elements in the nares of the patient. Asymmetric nasal delivery elements may cause the peak expiratory pressure to decrease due to the differing cross-sectional areas between the two nasal delivery elements at the nose. For example, the different internal diameters for each nasal delivery element may cause each nasal delivery element may result in or provide a different peak expiratory pressure. For example, a smaller diameter (and thus smaller cross-sectional area) of a nasal delivery element may result in or provide a reduced peak expiratory pressure when compared to a nasal delivery element having a larger diameter (and thus larger cross-sectional area).

[0279] The pressure experience when exhaling through an asymmetric nasal interface may be higher than with a symmetric one, which may be advantageous as higher positive end-expiratory pressure (PEEP) can be beneficial for the treatment for COPD (pressure here referring to the intrathoracic pressure). Increasing the cross-sectional area of symmetric nasal delivery elements carries the risk of fully occluding the patient's nares. Using asymmetric nasal delivery elements can allow for an increase in total cross-sectional area of the nasal delivery elements within the nares without the accompanying occlusion risk. For example, the use of asymmetric nasal delivery elements can provide an increase in the cross- sectional area of one of the nasal delivery elements, but not the other, or may provide a decrease the cross-sectional area of the other nasal delivery element.

[0280] Partially unidirectional flow may reduce turbulence in the patient's nasal cavity, which may improve therapy comfort. During exhalation, a patient may be breathing against less pressure in the system as one naris may be open to the atmosphere, or a nasal delivery element may have a greater internal diameter compared to the other nasal delivery element or otherwise have less resistance to exhalation flow compared to the other nasal delivery element, which may reduce the pressure required to exhale.

[0281] In an example, an asymmetric nasal interface used with (e.g., coupled via a conduit or breathing tube) a flow generator, such as an AIRVO™ 3 flow generator from Fisher & Paykel Healthcare Limited, provides less resistance to flow in the system as compared to a symmetric nasal interface. As discussed above, this may be due to the larger diameter / cross-sectional area of one nasal delivery element compared to either nasal delivery element in a conventional symmetric nasal interface. This lower resistance to flow may allow the motor speed of a motor driving a blower in the flow generator to drop from a range of 18,000 - 22,000 RPM to a range of 14,000 - 18,000 RPM, while continuing to achieve a suitable flow and / or pressure for the desired therapy, such as about 10 litres per minute (L / min) or higher.

[0282] 2.2. Asymmetric nasal cannula

[0283] FIGS. 8-15 show an exemplary breathing circuit 400 and / or patient interface 500. The breathing circuit 400 comprises at least patient interface 500 and a supply conduit 520. The patient interface 500 comprises a nasal cannula or nasal interface 500 with asymmetric nasal delivery elements 411, 412.

[0284] The nasal interface 500 provides a patient with a patient interface suitable for the delivery of a flow of gases to the patient's nasal cavity / nares. In some configurations, the nasal interface 500 is adapted to deliver a flow of gases over a wide flow range (e.g., about 1 L / min, or higher depending on other therapy applications, perhaps such as 10 - 60 L / min or higher).

[0285] The nasal interface 500 comprises a face mount part 410 including a pair of asymmetric tubular nasal prongs 411 and 412, integrally moulded with or removably attached to the face mount part 410, and a gases manifold 420 part that is removably attached or integrally moulded to the conduit 520.

[0286] The gases manifold 420 is insertable into the face mount part 410. The face mount part 410 may comprise at least one substantially horizontal side entry passage 418a, 418b to the interior of a base portion or cannula body 418 of the face mount part 410 for releasably receiving the outlet of the gases manifold 420 therethrough. The gases manifold 420 is optionally insertable into the face mount part 410 from either of two opposing horizontal directions, i.e. from either left side or the right side. In this manner, the position or location of the gases manifold 420 is reconfigurable with respect to the face mount part 410. In other words, a user may choose to have the manifold part 420 (and the conduit 520 extending therefrom) extend from either the left side or the right side of the face mount part 410 of the nasal interface 500 depending on what is most convenient, for example depending on which side of the user the gas source or ventilator is located. In an alternative configuration, the gases manifold 420 is not reconfigurable with respect to the face mount part 410.

[0287] The face mount part 410 may comprise a pair of opposed side entry passages 418a, 418b to the interior of the base portion or cannula body 418, each adapted to releasably receive the outlet of the gases manifold 420 therethrough.

[0288] The face mount part 500 is formed from a soft, flexible material such as silicone or other suitable material known in the art. The nasal prongs 411 and 412 are preferably supple and may be formed from a sufficiently thin layer of silicone to achieve this property.

[0289] The gases manifold 420 is formed from a relatively harder material such as polycarbonate, a high-density polyethylene (HDPE) or any other suitable plastics material known in the art. The face mount part 410 provides a soft interfacing component to the patient for comfortably delivering the flow of gases through the nasal prongs 411 and 412, while the gases manifold 420 fluidly couples the conduit 520 to the nasal prongs 411 and 412 of the face mount part 410.

[0290] The nasal prongs 411 and 412 are curved to extend into the patient's nares in use and to provide a smooth flow path for gases to flow through. The inner surfaces of the prongs 411 and 412 may be contoured to reduce noise. The bases of the prongs 411 and 412 may include curved surfaces to provide for smoother gases flow into the prongs. This may reduce the noise level during operation.

[0291] The nasal prongs 411 and 412 are substantially hollow and substantially tubular in shape. The nasal prongs 411 and 412 may be consistent in diameter along their lengths or alternatively may be shaped to fit the contours of the nares.

[0292] The face mount part 410 is shaped to generally follow the contours of a patient's face around the upper lip area. The face mount part 410 is moulded or preformed to be able to conform to and / or is pliable to adapt, accommodate and / or correspond with the contours of the user's face, in the region of the face where the cannula is to be located.

[0293] The asymmetry of the nasal prongs 411 and 412 may reduce the chance of accidental occlusion of both nares. At least one of the nasal prongs 411 and 412 is therefore sized to maintain a sufficient gap between the outer surface of the prongs 411 and 412 and the patient's skin to avoid sealing the gas path between the nasal interface 500 and patient. It should be understood that in the context of the present disclosure, the nasal prongs 411 and 412 are asymmetric, as described below. The face mount part 410 comprises the base part or cannula body 418 from which the nasal prongs 411 and 412 extend, and two side arms comprising wing portions 413 and 414 extending laterally from either side of the cannula body 418. The wing portions 413 and 414 are integrally formed with the cannula body 418 but may alternatively be separate parts.

[0294] In some examples, adhesive pads may be provided on each wing portion 412, 414 to facilitate coupling of the cannula 500 to the patient - especially for younger children (e.g., under 5 years old).

[0295] The gases manifold 420 is generally tubular in shape, having a substantially annular gases inlet 421 at one end, and that curves around into an elongate oval outlet at the opposing end. The inlet 421 may be removably attachable to a conduit 520, such as via a threaded engagement, or alternatively via a snap-fit coupling or any other type of coupling known in the art. Alternatively, the inlet is fixedly coupled or integrally formed with a conduit 520.

[0296] The shape of the outlet 423 corresponds with and fits into the cannula body 418, e.g., with a friction fit or snap fit engagement, such that substantial force, or at least a deliberate force applied by a user, is required to separate the manifold 420 from the face mount part 410.

[0297] An effective seal is formed between the outlet 423 and the cannula body 418 upon engagement of the two parts 418 and 420. As discussed below, and as shown in FIG. 12, the gases manifold 420 may comprise a retaining flange 420b around a face thereof which is removably received in a complementary resilient rim 418d of the cannula body 418. The engagement of the retaining flange 420b with the complementary resilient rim 418d of the cannula body 418 assists with forming a seal between the gases manifold 420 and the cannula body 418.

[0298] The nasal prongs 411, 412 are aligned with corresponding apertures extending through an upper surface of the cannula body 418 to fluidly connect the manifold outlet 423 with the nasal prongs 411 and 412 when coupled.

[0299] A headgear may be used to retain the nasal interface 500 against the patient's face. The headgear comprises a head strap 510. The head strap 510 may comprise a single continuous length and be adapted to extend, in use, along the patient's cheeks, above the ears and about the back of the head. The head strap 510 may be adjustable, and / or may extend around other portions of the patient's head.

[0300] 2.3. Asymmetric prongs

[0301] Referring to FIGS. 8-15, in some configurations a nasal interface 500 of the present disclosure comprises a first prong 411 and a second prong 412 that are asymmetrical to each other (i.e., the prongs are not identical), and a gases manifold 420 comprising a gases inlet 421. The first prong 411 and the second prong 412 are in fluid communication with the gases inlet 421. The first prong 411 and the second prong 412 can be considered asymmetric nasal delivery elements. The first prong 411 and the second prong 412 are asymmetrical to each other and / or are not symmetrical to each other and / or differ in shape and configuration to each other and / or are asymmetrical when compared to each other. The nasal interface is configured such that at least about 60% of a total volumetric flow rate of gases flow into the gases inlet 421 is delivered out of the nasal interface through the first prong 411.

[0302] The gases inlet 421 may be at a side of the gases manifold 420. In alternative configurations, the gases inlet 421 may be at a different location on the gases manifold 420. For example, the gases inlet 421 may enter the front of the gases manifold 420, at or near a centre of the gases manifold 420 or at or near one side of the gases manifold 420.

[0303] The total volumetric flow rate of gases flow may change based on a patient's breathing cycle and internal nasal geometry. The figures and proportions herein are when the nasal interface isn't being worn and before any influence from the patient's respiration and / or nasal geometry.

[0304] By way of example, if a blower of a respiratory therapy apparatus is generating flow of 500 L / min and that is delivered into the gases inlet 421 of an asymmetric nasal cannula, at least about 60 L / min would pass into the first prong 411 and be delivered out of the nasal interface 500, to the patient, through the first prong 411. The remainder of the total gases flow would be delivered through the second prong 412. In the example above, about 40 L / min or less would pass through the second prong 412 and be delivered out of the nasal interface 500 through the second prong 412. Some of the total gases flow may be vented to atmosphere rather than being delivered through the first prong 411 or the second prong 412.

[0305] The nasal interface 500 is configured to cause an asymmetrical flow of gases at, into and / or out of a patient's nares.

[0306] In some configurations, the first and second prongs 411, 412 are configured to engage with the nasal passages in an unsealed (non-sealing) manner. In some configurations, at least the second prong 412 is configured to engage with a nasal passage in a non-sealing manner.

[0307] In some configurations, the first and second prongs 411, 412 allow exhaled gases to escape around the first and second prongs.

[0308] In some configurations, the first and second prongs 411, 412 are configured to provide gases to the patient without interfering with the patient's spontaneous respiration.

[0309] The first prong 411 has a first prong outlet 411a defined by an opening at its tip or terminal end 411b for delivery of gases from the first prong 411. Gases delivered through the first prong 411 exit the first prong via the first prong outlet 411a.

[0310] The second prong 412 has a second prong outlet 412a defined by an opening at its tip or terminal end 412b for delivery of gases from the second prong 412. Gases delivered through the second prong 412 exit the second prong via the second prong outlet 412a.

[0311] Referring to FIGS. 12 to 15, in some configurations of a nasal interface 500, the first prong 411 has a larger inner diameter ID1 and / or a larger inner cross-sectional area Al in a direction transverse to gases flow GFD 1 through the first prong 411 than a corresponding inner diameter ID2 and / or inner cross- sectional area A2 of the second prong 412 in a direction transverse to gases flow GFD2 through the second prong 412.

[0312] ID1, ID2, Al and A2 may be measured at substantially the same location along first prong 411 and second prong 412 (for example, the same distance along the prong length from the base of each prong or from the outlet of each prong). This may be a useful reference for curved and / or angled prongs. In some embodiments, ID1, ID2, Al and A2 may be measured along the same plane. This may be a useful reference for straight prongs.

[0313] In some configurations, the direction transverse to gases flow is substantially perpendicular or normal to gases flow through the respective prong 411, 412. Alternatively, the direction transverse to gases flow could be at an acute or obtuse angle relative to gases flow through the respective prong 411, 412.

[0314] The inner diameter(s) ID1, ID2 and / or inner cross-sectional area(s) Al, A2 could be substantially constant along the length of the prongs 411, 412. Alternatively, the inner diameter ID1, ID2 and / or inner cross-sectional area A 1 , A2 could vary along at least part of the length of the prongs 411, 412. For example, the prongs 411, 412 may taper from a wider dimension at their bases near the cannula body 418 than at their tips or terminal ends 411b, 412b. The inner diameter ID1, ID2 and cross-sectional areaAl, A2 of relevance could be at the outlets 41 la, 412a of the prongs and / or at the distal portions of the prongs 411, 412 adjacent the outlets 411a, 412a.

[0315] The inner surface at the base of each prong 411, 412 may be radiused or chamfered to reduce the pressure and velocity drop of gases as the gases change flow direction within the manifold. This can help reduce noise and improve delivery of therapy.

[0316] The nasal interface 500 may be configured such that between about 60% and about 90% of the total volumetric flow rate of gases flow into the gases inlet 421 is delivered out of the nasal interface 500 through the first prong 411. The nasal interface may be configured such that between about 60% and about 80% of the total volumetric flow rate of gases flow into the gases inlet 421 is delivered out of the nasal interface 500 through the first prong 411. The nasal interface may be configured such between about 65% and about 80% of the total volumetric flow rate of gases flow into the gases inlet 421 is delivered out of the nasal interface 500 through the first prong 411. The nasal interface may be configured such that between about 70% and about 80% of the total volumetric flow rate of gases flow into the gases inlet 421 is delivered out of the nasal interface 500 through the first prong 411. The nasal interface may be configured such that between about 70% and about 75% of the total volumetric flow rate of gases flow into the gases inlet 421 is delivered out of the nasal interface 500 through the first prong 411. The nasal interface may be configured such that about 70% of the total volumetric flow rate of gases flow into the gases inlet 421 is delivered out of the nasal interface 500 through the first prong 411.

[0317] Having a ratio of flow rates between the prongs 411, 412 of at least about 60:40 has been found sufficient to start seeing the benefits of asymmetrical flow describe below. A ratio of between about 70:30 and about 75:25 is believed to be optimal. The proportion of the total volumetric flow rate being delivered through each prong 411, 412 can be determined by delivering gases with a known volumetric flow rate to the gases inlet 421 of the nasal interface 500 while the nasal interface is not applied to a patient's nares. The volumetric flow rate exiting each outlet 41 la, 412a can be measured by a suitable flow meter or sensor to determine the proportion of the total volumetric flow rate of gases flow into the gases inlet 421 that is exiting the outlet 411a, 412a of each prong 411, 412.

[0318] The first prong 411 may have an inner diameter ID1 of between about 4 mm and about 10 mm, optionally between about 5 mm and about 9 mm, optionally between about 6 mm and about 8 mm, optionally about 4 mm, about 5 mm, about 6 mm, about 7 mm, about 8 mm, about 9 mm, about 10 mm, or any diameter between any two of those diameters.

[0319] The second prong 412 may have an inner diameter ID2 of between about 2 mm and about 8 mm, optionally between about 3 mm and about 7 mm, optionally between about 4 mm and about 6 mm, optionally about 2 mm, about 3 mm, about 4 mm, about 5 mm, about 6 mm, about 7 mm, about 8 mm, or any diameter between any two of those diameters.

[0320] In some configurations, the first prong 411 and / or the second prong 412 has a wall thickness of between about 0. 1 mm and about 0.5 mm. Therefore, at least double the wall thickness can be added to the inner diameter values to get the associated outer diameter values.

[0321] The nasal interface 500 may be configured such that between about 75% and about 80% of the total gases flow is delivered through the first prong 411.

[0322] The nasal interface 500 may be configured such that about 75% of the total gases flow is delivered through the first prong 411.

[0323] The nasal interface 500 may be configured such that about 80% of the total gases flow is delivered through the first prong 411.

[0324] The first prong 411 may have has an inner cross-sectional area Al of between about 15 mm2and about 80 mm2, optionally between about 20 mm2and about 75 mm2, optionally between about 25 mm2and about 70 mm2, optionally between about 30 mm2and about 65 mm2, optionally between about 35 mm2and about 60 mm2, optionally between about 40 mm2and about 55 mm2, optionally between about 45 mm2and about 50 mm2, optionally about 15 mm2, about 16 mm2, about 17 mm2, about 18 mm2, about 19 mm2, about 20 mm2, about 21 mm2, about 22 mm2, about 23 mm2, about 24 mm2, about 25 mm2, about 26 mm2, about 27 mm2, about 28 mm2, about 29 mm2, about 30 mm2, about 31 mm2, about 32 mm2, about 33 mm2, about 34 mm2, about 35 mm2, about 36 mm2, about 37 mm2, about 38 mm2, about 39 mm2, about 40 mm2, about 41 mm2, about 42 mm2, about 43 mm2, about 44 mm2, about 45 mm2, about 46 mm2, about 47 mm2, about 48 mm2, about 49 mm2, about 50 mm2, about 51 mm2, about 52 mm2, about 53 mm2, about 54 mm2, about 55 mm2, about 56 mm2, about 57 mm2, about 58 mm2, about 59 mm2, about 60 mm2, about 61 mm2, about 62 mm2, about 63 mm2, about 64 mm2, about 65 mm2, about 66 mm2, about 67 mm2, about 68 mm2, about 69 mm2, about 70 mm2, about 71 mm2, about 72 mm2, about 73 mm2, about 74 mm2, about 75 mm2, about 76 mm2, about 77 mm2, about 78 mm2, about 79 mm2, about 80 mm2, or any cross-sectional area between any two of those cross-sectional areas.

[0325] The second prong 412 may have an inner cross-sectional area A2 of between about 5 mm2and about 50 mm2, optionally between about 10 mm2and about 45 mm2, optionally between about 15 mm2and about 40 mm2, optionally between about 20 mm2and about 35 mm2, optionally between about 25 mm2and about 30 mm2, optionally about 5 mm2, about 6 mm2, about 7 mm2, about 8 mm2, about 9 mm2, about 10 mm2, about 11 mm2, about 12 mm2, about 13 mm2, about 14 mm2, about 15 mm2, about 16 mm2, about 17 mm2, about 18 mm2, about 19 mm2, about 20 mm2, about 21 mm2, about 22 mm2, about 23 mm2, about

[0326] 24 mm2, about 25 mm2, about 26 mm2, about 27 mm2, about 28 mm2, about 29 mm2, about 30 mm2, about 31 mm2, about 32 mm2, about 33 mm2, about 34 mm2, about 35 mm2, about 36 mm2, about 37 mm2, about 38 mm2, about 39 mm2, about 40 mm2, about 41 mm2, about 42 mm2, about 43 mm2, about

[0327] 44 mm2, about 45 mm2, about 46 mm2, about 47 mm2, about 48 mm2, about 49 mm2, about 50 mm2, or any cross-sectional area between any two of those cross-sectional areas.

[0328] Having specific differences between the inner diameters ID1, ID2 and / or the inner cross-sectional areas Al, A2 can contribute to desired levels of asymmetry.

[0329] A combined inner cross-sectional area (A 1 + A2) of the first prong 411 and the second prong 412 may be between about 20 mm2and about 130 mm2, optionally between about 30 mm2and about 120 mm2, optionally between about 40 mm2and about 110 mm2, optionally between about 50 mm2and about 100 mm2, optionally between about 60 mm2and about 90 mm2, optionally between about 70 mm2and about 80 mm2, optionally about 20 mm2, about 25 mm2, about 30 mm2, about 35 mm2, about 40 mm2, about 45 mm2, about 50 mm2, about 55 mm2, about 60 mm2, about 65 mm2, about 70 mm2, about 75 mm2, about 80 mm2, about 85 mm2, about 90 mm2, about 95 mm2, about 100 mm2, about 105 mm2, about 110 mm2, about 115 mm2, about 120 mm2, about 125 mm2, about 130 mm2, or any cross-sectional area between any two of those cross- sectional areas.

[0330] A ratio of the inner cross-sectional area Al of the first prong 411 to the inner cross-sectional area A2 of the second prong 412 may be between about 60:40 and about 80:20; optionally between about 65:35 and about 80:20; optionally between about 70:30 and about 80:20; optionally between about 70:30 and about 75:25; optionally about 70:30, about 71:29, about 72:28, about 73:27, about 74:26, or about 75:25; optionally between about 75:25 and 80:20; optionally about 75:25, about 76:24, about 77:23, about 78:22, about 79:21, or about 80:20.

[0331] Pressure and flow may be measured and controlled in the nares simultaneously or separately. Flow may be continuous in one naris, while it is varied in the other naris according to the breathing cycle. Different interfaces, each delivering asymmetrical flow in the nose, may be used to continuously deliver supplemental oxygen, and to deliver a continuous or variable flow of gases to the nares of the patient. In some examples, one nasal delivery element may be used to deliver oxygen, gases, aerosols or the like to the patient, while another nasal delivery element may be used to deliver a higher flow of air, or a different flow of oxygen, gases, aerosols or the like to the patient. In further examples, each nasal delivery element may supply different flow rates to the patient, and may connect to different flow generating elements.

