Method and system for characterising flow paths

Abstract

Embodiments of the invention are directed to methods of characterising flow paths within a patient's respiratory airways. The method may comprise determining a pressure flow correlation between an airway pressure and a corresponding flow rate of gases at the patient, receiving a first input relating to a flow of gases provided to the patient, determining a second input relating to a flow of gases at the patient based on the pressure flow correlation, and characterising one or more flow paths of delivered gases within the respiratory airways of the patient based on the first input and the second input.

Description

METHOD AND SYSTEM FOR CHARACTERISING FLOW PATHSTechnical Field

[0001] The present invention relates to a method and system for characterising flow paths within a patient's respiratory airways. In particular, embodiments of the invention may relate to methods and systems for characterising flow paths within a patient's respiratory airways during respiratory support delivered via a non-sealing patient interface, although the scope of the invention may not necessarily be limited thereto.Background of Invention

[0002] When providing respiratory support, for example in medical procedures where it is beneficial to provide oxygenation to a patient, it is often desirable for a clinician to know various respiratory parameters, such as flow paths of a provided gas within the patient's respiratory airways, airway patency, whether an input flow rate of gases provided by the respiratory support meets an inspiratory demand of the patient, a proportion of expired CO2, tidal volume and the like. Such parameters are not always readily available and may not be easily measurable during such medical procedures.

[0003] A reference herein to a patent document or any other matter identified as prior art, is not to be taken as an admission that the document or other matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.Summary of Invention

[0004] According to one aspect of the invention, there is provided a method of characterising flow paths within a patient's respiratory airways, the method comprising determining a pressure flow correlation between an airway pressure and a corresponding flow rate of gases at the patient, receiving a first input relating to a flow of gases provided to the patient, determining a second input relating to a flow of gases at the patient based on the pressure flow correlation, andcharacterising one or more flow paths of delivered gases within the respiratory airways of the patient based on the first input and the second input.

[0005] Knowledge of flow path characterisation may be beneficial in a number of ways. For example, knowledge of the flow pathways within a patient's respiratory airways may enable determination of certain aspects of the patients' physiological state and whether a particular therapy, or form of respiratory support, will be effective. It is therefore desirable to provide a method and / or system for characterising flow paths within a patient's respiratory airways to thereby facilitate critical decision making by clinicians. For example, information regarding flow paths within the patient's respiratory airways may enable a clinician to make a critical decision on whether to change a type of therapy provided to the patient so as to provide a better therapeutic effect at the patient. Moreover, the information may enable the clinician to make such critical decision in a more timely manner.

[0006] It can often be challenging to determine patient flow paths and respiratory parameters when using a non-sealing patient interface such as a non-sealing nasal cannula to deliver respiratory support, for example, due to leakage. Embodiments of the present invention provide methods of estimating a flow of gases at the patient (e.g. a flow rate of gases at the patient referred to herein as Qm) using a pressure flow correlation.

[0007] The flow of gases at the patient may include the patient's inspiratory and expiratory flow (also referred to herein as patient flow) and / or a portion of the flow of gases provided to the patient from a flow source. The flow rate of gases at the patient may include the patient's inspiratory and expiratory flow rate (also referred to herein as patient flow (rate)) and / or a portion of the flow rate of gases provided to the patient from a flow source.

[0008] In some embodiments of the method, determining the second input may include determining the second input based on a measured pressure at the patient and the pressure flow correlation. In some embodiments, the second input may be a flow rate of gases at the patient corresponding to the measured pressure at the patient as determined by the pressure flow correlation.

[0009] In some embodiments, determining the pressure flow correlation may includereceiving one or more input flow rate values, each input flow rate being a flow rate of gases provided to the patient from a flow source, receiving, for each input flow rate value, a corresponding measured characteristic airway pressure value, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the one or more received input flow rate values and the corresponding one or more measured characteristic airway pressure values.

[0010] In some embodiments, determining the pressure flow correlation may include receiving a plurality of input flow rate values, each input flow rate being a flow rate of gases provided to the patient, receiving, for each input flow rate value, a corresponding measured characteristic airway pressure value, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the plurality of input flow rate values and corresponding measured characteristic airway pressure values.

[0011] In some embodiments, determining the pressure flow correlation may include receiving two input flow rate values, each input flow rate being a flow rate of gases provided to the patient, receiving, for each input flow rate value, a corresponding measured characteristic airway pressure value, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the two input flow rate values and the corresponding two measured characteristic airway pressure values.

[0012] In some embodiments, determining the pressure flow correlation may include receiving a single input flow rate value being a flow rate of gases provided to the patient, receiving, for the input flow rate value, a corresponding measured characteristic airway pressure value,determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the single input flow rate value and the corresponding measured characteristic airway pressure value.

[0013] In some embodiments, the single input flow rate value may be a non-zero single input flow rate value. Determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient may include determining the relationship based on an input flow rate of zero and the corresponding measured characteristic airway pressure value, and the non-zero single input flow rate value and the corresponding measured characteristic airway pressure value.

[0014] In some embodiments, determining the relationship between an airway pressure and a corresponding flow rate of gases at the patient may include determining the relationship based on any one or more of a linear fitted curve of the one or more single input flow rate values and the corresponding measured characteristic airway pressure values, a non-linear fitted curve of the one or more single input flow rate values and the corresponding measured characteristic airway pressure values, and an equation governing the one or more single input flow rate values and the corresponding measured characteristic airway pressure values.

[0015] In some embodiments, determining the pressure flow correlation may include receiving a single input flow rate value being a flow rate of gases provided to the patient, receiving, for the input flow rate value, a corresponding measured characteristic airway pressure value, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on a predetermined pressure flow correlation corresponding to the single input flow rate value and the corresponding measured characteristic airwaypressure value, wherein the predetermined pressure flow correlation is selected from a library of predetermined pressure flow correlations.

[0016] In some embodiments, receiving, for the input flow rate value, a corresponding measured characteristic airway pressure value may include receiving a corresponding measured characteristic airway pressure value when the patient's mouth is closed.

[0017] In some embodiments, the corresponding measured characteristic airway pressure value may be a generally stable measured airway pressure value indicative of an airway pressure value when the patient's flow is zero including any one or more of a plateau pressure value, an airway pressure value during a breath pause, and an airway pressure value during a breath transition between inspiration and expiration.

[0018] In some embodiments, the method may include receiving, for each input flow rate value, a plurality of corresponding measured airway pressure values over one or more breath cycles, and determining the characteristic airway pressure value for each input flow rate value based on a mean pressure value of the plurality of corresponding measured airway pressure values.

[0019] In some embodiments, the input flow rate value may be a flow rate value between 0 to 150 LPM, or 0 to 90 LPM, or 0 to 70LPM, or 0 to 50 LPM, or 0 to 40LPM, or 10 to 90LPM, or 20 to 60LPM, or 20 to 50LPM.

[0020] In some embodiments, the predetermined range of input flow rate values may include a range of input flow rate values between 0 to 150 LPM, or 0 to 90 LPM, or 0 to 70LPM, or 0 to 50 LPM, or 0 to 40LPM, or 10 to 90LPM, or 20 to 60LPM, or 20 to 50LPM.

[0021] In some embodiments, the first input may be indicative of an input flow rate of gases provided to the patient. In some embodiments, the second input may be indicative of a flow rate of gases at the nose of the patient.

[0022] In some embodiments, the input flow rate of gases may be a flow rate value between about 5 to 150 LPM, or 20 to 90 LPM, o 40 to 70 LPM.

[0023] In some embodiments, characterising one or more flow paths of delivered gases within the respiratory airways of the patient may include any one or more of: determining a mouth open condition, determining a mouth closed condition, determining a nasal passage not obstructed condition, determining a nasal passage obstructed condition, determining a numerical value indicative of a proportion of delivered gases passing through the mouth or nose.

[0024] In some embodiments, the method may further include determining one or more respiratory parameters of the patient.

[0025] In some embodiments, the one or more respiratory parameters may include any one or more of: input flow rate of gases provided to the patient exceeding inspiratory demand, input flow rate of gases provided to the patient not meeting inspiratory demand, an expired proportion of CO2, and tidal volume.

[0026] In some embodiments, the step of characterising may include characterising one or more flow paths of delivered gases within the respiratory airways of the patient based on the first input and the second input.

[0027] In some embodiments, the first input may be indicative of an input flow rate of gases provided via a non-sealing patient interface to the patient.

[0028] In some embodiments, the step of characterising one or more flow paths may include determining whether the mouth of the patient is open or closed based on a comparison of the first input and the second input.

[0029] In some embodiments, the step of characterising one or more flow paths may include determining a mouth open condition, if the second input is not greater than the first input at any point over a full respiratory cycle.

[0030] In some embodiments, the method may further include determining a numerical value (k) indicative of a proportion of delivered gases passing through the mouth based onwhereinQj(t) is the first input indicative of an input flow rate of gases provided via a non- sealing patient interface, andQm(t) is the second input indicative of a flow rate of gases at the patient determined based on the pressure flow correlation.

[0031] In some embodiments, the step of characterising one or more flow paths may include determining either one or both of a mouth open condition, and a nasal passage obstructed condition, if the first input substantially equals the second input consistently over a full respiratory cycle.

[0032] In some embodiments, the step of characterising one or more flow paths may further include determining a mouth closed condition if the second input is greater than the first input at any point over a full respiratory cycle.

[0033] In some embodiments, the method may further includereceiving a third input indicative of a measured fraction of CO2 at the nose of the patient, and determining an expired fraction of CO2 (FEco2) based onwhereinQj(t) is the first input indicative of an input flow rate of gases provided via a nonsealing patient interface,Qm(t) is the second input indicative of a flow rate of gases at the patient determined based on the pressure flow correlation, andFm_nose_co2 (t) is the third input indicative of a measured fraction of CO2 at the nose of the patient.

[0034] In some embodiments, the method may include determining any one or more of a mouth closed condition, a nasal passage not obstructed condition, and that the input flow rate of gases exceeds inspiratory demand if the second input exceeds the first input at any point in time during a respiratory cycle and the second input is consistently greater than zero during the respiratory cycle.

[0035] In some embodiments, the method may include determining any one or more of a mouth closed condition, a nasal passage not obstructed condition, and that the input flow rate of gases does not meet inspiratory demand if the second input exceeds the first input at any point in time during a respiratory cycle and the second input drops below zero at any point during the respiratory cycle.

[0036] In some embodiments, the method may include determining any one or more of a mouth closed condition, a nasal passage not obstructed condition, and that the input flow rate of gases does not meet inspiratory demandif the second input exceeds the first input at any point in time during a respiratory cycle and the second input drops below zero at any point during an inspiratory phase of the respiratory cycle.

[0037] In some embodiments, receiving the second input may include determining one or more discrete values indicative of a flow of gases at the nose of the patient at any time during a respiratory cycle, each discrete value being determined based on a measured pressure at the patient and the pressure flow correlation.

[0038] In some embodiments, receiving the first input may include receiving one or more discrete values relating to a flow of gases provided to the patient at any time during a respiratory cycle.

[0039] In some embodiments, the method may further include generating an output based on the characterisation of one or more flow paths of delivered gases within the respiratory airways of the patient.

[0040] In some embodiments, the method may further include displaying the output on a graphical user interface.

[0041] In some embodiments, the step of displaying may further include displaying the output textually, numerically and / or graphically.

[0042] In some embodiments, the method may further include providing a flow of gases to the patient via a non-sealing patient interface.

[0043] In some embodiments, the method may further include sensing the flow of gases provided to the patient to provide the first input.

[0044] In some embodiments, the method may further include sensing a pressure at the nose of the patient to determine the second input.

[0045] In some embodiments, wherein sensing the flow of gases provided to the patient includes sensing a flow rate of the flow of gases provided to the patient.

[0046] In some embodiments, sensing the flow of gases at the patient may include sensing a flow rate of the flow of gases at the patient.

[0047] In some embodiments, the method may further include any one or more of sensing a proportion of CO2 in the flow of gases leaving the patient through the mouth or nose of the patient, and sensing a proportion of O2 in the flow of gases at the mouth or nose of the patient.

[0048] According to another aspect of the invention, there is provided a non-transitory computer readable medium having stored thereon software instructions that when executed by a processor, causes the processor to perform the method of characterising flow paths within a patient's respiratory airways as described herein.

[0049] According to another aspect of the invention, there is provided a respiratory support system controller for characterising flow paths within a patient's respiratory airways, the controller being configured to perform the method of characterising flow paths within a patient's respiratory airways as described herein.

[0050] According to another aspect of the invention, there is provided a respiratory support system comprising a respiratory support system controller for characterising flow paths within a patient's respiratory airways as described herein.

[0051] In some embodiments, the respiratory support system may further include one or more input flow sensors for measuring the flow of gases provided to the patient.

[0052] In some embodiments, the input flow sensors may be configured to measure a flow rate of the flow of gases provided to the patient.

[0053] In some embodiments, the respiratory support system may further include any one or more of a flow source for generating the flow of gases provided to the patient, and a humidifier for humidifying the flow of gases provided to the patient.

[0054] According to yet another aspect of the invention, there is provided a computer method of characterising flow paths within respiratory airways, the method comprisingdetermining a pressure flow correlation between an airway pressure and a corresponding flow rate of gases at the patient, receiving a first input relating to a flow of gases provided to a non-sealing gas delivery patient interface, receiving, from one or more sensor units, a measured pressure at the non-sealing gas delivery patient interface, and determining a second input relating to a flow of gases at or proximate the non-sealing gas delivery patient interface based on the measured pressure and the pressure flow correlation, characterising, via a processor, one or more flow paths of delivered gases within the respiratory airways based on the first input and / or the second input.

[0055] In some embodiments, receiving the measured pressure may include receiving the measured pressure proximate and outside the non-sealing gas delivery patient interface. Determining the second input may include determining the second input proximate and outside the non-sealing gas delivery patient interface.

[0056] In some embodiments, the first input may be indicative of an input flow rate of gases provided to the non-sealing gas delivery patient interface. The second input may be indicative of a flow rate of gases at or proximate the non-sealing gas delivery patient interface.

[0057] In some embodiments, characterising one or more flow paths of delivered gases within the respiratory airways may include any one or more of: determining a mouth open condition, determining a mouth closed condition, determining a nasal passage not obstructed condition, determining a nasal passage obstructed condition, determining a numerical value indicative of a proportion of delivered gases passing through the mouth or nose.

[0058] In some embodiments, the method may further including determining one or more respiratory parameters.

[0059] In some embodiments, the one or more respiratory parameters may include any one or more of: input flow rate of gases exceeding inspiratory demand, input flow rate of gases not meeting inspiratory demand, an expired proportion of CO2, and tidal volume.

[0060] According to a further aspect of the invention, there is provided a respiratory support system for characterising flow paths within a patient's respiratory airways, the system comprising a flow source for providing an input flow of gases to the patient, and a controller being configured to determine a pressure flow correlation between an airway pressure and a corresponding flow rate of gases at the patient, receive a first input relating to the input flow of gases provided to the patient from the flow source, determine a second input relating to a flow of gases at the patient based on the pressure flow correlation, and characterise one or more flow paths of delivered gases within the respiratory airways of the patient based on the first input and the second input.

[0061] In some embodiments, the respiratory support system may further include a pressure sensor for measuring an airway pressure in a nasal passage of the patient. The controller may be configured to determine the second input based on a measured patient airway pressure received from the pressure sensor and the pressure flow correlation. The second input may be a flow rate of gases at the patient corresponding to the measured pressure at the patient as determined by the pressure flow correlation.

[0062] In some embodiments, the controller may be configured to determine the pressure flow correlation byreceiving one or more input flow rate values, each input flow rate being a flow rate of gases provided to the patient from the flow source, receiving, for each input flow rate value, a corresponding measured characteristic airway pressure value from the pressure sensor, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the one or more received input flow rate values and the corresponding one or more measured characteristic airway pressure values.

[0063] In some embodiments, the controller may be configured to determine the pressure flow correlation by receiving a plurality of input flow rate values, each input flow rate being a flow rate of gases provided to the patient from the flow source, receiving, for each input flow rate value, a corresponding measured characteristic airway pressure value from the pressure sensor, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the plurality of input flow rate values and corresponding measured characteristic airway pressure values.

[0064] In some embodiments, the controller may be configured to determine the pressure flow correlation by receiving two input flow rate values, each input flow rate being a flow rate of gases provided to the patient from the flow source, receiving, for each input flow rate value, a corresponding measured characteristic airway pressure value from the pressure sensor, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the two input flow rate values and the corresponding two measured characteristic airway pressure values.

[0065] In some embodiments, the controller may be configured to determine the pressure flow correlation by receiving a single input flow rate value being a flow rate of gases provided to the patient from the flow source,receiving, for the input flow rate value, a corresponding measured characteristic airway pressure value from the pressure sensor, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the single input flow rate value and the corresponding measured characteristic airway pressure value.

[0066] In some embodiments, the single input flow rate value may be a non-zero single input flow rate value. The controller may be configured to determine the relationship based on an input flow rate of zero and the corresponding measured characteristic airway pressure value from the pressure sensor, and the non-zero single input flow rate value and the corresponding measured characteristic airway pressure value from the pressure sensor.

[0067] In some embodiments, the controller may be configured to determine the relationship between an airway pressure and a corresponding flow rate of gases at the patient based on any one or more of a linear fitted curve of the one or more single input flow rate values and the corresponding measured characteristic airway pressure values, a non-linear fitted curve of the one or more single input flow rate values and the corresponding measured characteristic airway pressure values, and an equation governing the one or more single input flow rate values and the corresponding measured characteristic airway pressure values.

[0068] In some embodiments, the controller may be configured to determine the pressure flow correlation by receiving a single input flow rate value being a flow rate of gases provided to the patient from the flow source, receiving, for the input flow rate value, a corresponding measured characteristic airway pressure value from the pressure sensor, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on a predetermined pressure flow correlation corresponding tothe single input flow rate value and the corresponding measured characteristic airway pressure value, wherein the predetermined pressure flow correlation is selected from a library of predetermined pressure flow correlations.

[0069] In some embodiments, the controller may be configured to determine the corresponding measured characteristic airway pressure value based on a generally stable measured airway pressure value from the pressure sensor as indicative of an airway pressure value when the patient's flow is zero including any one or more of a plateau pressure value, an airway pressure value during a breath pause, and an airway pressure value during a breath transition between inspiration and expiration.

[0070] In some embodiments, the controller may be configured to receive, for each input flow rate value, a plurality of corresponding measured airway pressure values from the pressure sensor over one or more breath cycles, and determine the characteristic airway pressure value for each input flow rate value based on a mean pressure value of the plurality of corresponding measured airway pressure values.

[0071] In some embodiments, the input flow rate value may be a flow rate value between 0 to 150 LPM, or 0 to 90 LPM, or 0 to 70LPM, or 0 to 50 LPM, or 0 to 40LPM, or 10 to 90LPM, or 20 to 60LPM, or 20 to 50LPM.

[0072] In some embodiments, the predetermined range of input flow rate values may include a range of input flow rate values between 0 to 150 LPM, or 0 to 90 LPM, or 0 to 70LPM, or 0 to 50 LPM, or 0 to 40LPM, or 10 to 90LPM, or 20 to 60LPM, or 20 to 50LPM.

[0073] In some embodiments, wherein the first input may be indicative of an input flow rate of gases provided to the patient from the flow source. The second input may be indicative of a flow rate of gases at the nose of the patient.

[0074] In some embodiments, the input flow rate of gases may be a flow rate value between about 5 to 150 LPM, or 20 to 90 LPM, or 40 to 70 LPM.

[0075] In some embodiments, the controller may be configured to characterise one or more flow paths of delivered gases within the respiratory airways of the patient by determining any one or more of: a mouth open condition, a mouth closed condition, a nasal passage not obstructed condition, a nasal passage obstructed condition, a numerical value indicative of a proportion of delivered gases passing through the mouth or nose.

[0076] In some embodiments, the controller may be further configured to determine one or more respiratory parameters of the patient.

[0077] The one or more respiratory parameters may include any one or more of: input flow rate of gases provided to the patient exceeding inspiratory demand, input flow rate of gases provided to the patient not meeting inspiratory demand, an expired proportion of CO2, and tidal volume.

[0078] In some embodiments, the respiratory support system may further include a nonsealing patient interface for providing the input flow of gases to the patient. The first input may be indicative of an input flow rate of gases provided via the non-sealing patient interface.

[0079] In some embodiments, the controller may be configured to determine whether the mouth of the patient is open or closed based on a comparison of the first input and the second input.

[0080] In some embodiments, the controller may be configured to determining a mouth open condition if the second input is not greater than the first input at any point over a full respiratory cycle.

[0081] In some embodiments, the controller may be further configured to determine a numerical value (k) indicative of a proportion of delivered gases passing through the mouth based onwhereinQj(t) is the first input indicative of an input flow rate of gases provided via a nonsealing patient interface, andQm(t) is the second input indicative of a flow rate of gases at the patient determined based on the pressure flow correlation.

[0082] In some embodiments, the controller may be configured to characterise one or more flow paths by determining either one or both of a mouth open condition, and a nasal passage obstructed condition if the first input substantially equals the second input consistently over a full respiratory cycle.

[0083] In some embodiments, the controller may be configured to characterise one or more flow paths by further determining a mouth closed condition if the second input is greater than the first input at any point over a full respiratory cycle.

[0084] In some embodiments, the respiratory support system may further include a gas fraction sensor, and wherein the controller is further configured to receive a third input indicative of a measured fraction of CO2 at the nose of the patient from the gas fraction sensor, and determining an expired fraction of CO2 (FEco2) based onwhereinQj(t) is the first input indicative of an input flow rate of gases provided via a nonsealing patient interface,Qm(t) is the second input indicative of a flow rate of gases at the patient determined based on the pressure flow correlation, andFm_nose_co2 (t) is the third input indicative of a measured fraction of CO2 at the nose of the patient from the gas fraction sensor.

[0085] In some embodiments, the controller may be configured to determine any one or more of a mouth closed condition, a nasal passage not obstructed condition, and that the input flow rate of gases exceeds inspiratory demand if the second input exceeds the first input at any point in time during a respiratory cycle and the second input is consistently greater than zero during the respiratory cycle.

[0086] In some embodiments, the controller may be configured to determine any one or more of a mouth closed condition, a nasal passage not obstructed condition, and that the input flow rate of gases does not meet inspiratory demand if the second input exceeds the first input at any point in time during a respiratory cycle and the second input drops below zero at any point during the respiratory cycle.

[0087] In some embodiments, the controller may be configured to determine any one or more of a mouth closed condition, a nasal passage not obstructed condition, and that the input flow rate of gases does not meet inspiratory demand if the second input exceeds the first input at any point in time during a respiratory cycle and the second input drops below zero at any point during an inspiratory phase of the respiratory cycle.

[0088] In some embodiments, the controller may be configured to determine the second input by determining one or more discrete values indicative of a flow of gases at the nose of the patient at any time during a respiratory cycle. Each discrete value may be determined based on a measured pressure at the patient and the pressure flow correlation.

[0089] In some embodiments, the controller may be configured to receive the first input by receiving one or more discrete values relating to a flow of gases provided to the patient at any time during a respiratory cycle.

[0090] In some embodiments, the respiratory support system may further include a graphical user interface. The controller may be configured to generate an output based on the characterisation of one or more flow paths of delivered gases within the respiratory airways of the patient for display on the graphical user interface.

[0091] In some embodiments, the output may include textual, numerical and / or graphical output.

[0092] In some embodiments, the respiratory support system may further include one or more input flow sensors for measuring the flow of gases provided to the patient including either one or both of the first input, and the input flow rate values, wherein each input flow rate is a flow rate of gases provided to the patient from the flow source.

[0093] In some embodiments, the input flow sensors may be configured to measure a flow rate of the flow of gases provided to the patient.