[0332] 3. Hybrid respiratory therapy

[0333] Conventional continuous positive airway pressure (CPAP) therapy is a well-established treatment for sleep apnoea and other respiratory disorders. In conventional CPAP therapy, a user sets a target pressure and a flow generator will be controlled to pressurise air so as to achieve this target pressure at the airways of the patient, by the delivery of the flow of pressurised gases through a sealing patient interface. As such, conventional CPAP can be considered a pressure-based respiratory therapy. It can also be considered a pressure -controlled respiratory therapy, in reference to the key therapy parameter being controlled, pressure. The constant positive pressure provided helps to keep the patient's airways open and can improve and / or assist with ventilation, e.g., by increasing functional residual capacity (FRC) of the lungs.

[0334] In conventional CPAP, there will be a permitted rate at which gases leak from the sealed patient interface. This leak is due to bias holes or vents in the patient interface that are provided to avoid overpressure conditions, especially during patient exhalations. The leak is generally uncontrolled, in that the flow generator does not adjust its output in real time based on the leak flow rate, for example. The leak flow rate occurring at any point in time is largely dependent on the patient’s breathing activity i.e., whether or not they are exhaling or inhaling, and how strongly. The leak flow rate may also be constrained by the geometry of the bias holes or vent(s).

[0335] Conventional nasal high flow (NHF) therapy involves delivery of a high flow rate of heated and humidified gases to the nasal passages of a patient and can be used to treat patients suffering from a variety of respiratory conditions and disorders. Patients with low blood oxygen levels (hypoxemic) and / or high blood carbon dioxide levels (hypercapnic) are often treated with NHF therapy.

[0336] In NHF therapy, unsealed or non-sealing patient interfaces are typically used. An example of an unsealed patient interface is a nasal cannula, such as the nasal cannula(s) described previously. In conventional NHF therapy, a user sets a target flow rate, and a flow generator will be controlled to deliver and maintain this target flow rate to an unsealed patient interface. As such, NHF therapy can be considered a flowbased respiratory therapy. It can also be considered a flow-controlled respiratory therapy, in reference to the key therapy parameter being controlled, flow rate.

[0337] The high flow rate of the gases provided in conventional NHF therapy has been shown to provide benefits such as anatomical dead space clearance, reduced respiratory effort, and improved ventilation. In addition, the heated, humidified flow of gases delivered, and the unobtrusive nasal interfaces commonly used in NHF therapy together can offer a comfortable and tolerable form of respiratory therapy. NHF therapy intentionally allows a high degree of leak between the patient interface and the patient’s nares (nostrils) in order to prevent pressure-related injuries from occurring and to allow for flushing of gases from the upper airways. This allowance of leak can, however, result in variable leak flow rates and fluctuations in airway pressure over the patient's breathing cycle. NHF therapy is also generally not able to achieve the levels of pressure that are typically associated with CPAP therapy, which are needed in order to keep the patient's airway open during apnoeas.

[0338] Conventional CPAP and NHF therapies thus may each entail one or more trade-offs for patients who require extended periods of respiratory therapy. CPAP therapy requires the use of more intrusive, sealing patient interfaces (nasal pillows, nasal masks, full-face masks, etc.) and does not offer dead space clearance which affects its usefulness for treating hypercapnic patients, in particular. On the other hand, NHF therapy is less intrusive and more comfortable (and therefore more tolerable), but for these very reasons it might not reach the pressure levels associated with CPAP (particularly on inspiration). These trade-offs may lead to a reduction in the overall effectiveness of the therapy i.e. by not offering both pressure support and dead space washout, and / or a decreased adherence to treatment protocols.

[0339] In some examples, the control methods of the present disclosure, specifically, the use of a minimum flow parameter such as a floor flow rate or floor pressure in the control of the flow of gases delivered to the patient, may additionally be at least somewhat beneficial when implemented alongside or as part of an automatic oxygen control system (i.e., an FiO2 controller). In such examples, automatic oxygen control systems may thus provide an increasing flow on inspiration which will help to ensure that the patient receives sufficient oxygen, while the flow rate floor may be implemented on expiration will reduce oxygen wastage (although not eliminate it). In these examples, oxygen control systems may operate independently of the flow generator, so if the flow rate changes (i.e., motor speeds up, drawing in more ambient air), the oxygen control system may attempt to adjust the oxygen level in the flow of gases delivered to maintain the same fraction of oxygen in the flow of gases. In this sense, the oxygen control system may thus affect the flow rate.

[0340] In existing respiratory therapy systems, including those utilising unsealed patient interfaces, such as nasal cannulas with nasal delivery elements, it can be difficult to optimise both dead space clearance and the level of pressure provided to the patient. Optimising dead space clearance typically requires maintaining a high degree of leak between the nasal delivery elements and the patient’s nares, which conflicts with pressure optimisation, as it is difficult to increase pressure when there is a high degree of leak out of the patient interface. As referred to above, the high degree of leak also means that pressure levels may vary considerably throughout the patient’s respiratory cycle — decreasing on inspirations and increasing during expirations. For example, to increase the level of pressure provided to a patient in a conventional NHF therapy system, the flow rate may need to be increased considerably above the typical NHF therapy ranges. Excessively high flow rates may cause patient discomfort and increased drying of the airways, which may lead to reduced compliance of the patient to the therapy. Additional heating and humidification over and above that usually provided in NHF therapy may also be necessary to prevent drying of the airways when very high flow rates are provided. Lastly, such very high flow rates may also result in excessive exhalation resistance, which may be uncomfortable for the patient and even increase their work of breathing.

[0341] A nasal delivery element of a nasal interface with a smaller diameter will occlude a smaller fraction of a nasal passage opening of the patient, and thus may allow a higher degree of leak, resulting in a lower pressure being provided to a patient. Conversely, a nasal delivery element with a larger diameter will occlude a larger fraction of a nasal passage opening of the patient, and thus may allow a lower degree of leak, and therefore provision of higher pressures to the airways. A larger prong may not be as efficient at clearing anatomical dead space from the patient’s airways, however, due to the reduced degree of leakage that is possible.

[0342] The present disclosure relates to examples of breathing assistance apparatuses and respiratory therapy systems which are configured to control a flow rate of the flow of gases output by a flow generator to provide relatively a constant pressure at a patient’s airways, while also maintaining effective dead space clearance. As such, the apparatuses and systems of the present disclosure allow for one or more of the therapeutic effects of a pressure-based respiratory therapy such as CPAP therapy (e.g., a pressure which is sufficient to keep the patient's airways open) to be provided to a patient, whilst also providing one or more of the therapeutic effects of a flow-based respiratory therapy such as NHF therapy (e.g., effective dead space clearance) to the patient.

[0343] The methods, apparatuses and systems of the present disclosure are thus configured to provide pressures in the typical range for CPAP therapy, while also allowing for a high degree of leak, which enables effective dead space clearance throughout therapy. This combination may offer a therapy that has improved comfort and reduces patient respiratory effort, as compared to either conventional CPAP or NHF therapies. As will be explained, the combination of the provision of a pressure-based respiratory therapy and effective dead space clearance is achieved through a control method in combination with an unsealed nasal interface, which may be an asymmetric nasal interface such as those described above.

[0344] A therapy that offers a combination of one or more of the therapeutic effects of a pressure-based respiratory therapy and one or more of the therapeutic effects of a flow-based respiratory therapy such as NHF therapy may be considered a hybrid respiratory therapy. It may be considered or referred to as a combination flow-pressure therapy, or a high flow-CPAP therapy.

[0345] As will be discussed, the control methods of the present disclosure allow a breathing assistance apparatus to be controlled to provide CPAP-level pressures at the nares of a patient while offering a sufficient degree of leak that allows for dead space washout and increased comfort as compared to conventional CPAP. In examples, the systems and methods of the present disclosure may be configured to provide up to 20 cmH20 of pressure to the airways of the patient, whilst using an unsealed nasal interface which also provides for dead space washout. It is well understood in the art that between about 3 and about 5 cmH20 is the lower threshold of pressure for atypical CPAP therapy. The level of pressure able to be provided to the patient by the flow generator may depend on a range of factors. The factors may relate to the patient and / or the respiratory therapy system being used to provide the therapy to the patient. The factors may include any one or more of the following: the size of the cannula, specifically the dimensions of the prongs, or the topology and geometry of the patient’s nasal passages, or the strength of the patient’s breathing.

[0346] In a first embodiment, a user may set a minimum flow parameter such as a floor flow rate or floor pressure for the flow generator of the breathing assistance apparatus. The floor flow rate may represent a minimum allowable flow rate for the flow of gases output by the flow generator. The floor flow rate may correspond to a desired (minimum) level of dead space washout provided by the apparatus during the expiration of the patient. In some examples, the minimum flow parameter may be stored in the memory of the apparatus, instead of being provided as input by the user.

[0347] In a second embodiment, a user may set a target flow rate for the flow generator of the breathing assistance apparatus, for example, 30 L / min. The user may also select whether to provide the target flow rate as a constant flow (i.e., for a conventional NHF therapy) or as an average flow rate (for a hybrid respiratory therapy as described herein). The user can also specify what type and / or size of patient interface is being used (e.g., whether it is an asymmetric or symmetric nasal cannula, and the size of the nasal cannula). This input is then provided to the controller for use in a control method of the present disclosure to provide a flow of gases to the patient according to the user’s selections, as will be discussed.

[0348] The user may also input details relating to the patient interface and / or the airways of the patient. For example, the patient may input details relating to the patient interface such as what type and / or size of patient interface is being used (e.g., whether it is an asymmetric or symmetric nasal cannula, and the size of the nasal cannula). The user may also input details relating to the patient’s airways, such as the size or characteristics of the nares of the patient where a nasal cannula is used.

[0349] In some examples, the user may input one or more nasal resistance parameters, each representative or indicative of the pneumatic resistance between one or both prongs of the nasal cannula and the one or both corresponding nares of the patient. This input is then provided to the controller for use in the control method of the present disclosure to provide a flow of gases to the patient according to the user’s selections.

[0350] In some examples, the input may relate to an estimated or measured degree of naris occlusion. The estimated or measured degree of naris occlusion may relate to the degree of occlusion of both nares, or may relate to the degree of occlusion of only the naris with the large prong, or may relate to the degree of occlusion of only the naris with the small prong. The input relating to an estimated or measured degree of naris occlusion may be a percentage or ratio. In some examples, the user input relating to the degree of naris occlusion may be selected from a range of pre-defined options. The predefined options may relate to a percentage of occlusion for a naris, e.g., 60%, 80%, etc. The input relating to an estimated or measured degree of naris occlusion may be used by the controller to determine or estimate one or more nasal resistance parameters.

[0351] As discussed above, a first nasal delivery element of a nasal interface with a smaller diameter may more effectively clear patient dead space than a nasal delivery element with a larger diameter. Effective clearance of dead space reduces the amount of carbon dioxide rebreathing that occurs during patient respiration. Concurrently, a second nasal delivery element of the nasal interface with a larger diameter may reduce the leak that occurs around the second nasal delivery element of the nasal interface and may result in a higher delivered pressure during both inspiration and expiration. The larger diameter may allow for a higher patient expiratory pressure which may act to decrease respiratory rate and improve ventilation.

[0352] In specific examples, the systems and methods of the present disclosure utilise control of the flow rate of a flow of gases output by a flow generator in combination with asymmetric nasal delivery elements of an unsealed nasal interface to deliver respiratory gases to a patient at a stable pressure at the patient’s airways. In examples, the term ‘patient’s airways’ may refer to the nasal passages and / or upper airways of the patient. The pressure provided at the airways of the patient may be sufficient to provide a pressurebased respiratory therapy to the patient while maintaining at least some of the benefits of flow-based respiratory therapy. The use of the asymmetric nasal delivery elements can also provide increased dead space clearance in the upper airways of the patient.

[0353] The systems and methods of the present disclosure may provide a therapy with improved patient comfort as compared to conventional CPAP, as well dead space clearance, whilst also providing at least some of the therapeutic effects of a pressure-based respiratory therapy, such as providing a pressure or pressures which is / are sufficient to keep the patient's airway open and improve ventilation. Additionally, the systems and methods of the present disclosure may result in reduced noise levels as experienced by the patient or those nearby to the breathing assistance apparatus during use.

[0354] Additionally, the present invention may provide for built-in expiratory relief, wherein the flow rate of the flow of gases output by the flow generator will reduce during expiration in order to control the leak flow from patient interface, thereby also reducing how much resistance to exhalation the patient experiences. This may also reduce the peak pressure during exhalation / expiration (‘peak expiratory pressure’). Due to the decrease in peak expiratory pressure, the volume of acoustic noise may also be reduced.

[0355] The sizing of the nasal delivery elements and / or the asymmetry of the flow of gases caused by the nasal delivery elements can reduce the resistance to flow through the patient interface, which can achieve desired flow rates using lower back pressure and / or lower motor speeds of the flow generator used to output the flow of gases.

[0356] By offering a combination of the effects of a flow-based therapy (e.g., NHF) and a pressure-based therapy (e.g., CPAP), the systems and methods of the present disclosure have the potential to significantly improve the treatment of patients with a variety of respiratory conditions, by providing improved comfort, reducing respiratory effort in patients.

[0357] The present disclosure relates to a breathing assistance apparatus configured to provide a flow of gases to be delivered to a patient via a patient interface for respiratory therapy. Specifically, the present disclosure relates to a control method which allows the breathing assistance apparatus to be controlled to provide one or more of the benefits of a pressure-based respiratory therapy (e.g., CPAP -level pressures in one or both the nares of a patient) while also offering one or more of the benefits of a flow-based respiratory therapy (e.g., providing a degree of leak throughout therapy that may allow for dead space washout and increased comfort as compared to conventional CPAP). The present disclosure also relates to an apparatus and system implementing the control method, as well as a non-volatile computer-readable memory with instructions to carry out the control method.

[0358] As described in relation to FIG. 1, the breathing assistance apparatus 10 may comprise at least a flow generator 11 configured to output a flow of gases according to one or more parameters, and a controller 14 configured to control at least the operation of the flow generator 11. The one or more parameters of the flow of gases output by the flow generator may be controlled by the controller, and comprise at least a flow rate of the flow of gases.

[0359] As previously described, a supply conduit 20 may be coupled to the breathing assistance apparatus 10 at a first end, and a patient interface 30 at a second end. The supply conduit 20 is configured to convey the flow of gases output by the flow generator 11 to the patient interface 30, which is configured to receive the flow of gases from the supply conduit 20 and deliver the flow of gases to the patient.

[0360] In some examples, as previously described in relation to FIG. 1, the breathing assistance apparatus 10 further comprises a humidifier 12 configured to heat and humidify the flow of gases output by the flow generator 11. The controller 14 may be further configured to control the operation of the humidifier 12, as previously described.

[0361] The controller 14 is configured to receive data indicative or representative of the flow rate of the flow of gases output by the flow generator from one or more flow sensors. The controller is also configured receive data indicative or representative of a pressure of the flow of gases output by the flow generator from one or more pressure sensors. The one or more flow sensors and / or one or more pressure sensors may be a part of or within the sensor module 1112.

[0362] The controller is further configured to perform a control method which will be described below. The control method is adapted to allow the breathing assistance apparatus to be controlled, in combination with the patient interface, to provide one or more of the benefits of a pressure-based respiratory therapy while also offering one or more of the benefits of a flow-based respiratory therapy.

[0363] The control method comprises at least the steps of first determining a target pressure for the flow of gases delivered to the patient via the patient interface, and then controlling the flow generator to output the flow of gases at one or more flow rates to aim to deliver the flow of gases to the patient via the patient interface at substantially the target pressure.

[0364] In the first embodiment, the target pressure may be based at least in part on: the data from the one or more flow sensors indicative or representative of the flow rate of the flow of gases output by the flow generator, the data from the one or more pressure sensors indicative or representative of the pressure of the flow of gases output by the flow generator, and a minimum flow parameter. The minimum flow parameter may be a floor flow rate or a floor pressure. The minimum flow parameter may be received by the controller as user input, or determined by the controller, or otherwise stored in a memory associated with the controller.

[0365] In the second embodiment, the target pressure may be based at least in part on: the data from the one or more flow sensors indicative or representative of the flow rate of the flow of gases output by the flow generator, the data from the one or more pressure sensors indicative or representative of the pressure of the flow of gases output by the flow generator, and a user-specified therapy value. The user-specified therapy value may be received by the controller as user input, or determined by the controller, or otherwise stored in a memory associated with the controller.

[0366] The control methods of the present disclosure allow a breathing assistance apparatus to be controlled to provide therapeutic pressure levels (e.g. pressure levels suited for CPAP therapy), in the nares of a patient while offering a degree of leak throughout therapy that may allow for dead space washout and increased comfort as compared to conventional CPAP.

[0367] In examples, the systems and methods of the present disclosure may be configured to provide up to about 20 cmfbO of pressure to the airways of the patient, whilst using an unsealed nasal interface which also provides for dead space washout. It is well understood that between about 3 and about 4 cmfbO of pressure is the lower end of the typical range of pressure levels in CPAP therapy, while 20-25 cmfbO represent the upper ranges. It is also known that a large portion of non-acute CPAP users receive between 8 and 14 cmFbO. with the average pressure level across most adult patient / user populations being around 10 cmfbO. In examples, the apparatus, methods, and systems of the present disclosure may be configured to provide a pressure of between about 4 cmFbO and about 20 cmFbO at the airways of the patient. In some examples, the range of pressures delivered may be between about 4 cmFbO and about 20 cmFbO. In some examples, the range of pressures delivered may be between about 4 cmFbO and about 15 cmfbO. In some examples, the range of pressures delivered may be between about 6 cmFbO and about 15 cmPbO. In some examples, the range of pressures delivered may be between about 4 cmFbO and about 8 cmfbO.

[0368] This approach is also distinct from conventional high flow therapy, wherein the user sets a target flow rate, and the flow generator is controlled to maintain this flow rate consistently. According to the control method of the present disclosure, the flow rate of the gases output by the flow generator will vary relative to or approximately relative to the patient’s breathing, in order to maintain a substantially consistent pressure (i.e. a CPAP -level of pressure) at the patient’s airways (e.g., at the entrance to or in the patient’s nasal passages).

[0369] 3.1. User interface

[0370] In some examples, the breathing assistance apparatus may further comprise a user interface comprising a display and one or more input devices, such as those previously described. The controller is configured to receive user input from the one or more input devices of the user interface, and to output to the display one or more parameters of the flow of gases via the display of the user interface.

[0371] In examples, user input(s) may relate to the minimum flow parameter, such as the floor flow rate or floor pressure, which is used by the control method of the present disclosure as one of the inputs.

[0372] In examples, user input(s) may relate to the user specified therapy value which is used by the control method of the present disclosure as one of the inputs. The user-specified therapy value may relate to a target for one or more parameters of the flow of gases at or about the patient interface. The user-specified therapy value may be a target flow rate or a target pressure of the flow of gases at or about the patient interface.

[0373] In some examples, the user-specified therapy value may be a target flow rate. The target flow rate may be a target for the leak flow rate of the flow of gases out of the patient interface. The target flow rate may be an average flow rate, a mean flow rate, a weighted average flow rate, or similar. The target average flow rate may be a rolling average of the flow rate taken over a set period of time. The actual flow rate may be measurable or able to be estimated by the controller.

[0374] The leak flow rate of the flow of gases out of the patient interface and the pressure of the gases delivered to the patient via the patient interface may be proportional to or be otherwise related to one another. As such, delivery of the flow of gases to the patient substantially at the target pressure may maintain the flow of gases leaking from the patient interface at substantially the target average flow rate.

[0375] The user input may alternatively, or additionally, relate to one or more aspects of the patient interface and / or supply conduit (collectively referred to as the breathing circuit) being used to provide the present respiratory therapy to the patient, and / or to one or more aspects or parameters of the patient, for example relating to their size, or more specifically to the dimensions of their airways, and more specifically to the dimensions of their nares. As described above, in some examples, the input may relate to an estimated or measured degree of naris occlusion of the patient.

[0376] The user may input the type and / or model of one or more of the components of the breathing circuit. The type and / or model of one or more of the components of the breathing circuit may be preprogrammed in the memory of the breathing assistance apparatus, which allows one or more other details relating to the breathing circuit e.g., geometry, flow resistance, flow-pressure curves, etc., to be looked-up based on the user input. In other cases, the user could input specific parameters of the one or more aspects of the breathing circuit, such as the supply conduit e.g., diameter and / or length of the supply conduit, and / or the patient interface, e.g., nasal cannula size, nasal delivery element size, etc.

[0377] The one or more details relating to the breathing circuit may relate to any one or more of the details of the patient interface. The details of the patient interface may be a general grouping of the patient interface such as the size, type, or model of patient interface (e.g., symmetric nasal cannula, asymmetric nasal cannula, or other types of patient interfaces), or may relate to more specific details of the patient interface such as the dimensions or other characteristics of the nasal delivery element(s) and / or manifold. Such characteristics may relate to whether a patient interface is adapted for providing an asymmetric flow of gases at the patient’s airways, for example.

[0378] Additionally, the one or more details relating to the breathing circuit may relate to any one or more of the details of the supply conduit. The details of the supply conduit may similarly be a general grouping of the supply conduit such as the size or type of supply conduit, or may relate to more specific details of the supply conduit such as the internal geometry and / or length of the supply conduit.

[0379] In some examples, the user input may relate specifically to one or more nasal resistance parameters, each nasal resistance parameter being representative or indicative of the pneumatic resistance between one or both prongs of the nasal cannula and the one or both corresponding naris or nares of the patient. In other examples, the controller may be configured to estimate one or more nasal resistance parameters based on user input relating to the one or more aspects of the breathing circuit and / or relating to one or more aspects or parameters of the patient, such as relating to their size, or more specifically to the dimensions of their airways.

[0380] In other examples, the user input relating to the breathing circuit may be used by the controller to determine or look up (e.g., in memory) one or more nasal resistance parameters. The one or more nasal resistance parameters may be used in the control method of the present disclosure as input, as will be explained. The one or more nasal resistance parameters may be based on at least the user inputted details relating to the patient interface and / or patient.

[0381] The controller may be configured to estimate or look up one or more nasal resistance parameters. The controller may be configured to estimate or look up one or more nasal resistance parameters based on the inputted information relating to the breathing circuit and / or the patient’s airways.

[0382] In some examples, the controller may have stored in memory models or details of each of a number of breathing circuits and / or patient interfaces and / or supply conduits, as well as a number of nominal patient upper airway passages. There may be multiple models, each with parameters, including nasal resistance parameters, calibrated for different types and / or sizes of patient interface and / or breathing circuits and / or patients.

[0383] In other examples, one or more nasal resistance parameters may be determined or identified by the controller, for example using one or more of the sensors in data connection to the controller, such as pressure or flow sensors. In other examples, the breathing assistance apparatus may be configured to identify the patient interface and / or supply conduit attached to the apparatus, for example by using one or more electronic identification circuits, RFID antennas, or similar, and estimate the nasal resistance parameters based on the detected interface and / or conduit.

[0384] In other examples, the user input relating to the breathing circuit may be used by the controller to determine or look up (e.g., in memory) one or more flow resistance constants. The one or more flow resistance constants may be used in the control method of the present disclosure as input, as will be explained. The one or more flow resistance constants may be based on at least the user inputted details relating to the patient interface and / or supply conduit.

[0385] The controller may be configured to estimate or look up one or more flow resistance constants associated with the breathing circuit being used to provide the respiratory therapy based on the inputted information relating to the breathing circuit.

[0386] In some examples, the controller may have stored in memory models or details of each of a number of breathing circuits and / or patient interfaces and / or supply conduits, as well as nominal patient upper airway passages. There may be multiple models, each with parameters (e.g., some flow resistance values) calibrated for different types and / or sizes of patient interface and / or breathing circuits.

[0387] In other examples, one or more details relating to the breathing circuit may be determined or identified by the controller, for example using one or more of the sensors in data connection to the controller, such as pressure or flow sensors. In other examples, the breathing assistance apparatus may be configured to identify the patient interface and / or supply conduit attached to the apparatus, for example by using one or more electronic identification circuits, RFID antennas, or similar.

[0388] A user may provide such input when setting up a breathing assistance apparatus, for example, when setting up a respiratory therapy session, or when setting up a new patient for use with the breathing assistance apparatus. The user may thus set a minimum flow parameter, such as floor flow rate or floor pressure. Alternatively, the user may set a user specified therapy value, for example the user may thus set a target flow rate e.g. 30 L / min and select whether to provide this as a constant flow (i.e., for a conventional NHF therapy) or as an average flow rate. The user can also specify what type and / or size of patient interface is being used and / or what size of patient (e.g., whether it is an asymmetric or symmetric nasal cannula, and the size of the nasal cannula and patient’s nares). This input is then provided to the controller for use in the control method of the present disclosure to provide a flow of gases to the patient according to the user’s selections.

[0389] 3.2. Patient interfaces, sensors & data

[0390] As described previously, the breathing assistance apparatus 10 comprises a housing 16, and the flow generator 11 is located within the housing 16. In examples, the breathing assistance apparatus further comprises one or more flow sensors. The one or more flow sensors may be located within the breathing assistance apparatus housing 16. The one or more flow sensors may be positioned at an outlet of the flow generator 11. The one or more flow sensors may comprise ultrasonic transducers configured to provide one or more signal(s) indicative of the flow rate of the flow of gases output by the flow generator.

[0391] Similarly, the breathing assistance apparatus 10 may comprise one or more pressure sensors. The one or more pressure sensors may also be located within the breathing assistance apparatus housing 16. The one or more pressure sensors may be positioned at an outlet of the flow generator 11 and may be configured to provide one or more signal(s) indicative of the pressure of the flow of gases output by the flow generator.

[0392] The flow and / or pressure sensor(s) may further be configured to estimate or determine the flow and / or pressure at one or more locations within the breathing circuit or the airways of the patient. For example, the flow sensor(s) of the apparatus may be configured to estimate one or more flow rates of the gases provided to the patient via the patient interface. Similarly, the pressure sensor(s) of the apparatus may be configured to estimate one or more pressures of the gases provided to the patient via the patient interface. For example, the controller may be configured to estimate the pressure of the gases provided in the patient interface using at least in part on the signals provided by the pressure sensor(s) of the apparatus. The controller may be further configured to estimate a pressure drop along the supply conduit based at least in part on signals provided by the flow sensor(s) of the apparatus, and a known flow resistance of supply conduit.

[0393] When used with an asymmetric nasal cannula, the one prong of the nasal cannula that more substantially occludes a naris of the patient may reduce the leak that occurs around that particular nasal delivery element, or more specifically, the particular nasal prong. This may result in an overall reduction in leak between the interface and patient. In turn, this may result in a higher delivered pressure during both inspiration and expiration of the patient. As such, one or more of the benefits of a pressure based respiratory may be provided to the patient.

[0394] On the other hand, having two large prongs with a high degree of naris occlusion and / or that substantially occlude both nares may result in significantly reduced leakage around the nasal prongs. The significant reduction in leakage may diminish the degree of, if any, dead space washout and thus not provide this benefit of a flow based respiratory therapy.

[0395] In the examples described below, it is to be understood that a nasal cannula adapted to cause an asymmetric flow of gases may achieve the described benefits of a flow-based therapy (in particular a nasal high flow therapy) noted to a higher degree than a nasal cannula adapted to cause a symmetric flow of gases.

[0396] An asymmetric nasal cannula may further enable higher quality pneumatic signals to be detected by the pressure and / or flow sensor(s) located at the breathing assistance apparatus. Better quality signals may enable the controller to implement more reliable and / or accurate control methods that might not be otherwise possible or sufficiently reliable in conventional nasal high flow therapy systems (where signal quality can be very poor, due to the high degree of leakage around the nasal cannula).

[0397] A higher quality feedback signal may be achieved as the flows through, and pressures present at the larger prong of the nasal cannula will typically be higher due to the significant occlusion of the naris by the prong. As a result, the flow and / or pressure signal(s) able to be transmitted from said larger prong, along the breathing circuit, and back to the flow and / or pressure sensor(s) located at the apparatus will tend to be stronger, ultimately resulting in a better signal -noise ratio.

[0398] A consequence of the above considerations is that the patient interface when used in a respiratory therapy system according to the present disclosure is preferably a non-sealing nasal cannula and may be a nonsealing nasal cannula that comprises a large, high-occlusion prong, and a small, high-leakage prong.

[0399] The controller is configured to receive data indicative or representative of the flow rate of the flow of gases output by the flow generator from the one or more flow sensors described previously.

[0400] The received data indicative or representative of the flow rate of the flow of gases output by the flow generator may be indicative or representative of an average flow rate of the flow of gases output by the flow generator. The average flow rate of the gases may be a rolling average. The rolling average may be taken over a set period of time. The average flow rate of the flow of gases output by the flow generator may be taken over one patient respiratory cycle or may be taken over multiple patient respiratory cycles.

[0401] The received data indicative or representative of the flow rate of the flow of gases output by the flow generator may also be indicative or representative of an instantaneous flow rate value of the flow of gases output by the flow generator. The instantaneous flow rate values could be used to determine an average flow rate value or values. The flow sensor(s) may provide real time data to the controller, which would calculate the average(s). The average flow rate value may be used for aspects of the control method, and the instantaneous flow rate value may be used for other aspects of the control method.

[0402] The controller is further configured to receive data indicative or representative of the pressure of the flow of gases output by the flow generator from the one or more pressure sensors described previously.

[0403] The received data indicative or representative of the pressure of the flow of gases output by the flow generator may be indicative or representative of an average pressure of the flow of gases output by the flow generator. The average pressure of the gases may be a rolling average. The rolling average may be taken over a set period of time. The average pressure of the flow of gases output by the flow generator may be taken over one patient respiratory cycle or may be taken over multiple patient respiratory cycles.

[0404] The received data indicative or representative of the pressure of the flow of gases output by the flow generator may also be indicative or representative of an instantaneous pressure value of the flow of gases output by the flow generator. The instantaneous pressure values could be used to determine an average pressure value or values. The flow sensor(s) may provide real time data to the controller, which would calculate the average(s). The average pressure value may be used for aspects of the control method, and the instantaneous pressure value may be used for other aspects of the control method.

[0405] As previously discussed, the flow generator 11 may comprise a blower 1111. The controller 14 may be configured to control the motor speed of the blower 1111. The motor speed of the blower may be controlled such that the flow generator outputs the flow of gases according to one or more parameters e.g. flow rate and / or pressure.

[0406] In such examples the breathing assistance apparatus 10 may further comprise one or more motor speed sensors 1113 configured to provide data indicative or representative of the motor speed of the blower 1111. The controller 14 is further configured to receive data indicative or representative of the motor speed of the blower from the one or more motor speed sensors 1113. As will be appreciated, the data indicative or representative of the motor speed of the blower may be a running average of the motor speed or may be an instantaneous value of the motor speed.

[0407] 4. Control aspects

[0408] The controller 14 of the breathing assistance apparatus 10 is further configured to perform one or more control methods which will be described hereafter. The control methods are adapted to control the breathing assistance apparatus 10, which, in combination with the patient interface 30, provide one or more of the benefits of a pressure-based respiratory therapy while also offering one or more of the benefits of a flow-based respiratory therapy.

[0409] The control methods will be described in relation to FIGS. 16-20, which show flow charts of different variations of control method 2000, and more specifically FIGS 19 and 20, which show flow charts of a first embodiment of control method 2000, and a second embodiment of control method 2000 respectively. The controller 14 of the breathing assistance apparatus 10 previously described is configured to perform the control method 2000. The breathing assistance apparatus 10 may be connected with a supply conduit 20 and patient interface 30, as previously discussed.

[0410] The controller 14 may be configured to firstly initiate therapy. The therapy may be initiated according to one or more therapy parameters. The one or more therapy parameters may relate to one or more of: a target flow rate(s), or a target pressure(s), or a target oxygen concentration(s), or a target gases temperature(s). The therapy being a respiratory therapy for providing a flow of gases to a patient. The controller 14 may then proceed to perform the control method 2000, as will be explained.

[0411] FIG. 16 shows a first variation of the control method 2000. At step 2020, the controller is configured to determine a target pressure for the flow of gases delivered to the patient. The controller takes one or more inputs, for example from one or more sensors, and outputs a target pressure for the flow of gases to be delivered to the patient. This target pressure may be a pressure level sufficient to provide one or more benefits of a pressure-based therapy. For example, the target pressure may be of a level which is sufficient to keep the airways of the patient open. At step 2030, the controller is configured to control the flow rate of the flow of gases output by the flow generator. The controller is configured to control the flow rate of the gases output by the flow generator to aim to deliver and maintain the pressure of the flow of gases delivered to the patient at substantially the target pressure. More specifically, at step 2030, the controller may be configured to control the flow generator to output the flow of gases at the target flow rates to aim to deliver the flow of gases to the patient via the patient interface substantially at the target pressure. The target flow rate may vary over time, and this step may comprise controlling the flow generator to output the flow of gases at one or more flow rates. In some examples, the controller controls the flow rate of the flow of gases by controlling the motor speed of the blower of the flow generator, as will be explained. In other examples, the flow rate of the flow of gases could be controlled based on other output signals, such as additional flow or pressure feedback.

[0412] Finally, at step 2040, the breathing assistance apparatus is configured to deliver the flow of gases to the patient via the patient interface. If the previous steps of the control method 2000 are performed successfully, the flow of gases delivered to the patient via the patient interface are delivered to the patient at substantially the target pressure determined at step 2020.

[0413] 4.1. Receiving inputs

[0414] FIGS. 17-20 show further variations of the control method 2000. These variations include an additional step 2005 in which the controller 14 receives input, and step 2015 in which the controller receives sensor data.

[0415] In the first embodiment, the input received at step 2005 is a minimum flow parameter. The minimum flow parameter may be a floor flow rate or a floor pressure. The floor flow rate represents a minimum allowable flow rate for the flow of gases to be delivered to the patient. The floor pressure represents a minimum allowable pressure for the flow of gases to be delivered to the patient.

[0416] In the second embodiment, the input received at step 2005 is a user-specified therapy value. The user- specified therapy value may relate to a target for one or more parameters of the flow of gases at or about the patient interface. The user-specified therapy value may be a target flow rate or a target pressure of the flow of gases at or about the patient interface. In some examples, the user-specified therapy value may be a target flow rate. As previously discussed, the user-specified therapy value may be received as input to the controller via the user interface.

[0417] As previously discussed, the input, such as the user-specified therapy value or minimum flow parameter may be received as input to the controller via the user interface, or may be predetermined and stored in the memory of the controller. In some examples, the controller may be configured to determine a user- specified therapy value or a minimum flow parameter based on information relating to any one or more of: one or more characteristics of the patient, one or more characteristics the patient interface, one or more characteristics the supply conduit, the type of therapy being provided to the patient, or the therapy parameters of the therapy being provided to the patient. In some examples, at step 2005 the controller 14 may be configured to determine an average flow rate setting. In such examples, the average flow rate setting may be a desired average flow rate for the flow of gases delivered to the patient. In these examples, the controller 14 may be configured to determine the floor flow rate based at least in part on the average flow rate setting received.

[0418] At step 2005, the controller 14 may be further configured to receive additional user input relating to one or more nasal resistance parameters or one or more flow resistance constants, and / or one or more details or characteristics of any one or more of: the patient (e.g. relating to their airways), or the patient interface or supply conduit (collectively referred to as the breathing circuit) being used to provide the present respiratory therapy to the patient. The details or characteristics of the patient and / or the breathing circuit may enable the determination or estimation of one or more nasal resistance parameters or one or more flow resistance constants as previously discussed. Additionally, or alternatively, the controller is configured to determine or estimate the one or more nasal resistance parameters or one or more flow resistance constants based on information stored in memory.

[0419] Still referring to FIGS. 17-20, at step 2015, the controller 14 is configured to receive sensor data after therapy has been initiated. The sensor data may be any such sensor data as has been previously discussed. For example, at step 2015, the controller may be configured to receive data indicative or representative of the flow rate of the flow of gases output by the flow generator. The flow rate data may be received from one or more flow sensors. The controller may also be configured receive data indicative or representative of a pressure of the flow of gases output by the flow generator. The pressure data may similarly be received from one or more pressure sensors. The sensor data may comprise an instantaneous measurement(s) and / or an average measurement(s) taken over a period of time.

[0420] At step 2020, the controller 14 is configured to determine a target pressure for the flow of gases delivered to the patient. The target pressure is based at least in part on the sensor data received at step 2015.

[0421] In some examples of the first embodiment, the controller may be further configured to determine the target pressure based at least in part on the minimum flow parameter e.g., the floor flow rate or floor pressure received at step 2005, and the sensor data received at step 2015. In some examples, the target pressure is further based on received or estimated data indicative or representative of a pressure delivered to the patient, which may be based at least on the sensor data received at step 2015.

[0422] In some examples of the second embodiment, the controller may be further configured to determine the target pressure based at least in part on the user-specified therapy value received at step 2005. The target pressure may also be based on user input relating to details of the one or more breathing circuit components, which may be received at step 2005. Specifically, the sensor data may comprise the data indicative or representative of the flow rate of the flow of gases output by the flow generator, and the data indicative or representative of the pressure of the flow of gases output by the flow generator.

[0423] In either of these examples, the controller is first configured to receive or estimate data indicative or representative of a pressure delivered to the patient. The pressure of the flow of gases delivered to the patient may be the pressure of the flow of gases at or about the patient’s airways. More specifically, the pressure of the flow of gases delivered to the patient may be the pressure of the flow of gases at or near the patient's nares or the entrances to the patient’s nares. The pressure of the flow of gases delivered to the patient may be the pressure of the flow of gases within the patient interface.

[0424] In some examples, the controller is configured to receive data indicative or representative of a pressure delivered to the patient from one or more pressure sensors. The one or more pressure sensors providing the data indicative or representative of a pressure delivered to the patient may take readings at or around the airways of the patient and / or the patient interface.

[0425] In other examples, the controller is configured to estimate the pressure of the flow of gases delivered to the patient. In these examples, and as will be explained further below, the pressure of the flow of gases delivered to the patient may be estimated based at least in part on the data indicative or representative of the flow rate of the flow of gases and the data indicative or representative of the pressure of the flow of gases.

[0426] In these examples, the target pressure may be further based on one or more nasal resistance parameters. The one or more nasal resistance parameters may be those received at step 2005 or otherwise estimated by the controller. The nasal resistance parameters may be estimated by the controller using received flow rate data and / or pressure data and / or other inputs including parameters of the breathing circuit (e.g. relating to flow resistance).

[0427] In some examples, the target pressure corresponds to the floor or minimum pressure. In these examples, the controller is configured to determine a target pressure for the flow of gases delivered to the patient via the patient interface. The floor or minimum pressure is a pressure level that the controller aims to keep the flow of gases output by the flow generator at or above throughout a therapy session.

[0428] Similarly to the target pressure, the floor or minimum pressure can be based at least in part on the data indicative or representative of the flow rate of the flow of gases output by the flow generator and the data indicative or representative of the pressure of the flow of gases output by the flow generator. In some examples of the first embodiment, the floor or minimum pressure may be further based on the floor flow rate and / or one or more nasal resistance parameters. In some examples of the second embodiment, the floor or minimum pressure may be based on the user-specified therapy value,

[0429] Referring to FIGS. 16 to 20, at step 2030, the controller is then configured to control the flow rate of the flow of gases output by the flow generator. The controller is configured to control the flow rate of the gases output by the flow generator to aim to deliver and maintain the pressure of the flow of gases delivered to the patient substantially at the target pressure.

[0430] More specifically, at step 2030, the controller can be configured to control the flow generator to output the flow of gases at a target flow rate (as will be discussed later, with reference to the determination of a target flow rate at step 2025) to aim to deliver the flow of gases to the patient via the patient interface substantially at the target pressure (e.g., as determined at step 2020). The target flow rate may vary over time, and this step may comprise controlling the flow generator to output the flow of gases at one or more flow rates. For example, the flow rate may change with each iteration of the control method.

[0431] In some examples, the controller controls the flow rate of the flow of gases by controlling the motor speed of the blower of the flow generator, as will be explained. In other examples, the flow rate of the flow of gases could be controlled based on other output signals, such as additional flow or pressure feedback signals.

[0432] In examples where the target pressure is or may be a target minimum pressure, the controller can be configured to determine a target flow rate for the blower based at least in part on the determined target minimum pressure of the flow of gases delivered to the patient. The controller is then configured to control the flow generator to output the flow of gases at the target flow rate to deliver the flow of gases to the patient via the patient interface, at or above the target minimum pressure.

[0433] Finally, at step 2040 of the control method 2000, the breathing assistance apparatus is configured to deliver the flow of gases to the patient via a patient interface. If the previous steps of the control method 2000 are performed successfully, the flow of gases delivered to the patient via the patient interface are delivered to the patient at substantially the target pressure determined at step 2020.