[0094] In some embodiments, the respiratory support system may include a single input flow sensor for measuring the flow of gases provided to the patient including the first input and the input flow rate values.

[0095] In some embodiments, the respiratory support system may further include a humidifier for humidifying the flow of gases provided to the patient.

[0096] According to another aspect of the invention, there is provided a method of characterising flow paths within a patient's respiratory airways, the method comprising determining a pressure flow correlation between a patient pressure and a corresponding flow rate of gases at the patient, receiving a first input relating to a flow of gases provided to the patient, determining a second input relating to a flow of gases at the patient based on the pressure flow correlation, and characterising one or more flow paths of delivered gases within the respiratory airways of the patient based on the first input and the second input.

[0097] Patient pressure as referred to herein may include a pressure value associated with the patient. For example, patient pressure may include airway pressure as described herein.

[0098] In some embodiments, determining the pressure flow correlation may include receiving one or more input flow rate values, each input flow rate being a flow rate of gases provided to the patient from a flow source, receiving, for each input flow rate value, a corresponding measured characteristic patient pressure value, determining a relationship between a patient pressure and a corresponding flow rate of gases at the patient based on the one or more received input flow rate values and the corresponding one or more measured characteristic patient pressure values.

[0099] In some embodiments, determining the pressure flow correlation may include receiving a plurality of input flow rate values, each input flow rate being a flow rate of gases provided to the patient, receiving, for each input flow rate value, a corresponding measured characteristic patient pressure value, determining a relationship between a patient pressure and a corresponding flow rate of gases at the patient based on the plurality of input flow rate values and corresponding measured characteristic patient pressure values.

[0100] In some embodiments, determining the pressure flow correlation may includereceiving two input flow rate values, each input flow rate being a flow rate of gases provided to the patient, receiving, for each input flow rate value, a corresponding measured characteristic patient pressure value, determining a relationship between a patient pressure and a corresponding flow rate of gases at the patient based on the two input flow rate values and the corresponding two measured characteristic patient pressure values.

[0101] In some embodiments, determining the pressure flow correlation may include receiving a single input flow rate value being a flow rate of gases provided to the patient, receiving, for the input flow rate value, a corresponding measured characteristic patient pressure value, determining a relationship between a patient pressure and a corresponding flow rate of gases at the patient based on the single input flow rate value and the corresponding measured characteristic patient pressure value.

[0102] In some embodiments, the single input flow rate value may be a non-zero single input flow rate value. In some embodiments, determining a relationship between a patient pressure and a corresponding flow rate of gases at the patient may include determining the relationship based on an input flow rate of zero and the corresponding measured characteristic patient pressure value, and the non-zero single input flow rate value and the corresponding measured characteristic patient pressure value.

[0103] In some embodiments, determining the pressure flow correlation may include receiving a single input flow rate value being a flow rate of gases provided to the patient, receiving, for the input flow rate value, a corresponding measured characteristic patient pressure value, determining a relationship between a patient pressure and a corresponding flow rate of gases at the patient based on a predetermined pressure flow correlationcorresponding to the single input flow rate value and the corresponding measured characteristic patient pressure value, wherein the predetermined pressure flow correlation is selected from a library of predetermined pressure flow correlations.

[0104] In some embodiments, the patient pressure may be an airway pressure of the patient.

[0105] In some embodiments, the characteristic patient pressure value may be a characteristic airway pressure value of the patient.

[0106] According to other aspects of the invention, there is provided a non-transitory computer readable medium having stored thereon software instructions that when executed by a processor, causes the processor to perform a method as described herein.

[0107] According to other aspects of the invention, there is provided a respiratory support system controller for characterising flow paths within a patient's respiratory airways, the controller being configured to perform a method as described herein.

[0108] According to other aspects of the invention, there is provided a respiratory support system comprising a controller as described herein.

[0109] In some embodiments, the respiratory support system may further include one or more input flow sensors for measuring the flow of gases provided to the patient.

[0110] In some embodiments, the input flow sensors may be configured to measure a flow rate of the flow of gases provided to the patient including either one or both of the first input, and the input flow rate values, wherein each input flow rate is a flow rate of gases provided to the patient from the flow source.

[0111] In some embodiments, the respiratory support system may further include any one or more of a flow source for generating the flow of gases provided to the patient, and a humidifier for humidifying the flow of gases provided to the patient.

[0112] According to one aspect, there is provided a respiratory support system for characterising flow paths within a patient's respiratory airways, the system comprising a flow source for providing an input flow of gases to the patient, anda controller being configured to determine a pressure flow correlation between an airway pressure and a corresponding flow rate of gases at the patient, receive a first input relating to the input flow of gases provided to the patient from the flow source, determine a second input relating to a flow of gases at the patient based on the pressure flow correlation, and characterise one or more flow paths of delivered gases within the respiratory airways of the patient based on the first input and the second input.

[0113] Optionally, the respiratory support system may further include a pressure sensor for providing a measured pressure (also referred to as a sensed pressure). The measured pressure may be usable to determine a calculated airway pressure. The calculated airway pressure may be representative of the airway pressure in a nasal passage of the patient. The controller may be configured to determine the second input based on the calculated airway pressure and the pressure flow correlation. The second input may be a flow rate of gases at the patient corresponding to the calculated airway pressure as determined by the pressure flow correlation.

[0114] As described herein, the controller may derive the calculated airway pressure in any suitable manner. For example, the controller may derive the calculated airway pressure directly from a measured pressure in, at or proximate the patient's nose. In some embodiments, the controller may derive the calculated airway pressure from a system pressure value measured at any suitable location in a system flow path of the respiratory support system, and a pressure difference downstream of the pressure sensor location in the system flow path.

[0115] Optionally, the measured pressure is a measurement of the airway pressure of the nasal passage of the patient. The controller may be operatively configured to determine the calculated airway pressure based on the measured pressure.

[0116] Optionally, the pressure sensor may include a sensing element configured for placement in, at or proximate the nasal passage of the patient.

[0117] Optionally, the pressure sensor may include a sensing element operatively coupled in fluid communication with a sampling conduit. The sampling conduit may have a distal end being adapted for placement in, at or proximate the nasal passage of the patient.

[0118] Optionally, the respiratory support system may further include a patient interface for providing the input flow of gases to the patient. At least a portion of the pressure sensor may be coupled to, or integral with the patient interface.

[0119] Optionally, the respiratory support system may further include a patient interface for providing the input flow of gases to the patient. A portion of the sampling conduit may be coupled to, or integral with the patient interface.

[0120] Optionally, the respiratory support system may further include a patient interface for providing the input flow of gases to the patient. The respiratory support system may define a system flow path extending from the flow source to the patient interface, the system flow path being a flow path of the input flow of gases from the flow source to one or more outlets of the patient interface.

[0121] Optionally, the pressure sensor is configured to detect the measured pressure at a location external to the system flow path.

[0122] Optionally, the pressure sensor is configured to detect a system pressure. The system pressure may be measured at any location within system flow path.

[0123] Optionally, the system pressure is measured in, at or proximate a location being any one of the flow source, a humidifier for humidifying the flow of gases provided to the patient, the patient interface, any location within a conduit of the respiratory system coupled to any one or more of the flow source, humidifier, or patient interface, for delivering the input flow of gases from the flow source to the patient interface.

[0124] Optionally, the calculated airway pressure is determined based on the system pressure, anda pressure difference indicative of flow resistance across a portion of the system flow path between the location of the measured pressure and the one or more outlets of the patient interface.

[0125] Optionally, the calculated airway pressure is determined by subtracting the pressure difference from the system pressure.

[0126] Optionally, the controller may be configured to determine the pressure flow correlation by receiving one or more input flow rate values, each input flow rate being a flow rate of gases provided to the patient from the flow source, receiving, for each input flow rate value, a corresponding characteristic airway pressure value determined based on the measured pressure from the pressure sensor, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the one or more received input flow rate values and the corresponding one or more characteristic airway pressure values.

[0127] Optionally, the controller may be configured to determine the pressure flow correlation by receiving a plurality of input flow rate values, each input flow rate being a flow rate of gases provided to the patient from the flow source, receiving, for each input flow rate value, a corresponding characteristic airway pressure value determined based on the measured pressure from the pressure sensor, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the plurality of input flow rate values and corresponding characteristic airway pressure values.

[0128] Optionally, the controller may be configured to determine the pressure flow correlation by receiving two input flow rate values, each input flow rate being a flow rate of gases provided to the patient from the flow source, receiving, for each input flow rate value, a corresponding characteristic airway pressure value determined based on the measured pressure from the pressure sensor,determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the two input flow rate values and the corresponding two characteristic airway pressure values.

[0129] Optionally, the controller may be configured to determine the pressure flow correlation by receiving a single input flow rate value being a flow rate of gases provided to the patient from the flow source, receiving, for the input flow rate value, a corresponding characteristic airway pressure value determined based on the measured pressure from the pressure sensor, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the single input flow rate value and the corresponding characteristic airway pressure value.

[0130] Optionally, the single input flow rate value is a non-zero single input flow rate value. The controller may be configured to determine the relationship based on an input flow rate of zero and the corresponding characteristic airway pressure value, and the non-zero single input flow rate value and the corresponding characteristic airway pressure value.

[0131] Optionally, the controller is configured to determine the relationship between an airway pressure and a corresponding flow rate of gases at the patient based on any one or more of a linear fitted curve of the one or more single input flow rate values and the corresponding characteristic airway pressure values, a non-linear fitted curve of the one or more single input flow rate values and the corresponding characteristic airway pressure values, and an equation governing the one or more single input flow rate values and the corresponding characteristic airway pressure values.

[0132] Optionally, the controller is configured to determine the pressure flow correlation by receiving a single input flow rate value being a flow rate of gases provided to the patient from the flow source, receiving, for the input flow rate value, a corresponding characteristic airway pressure value determined based on the measured pressure from the pressure sensor, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on a predetermined pressure flow correlation corresponding to the single input flow rate value and the corresponding characteristic airway pressure value, wherein the predetermined pressure flow correlation is selected from a library of predetermined pressure flow correlations.

[0133] Optionally, the controller is configured to determine the corresponding characteristic airway pressure value based on a generally stable measured pressure value from the pressure sensor (e.g.as indicative of an airway pressure value when the patient's flow is generally zero), the generally stable measured pressure value is optionally including any one or more of, or an average of, a plateau pressure value, a calculated airway pressure value during a breath pause, and a calculated airway pressure value during a breath transition between inspiration and expiration.

[0134] Optionally, the controller is configured to determine the characteristic airway pressure value based on the generally stable measured pressure value, and a pressure difference indicative of flow resistance across a portion of system flow path between a location corresponding to the measured pressure and the one or more outlets of the patient interface.

[0135] Optionally, the characteristic airway pressure value is determined by subtracting the pressure difference from the generally stable measured pressure value.

[0136] Optionally, the controller is configured to receive, for each input flow rate value, a plurality of corresponding measured pressure values from the pressure sensor over one or more breath cycles, anddetermine the characteristic airway pressure value for each input flow rate value based on a mean pressure value of the plurality of corresponding measured pressure values.

[0137] Optionally, the controller is configured to receive, for each input flow rate value, a plurality of corresponding measured pressure values from the pressure sensor over one or more breath cycles, determine a plurality of calculated airway pressure values, each calculated airway pressure value being based on a respective measured pressure value and an associated pressure difference, and determine the characteristic airway pressure value for each input flow rate value based on a mean pressure value of the plurality of calculated airway pressure values.

[0138] Optionally, the input flow rate value is a flow rate value between 0 to 150 LPM, or 0 to 90 LPM, or 0 to 70LPM, or 0 to 50 LPM, or 0 to 40LPM, or 10 to 90LPM, or 20 to 60LPM, or 20 to 50LPM.

[0139] Optionally, the plurality of input flow rate values is selected from a predetermined range of input flow rate values including a range of input flow rate values between 0 to 150 LPM, or 0 to 90 LPM, or 0 to 70LPM, or 0 to 50 LPM, or 0 to 40LPM, or 10 to 90LPM, or 20 to 60LPM, or 20 to 50LPM.

[0140] Optionally, the first input is indicative of an input flow rate of gases provided to the patient from the flow source. The second input may be indicative of a flow rate of gases at the nose of the patient.

[0141] Optionally, the input flow rate of gases has a flow rate value between about 5 to 150 LPM, or 20 to 90 LPM, or 40 to 70 LPM.

[0142] Optionally, the controller is configured to characterise one or more flow paths of delivered gases within the respiratory airways of the patient by determining any one or more of: a mouth open condition, a mouth closed condition,a nasal passage not obstructed condition, a nasal passage obstructed condition, a numerical value indicative of a proportion of delivered gases passing through the mouth or nose.

[0143] Optionally, the controller is further configured to determine one or more respiratory parameters of the patient.

[0144] Optionally, the one or more respiratory parameters includes any one or more of: input flow rate of gases provided to the patient exceeding inspiratory demand, input flow rate of gases provided to the patient not meeting inspiratory demand, an expired proportion of CO2, and tidal volume.

[0145] Optionally, the respiratory support system further includes a non-sealing patient interface for providing the input flow of gases to the patient, wherein the first input is indicative of an input flow rate of gases provided via the non-sealing patient interface.

[0146] Optionally, the controller is configured to determine whether the mouth of the patient is open or closed based on a comparison of the first input and the second input.

[0147] Optionally, the controller is configured to determine a mouth open condition if the second input is not greater than the first input at any point over a full respiratory cycle.

[0148] Optionally, the controller is further configured to determine a numerical value (k) indicative of a proportion of delivered gases passing through the mouth based onwhereinQj(t) is the first input indicative of an input flow rate of gases provided via a non- sealing patient interface, andQm(t) is the second input indicative of a flow rate of gases at the patient determined based on the pressure flow correlation.

[0149] Optionally, the controller is configured to characterise one or more flow paths by determining either one or both of a mouth open condition, and a nasal passage obstructed condition if the first input substantially equals the second input consistently over a full respiratory cycle.

[0150] Optionally, the controller is configured to characterise one or more flow paths by further determining a mouth closed condition if the second input is greater than the first input at any point over a full respiratory cycle.

[0151] Optionally, the respiratory support system further includes a gas fraction sensor.The controller may be further configured to receive a third input indicative of a measured fraction of CO2 at the nose of the patient from the gas fraction sensor, and determining an expired fraction of CO2 (FEco2) based onwhereinQi(t) is the first input indicative of an input flow rate of gases provided via a nonsealing patient interface,Qm(t) is the second input indicative of a flow rate of gases at the patient determined based on the pressure flow correlation, andFm_nose_co2 (t) is the third input indicative of a measured fraction of CO2 at the nose of the patient from the gas fraction sensor.

[0152] Optionally, the controller is configured to determine any one or more ofa mouth closed condition, a nasal passage not obstructed condition, and that the input flow rate of gases exceeds inspiratory demand if the second input exceeds the first input at any point in time during a respiratory cycle and the second input is consistently greater than zero during the respiratory cycle.

[0153] Optionally, the controller is configured to determine any one or more of a mouth closed condition, a nasal passage not obstructed condition, and that the input flow rate of gases does not meet inspiratory demand if the second input exceeds the first input at any point in time during a respiratory cycle and the second input drops below zero at any point during the respiratory cycle.

[0154] Optionally, the controller is configured to determine any one or more of a mouth closed condition, a nasal passage not obstructed condition, and that the input flow rate of gases does not meet inspiratory demand if the second input exceeds the first input at any point in time during a respiratory cycle and the second input drops below zero at any point during an inspiratory phase of the respiratory cycle.

[0155] Optionally, the controller is configured to determine the second input by determining one or more discrete values indicative of a flow of gases at the nose of the patient at any time during a respiratory cycle, each discrete value being determined based on the measured pressure and the pressure flow correlation.

[0156] Optionally, the controller is configured to receive the first input by receiving one or more discrete values relating to a flow of gases provided to the patient at any time during a respiratory cycle.

[0157] Optionally, the respiratory support system further includes a graphical user interface. The controller may be configured to generate an output based on thecharacterisation of one or more flow paths of delivered gases within the respiratory airways of the patient for display on the graphical user interface.

[0158] Optionally, the output may include textual, numerical and / or graphical output.

[0159] Optionally, the respiratory support system further includes one or more input flow sensors for measuring the flow of gases provided to the patient including either one or both of the first input, and the input flow rate values, wherein each input flow rate is a flow rate of gases provided to the patient from the flow source.

[0160] Optionally, the input flow sensors are configured to measure a flow rate of the flow of gases provided to the patient.

[0161] Optionally, the respiratory support system includes a single input flow sensor for measuring the flow of gases provided to the patient including the first input and the input flow rate values.

[0162] Optionally, the respiratory support system further includes a humidifier for humidifying the flow of gases provided to the patient.

[0163] According to another aspect, there is provided a method of characterising flow paths within a patient's respiratory airways, the method comprising determining a pressure flow correlation between an airway pressure and a corresponding flow rate of gases at the patient, receiving a first input relating to an input flow of gases provided to a patient from a flow source, determining a second input relating to a flow of gases at the patient based on the pressure flow correlation, and characterising one or more flow paths of delivered gases within the respiratory airways of the patient based on the first input and the second input.

[0164] Optionally, the method may further includereceiving, via a pressure sensor, a measured pressure, the measured pressure being usable to determine a calculated airway pressure, the calculated airway pressure being representative of the airway pressure in a nasal passage of the patient, and determining the second input based on the calculated airway pressure and the pressure flow correlation, the second input being a flow rate of gases at the patient corresponding to the calculated airway pressure as determined by the pressure flow correlation.

[0165] Optionally, the measured pressure is a measurement of the airway pressure of the nasal passage of the patient, and wherein the method includes determining the calculated airway pressure based on the measured pressure.

[0166] Optionally, the pressure sensor includes a sensing element configured for placement in, at or proximate the nasal passage of the patient.

[0167] Optionally, the pressure sensor includes a sensing element operatively coupled in fluid communication with a sampling conduit, the sampling conduit having a distal end being adapted for placement in, at or proximate the nasal passage of the patient.

[0168] Optionally, the method further includes providing, via a patient interface, the input flow of gases to the patient, wherein at least a portion of the pressure sensor is coupled to, or integral with the patient interface.

[0169] Optionally, the method further includes providing, via a patient interface, the input flow of gases to the patient, wherein a portion of the sampling conduit is coupled to, or integral with the patient interface.

[0170] Optionally, the method further includes providing, via a patient interface, the input flow of gases to the patient, and providing a system flow path extending from the flow source to the patient interface, the system flow path being a flow path of the input flow of gases from the flow source to one or more outlets of the patient interface.

[0171] Optionally, the method includes detecting, via the pressure sensor, the measured pressure at a location external to the system flow path.

[0172] Optionally, the method includes detecting, via the pressure sensor, a system pressure, the system pressure being measured at any location within system flow path.

[0173] Optionally, the method includes measuring the system pressure in, at or proximate a location being any one of the flow source, a humidifier for humidifying the flow of gases provided to the patient, the patient interface, any location within a conduit of the respiratory system coupled to any one or more of the flow source, humidifier, or patient interface, for delivering the input flow of gases from the flow source to the patient interface.

[0174] Optionally, the method includes determining the calculated airway pressure based on the system pressure, and a pressure difference indicative of flow resistance across a portion of the system flow path between the location of the measured pressure and the one or more outlets of the patient interface.

[0175] Optionally, the method may include determining the calculated airway pressure by subtracting the pressure difference from the system pressure.

[0176] Optionally, the method may include determining the pressure flow correlation by receiving one or more input flow rate values, each input flow rate being a flow rate of gases provided to the patient from the flow source, receiving, for each input flow rate value, a corresponding characteristic airway pressure value determined based on the measured pressure from the pressure sensor, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the one or more received input flow rate values and the corresponding one or more characteristic airway pressure values.

[0177] Optionally, the method may include determining the pressure flow correlation by receiving a plurality of input flow rate values, each input flow rate being a flow rate of gases provided to the patient from the flow source,receiving, for each input flow rate value, a corresponding characteristic airway pressure value determined based on the measured pressure from the pressure sensor, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the plurality of input flow rate values and corresponding characteristic airway pressure values.

[0178] Optionally, the method may include determining the pressure flow correlation by receiving two input flow rate values, each input flow rate being a flow rate of gases provided to the patient from the flow source, receiving, for each input flow rate value, a corresponding characteristic airway pressure value determined based on the measured pressure from the pressure sensor, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the two input flow rate values and the corresponding two characteristic airway pressure values.

[0179] Optionally, the method may include determining the pressure flow correlation by receiving a single input flow rate value being a flow rate of gases provided to the patient from the flow source, receiving, for the input flow rate value, a corresponding characteristic airway pressure value determined based on the measured pressure from the pressure sensor, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the single input flow rate value and the corresponding characteristic airway pressure value.

[0180] Optionally, the single input flow rate value is a non-zero single input flow rate value. The method may include determining the relationship based on an input flow rate of zero and the corresponding characteristic airway pressure value, and the non-zero single input flow rate value and the corresponding characteristic airway pressure value.

[0181] Optionally, the method may include determining the relationship between an airway pressure and a corresponding flow rate of gases at the patient based on any one or more ofa linear fitted curve of the one or more single input flow rate values and the corresponding characteristic airway pressure values, a non-linear fitted curve of the one or more single input flow rate values and the corresponding characteristic airway pressure values, and an equation governing the one or more single input flow rate values and the corresponding characteristic airway pressure values.

[0182] Optionally, the method may include determining the pressure flow correlation by receiving a single input flow rate value being a flow rate of gases provided to the patient from the flow source, receiving, for the input flow rate value, a corresponding characteristic airway pressure value determined based on the measured pressure from the pressure sensor, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on a predetermined pressure flow correlation corresponding to the single input flow rate value and the corresponding characteristic airway pressure value, wherein the predetermined pressure flow correlation is selected from a library of predetermined pressure flow correlations.

[0183] Optionally, the method may include determining the corresponding characteristic airway pressure value based on a generally stable measured pressure value from the pressure sensor (e.g.as indicative of an airway pressure value when the patient's flow is generally zero), the generally stable measured pressure value is optionally including any one or more of, or an average of, a plateau pressure value, a calculated airway pressure value during a breath pause, and a calculated airway pressure value during a breath transition between inspiration and expiration.

[0184] Optionally, the method may include determining the characteristic airway pressure value based on the generally stable measured pressure value, and a pressure difference indicative of flow resistance across a portion of system flow path between a location corresponding to the measured pressure and the one or more outlets of the patient interface.

[0185] Optionally, the method may include determining the characteristic airway pressure by subtracting the pressure difference from the generally stable measured pressure value.

[0186] Optionally, the method may include receiving, for each input flow rate value, a plurality of corresponding measured pressure values from the pressure sensor over one or more breath cycles, and determining the characteristic airway pressure value for each input flow rate value based on a mean pressure value of the plurality of corresponding measured pressure values.

[0187] Optionally, the method may include receiving, for each input flow rate value, a plurality of corresponding measured pressure values from the pressure sensor over one or more breath cycles, determining a plurality of calculated airway pressure values, each calculated airway pressure value being based on a respective measured pressure value and an associated pressure difference, and determining the characteristic airway pressure value for each input flow rate value based on a mean pressure value of the plurality of calculated airway pressure values.

[0188] Optionally, the method may include providing the input flow rate value at a flow rate value of between 0 to 150 LPM, or 0 to 90 LPM, or 0 to 70LPM, or 0 to 50 LPM, or 0 to 40LPM, or 10 to 90LPM, or 20 to 60LPM, or 20 to 50LPM.

[0189] Optionally, the method may include selecting the plurality of input flow rate values from a predetermined range of input flow rate values including a range of input flow rate values between 0 to 150 LPM, or 0 to 90 LPM, or 0 to 70LPM, or 0 to 50 LPM, or 0 to 40LPM, or 10 to 90LPM, or 20 to 60LPM, or 20 to 50LPM.