[0434] 4.2. Determining target flow rate

[0435] As shown in FIGS. 18 to 20, after step 2020 of determining a target pressure for the flow of gases delivered to the patient, the control method proceeds to step 2025. At step 2025, the controller is then configured to determine a target flow rate for the flow of gases output by the flow generator. In these examples, the controller may further be configured to determine a target motor speed that achieves the target flow rate for the flow of gases output by the flow generator. The target flow rate for the flow of gases and the target motor speed can be based at least in part on the target pressure of the flow of gases delivered to the patient determined at step 2020.

[0436] The control method of the present disclosure can be configured to vary the flow rate of the flow of gases output by the flow generator to deliver and maintain a substantially constant pressure at the patient interface. As such, the flow rate of the flow of gases output by the flow generator will vary relative to the spontaneous breathing of the patient. In some cases, according to the control method, because the flow rate varies with the patient’s breathing, higher pressures may not be provided during expiration. This is because the patient breathes against the flow of gases being delivered in the patient interface, causing the pressure in the patient interface to increase. This increase in pressure caused by the patient expiring against the flow of gases thereby causes the flow rate of the gases to be reduced in response. In some cases, the peak expiratory pressure provided may not provide sufficient therapeutic benefit for the patient. A high peak expiratory pressure may be beneficial for some patients as it can decrease respiratory rate (by lengthening the expiratory phase of their breathing) and helps to keep the airways open. To ensure higher peak expiratory pressures are provided, the use of a minimum flow parameter such as the floor flow rate or floor pressure can be implemented. The floor flow rate represents a minimum allowable flow rate for the flow of gases. The control system may have one or more further variables that allows for the maintaining or setting of a minimum flow rate or motor speed. If the controller tries to reduce the flow rate such that the flow rate will fall below the floor flow rate (e.g., during patient expiration), the controller acts against this change and try to keep the flow rate at / above the floor flow rate or motor speed. The result is that the flow rate of the flow of gases output by the flow generator may be held substantially constant at or about the floor flow rate during expiration of the patient.

[0437] The determination of the target flow rate used may thus be based on the floor flow rate. In this way, the target flow rate may be no lower than about the floor flow rate. As previously described, the floor flow rate may be stored in the memory of the controller and thus may be received by the controller via memory. Alternatively, the floor flow rate may be provided as user input. In other examples the floor flow rate may be determined by the controller based on one or more characteristics of the breathing circuit. The floor flow rate may thus allow the flow rate to be kept above a minimum level to ensure the delivery of the flow of gases to the patient via the patient interface substantially at or above the target pressure.

[0438] It will be appreciated that following step 2025 the controller is then configured to perform step 2030 of controlling the flow rate of the flow of gases output by the flow generator based on the target flow rate, as previously described. Additionally, following step 2025, the breathing assistance apparatus is configured to deliver the flow of gases to the patient via a patient interface, according to step 2030, also as previously described. If the previous steps of the control method 2000 are performed correctly, the flow of gases delivered to the patient via the patient interface are delivered to the patient at substantially the target pressure determined at step 2020.

[0439] 4.3. First embodiment of control method

[0440] In the first embodiment of the control method, to ensure higher peak expiratory pressures are provided, a minimum flow parameter limitation is implemented. The minimum flow parameter comprises a floor flow rate or a floor pressure.

[0441] In examples where the minimum flow parameter comprises a floor flow rate, the floor flow rate represents a minimum allowable flow rate for the flow of gases. The minimum allowable flow rate, represented by the floor flow rate, may correspond to a flow rate that will result in a certain sufficient or minimum peak expiratory pressure (i.e., a therapeutically desired pressure) being maintained. The control system may have one or more further parameters that allow for the maintaining or setting of a minimum flow rate or motor speed. If the controller tries to reduce the flow rate such that the flow rate will fall below the floor flow rate (e.g., during patient expiration), the controller acts against this change and keeps the flow rate at or above the floor flow rate (or corresponding floor motor speed). The result is that the flow rate of the flow of gases output by the flow generator may be held substantially constant at or about the floor flow rate throughout at least a portion of the expiration period of the patient. In some examples, the determination of the target flow rate may be based on the floor flow rate. In this way, the target flow rate may be no lower than the floor flow rate or in some cases may be slightly above or slightly below the floor flow rate.

[0442] In examples where the minimum flow parameter comprises a floor pressure, the floor pressure represents a minimum allowable pressure for the flow of gases. The floor pressure may be the minimum allowable pressure for the flow of gases output by the flow generator or elsewhere in the flow path. The minimum allowable pressure represented by the floor pressure may correspond to a pressure level that will result in a certain sufficient or minimum peak expiratory pressure (i.e., a therapeutically desired pressure) being maintained.

[0443] In some examples, the determination of the target pressure of the flow of gases delivered to the patient may be based on the floor pressure. In this way, the target pressure may be no lower than the floor pressure or in some cases may be slightly above or slightly below the floor pressure.

[0444] 4.3.1. Estimating patient end pressure

[0445] Referring now to FIG. 19 specifically, a further variation of the control method 2000 showing an example of the first embodiment is shown. In this example of the first embodiment, the control method 2000 is the same as that shown in FIGS. 16-18, but further comprises steps 2022, of estimating the pressure of the flow of gases delivered to the patient, and step 2024, of estimating the flow rate of the patient’s breathing. Step 2005 shows the input received is a minimum flow parameter as previously described.

[0446] In some examples, the steps 2022, 2024 and 2020 may be performed concurrently, such that step 2022 is performed after step 2015, and the output of step 2022 may be used as an input to step 2024. The output of step 2024 may then be used in step 2020 to determine the target pressure for the flow of gases delivered to the patient. However, it will be appreciated that in other examples, steps 2022, 2024 and 2020 may be performed in parallel.

[0447] At step 2022, the controller is configured to estimate the pressure of the flow of gases delivered to the patient. The pressure of the flow of gases delivered to the patient may be the pressure of the flow of gases at or about the patient’s airways. More specifically, the pressure of the flow of gases delivered to the patient may be the pressure of the flow of gases at or near the patient's nares or the entrances to the patient’s nares, or within the patient interface.

[0448] The pressure of the flow of gases delivered to the patient may be estimated based at least in part on the data indicative or representative of the flow rate of the flow of gases and the data indicative or representative of the pressure of the flow of gases.

[0449] Several examples of methods for estimating the pressure of the flow of gases delivered to the patient will now be explained. It will be appreciated that other methods may be employed without departing from the scope of the present invention. In some alternative examples, the pressure of the flow of gases delivered to the patient may be measured, for example by one or more sensors configured to measure the pressure of the flow of gases delivered to the patient. The one or more sensors may be located or partially located at or near the airways of the patient. The one or more sensors may be located or partially located at or about the patient interface.

[0450] 4.3.1.1. Using nasal resistance parameters

[0451] Still referring to the example of the first embodiment shown in FIG. 19, in some examples, at step 2022, the controller is configured to estimate the pressure of the flow of gases delivered to the patient based at least in part on the data indicative or representative of the flow rate of the flow of gases and the data indicative or representative of the pressure of the flow of gases, and one or more estimated nasal resistance parameters.

[0452] As discussed above, the controller may be configured to receive or estimate one or more nasal resistance parameters. The nasal resistance parameter(s) may be representative or indicative of the pneumatic resistance between one or both prongs of the nasal cannula and the one or both corresponding nares of the patient. For example, a first nasal resistance parameter may be representative or indicative of the pneumatic resistance between the first prong of the nasal interface and the corresponding naris of the patient in which it is located during the provision of therapy. Similarly, a second nasal resistance parameter may be representative or indicative of the pneumatic resistance between the second prong of the nasal interface and the corresponding naris of the patient in which it is located during the provision of therapy.

[0453] At this step, the controller may be configured to estimate the pressure of the flow of gases delivered to the patient using one or more algorithms. The one or more algorithms may take as input one or more estimated nasal resistance parameters, and one or both of the data indicative or representative of the flow rate of the flow of gases and the data indicative or representative of the pressure of the flow of gases.

[0454] In one example, the pressure of the flow of gases delivered to the patient may utilise the measured pressure of the flow of gases and subtract one or more pressure drops associated with the flow path between the flow generator and the patient.

[0455] In a further example, the pressure of the flow of gases delivered to the patient may be a linear approximation relating to the leak flow rate and nasal resistance. For example, the controller is configured to implement the following equation to estimate the pressure of the flow of gases delivered to the patient:

[0456] ^delivered — R * Qieak

[0457] Where Paeitvered is the estimated pressure of the flow of gases delivered to the patient, Qieak is the leak flow rate of the flow of gases out of the patient’s nares, and R is a nasal resistance parameter associated with one or more aspects of the patient’s nares or a naris. Qieak may be estimated by the controller based at least on one or both of the data indicative or representative of the flow rate of the flow of gases and the data indicative or representative of the pressure of the flow of gases.

[0458] In some further examples, the above equation may also be represented as:

[0459] ^delivered ~ R * Qteak + Qbreath) where Qbreath is the averaged flow rate of the patient’s breathing, the flow rate of the flow gases breathed in / out by the patient. Because gases in is equal to gases out on average, the Qbreath term will average to approximately zero. As such, the value for Qbreath can be considered to equate to zero in this equation. This leaves the Qieak term as the remaining term, which models the flow of gases that exits the nasal cannula prongs and flows between the outer walls of the nasal prongs and the inner walls of the nares i.e., the flow rate of the flow gases that is not breathed in by the patient, but does contributed to pressure in the nares or at the exit of the nasal prongs.

[0460] In some examples, Qieak may be an instantaneous estimate or measurement of the leak flow rate of the flow of gases out of the patient’s nares. In other examples, Qieak may be an average of measurements taken over a period of time, and as such, Paeiivered may also be an average.

[0461] 4.3. 1.2. Using flow resistance constants

[0462] In some further examples of the first embodiment, the controller is also configured to receive or estimate one or more flow resistance constants. The one or more flow resistance constants may be representative or indicative of the pneumatic resistance of one or more portions of the breathing circuit. The one or more portions of the breathing circuit may relate to the breathing circuit as a whole, or any one or more aspects of the breathing circuit positioned between an outlet of the flow generator and the airways of the patient. For example, a flow path pneumatic resistance parameter may relate to the flow path pneumatic resistance of the supply conduit. A flow path pneumatic resistance parameter may additionally, or alternatively relate to the patient interface.

[0463] In these further examples, at step 2022, the controller may be configured to estimate the pressure of the flow of gases delivered to the patient based at least in part on the data indicative or representative of the flow rate of the flow of gases and the data indicative or representative of the pressure of the flow of gases, and one or more estimated nasal resistance parameters, and further, on the one or more flow path pneumatic resistance parameters.

[0464] The pressure of the flow of gases delivered to the patient may utilise the measured pressure of the flow of gases and subtract one or more pressure drops associated with the flow path between the flow generator and the patient.

[0465] In an example, the controller is configured to implement the following equation to estimate the pressure of the flow of gases delivered to the patient: Where Paeiivered is the estimated pressure of the flow of gases delivered to the patient, Pbiower is the measured pressure of the flow of gases output by the flow generator, Qbiower is the measured flow rate of the flow of gases output by the flow generator, and k±and k2are flow resistance constants associated with one or more aspects of the flow path and / or breathing circuit connected to the breathing assistance apparatus. The Pbiower may be an instantaneous measurement of the pressure of the flow of gases output by the flow generator, similarly, Qbiower may he an instantaneous measurement of the flow rate of the flow of gases output by the flow generator. In other examples, Pbiowerand QbiowermaY he averages of measurements taken over a period of time, and as such, PaeiiveredmaY also he an average.

[0466] In some examples, one flow resistance constant may be used to estimate the pressure of the flow of gases delivered to the patient. In other examples, a plurality of flow resistance constants may be used. Additional flow resistance constants may allow for a more precise estimation of pressure drop(s) along the flow path. Additional different flow resistance constants may relate to different components in the flow path from the flow generator, including the airways of the patient. Each of the flow resistance constants may relate to the flow resistance of an aspect of the flow path / breathing circuit being used to convey and deliver the flow of gases from the flow generator to the patient, and / or may relate to one or more aspects of the airways of the specific patient receiving the flow of gases. The one or more flow resistance constants may be based on at least on one or more characteristics of the patient interface. The one or more flow resistance constants may be based on at least on one or more characteristics of the supply conduit.

[0467] As previously discussed, the one or more flow resistance constants may be user-specified. The user may input details relating to the patient interface and / or supply conduit (collectively referred to as the breathing circuit) being used to provide the present respiratory therapy to the patient. The user may input one or more details relating to the specific breathing circuit providing the respiratory therapy. The user input relating to the breathing circuit may be used by the controller to determine one or more flow resistance constants.

[0468] The one or more details relating to the breathing circuit may relate to any one or more of the details of the patient interface. The details of the patient interface may be a general grouping of the patient interface such as the size, type, or model of patient interface, or may relate to more specific details of the patient interface such as the dimensions or other characteristics of the nasal prong(s) and / or manifold. Such characteristics may relate to whether a patient interface is adapted for providing an asymmetric flow of gases at the patient’s airways for example. As described above, the user input may relate to an estimated or measured degree of naris occlusion. The input relating to an estimated or measured degree of naris occlusion may be a percentage or ratio for one or both nares.

[0469] Additionally, one or more details relating to the breathing circuit may relate to any one or more of the details of the supply conduit. The details of the supply conduit may similarly be a general grouping of the supply conduit such as the size or type of supply conduit, or may relate to more specific details of the supply conduit such as the internal geometry and / or length of the supply conduit.

[0470] 4.3.2. Estimating flow rate of patients ’ breathing

[0471] Referring again to FIG. 19 showing an example of the first embodiment, once the controller has estimated the pressure of the flow of gases at or near the patient's nares at step 2022, the controller then proceeds to step 2024. At step 2024, the controller is configured to estimate a flow rate of the patient’s breathing. The estimation of the flow rate of the patient’s breathing may relate to the flow rate of the patient’s breath out of and into their airways.

[0472] The direction of the flow rate of the patient’s breathing may be defined relative to the direction of the flow rate of the flow of gases output by the flow generator. For example, a positive flow rate of the patient’s breathing may indicate a flow of gases in the same direction as the flow of gases output by the flow generator and provided to the patient (i.e. into the airways of the patient). Conversely, a negative flow rate of the patient’s breathing may indicate a flow of gases against the direction of the flow of gases output by the flow generator and provided to the patient (i.e. out of the airways of the patient).

[0473] In some examples, the controller may be configured to estimate a flow rate of the patient’s breathing based at least in part on the estimated pressure of the flow of gases at or near the patient's nares determined at step 2022, and the data indicative or representative of the flow rate of the flow of gases.

[0474] In an example, the pressure of the flow of gases delivered to the patient may be determined using a series of equations. The series of equations may firstly determine the leak flow rate of the flow of gases out of the prongs based on the estimated pressure of the flow of gases delivered to the patient, and a nasal resistance parameter. The series of equations may then secondly determine the flow rate of the patient’s breathing based on the estimated leak flow rate and the measured flow rate of the flow of gases output by the flow generator.

[0475] For example, the controller may be configured to implement the following equations to estimate the flow rate of the patient’s breathing at a given time: and

[0476] Q breath Q blower ~ Qleak

[0477] Where Paeitvered is the estimated pressure of the flow of gases delivered to the patient, Qieak is the instantaneous leak flow rate of the flow of gases out of the patient’s nares, R is a nasal resistance parameter associated with one or more aspects of the patient’s nares or a naris, Qbiower is the measured flow rate of the flow of gases output by the flow generator, and Qbreath is the instantaneous estimate of the flow rate of the patient’s breathing. As described above, the value for Paeitvered may be estimated by the controller at step 2022. The value for Paeiivered may be estimated based at least on one or more nasal resistance parameters, and one or both of the data indicative or representative of the flow rate of the flow of gases and the data indicative or representative of the pressure of the flow of gases. As explained above, Qbreath relates to the flow rate of the patient’s breathing, which averages to zero over a given time period, however in this example, the Qbreath value is instantaneous. Similarly, in these equations, the Qieak value is instantaneous.

[0478] 4.3.3. Determining target pressure

[0479] Referring again to FIG. 19 showing an example of the first embodiment, once the controller has estimated the flow rate of the patient’s breathing at step 2024, the controller then proceeds to step 2020. At step 2020, as previously explained in relation to FIGS. 16-18, the controller is configured to determine a target pressure for the flow of gases delivered to the patient.

[0480] 4.3.3.1. Using patient breath flow rate

[0481] In the example of the first embodiment shown in FIG. 19, the controller is configured to determine the target pressure for the flow of gases delivered to the patient based at least in part on the estimated flow rate of the patient’s breathing.

[0482] In an example, the target pressure of the flow of gases delivered to the patient may be determined using a series of equations which firstly determine a target flow rate of the flow of gases output by the flow generator based on the determined pressure of the flow of gases delivered to the patient and a nasal resistance parameter; and then secondly determine the flow rate of the patient’s breathing based on the leak flow rate and the measured flow rate of the flow of gases output by the flow generator.

[0483] For example, the controller can be configured to implement the following equations to estimate the flow rate of the patient’s breathing:

[0484] Qblower, target = clamp(Qblower+ Qbreatb, min flow, max flow)

[0485] ^delivered — R * (.Qblower Qbreath)

[0486] Where Qtuower, target is the target total flow rate of the flow of gases output by the flow generator, Qblower is the measured flow rate of the flow of gases output by the flow generator, Qbreatbis the estimated flow rate of the patient’s breathing, such as that determined at step 2024, Paeiivered is the estimated pressure of the flow of gases delivered to the patient, R is a nasal resistance parameter associated with one or more aspects of the patient’s nares or a naris, specifically the resistance between the nares and the cannula prongs, and k1and k2are flow resistance constants associated with one or more aspects of the flow path and / or breathing circuit connected to the breathing assistance apparatus. Here, clampQ is a function that clamps the value of to increase its flow rate in order to maintain the target flow rate Qbiower, target t° values of (Qbiower + Qbreath between minflow and maxflow — i.e., it cannot be lower than the pre-defined minimum flow value or greater than the pre-defined maximum flow value. In these examples, the minflow may be the floor flow rate, Qfi00r- Insome examples, in the second equation used to estimate Pdeitvered the value of Qbiower used may be the value of Qbiower, target determined by the first equation, as Qbiower will be controlled to the value of Qbiower, target- So, the value of Qbiower used inthe calculation of Pdeitvered might not have the same value as it had when Qbiower, target was calculated.

[0487] Qbiower, target factors in Qbreatii- the flow rate of the patient’s breathing, which may be acting with or against the positive direction (into the patient’s airways) of Qbiower- the flow rate of the flow of gases output by the flow generator. When the patient inhales, the flow generator needs to speed up to increase its flow rate in order to maintain the target flow rate Qbiower, target- Similarly, when the patient exhales, the flow generator needs to slow down to decrease its flow rate in order to maintain the target flow rate Qbiower, targets and to prevent excessive resistance and / or back pressure.

[0488] As described above, the value for Pdeitvered may also be estimated by the controller at step 2022. The value for Ptarget may alternatively be estimated based at least on one or more nasal resistance parameters, instead of one or more flow resistance constants.

[0489] In this example, a positive patient breath flow rate (i.e., the patient inhaling) causes an increase in the motor speed, as the flow generator tries to maintain a substantially constant nasal pressure Pdeitvered , while a negative patient breath flow rate (i.e., the patient exhaling) causes a decrease or maintaining of a constant motor speed, as the blower is trying to maintain a substantially constant flow rate. The target pressure stays about the same throughout the expiratory phase of the patient’s breathing, however, such that the floor flow rate can be said to enable a pressure increase when the patient expires / exhales due to the target blower flow rate to increase its flow rate in order to maintain the target flow rate Qbiower, targetnotfalling lower due to the floor flow rate. This causes a pressure build-up, as expiratory pressure goes above the pressure that is the target during inspiratory phases.

[0490] 4.3.3.2. Using floor flow rate

[0491] In other examples of the first embodiment, such as the example control methods shown in FIGS .16-18, the controller may be configured to utilise one or more algorithms to determine the target pressure for the flow of gases delivered to the patient. The one or more algorithms take as input at least the floor flow rate, and sensor data received. The one or more algorithms may output the target pressure for the flow of gases delivered to the patient.

[0492] In an example, the controller may be configured to implement the following equation to determine the target pressure for the flow of gases delivered to the patient, i.e. at the patient or patient interface:

[0493] Where Ptarget is the target pressure of the flow of gases delivered to the patient, Pbiower is the data indicative or representative of the pressure of the flow of gases output by the flow generator, Qbiower is the data indicative or representative of the flow rate of the flow of gases output by the flow generator, Q floor is the floor flow rate, and Pois a constant term which may be preprogrammed and / or stored in the memory of the controller. More specifically, Pomay be a constant pressure term, which may account for the ‘fixed’ or intrinsic pressure drop along the internal flow path of the flow generator. The internal flow path of the flow generator may include the passage between blower outlet and the flow generator outlet, and the passage through the humidifier chamber.

[0494] The data indicative or representative of the flow rate of the flow of gases output by the flow generator comprises at least data indicative or representative of the average flow rate of the flow of gases. Similarly, the data indicative or representative of the pressure of the flow of gases output by the flow generator comprises at least data indicative or representative of the average pressure of the flow of gases output by the flow generator.

[0495] 4.4. Second embodiment examples

[0496] Referring now to FIG. 20 specifically, a further variation of the control method 2000 showing an example of the second embodiment is shown. In this example of the second embodiment, the control method 2000 is the same as that shown in FIGS. 16-18, but further comprises step 2022, of estimating the pressure of the flow of gases delivered to the patient.

[0497] Step 2005 shows the input received is a user specified therapy value, as previously described with respect to the second embodiment. The user-specified therapy value may relate to a target for one or more parameters of the flow of gases at or about the patient interface. The user-specified therapy value may be a target flow rate or a target pressure of the flow of gases at or about the patient interface. In some examples, the user-specified therapy value may be a target flow rate. As previously discussed, the user- specified therapy value may be received as input to the controller via the user interface.

[0498] At step 2005 of the example of the second embodiment, the controller 14 may be further configured to receive user input relating to one or more details of the patient interface and / or supply conduit (collectively referred to as the breathing circuit) being used to provide the present respiratory therapy to the patient, as previously discussed.

[0499] At step 2020 of the example of the second embodiment, the controller 14 is configured to determine a target pressure for the flow of gases delivered to the patient. In these variations, the target pressure is based at least in part on: the user-specified therapy value received at step 2005, and the sensor data received at step 2015. The target pressure may also be based on user input relating to details of the one or more breathing circuit components, which may be received at step 2005. Specifically, the sensor data may comprise the data indicative or representative of the flow rate of the flow of gases output by the flow generator, and the data indicative or representative of the pressure of the flow of gases output by the flow generator.

[0500] In some examples, the target pressure may be a target minimum pressure. In these examples, the controller is configured to determine a target minimum pressure for the flow of gases delivered to the patient via the patient interface. The target minimum pressure is a pressure level that the controller aims to keep the flow of gases output by the flow generator above. Similarly to the target pressure, the target minimum pressure is based at least in part on: the user-specified therapy value, the data indicative or representative of the flow rate of the flow of gases output by the flow generator, the data indicative or representative of the pressure of the flow of gases output by the flow generator.

[0501] In some examples of the second embodiment at step 2020, the controller is configured to utilise one or more algorithms to determine the target pressure for the flow of gases delivered to the patient. The one or more algorithms take as input at least the user-specified therapy value, sensor data received, and output the target pressure for the flow of gases delivered to the patient.

[0502] In an example, the controller may be configured to implement the following equation to determine the target pressure for the flow of gases delivered to the patient, i.e. at the patient or patient interface:

[0503] Where Ptarget is the target pressure of the flow of gases delivered to the patient, Pbiower is the data indicative or representative of the pressure of the flow of gases output by the flow generator, Qbiower is the data indicative or representative of the flow rate of the flow of gases output by the flow generator, TVuseris the user-specified therapy value, and Pois a constant term which may be preprogrammed and / or stored in the memory of the controller. More specifically, Pomay be a constant pressure term, which may account for the ‘fixed’ or intrinsic pressure drop along the internal flow path of the flow generator. The internal flow path of the flow generator may include the passage between blower outlet and the flow generator outlet, and the passage through the humidifier chamber.

[0504] The data indicative or representative of the flow rate of the flow of gases output by the flow generator comprises at least data indicative or representative of the average flow rate of the flow of gases. Similarly, the data indicative or representative of the pressure of the flow of gases output by the flow generator comprises at least data indicative or representative of the average pressure of the flow of gases output by the flow generator.

[0505] In some examples, the controller may be configured to determine the target pressure for the flow of gases delivered to the patient and / or perform the first control loop continuously. The average flow rate data and average pressure data may similarly be rolling average values which are updated continuously. In other examples, the controller may be configured to determine the target pressure for the flow of gases delivered to the patient and / or perform the first control loop at set intervals. The set intervals may be preprogrammed, or may be based on one or more therapy settings, patient settings, or therapy parameters. In such examples, the average flow rate data and average pressure data may be rolling average values which are updated at said set intervals, or may alternatively be updated continuously.

[0506] In the example of the second embodiment shown in FIG. 20, the control method 2000 further comprises step 2022 of estimating the pressure of the flow of gases delivered to the patient. In this step, the controller is configured to estimate the pressure of the flow of gases delivered to the patient. The controller is configured to estimate the pressure of the flow of gases delivered to the patient based at least in part on the data indicative or representative of the pressure of the flow of gases output by the flow generator, the data indicative or representative of the flow rate of the flow of gases output by the flow generator, and one or more flow resistance constants.

[0507] The pressure of the flow of gases delivered to the patient may utilise the measured pressure of the flow of gases and subtract one or more pressure drops associated with the flow path between the flow generator and the patient.

[0508] In an example, the controller is configured to implement the following equation to estimate the pressure of the flow of gases delivered to the patient:

[0509] Where Paeiivered is the estimated pressure of the flow of gases delivered to the patient, Pbiower is the measured pressure of the flow of gases output by the flow generator, Qbiower is the measured flow rate of the flow of gases output by the flow generator, and k±and k2are flow resistance constants associated with one or more aspects of the flow path and / or breathing circuit connected to the breathing assistance apparatus. The Pbiower may he an instantaneous measurement of the pressure of the flow of gases output by the flow generator, similarly, Qbiower may he an instantaneous measurement of the flow rate of the flow of gases output by the flow generator. In other examples, Pbiower and QbiowermaY be averages of measurements taken over a period of time, and as such, PaeiiveredmaYalsohe an average.

[0510] In some examples, one flow resistance constant may be used to estimate the pressure of the flow of gases delivered to the patient. In other examples, a plurality of flow resistance constants may be used.

[0511] Additional flow resistance constants may allow for a more precise estimation of pressure drop(s) along the flow path. Additional different flow resistance constants may relate to different components in the flow path from the flow generator, including the airways of the patient. Each of the flow resistance constants may relate to the flow resistance of an aspect of the flow path / breathing circuit being used to convey and deliver the flow of gases from the flow generator to the patient, and / or may relate to one or more aspects of the airways of the specific patient receiving the flow of gases. The one or more flow resistance constants may be based on at least on one or more characteristics of the patient interface. The one or more flow resistance constants may be based on at least on one or more characteristics of the supply conduit.

[0512] As previously discussed, the one or more flow resistance constants may be user-specified. The user may input details relating to the patient interface and / or supply conduit (collectively referred to as the breathing circuit) being used to provide the present respiratory therapy to the patient. The user may input one or more details relating to the specific breathing circuit providing the respiratory therapy. The user input relating to the breathing circuit may be used by the controller to determine one or more flow resistance constants.

[0513] The one or more details relating to the breathing circuit may relate to any one or more of the details of the patient interface. The details of the patient interface may be a general grouping of the patient interface such as the size, type, or model of patient interface, or may relate to more specific details of the patient interface such as the dimensions or other characteristics of the nasal prong(s) and / or manifold. Such characteristics may relate to whether a patient interface is adapted for providing an asymmetric flow of gases at the patient’s airways for example.

[0514] Additionally, the one or more details relating to the breathing circuit may relate to any one or more of the details of the supply conduit. The details of the supply conduit may similarly be a general grouping of the supply conduit such as the size or type of supply conduit, or may relate to more specific details of the supply conduit such as the internal geometry and / or length of the supply conduit.

[0515] In some examples, the controller may be configured to estimate the pressure of the flow of gases delivered to the patient continuously. The average flow rate data and average pressure data may similarly be rolling average values which are updated continuously. In other examples, the controller may be configured to estimate the pressure of the flow of gases delivered to the patient periodically, for example at set intervals. The set intervals may be preprogrammed, or may be based on one or more therapy settings, patient settings, or therapy parameters. In such examples, the average flow rate data and average pressure data may be rolling average values which are updated at said set intervals, or may alternatively be updated continuously.

[0516] At step 2025 of the example of the second embodiment, controller is configured to determine a target flow rate for the flow of gases output by the flow generator. In these examples, the controller may further be configured to determine a target motor speed that achieves the target flow rate for the flow of gases output by the flow generator. The target flow rate for the flow of gases and / or the target motor speed may be based at least in part on the target pressure of the flow of gases delivered to the patient determined at step 2020, and the estimated pressure of the flow of gases delivered to the patient from step 2022.

[0517] The target flow rate and / or the target motor speed may therefore correspond to the flow rate and motor speed expected to produce the target pressure at or near the airways of the patient, given the estimated pressure of the flow of gases delivered to the patient. Accordingly, if the estimated pressure is below the target pressure, the controller may determine a higher target flow rate and / or a higher target motor speed. Conversely, if the estimated pressure is above the target pressure, the controller may determine a reduced target flow rate and / or target motor speed. As such, it will be appreciated that the target flow rate follows the pressure target, and the controller adjusts the target flow rate and / or motor speed so as to minimise the difference between the estimated pressure of the flow of gases delivered to the patient, and the target pressure.

[0518] Because the target flow rate and / or target motor speed are determined with reference to the estimated pressure rather than independently of it, the controller is able to make more appropriate and proportionate adjustments to the flow of gases output by the flow generator. The use of the estimated pressure allows the controller to infer the relationship between changes in the flow rate and / or motor speed and the resulting delivered pressure. This prevents the controller from relying on guess-based or unduly coarse adjustments to the flow rate in an effort to reach the target pressure. Instead, the controller builds upon current and prior estimates of the delivered pressure to determine how much the target flow rate must change to achieve the target pressure. This results in a more stable control response and reduces the likelihood of overshoot, oscillation, or delays in reaching the target pressure of the flow of gases delivered to the patient.

[0519] 4.5. Control loop examples

[0520] In some examples, the controller is configured to implement a first control loop and a second control loop. The first control loop may comprise a first method, and the second control loop may comprise a second method. In these examples, the second control loop takes as input one or more outputs from the first control loop. The first control loop and the second control loop may be performed by the controller subsequently, or may be performed by the controller in parallel. Step 2020 of determining a target pressure for the delivered flow of gases may be considered to form at least a part of the first control loop, and step 2030 of controlling the flow rate of the flow of gases may be considered to form at least a part of the second control loop.

[0521] 4.5.1. First control loop

[0522] In the first control loop the controller is configured to at least determine the target pressure for the flow of gases delivered to the patient. The first control loop may be considered to be equivalent to at least step 2020 of the control method 2000 shown in any one of FIGS. 16 to 20. Step 2015 may also be considered a part of the first control loop, as well as the second control loop.

[0523] Specifically in the example method of the first embodiment shown in FIG. 19, steps 2022 and 2024 may also be included in the first control loop. In some examples, the controller may be configured to perform the first control loop continuously. The average flow rate data and average pressure data may be rolling average values which are updated continuously. In other examples, the controller may be configured to perform the first control loop at set intervals. The set intervals may be preprogrammed, or may be based on one or more therapy settings, patient settings, or therapy parameters. In such examples, the average flow rate data and average pressure data may be rolling average values which are updated at said set intervals, or may alternatively be updated continuously.

[0524] 4.5.2. Second control loop

[0525] In the second control loop, the controller is configured to control the flow rate of the gases output by the flow generator. The output of the first control loop may be an input to the second control loop. The second control loop may be considered equivalent to at least step 2030 of the control method 2000. In the examples shown in FIGS. 18 and 19, the second control loop may encompass step 2025 and step 2030 of control method 2000. In the example shown in FIG. 20, the second control loop may encompass step 2022, step 2025, and step 2030 of control method 2000. Step 2015 may also be considered a part of the second control loop, as well as the first control loop.

[0526] In the second control loop, the controller is configured to control the flow rate of the gases output by the flow generator to aim to deliver and maintain the pressure of the flow of gases delivered to the patient at substantially the target pressure determined by the first control loop (i.e. at step 2020). More specifically, at this step, the controller may be configured to control the flow generator to output the flow of gases at one or more flow rates to aim to deliver the flow of gases to the patient via the patient interface at substantially the target pressure determined by the first control loop.

[0527] In some examples, the controller may be configured to execute the second control loop continuously. The average flow rate data and average pressure data may similarly be rolling average values which are updated continuously. In other examples, the controller may be configured to perform the second control loop periodically, for example at set intervals. The set intervals may be preprogrammed, or may be based on one or more therapy settings, patient settings, or therapy parameters. In such examples, the average flow rate data and average pressure data may be rolling average values which are updated at said set intervals or may alternatively be updated continuously.

[0528] In examples, the controller may be configured to perform the first control loop and the second control loop with different regularity. For example, the controller may be configured to perform the first control loop over a longer time period than the second control loop. The first control loop may be performed over a longer time period such that the average of the flow and pressure readings can be taken over a timeframe that diminishes / smooths out any anomalous or false readings, which could produce highly variable outputs due to unexpected transient variations in the patient’s breath cycle and / or other noise. For example, the controller may be configured to output from the first control loop at a lower frequency, such as, for example, at 0.05 Hz, whereas the controller may be configured to output from the second control loop at a higher frequency, such as, for example, at 500 Hz.

[0529] It will be appreciated that the frequency of the output of the first and / or second control loops may be faster or slower, depending on variables such as the speed of the sensors and available computational resources. Preferably, the second control loop at least needs to run fast enough to control the flow rate of the flow of gases output by the flow generator relative to patient breathing. In other examples, the controller may be configured to perform the first control loop and the second control loop at the same regularity.

[0530] 4.6. Motor speed control

[0531] In some further examples, at step 2025, the controller may be further configured to determine a target motor speed to achieve the target flow rate for the flow of gases. The target flow rate and the target motor speed may be proportional. The target flow rate for the flow of gases and / or the target motor speed may be based at least in part on the target pressure of the flow of gases delivered to the patient determined at step 2020.

[0532] In further examples, at step 2025, the controller is configured to determine the target flow rate and / or target motor speed based at least in part on the target pressure of the flow of gases delivered to the patient determined at step 2020, and on data indicative or representative of the motor speed of the blower. The data indicative or representative of the motor speed of the blower may be received by the controller, for example at step 2015. Similarly to the received pressure and flow rate data, the data indicative or representative of the motor speed of the blower may be an instantaneous motor speed measurement, or may be an average motor speed measurement taken over a period of time.

[0533] In some examples, the controller is configured to determine the target flow rate and / or motor speed based at least in part on: the target pressure of the flow of gases delivered to the patient determined at step 2020, on data indicative or representative of the motor speed of the blower, and on data indicative or representative of the pressure of the flow of gases delivered to the patient.

[0534] The data indicative or representative of the pressure of the flow of gases delivered to the patient comprises at least data indicative or representative of the average pressure of the flow of gases delivered to the patient. The pressure of the flow of gases delivered to the patient may be the pressure of the gases at the patient end of the supply conduit, and / or the pressure in the patient interface, and / or the pressure in the upper airways of the patient.

[0535] In some examples, the controller is configured to control the target flow rate and / or motor speed using a proportional-integral-derivative (PID) controller. The PID controller utilises three tuned gain constants that are specific to, and may be tuned based on, one or more aspects of the breathing circuit and / or the respiratory therapy system.

[0536] The PID controller takes as input at least: the determined target pressure of the flow of gases delivered to the patient, the data indicative or representative of the motor speed of the blower, and the data indicative or representative of the pressure of the flow of gases delivered to the patient. The PID controller functions to aim to deliver and maintain the flow of gases delivered to the patient at substantially the target pressure determined at step 2020, by adjusting the motor speed of the flow generator blower motor and / or the flow rate of gases based on the difference (error) between the current data indicative or representative of the pressure of the flow of gases delivered to the patient, and the target pressure of the flow of gases delivered to the patient.

[0537] In some examples, the PID controller can be slow to respond to changes in the measured pressure of the flow of gases delivered to the patient, depending on controller tuning. Additionally, the PID controller relies on a linear model of the respiratory therapy system, which is a linearised form of an inherently nonlinear system (the respiratory therapy system herein described), so may not always precisely or accurately capture the behaviour of the system.

[0538] In an alternative example, the controller may be configured to use a non-linear model to control the target flow rate and / or motor speed. In such examples, the controller, or at least the portion of the controller configured to implement the non-linear model may be considered a non-linear controller. The non-linear model may have one or more non-linear terms that represent the behaviour of the blower and flows of gases in the system. The one or more non-linear terms may represent a relationship between the target pressure of the flow of gases delivered to the patient determined at step 2020, the measured data indicative or representative of the pressure of the flow of gases delivered to the patient, and the measured data indicative or representative of the motor speed of the blower.

[0539] The non-linear controller may function to aim to maintain the target pressure of the flow of gases delivered to the patient determined at step 2020, by determining a target flow rate and / or motor speed based at least in part on the one or more non-linear terms and the data indicative or representative of the motor speed of the blower. The non-linear controller may be configured to determine the target flow rate and / or motor speed based further on the data indicative or representative of the pressure of the flow of gases output by the blower, and the data indicative of representative of the flow rate of the flow of gases output by the blower. The controller may be faster and more accurate in performing the non-linear control than with an alternative linear approach such as the PID controller previously described, while the respiratory therapy provided to the patient remains substantially the same. The non-linear controller may be faster and more accurate than a similar linear controller as aspects of the system (specifically the blower motor speed and pressure relationship) which also have non-linear behaviours. Linear controllers use linearised models that only approximate part of the behaviour and can only be tuned for a small region of the behaviour. Using linear control may lead to significant error in some aspects of the control system and the controller can take a long time to respond appropriately. This is acceptable in stable systems (e.g., providing a constant target flow rate or pressure), but becomes problematic in more complex system such as when performing breath-synchronised, leak-controlled pressure control.

[0540] In some examples at step 2030, the controller may be configured to control the flow generator to output the flow of gases at one or more flow rates by controlling the motor speed of the blower of the flow generator. The controller may be configured to output one or more control signals to the blower of the flow generator to control the motor speed of the blower. In other examples, the controller may be configured to control the flow generator to output the flow of gases at one or more flow rates based on other output signals (i.e. not just motor speed). The control of the blower may be through pulse width modulation (PWM) control, or, a revolutions per minute (RPM) signal may be output to a dedicated motor controller that converts the RPM to PWM or a proportional current signal, for example. Alternatively, if electrical current feedback in the blower is available via current sensing, the control of the motor speed may be a direct control based on a provided, and controlled current (i.e., where current is proportional to motor speed). It will be appreciated that any appropriate form of blower control may be utilised.

[0541] At step 2030, the blower may be controlled to output the flow of gases at one or more flow rates to aim to deliver and maintain the flow of gases to the patient via the patient interface at substantially the target pressure. In such examples, the breathing assistance apparatus may further comprise one or more motor speed sensors configured to provide data indicative or representative of the motor speed of the blower. Alternatively, or additionally, a motor current sensor or sensors (e.g., motor phase current sensors) may provide data indicative or representative of the motor speed of the blower. The measured motor current may be proportional to the motor speed and therefore indicative or representative of the motor speed.

[0542] At step 2030, in some examples, the controller is configured to control the motor speed of the blower based on the target motor speed determined at step 2025. The controller may be configured to control the motor speed of the blower to meet the target motor speed. The controller may output a target motor speed which acts as the control signal for the blower motor. The controller may directly communicate with the motor, or a dedicated motor controller, but in either case the motor is driven via driver circuit. The motor controller may convert a received motor speed signal (e.g., in RPM) to a PWM signal suitable for the motor driver.

[0543] In examples, the motor speed may vary relative to the breathing of the patient, for example the motor speed may vary in synchronisation or approximate synchronisation with the breathing of the patient. The target motor speed is based at least in part on the pressure and / or flow rate of the flow of gases output by the flow generator according to the disclosed control method. The target flow rate may be based on the breathing of the patient. Because the flow rate (and patient interface pressure) will vary or try to vary with the patient’s breathing cycle, the controller will constantly adjust the motor speed (and therefore flow rate / pressure output) throughout the breathing cycle of the patient.

[0544] 4. 7. Adaptive resistance function

[0545] In another example of the first embodiment, the controller of the present disclosure is further configured to estimate the one or more nasal resistance parameters and dynamically update the estimate over time. As described above, the one or more nasal resistance parameters are each representative or indicative of the pneumatic resistance between one or both prongs of the nasal cannula and the one or both corresponding nares of the patient.