[0190] Optionally, the first input is indicative of an input flow rate of gases provided to the patient from the flow source. The second input may be indicative of a flow rate of gases at the nose of the patient.

[0191] Optionally, the method may include providing the input flow rate of gases at a flow rate value of between about 5 to 150 LPM, or 20 to 90 LPM, or 40 to 70 LPM.

[0192] Optionally, the method may include characterising one or more flow paths of delivered gases within the respiratory airways of the patient by determining any one or more of: a mouth open condition, a mouth closed condition, a nasal passage not obstructed condition, a nasal passage obstructed condition, a numerical value indicative of a proportion of delivered gases passing through the mouth or nose.

[0193] Optionally, the method may further include determining one or more respiratory parameters of the patient.

[0194] Optionally, determining the one or more respiratory parameters includes determining any one or more of: input flow rate of gases provided to the patient exceeding inspiratory demand, input flow rate of gases provided to the patient not meeting inspiratory demand, an expired proportion of CO2, and tidal volume.

[0195] Optionally, the method may further include providing, via a non-sealing patient interface, the input flow of gases to the patient. The first input may be indicative of an input flow rate of gases provided via the non-sealing patient interface.

[0196] Optionally, the method includes determining whether the mouth of the patient is open or closed based on a comparison of the first input and the second input.

[0197] Optionally, the method includes determining a mouth open condition if the second input is not greater than the first input at any point over a full respiratory cycle.

[0198] Optionally, the method includes determining a numerical value (k) indicative of a proportion of delivered gases passing through the mouth based onwhereinQj(t) is the first input indicative of an input flow rate of gases provided via a nonsealing patient interface, andQm(t) is the second input indicative of a flow rate of gases at the patient determined based on the pressure flow correlation.

[0199] Optionally, the method includes characterising one or more flow paths by determining either one or both of a mouth open condition, and a nasal passage obstructed condition if the first input substantially equals the second input consistently over a full respiratory cycle.

[0200] Optionally, the method includes characterising one or more flow paths by further determining a mouth closed condition if the second input is greater than the first input at any point over a full respiratory cycle.

[0201] Optionally, the method further includes receiving a third input indicative of a measured fraction of CO2 at the nose of the patient from a gas fraction sensor, and determining an expired fraction of CO2 (FE Co2) based onwhereinQi(t) is the first input indicative of an input flow rate of gases provided via a nonsealing patient interface,Qm(t) is the second input indicative of a flow rate of gases at the patient determined based on the pressure flow correlation, andFm_nose_CO2 (t) is the third input indicative of a measured fraction of CO2 at the nose of the patient from the gas fraction sensor.

[0202] Optionally, the method includes determining any one or more of a mouth closed condition, a nasal passage not obstructed condition, and that the input flow rate of gases exceeds inspiratory demand if the second input exceeds the first input at any point in time during a respiratory cycle and the second input is consistently greater than zero during the respiratory cycle.

[0203] Optionally, the method may include determining any one or more of a mouth closed condition, a nasal passage not obstructed condition, and that the input flow rate of gases does not meet inspiratory demand if the second input exceeds the first input at any point in time during a respiratory cycle and the second input drops below zero at any point during the respiratory cycle.

[0204] Optionally, the method includes determining any one or more of a mouth closed condition, a nasal passage not obstructed condition, and that the input flow rate of gases does not meet inspiratory demand if the second input exceeds the first input at any point in time during a respiratory cycle and the second input drops below zero at any point during an inspiratory phase of the respiratory cycle.

[0205] Optionally, the method includes determining the second input by determining one or more discrete values indicative of a flow of gases at the nose of the patient at any time during a respiratory cycle, each discrete value being determined based on the measured pressure and the pressure flow correlation.

[0206] Optionally, the method may include receiving the first input by receiving one or more discrete values relating to a flow of gases provided to the patient at any time during a respiratory cycle.

[0207] Optionally, the method may further include generating an output based on the characterisation of one or more flow paths of delivered gases within the respiratory airways of the patient for display on a graphical user interface.

[0208] Optionally, the output includes textual, numerical and / or graphical output.

[0209] Optionally, the method further includes measuring, via one or more input flow sensors, the flow of gases provided to the patient including either one or both of the first input, and the input flow rate values, wherein each input flow rate is a flow rate of gases provided to the patient from the flow source.

[0210] Optionally, the method includes measuring, via the input flow sensors, a flow rate of the flow of gases provided to the patient.

[0211] Optionally, the method includes measuring, via a single input flow sensor, the flow of gases provided to the patient including the first input and the input flow rate values.

[0212] Optionally, the method further provides a humidifier for humidifying the flow of gases provided to the patient.

[0213] In order that the invention may be more readily understood and put into practice, one or more preferred embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings.

[0214] It will be appreciated that for simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.Brief Description of Drawings

[0215] Figure 1 is a schematic diagram illustrating a respiratory support system in accordance with one embodiment of the invention.

[0216] Figures 2A illustrates flow paths within a patient's respiratory airways during an inspiratory phase of the patient's respiratory cycle during a mouth open condition and anasal passage not obstructed (e.g. soft palate open) condition of the patient, when the input flow rate of gases provided to the patient exceeds the inspiratory demand of the patient.

[0217] Figure 2B illustrates flow paths within a patient's respiratory airways during an expiratory phase of the patient's respiratory cycle during a mouth open condition and a nasal passage not obstructed (e.g. soft palate open) condition of the patient.

[0218] Figure 2C illustrates flow paths within a patient's respiratory airways during an inspiratory phase of the patient's respiratory cycle during a mouth open condition and a nasal passage not obstructed (e.g. soft palate open) condition of the patient, when the input flow rate of gases provided to the patient does not meet the inspiratory demand of the patient.

[0219] Figures 3A illustrates flow paths within a patient's respiratory airways during an inspiratory phase of the patient's respiratory cycle during a mouth open condition and a nasal passage obstructed (e.g. soft palate closed) condition of the patient.

[0220] Figures 3B illustrates flow paths within a patient's respiratory airways during an expiratory phase of the patient's respiratory cycle during a mouth open condition and a nasal passage obstructed (e.g. soft palate closed) condition of the patient.

[0221] Figures 4A illustrates flow paths within a patient's respiratory airways during an inspiratory phase of the patient's respiratory cycle during a mouth closed condition and a nasal passage not obstructed (e.g. soft palate open) condition of the patient, when the input flow rate of gases provided to the patient exceeds the inspiratory demand of the patient.

[0222] Figure 4B illustrates flow paths within a patient's respiratory airways during an expiratory phase of the patient's respiratory cycle during a mouth closed condition and a nasal passage not obstructed (e.g. soft palate open) condition of the patient.

[0223] Figure 4C illustrates flow paths within a patient's respiratory airways during an inspiratory phase of the patient's respiratory cycle during a mouth closed condition and a nasal passage not obstructed (e.g. soft palate open) condition of the patient, when the input flow rate of gases provided to the patient does not meet the inspiratory demand of the patient.

[0224] Figure 5A is a high-level flow diagram summarising a method of characterising flow paths within a patient's respiratory airways according to some embodiments of the invention.

[0225] Figure 5B is a flow diagram summarising a method of characterising flow paths within a patient's respiratory airways according to one embodiment of the method of Figure 5A.

[0226] Figure 5C is a flow diagram summarising a method of deriving a calculated airway pressure based on a measured system pressure and a pressure difference indicative of flow resistance across a portion of a system flow path of the respiratory support system.

[0227] Figures 6A and 6B illustrate one example non-sealing patient interface and patient sensing configuration associated with the method of characterising flow paths as summarised in Figure 5B.

[0228] Figures 6C and 6D illustrate different examples of patient sensing configurations associated with the non-sealing patient interface illustrated in Figures 6A and 6B.

[0229] Figure 6E is an airway pressure waveform illustrating pressure changes in the patient's airway during the phases of a breath cycle.

[0230] Figure 6F illustrates stacked pressure waveforms including a system pressure waveform showing pressure changes in the sensed system pressure during phases of two breath cycles, and an offset relationship between the sensed system pressure, a pressure difference indicative of flow resistance across a portion of a system flow path of the respiratory support system, and corresponding calculated airway pressure.

[0231] Figures 7A to 7D are flow diagrams illustrating different methods of determining a pressure flow correlation as a part of a method of characterising flow paths according to different embodiments.

[0232] Figure 7E illustrates a relationship between two different pressure flow correlations, a first pressure flow correlation being a correlation between the measured pressure when the pressure sensor is configured to detect a system pressure and the flowrate of gases at the patient, and the second correlation being a correlation between the calculated airway pressure and the flow rate of gases at the patient.

[0233] Figure 8A is a detailed flow diagram illustrating methods of characterising flow paths within a patient's respiratory airways as shown in Figures 5A and 5B.

[0234] Figure 8B is a detailed flow diagram illustrating methods of characterising flow paths within a patient's respiratory airways as shown in Figures 5A and 5B.

[0235] Figures 9A to 9E are graphs illustrating a comparison between example waveforms of an input flow rate of gases provided to the patient and a measured flow rate of gases at the patient corresponding to different flow path characterisations as determined using the methods shown in Figures 8A and 8B.

[0236] Figure 10A is a flow diagram detailing steps for determining one or more other respiratory parameter associated with the patient in accordance with the method shown in Figure 8A.

[0237] Figure 10B is a flow diagram detailing steps for determining one or more other respiratory parameter associated with the patient in accordance with the method shown in Figure 8B.Detailed DescriptionOverview

[0238] Embodiments of the invention provide various methods and systems for characterising flow paths within a patient's respiratory airways, for example during a medical procedure such as a medical procedure involving the provision of respiratory support e.g. oxygen therapy. In particular, the embodiments described herein relate to methods of characterising flow paths within a patient's respiratory airways when respiratory support is delivered via a non-sealing patient interface such as a non-sealing nasal cannula.

[0239] When using a non-sealing patient interface such as a non-sealing nasal cannula to deliver respiratory support, it can often be difficult to determine the flow of gases at the patient (Qm) due to a number of variables associated with the nature of non-sealing flowdelivery, thereby making it challenging to accurately characterise patient flow paths. For instance, leakage around the non-sealing patient interface may vary depending on the delivered flow and patient condition and anatomy. Moreover, in some cases, depending on factors such as the delivered flow rate, the delivered respiratory support may be mixed with ambient air, for example during entrainment when ambient air is inhaled by the patient. In addition, the proportion of leakage and entrainment may change during the course of therapy, for example with patient movement, airway blockages and / or obstructions, and / or environmental factors. All of these factors may contribute to difficulties in the accuracy and reliability of characterising and determining patient flow parameters.

[0240] Providing the ability to determine or estimate the flow of gases at the patient (Qm) (to allow determination of patient flow paths and optionally other respiratory parameters) advantageously enables further knowledge of patient condition to customise and optimise therapy provided to the individual patient, which may improve clinical outcomes.

[0241] A patient's respiratory airways may refer to the patient's upper and / or lower airways, which may include any one or more of the patient's nose, mouth, sinuses, pharynx, and larynx, the trachea (windpipe), bronchial tubes, and lungs. Characterising flow paths within a patient's respiratory airways may include any qualitative and / or quantitative determinations in relation to the flow of one or more gases within the patient's respiratory airways. Examples of qualitative determinations may include determination of categorical variables (e.g. binary data) which indicate any one or more of a mouth open or closed condition, and a nasal passage not obstructed (e.g. soft palate open) / closed condition. An example of a quantitative determination may include the determination of a numerical value (e.g. 'k') indicative of a proportion of delivered gases passing through the patient's mouth or nose. More specific examples of flow path characterisations will be discussed in further detail below with reference to Figures 2A to 4C.

[0242] Medical procedures should be considered broadly and can comprise any aspect of providing a medical procedure, comprising operative procedures, pre and post -operative procedures, any time prior to, during or after sedation or anaesthesia (sedation and anaesthesia more generally referred to herein as "anaesthetic procedures"), includingadministering sedatives and / or anaesthetics, during oxygenation and pre-oxygenation phases or procedures, or at any other time without limitation. A medical procedure can also involve providing respiratory support such as high flow respiratory support. In the context of this specification, medical procedure can also encompass monitoring a patient, whether or not a particular procedure is being provided to the patient. The embodiments described are not just restricted to use in medical procedures. It could be used in ICU, or any other situation where respiratory support is provided.

[0243] To provide the respiratory support, one or more gases is provided to the patient. The one or more gases may be provided to the patient at a predetermined input flow rate. The input flow rate of gases delivered to the patient may be provided at any suitable flow rate in accordance with patient requirements. In some embodiments, high flow respiratory support may be provided to a patient in which gases delivered to the patient is provided at a high flow rate.

[0244] In this specification, "high flow" means, without limitation, any gas flow with a flow rate that is higher than usual / normal, such as higher than the normal inspiration flow rate of a healthy patient. It can be provided by an open or non-sealing respiratory system in which substantial leak may occur at the entrance of the patient's airways due to an open or non-sealing patient interface, for example a nasal cannula having non-sealing nasal prongs. In some embodiments, "high flow" respiratory support may be provided via a non-sealing patient interface, for example as described in further detail below with reference to Figures 6A to 6D. Typically, high flow respiratory support is provided with humidification to improve patient comfort, compliance and safety. Alternatively, or additionally, it can be higher than some other threshold flow rate that is relevant to the context - for example, where providing a gas flow to a patient at a flow rate to meet inspiratory demand, that flow rate might be deemed "high flow" as it is higher than a nominal flow rate that might have otherwise been provided. "High flow" is therefore context dependent, and what constitutes "high flow" depends on many factors such as the health state of the patient, type of procedure / therapy / support being provided, the nature of the patient (big, small, adult child) and the like. Those skilled in the art would understand from context what constitutes "high flow". It is a magnitude of flow rate that is over and above a flow rate that might otherwise be provided.

[0245] Without limitation, some indicative values of high flow can be as follows.

[0246] In some configurations, delivery of gases to a patient is provided at a flow rate of greater than or equal to about 5 or 10 litres per minute (5 or 10 LPM or L / min).

[0247] In some configurations, delivery of gases to a patient at a flow rate of about 5 or 10 LPM to about 150 LPM, or about 15 LPM to about 95 LPM, or about 20 LPM to about 90 LPM, or about 25 LPM to about 85 LPM, or about 30 LPM to about 80 LPM, or about 35 LPM to about 75 LPM, or about 40 LPM to about 70 LPM, or about 45 LPM to about 65 LPM, or about 50 LPM to about 60 LPM. For example, according to those various embodiments and configurations described herein, a flow rate of gases supplied or provided to an interface via a system or from a flow source, may comprise, but is not limited to, flows of at least about 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150 LPM, or more, and useful ranges may be selected to be any of these values (for example, about 20 LPM to about 90 LPM, about 40 LPM to about 70 LPM, about 40 LPM to about 80 LPM, about 50 LPM to about 80 LPM, about 60 LPM to about 80 LPM, about 70 LPM to about 100 LPM, about 70 LPM to about 80 LPM).

[0248] In "high flow", the gas delivered will be chosen depending on for example the intended form of respiratory support. Gases delivered may comprise a percentage of oxygen. In some configurations, the percentage of oxygen in the gases delivered may be about 15% to about 100%, about 20% to about 100%, or about 21% to about 100%, or about 30% to about 100%, or about 40% to about 100%, or about 50% to about 100%, or about 60% to about 100%, or about 70% to about 100%, or about 80% to about 100%, or about 90% to about 100%, or about 100%, or 100%.

[0249] Flow rates for "high flow" for premature / infants / paediatrics (with body mass in the range of about 1 to about 30 kg) can be different. The flow rate can be set to 0.4-0.8 L / min / kg with a minimum of about 0.5 L / min and a maximum of about 70 L / min. For patients under 2 kg maximum flow is set to 8 L / min.

[0250] In some embodiments, the flow rate of gases (input gases) provided to a patient during respiratory support can be time-varying (e.g. oscillating). This time-varying flow rate can help with therapy.

[0251] As an example, the time-varying flow rates can step between a first flow rate and second flow rate, one or both of which can fall in the range of about OLPM to 70LPM. For example, the time-varying flow rate may be in the range of: about 0% to about 200% of an average flow rate, about 0% to 100% of the average flow rate, about 100% to 200% of the average flow rate, or about 50% to 150% of the average flow rate, and / or is in the range of about 0-140LPM, about 0-70LPM, about 70-140LPM, about 40-100LPM, or about 20-60LPM

[0252] In the above ranges, the average flow rate may refer to the effective average flow rate of input gases provided to the patient when a time-varying flow rate is used.

[0253] It will be understood that the above example ranges are not limiting flow rates.

[0254] Advantageously, High flow has been found effective in meeting or exceeding the patient's normal real inspiratory flow, to increase oxygenation of the patient and / or reduce effort in breathing. Additionally, high flow may generate a flushing effect in the nasopharynx such that the anatomical dead space of the upper airways is flushed by the high incoming gas flows. This creates a reservoir of fresh gas available of each and every breath, while minimising re-breathing of carbon dioxide, nitrogen, etc.

[0255] Embodiments of methods and systems described herein may also determine one or more other respiratory parameters associated with the patient. Similarly, these other respiratory parameters may include qualitative and / or quantitative determinations. For example, the one or more other respiratory parameters may include any one or more of determinations of whether an input flow rate of gases provided to the patient meets the inspiratory demand of the patient, an expired proportion of CO2, an expired proportion of O2, tidal volume, and the like.

[0256] Generally, when considering whether a flow of gases provided to the patient at a predetermined flow rate is considered to meet or exceed the patient's inspiratory demand, a comparison is made between the delivered flow rate of gases passing through the pharynx and into the patient's lungs with an inspiratory demand of the patient.

[0257] In this specification, reference to "proportion" in the context of a gas species refers to any relative measure of a constituent gas component in a total gas comprising two or more constituent gas components. For example, proportion in the context of a gas species could cover: volume fraction, fraction, volume concentration, concentration, molarity, mass fraction, and partial pressure.

[0258] The proportion measured may be the parameter that is measured by the sensor being used, be it concentration, fraction, partial pressure or otherwise. The proportion determined may be the parameter desired by a user and / or processed by a component of a respiratory support system or associated with a respiratory support system.

[0259] In this specification, any reference to "concentration" can also be termed "fraction" and can be indicated as percentage by volume of the gas of interest versus the volume of constituent gases overall in the gas flow in question, be it exhaled gas flow, apparatus flow or any other flow. However, the parameter could be a different measure and the gas could be different - these are just examples.Respiratory Support System

[0260] Figure 1 shows a respiratory support system 10 for providing a therapeutic gas flow therapy or other form of respiratory support to a patient. In some embodiments, the system 10 is configured to deliver a constant flow rate of gases to the patient 16. In other embodiments, the system 10 may be configured for delivering a time-varying flow rate ofgases to the patient 16. The system 10 may include any suitable arrangement of integrated units or separate modular components to provide the necessary system functionality. For example, components described herein as shown in each of the boxes 11, 50 may be provided as single integrated unit, or as separate modular components. The system 10 may be used for any suitable purpose including preoxygenation during an anaesthetic procedure, during an anaesthetic procedure, high flow respiratory support, ventilation, whilst treating patients in respiratory distress, treating patients with obstructive sleep apnoea or in any other application where monitoring of an aspect of patient breathing is desired.

[0261] The system 10 comprises a flow source 50 for providing an input flow rate of gases 31 such as oxygen, or a mix of oxygen and one or more other gases. Alternatively, the system 10 can have a connection for coupling to an external flow source (not shown). As such, the flow source might be considered to form part of the system 10 or be separate to it, depending on context. In embodiments having an external flow source, the system 10 may include one or more connection ports for connection to the external flow source. Moreover, one or more parts of a flow source may form part of the system 10, and one or more other parts of the flow source may be external to the system 10.

[0262] For example, the flow source may include an in-wall oxygen supply, a tank of oxygen 50A, one or more tanks of other gases and / or a high flow respiratory support apparatus having a blower / flow generator 50B. Figure 1 shows a flow source 50 having a flow generator 50B. By way of a non-limiting illustrative example, the flow generator 50B includes an optional air inlet 50C and optional connection to an Ch source (such as tank or O2 generator) 50A via a shut off valve and / or regulator and / or other gas flow control 50D. The flow source could be one or a combination of a flow generator, O2 source, air source as described.

[0263] The flow source 50 may provide a (high) flow of gases that can be delivered to a patient 16 via a delivery conduit, and patient interface 51. As described in further detail below with respect to the different embodiments, the patient interface 51 may be an unsealed (also termed "non-sealing") interface, or an interface having a combination of sealing and non-sealing components. The gas flow provided by the flow source 50 may have a continuous flow rate. In particular, the gas flow provided by the flow source 50 may have acontinuous flow rate independent of the patient's breathing. Moreover, the continuous flow rate of the gas flow provided by the flow source 50 may be time-varying or generally constant.

[0264] The flow source could provide a flow rate of between, e.g. about 0.5 L / min and about 375 L / min, or any range within that range, or even ranges with higher or lower limits.

[0265] A humidifier 52 can optionally be provided between the flow source 50 and the patient 16 to provide humidification of the delivered gases 31. The humidifier 52 may be integrated with the flow source 10 to form an integrated unit 59. Alternatively, the humidifier 52 may be a modular component provided separately, and coupled to the flow source 50. In some embodiments, the humidifier 52 may be a standalone humidifier with a chamber and base, whereby the humidifier 52 is coupled to the flow source 50 via conduits or other suitable connectors.

[0266] One or more sensors 53A, 53B, 53C, 53D such as pressure, flow rate, oxygen fraction or other gas fraction, full or partial pressure, humidity, temperature or other sensors can be placed throughout the system 10 and / or at, on or near the patient 16. In particular, any one or more of the sensors 53A, 53B, 53C, 53D may be a pressure sensor configured to sense a system pressure at a suitable location within a system flow path of the respiratory support system 10. As described further herein with reference to Figures 5C, 6F and 6G, the system pressure may be usable for determining a calculated airway pressure, to facilitate characterising flow paths of the within the patient's respiratory airways. Alternatively, or additionally, sensors from which such parameters can be derived could be used. In addition, or alternatively, the sensors 53A-53D can be one or more physiological sensors for sensing patient physiological parameters such as, heart rate, oxygen saturation (e.g. pulse oximeter sensor 54E), partial pressure of oxygen in the blood, respiratory rate, partial pressure of O2 and / or CO2 in the blood. Alternatively, or additionally, sensors from which such parameters can be derived could be used. Other patient sensors could comprise EEG sensors, torso bands to detect breathing, and any other suitable sensors. In some configurations the humidifier 52 may be optional, or it may be preferred due to the advantages of humidified gases helping to maintain the condition of the airways. Humidification is typically used with high flow gas flows to increase patient comfort, compliance, support and and / or safety. Oneor more of the sensors may form part of the system 10, or be external thereto, with the system 10 receiving inputs from any one or more of the external sensors.

[0267] In some embodiments as discussed in further detail below, flow sensors and / or pressure sensors may be used to measure a flow of gases at the patient's 16 nose and / or mouth, more specifically at the patient's 16 nose. Some exemplary embodiments of different sensor configurations are described in further detail below with reference to Figures 6A to 6D.

[0268] Moreover, one or more sensors 14 for measuring a gas parameter (of a target gas) of the patient composite gas outflow may be provided. That is, depending on the target gas (e.g., oxygen, carbon dioxide, nitrogen, helium and / or an anaesthetic agent such as sevoflurane), one or more sensors may be provided to sense that gas proportion in the composite gas outflow. Each sensor may be a mainstream, a side stream sensor, or any other suitable sensor, and can be placed proximate (in, on, near) the nose and / or mouth of the patient 16. Other positions are possible. By way of a non-limiting example, the system 10 may provide one or more sensors 14 to measure one or both of a fraction of CO2 and a fraction of O2 in the composite gas outflow at the patient's nose or mouth. As described in further detail below with reference to Figures 6C and 6D, one or more sensors / devices for measuring oxygen fraction or carbon dioxide or other gas fraction (e.g. the one or more sensors / devices may comprise a capnograph) may be provided in the system 10.