[0546] As described above, the nasal resistance parameter(s) can be used in the control methods described herein, specifically estimate the pressure of the flow of gases delivered to the patient. The estimation of the one or more nasal resistance parameters, and subsequent updating of the estimate overtime may eliminate the requirement of manual input of nasal resistance parameter(s), or input of a cannula type or model (which nasal resistance parameter(s) can be determined from). In some cases, such input may be burdensome to users and might be skipped (unless starting therapy is locked until this information is input). This is worsened by the fact that there many potentially compatible cannula models and sizes for use with a breathing assistance apparatus, which would in theory all need to have calibrated resistance values stored in memory, in order for the control methods of the present disclosure to function as intended. Additionally, even if this information is correctly input at the start of therapy, if the patient interface is swapped at any point after the beginning of therapy, the nasal resistance parameter(s) will no longer be accurate.

[0547] As such, the controller can dynamically estimate the nasal resistance parameter(s) throughout the provision of therapy to the patient. This ensures that the estimated nasal resistance parameter(s) are such that the flow rate targeted on inspiration of the patient is suitable for the specific patient and patient interface (i.e., sufficiently high, but not too high).

[0548] In such examples, the control method of the present disclosure may comprise a further step subsequent to the step of estimating the pressure of the flow of gases at or near the patient's nares, for example step 2022 in FIG. 19. In these examples, the control method may begin with a nominal value(s) for one or more nasal resistance parameter(s). In the further step, the controller is configured to perform a comparison of an estimated nasal resistance parameter with an expected value. In the first instance, the estimated nasal resistance parameter is the nominal nasal resistance parameter.

[0549] The controller then compares the estimated nasal resistance parameter with an expected value. The controller is configured to determine a deviation between the estimated nasal resistance parameter and the expected value based on a comparison of any one or more of a: flow rate, pressure, or a parameter of the flow of the patient’s breathing with an expected value indicating a deviation from the expected value. In examples, the parameter of the flow of the patient’s breathing is a peak inspiratory flow rate, a minute ventilation, or a variance metric of the flow rate of the patient’s breathing. The controller is then further configured to update the estimated nasal resistance parameter based on the determined deviation.

[0550] In some examples, the inspiratory flow rate is used for the comparison. The inspiratory flow rate may be the flow rate of the flow of gases output by the flow generator, or at least the target flow rate that the controller determines to be the flow rate of the flow of gases output by the flow generator. By way of the control methods described herein, the target flow rate of the flow of gases output by the flow generator will increase on patient inspiration, but that depends on the estimates of F’de rered, which in turn depend on the estimated nasal resistance parameter(s). The controller will receive a target flow rate and set a motor speed that corresponds to that target flow rate. If that motor speed doesn’t result in the expected measured flow rate, then the nasal resistance estimate(s) may therefore be incorrect, and may need to be updated. As such, if the inspiratory flow rate is larger than expected i.e., the peak flow rate is higher than what is expected, then the controller can decide that the assumed nasal resistance parameter(s) has been overestimated. This indicates that the nasal cannula fit is looser than expected. The controller then updates the nasal resistance parameter(s) accordingly, for example based on the deviation.

[0551] Similarly, if the inspiratory flow rate is smaller than expected i.e., the peak flow rate is lower than what is expected, this indicates that the assumed nasal resistance parameter(s) has been underestimated. This indicates that the nasal cannula fit is not lose enough. The controller then updates the nasal resistance parameter(s) accordingly, for example based on the deviation.

[0552] The above steps can be repeated to iteratively narrow down the assumed resistance towards the ‘true’ value and enable the control system to adapt to changes in resistance, for example, if the nasal cannula is swapped mid-therapy or a partial blockage occurs.

[0553] The controller may be configured to perform the comparison after an inspiratory phase of the patient's breath cycle. In some examples, the controller, may be configured to perform the comparison after providing a maximum or peak flow rate of the flow of gases.

[0554] In further examples of the first embodiment, the controller is configured to update the estimated nasal resistance parameter during therapy in a manner that mitigates transient deviations in measured flow or pressure. The transient deviations in measured flow or pressure may be caused by certain activities of the patient. Such activities include those that require an open mouth and can give rise to mouth breathing, such as talking and eating. Mouth breathing can result in unexpected and large changes (e.g. typically drops) in the pressure signal transmitted down the breathing tube, since the patient exhales (and / or inhales) flow through their mouth, rather than into and out of the nasal patient interface. As such, mouth breathing can introduce additional error in the estimation of the pressure and / or flow rate of gases delivered to the patient, and can result in undesirable transient changes in the flow parameters of the flow of gases output by the flow generator. These transient changes can lead to instability or amplification of fluctuations that do not correspond to the patient’s breathing. In these examples, to address these effects, the controller is configured to update the estimated nasal resistance parameter at a variable rate, which may be based on one or more factors.

[0555] In some examples, the controller is configured to update the estimated nasal resistance parameter at a rate that is proportional to one or more characteristics associated with the expiratory phase of the patient’s breathing. The one or more characteristics may include a peak expiratory flow rate, an integral of the expiratory flow, or an instantaneous expiratory flow value. Because such characteristics reflect the flow of gases through the nasal prongs of the nasal cannula and not the oral flow, they may be reduced during periods in which the patient breathes through the mouth. By updating the estimated nasal resistance parameter at a rate that depends on such expiratory flow characteristics, the controller can dampen the effect of transient deviations in the estimated patient flow and stabilise resulting swings or spikes in flow rate and / or pressure. In further examples, the controller is configured to update the estimated nasal resistance parameter at a rate that depends on the direction of change of the estimated nasal resistance parameter with respect to a current or historical value. In such examples, if an update would increase the estimated nasal resistance parameter relative to a long-term average value or relative to a most-recent value, the controller may update the parameter at a different rate than would be used for an update that decreases the parameter. By adjusting the rate in this manner, the controller can reduce the likelihood of large swings in the estimated nasal resistance parameter during periods in which non-breathing activities cause transient deviations in measured flow or pressure. This ensures that the estimate changes gradually and remains representative of the pneumatic resistance between the nasal cannula prongs and the patient’s nares.

[0556] In additional examples, the controller is configured to update the estimated nasal resistance parameter at a reduced rate during an initialisation state of the apparatus. During the initialisation state of the apparatus, filters and other estimation processes may not yet have stabilised, and the estimate of the pressure and / or flow rate of the patient’s breathing may have a larger error. By reducing the rate of updating the estimated nasal resistance parameter during such an initialisation phase, for example by halving the updating rate, the controller can prevent excessive adjustment of the parameter before the filters have reached a stable operating state. Once the initialisation state has concluded, the updating rate may return to a normal value.

[0557] Any of the above mechanisms may be employed individually or in combination. In examples, the controller may be configured to perform an update of the estimated nasal resistance parameter if either an expiratory-flow-based condition is met or if the update would increase the estimated nasal resistance parameter relative to a current or long-term average value. In such examples, the updating behaviour adapts both to the physiological characteristics of nasal expiratory flow and to the historical behaviour of the estimated nasal resistance parameter, thereby producing a stable and responsive estimate.

[0558] In some examples, the controller may additionally update the estimated pressure of the flow of gases delivered to the patient based on the same principles. In such examples, transient deviations in measured flow rate or pressure caused by mouth breathing may influence both the estimated nasal resistance parameter and the estimated delivered pressure. By updating these estimates based on expiratory-flow characteristics and / or direction-dependent updating rates, and / or initialisation-dependent updating rates, the controller may improve the stability of the estimation processes and reduce the tendency for the control system to respond to non-breathing activities with undesired changes in the flow of gases provided to the patient.

[0559] These examples thereby enable the controller to maintain stable operation and to dampen or prevent large, undesirable transient changes in estimated flow rate or pressure during therapy, particularly during periods in which the patient engages in certain activities requiring an open mouth.

[0560] In a further example of the first embodiment, the controller is configured to regulate the parameters of the flow of gases delivered to the patient by limiting one or both of the maximum instantaneous flow rate of the flow of gases delivered to the patient and the average flow rate of the flow of gases delivered to the patient (also known as minute ventilation). High instantaneous flow rates and / or high average flow rates of the flow of gases delivered to the patient can cause discomfort to the patient. When the instantaneous flow rate of the flow of gases delivered to the patient is high, the patient may experience a sudden or forceful jet of air entering the nasal passages. This can create a sensation of excessive pressure at the nares, nasal dryness, or irritation of the nasal mucosa. The airflow may also feel intrusive or overwhelming, particularly when it occurs abruptly relative to the patient’s natural breathing pattern.

[0561] A high average flow rate of the flow of gases delivered to the patient can contribute to discomfort because the patient may feel that they are being supplied with more flow than is necessary for their level of demand. This can increase resistance to therapy use, create difficulty in maintaining a natural breathing rhythm, or lead to increased leakage around the patient interface. Sustained elevation of total delivered flow may also increase drying of the airway.

[0562] To mitigate such effects, the controller is configured to operate in accordance with predetermined targets relating to the estimated flow rate of the flow of gases delivered to the patient. These targets comprise a maximum instantaneous flow rate of the flow of gases delivered to the patient and a maximum average flow rate of the flow of gases delivered to the patient (e.g. a maximum minute ventilation), above the set flow provided by the flow generator. In these examples, the controller adjusts the estimated nasal resistance parameter such that the estimated flow rate of the flow of gases delivered to the patient remains within the predetermined targets.

[0563] In some examples, the controller is configured to estimate a value of the nasal resistance parameter that corresponds to compliance with a target maximum instantaneous flow rate of the flow of gases delivered to the patient. In additional examples, the controller is configured to estimate a value of the nasal resistance parameter that corresponds to compliance with a target maximum average flow rate of the flow of gases delivered to the patient or patient minute ventilation. If the values of the estimated nasal resistance parameter obtained from these targets differ, the controller may reconcile the values by selecting the more conservative value, for example by selecting the larger of the two estimated nasal resistance parameter values. By doing so, the controller ensures that both instantaneous and average flow limits above the set flow are satisfied.

[0564] In some examples, the maximum instantaneous flow rate of the flow of gases delivered to the patient and / or the maximum average flow rate of the flow of gases delivered to the patient may be defined and / or adjusted by the user. In such examples, the controller may present selectable support levels which allow the user to specify a desired level of support or comfort desired by the patient. The controller may be configured to apply a corresponding threshold or limit on the permitted increase in the flow rate of the flow of gases delivered to the patient above the set flow rate based on the selected desired support level. The set flow rate may be an average flow rate which the flow generator is delivering to the airways of the patient. For example, a user may select a support level corresponding to lower level of desired support, a moderate level of desired support, or higher level of desired support. Each support level corresponds to a maximum instantaneous flow rate increase above the set flow rate and a maximum average flow rate increase above the set flow rate. In representative examples, a lower desired support level may correspond to up to approximately 15 L / min of instantaneous flow rate above the set flow rate and up to approximately 4 L / min of average flow rate above the set flow rate. A moderate desired support level may correspond to up to approximately 20 L / min of instantaneous flow rate above the set flow rate and up to approximately 8 L / min of average flow rate above the set flow rate. A higher desired support level may correspond to up to approximately 25 L / min of instantaneous flow rate above the set flow rate and up to approximately 12 L / min of average flow rate above the set flow rate.

[0565] In such examples, the controller is configured to adjust the estimated nasal resistance parameter such that flow rate of the flow of gases delivered to the patient does not exceed the support level defined thresholds. In this way, the user is able to select a comfort setting that directly influences the allowable deviation of the flow rate of the flow of gases delivered to the patient above the set flow rate, and the controller applies appropriate adjustments to the estimated nasal resistance parameter to achieve the selected limits while maintaining stable delivery of therapy.

[0566] 5. Graphical representation

[0567] FIG. 21 shows graphs 5000, 5100, and 5200 which are examples of how various flows and pressures may vary over the course of several breathing cycles of the patient based on the control methods of the present disclosure utilising a minimum flow parameter comprising a floor flow rate, and in response to the motor speed of the blower being controlled according to the previously described methods. It will be appreciated that graphs 5000, 5100, and 5200 represent data from the same time period. The graphs 5000, 5100, and 5200 show examples of the flows and pressure as a result of the control method of the first embodiment, such as that shown in the example of FIG. 19.

[0568] It is understood that the shape and scale of the waveforms will vary between patients and systems and may also exhibit intra-patient variation over time (e.g., due to changes in the patient’s activity, sleep / awake state, etc.). Graphs 5000, 5100, and 5200 show a single example of various flows and pressures for an example patient over a period of time, and it will be appreciated that many alternatives are likely, based on different patients, breathing circuits, and flow generators.

[0569] Graph 5000 shows an example of the flows occurring at different points of the flow path over a time period. The flow rates are shown in litres per minute (L / min).

[0570] Line 5005 shows the variation of the flow rate of the flow of gases associated with the patient’s breathing over time. This patient flow rate signal shown by line 5005 may not actually be measured by the apparatus in all examples. It is shown to explain the operation of the therapy, but the control system doesn’t necessarily need the patient’s breath flow rate to function. As shown, the flow rate of the patient’s breathing alternates between a positive flow rate when the patient is inhaling, and a negative flow rate when the patient is exhaling.

[0571] Line 5010 shows the instantaneous flow rate of the flow of gases output by the flow generator. As shown, the instantaneous flow rate of the flow of gases output by the flow generator varies relative to the breathing of the patient, for example the instantaneous flow rate may vary in synchronisation or approximate synchronisation with the breathing of the patient. The average flow rate in this example is around 30-35 L / min and corresponds approximately to the flow rate of leak via the patient’s nose.

[0572] Line 5015 shows the floor flow rate received or estimated by the controller, and used in the control of the flow of gases output by the flow generator. As shown, the floor flow rate is constant at the set value throughout the stages of the patients breathing cycle. The floor flow rate represented by line 5015 is shown for illustrative purposes.

[0573] As shown, the flow rate of the flow of gases output by the flow generator represented by line 5010 is limited from dropping below approximately the floor flow rate. The exhalation of the patient may cause the flow rate of the of the flow of gases output by the flow generator to drop from inhalation values. As shown, the flow rate of the flow of gases output by the flow generator may briefly drop slightly below the floor flow rate due to the change in the patient’s breathing from inspiration to expiration. However, the control method of the present disclosure then, by determining an updated target pressure for the flow of gases delivered to the patient, compensates to control the flow rate of the flow of gases output by the flow generator to be approximately the floor flow rate upon exhalation of the patient.

[0574] Graph 5100 shows an example of the pressures occurring at different points of the flow path over a time period. The pressures are shown in centimetres of water (cmH20).

[0575] Line 5120 shows the pressure of the flow of gases output by the flow generator. As shown, the pressure of the flow of gases output by the flow generator varies relative to the breathing of the patient, for example the pressure may vary in synchronisation or approximate synchronisation with the breathing of the patient. As shown, the pressure of the flow of gases output by the flow generator increases during both patient inspiration and expiration.

[0576] Because of the substantially constant flow rate (i.e. the floor flow rate) delivered throughout expiration of the patient, the patient may also be provided with a constant or increased pressure while they breathe out (PEEP). This constant or increased pressure may help to keep airways open and extending the expiratory duration (thereby lowering respiratory rate). At the same time, because the control system is trying to maintain a target pressure for the flow of gases delivered to the patient, and this pressure tends to decrease during inspiration as the patient breathes in, the flow rate will increase.

[0577] Line 5125 shows the estimated pressure of the flow of gases delivered to the patient (i.e. at the nares of the patient). The pressure of the flow of gases delivered to the patient is relatively constant during the exhalation of the patient. This is due to the control method of the present disclosure controlling to the floor flow rate, the controller varies the flow rate of the gases output by the flow generator such that it increases during inspiration (to provide pressure support) and is substantially constant during expiration (where the patient’s exhalations will generate backpressure and less pressure support is desired).

[0578] The result is a substantially consistent level of pressure at the patient’s airways during exhalation, or more specifically at the entrance to the patient’s nasal passages. The pressure of the flow of gases delivered to the patient may be suitable for providing one or more of the benefits of a pressure based respiratory therapy. As shown, the pressure of the flow of gases delivered to the patient is held at a relatively constant level of about 7 cmtTO. It will be appreciated that a higher floor flow rate may yield a higher patient pressure on exhalation. For example, up to 20 cmFLO, and vice-versa for lower floor flow rates.

[0579] Graph 5200 shows an example of the variation of the motor speed of the blower over a time period. The motor speed is shown in revolutions per minute (rpm). Line 5230 shows how the motor speed varies over time. The behaviour of the flow rate of the flow of gases output by the flow generator, as shown by line 5010, is a result of the motor speed, as shown by line 5230.

[0580] As shown by these graphs, the motor speed (line 5230) and both the flow rate (line 5010) and pressure (line 5120) of the flow of gases output by the flow generator varies relative to the breathing of the patient (line 5005), for example the flow rate and pressure may vary in synchronisation or approximate synchronisation with patient’s breathing (line 5005). The flow rate of the flow of gases output by the flow generator (line 5010) will be controlled to the floor flow rate (line 5015) when the patient’s breathing (e.g. exhalation) causes the flow rate of the flow of gases output by the flow generator to drop. Thus, the floor flow rate acts to maintain a relatively constant flow rate during patient exhalation, whilst also providing a level of pressure of the flow of gases delivered to the patient (line 5125) (e.g. a therapeutic CPAP pressure).

[0581] As shown, the flow rate of the flow of gases output by the flow generator increases during patient inhalations so as to reach a target patient-end pressure. During patient exhalations, the flow generator provides a substantially constant flow rate (e.g. the floor flow rate). The constant (floor) flow rate during patient exhalations results in increasing expiratory pressure, helping to keep the airways open and reducing respiratory rate. When used with an unsealed nasal cannula, this allows dead space washout to occur.

[0582] As such, the therapy dynamic with the flow rate floor is now one of constant flow during expiration and increasing flow during inspiration. Because of the constant flow rate delivery throughout expiration, the patient will be provided with increased pressure while they breathe out (PEEP), helping to keep airways open and extending the expiratory duration (thereby lowering respiratory rate). At the same time, because the control system is trying to maintain a target pressure for the flow of gases delivered to the patient, and this pressure tends to decrease during inspiration as the patient breathes in, the flow rate will increase.

[0583] In other words, the control method of the present disclosure allows the patient to receive a ‘boost’ in pressure during expiration and a ‘boost’ in flow during inspiration. In this sense, this control method provides another way to provide a hybrid respiratory therapy combining the benefits of a pressure based respiratory therapy (e.g. CPAP) and a flow based respiratory therapy (e.g. NHF therapy).

[0584] The control method of the present disclosure allows for peak inspiratory demand to be reached, so the user only needs to set the floor flow rate based on the desired level of washout required.

[0585] FIG. 22 shows graphs 4000, 4100, and 4200 which are examples of how various flows and pressures may vary over the course of several breathing cycles of the patient based on the control methods of the present disclosure utilising a minimum flow parameter comprising a floor pressure, and in response to the motor speed of the blower being controlled according to the previously described methods. It will be appreciated that graphs 4000, 4100, and 4200 relate to similar readings and use the same type of graphs as those shown in 5000, 5100, and 5200, but relate to a variation utilising a minimum flow parameter comprising a floor pressure, rather than a floor flow rate as shown in FIG. 20. Graphs 4000, 4100, and 4200 represent data from the same time period. Similarly to FIG. 20, the graphs 4000, 4100, and 4200 show examples of the flows and pressure as a result of the control method of the first embodiment, such as that shown in the example of FIG. 19.

[0586] It is understood that the shape and scale of the waveforms will vary between patients and systems and may also exhibit intra-patient variation over time (e.g., due to changes in the patient’s activity, sleep / awake state, etc.). Graphs 4000, 4100, and 4200 show a single example of various flows and pressures for an example patient over a period of time, and it will be appreciated that many alternatives are likely, based on different patients, breathing circuits, and flow generators.

[0587] Graph 4000 shows an example of the flows occurring at different points of the flow path over a time period. The flow rates are shown in litres per minute (L / min). Line 4005, similarly to line 5005, shows the variation of the flow rate of the flow of gases associated with the patient’s breathing over time.

[0588] Similarly to line 5010, line 4010 shows the instantaneous flow rate of the flow of gases output by the flow generator. As shown, the instantaneous flow rate of the flow of gases output by the flow generator varies relative to the breathing of the patient, for example the instantaneous flow rate may vary in synchronisation or approximate synchronisation with the breathing of the patient. The average flow rate in this example is around 30-35 L / min and corresponds approximately to the flow rate of leak via the patient’s nose.

[0589] Line 4015 shows the floor flow rate received or estimated by the controller, and used in the control of the flow of gases output by the flow generator. As shown, the floor flow rate is constant at the set value throughout the stages of the patients breathing cycle. The floor flow rate represented by line 4015 is shown for illustrative purposes, and may be changed based on user input for example.

[0590] As compared with the graph 5000 shown in FIG. 20, in this example the flow rate of the flow of gases output by the flow generator represented by line 4010 is not limited from dropping below the floor flow rate. As such, the exhalation of the patient may cause the flow rate of the of the flow of gases output by the flow generator to drop below the floor flow rate.