[0269] The composite gas outflow of the patient is a leaked gas flow combined with an exhaled (or expired) gas flow of the patient 16. Leak gas flow may comprise any excess gas flow from the delivered respiratory support that is not inhaled and / or has not entered the lower airways of the patient by the patient and escapes to ambient via the mouth and / or nose.

[0270] In various embodiments, one or more pressure or flow sensors and / or one or more sensors 14 for measuring a gas parameter (of a target gas) of the patient composite gas outflow may be releasably or permanently mounted to or proximate the patient interface 51, the patient's nose and / or mouth such that the sensing elements of the one or more flow sensors and / or one or more sensors 14 are in direct fluid communication with the sensed gases at the patient. Specific example embodiment of a non-sealing patient interface 210 andsensor 212 arrangement will be discussed in further detail with reference to Figures 6A to 6D. In some embodiments, one or more pressure or flow sensors and / or one or more sensors 14 may be releasably or permanently mounted elsewhere in the respiratory support system 10, for example, upstream of the patient interface 51. Typically, when the sensor(s) are mounted elsewhere in the system 10, the sensing elements of the sensor(s) may be coupled with one or more gas conduits, sampling tubes, sampling lines and / or sampling probes to facilitate fluid communication with sensed gases at the patient 16. Elaborating further, the one or more gas conduits, sampling tubes and / or sampling probes may be positioned proximate the patient's mouth and / or nose so as to provide fluid communication between the sensed gases at the patient and the sensing element of the one or more flow sensors and / or one or more sensors 14. For ease of reference and succinctness, throughout the specification, reference to any one or more sensor(s) or sensor unit(s) (e.g. gas fraction sensors / sensors for measuring concentration of gaseous species) may include sensing element(s) and / or gas conduit(s), sampling tube(s), sampling line(s) and / or sampling probe(s) and the like to facilitate fluid communication with gases at the patient 16 and a gas sensing component or element or apparatus such as a capnography machine.

[0271] The output from the sensors can be transmitted to a controller 19 to facilitate control of one or more functions provided by the system 10, including among other things, to vary the flow of gases provided to the patient 16. In some embodiments, the controller 19 executes software instructions stored therein to characterise flow paths within the patient's 16 respiratory airways based on any one or more input parameters received from one or more the sensors described herein. Furthermore, the controller 19 may be configured to execute software instructions stored therein to determine one or more other respiratory parameters associated with the patient 16. This will be described in further detail below.

[0272] Alternatively, or additionally, the controller 19 may be configured to receive input from a user. The controller 19 is coupled to the flow source 50, humidifier 52 and sensors 53A to 53D, 14. The controller 19 may be configured to operate the flow source 50 to provide the delivered flow of gases to the patient 16. It can also operate a gas flow modulator(s) (including the flow source) to control the flow, pressure, volume and / or other parameters of gases provided by the flow source 50 based on feedback from one or more sensors (e.g. 53A to 53D, 14), or optionally without feedback (e.g. using default settings). The controller 19 canalso control any other suitable parameters of the flow source 50 to meet oxygenation requirements and / or CO2 removal. The controller 19 can also control the humidifier 52 based on feed-back from the sensors 53A-53D, 14. Based on input from the sensors, the controller 19 can determine oxygenation requirements and provide information to prompt a medical professional to control the components of the respiratory support system 10 so as to provide the desired respiratory support (e.g. flow rate, O2 fraction, humidity, etc.) and / or control parameters of the flow source 50, gas flow modulator(s) and / or humidifier 52 as required. Alternatively, the controller 19 could be provided as a monitoring apparatus for providing information to a medical professional and / or communicating control parameters of the respiratory support system 10 to prompt decision making by the medical profession to determine a desired respiratory support. Based on information provided by the controller 19, the medical professional can then control the respiratory support system 10 to provide the desired respiratory support. As such, in some embodiments, the controller 19 may not always determine oxygenation requirements and control parameters of the system 10.

[0273] The controller 19 may also be configured to operate the system 10 so that the flow of gases provided to the patient 16 has a time-varying flow rate that provides respiratory support. For example, a time-varying flow rate may be a flow rate oscillating about a mean flow rate at a given frequency. The controller 19 may control operations of the flow generator 50B or any other suitable gas modulator to provide the time-varying flow rate in the flow of gases provided to the patient 16. A gas modulator can be used to modulate (that is, varying, modify, adjust or otherwise control parameters of the gas flow). Each gas flow modulator can be provided in the flow source (and the flow source itself can be a gas flow modulator), after the flow source and before the humidifier, after the humidifier, and / or in any other suitable place in the system 10 to modulate the gas flow as required. The controller 19 can also operate the gas flow modulator(s) (including the flow source) to control the flow, pressure, volume and / or other parameters of gas provided by the flow source based on feedback from sensors, or optionally without feedback (e.g. using default settings). The controller 19 can also control any other suitable parameters of the flow source to meet oxygenation requirements. In some embodiments, the system 10 may also comprise a pressure relief valve.

[0274] In embodiments requiring a varying gas proportion in the flow of gases provided to the patient 16, the controller 19 may be additionally or alternatively configured to operate the system 10 so that the gas flow has a time-varying gas proportion (such as O2 fraction or other gas fraction and / or O2 partial pressure or other gas partial pressure) that provides therapy / respiratory support. For example, a time-varying gas proportion may be a gas proportion oscillating about a mean gas proportion at a given frequency In some example embodiments, the controller 19 may control a proportional valve coupled to an O2 source 50A. The controller 19 can then measure the composite gas outflow and or determine (e.g. obtain an estimate of) the gas parameter using any of the following techniques. In one embodiment, there are two proportional valves that operate 180 degrees out of phase. As one opens, the other closes. One controls O2 fraction in the delivered gas flow, and the other controls air fraction in the delivered gas flow, but together keeping the total gas flow rate constant. In another alternative, a single proportional valve is used with an impeller where the proportional valve controls an O2 fraction and the impeller controls the flow rate. In some embodiments, the single proportional valve may be used before or after the impeller. Where the single proportional valve is used before the impeller, the proportional valve controls the O2 fraction into the inlet of the impeller along with the ambient air. In some embodiments, more than one proportional valve may be used with an impeller and may be positioned anywhere in the system with respect to the impeller. The controller 19 can control the proportional valve(s) to operate as required to achieve the time-varying gas proportion.

[0275] In some embodiments, the controller 19 may be a specialist controller operatively configured to receive input from the one or more sensors 53A to 53D, 14, and / or one or more pressure / flow sensors (e.g. see Figures 6A to 6D) to characterise flow paths within a patient's respiratory airways as described herein. In particular, the controller 19 may be used to determine a pressure flow correlation as described herein with reference to Figures 7A to 7D. One or more separate controllers (not shown) may be provided in the respiratory support system 10 for interfacing and controlling with the flow source 50 and / or humidifier 52. In another embodiment, a separate controller may be used to determine a pressure flow correlation as described herein with reference to Figures 7A to 7D. The pressure flow correlation as determined by the separate controller may be accessible by controller 19 tocharacterise flow paths / determine respiratory parameters during provision of respiratory support via system 10.

[0276] An input / output user interface 54 (such as a display and / or input device) is provided. The input device is for receiving information from a user (e.g. clinician or patient) that can be used for example for determining oxygenation requirements, anaesthetic gas agent, detection (e.g. breath detection, detection with respect to inspiratory or expiratory phases of the patient's breathing, detection in relation to a state of the patient), flow rates, gas fractions, partial pressures and / or any other parameter that might be controlled by the system 10.

[0277] In some embodiments, the user interface 54 may include a graphical user interface for displaying visual output to provide a visual indication of the characterisation of the one or more flow paths of delivered gases within the respiratory airways of the patient 16. The graphical user interface may further display output to provide visual indications of the one or more determined respiratory parameters associated with the patient 16. The output may be displayed on the graphical user interface textually, numerically and / or graphically. In some embodiments, the user interface 54 may be configured to generate audio output (e.g. in the form of audio messages) to provide an indication of the characterisation of the one or more flow paths of delivered gases within the respiratory airways of the patient 16, and / or one or more determined respiratory parameters associated with the patient 16. The visual and / or audio output may be generated based on real-time or near real-time sensor data continuously during a medical procedure. In some embodiments, the visual and / or audio output may be updated continuously or periodically, for example during or after each respiratory cycle here.Flow Paths in Respiratory Airways

[0278] The characterisation of one or more flow paths of delivered gases within the respiratory airways of the patient can be conducted in a number of different ways. In some embodiments, the flow paths within the patient's 16 respiratory airways can be characterised by determining whether the patient's mouth is open or closed. In some embodiments, it may be additionally determined whether the patient's nasal passage is obstructed or not obstructed. Such a determination of whether the patient's nasal passage is obstructed or notobstructed is typically made when the patient is breathing. Typically, the nasal passage refers to the passage between the nasal and oral cavity of the patient. In one example, the nasal passage may not be obstructed if the soft palate is open. Similarly, the nasal passage may be obstructed if the soft palate is closed. As such, a determination that the nasal passage is not obstructed may suggest that the soft palate is open, and a determination that the nasal passage is obstructed may suggest that the soft palate is closed. It may often be observed that a nasal passage obstructed (e.g. soft palate closed) or not obstructed condition in a patient may be temporary. In other examples, the patient's anatomical structure or underlying patient condition may give rise to a nasal passage obstruction that persists. Throughout the specification, the condition of the soft palate in either an open or closed position may be described as examples of not obstructed or obstructed conditions of the nasal passage, for example as described below with reference to Figures 2A to 4C. In practice, the controller 19 may determine whether the nasal passage is obstructed or not obstructed and this may infer whether the soft palate is closed or open respectively.

[0279] As described in further detail below, characterising one or more flow paths of delivered gases within the respiratory airways of the patient may include any one or more of: determining a mouth open condition, determining a mouth closed condition, determining a nasal passage not obstructed (e.g. soft palate open) condition, determining a nasal passage obstructed (e.g. soft palate closed) condition, determining a numerical value (e.g. 'k') indicative of a proportion of delivered gases passing through the mouth or nose.

[0280] In various embodiments of methods for characterising flow paths and / or determining respiratory parameters as described herein, any one or more of the flow path characterisations and respiratory parameters may be determined at various steps of the methods. Where the determination of more than one of the flow path characterisations and / or respiratory parameters are possible, the controller 19 may determine any one or more, or all of the possible flow path characterisations and respiratory parameters, and provide an output presenting the any one or more, or all of the possible determinations. Similarly, any one or more steps of any method described herein can be combined with anyone or more steps of any other method to determine a combination of flow path characterisations and / or respiratory parameters, where appropriate.

[0281] As shown in Figure 2A, a flow of gases 100 is provided to the patient 16 via the patient's nares 106 by a respiratory support system 10 at a constant or time-varying flow rate, for example during high flow respiratory support. The flow of gases 100 may have a fixed concentration of O2 or a varying concentration of O2. Figure 2A illustrates an inspiratory phase of the patient's respiratory cycle. During the inspiratory phase, a portion of the delivered gases 100 passes through the pharynx and into the patient's lungs. As the patient's 16 mouth 102 and soft palate 104 are both open, a flow of gases leaving the patient may pass through both the mouth 102 and nose 106 of the patient during the inspiratory phase. The flow of gases leaving the patient is a portion of the delivered gases 100.

[0282] Typically, the flow rate of the input flow of gases 100 (referred to herein as Qi) is a known value of the gas flow generator 50B. In some embodiments, the flow rate Qi may be measured (e.g. via a flow sensor) in or at the patient interface 51, in or at the patient's respiratory airways, or at any suitable location in the respiratory support system 10 upstream of the patient interface 51.

[0283] Figure 2B illustrates flow path conditions during an expiratory phase of the patient's 16 respiratory cycle. During the expiratory phase, a flow of gases leaving the patient may pass through both the mouth 102 and nose 106 of the patient 16. A portion of the delivered gases 100 may leave the patient 16 via the patient's mouth 102 and / or nose 106. Moreover, gases exhaled 108 by the patient 16 may leave the patient 16 via the patient's mouth 102 due to a lower resistance pathway (when compared to the resistance of the pathway out of the nose).

[0284] In this scenario illustrated in Figures 2A and 2B, the characterisation of one or more flow paths of delivered gases 100 within the respiratory airways of the patient 16 can include a determination of a mouth open condition and a nasal passage not obstructed (e.g. soft palate open) condition. It may also be determined that in this scenario, the input flow rate of gases 100 provided to the patient 16 exceeds the inspiratory demand of the patient 16 in Figure 2A.

[0285] In the mouth open condition, where the mouth 102 of the patient 16 is open, this refers to the mouth 102 being open to an extent such that a substantial flow of gases can pass through the mouth 102. In the nasal passage not obstructed (e.g. soft palate open) condition, where the soft palate 104 of the patient is open, this refers to the soft palate 104 being open to an extent such that a substantial flow of gases can pass the soft palate 104 (i.e. the flow path between the nasal and oral cavity / lower airways is not obstructed and gases can flow from the nasal cavity to the oral cavity / lower airways).

[0286] Conversely, in a mouth closed condition, where the mouth 102 of the patient 16 is closed, this refers to the mouth being closed to an extent such that a substantial flow of gases cannot pass through the mouth 102, to or from atmosphere. In a soft palate 104 closed condition, where the soft palate 104 of the patient is closed, this refers to the soft palate 104 being closed to an extent such that a substantial flow of gases cannot pass the soft palate 104 (i.e. gases cannot substantially pass between the nasal and oral cavity / lower airways as the flow path is obstructed e.g. by the soft palate).

[0287] A different scenario will now be described with reference to Figure 2C. As shown in Figure 2C, a flow of gases 100 is provided to the patient 16 via the patient's nares 106.Figure 2C illustrates an inspiratory phase of the patient's respiratory cycle. During the inspiratory phase, a portion of the delivered gases 100 passes through the pharynx and into the patient's lungs. As the patient's 16 mouth 102 and soft palate 104 are both open, the patient entrains ambient air through the mouth 102. In some cases, a portion of the delivered gases 100 may leave the patient via the patient's nose 106. In this scenario, the characterisation of one or more flow paths of delivered gases 100 within the respiratory airways of the patient 16 can include a determination of a mouth open condition and a nasal passage not obstructed (e.g. soft palate open) condition.

[0288] A further scenario will now be described with reference to Figures 3A and 3B. A flow of gases 100 is provided to the patient 16 via the patient's nares 106. Like numerals refer to like features previously described. Figure 3A illustrates an inspiratory phase of the patient's respiratory cycle. During the inspiratory phase, none (or a negligible amount) of the delivered gases 100 passes through the pharynx and into the patient's lungs as the patient's 16 soft palate 104 is closed and all (or almost all) of the delivered gases 100 leaves thepatient 16 through the nose 106. The patient's mouth 102 is open. As such, the patient entrains ambient air 110 through the mouth 102 during the inspiratory phase.

[0289] Figure 3B illustrates an expiratory phase of the patient's respiratory cycle. During the expiratory phase, none (or a negligible amount) of the delivered gases 100 passes through the pharynx and into the patient's lungs, or enters the oral cavity, as the patient's 16 soft palate 104 is closed and all (or almost all) of the delivered gases 100 leaves the patient 16 through the nose 106. The patient's mouth 102 is open. As such, the patient's exhales gases 108 pass through the mouth 102 during the expiratory phase.

[0290] In this scenario as illustrated in Figures 3A and 3B, the characterisation of one or more flow paths of delivered gases 100 within the respiratory airways of the patient 16 can include a determination of a mouth open condition and a nasal passage obstructed (e.g. soft palate closed) condition.

[0291] Yet another scenario will now be described with reference to Figures 4A and 4B. A flow of gases 100 is provided to the patient 16 via the patient's nares 106. Like numerals refer to like features previously described. Figure 4A illustrates an inspiratory phase of the patient's respiratory cycle. During the inspiratory phase, a portion of the delivered gases 100 passes through the pharynx and into the patient's lungs. As the patient's 16 mouth 102 is closed and the soft palate 104 is open, a flow of gases leaving the patient passes through the nose 106 of the patient during the inspiratory phase. No (or a negligible amount of) gases pass through the mouth 102 of the patient. Moreover, a portion of the delivered gases 100 may leave the patient 16 via the patient's nose 106 during inspiration.

[0292] Figure 4B illustrates flow path conditions during an expiratory phase of the patient's 16 respiratory cycle. During the expiratory phase, a flow of gases leaving the patient passes through the nose 106 of the patient 16. No (or a negligible amount of) gases pass through the mouth 102 of the patient as the patient's mouth 102 is closed. A portion of the delivered gases 100 may leave the patient 16 via the patient's nose 106. Moreover, gases exhaled 108 by the patient 16 leave the patient 16 via the patient's nose 106.

[0293] In this scenario illustrated in Figures 4A and 4B, the characterisation of one or more flow paths of delivered gases 100 within the respiratory airways of the patient 16 caninclude a determination of a mouth closed condition and a nasal passage not obstructed (e.g. soft palate open) condition. In relation to the scenario illustrated in Figure 4A, it may also be determined that, the input flow rate of gases 100 provided to the patient 16 exceeds the inspiratory demand of the patient 16.

[0294] A different scenario will now be described with reference to Figure 4C. As shown in Figure 4C, a flow of gases 100 is provided to the patient 16 via the patient's nares 106. Like numerals refer to like features previously described. Figure 4C illustrates an inspiratory phase of the patient's respiratory cycle. During the inspiratory phase, a portion of the delivered gases 100 passes through the pharynx and into the patient's lungs. As the patient's 16 mouth 102 is closed and the soft palate 104 is open, the patient entrains ambient air through the nose 106 only. No gases pass through the mouth 102 of the patient 16 as it is closed.Moreover, there is no flow of gases leaving the patient during the inspiratory phase. In this scenario, the characterisation of one or more flow paths of delivered gases 100 within the respiratory airways of the patient 16 can include a determination of a mouth closed condition and a nasal passage not obstructed (e.g. soft palate open) condition. In addition, it can be determined that the input flow rate of gases 100 provided to the patient 16 does not meet the inspiratory demand of the patient 16.

[0295] In some embodiments, a numerical value (e.g. k) indicative of a proportion of delivered gases passing through the mouth 102 or nose 106 of the patient 16 (such as a proportion of the volumetric flow rate and / or the mass flow rate of delivered gases passing through the mouth 102 or nose 106 of the patient 16) may also be determined. This will be described in further detail below with reference to Figures 8 to 10.

[0296] In all embodiments of the invention as described herein, it is assumed that the patient 16 is breathing (e.g., the patient 16 is not apnoeic). In some embodiments, the patient's breathing may be depressed by anaesthetic agents, for example during a medical procedure. In some embodiments, the patient may be breathing during at least part of a medical procedure, however, it should be understood that there may be periods during the medical procedure when the patient could become apnoeic.Characterising Flow Paths

[0297] Methods and systems of characterising flow paths within the patient's 16 respiratory airways in accordance with embodiments of the invention will now be described below. In some embodiments, one or more other respiratory parameters can also be determined.

[0298] As summarised in the flow diagram 200 of Figure 5A, methods of characterising flow paths within the patient's 16 respiratory airways, and for optionally determining one or more other respiratory parameters, may include the general steps of providing 202 a flow of gases to the patient via a patient interface 51 of the respiratory support system 10, and measuring 204 a flow of gases at the patient's nose using one or more sensors (the one or more sensors may be provided by / on or proximate the patient interface 51, or elsewhere in the system e.g. in the system flow path), and characterising 206 one or more flow paths of delivered gases 100 within the respiratory airways of the patient 16 based on a comparison between the flow of gases provided to the patient 16 via the patient interface 51 and the flow of gases at the patient as estimated based on one or more sensor measurements. To elaborate further, measuring 204 a flow of gases at the patient may include measuring a pressure at the patient. The measured pressure may provide an indication of a flow rate of gases at the patient (e.g. the patient's nose).

[0299] The flow diagram 301 of Figure 5B provides a more detailed example of a method of characterising flow paths within the patient's 16 respiratory airways, and for optionally determining one or more other respiratory parameters.

[0300] At initial step 302, a controller may determine a patient specific pressure flow correlation. The pressure flow correlation provides a correlation between an airway pressure of the patient and a corresponding flow rate of gases at the patient. The pressure flow correlation may provide a correlation between an airway pressure and a corresponding flow rate of gases at the patient across a range of flow rates. The pressure flow correlation may be a relationship between an airway pressure and a corresponding flow rate of gases at the patient.

[0301] Typically, the pressure flow correlation is determined by the controller when the patient interface 51 is mounted on the patient 16. The pressure flow correlation can be determined during provision of respiratory support. The pressure flow correlation may be determined prior to the commencement of a procedure (e.g. when respiratory support is provided at a required input flow rate). Alternatively, the pressure flow correlation could be determined during a course of a procedure. As explained in further detail below, the pressure flow correlation will be used to determine an estimated value for a flow rate of gases at the patient (Qm) during respiratory support e.g. before or during the course of a procedure, for example when respiratory support is provided at predetermined flow rate(s). Different example methods of determining the patient specific pressure flow correlation will be described below with reference to Figures 7A to 7E.

[0302] At step 304, a flow of gases from a flow source (also referred to herein as input flow) is provided to the patient (e.g. before or during a medical procedure or to commence a medical procedure). The flow rate of the input flow may be known from the flow source or via measurement from any suitable flow sensor as described herein.

[0303] At step 306, a flow of gases at the patient (e.g. a flow rate of gases at the patient's nares) may be determined based on the pressure flow correlation.

[0304] In some embodiments, a pressure sensor may be provided to measure the patient's airway pressure (e.g. see Figures 6A to 6D) and a measured / calculated pressure at the patient may be used in combination with the pressure flow correlation to determine the flow rate of gases at the patient's nares.

[0305] In some embodiments, a pressure sensor 53A, 53B, 53C, 53D may be provided to detect a system pressure (Psys), which can be a measured pressure at any location within system flow path. The respiratory support system 10 defines a system flow path extending from the flow source 50B to the patient interface 51. Generally, the system flow path is a flow path of the input flow of gases from the flow source 51 to one or more outlets of the patient interface 51. In these embodiments, a calculated airway pressure (Pm) can be derived based on the system pressure (Psys) and a pressure difference (Prtf). The pressure difference (Prtf) is a pressure due to flow resistance across a portion of the system flow path between the location of the measured pressure (Psys) and one or more outlets of the patient interface51. The determination of the calculated airway pressure (Pm) in this embodiment will be described in further detail below with reference to Figure 5C. The calculated airway pressure may be used in combination with the pressure flow correlation to determine the flow rate of gases at the patient's nares.

[0306] At step 308, the determined flow rate of gases at the patient in step 306 is compared with the input flow rate discussed in step 304.

[0307] At step 310, the controller characterises one or more flow paths of delivered gases within the respiratory airways of the patient based on the outcome of the comparison in step 308. Optionally, the controller may further determine one or more other parameters such as one or more other respiratory parameters. Further detail of the comparison, outcomes of the comparison and characterisation and determination of respiratory parameters will be described in further detail below with reference to Figures 8A to 10B.

[0308] Now referring to Figure 5C, summarising a method of determining the calculated airway pressure (Pm) based on a system pressure (Psys) measurement in the system flow path of the respiratory support system 10 and a pressure difference (Prtf) indicative of flow resistance downstream of the system flow path from the measurement location of the system pressure (Psys).