[0591] Graph 4100 shows an example of the pressures occurring at different points of the flow path over a time period. The pressures are shown in centimetres of water (cmtTO).

[0592] Line 4115 shows the floor pressure received or estimated by the controller, and used in the control of the flow of gases output by the flow generator. As shown, the floor pressure is constant at the set value throughout the stages of the patients breathing cycle. The floor pressure represented by line 4115 is shown for illustrative purposes, and may be changed based on user input for example.

[0593] Line 4120 shows the pressure of the flow of gases output by the flow generator. As shown, the pressure of the flow of gases output by the flow generator varies relative to the breathing of the patient, for example the pressure may vary in synchronisation or approximate synchronisation with the breathing of the patient. As shown, the pressure of the flow of gases output by the flow generator increases during patient inspiration but is limited to the floor pressure during patient expiration. The pressure of the flow of gases output by the flow generator is held relatively constant during the exhalation of the patient. This is due to the control method of the present disclosure controlling to the floor pressure. The controller varies the pressure of the gases output by the flow generator such that it increases during inspiration (to provide pressure support) and is substantially constant (at the floor pressure) during expiration (where the patient’s exhalations will generate backpressure and thus less pressure support is desired).

[0594] Line 4125 shows the estimated pressure of the flow of gases delivered to the patient (i.e. at the nares of the patient). As shown, the pressure of the flow of gases delivered to the patient is steadily increased to a peak pressure at the patient’s airways during exhalation. The pressure of the flow of gases delivered to the patient during exhalation may be suitable for providing one or more of the benefits of a pressure based respiratory therapy. As shown, the pressure of the flow of gases delivered to the patient is steadily increases to about 5 cmtLO during patient exhalation. It will be appreciated that a higher floor pressure may yield a higher patient pressure on exhalation. For example, up to 20 cmFLO, and vice-versa for lower floor pressures.

[0595] Because of the substantially constant floor pressure of the flow of gases output by the flow generator throughout expiration of the patient, the patient may be provided with a steadily increasing pressure at their airways while they breathe out (PEEP). This increasing pressure at their airways may help to keep airways open and extending the expiratory duration (thereby lowering respiratory rate). Similarly, because the control system is trying to maintain a target pressure for the flow of gases output by the flow generator, the pressure at the patient’s airways tends to decrease during inspiration as the patient breathes in and the flow rate increases.

[0596] Graph 4200 shows an example of the variation of the motor speed of the blower over a time period. The motor speed is shown in revolutions per minute (rpm). Line 4230 shows how the motor speed varies over time. The behaviour of the flow rate of the flow of gases output by the flow generator, as shown by line 4010, is a result of the motor speed, as shown by line 4230.

[0597] As shown by these graphs, the motor speed (line 4230) and both the flow rate (line 4010) and pressure (line 4120) of the flow of gases output by the flow generator varies relative to the breathing of the patient (line 4005), for example the flow rate and pressure may vary in synchronisation or approximate synchronisation with patient’s breathing (represented for example by line 4005). During patient inhalations, the controller tries to maintain a constant target pressure (shown by line 4125) at the airways of the patient, which results in the flow generator increasing the flow rate of the gases output by the flow generator. The pressure of the flow of gases output by the flow generator (shown by line 4120) will increase accordingly. During patient exhalations, the flow rate of the patient’s breathing (shown by line 4005), being against the flow rate of the flow of gases output by the flow generator (shown by line 4010) starts to cause an increase in back-pressure. The pressure at the airways of the patient (shown by line 4125) thus increases and the flow rate of the flow of gases output by the flow generator (shown by line 4010) slows down. The motor speed (line 4230) and flow rate (4010) thus decrease until the blower pressure hits the floor pressure (shown by line 4115).

[0598] During patient exhalations, the flow generator provides a substantially constant pressure (shown by line 4120). The constant pressure during patient exhalations results in increasing pressure at the airways of the patient (shown by line 4125), helping to keep the airways open and reducing respiratory rate. This improves comfort as the resistance the patient breathes against backs off slightly as they reach the ‘peak’ of their exhalation. When used with an unsealed nasal cannula, this allows dead space washout to occur. Inspiratory phases are the same as in the previous methods disclosed, such as in relation to FIG. 20.

[0599] FIG. 23 shows graphs 3000, 3500, and 3200 which are examples of how various flows and pressures may vary over the course of several breathing cycles of the patient based on the control methods of the present disclosure utilising a user-specified therapy value comprising an average flow rate, and in response to the motor speed of the blower being controlled according to the previously described methods. It will be appreciated that graphs 3000, 3500, and 3200 represent data from the same time period. The shape and scale of the waveforms will vary between patients and systems and may also exhibit intra-patient variation overtime (e.g., due to changes in the patient’s activity, sleep / awake state, etc.). Graphs 3000, 3500, and 3200 show a single example of various flows and pressures for an example patient over a period of time, and it will be appreciated that many alternatives are likely, based on different patients, breathing circuits, and flow generators. The graphs 3000, 3100, and 3200 show examples of the flows and pressure as a result of the control method of the second embodiment, such as that shown in the example of FIG. 20.

[0600] Graph 3000 shows an example of the flows occurring at different points of the flow path over a time period. The flow rates are shown in litres per minute (L / min). Line 3005 shows the variation of the flow rate of the flow of gases associated with the patient’s breathing overtime. This patient flow rate signal shown by line 3005 may not actually be measured by the apparatus in all examples. It is shown to explain the operation of the therapy, but the control system doesn’t necessarily need the patient’s breath flow rate to function. As shown, the flow rate of the patient’s breathing alternates between a positive flow rate when the patient is inhaling, and a negative flow rate when the patient is exhaling. Line 3015 shows the flow rate of gases flowing out of the patient interface, the average flow rate. As shown, the average flow rate is relatively constant. Line 3010 shows the instantaneous flow rate of the flow of gases output by the flow generator. As shown, the instantaneous flow rate of the flow of gases output by the flow generator varies in synchronisation or approximate synchronisation with the breathing of the patient. The average flow rate in this example is around 30-35 L / min and corresponds approximately to the flow rate of leak via the patient’s nose.

[0601] Graph 3200 shows an example of the variation of the motor speed of the blower over a time period. The motor speed is shown in revolutions per minute (rpm). Line 3230 shows how the motor speed varies over time. The behaviour of the flow rate of the flow of gases output by the flow generator, as shown by line 3010, is a result of the motor speed, as shown by line 3230.

[0602] Graph 3500 shows an example of the pressures occurring at different points of the flow path over a time period. The pressures are shown in centimetres of water (cmtLO). Line 3120 shows the pressure of the flow of gases output by the flow generator. As shown, the pressure of the flow of gases output by the flow generator varies in synchronisation or approximate synchronisation with the breathing of the patient. Line 3125 shows the estimated pressure of the flow of gases delivered to the patient. Similarly to the average flow rate shown by line 3015, the pressure of the flow of gases delivered to the patient (shown by line 3125) is also relatively constant. This is due to the control method controlling to the average flow rate, the controller varies the flow rate of the gases output by the flow generator such that it increases during inspiration (to provide pressure support) and decreases during expiration (where the patient’s exhalations will generate backpressure and less pressure support is desired). The result is a substantially consistent level of pressure at the patient’s airways, or more specifically at the entrance to the patient’s nasal passages. The pressure of the flow of gases delivered to the patient may be suitable for providing one or more of the benefits of a pressure based respiratory therapy. As shown, the pressure of the flow of gases delivered to the patient is held at a relatively constant level of about 4 cmtLO. It will be appreciated that a higher average flow rats will yield higher patient pressures, for example, up to 20 cml O. and vice- versa for lower flow rates.

[0603] As shown by these graphs, the motor speed (line 3230) and both the flow rate (line 3010) and pressure (line 3120) of the flow of gases output by the flow generator will vary in synchronisation or approximate synchronisation with patient’s breathing (line 3005), in order to maintain a relatively constant leak flow rate (line 3015) and a pressure of the flow of gases delivered to the patient (line 3125) (the therapeutic CPAP pressure).

[0604] Where in the foregoing description reference has been made to elements or integers having known equivalents, then such equivalents are included as if they were individually set forth. Although embodiments have been described with reference to a number of illustrative embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the preferred embodiments should be considered in a descriptive sense only and not for purposes of limitation, and also the technical scope of the invention is not limited to the embodiments. Furthermore, the present invention is defined not by the detailed description of the invention but by the appended claims, and all differences within the scope will be construed as being comprised in the present disclosure.

[0605] Many modifications will be apparent to those skilled in the art without departing from the scope of the present invention as herein described with reference to the accompanying drawings.

Claims

CLAIMS1. A breathing assistance apparatus configured to provide a flow of gases to be delivered to a patient via a patient interface for respiratory therapy, comprising: a flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases; and a controller configured to: receive a user-specified therapy value, receive data indicative or representative of the flow rate of the flow of gases output by the flow generator from one or more flow sensors, receive data indicative or representative of a pressure of the flow of gases output by the flow generator from one or more pressure sensors, determine a target pressure for the flow of gases delivered to the patient via the patient interface, wherein the target pressure is based at least in part on: the user-specified therapy value, the data indicative or representative of the flow rate of the flow of gases output by the flow generator, and the data indicative or representative of the pressure of the flow of gases output by the flow generator, and control the flow rate of the flow of gases output by the flow generator to deliver the flow of gases to the patient via the patient interface at substantially the target pressure.

2. The breathing assistance apparatus as claimed in claim 1, wherein the flow generator is configured to be coupled to a supply conduit at a first end, and wherein the supply conduit is configured to convey the flow of gases output by the flow generator.

3. The breathing assistance apparatus as claimed in claim 2, wherein the supply conduit is configured to be coupled to the patient interface at a second end, and wherein the patient interface is configured to receive the flow of gases from the supply conduit and deliver the flow of gases to the patient.

4. A respiratory therapy system for delivering a flow of gases to a patient for respiratory therapy, comprising: a breathing assistance apparatus comprising at least a flow generator, the flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases;a supply conduit coupled at a first end to the flow generator and configured to convey the flow of gases output by the flow generator; a patient interface coupled to a second end of the supply conduit and configured to receive the flow of gases from the supply conduit and deliver the flow of gases to the patient; and a controller configured to: receive a user-specified therapy value, receive data indicative or representative of the flow rate of the flow of gases output by the flow generator from one or more flow sensors, receive data indicative or representative of the pressure of the flow of gases output by the flow generator from one or more pressure sensors, determine a target pressure for the flow of gases delivered to the patient, wherein the target pressure is based at least in part on: the user-specified therapy value, the data indicative or representative of the flow rate of the flow of gases output by the flow generator, and the data indicative or representative of the pressure of the flow of gases output by the flow generator, and control the flow rate of the flow of gases output by the flow generator to deliver the flow of gases to the patient at substantially the target pressure.

5. The breathing assistance apparatus or respiratory therapy system as claimed in any preceding claim, wherein the patient interface is an unsealed patient interface.

6. The breathing assistance apparatus or respiratory therapy system as claimed in claim 5, wherein the unsealed patient interface is a non-sealing nasal cannula.

7. The breathing assistance apparatus or respiratory therapy system as claimed in claim 6, wherein the non-sealing nasal cannula is configured to cause an asymmetrical flow of gases at the patient's nares.

8. A respiratory therapy system for delivering a flow of gases to a patient for respiratory therapy, comprising: a breathing assistance apparatus comprising at least a flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases;a supply conduit coupled at a first end to the flow generator and configured to convey the flow of gases output by the flow generator; a patient interface coupled to a second end of the supply conduit and configured to receive the flow of gases from the supply conduit and deliver the flow of gases to the patient, wherein the patient interface is a non-sealing nasal cannula configured to cause an asymmetrical flow of gases at the patient's nares; and a controller configured to: determine a target pressure for the flow of gases delivered to the patient via the patient interface, and control the flow rate of the flow of gases output by the flow generator to deliver and maintain the pressure of the flow of gases delivered to the patient at substantially the target pressure.

9. The respiratory therapy system as claimed in claim 8, wherein the controller is further configured to: receive a user-specified therapy value, receive data indicative or representative of the flow rate of the flow of gases output by the flow generator from one or more flow sensors, and receive data indicative or representative of the pressure of the flow of gases output by the flow generator from one or more pressure sensors.

10. The breathing assistance apparatus or respiratory therapy system as claimed in any preceding claim, wherein the target pressure is sufficient to keep the airways of the patient open when delivered to the airways of the patient.

11. The breathing assistance apparatus or respiratory therapy system as claimed in claim 10, wherein the target pressure is between about 3cmH2O and about 8 cmH20.

12. The breathing assistance apparatus or respiratory therapy system as claimed in any preceding claim, wherein the flow of gases delivered to the patient at substantially the target pressure further provides a level of leak flow out of the patient interface.

13. The breathing assistance apparatus or respiratory therapy system as claimed in claim 12 wherein the level of leak flow is sufficient to substantially clear exhaled CO2 from the airways of the patient.

14. The respiratory therapy system as claimed in claim 8, wherein the controller is further configured to: receive a user-specified therapy value, receive data indicative or representative of the flow rate of the flow of gases output by the flow generator from one or more flow sensors, and receive dataindicative or representative of the pressure of the flow of gases output by the flow generator from one or more pressure sensors.

15. The respiratory therapy system as claimed in claim 14, wherein the controller is configured to determine the target pressure based at least in part on: the user-specified therapy value, the data indicative or representative of the flow rate of the flow of gases output by the flow generator, and the data indicative or representative of the pressure of the flow of gases output by the flow generator.

16. The breathing assistance apparatus or respiratory therapy system as claimed in any preceding claim, wherein the non-sealing nasal cannula comprises a first prong and a second prong, and wherein at least one of the first prong and the second prong is sized to maintain a sufficient gap between the outer surface of the prong and a patient's skin to avoid sealing a gas path between the non-sealing nasal cannula and the patient.

17. The breathing assistance apparatus or respiratory therapy system as claimed in claim 16, wherein the first prong has a larger inner cross-sectional area in a direction transverse to gases flow through the first prong than a corresponding inner cross-sectional area of the second prong in a direction transverse to gases flow through the second prong.

18. The breathing assistance apparatus or respiratory therapy system as claimed in claim 16 or claim 17, wherein at least the first prong is made of an elastomeric material that enables the first prong to deform and set its shape in use in response to temperature and contact with the patient's naris.

19. The breathing assistance apparatus or respiratory therapy system as claimed in claim 18, wherein the first prong is configured to deform and set its shape in use to substantially match the internal shape of the patient's naris.

20. The breathing assistance apparatus or respiratory therapy system as claimed in any one of claims 1-7 or 9-19, wherein the user-specified therapy value relates to a target for one or more parameters of the flow of gases at or about the patient interface.

21. The breathing assistance apparatus or respiratory therapy system as claimed in claim 20, wherein the user-specified therapy value is a target average flow rate.

22. The breathing assistance apparatus or respiratory therapy system as claimed in claim 21, wherein the target average flow rate is a target for an average of the leak flow rate of the flow of gases out of the patient interface over a set period of time.

23. The breathing assistance apparatus or respiratory therapy system as claimed in claim 21 or claim 22, wherein the delivery of the flow of gases to the patient at substantially the target pressure maintains the flow of gases leaking from the patient interface at substantially the target average flow rate.

24. The breathing assistance apparatus or respiratory therapy system as claimed in any one of claims 1-7 or 9-23, wherein the controller is configured to implement a first control loop and a second control loop, and wherein the first control loop comprises a first method, and the second control loop comprises a second method, and wherein the second control loop takes as input one or more outputs from the first control loop.

25. The breathing assistance apparatus or respiratory therapy system as claimed in claim 24, wherein in the first control loop the controller is configured to determine and output the target pressure for the flow of gases delivered to the patient.

26. The breathing assistance apparatus or respiratory therapy system as claimed in claim 24 or claim 25, wherein in the first control loop the controller is configured to determine the target pressure for the flow of gases delivered to the patient based at least in part on: the user-specified therapy value, the data indicative or representative of the flow rate of the flow of gases output by the flow generator, and the data indicative or representative of the pressure of the flow of gases output by the flow generator.

27. The breathing assistance apparatus or respiratory therapy system as claimed in claim 26, wherein the data indicative or representative of the flow rate of the flow of gases output by the flow generator comprises at least data indicative or representative of the average flow rate of the flow of gases output by the flow generator.

28. The breathing assistance apparatus or respiratory therapy system as claimed in claim 26 or claim 27, wherein the data indicative or representative of the pressure of the flow of gases output by the flow generator comprises at least data indicative or representative of the average pressure of the flow of gases output by the flow generator.

29. The breathing assistance apparatus or respiratory therapy system as claimed in any preceding claim, wherein the flow generator comprises a blower, and the control of the flow generator to output the flow of gases at one or more flow rates by the controller comprises controlling the motor speed of the blower.

30. The breathing assistance apparatus or respiratory therapy system as claimed in claim 29, wherein the motor speed of the blower is controlled to output the flow of gases to deliver the flow of gases to the patient via the patient interface at substantially the target pressure.

31. The breathing assistance apparatus or respiratory therapy system as claimed in any one of claims 1-7 or 9-30, wherein the breathing assistance apparatus or respiratory therapy system further comprises one or more motor speed sensors configured to provide data indicative or representative of the motor speed of the blower.

32. The breathing assistance apparatus or respiratory therapy system as claimed in claim 31, wherein in the second control loop the controller is configured to determine a target motor speed for the blower based at least in part on the determined target pressure of the flow of gases delivered to the patient.

33. The breathing assistance apparatus or respiratory therapy system as claimed in claim 32, wherein the second control loop is configured to determine the target motor speed for the blower based further on data indicative or representative of the motor speed of the blower.

34. The breathing assistance apparatus or respiratory therapy system as claimed in claim 32 or claim 33, wherein the second control loop is configured to determine the target motor speed for the blower based further on data indicative or representative of the pressure of the flow of gases delivered to the patient.

35. The breathing assistance apparatus or respiratory therapy system as claimed in claim 34, wherein the data indicative or representative of the pressure of the flow of gases delivered to the patient comprises at least data indicative or representative of the average pressure of the flow of gases delivered to the patient.

36. The breathing assistance apparatus or respiratory therapy system as claimed in claim 35, wherein the data indicative or representative of the pressure of the flow of gases delivered to the patient is an estimation of the pressure of the flow of gases delivered to the patient.

37. The breathing assistance apparatus or respiratory therapy system as claimed in any one of claims 32-36, wherein the controller is configured to determine the target motor speed for the blower using a proportional-integral-derivative controller which takes as input at least: the determined target pressure of the flow of gases delivered to the patient, the data indicative or representative of the motor speed of the blower, and the data indicative or representative of the pressure of the flow of gases delivered to the patient.

38. The breathing assistance apparatus or respiratory therapy system as claimed in any one of claims 32-36, wherein the controller is configured to determine the target motor speed for the blower using a non-linear model which takes as input at least: the determined target pressure of the flow of gases delivered to the patient, the data indicative or representative of the motor speed of the blower, and the data indicative or representative of the pressure of the flow of gases delivered to the patient.

39. The breathing assistance apparatus or respiratory therapy system as claimed in claim 38, wherein the non-linear model represents a relationship between the target pressure of the flow of gases delivered to the patient and the measured data indicative or representative of the pressure of the flow of gases delivered to the patient.

40. The breathing assistance apparatus or respiratory therapy system as claimed in any one of claims 32-39, wherein the controller is configured to control the motor speed of the blower based on the target motor speed.

41. The breathing assistance apparatus or respiratory therapy system as claimed in claim 40, wherein the controller is configured to control the motor speed of the blower to meet the target motor speed.

42. The breathing assistance apparatus or respiratory therapy system as claimed in any one of claims 1-7 or 9-41, wherein the controller is configured to estimate the pressure of the flow of gases delivered to the patient based at least in part on: the data indicative or representative of the pressure of the flow of gases output by the flow generator, the data indicative or representative of the flow rate of the flow of gases output by the flow generator, and one or more flow resistance constants.

43. The breathing assistance apparatus or respiratory therapy system as claimed in claim 42, wherein the one or more flow resistance constants are based on at least the patient interface.

44. The breathing assistance apparatus or respiratory therapy system as claimed in claim 42 or claim 43, wherein the one or more flow resistance constants are user-specified.

45. The breathing assistance apparatus or respiratory therapy system as claimed in any one of claims 1-7 or 9-44, wherein the breathing assistance apparatus further comprises a housing, and wherein the flow generator is located within the breathing assistance apparatus housing.

46. The breathing assistance apparatus or respiratory therapy system as claimed in claim 45, wherein the breathing assistance apparatus further comprises the one or more flow sensors, and wherein the one or more flow sensors are located within the breathing assistance apparatus housing.

47. The breathing assistance apparatus or respiratory therapy system as claimed in claim 46, wherein the one or more flow sensors are positioned at an outlet of the flow generator.

48. The breathing assistance apparatus or respiratory therapy system as claimed in claim 46 or claim 47, wherein the one or more flow sensors comprise ultrasonic transducers.

49. The breathing assistance apparatus or respiratory therapy system as claimed in any one of claims 45-48, wherein the breathing assistance apparatus further comprises the one or more pressure sensors, and wherein the one or more pressure sensors are located within the breathing assistance apparatus housing.

50. The breathing assistance apparatus or respiratory therapy system as claimed in claim 49, wherein the one or more pressure sensors are positioned at an outlet of the flow generator.

51. The breathing assistance apparatus or respiratory therapy system as claimed in any of the preceding claims, wherein the breathing assistance apparatus further comprises a user interface comprising a display and one or more input devices.

52. The breathing assistance apparatus or respiratory therapy system as claimed in claim 51, wherein the display is configured to display one or more parameters of the flow of gases.

53. The breathing assistance apparatus or respiratory therapy system as claimed in claim 52, wherein the one or more parameters of the flow of gases comprise one or more of the flow rate of the flow of gases output by the flow generator, and the pressure of the flow of gases delivered to the patient.

54. The breathing assistance apparatus or respiratory therapy system as claimed in any one of claims 51-53, wherein the one or more input devices are configured to receive input from a user, wherein the input from the user comprises at least a user-specified therapy value.

55. The breathing assistance apparatus or respiratory therapy system as claimed in any preceding claim, wherein the breathing assistance apparatus further comprises a humidifier configured to heat and humidify the flow of gases output by the flow generator.

56. The breathing assistance apparatus or respiratory therapy system as claimed in any preceding claim, wherein the target pressure is a target minimum pressure for the flow of gases delivered to the patient via the patient interface.

57. The breathing assistance apparatus or respiratory therapy system as claimed in claim 56, wherein the controller is configured to determine the target flow rate for the blower based at least in part on the determined target minimum pressure of the flow of gases delivered to the patient, and to control the flow generator to output the flow of gases at the target flow rate to deliver the flow of gases to the patient via the patient interface at or above the target minimum pressure.

58. The breathing assistance apparatus or respiratory therapy system as claimed in any one of claims 1- 55, wherein the controller is configured to determine a target flow rate for the blower based at least in part on the determined target pressure of the flow of gases delivered to the patient, and a set minimum flow rate.

59. The breathing assistance apparatus or respiratory therapy system as claimed in claim 58, wherein the controller is configured to control the flow generator to output the flow of gases at the target flow rate to deliver the flow of gases to the patient via the patient interface at or above the target pressure.

60. A method for controlling the pressure of a flow of gases delivered to a patient for respiratory therapy, the method comprising: controlling a flow generator to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases, and wherein the flow of gases output by the flow generator is configured to be delivered to the patient via a patient interface; receiving a user-specified therapy value; receiving data indicative or representative of the flow rate of the flow of gases output by the flow generator from one or more flow sensors; receiving data indicative or representative of a pressure of the flow of gases output by the flow generator from one or more pressure sensors; determining a target pressure for the flow of gases delivered to the patient, wherein the target pressure is based at least in part on: the user-specified therapy value, the data indicative or representative of the flow rate of the flow of gases output by the flow generator, and the data indicative or representative of the pressure of the flow of gases output by the flow generator; andcontrol the flow rate of the flow of gases output by the flow generator to deliver the flow of gases to the patient at substantially the target pressure.

61. A breathing assistance apparatus configured to provide a flow of gases to be delivered to a patient via a patient interface for respiratory therapy, comprising: a flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases; and a controller configured to: receive a user-specified therapy value, receive data indicative or representative of the flow rate of the flow of gases output by the flow generator from one or more flow sensors, receive data indicative or representative of a pressure of the flow of gases output by the flow generator from one or more pressure sensors, determine a target minimum pressure for the flow of gases delivered to the patient via the patient interface, wherein the target minimum pressure is based at least in part on: the user-specified therapy value, the data indicative or representative of the flow rate of the flow of gases output by the flow generator, the data indicative or representative of the pressure of the flow of gases output by the flow generator, and determine a target flow rate for the blower based at least in part on the determined target minimum pressure of the flow of gases delivered to the patient, and control the flow generator to output the flow of gases at the target flow rate to deliver the flow of gases to the patient via the patient interface at or above the target minimum pressure.

62. A breathing assistance apparatus configured to provide a flow of gases to be delivered to a patient via a patient interface for respiratory therapy, comprising: a flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases; and a controller configured to: receive a user-specified therapy value,receive data indicative or representative of the flow rate of the flow of gases output by the flow generator from one or more flow sensors, receive data indicative or representative of a pressure of the flow of gases output by the flow generator from one or more pressure sensors, determine a target pressure for the flow of gases delivered to the patient via the patient interface, wherein the target pressure is based at least in part on: the user-specified therapy value, the data indicative or representative of the flow rate of the flow of gases output by the flow generator, the data indicative or representative of the pressure of the flow of gases output by the flow generator, and determine a target flow rate for the blower based at least in part on the determined target pressure of the flow of gases delivered to the patient, and a set minimum flow rate, and control the flow generator to output the flow of gases at the target flow rate to deliver the flow of gases to the patient via the patient interface at or above the target pressure.

63. A breathing assistance apparatus configured to provide a flow of gases to be delivered to a patient via a patient interface for respiratory therapy, comprising: a flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases; and a controller configured to: receive a minimum flow parameter representing a minimum allowable parameter relating to the flow of gases, receive data indicative or representative of a flow rate of the flow of gases, receive or estimate data indicative or representative of a pressure at or near the patient's nares, determine a target pressure for the flow of gases delivered to the patient, wherein the target pressure is based at least in part on: the data indicative or representative of the flow rate of the flow of gases, the data indicative or representative of the pressure at or near the patient's nares, and the minimum flow parameter, and control the flow rate of the flow of gases output by the flow generator to deliver the flow of gases to the patient at substantially the target pressure.

64. The breathing assistance apparatus as claimed in claim 63, wherein the minimum flow parameter is a floor flow rate representing a minimum allowable flow rate for the flow of gases.

65. A breathing assistance apparatus configured to provide a flow of gases to be delivered to a patient via a patient interface for respiratory therapy, comprising: a flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases; and a controller configured to: receive a floor flow rate representing a minimum allowable flow rate for the flow of gases, receive data indicative or representative of a flow rate of the flow of gases, receive or estimate data indicative or representative of a pressure at or near the patient's nares, determine a target pressure for the flow of gases delivered to the patient, wherein the target pressure is based at least in part on: the data indicative or representative of the flow rate of the flow of gases, the data indicative or representative of the pressure at or near the patient's nares, and the floor flow rate, and control the flow rate of the flow of gases output by the flow generator to deliver the flow of gases to the patient at substantially the target pressure.

66. The breathing assistance apparatus as claimed in claim 64 or claim 65, wherein the controller is further configured to receive data indicative or representative of a pressure of the flow of gases output by the flow generator.

67. The breathing assistance apparatus as claimed in claim 66, wherein the controller is configured to estimate the data indicative or representative of a pressure at or near the patient's nares based at least in part on the data indicative or representative of the flow rate of the flow of gases, and the data indicative or representative of the pressure of the flow of gases output by the flow generator.

68. The breathing assistance apparatus as claimed in any one of claims 64 to 67, wherein the controller is further configured to estimate a flow rate of the patient’s breathing based at least in part on the received or estimated data indicative or representative of a pressure at or near the patient's nares and the data indicative or representative of the flow rate of the flow of gases.

69. The breathing assistance apparatus as claimed in claim 68, wherein the controller is configured to determine the target pressure for the flow of gases delivered to the patient based on the estimated flow rate of the patient’s breathing.

70. The breathing assistance apparatus as claimed in any one of claims 64 to 69, wherein the controller is further configured to determine a target flow rate for the flow of gases output by the flow generator based on the determined target pressure for the flow of gases delivered to the patient, wherein the target flow rate is no lower than the floor flow rate.

71. A breathing assistance apparatus configured to provide a flow of gases to be delivered to a patient via a patient interface for respiratory therapy, comprising: a flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases; and a controller configured to: receive a floor flow rate representing a minimum allowable flow rate for the flow of gases, receive data indicative or representative of a flow rate of the flow of gases, receive data indicative or representative of a pressure of the flow of gases, estimate a pressure of the flow of gases at or near the patient's nares based at least in part on the data indicative or representative of the flow rate of the flow of gases and the data indicative or representative of the pressure of the flow of gases, estimate a flow rate of the patient’s breathing based at least in part on the estimated pressure of the flow of gases at or near the patient's nares and the data indicative or representative of the flow rate of the flow of gases, determine a target pressure for the flow of gases delivered to the patient based at least in part on the estimated flow rate of the patient’s breathing, determine a target flow rate for the flow of gases output by the flow generator based on the determined target pressure for the flow of gases delivered to the patient, wherein the target flow rate is no lower than the floor flow rate, and control the flow rate of the flow of gases output by the flow generator based on the target flow rate.

72. The breathing assistance apparatus as claimed in claim 71, wherein the controller is configured to control the flow rate of the flow of gases output by the flow generator to deliver the flow of gases to the patient at substantially the target pressure.

73. The breathing assistance apparatus as claimed in claim 63, wherein the minimum flow parameter is a floor pressure representing a minimum allowable pressure for the flow of gases.

74. A breathing assistance apparatus configured to provide a flow of gases to be delivered to a patient via a patient interface for respiratory therapy, comprising: a flow generator configured to output a flow of gases according to one or more parameters, wherein the one or more parameters comprise at least a flow rate of the flow of gases; and a controller configured to: receive a floor pressure representing a minimum allowable pressure for the flow of gases, receive data indicative or representative of a flow rate of the flow of gases, receive or estimate data indicative or representative of a pressure at or near the patient's nares, determine a target pressure for the flow of gases delivered to the patient, wherein the target pressure is based at least in part on: the data indicative or representative of the flow rate of the flow of gases, the data indicative or representative of the pressure at or near the patient's nares, and the floor pressure, and control the flow rate of the flow of gases output by the flow generator to deliver the flow of gases to the patient at substantially the target pressure.

75. The breathing assistance apparatus as claimed in any one of claims 63 to 74, wherein the target pressure is sufficient to keep the airways of the patient open when delivered to the airways of the patient.

76. The breathing assistance apparatus as claimed in claim 75, wherein the target pressure is between about 3cmH2O and about 8 cmH20.

77. The breathing assistance apparatus as claimed in any one of claims 63 to 76, wherein the flow of gases delivered to the patient at substantially the target pressure further provides a level of leak flow out of the patient interface.

78. The breathing assistance apparatus as claimed in claim 77, wherein the level of leak flow is sufficient to substantially clear exhaled CO2 from the airways of the patient.

79. The breathing assistance apparatus as claimed in any one of claims 63 to 78, wherein the controller is further configured to receive or estimate one or more nasal resistance parameters, each nasal resistance parameter representative or indicative of the pneumatic resistance between one or both prongs of the nasal cannula and the one or both corresponding nares of the patient.

80. The breathing assistance apparatus as claimed in claim 79, wherein the controller is further configured to estimate the pressure of the flow of gases at or near the patient's nares based at least in part on: the data indicative or representative of the flow rate of the flow of gases, the data indicative or representative of the pressure of the flow of gases, and one or more estimated nasal resistance parameters.

81. The breathing assistance apparatus as claimed in any one of claims 63 to 80, wherein the controller is further configured to receive or estimate one or more flow resistance constants, each representative or indicative of the pneumatic resistance of one or more portions of the flow path between an outlet of the flow generator and a patient interface.

82. The breathing assistance apparatus as claimed in claim 81, wherein the controller is further configured to estimate the pressure of the flow of gases at or near the patient's nares based at least in part on: the data indicative or representative of the flow rate of the flow of gases, the data indicative or representative of the pressure of the flow of gases, and the one or more flow resistance constants.

83. The breathing assistance apparatus as claimed in claim 79 or claim 80, wherein subsequent to the step of estimating the pressure of the flow of gases at or near the patient's nares, the controller is further configured to perform a comparison of an estimated nasal resistance parameter with an expected value.

84. The breathing assistance apparatus as claimed in claim 83, wherein the controller is configured to perform the comparison after an inspiratory phase of the patient's breath cycle.

85. The breathing assistance apparatus as claimed in claim 83 or claim 84, wherein the controller is configured to perform the comparison after providing a maximum or peak flow rate of the flow of gases.

86. The breathing assistance apparatus as claimed in any one of claims 83 to 85, wherein the controller is further configured to revise the nasal resistance parameter based on a determined deviation between the estimated nasal resistance parameter and the expected value.

87. The breathing assistance apparatus as claimed in any one of claims 83 to 86, wherein the controller is further configured to determine a deviation between the estimated nasal resistance parameter and the expected value based on a comparison of any one or more of a: flow rate, pressure, or a parameter of the flow of the patient’s breathing with an expected value indicating a deviation from the expected value.

88. The breathing assistance apparatus as claimed in claim 87, wherein the parameter of the flow of the patient’s breathing is a peak inspiratory flow rate, a minute ventilation, or a variance metric of the flow rate of the patient’s breathing.

89. The breathing assistance apparatus as claimed in claim 87 or claim 88, wherein the controller is further configured to update the estimated nasal resistance parameter based on the determined deviation based on a comparison.

90. The breathing assistance apparatus as claimed in any one of claims 63 to 89, wherein the flow generator is configured to be coupled to a supply conduit at a first end, and wherein the supply conduit is configured to convey the flow of gases output by the flow generator.

91. The breathing assistance apparatus as claimed in claim 90, wherein the supply conduit is configured to be coupled to the patient interface at a second end, and wherein the patient interface is configured to receive the flow of gases from the supply conduit and deliver the flow of gases to the patient92. The breathing assistance apparatus as claimed in claim 91, wherein the patient interface is an unsealed patient interface.

93. The breathing assistance apparatus as claimed in claim 92, wherein the unsealed patient interface is a non-sealing nasal cannula.

94. The breathing assistance apparatus as claimed in claim 93, wherein the non-sealing nasal cannula is configured to cause an asymmetrical flow of gases at or near the patient's nares.

95. The breathing assistance apparatus as claimed in claim 94, wherein the non-sealing nasal cannula comprises a first prong and a second prong, and wherein at least one of the first prong and thesecond prong is sized to maintain a sufficient gap between the outer surface of the prong and a patient's skin to avoid sealing a gas path between the non-sealing nasal cannula and the patient.

96. The breathing assistance apparatus as claimed in claim 95, wherein the first prong has a larger inner cross-sectional area in a direction transverse to gases flow through the first prong than a corresponding inner cross-sectional area of the second prong in a direction transverse to gases flow through the second prong.

97. The breathing assistance apparatus as claimed in claim 95 or claim 96, wherein at least the first prong is made of an elastomeric material that enables the first prong to deform and set its shape in use in response to temperature and contact with the patient's naris.

98. The breathing assistance apparatus as claimed in any one of claims 95 to 97, wherein the first prong is configured to deform and set its shape in use to substantially match the internal shape of the patient's naris.

99. The breathing assistance apparatus as claimed in claim 93, wherein the non-sealing nasal cannula is configured to cause a substantially symmetrical flow of gases at or near the patient's nares.

100. The breathing assistance apparatus as claimed in claim 99, wherein the non-sealing nasal cannula comprises a first prong and a second prong, and wherein the inner cross-sectional area in a direction transverse to gases flow through the first prong is substantially equal to the corresponding inner cross-sectional area of the second prong.

101. The breathing assistance apparatus as claimed in any one of claims 63 to 100, wherein the minimum flow parameter is received as user input.

102. The breathing assistance apparatus as claimed in any one of claims 63 to 101, wherein the data indicative or representative of the flow rate of the flow of gases is indicative or representative of an instantaneous flow rate of the flow of gases.

103. The breathing assistance apparatus as claimed in any one of claims 63 to 101, wherein the data indicative or representative of the flow rate of the flow of gases is indicative or representative of an average flow rate of the flow of gases.

104. The breathing assistance apparatus as claimed in any one of claims 63 to 103, wherein the data indicative or representative of the pressure of the flow of gases is indicative or representative of an instantaneous pressure of the flow of gases.

105. The breathing assistance apparatus as claimed in any one or claims 63 to 103, wherein the data indicative or representative of the pressure of the flow of gases is indicative or representative of an average pressure of the flow of gases.

106. The breathing assistance apparatus as claimed in any one of claims 63 to 105, wherein the data indicative or representative of the pressure at or near the patient's nares is an instantaneous pressure at or near the patient's nares.

107. The breathing assistance apparatus as claimed in any one of claims 63 to 106, wherein the controller is configured to implement a first control loop and a second control loop, and wherein the first control loop comprises a first method, and the second control loop comprises a second method, and wherein the second control loop takes as input one or more outputs from the first control loop.

108. The breathing assistance apparatus as claimed in claim 107, wherein in the first control loop the controller is configured to determine and output the target pressure for the flow of gases delivered to the patient.

109. The breathing assistance apparatus as claimed in claim 108, wherein in the first control loop the controller is configured to determine the target pressure for the flow of gases delivered to the patient based at least in part on: the data indicative or representative of the flow rate of the flow of gases, the data indicative or representative of the pressure at or near the patient's nares, and the minimum flow parameter.

110. The breathing assistance apparatus as claimed in claim 107 or claim 108, wherein the second control loop is configured to determine a target flow rate for the flow of gases output by the flow generator.

111. The breathing assistance apparatus as claimed in claim 110, wherein the second control loop is configured to determine a target flow rate for the flow of gases output by the flow generator based at least in part on: the determined target pressure for the flow of gases delivered to the patient.

112. The breathing assistance apparatus as claimed in any one of claims 63 to 111, wherein the flow generator comprises a blower, and the control of the flow rate of the flow of gases output by the flow generator comprises controlling the motor speed of the blower.

113. The breathing assistance apparatus as claimed in claim 112, wherein the motor speed of the blower is controlled to output the flow of gases to deliver the flow of gases to the patient via the patient interface at substantially the target pressure.

114. The breathing assistance apparatus as claimed in claim 112 or claim 113, wherein the breathing assistance apparatus or respiratory therapy system further comprises one or more motor speed sensors configured to provide data indicative or representative of the motor speed of the blower.

115. The breathing assistance apparatus as claimed in claim 114, wherein the controller is configured to determine a target motor speed for the blower based at least in part on the determined target pressure of the flow of gases delivered to the patient.

116. The breathing assistance apparatus as claimed in claim 115, wherein the controller is configured to determine the target motor speed for the blower based further on data indicative or representative of the motor speed of the blower.

117. The breathing assistance apparatus as claimed in claim 115 or claim 116, wherein the controller is configured to determine the target motor speed for the blower based further on data indicative or representative of the pressure of the flow of gases delivered to the patient.

118. The breathing assistance apparatus as claimed in any one of claims 63 to 117, wherein the breathing assistance apparatus further comprises one or more flow sensors, the one or more flow sensors configured to provide data indicative or representative of the flow rate of the flow of gases, and wherein the one or more flow sensors are located within the breathing assistance apparatus housing.

119. The breathing assistance apparatus as claimed in claim 118, wherein the one or more flow sensors are positioned at an outlet of the flow generator.

120. The breathing assistance apparatus as claimed in claim 119, wherein the one or more flow sensors comprise ultrasonic transducers.

121. The breathing assistance apparatus as claimed in any one of claims 63 to 120, wherein the breathing assistance apparatus further comprises the one or more pressure sensors, wherein the one or more pressure sensors are configured to provide data indicative or representative of a pressure of the flow of gases and wherein the one or more pressure sensors are located within the breathing assistance apparatus housing.

122. The breathing assistance apparatus as claimed in claim 121, wherein the one or more pressure sensors are positioned at an outlet of the flow generator.

123. The breathing assistance apparatus as claimed in any one of claims 63 to 122, wherein the breathing assistance apparatus further comprises a user interface comprising a display and one or more input devices.

124. The breathing assistance apparatus as claimed in claim 123, wherein the display is configured to display one or more parameters of the flow of gases, and wherein the one or more parameters of the flow of gases comprise one or more of the flow rate of the flow of gases output by the flow generator, and the pressure of the flow of gases delivered to the patient.

125. The breathing assistance apparatus as claimed in claim 123 or claim 124, wherein the one or more input devices are configured to receive input from a user, wherein the input from the user comprises at least the minimum flow parameter.

126. The breathing assistance apparatus as claimed in any one of claims 63 to 125, wherein the breathing assistance apparatus further comprises a humidifier configured to heat and humidify the flow of gases output by the flow generator.

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