[0309] At step 322, the controller 19 acquires a measurement of the system pressure (Psys) from one or more pressure sensors (e.g., pressure sensors 53A, 53B, 53C, 53D) positioned at various locations along the system flow path of the respiratory support system 10. In certain embodiments, the controller may sample a single pressure value from a selected pressure sensor. In alternative embodiments, the controller 19 may sample multiple pressure values from a single sensor and compute an average or mean value to determine the system pressure (Psys). In further embodiments, the controller 19 may obtain pressure readings from multiple sensors distributed throughout the system flow path. When multiple sensors are utilised, the controller 19 may determine a separate system pressure (Psys) value corresponding to each sensor location.

[0310] At step 324, the controller 19 determines one or more pressure difference (P rtf) values indicative of flow resistance downstream of the system flow path from each of thepressure sensing locations of the system pressure (Psys). The pressure difference (Prtf) may be constant or variable with respect to input flow rate. In some embodiments, the pressure difference (Prtf) is a function of the input flow rate (Qo) and the cumulative flow resistance of downstream system components, such as the humidifier 52, the patient interface 51, and any interconnecting and associated conduits in the system flow path downstream of the corresponding pressure sensor.

[0311] In certain embodiments, predetermined pressure difference (Prtf) values may be derived for each pressure sensor location along the system flow path for one or more input flow rates (Qo). These predetermined pressure difference (Prtf) values may be stored in the memory of controller 19 and retrieved as required during operation. In some embodiments, a range of pressure difference (Prtf) values may be derived across a range of input flow rates (Qo) prior to mounting the patient interface 51 on a patient, for example during system setup. This may involve measuring the absolute pressure relative to atmospheric pressure at one or more pressure sensor locations (e.g. at sensors 53A to 53D) across a range of input flow rates (Qo) before the patient interface 51 is connected to the patient. Based on these measurements, a relationship between the pressure difference (Prtf) and the input flow rate (Qo) may be determined. This relationship may be represented as a calibration curve or other suitable mathematical model. As such, the order of step 324 and 322 may be reversed. In some embodiments, method steps 324 and 322 may be executed concurrently.

[0312] At step 326, for a given input flow rate (Qo) and a given pressure sensor location from which the system pressure ( Psys) is measured, a calculated airway pressure (Pm) may be derived by subtracting the pressure difference (Prtf) downstream of the given pressure sensor location (as determined in step 324) from the sensed system pressure ( Psys) (as determined in step 322) by the pressure sensor from the given pressure sensor location. As such:Pm = Psys - Prtf

[0313] The calculated airway pressure (Pm) values can be used as described herein to determine characteristic airway pressure values for determination of the pressure flow correlation.

[0314] The calculated airway pressure (Pm) can be used as described herein to determine a flow rate of gases at the patient (Qm) (e.g. using the pressure flow correlation), and in different methods to characterise the patient's flow path, and optionally determine one or more respiratory parameters.

[0315] The calculated airway pressure (Pm) may be used in a similar way to the measured pressure (Pm) as described herein in other embodiments to characterise flow paths and optionally determine one or more respiratory parameters.

[0316] Accordingly, the execution of methods characterising flow paths within the patient's 16 respiratory airways, and for optionally determining one or more other respiratory parameters, by controller 19 according to these embodiments may include the steps of determining a pressure flow correlation between an airway pressure and a corresponding flow rate of gases at the patient (see Figures 7A to 7E), receiving a first input relating to a flow of gases provided to the patient 202, 304 (e.g., from a flow rate sensor 53A to 53D), determining a second input relating to a flow of gases at the nose 106 of the patient 16 (e.g., from a pressure sensor located in the system flow path [e.g. see Figure 1 and pressure sensors 53A to 53D] or a pressure sensor provided externally of the system flow path, and positioned in, at or proximate the patient's nose 106 [e.g. see Figures 6A to 6D]) 204, 306 based on the pressure flow correlation, and characterising one or more flow paths of delivered gases within the respiratory airways of the patient 16 based on the first input and the second input 206, 310.

[0317] In step 208 of the summary method 200, the controller 19 may optionally generate output to provide indications of the characterisation, for example audibly via audio messages or visually via a graphical user interface associated with the controller 19.Displaying the visual indications may include displaying the visual indications textually, numerically and / or graphically. In some embodiments, the visual indications may include LED output of any colour. Different colours may indicate different characterisations and / or respiratory parameters. For example, a green LED output may indicate that flow is being delivered to the patient, such as when the soft palate is open and / or the patient's inspiratorydemand is being met. A red LED output may indicate that flow is not being delivered, such as when the soft palate is closed. Other colours may be used to provide other appropriate indications.

[0318] The first input relating to a flow of gases provided to the patient may be received from one or more sensors 53A to 53D provided in the respiratory support system 10. In some embodiments, the first input may be a flow rate of the flow of gases provided to the patient 16. In some embodiments, the controller 19 may include a sensing module to sense the flow of gases provided to the patient 16. In some embodiments, the sensing module may be separate to the controller 19. In some embodiments, respiratory support system 10 may include a manual flow meter to provide the respiratory support separately to the controller 19. The supplied flow rate on the manual flow meter may be transmitted to the controller 19 to provide an indication of a flow rate of gases provided to the patient. In some embodiments the controller can determine the first input as a result of a user manually inputting the first input via the input interface 54.Determining Airway Pressure

[0319] As described herein, a number of different ways could be used to derive a suitable airway pressure value (Pm) which is representative of the true pressure value of the patient's airways. In some embodiments, a direct measurement of the airway pressure (Pm) may be conducted (to derive the calculated airway pressure (Pm)) as described below with reference to Figures 6A to 6D. In other embodiments, the airway pressure can be calculated (to derive the calculated airway pressure (Pm)) as described herein with reference to Figure 5C, based on a system pressure (Psys) measurement and a pressure difference (Prtf) downstream from the system pressure measurement.Non-sealing Patient Interface and Flow Sensing

[0320] Figures 6A to 6D illustrate example patient interface configurations including provision of a non-sealing patient interface in the form of a non-sealing nasal cannula 210 for providing an input flow of gases to the patient 16, and various sensor configurations and / or arrangements to measure a flow of gases at the patient to determine a directly measuredairway pressure (Pm) of the patient's airways. The controller may derive the calculated airway pressure from the directly measured pressure in, at or proximate the patient's airway.

[0321] As previously mentioned, the flow of gases at the patient may include a combination of patient flow (patient inspiration and expiration) and / or at least a portion of the flow of gases provided to the patient 16. Throughout the specification, the flow of gases at the patient may refer to a flow of gases at or proximate the nose, nares, nasal cavity, oropharynx or at any suitable location(s) within the patient's airways. Typically, 'a flow of gases at the nose of the patient' may refer to a flow of gases at or proximate the nose, nares, nasal cavity, oropharynx or any other suitable location(s) within the patient's nasal airways.

[0322] As mentioned, the first input may be a flow rate of the flow of gases provided to the patient 16 via the non-sealing nasal cannula 210. The first input may be known from the flow source 50 or controller 19 as this is typically a preset value by a clinician. Alternatively, or in combination, the first input may be received or calculated based on a flow sensor sensors 53A to 53D provided in the respiratory support system 10, as previously described.

[0323] The second input may be a flow rate of the flow of gases at the nose 106 of the patient 16. In relation to the second input, the flow of gases at the patient may be leaving or entering the patient at different respiratory phases (e.g. inspiration / expiration phase) of each respiratory cycle.

[0324] The second input can be determined based on a sensor input relating to a flow of gases at the nose 106 of the patient as provided by one or more sensor units positioned within or proximate either one or both of the patient's nares, integral to or separately from the patient interface 210, or elsewhere in the system 10 as previously discussed. In some embodiments, the one or more sensor units may be positioned elsewhere in the patient's airway, for example in the nasal cavity or the oropharynx. In some embodiments, the one or more sensor units may be positioned in one or both nares, adjacent one or both nares, in the nasal cavity, the oropharynx or in any other suitable location. In some embodiments, the one or more sensor units may be mounted to or separately provided and associated with one or both nasal prongs 214 of the nasal cannula 210. When two or more sensors are deployed, an average sensor value may be used by the controller 19.

[0325] More specifically, the one or more sensor units may measure a pressure (Pm) at the nose 106 of the patient 16. As such, the one or more sensor units may be pressure sensors. The measured pressure (Pm) is an airway pressure which may be measured from the patient's airways (e.g. at or adjacent nares 106). The airway pressure is associated with the flow of gases at the patient at different respiratory phases of each respiratory cycle. As such, the measured pressure (Pm) may be used to determine a flow rate of gases at the patient based on the pressure flow correlation as described herein with reference to Figures 7A to 7D. As discussed in further detail below with reference Figures 8A to 10B, the determined flow rate of gases at the patient (Qm) may be used in different methods to characterise the patient's flow path, and optionally determine one or more respiratory parameters.

[0326] In one embodiment, the one or more sensor units for determining the second input may be integrated with or mounted to the non-sealing patient interface 210. An example of such a patient interface 210 and sensor arrangement is described below with reference to Figures 6A and 6B.

[0327] As shown in Figure 6A, a non-sealing nasal cannula 210 may be mounted at the patient's nares 106 to deliver a flow of gases to the patient 16 from the flow source 50 of the respiratory support system 10 (input flow Qo, Qi). The flow rate of the input flow may be suitable for high flow respiratory support as described herein.

[0328] As described in further detail below, a pressure flow correlation is determined. As described, the input flow rate may be adjusted (e.g. incrementally) to obtain a pressure flow correlation during respiratory support e.g. prior to, or during, the commencement of a medical procedure. In some instances, the pressure flow correlation may be determined during a medical procedure. In some embodiments, the pressure flow correlation may be determined and refined or adjusted with additional data obtained during respiratory support. For the sake of clarity, the input flow rate is referred to as Qowhen used to determine the pressure flow correlation.

[0329] During respiratory support e.g. before or during the procedure, the input flow rate is further used in the characterisation of flow paths and optional determination of respiratory parameters. The input flow rate is referred to as Qi when used to provide respiratory support and used to characterise patient flow paths and respiratory parameters.

[0330] A sensor 212 such as a pressure sensor (or associated conduit) may be positioned within one of the patient's nasal passages, or at or near the opening of the nasal passage and typically outside the prongs of the nasal cannula 210 to measure airway pressure (Pm). Alternatively, the sensor 212 may be located in the nasal cavity or the oropharynx, or elsewhere in the patient's nasal airway. In some embodiments, the pressure sensor 212 may be mounted to an external surface of a nasal prong of the nasal cannula 210.

[0331] As more clearly shown in Figure 6B, the pressure sensor 212 (e.g. its associated sampling conduit) may be positioned in the patient's nasal passage (or elsewhere as previously discussed) adjacent the non-sealing patient interface 210. In particular, the pressure sensor 212 may be independent and separate to the non-sealing patient interface 210. In some embodiments, the pressure sensor 212 may be mounted or releasably mounted to the nasal cannula 210. For example, the pressure sensor 212 may be mounted or releasably mounted to a nasal prong 214 of the nasal cannula 210. In some embodiments, the pressure sensor 212 may be integrally formed with, or permanently attached to the nonsealing patient interface 210 e.g. as part of, or attached to, a nasal prong 214.

[0332] As described below with reference to Figures 7A to 7D, pressure measurements via pressure sensor 212 can be used to determine characteristic airway pressure values for determination of the pressure flow correlation. To characterise the patient's flow paths and optionally determine one or more respiratory parameters, the pressure measurements are used in conjunction with the pressure flow correlation to determine the flow rate of gases at the patient (Qm).

[0333] As described below with reference to Figures 6F and 7E, the characteristic airway pressure values and the pressure flow correlations can also be derived using calculated airway pressure values (Pm), where the calculated airway pressure values (Pm) are determined based on corresponding system pressure values (Psys) and pressure difference values (Prtf) downstream of the system pressure measurements.

[0334] To measure other respiratory parameters, such as O2 or CO2 fraction at the patient's nose and / or mouth, additional sensors or measurement apparatus 216, 218 may be provided at the patient 16 as illustrated in Figures 6C and 6D. In some embodiments, gas fraction sensors 216, 218 may be used to determine the concentration or proportion of agaseous species of interest. In some embodiments, the gas fraction sensors 216, 218 delivers gases to a sampling component or device e.g. a capnography machine. The gas sensor (e.g. sampling line) may be arranged at or adjacent the patient's nose and / or mouth.Pressure Flow Correlation

[0335] Embodiments of a method of determining the pressure flow correlation may be summarised as receiving one or more input flow rate values (Qo), each input flow rate (Qo) being a flow rate of gases provided to the patient 16 from a flow source 50; receiving, for each input flow rate value (Qo), a corresponding characteristic airway pressure value (Po); and determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the one or more received input flow rate values (Qo) and the corresponding one or more characteristic airway pressure values (Po). The relationship may be used to provide the pressure flow correlation.

[0336] Generally, the determined relationship between the one or more received input flow rate values (Qo) and the corresponding one or more characteristic airway pressure values (Po) also governs the relationship between the airway pressure and the flow rate of gases at the patient in the pressure flow correlation.

[0337] The input flow rate value (Qo) may be a flow rate value between about 0 to about 150 LPM, or between about 0 to about 90 LPM, or between about 0 to about 70 LPM, or between about 0 to about 50 LPM, or between about 0 to about 40 LPM, or between about 10 to about 90 LPM, or between about 20 to about 60 LPM, or between about 20 to about 50 LPM. The input flow rate value (Qo) may be a 'high flow' flow rate provided during high flow respiratory support.

[0338] In embodiments in which more than one input flow rate values (Qo) are provided, the input flow rate values (Qo) may be increased or decreased incrementally. As mentioned herein, the input flow rate (Qo) may be a time-varying flow rate, such as an oscillating flow rate. In these embodiments, changes in the input flow rate (Qo) value may be obtained at predetermined time intervals in the time-varying flow rate.

[0339] The predetermined range of input flow rate values may be a range of input flow rate values between about 0 to about 150 LPM, or about 0 to about 90 LPM, or about 0 toabout 70 LPM, or about 0 to about 50 LPM, or about 0 to about 40 LPM, or about 10 to about 90 LPM, or about 20 to about 60 LPM, or about 20 to about 50 LPM. The predetermined range of input flow rate values may be or include a 'high flow' flow rate provided during high flow respiratory support.

[0340] The first input may be indicative of an input flow rate of gases provided to the patient. The input flow rate of gases may be a flow rate value between about 5 to about 150 LPM, or between about 20 to about 90 LPM, or between about 40 to about 70 LPM. The input flow rate of gases may be a 'high flow' flow rate provided during high flow respiratory support. The second input may be indicative of a flow rate of gases at the nose of the patient.

[0341] A characteristic airway pressure as used herein specifically refers to an airway pressure of the patient when the patient flow is generally zero. Typically, the patient flow is generally zero when the patient is substantially not inspiring or expiring, for example as illustrated in regions 410, 414, 416, 412 of in the pressure curve in Figure 6E as discussed in further detail below. The characteristic airway pressure may be influenced by the anatomy of the patient's airway and is generally a different value for each patient. Moreover, the characteristic airway pressure typically changes with changes in the input flow rate (Qo).

[0342] In some embodiments, the characteristic airway pressure can be directly measured in, at or proximate the patient (e.g. using sensor 212). As described below with reference to Figure 6F, in some embodiments, the characteristic airway pressure can be calculated based on measurements of system pressure ( Psys) and the corresponding pressure difference (Prtf) downstream of the system pressure measurement, as described herein with reference to Figure 5C.

[0343] When receiving, for the input flow rate value, a corresponding characteristic airway pressure value, the patient's mouth is closed. When the patient's mouth is closed it is considered that the flow rate of gases provided to the patient substantially flows out of the patient's nose, and not the mouth. The patient's mouth may be ensured to be closed. The patient's mouth may be closed by a clinician or other health professional, or the patient may be instructed to close their mouth. In some embodiments, the patient's mouth closed condition may be detected by any suitable detection method, for example as described inPCT publication no. WO / 2024 / 180517 entitled "METHOD AND SYSTEM FOR CHARACTERISINGFLOW PATHS", the entire disclosure of which is incorporated herein by reference.

[0344] To estimate the characteristic airway pressure of a specific patient for a specific input flow rate (Qo), the controller 19 may analyse measured / calculated airway pressure values, or system pressure values from a pressure sensor located in the system flow path. For example, the controller 19 may analyse and determine a stable or consistent pressure value as indicative of the characteristic airway pressure, or an intermediate pressure value.

[0345] The pressure curve 400 illustrating changes in patient airway pressure during two example respiratory cycles are illustrated in Figure 6E. The pressure values of pressure curve 400 may be obtained from pressure sensor 212 configured to directly measure an airway pressure at, in or proximate the patient's nares, or from calculated airway pressure values over time as determined from system pressure measurements (as described above). Each respiratory cycle includes an inspiratory phase defining a peak inspiration pressure 402, 404, and an expiratory phase defining a peak expiration pressure 406, 408. The patient's flow may be considered as generally zero at various time periods throughout the respiratory cycles. For example, at transition regions 410, 412 when the patient 16 transitions from the inspiratory phase to the expiratory phase, at region 414 at or towards the end of the expiration phase (plateau pressure), and at region 416 where there may be a brief pause between consecutive breath cycles, it may be considered that the patient flow is generally zero, and a corresponding measured or calculated airway pressure value during these times may be indicative of a characteristic airway pressure (Po). Moreover, as the measured or calculated airway pressure values corresponding to the regions 410, 414, 416, 412 would be a generally stable and consistent value in the pressure curve, a controller may determine a most stable and / or consistent value in the patient airway pressure measurements as the characteristic airway pressure (Po).

[0346] In some embodiments, a breath pause 416 may include a breath hold. In particular, the patient may be instructed to intentionally hold their breath momentarily at any time during the patients respiratory cycle(s) to facilitate measurement of characteristic airway pressure(s) of the patient.

[0347] In one example, the controller 19 may determine a measured or calculated airway pressure value from the pressure sensor 212 as indicative of the characteristic airway pressure (Po) when the patient's flow is generally zero (e.g. a generally stable measured airway pressure value). In one example, the controller 19 may determine a calculated airway pressure (Pm), as determined from the system pressure measurement, as indicative of the characteristic airway pressure (Po) when the patient's flow is generally zero (e.g. a generally stable measured airway pressure value). This may include any one or more of a plateau pressure value, an airway pressure value during a breath pause, and an airway pressure value during a breath transition between inspiration and expiration.

[0348] In some embodiments, the controller 19 may calculate mean airway pressure value as indicative of the characteristic airway pressure (Po). More specifically, for each input flow rate value (Qo), a plurality of corresponding airway pressure values over one or more breath cycles may be measured by the pressure sensor 212 or derived from the system pressure (Psys) measurements, and a mean airway pressure value may be calculated over any one or more breath cycles. The mean airway pressure value would typically not be calculated based on any partial breath cycles (e.g. 0.5, 1.5 or 2.5 breath cycles), but a discrete number of whole breath cycles to more accurately determine the mean airway pressure value. Typically, the mean airway pressure value would be calculated over a minimum number of whole breath cycles, above which partial breath cycles may be used to contribute to calculation of the mean airway pressure value. In some embodiments, the minimum number of whole breath cycles may be 5 or 10 whole breath cycles. As the net total of the patient's inhaled flow and exhaled flow is generally zero, such a mean airway pressure value may be representative of when the patients flow is generally zero, and may be calculated to provide an indication of the characteristic airway pressure (Po).

[0349] Now referring to Figure 6F, which illustrates, for understanding, a stacked pressure waveforms plot 420 showing a system pressure waveform 430 offset from a calculated airway pressure waveform 432. Each of the pressure waveforms 430, 432 illustrating pressure changes during two respiratory cycles. For the calculated airway pressure waveform 432, this should be understood to correspond to the pressure curve 400 and like numerals refer to those previously described with reference to Figure 6E.

[0350] As previously described with reference to Figure 5C, the patient's airway pressure values may be calculated based on system pressure (Psys) values sensed using any one or more pressure sensors (e.g. 53A to 53D) located in the system flow path of the respiratory support system 10, and subtracting from it, a pressure difference (Prtf) due to flow resistance downstream of the corresponding pressure sensor(s). In some embodiments, the characteristic airway pressure (Po) may be calculated in a similar manner i.e. calculated similarly based on the calculated airway pressure (Pm) values.

[0351] As illustrated by system pressure (Psys) waveform 430 of Figure 6F, for a constant input flow rate (Qo), a sensed system pressure (Psys) exhibits pressure peaks 426, 428, each corresponding to a peak expiratory pressure of the patient's airway pressure; and pressure peaks 422, 424, each corresponding to peak inspiratory pressure of the patient's airway pressure. The system pressure waveform 430 also provides intermediate pressure values 434, 436, each corresponding to a transition pressure, plateau pressure, or a breath pause during which the patient's flow may be considered as generally zero at various time periods throughout the respiratory cycles. These intermediate pressure values (Po*), after subtracting the pressure difference (Prtf), may generally correspond to the characteristic airway pressure values (Po) of the patient.

[0352] As such, the system pressure (Psys) waveform 430 shows that the system pressure (Psys) is offset from corresponding patient airway pressure values (calculated airway pressure (Pm) values) by the pressure difference (Prtf) as illustrated for understanding in Figure 6F. In some embodiments, the system pressure (Psys) measurements may be used to derive the calculated patient airway pressure valves (as illustrated for understanding in waveform 432), including the characteristic airway pressure values (Po). For example, similar to the methods previously described with reference to Figure 6E, the controller 19 may determine a most stable and / or consistent value in the system pressure (Psys) measurements as the intermediate pressure value (Po*). Once the relevant intermediate pressure value (Po*) is determined by the controller 19, the controller 19 can proceed to determine a calculated characteristic airway pressure (Po) valve by subtracting the pressure difference (Prtf) :Po* - Prtf = Po

[0353] Some example methods of determining the pressure difference (Prtf) are described herein with reference to Figure 5C.

[0354] In another example, the controller 19 may determine a most stable and / or consistent value in the calculated airway pressure (Pm) values which corresponds to the characteristic airway pressure (Po).

[0355] As above, the characteristic airway pressure (Po) may correspond to a plateau pressure value, an airway pressure value during a breath pause, and / or an airway pressure value during a breath transition between inspiration and expiration. In some embodiments, the patient may be instructed to intentionally hold their breath momentarily at any time during the patients respiratory cycle(s) to facilitate determination of the characteristic airway pressure (Po).

[0356] In some embodiments, the controller 19 may calculate a mean calculated airway pressure as indicative of the characteristic airway pressure (Po). In some examples, the controller 19 may calculate a mean system pressure value (similar to the calculation of the mean airway pressure value as described with respect to Figure 6E) as indicative of the intermediate pressure value (Po*), and accordingly determine a calculated characteristic airway pressure (Po).

[0357] In some embodiments, any one or more of the above methods of determining characteristic airway pressure (Po) may be used in combination, and an average airway pressure value of the one or more determined characteristic airway pressures may be used as the characteristic airway pressure (Po).

[0358] As described in further detail below with reference to Figures 7A to 7E, the relationship between the input flow rate (Qo) and the corresponding characteristic airway pressure (Po) may be determined in any suitable manner, for example using linear or nonlinear regression (linear / non-linear fitted curves or a piecewise combination of fitted curves), based on a library of predetermined correlations, or by determining an equation that generally governs the relationship.Flow Sweep

[0359] A first method 220 of determining the pressure flow correlation according to one embodiment will now be described with reference to Figure 7A.

[0360] In summary, the first method 220 may include receiving a plurality of input flow rate values (Qo), each input flow rate (Qo) being a flow rate of gases provided to the patient 16 from a flow source 50; receiving, for each input flow rate value (Qo), a corresponding characteristic airway pressure value (Po); and determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the plurality of input flow rate values (Qo) and corresponding characteristic airway pressure values (Po).

[0361] Prior to execution of the method 220, at step 222 a non-sealing patient interface 210 is mounted to the patient 16 to provide an input flow rate (Qo) of gases to the patient 16.

[0362] At step 224, an input flow rate (Qo) (e.g. initially at 0LPM or another initial flow rate value, and increasing across a predetermined range or initially at a maximum flow rate and decreasing across a predetermined range) may be set via controller 19 such that the flow source 50 provides an input flow of gases to the patient 16 (e.g. to the non-sealing patient interface 210) at the input flow rate (Qo). The increase and / or decrease in flow rate across a predetermined range may be incremental, obtained at various time intervals when a timevarying input flow rate is provided.

[0363] At step 226, the patient 16 may be instructed or otherwise ensured to be in a mouth closed condition during the execution of the method 220 so that all flow exits via the patient's nose 106. In some embodiments step 226 may be carried out prior to step 224, or prior to step 222.

[0364] At step 228, the controller 19 receives pressure sensor 212 or one or more of 53A to 53D measurements continuously. In some embodiments, pressure sensor 212 may be measuring the patient's airway pressure in the nasal passage. Alternatively, pressure sensor (e.g. 53A to 53D) may sense a system pressure (Psys) from which a calculated airway pressure can be determined as described. Throughout the specification, obtaining of sensor measurements continuously means substantially continuously. The frequency of sensor measurement samples may be high enough to substantially and accurately capture abreathing waveform. For example, a sampling frequency of 5 Hz or higher may be used. More specifically, a sampling frequency of 10 Hz, or 20 Hz, or 50 Hz may be used.

[0365] At step 230, for the set input flow rate value (Qo) from step 224, the controller determines a corresponding characteristic airway pressure value (Po) as described herein with reference to Figures 6E and 6F.

[0366] At step 232, the input flow rate (Qo) is adjusted (e.g. increased or decreased, or obtained at a different time interval of an input gas flow having a time varying flow rate) and the method 220 returns to step 224 to determine another corresponding characteristic airway pressure value (Po) for the adjusted input flow rate (Qo). Adjustment of the input flow rate (Qo) may be incremental. Adjustment may be in 5 LPM or 10 LPM or 20 LPM increments.

[0367] The method executes steps 224 to 232 until a corresponding characteristic airway pressure value (Po) is measured for each input flow rate (Qo) in a predetermined range.

[0368] At step 234, a relationship between the plurality of input flow rate values (Qo) and the corresponding range of characteristic airway pressure values (Po) may be determined. For example, based on regression analysis. For example, a linear or non-linear best fit curve or an equation may be determined based on the plurality of input flow rate values (Qo) and the corresponding range of characteristic airway pressure values (Po). The relationship (e.g. the best fit curve or equation as illustrated in graph 236) may be used to provide the pressure flow correlation.Two-points

[0369] A second method 240 of determining the pressure flow correlation according to one embodiment will now be described with reference to Figure 7B.

[0370] In summary, the second method 240 may include receiving two input flow rate values (Qo), each input flow rate (Qo) being a flow rate of gases provided to the patient; receiving, for each input flow rate value (Qo), a corresponding characteristic airway pressure value (Po); and determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the two input flow rate values (Qo) and the corresponding two characteristic airway pressure values (Po).

[0371] Whilst not shown in Figure 7B, a non-sealing patient interface 210 is mounted to the patient 16 to provide an input flow rate (Qo) of gases to the patient 16 prior to the execution of the method 240.

[0372] At step 242, an input flow rate (Qo) (e.g. initially at 0LPM or another initial flow rate value, and increasing or initially at a maximum flow rate and decreasing) may be set via controller 19 such that the flow source 50 provides an input flow of gases to the patient 16 (e.g. to the non-sealing patient interface 210) at the input flow rate (Qo).

[0373] At step 244, the patient 16 may be instructed or otherwise ensured to be in a mouth closed condition during the execution of the method 200 so that all flow exits via the patient's nose 106. In some embodiments, step 244 may be carried out prior to step 242.

[0374] At step 246, the controller 19 receives pressure sensor 212 or one or more of 53A to 53D measurements continuously. Pressure sensor 212 may be measuring the patient's airway pressure in the nasal passage. Alternatively, pressure sensor (e.g. 53A to 53D) may sense a system pressure (Psys) from which a calculated airway pressure can be determined.

[0375] At step 248, for the set input flow rate value (Qo) from step 224, the controller determines a corresponding characteristic airway pressure value (Po) as described herein with reference to Figures 6E and 6F.

[0376] At step 250, the input flow rate (Qo) is adjusted to a second setpoint value (e.g. increased or decreased, or obtained at a different time interval of an input gas flow having a time varying flow rate) and the method 240 returns to step 242 to determine another corresponding characteristic airway pressure value (Po) for the second input flow rate (Qo) -

[0377] The method executes steps 242 to 250 until a corresponding characteristic airway pressure value (Po) is measured for optionally an input flow rate (Qo) of zero and two additional setpoint input flow rate values (see graph 254).

[0378] At step 252, a relationship between the plurality of input flow rate values (Qo) and the corresponding range of characteristic airway pressure values (Po) may be determined. For example, based on regression analysis. More specifically, a linear or nonlinear best fit curve or an equation may be determined based on the plurality of input flowrate values (Qo) and the corresponding range of characteristic airway pressure values (Po).The relationship (e.g. the best fit curve or equation, as illustrated in graph 254) may be used to provide the pressure flow correlation.Single point and predetermined library

[0379] A third method 260 of determining the pressure flow correlation according to one embodiment will now be described with reference to Figure 7C.

[0380] In summary, the third method 260 may include receiving a single input flow rate value (Qo) being a flow rate of gases provided to the patient; receiving, for the input flow rate value (Qo), a corresponding characteristic airway pressure value (Po); and determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on a predetermined pressure flow correlation corresponding to the single input flow rate value (Qo) and the corresponding characteristic airway pressure value (Po), wherein the predetermined pressure flow correlation is selected from a library of predetermined pressure flow correlations.

[0381] Whilst not shown in Figure 7C, a non-sealing patient interface 210 is mounted to the patient 16 to provide an input flow rate (Qo) of gases to the patient 16 prior to the execution of the method 260.

[0382] At step 262, an input flow rate (Qo) (e.g. initially at 0LPM, and increasing to a setpoint flow rate value or initially at a setpoint flow rate value and decreasing to 0, or alternatively any single setpoint flow rate value) may be set via controller 19 such that the flow source 50 provides an input flow of gases to the patient 16 (e.g. to the non-sealing patient interface 210) at the input flow rate (Qo).

[0383] At step 264, the patient 16 may be instructed or otherwise ensured to be in a mouth closed condition during the execution of the method 260 so that all flow exits via the patient's nose 106. In some embodiments, step 264 may be carried out prior to step 262.

[0384] At step 266, the controller 19 receives pressure sensor 212 or one or more of 53A to 53D measurements continuously. Pressure sensor 212 may be measuring the patient'sairway pressure in the nasal passage. Alternatively, pressure sensor (e.g. 53A to 53D) may sense a system pressure (Psys) from which a calculated airway pressure can be determined.

[0385] At step 268, for the set input flow rate value (Qo) from step 262, the controller determines a corresponding characteristic airway pressure value (Po) as described herein with reference to Figures 6E and 6F.

[0386] At optional step 270, the input flow rate (Qo) can be adjusted to the single setpoint value or from the single setpoint value to 0 and the method 260 returns to step 262 for one more iteration to determine another corresponding characteristic airway pressure value (Po) for the adjusted input flow rate (Qo).

[0387] At step 272, the controller 19 searches within a library 276 of predetermined pressure flow correlations 276 and selects a predetermined pressure flow correlation 278 that corresponds to the input flow rate value(s) (Qo) and corresponding characteristic airway pressure value(s) (Po) (see graph 275).

[0388] At step 274, a relationship between the input flow rate value(s) (Qo) and the corresponding characteristic airway pressure value(s) (Po) may be determined based on the selected predetermined pressure flow correlation from the library, as illustrated in graph 275. The relationship may be used to provide the pressure flow correlation.Single point

[0389] A fourth method 280 of determining the pressure flow correlation according to one embodiment will now be described with reference to Figure 7D.

[0390] In summary, the fourth method 280 may including receiving a single input flow rate value (Qo) being a flow rate of gases provided to the patient; receiving, for the input flow rate value (Qo), a corresponding characteristic airway pressure value (Po); and determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the single input flow rate value (Qo) and the corresponding characteristic airway pressure value (Po).

[0391] Moreover, the single input flow rate value (Qo) may be a non-zero single input flow rate value. Determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient may include determining the relationship based on an input flow rate of zero and the corresponding characteristic airway pressure value (Po), and the non-zero single input flow rate value and the corresponding characteristic airway pressure value.

[0392] Whilst not shown in Figure 7D, a non-sealing patient interface 210 is mounted to the patient 16 to provide an input flow rate (Qo) of gases to the patient 16 prior to the execution of the method 280.

[0393] At step 282, an input flow rate (Qo) (e.g. 0LPM or a setpoint input flow rate value) may be set via controller 19 such that the flow source 50 provides an input flow of gases to the patient 16 (e.g. to the non-sealing patient interface 210) at the input flow rate (Qo).

[0394] At step 284, the patient 16 may be instructed or otherwise ensured to be in a mouth closed condition during the execution of the method 200 so that all flow exits via the patient's nose 106. In some embodiments, step 284 may be carried out prior to step 282.

[0395] At step 286, the controller 19 receives pressure sensor 212 or one or more of 53A to 53D measurements continuously. Pressure sensor 212 may be measuring the patient's airway pressure in the nasal passage. Alternatively, pressure sensor (e.g. 53A to 53D) may sense a system pressure (Psys) from which a calculated airway pressure can be determined.

[0396] At step 288, for an input flow of 0LPM or the set input flow rate value (Qo) from step 282, the controller determines a corresponding characteristic airway pressure value (Po) as described herein with reference to Figures 6E and 6F.

[0397] At step 290, the input flow rate (Qo) is adjusted to the other of: 0LPM or the single setpoint value, and the method 280 returns to step 282 for a second iteration to determine another corresponding characteristic airway pressure value (Po) for the adjusted input flow rate (Qo). In some embodiments, if the input flow rate (Qo) is a setpoint input flow rate value at step 282 (e.g. non-zero value), a predetermined pressure value may be used for the corresponding characteristic airway pressure value (Po) when the input flow rate (Qo) is 0LPM. In these embodiments, step 290 may be optionally omitted.

[0398] At step 292, a relationship between the input flow rate value(s) (Qo) and the corresponding range of characteristic airway pressure value(s) (Po) may be determined. For example, based on regression analysis. For example, a linear or non-linear best fit curve or an equation may be determined based on the input flow rate value(s) (Qo) and the corresponding characteristic airway pressure value(s) (Po). The relationship (e.g. the best fit line or equation, as illustrated in graph 294) may be used to provide the pressure flow correlation.

[0399] As mentioned, a single non-zero input flow rate (Qo) and its corresponding characteristic airway pressure (Po) may be used to determine a relationship between the range of input flow rate value(s) (Qo) and the corresponding range of characteristic airway pressure value(s) (Po) in step 292 (e.g. without a corresponding characteristic airway pressure (Po) measurement or calculation at an input flow rate of OLPM).

[0400] It will be understood that, as described herein, the controller 19 may determine the characteristic airway pressure (Po) in steps 230, 248. 268, 288 in any suitable manner. For example, if the respiratory support system 10 includes a pressure sensor 212 configured to directly measure the patient's airway pressure, the controller 19 may determine the characteristic airway pressure (Po) as described herein with reference to Figure 6E. If the respiratory support system 10 includes a pressure sensor (e.g. 53A to 53D) configured to measure a system pressure (Psys) in the system flow path of the respiratory support system 10, the controller 19 may determine the characteristic airway pressure (Po) as described herein with reference to Figure 6F.

[0401] Now referring to Figure 7E, in which a relationship between characteristic airway pressure (Po) and corresponding intermediate pressure (Po*) from system pressure (Psys) measurements is illustrated for understanding. As the pressure difference (Prtf) downstream of the pressure sensor (e.g. 53A to 53D) in the system flow path varies based on the input flow rate (Qo), a corresponding pressure difference (Prtf) may be known or determined for the flow rate at which each intermediate pressure (Po*) value is determined. The pressure difference (Prtf) may vary linearly or non-linearly with different input flow rates (Qo). In the specific example shown in Figure 7E, the pressure difference ( Prtf) increases as input flow rate (Qo) increases. As such, and as described with respect to Figure 6F, the controller 19 maydetermine the characteristic airway pressure (Po) for a given input flow rate based on the corresponding intermediate pressure (Po*) value, and subtracting from the intermediate pressure (Po*) value a corresponding pressure difference (Prtf) at the given input flow rate.

[0402] It will be appreciated that other suitable methods of determining a pressure flow correlation may be used. The regression analysis discussed above in relation to methods 210, 240 and 280 may provide a linear or non-linear correlation based on a linear, quadratic or higher order polynomial, or any other correlation.

[0403] Moreover, the pressure flow correlation may be updated, adjusted or refined as additional data points are collected by the controller 19 during provision of respiratory support. For example, the pressure flow correlation can be updated during provision of respiratory support therapy or any other suitable time. For any given input flow rate (Qo), a characteristic airway pressure (Po) may be determined (e.g. as described herein with reference to Figures 6E and 6F), and new Qoand Povalues may be added to the existing pressure flow correlation datapoints or replace existing Qoand Povalues in the dataset for regression analysis. Thus, this process may be carried out if the input flow rate (Qo) is changed during respiratory support.

[0404] Initiation of a pressure flow correlation determination by the controller 19 may be triggered by a user command, which may be issued via interaction with a user interface of a device (e.g. the controller 19 or a separate device in communication with the controller 19), such as by actuating a button or selecting an area on a graphical user interface (GUI). This initiation may typically occur at the commencement of respiratory support, to determine an initial pressure flow correlation prior to a procedure. During the procedure, characterisation of flow paths and, optionally, determination of respiratory parameters, as described in further detail below, may be performed. Alternatively, the pressure flow correlation may be determined during the provision of respiratory support.

[0405] In some embodiments, the pressure flow correlation may be automatically determined upon activation of the flow source 50 and controller 19, and / or upon configuration of an input flow rate (Qo) intended for delivery to the patient.

[0406] Prior to initiating the pressure flow correlation determination routine, the user may ensure that the patient's mouth is closed. Alternatively, the controller 19 may prompt the user to confirm that the patient's mouth is closed either following the user's selection to initiate the pressure flow correlation determination or during any of the automatic determination routines described.

[0407] The user may also provide an explicit input to the controller 19 indicating that the patient's mouth is closed, for example, by selecting a designated button or GUI region. Upon receipt of such input, the controller 19 may proceed to initiate any of the described pressure flow correlation determination routines.

[0408] In some embodiments, the pressure flow correlation may be affected if the patient changes position or if the position of the non-sealing patient interface 210 is adjusted. In these cases, a pressure flow correlation determination may be repeated using any one or more of the methods described herein e.g. if the patient changes position, e.g. the controller 19 may execute any one or more of the methods described herein to determine a new pressure flow correlation in response to a user command such as a button press and / or touch screen interaction.Characterisation of Flow Paths and Determination of Respiratory Parameters

[0409] Figure 8A illustrates a method 300 of characterising flow paths within the patient's 16 respiratory airways, and for optionally determining one or more other respiratory parameters in accordance with the method summaries 200, 301 as previously described with reference to Figures 5A and 5B, as executed by the controller 19. Figure 8A illustrates method steps 310 to 332 for characterising flow paths and optionally determining one or more other respiratory parameters based on the first input Q (t) and the second input (Qm(t)) at least over a full respiratory cycle of the patient 16.

[0410] When the non-sealing patient interface 210 (Figures 6A &6B) is used, the controller 19 is operatively configured to receive a first input (Qi(t)) indicative of an input flow rate of gases 100 provided to and via the non-sealing patient interface 210 to the nose 160 of the patient 16.

[0411] A measured or calculated patient airway pressure (Pm) from sensor 212 or calculated patient airway pressure (Pm) based on sensed system pressure (Psys) and a corresponding pressure difference (Prtf) can be used in conjunction with the determined pressure flow correlation (e.g. in accordance with methods 220, 240, 260, 280 as described herein) to determine a second input (Qm(t)) indicative of a flow rate of gases at the patient 16. In other words, for a patient airway pressure (Pm) (either measured using sensor 212 or calculated based on Psys and Prtf), the pressure flow correlation can be used to determine a corresponding flow rate value. The determined corresponding flow rate value may be used as the second input (Qm(t)).

[0412] The controller 19 is operatively configured to characterise one or more flow paths of delivered gases 100 within the respiratory airways of the patient 16 based on a comparison of the first input (Q (t)) and the second input (Qm(t)) .

[0413] At step 310, the controller 19 receives the first input Q (t), and the second input (Q.m(t)) at least over a full respiratory cycle of the patient 16.

[0414] At query step 312, the controller 19 determines whether the second input (Qm(t)) is greater than the first input (Qj(t)) at any point over the full respiratory cycle. If not, the method 300 proceeds to step 314. If so, the method proceeds to step 326.

[0415] At step 314, the controller 19 determines a mouth open condition associated with the patient 16.

[0416] Once the controller 19 determine a mouth open condition, the controller 19 can determine a numerical value indicative of a proportion of delivered gases passing through the mouth or nose. The controller can determine a numerical value (k) indicative of a proportion of delivered gases passing through the mouth based on equation [1] below.whereinQj(t) is the first input indicative of an input flow rate of gases 100 provided to a non-sealing patient interface (e.g. 210), andQm(t) is the second input determined based on the airway pressure (Pm) at the patient and the pressure flow correlation discussed above. Qm(t) is indicative of a flow rate of gases at the nose of the patient 16.

[0417] The calculation of k is also described with respect to further details of the method 300 as set out in Figure 10A.

[0418] At query step 316, the controller 19 determines if the first input Qj(t) substantially equals the second input Qm(t) consistently over the full respiratory cycle. If so, the method 300 proceeds to step 318. If not, the method 300 proceeds to step 319.

[0419] At step 318, the method determines a mouth open condition and a nasal passage obstructed (e.g. soft palate closed) condition associated with the patient 16. The graph in Figure 9E illustrates a comparison between the first input Q (t) and the second input Qm(t) over a full respiratory cycle of the patient 16 when the patient's mouth is open, and soft palate is closed.

[0420] At step 319, the method 300 determines a mouth open condition and a nasal passage not obstructed (e.g. soft palate open) condition associated with the patient 16. The graphs in Figures 9A and 9B provide example traces illustrating the flow path characterisation as determined in this step.

[0421] As shown in Figure 9A, the second input Qm(t) is consistently less than the first input over a full respiratory cycle. As illustrated in Figure 9B, the second input Qm(t) is also consistently less than the first input Qj(t) over the full respiratory cycle. Figure 9A may illustrate an example waveform for the second input second input Qm(t) for one patient when the first input Q (t) is about 70 (l / min), and Figure 9B may illustrate an example waveform for the second input second input Qm(t) for another patient when the first input Qj(t) is about 10 (l / min). In both Figures 9A and 9B, the example waveforms illustrate the flow path determination of step 319 in which the patient's mouth is open and soft palate is open.

[0422] At step 326, the controller 19 determines a mouth closed condition (if the second input Qm(t) is greater than the first input Qj(t) at any point over the full respiratory cycle as determined in query step 312).

[0423] Once the controller 19 determines that the patient's mouth is closed, one or more other respiratory parameters may be determined. For example, the controller 19 may determine an expired fraction of CO2 (FEco2) of the exhaled gas flow associated with the patient 16. The controller 19 may receive a third input Fm_nose_co2 (t) indicative of a measured fraction of CO2 at the nose of the patient. The respiratory support system 10 may provide a gas sampling sensor 14 proximate the patient's nose to measure the third input Fm_nose_co2 (t) (also see sensor 218 in Figure 6D). In particular, the controller 19 may determine an expired fraction of CO2 (FEco2) based on equation [2] below:whereinQj(t) is the first input indicative of an input flow rate of gases 100 provided via the non-sealing patient interface (e.g. 210),Qm(t) is the second input determined based on the airway pressure (Pm) at the patient and the pressure flow correlation discussed above. Qm(t) is indicative of a flow rate of gases at the nose of the patient 16, andFm_nose_co2 (t) is the third input indicative of a measured fraction of CO2 in the composite gas outflow at the non-sealing patient interface (e.g. 210). The third input may be obtained from sensor measurements of one or more sensor units provided by, mounted to or proximate the non-sealing patient interface 210 such as sensors 216, 218 in Figures 6B and 6C, or provided elsewhere in the system 10.

[0424] The composite gas outflow of the patient is the leak gas flow combined with the exhaled (or expired) gas flow of the patient 16. In the FE^determination of equation [2], the exhaled gas flow, leak gas flow and thus, the composite gas outflow are substantially passing out of the nose of the patient 16, as the mouth is closed.

[0425] At query step 328, the controller 19 determines if the second input Qm(t) is consistently greater than zero during the respiratory cycle. If so, the method 300 proceeds to step 330. If not, the method 300 proceeds to step 332.

[0426] At step 330, the controller 19 determines a mouth closed condition, a nasal passage not obstructed (e.g. soft palate open) condition, and that the input flow rate of gases exceeds inspiratory demand. The graph in Figure 9C illustrates a comparison between the first input Q (t) and the second input Qm(t) over a full respiratory cycle of the patient 16 when the patient's mouth is closed, the soft palate is open, and the input flow rate of gases exceeds inspiratory demand. As illustrated in Figure 9C the second input Qm(t) exceeds the first input Q (t) during the expiration phase of the respiratory cycle and the second input Qm(t) is consistently greater than zero during the respiratory cycle.

[0427] At step 332, the controller 19 determines a mouth closed condition, a nasal passage not obstructed (e.g. soft palate open) condition, and that the input flow rate of gases does not meet inspiratory demand. The graph in Figure 9D illustrates a comparison between the first input Q (t) and the second input Qm(t) over a full respiratory cycle of the patient 16 when the patient's mouth is closed, the soft palate is open, and the input flow rate of gases does not meet inspiratory demand. As illustrated in Figure 9D the second input Qm(t) exceeds the first input Qj(t) during the expiration phase of the respiratory cycle and the second input Qm(t) drops below zero during the inspiration phase of the respiratory cycle.

[0428] After method steps 314, 326, 318, 319, 330 and 332, the method 300 may return to step 310 to measure / determine the first input second input Q (t) and second input Qm(t) for the next respiratory cycle so as to provide continuous patient monitoring.

[0429] In some of the embodiments, it may be desirable for the controller 19 to determine the respiratory phase of the patient (e.g. whether the patient is in an inspiration, an expiration phase of a respiratory cycle or a transition between the inspiration phase and expiration phase (e.g. during which the patient flow is zero)). The respiratory phase can be determined using any suitable manner. For example, using a sensor to measure a proportion of a gas species such as CO2 at the patient's mouth or nose. In these embodiments, a measured proportion of CO2 at the patient that is greater than the proportion of CO2 in ambient air may indicate that the patient is in an expiration phase). In other non-limiting examples, an ECG or respiratory torso band could be used. In some embodiments, the controller 19 may determine the respiratory phase (e.g. inspiration, expiration or transition between inspiration and expiration) based on input from one or more of the above sensors.For example, pressure measurements from sensor 212 as described herein with reference to Figures 6A to 6D may be used to determine the respiratory phase. In one embodiment, once the plateau pressure 414 (see Figure 6E) is determined, a pressure measurement above the plateau pressure 414 may correspond with an expiratory phase and a pressure measurement below the plateau pressure 414 may correspond with an inspiratory phase. Similarly, pressure measurements from one or more pressure sensors (e.g. 53A to 53D) provided in the system flow path of the respiratory support system 10 may be used to determine the respiratory phase (e.g. see Figure 6F). In another embodiment, the controller 19 may receive direct input (e.g. from another processor) indicative of a determined respiration phase.

[0430] In some embodiments, in relation to the calculation of an expired fraction of CO2 asdescribed herein, the controller 19 may determine when the patient is in an expiration phase of a respiratory cycle before calculating the expired fraction of CO2 (FEco2)- In some embodiments, the controller 19 may calculate a value for the expired fraction of CO2 (FECO2)atany time, or continuously throughout one or more respiratory cycles of the patient 16. A value for the expired fraction of CO2 (FEco2) during an inspiratory phase may be substantially zero.

[0431] Figure 8B illustrates a method 360 of characterising flow paths within the patient's 16 respiratory airways, and for optionally determining one or more other respiratory parameters in accordance with the method summaries 301, as executed by the controller 19. Figure 8B illustrates method steps 310 to 332 for characterising flow paths and optionally determining one or more other respiratory parameters based on one or more sample (discrete) measurements / values for first input Q (t) and the second input (Qm(t)). The sample measurements / values for first input Q (t) and the second input (Qm(t)) may be taken at any point in time during a respiratory cycle of the patient 16. The measurements may be sampled at any suitable frequency. For example, the measurements may be sampled at a frequency that is less than or greater than a breathing frequency of the patient.

[0432] At step 362, the controller 19 receives one or more sample measurements / values for the first input Q (t), and the second input (Qm(t)) at any point(s) in time during a respiratory cycle of the patient 16. Values for first input Q (t), and the second input (Qm(t)) may be sampled / determined concurrently such that for a given sampling time interval, asampled value for the first input Q (t) has a corresponding sampled / determined value for the second input (Qm(t)).

[0433] At query step 364, the controller 19 determines whether the second input (Qm(t)) is greater than the first input (Q (t)). If not, the method 360 proceeds to step 368. If so, the method 360 proceeds to step 366.

[0434] At step 366, the controller 19 determines a mouth closed condition associated with the patient 16. The controller 19 may further determine that the patient is in an expiratory phase of a respiratory cycle, and / or that the nasal passage of the patient 16 is not obstructed. As illustrated in Figures 9C and 9D, the second input Qm(t) exceeds the first input Qj(t) during the expiration phase of the respiratory cycle, when the patient's mouth is closed, and the nasal passage is not obstructed.

[0435] At query step 368, the controller 19 determines if the sampled / determined value for the first input Q (t) substantially equals the corresponding sampled / determined value for the second input Qm(t). If so, the method 360 proceeds to query step 370. If not, the method 368 proceeds to step 376.

[0436] At query step 370, the controller 19 may calculate a gradient of two or more sampled / determined values for the second input Qm(t). In some embodiments, if a timevarying first input Q (t) is provided, the controller 19 may calculate a gradient of two or more sampled / determined values for the second input Qm(t) minus the first input Q (t) (that is, the gradient of Qm(t) - Q (t)) . Typically, the two or more sampled / determined values are sampled at a frequency that is greater than a breathing frequency of the patient. In other words, the two or more values are generally taken within the same respiratory cycle. If the gradient is non- zero, the method 360 proceeds to step 372. If the gradient is substantially zero, the method 360 proceeds to step 374.

[0437] At step 372, the controller 19 may determine a breath paused condition. The controller 19 may further determine a mouth closed condition. As illustrated in Figures 9C and 9D, the second input Qm(t) intersects with the first input Q (t) momentarily when the patient is between the expiration phase and the inspiratory phase of the respiratory cycle, when the patient's mouth is closed. At this intersection, the gradient of Qm(t) is non-zero. Itmay be considered that the patient's breath is momentarily paused between the expiration phase and the inspiratory phase of the respiratory cycle.

[0438] At step 374, the controller 19 may determine a nasal passage obstructed (e.g. soft palate closed) condition. As illustrated in Figure 9E, the second input Qm(t) consistently equals first input Q (t), when the patient's nasal passage obstructed (e.g. soft palate closed). The value for the second input Qm(t) also remains constant through the respiratory cycle. As such, the gradient of Qm(t) is substantially zero when the patient's nasal passage obstructed (e.g. soft palate closed).

[0439] At query step 376, the controller 19 determines whether the sampled value for the second input Qm(t) is greater than 0. If so, the method 360 proceeds to query step 378. If not, the method 360 proceeds to step 382.

[0440] At query step 378, the controller 19 determines whether the patient is expiring. This may be determined according to any known suitable manner, for example as described herein. If the controller 19 determines that the patient is expiring, the method 360 proceeds to step 380. If the controller 19 determines that the patient is not expiring, the method 360 proceeds to step 384.

[0441] At step 380, the controller 19 may determine a mouth open condition. In addition, the controller 19 may determine a nasal passage not obstructed (e.g. soft palate open) condition. As illustrated in Figures 9A and 9B, first input Qj(t) exceeds the second input Qm(t), and the second input Qm(t) is greater than zero during the expiration phase of the respiratory cycle, when the patient's mouth is open, and the nasal passage is not obstructed.

[0442] At step 384, the controller 19 may determine a nasal passage not obstructed (e.g. soft palate open) condition. As illustrated in Figures 9A, 9B, 9C and 9D, during an inspiratory phase, at least some values for the second input Qm(t) are greater than zero and less than the corresponding values for the first input Qj(t) . As such, further measurements / determinations of the first input Q (t) and the second input Qm(t) over at least an entire respiratory cycle would be required to make any further characterisations at this step, for example as described above with reference to method 300.

[0443] At step 382, the controller 19 may determine a mouth closed condition. The controller 19 may further determine an inspiratory phase condition indicating that the patient is inspiring. Moreover, the controller 19 may determine that an inspiratory demand of the patient is not met. As illustrated in Figure 9D, for a least some values of the second input Qm(t) during the inspiratory phase, the second input Qm(t) is less than zero and less than corresponding values for the first input Qj(t), when the patient's mouth is closed and the inspiratory demand of the patient is not met.

[0444] After method steps 366, 372, 374, 380, 384 and 382, the method 360 may return to step 362 to take one or more subsequent sample measurements for the first input Q (t) and second input Qm(t) so as to provide continuous patient monitoring.

[0445] Now reverting to the method 300, the controller 19 may be operatively configured to determine one or more other respiratory parameters. The determination of one or more other respiratory parameters will now be described in further detail below with reference to Figure 10A. Figure 10A illustrates method steps 310 to 342 for determining one or more other respiratory parameters based on measurements / determinations for first input Qj(t) and the second input (Qm(t)) at least over a full respiratory cycle of the patient 16.

[0446] Steps 310, 312, 314 and 326 of method 300 as shown in Figure 10A are the same as those previously described with reference to Figure 8A.

[0447] At step 315, the controller 19 determines whether the patient is in an expiratory phase. The determination of the patient's respiratory phase may be based on known sensing techniques, for example as described herein. If the controller 19 determines that the patient is in an expiratory phase, the method 300 proceeds to step 334. If not, the method 300 returns to step 310.

[0448] In steps 334 and 336, the controller 19 determines that a numerical value (k) indicative of a proportion of delivered gases passing through the mouth is greater than zero (k>0). The controller may further calculate the specific numerical value (k) based on equation [1] above.

[0449] At step 326, the method determines a mouth closed condition and the controller 19 can determine a numerical value (k) indicative of a proportion of delivered gases passing through the mouth to be zero ( k=0 when mouth is closed).

[0450] Once the controller 19 has determined a mouth closed condition associated with the patient 16 in accordance with query step 326, the controller 19 may perform calculations to determine a tidal volume associated with the patient in accordance with steps 338, 340 and 342 as described below.

[0451] At query step 338, the controller 19 determines whether the patient 16 is currently in an expiration phase of a respiratory cycle. If so, the method 300 proceeds to step 340. If not, the method 300 proceeds to step 342. The controller 19 may determine whether the patient 16 is in an expiration phase of a respiratory cycle in any suitable matter, for example as previously described. In some embodiments, the controller 19 may be operatively configured to receive sensor input from measuring a proportion of CO2 at the patient's mouth or nose, an ECG, or respiratory torso band and determine a respiratory phase (e.g. inspiration, expiration or transition between inspiration and expiration) based on the sensor input. In another embodiment, the controller 19 may receive information directly indicative of a determined respiratory phase from another processor. Other known methods for determining a respiratory phase may be used.

[0452] At step 340, the controller 19 has determined that the patient 16 is in an expiration phase of a respiratory cycle. The controller 19 may then determine a tidal volume (VT) associated with the patient 16 based on an expiratory flow rate of gases at the patient 16 Qp_exp(t) in accordance with equation [3] below:whereinQj(t) is the first input indicative of an input flow rate of gases 100 provided via a non-sealing patient interface (e.g. 210),Qm(t) is the second input determined based on the airway pressure (Pm) at the patient and the pressure flow correlation discussed above. Qm(t) is indicative of a flow rate of gases at the nose of the patient 16, andQp_exp(t) is a flow rate of gases at the patient during an expiration phase of a respiratory cycle.

[0453] The integral in equation [3] is calculated across the expiration phase to determine the tidal volume.

[0454] At step 342, the controller 19 has determined that the patient 16 is in an inspiration phase of a respiratory cycle. The controller 19 may then determine a tidal volume (VT) associated with the patient 16 based on an inspiratory flow rate of gases at the patient 16 Qpjns(t) in accordance with equation [4] below:whereinQj(t) is the first input indicative of an input flow rate of gases 100 provided via a non-sealing patient interface (e.g. 210),Qm(t) is the second input determined based on the airway pressure (Pm) at the patient and the pressure flow correlation discussed above. Qm(t) is indicative of a flow rate of gases at the nose of the patient 16, andQpjns(t) is a flow rate of gases at the patient during an inspiration phase of a respiratory cycle.

[0455] The integral in equation [4] is calculated across the inspiration phase to determine the tidal volume.

[0456] After method steps 336, 340, 342, the method 300 may return to step 310 to measure / determine the first input second input Q (t) and second input Qm(t) for the next respiratory cycle so as to provide continuous patient monitoring.

[0457] Now reverting to the method 360, the controller 19 may be operatively configured to determine one or more other respiratory parameters. The determination of one or more other respiratory parameters will now be described in further detail below with reference to Figure 10B. Figure 10B illustrates method steps 362 to 398 determining one or more other respiratory parameters based on one or more sample measurements / determinations for first input Q (t) and the second input (Qm(t)) . The samplemeasurements / determinations for first input Q (t) and the second input (Qm(t)) may be taken / made at any point in time during a respiratory cycle of the patient 16. The measurements may be sampled at any suitable frequency. For example, the measurements may be sampled at a frequency that is less than or greater than a breathing frequency of the patient.

[0458] Steps 362, 364, 368, 376 and 378 of method 360 as shown in Figure 10B are the same as those previously described with reference to Figure 8B.

[0459] At step 362, the controller 19 receives one or more sample measurements / determinations for the first input Q (t), and the second input (Qm(t)) at any point(s) in time during a respiratory cycle of the patient 16.

[0460] At query step 364, the controller 19 determines whether the second input (Qm(t)) is greater than the first input (Q (t)). If so, the method 360 proceeds to step 386. If not, the method 360 proceeds to step 368.

[0461] At step 386, the controller 19 determines a mouth closed condition associated with the patient 16. The controller 19 may further determine that the patient is in an expiratory phase of a respiratory cycle. The controller 19 may further determine that a numerical value (k) indicative of a proportion of delivered gases passing through the mouth is zero (K=0).

[0462] At step 388, the controller 19 may determine a value for respiratory parameter patient flow (Qpatient) based on the equation Qpatient(t) = Qm(t)-Qi(t), wherein patient flow Qpatient is a flow rate of gases specifically attributable to the patient. For example, when the patient's mouth is closed (K=0), if an input flow rate Q (t) delivered by a non-sealing interface is 70LPM, and measured / determined flow rate Qm(t) is 90LPM, and the patient is exhaling, Qpatient(t) may be determined as 90LPM-70LPM = +20LPM. A positive Qpatient(t) may indicate that the patient is exhaling. In some embodiments, if the controller 19 is configured to continuously determine patient flow (Qpatient), the controller 19 may be selectively configured to determine a tidal volume (VT) associated with the patient 16 based on an expiratory flow rate of gases at the patient 16 Qp exp(t) in accordance with equation [3] above.

[0463] At query step 368, the controller 19 determines if the sampled / determined value for the first input Q (t) substantially equals the corresponding sampled / determined value for the second input Qm(t). If so, the method 360 proceeds to query step 390. If not, the method 368 proceeds to step 376.

[0464] At step 390, the controller 19 may determine that a numerical value (k) indicative of a proportion of delivered gases passing through the mouth is zero (K=0) .

[0465] At query step 376, the controller 19 determines whether the sampled / determined value for the second input Qm(t) is greater than 0. If so, the method 360 proceeds to query step 392. If not, the method 360 proceeds to step 396.

[0466] At step 392, the controller 19 may determine a mouth open condition associated with the patient 16. The controller 19 may further determine a nasal passage not obstructed (e.g. soft palate open) condition.

[0467] At query step 378, the controller 19 determines whether the patient is expiring. This may be determined according to any known suitable manner, for example as described herein. If the controller 19 determines that the patient is expiring, the method 360 proceeds to step 394. If the controller 19 determines that the patient is not expiring, the method 360 does not make any determinations at this stage and returns to step 362.

[0468] At step 394, the controller 19 may determine that a numerical value (k) indicative of a proportion of delivered gases passing through the mouth is greater than zero (K>0) . In addition, the controller 19 may calculate the specific numerical value (k) based on equation [1] above.

[0469] At step 396, the controller 19 may determine a mouth closed condition. In addition, the controller 19 may determine that a numerical value (k) indicative of a proportion of delivered gases passing through the mouth is zero (K=0) .

[0470] At step 398, the controller 19 may determine patient flow (Qpatient) based on the equation Qpatient(t) = Qm(t)-Qi(t), in a similar manner to step 388. For example, when the patient's mouth is closed (K=0), if an input flow rate Qj(t) delivered by a non-sealing interface is 70LPM, and measured / determined flow rate Qm(t) is 55LPM, and the patient is inhaling,Qpatient(t) may be determined as 55LPM-70LPM = -15LPM. A negative value for Qpatient(t) may indicate that the patient is inhaling.

[0471] After method steps 388, 390, 394, 396 and 398, the method 360 may return to step 362 to take / make one or more subsequent sample measurements / determinations for the first input Q (t) and second input Qm(t) so as to provide continuous patient monitoring.Output generation

[0472] The controller 19 may optionally generate an output to provide one or more indications of one or more flow path characterisations at any time during the execution of any one of the methods of characterising flow paths 300, 360 as described herein. It would be understood that at any stage of any one of the methods 300, 360 where a flow path characterisation made (e.g. nasal passage obstructed or not obstructed (e.g. soft palate closed / open), and / or a mouth open condition or a mouth closed condition), and / or where one or more other respiratory parameters are determined (e.g. input flow rate exceeds inspiratory demand), one or more outputs may be generated by the controller 19 to provide corresponding indication(s) to a clinician. As it will be appreciated, in any one of the flow path characterisation methods described herein, the controller 19 may make the determinations of any one or more, or all characterisations / calculations possible based on the received input(s), and similarly omit determinations of any one or more characterisations / calculations, for example based on application requirements. For example, where a determination of both a nasal passage obstructed or not obstructed (e.g. soft palate closed / open) condition, and a mouth open or closed condition is possible, the controller 19 may determine the nasal passage obstructed or not obstructed (e.g. soft palate closed / open) condition and omit the determination of a mouth open or closed condition, and vice versa.

[0473] Moreover, controller 19 may terminate execution of any one of the methods 300, 360 at any stage after a required characterisation has been made depending on the specific use case scenario, and optionally return to the start of the corresponding method 300, 360 for re-execution of the corresponding method for the following respiratory cycle so as to provide continuous patient monitoring over any suitable time period. For example, in method 300, the controller 19 may terminate execution of the method 300 at step 314 after determining a mouth open condition, or at step 326 after determining a mouth closedcondition and optionally return to step 310 for continuous monitoring of the next breathing cycle. In one embodiment, the methods 300, 360 may be executed continuously for each consecutive respiratory cycle. In another embodiment, the methods 300, 360 may be executed at regular or irregular intervals during a desired monitoring period, for consecutive or non-consecutive respiratory cycles of the patient 16.

[0474] The output may be generated in any suitable format, or a combination of different formats. For example, the controller 19 may generate the output audibly via audio messages or visually via a graphical user interface associated with the controller 19.Displaying the visual indications may include displaying the visual indications textually, numerically and / or graphically.

[0475] Advantageously, information pertaining to the characterisation of flow paths in a patient's respiratory airways can assist the clinician and patient in several ways. For example:• Information relating to flow paths in the patient's respiratory airways may allow determination of tidal volume, minute volume and other respiratory parameters associated with the patient for patient monitoring, thereby enabling clinicians to make better clinical decisions.• Information relating to flow paths in the patient's respiratory airways may allow the clinician to better understand whether a particular therapy is effective for a patient, by enabling more effective determination of whether the patient has nasal obstruction, or soft palate closure. When appropriate, clinicians can indicate alternative therapy based on the flow path information. For example, in the event that it has been determined that the patient has nasal obstruction, or soft palate closure, the clinician may select orally administering therapy rather than nasally administering therapy.• Automatic detection and notification of a mouth open / closed condition associated with the patient may benefit patient groups requiring additional airway pressure support. In particular, when the patient's mouth is open, the pressure benefit from nasal high flow respiratory support reduces, and when the patient's mouth is closed the airway pressure during high flow respiratorysupport is increased. When notified of a mouth closed condition, the clinician may take action to ensure that the mouth stays closed. When notified of a mouth open condition, the clinician may take action to close the mouth of the patient, if an increase in pressure is desired for the patient. Automatic detection is beneficial because it does not require continuous visual monitoring of the patient and allows the clinician to perform other tasks.• Automatic detection and notification of a mouth closed condition associated with the patient may also be beneficial for determination of the appropriate sampling location for the capnography and other gas species monitoring. For example, when notified of a mouth closed condition, a clinician may instead choose to sample at the nose for capnography if they are not already doing so.• Embodiments of the invention described herein may provide better approximation of the fraction of O2 that the patient is receiving during inspiration. This enables the clinician to better understand how much O2 from the gases delivered to the patient is reaching the patient due to physiology of that patient. Consequently, the clinician can have a better understanding of the oxygenation of the patient, and effectiveness of respiratory support. For example, this may be provided by knowledge of the nasal passage not obstructed (e.g. soft palate open) / closed condition as if the patients mouth is open but their soft palate is closed then the patient Is likely receiving less than the fraction of O2 of the high flow respiratory support, which the clinician may not be able to conclude from visual observation of the patient.Further statements defining example embodiments are as follows:1. A method of characterising flow paths within a patient's respiratory airways, the method comprising determining a pressure flow correlation between an airway pressure and a corresponding flow rate of gases at the patient, receiving a first input relating to an input flow of gases provided to a patient from a flow source,determining a second input relating to a flow of gases at the patient based on the pressure flow correlation, and characterising one or more flow paths of delivered gases within the respiratory airways of the patient based on the first input and the second input.2. The method of clause 1, further including receiving, via a pressure sensor, a measured pressure, the measured pressure being usable to determine a calculated airway pressure, the calculated airway pressure being representative of the airway pressure in a nasal passage of the patient, and determining the second input based on the calculated airway pressure and the pressure flow correlation, the second input being a flow rate of gases at the patient corresponding to the calculated airway pressure as determined by the pressure flow correlation.3. The method of clause 2, wherein the measured pressure is a measurement of the airway pressure of the nasal passage of the patient, and wherein the method includes determining the calculated airway pressure based on the measured pressure.4. The method of clause 2 or 3, wherein the pressure sensor includes a sensing element configured for placement in, at or proximate the nasal passage of the patient.5. The method of clause 2 or 3, wherein the pressure sensor includes a sensing element operatively coupled in fluid communication with a sampling conduit, the sampling conduit having a distal end being adapted for placement in, at or proximate the nasal passage of the patient.6. The method of any one of clauses 2 to 5, further including providing, via a patient interface, the input flow of gases to the patient, wherein at least a portion of the pressure sensor is coupled to, or integral with the patient interface.7. The method of clause 5, further including providing, via a patient interface, the input flow of gases to the patient, wherein a portion of the sampling conduit is coupled to, or integral with the patient interface.8. The method of any one of the clauses 2 to 5, further including providing, via a patient interface, the input flow of gases to the patient, and providing a system flow path extending from the flow source to the patient interface, the system flow path being a flow path of the input flow of gases from the flow source to one or more outlets of the patient interface.9. The method of clause 8, including detecting, via the pressure sensor, the measured pressure at a location external to the system flow path.10. The method of clause 8, including detecting, via the pressure sensor, a system pressure, the system pressure being measured at any location within system flow path.11. The method of clause 10, including measuring the system pressure in, at or proximate a location being any one of the flow source, a humidifier for humidifying the flow of gases provided to the patient, the patient interface, any location within a conduit of the respiratory system coupled to any one or more of the flow source, humidifier, or patient interface, for delivering the input flow of gases from the flow source to the patient interface.12. The method of clause 10 or 11, including determining the calculated airway pressure based on the system pressure, and a pressure difference indicative of flow resistance across a portion of the system flow path between the location of the measured pressure and the one or more outlets of the patient interface.13. The method of clause 12, including determining the calculated airway pressure by subtracting the pressure difference from the system pressure.14. The method of any one of clauses 2 to 13, including determining the pressure flow correlation by receiving one or more input flow rate values, each input flow rate being a flow rate of gases provided to the patient from the flow source, receiving, for each input flow rate value, a corresponding characteristic airway pressure value determined based on the measured pressure from the pressure sensor, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the one or more received input flow rate values and the corresponding one or more characteristic airway pressure values.15. The method of any one of clauses 2 to 13, including determining the pressure flow correlation by receiving a plurality of input flow rate values, each input flow rate being a flow rate of gases provided to the patient from the flow source, receiving, for each input flow rate value, a corresponding characteristic airway pressure value determined based on the measured pressure from the pressure sensor, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the plurality of input flow rate values and corresponding characteristic airway pressure values.16. The method of any one of clauses 2 to 13, including determining the pressure flow correlation by receiving two input flow rate values, each input flow rate being a flow rate of gases provided to the patient from the flow source, receiving, for each input flow rate value, a corresponding characteristic airway pressure value determined based on the measured pressure from the pressure sensor, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the two input flow rate values and the corresponding two characteristic airway pressure values.17. The method of any one of clauses 2 to 13, including determining the pressure flow correlation by receiving a single input flow rate value being a flow rate of gases provided to the patient from the flow source, receiving, for the input flow rate value, a corresponding characteristic airway pressure value determined based on the measured pressure from the pressure sensor, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the single input flow rate value and the corresponding characteristic airway pressure value.18. The method of clause 17, wherein the single input flow rate value is a non-zero single input flow rate value, and the method includes determining the relationship based on an input flow rate of zero and the corresponding characteristic airway pressure value, and the non-zero single input flow rate value and the corresponding characteristic airway pressure value.19. The method according to any one of clauses 14 to 18, including determining the relationship between an airway pressure and a corresponding flow rate of gases at the patient based on any one or more of a linear fitted curve of the one or more single input flow rate values and the corresponding characteristic airway pressure values, a non-linear fitted curve of the one or more single input flow rate values and the corresponding characteristic airway pressure values, and an equation governing the one or more single input flow rate values and the corresponding characteristic airway pressure values.20. The method of any one of clauses 2 to 13, including determining the pressure flow correlation by receiving a single input flow rate value being a flow rate of gases provided to the patient from the flow source,receiving, for the input flow rate value, a corresponding characteristic airway pressure value determined based on the measured pressure from the pressure sensor, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on a predetermined pressure flow correlation corresponding to the single input flow rate value and the corresponding characteristic airway pressure value, wherein the predetermined pressure flow correlation is selected from a library of predetermined pressure flow correlations.21. The method according to any one of clauses 14 to 20, including determining the corresponding characteristic airway pressure value based on a generally stable measured pressure value from the pressure sensor (e.g.as indicative of an airway pressure value when the patient's flow is generally zero), the generally stable measured pressure value is optionally including any one or more of, or an average of, a plateau pressure value, a calculated airway pressure value during a breath pause, and a calculated airway pressure value during a breath transition between inspiration and expiration.22. The method of clauses 21, including determining the characteristic airway pressure value based on the generally stable measured pressure value, and a pressure difference indicative of flow resistance across a portion of system flow path between a location corresponding to the measured pressure and the one or more outlets of the patient interface.23. The method of clause 22, including determining the characteristic airway pressure by subtracting the pressure difference from the generally stable measured pressure value.24. The method according to any one of clauses 14 to 21, including receiving, for each input flow rate value, a plurality of corresponding measured pressure values from the pressure sensor over one or more breath cycles, and determining the characteristic airway pressure value for each input flow rate value based on a mean pressure value of the plurality of corresponding measured pressure values.25. The method of clause 22 or 23, including receiving, for each input flow rate value, a plurality of corresponding measured pressure values from the pressure sensor over one or more breath cycles, determining a plurality of calculated airway pressure values, each calculated airway pressure value being based on a respective measured pressure value and an associated pressure difference, and determining the characteristic airway pressure value for each input flow rate value based on a mean pressure value of the plurality of calculated airway pressure values.26. The method according to any one of clauses 14 to 25, including providing the input flow rate value at a flow rate value of between 0 to 150 LPM, or 0 to 90 LPM, or 0 to 70LPM, or 0 to 50 LPM, or 0 to 40LPM, or 10 to 90LPM, or 20 to 60LPM, or 20 to 50LPM.27. The method of clause 15, including selecting the plurality of input flow rate values from a predetermined range of input flow rate values including a range of input flow rate values between 0 to 150 LPM, or 0 to 90 LPM, or 0 to 70LPM, or 0 to 50 LPM, or 0 to 40LPM, or 10 to 90LPM, or 20 to 60LPM, or 20 to 50LPM.28. The method according to any one of clauses 1 to 27, wherein the first input is indicative of an input flow rate of gases provided to the patient from the flow source, and the second input is indicative of a flow rate of gases at the nose of the patient.29. The method of clause 28, including providing the input flow rate of gases at a flow rate value of between about 5 to 150 LPM, or 20 to 90 LPM, or 40 to 70 LPM.30. The method according to any one of clauses 1 to 29, including characterising one or more flow paths of delivered gases within the respiratory airways of the patient by determining any one or more of: a mouth open condition, a mouth closed condition,a nasal passage not obstructed condition, a nasal passage obstructed condition, a numerical value indicative of a proportion of delivered gases passing through the mouth or nose.31. The method according to any one of clauses 1 to 30, further including determining one or more respiratory parameters of the patient.32. The method of clause 31, wherein determining the one or more respiratory parameters includes determining any one or more of: input flow rate of gases provided to the patient exceeding inspiratory demand, input flow rate of gases provided to the patient not meeting inspiratory demand, an expired proportion of CO2, and tidal volume.33. The method according to any one of clauses 1 to 32, further includingProviding, via a non-sealing patient interface, the input flow of gases to the patient, wherein the first input is indicative of an input flow rate of gases provided via the non-sealing patient interface.34. The method according to any one of clauses 1 to 33, including determining whether the mouth of the patient is open or closed based on a comparison of the first input and the second input.35. The method of clause 34, including determining a mouth open condition if the second input is not greater than the first input at any point over a full respiratory cycle.36. The method of clause 35, further including determining a numerical value (k) indicative of a proportion of delivered gases passing through the mouth based onwhereinQj(t) is the first input indicative of an input flow rate of gases provided via a nonsealing patient interface, andQm(t) is the second input indicative of a flow rate of gases at the patient determined based on the pressure flow correlation.37. The method according to any one of clauses 34 to 36, including characterising one or more flow paths by determining either one or both of a mouth open condition, and a nasal passage obstructed condition if the first input substantially equals the second input consistently over a full respiratory cycle.38. The method according to clause 34, including characterising one or more flow paths by further determining a mouth closed condition if the second input is greater than the first input at any point over a full respiratory cycle.39. The method of clause 38, further including receiving a third input indicative of a measured fraction of CO2 at the nose of the patient from a gas fraction sensor, and determining an expired fraction of CO2 (FEco2) based onwhereinQj(t) is the first input indicative of an input flow rate of gases provided via a nonsealing patient interface,Qm(t) is the second input indicative of a flow rate of gases at the patient determined based on the pressure flow correlation, andFm_nose_co2 (t) is the third input indicative of a measured fraction of CO2 at the nose of the patient from the gas fraction sensor.40. The method according to clause 38 or 39, including determining any one or more of a mouth closed condition, a nasal passage not obstructed condition, and that the input flow rate of gases exceeds inspiratory demand if the second input exceeds the first input at any point in time during a respiratory cycle and the second input is consistently greater than zero during the respiratory cycle.41. The method according to clause 38 or 39, including determining any one or more of a mouth closed condition, a nasal passage not obstructed condition, and that the input flow rate of gases does not meet inspiratory demand if the second input exceeds the first input at any point in time during a respiratory cycle and the second input drops below zero at any point during the respiratory cycle.42. The method according to clause 38 or 39, including determining any one or more of a mouth closed condition, a nasal passage not obstructed condition, and that the input flow rate of gases does not meet inspiratory demand if the second input exceeds the first input at any point in time during a respiratory cycle and the second input drops below zero at any point during an inspiratory phase of the respiratory cycle.43. The method according to any one of clauses 1 to 42, including determining the second input by determining one or more discrete values indicative of a flow of gases at the nose of the patient at any time during a respiratory cycle, each discrete value being determined based on the measured pressure and the pressure flow correlation.44. The method according to any one of clauses 1 to 43, including receiving the first input by receiving one or more discrete values relating to a flow of gases provided to the patient at any time during a respiratory cycle.45. The method according to any one of the clauses 1 to 44, further including generating an output based on the characterisation of one or more flow paths of delivered gases within the respiratory airways of the patient for display on a graphical user interface.46. The method according to clause 45, wherein the output includes textual, numerical and / or graphical output.47. The method of any one of clauses 1 to 46, further including measuring, via one or more input flow sensors, the flow of gases provided to the patient including either one or both of the first input, and the input flow rate values, wherein each input flow rate is a flow rate of gases provided to the patient from the flow source.48. The method of clause 47, including measuring, via the input flow sensors, a flow rate of the flow of gases provided to the patient.49. The method of clause 47 or 48, including measuring, via a single input flow sensor, the flow of gases provided to the patient including the first input and the input flow rate values.50. The method of any one of clauses 1 to 49, further providing a humidifier for humidifying the flow of gases provided to the patient.Interpretation

[0476] This specification, including the claims, is intended to be interpreted as follows:

[0477] Embodiments or examples described in the specification are intended to be illustrative of the invention, without limiting the scope thereof. The invention is capable of being practised with various modifications and additions as will readily occur to those skilled in the art. Accordingly, it is to be understood that the scope of the invention is not to be limited to the exact construction and operation described or illustrated, but only by the following claims.

[0478] Moreover, any feature or element described within one embodiment may be combined with any feature or element as described with respect to any other embodiment detailed within this specification, as deemed suitable and appropriate by those skilled in the art.

[0479] The mere disclosure of a method step or product element in the specification should not be construed as being essential to the invention claimed herein, except where it is either expressly stated to be so or expressly recited in a claim.

[0480] The terms in the claims have the broadest scope of meaning they would have been given by a person of ordinary skill in the art as of the relevant date.

[0481] The terms "a" and "an" mean "one or more", unless expressly specified otherwise.

[0482] Neither the title nor the abstract of the present application is to be taken as limiting in any way as the scope of the claimed invention.

[0483] Where the preamble of a claim recites a purpose, benefit or possible use of the claimed invention, it does not limit the claimed invention to having only that purpose, benefit or possible use.

[0484] It should be noted that terms of degree such as "generally", "substantially", "about" and "approximately" as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms of degree should be construed as including a deviation of the modified term if this deviation would not negate the meaning of the term it modifies.

[0485] In the specification, including the claims, the term "comprise", and variants of that term such as "comprises" or "comprising", are used to mean "including but not limited to", unless expressly specified otherwise, or unless in the context or usage an exclusive interpretation of the term is required.

[0486] Furthermore, the recitation of any numerical ranges by endpoints herein includes all numbers and fractions subsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.90, 4, and 5). It is also to be understood that all numbers and fractions thereof are presumed to be modified by the term "about" which means a variation up to a certain amount of the number to which reference is being made if the end result is not significantly changed.

[0487] As used herein, the wording "and / or" is intended to represent an inclusive-or. That is, "X and / or Y" is intended to mean X or Y or both, for example. As a further example, "X, Y, and / or Z" is intended to mean X or Y or Z or any combination thereof.

[0488] Throughout the specification, like reference numerals refer to like features described herein. As such, any instance where features or components are indicated with the same references implies a direct correlation to the similar or identical features or components as previously described in the specification.

[0489] The disclosure of any document referred to herein is incorporated by reference into this patent application as part of the present disclosure, but only for purposes of written description and enablement and should in no way be used to limit, define, or otherwise construe any term of the present application where the present application, without such incorporation by reference, would not have failed to provide an ascertainable meaning. Any incorporation by reference does not, in and of itself, constitute any endorsement or ratification of any statement, opinion or argument contained in any incorporated document.

Claims

The claims defining the invention are as follows:

1. A respiratory support system for characterising flow paths within a patient's respiratory airways, the system comprising a flow source for providing an input flow of gases to the patient, and a controller being configured to determine a pressure flow correlation between an airway pressure and a corresponding flow rate of gases at the patient, receive a first input relating to the input flow of gases provided to the patient from the flow source, determine a second input relating to a flow of gases at the patient based on the pressure flow correlation, and characterise one or more flow paths of delivered gases within the respiratory airways of the patient based on the first input and the second input.

2. The respiratory support system of claim 1, further including a pressure sensor for providing a measured pressure, the measured pressure being usable to determine a calculated airway pressure, the calculated airway pressure being representative of the airway pressure in a nasal passage of the patient, and wherein the controller is configured to determine the second input based on the calculated airway pressure and the pressure flow correlation, the second input being a flow rate of gases at the patient corresponding to the calculated airway pressure as determined by the pressure flow correlation.

3. The respiratory support system of claim 2, wherein the measured pressure is a measurement of the airway pressure of the nasal passage of the patient, and the controller is operatively configured to determine the calculated airway pressure based on the measured pressure.

4. The respiratory support system of claim 2 or 3, wherein the pressure sensor includes a sensing element configured for placement in, at or proximate the nasal passage of the patient.

5. The respiratory support system of claim 2 or 3, wherein the pressure sensor includes a sensing element operatively coupled in fluid communication with a sampling conduit, the sampling conduit having a distal end being adapted for placement in, at or proximate the nasal passage of the patient.

6. The respiratory support system of any one of claim 2 to 5, further including a patient interface for providing the input flow of gases to the patient, wherein at least a portion of the pressure sensor is coupled to, or integral with the patient interface.

7. The respiratory support system of claim 5, further including a patient interface for providing the input flow of gases to the patient, wherein a portion of the sampling conduit is coupled to, or integral with the patient interface.

8. The respiratory support system of any one of the claims 2 to 5, further including a patient interface for providing the input flow of gases to the patient, wherein the respiratory support system defines a system flow path extending from the flow source to the patient interface, the system flow path being a flow path of the input flow of gases from the flow source to one or more outlets of the patient interface.

9. The respiratory support system of claim 8, wherein pressure sensor is configured to detect the measured pressure at a location external to the system flow path.

10. The respiratory support system of claim 8, wherein the pressure sensor is configured to detect a system pressure, the system pressure being measured at any location within system flow path.

11. The respiratory support system of claim 10, wherein the system pressure is measured in, at or proximate a location being any one of the flow source, a humidifier for humidifying the flow of gases provided to the patient, the patient interface,any location within a conduit of the respiratory system coupled to any one or more of the flow source, humidifier, or patient interface, for delivering the input flow of gases from the flow source to the patient interface.

12. The respiratory support system of claim 10 or 11, wherein the calculated airway pressure is determined based on the system pressure, and a pressure difference indicative of flow resistance across a portion of the system flow path between the location of the measured pressure and the one or more outlets of the patient interface.

13. The respiratory support system of claim 12, wherein the calculated airway pressure is determined by subtracting the pressure difference from the system pressure.

14. The respiratory support system of any one of claims 2 to 13, wherein the controller is configured to determine the pressure flow correlation by receiving one or more input flow rate values, each input flow rate being a flow rate of gases provided to the patient from the flow source, receiving, for each input flow rate value, a corresponding characteristic airway pressure value determined based on the measured pressure from the pressure sensor, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the one or more received input flow rate values and the corresponding one or more characteristic airway pressure values.

15. The respiratory support system of any one of claims 2 to 13, wherein the controller is configured to determine the pressure flow correlation by receiving a plurality of input flow rate values, each input flow rate being a flow rate of gases provided to the patient from the flow source, receiving, for each input flow rate value, a corresponding characteristic airway pressure value determined based on the measured pressure from the pressure sensor,determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the plurality of input flow rate values and corresponding characteristic airway pressure values.

16. The respiratory support system of any one of claims 2 to 13, wherein the controller is configured to determine the pressure flow correlation by receiving two input flow rate values, each input flow rate being a flow rate of gases provided to the patient from the flow source, receiving, for each input flow rate value, a corresponding characteristic airway pressure value determined based on the measured pressure from the pressure sensor, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the two input flow rate values and the corresponding two characteristic airway pressure values.

17. The respiratory support system of any one of claims 2 to 13, wherein controller is configured to determine the pressure flow correlation by receiving a single input flow rate value being a flow rate of gases provided to the patient from the flow source, receiving, for the input flow rate value, a corresponding characteristic airway pressure value determined based on the measured pressure from the pressure sensor, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on the single input flow rate value and the corresponding characteristic airway pressure value.

18. The respiratory support system of claim 17, wherein the single input flow rate value is a non-zero single input flow rate value, and the controller is configured to determine the relationship based on an input flow rate of zero and the corresponding characteristic airway pressure value, and the non-zero single input flow rate value and the corresponding characteristic airway pressure value.

19. The respiratory support system according to any one of claims 14 to 18, wherein the controller is configured to determine the relationship between an airway pressure and a corresponding flow rate of gases at the patient based on any one or more of a linear fitted curve of the one or more single input flow rate values and the corresponding characteristic airway pressure values, a non-linear fitted curve of the one or more single input flow rate values and the corresponding characteristic airway pressure values, and an equation governing the one or more single input flow rate values and the corresponding characteristic airway pressure values.

20. The respiratory support system of any one of claims 2 to 13, wherein the controller is configured to determine the pressure flow correlation by receiving a single input flow rate value being a flow rate of gases provided to the patient from the flow source, receiving, for the input flow rate value, a corresponding characteristic airway pressure value determined based on the measured pressure from the pressure sensor, determining a relationship between an airway pressure and a corresponding flow rate of gases at the patient based on a predetermined pressure flow correlation corresponding to the single input flow rate value and the corresponding characteristic airway pressure value, wherein the predetermined pressure flow correlation is selected from a library of predetermined pressure flow correlations.

21. The respiratory support system according to any one of claims 14 to 20, wherein the controller is configured to determine the corresponding characteristic airway pressure value based on a generally stable measured pressure value from the pressure sensor (e.g.as indicative of an airway pressure value when the patient's flow is generally zero), the generally stable measured pressure value is optionally including any one or more of, or an average of, a plateau pressure value, a calculated airway pressure value during a breath pause, and a calculated airway pressure value during a breath transition between inspiration and expiration.

22. The respiratory support system of claim 21, wherein the controller is configured to determine the characteristic airway pressure value based on the generally stable measured pressure value, and a pressure difference indicative of flow resistance across a portion of system flow path between a location corresponding to the measured pressure and the one or more outlets of the patient interface.

23. The respiratory support system of 22, wherein the characteristic airway pressure value is determined by subtracting the pressure difference from the generally stable measured pressure value.

24. The respiratory support system according to any one of claims 14 to 21, wherein the controller is configured to receive, for each input flow rate value, a plurality of corresponding measured pressure values from the pressure sensor over one or more breath cycles, and determine the characteristic airway pressure value for each input flow rate value based on a mean pressure value of the plurality of corresponding measured pressure values.

25. The respiratory support system of claim 22 or 23, wherein the controller is configured to receive, for each input flow rate value, a plurality of corresponding measured pressure values from the pressure sensor over one or more breath cycles, determine a plurality of calculated airway pressure values, each calculated airway pressure value being based on a respective measured pressure value and an associated pressure difference, and determine the characteristic airway pressure value for each input flow rate value based on a mean pressure value of the plurality of calculated airway pressure values.

26. The respiratory support system according to any one of claims 14 to 25, wherein the input flow rate value is a flow rate value between 0 to 150 LPM, or 0 to 90 LPM, or 0 to 70LPM, or 0 to 50 LPM, or 0 to 40LPM, or 10 to 90LPM, or 20 to 60LPM, or 20 to 50LPM.

27. The respiratory support system of claim 15, wherein the plurality of input flow rate values is selected from a predetermined range of input flow rate values including a range of input flow rate values between 0 to 150 LPM, or 0 to 90 LPM, or 0 to 70LPM, or 0 to 50 LPM, or 0 to 40LPM, or 10 to 90LPM, or 20 to 60LPM, or 20 to 50LPM.

28. The respiratory support system according to any one of claims 1 to 27, wherein the first input is indicative of an input flow rate of gases provided to the patient from the flow source, and the second input is indicative of a flow rate of gases at the nose of the patient.

29. The respiratory support system of claim 28, wherein the input flow rate of gases has a flow rate value between about 5 to 150 LPM, or 20 to 90 LPM, or 40 to 70 LPM.

30. The respiratory support system according to any one of claims 1 to 29, wherein the controller is configured to characterise one or more flow paths of delivered gases within the respiratory airways of the patient by determining any one or more of: a mouth open condition, a mouth closed condition, a nasal passage not obstructed condition, a nasal passage obstructed condition, a numerical value indicative of a proportion of delivered gases passing through the mouth or nose.

31. The respiratory support system according to any one of claims 1 to 30, wherein the controller is further configured to determine one or more respiratory parameters of the patient.

32. The respiratory support system of claim 31, wherein the one or more respiratory parameters includes any one or more of: input flow rate of gases provided to the patient exceeding inspiratory demand, input flow rate of gases provided to the patient not meeting inspiratory demand,an expired proportion of CO2, and tidal volume.

33. The respiratory support system according to any one of claims 1 to 32, further including a non-sealing patient interface for providing the input flow of gases to the patient, wherein the first input is indicative of an input flow rate of gases provided via the non-sealing patient interface.

34. The respiratory support system according to any one of claims 1 to 33, wherein the controller is configured to determine whether the mouth of the patient is open or closed based on a comparison of the first input and the second input.

35. The respiratory support system of claim 34, wherein the controller is configured to determine a mouth open condition if the second input is not greater than the first input at any point over a full respiratory cycle.

36. The respiratory support system of claim 35, wherein the controller is further configured to determine a numerical value (k) indicative of a proportion of delivered gases passing through the mouth based onwhereinQj(t) is the first input indicative of an input flow rate of gases provided via a nonsealing patient interface, andQm(t) is the second input indicative of a flow rate of gases at the patient determined based on the pressure flow correlation.

37. The respiratory support system according to any one of claims 34 to 36, wherein the controller is configured to characterise one or more flow paths by determining either one or both of a mouth open condition, and a nasal passage obstructed condition if the first input substantially equals the second input consistently over a full respiratory cycle.

38. The respiratory support system according to claim 34, wherein the controller is configured to characterise one or more flow paths by further determining a mouth closed condition if the second input is greater than the first input at any point over a full respiratory cycle.

39. The respiratory support system of claim 38, further including a gas fraction sensor, and wherein the controller is further configured to receive a third input indicative of a measured fraction of CO2 at the nose of the patient from the gas fraction sensor, and determining an expired fraction of CO2 (FEco2) based onwhereinQj(t) is the first input indicative of an input flow rate of gases provided via a nonsealing patient interface,Qm(t) is the second input indicative of a flow rate of gases at the patient determined based on the pressure flow correlation, andFm_nose_co2 (t) is the third input indicative of a measured fraction of CO2 at the nose of the patient from the gas fraction sensor.

40. The respiratory support system according to claim 38 or 39, wherein the controller is configured to determine any one or more of a mouth closed condition,a nasal passage not obstructed condition, and that the input flow rate of gases exceeds inspiratory demand if the second input exceeds the first input at any point in time during a respiratory cycle and the second input is consistently greater than zero during the respiratory cycle.

41. The respiratory support system according to claim 38 or 39, wherein the controller is configured to determine any one or more of a mouth closed condition, a nasal passage not obstructed condition, and that the input flow rate of gases does not meet inspiratory demand if the second input exceeds the first input at any point in time during a respiratory cycle and the second input drops below zero at any point during the respiratory cycle.

42. The respiratory support system according to claim 38 or 39, wherein the controller is configured to determine any one or more of a mouth closed condition, a nasal passage not obstructed condition, and that the input flow rate of gases does not meet inspiratory demand if the second input exceeds the first input at any point in time during a respiratory cycle and the second input drops below zero at any point during an inspiratory phase of the respiratory cycle.

43. The respiratory support system according to any one of claims 1 to 42, wherein the controller is configured to determine the second input by determining one or more discrete values indicative of a flow of gases at the nose of the patient at any time during a respiratory cycle, each discrete value being determined based on the measured pressure and the pressure flow correlation.

44. The respiratory support system according to any one of claims 1 to 43, wherein the controller is configured to receive the first input by receiving one or more discrete values relating to a flow of gases provided to the patient at any time during a respiratory cycle.

45. The respiratory support system according to any one of the claims 1 to 44, further including a graphical user interface, wherein the controller is configured to generate an output based on the characterisation of one or more flow paths of delivered gases within the respiratory airways of the patient for display on the graphical user interface.

46. The respiratory support system according to claim 45, wherein the output includes textual, numerical and / or graphical output.

47. The respiratory support system of any one of claims 1 to 46, further including one or more input flow sensors for measuring the flow of gases provided to the patient including either one or both of the first input, and the input flow rate values, wherein each input flow rate is a flow rate of gases provided to the patient from the flow source.

48. The respiratory support system of claim 47, wherein the input flow sensors are configured to measure a flow rate of the flow of gases provided to the patient.

49. The respiratory support system of claim 47 or 48, including a single input flow sensor for measuring the flow of gases provided to the patient including the first input and the input flow rate values.

50. The respiratory support system of any one of claims 1 to 49, further including a humidifier for humidifying the flow of gases provided to the patient.

51. A method of characterising flow paths within a patient's respiratory airways, the method comprising determining a pressure flow correlation between an airway pressure and a corresponding flow rate of gases at the patient, receiving a first input relating to a flow of gases provided to the patient,determining a second input relating to a flow of gases at the patient based on the pressure flow correlation, and characterising one or more flow paths of delivered gases within the respiratory airways of the patient based on the first input and the second input.

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