Humidified respirator control

Abstract

To provide a humidification breathing apparatus and / or a method of operation that control humidity and / or temperature of humidified air in a flow path.SOLUTION: A humidification breathing apparatus for generating humidified air and delivering it to a patient at a desired humidity proximate to the patient comprises an air flow path and a controller for controlling operation of the humidification breathing apparatus, where the controller is configured to operate the humidification breathing apparatus to control humidity at a point in the flow path to achieve the desired delivered humidity proximate to the patient on the basis of the patient exhaled humidity and flow.SELECTED DRAWING: Figure 1B

Description

[Technical field]

[0001] The present invention relates to a humidified respiratory device and its control for providing humidified air of a desired humidity and temperature to a patient. [Background technology]

[0002] In respiratory devices that provide humidification, the intent is to provide humidified air of a desired humidity and / or temperature to a patient to achieve a desired patient comfort and / or treatment. Providing the desired humidity and / or temperature requires achieving and maintaining the humidity and / or temperature of the humidified air at the patient (i.e., near the patient's mouth and / or nose) because this is the humidity and temperature of the air that is ultimately delivered to the patient (Note: "near" can also be referred to as "at or near" or "proximate to"). In theory, this involves heating and / or humidifying the air passing through the respiratory device flow path from the flow generator to the patient (e.g., via conduits and patient interfaces) until the desired humidity and / or temperature is achieved and maintained proximate to the patient.

[0003] However, while controlling humidity and / or temperature closest to the patient is possible, it is technically and economically difficult. For example, using sensors to detect the humidity and / or temperature of the humidified air closest to the patient is expensive and has technical and health difficulties. Thus, what is traditionally controlled is not the humidity and / or temperature of the humidified air closest to the patient, but rather the humidity and / or temperature of the humidified air at some other point in the flow path, a point that is easier to monitor. A target temperature and / or humidity is determined for a particular point (humidifier outlet or end of conduit / hose) and that is the temperature and / or humidity that is controlled. The difficulty with this approach is that achieving and maintaining the target temperature and / or humidity at that point in the flow path does not guarantee that the desired humidity and / or temperature closest to the patient will be achieved and transmitted to the patient. The humidity and / or temperature of the humidified air may have changed by the time it reaches the patient. For example, if the temperature and / or humidity of the air at the end of the conduit is maintained at a target, variations in the humidity and temperature provided at the patient interface mean that the actual temperature and / or humidity delivered to the patient via the patient interface will differ in an unknown way from that at the end of the hose. This makes it difficult to know the actual temperature / humidity of the air at the patient and therefore difficult to deliver the desired temperature and / or humidity of the humidified air to the patient. Summary of the Invention [Problem to be solved by the invention]

[0004] It is an object of the present invention to provide a humidified respiratory device and / or method of operation that controls the humidity and / or temperature of humidified air in a flow path in a manner that improves the ability to deliver humidified air to a patient at a desired humidity and / or temperature. [Means for solving the problem]

[0005] In one aspect, the invention is said to reside in a humidified respiratory apparatus for generating and delivering humidified air of a desired humidity proximate to a patient, the apparatus comprising an air flow path and a controller for controlling operation of the humidified respiratory apparatus, the controller being configured to operate the humidified respiratory apparatus to control humidity at a point in the flow path to achieve the desired delivered humidity proximate to the patient based on the patient's exhaled humidity and flow rate.

[0006] Preferably, the device further comprises a conduit coupled to the patient interface which forms part of the flow path.

[0007] Preferably, the point in the flow path at which the controller is configured to control humidity is at or near the patient interface at the end of the conduit.

[0008] Preferably, the patient interface is a mask and the controller controls humidity at a point in the flow path to achieve a target humidity calculated from the patient's exhaled humidity and flow rate, the relationship between the target humidity, the patient's exhaled humidity and flow rate being based on a balance between the mass flow rate of water vapour into the mask and the mass flow rate of water vapour out of the mask.

[0009] Preferably, the mass flow rate of the water vapor is

number

number

number

number

[0010] Preferably, the relationship is: EOH_AH =f(A,J B ,M h ,h P ) (5) wherein: h P is the humidity provided to the mask by the patient (exhaled breath), A is the patient's peak flow rate, J B is the average flow rate (bias flow rate + leakage flow rate), M h is the mask humidity, EOH_AH is the (absolute) humidity at the end of the hose.

[0011] Preferably, the relationship is: EOH_AH=(Mask_AH-(A / (J B * p)) * Patient_AH) / (1-A / (J B * p)) (6) wherein: A is the patient's peak flow rate, J is the average flow rate Patient_T and Patient_AH are the temperature and humidity of the air exhaled by the patient.

[0012] Preferably, the point in the flow path at which the controller is configured to control humidity is at or near the humidifier outlet.

[0013] Preferably, the apparatus comprises a flow sensor for sensing the flow rate.

[0014] Preferably, the flow rate is average flow velocity, Peak flow velocity, Tidal volume The one or more characteristics of the flow rate are one or more of:

[0015] Preferably, the patient's breath humidity is Default, A value sensed using a sensor, A value calculated from one or more of the following: BMI, height, weight, body mass, or any other suitable physiological characteristics of the patient. One or more of the following:

[0016] Preferably, the controller is configured to operate the humidifier to control humidity by controlling the heater plate temperature, for example by controlling the duty cycle of the power supplied to the heater plate.

[0017] Preferably, the controller is further configured to operate the humidified respiratory device to control humidity based on mask information, for example an internal volume of the mask.

[0018] In another aspect, the invention is said to be a method of generating and delivering humidified air of a desired humidity proximate to a patient, the method comprising operating a humidified respiratory device to control humidity at a point in the flow path to achieve the desired delivered humidity proximate to the patient based on the patient's exhaled breath humidity and flow rate.

[0019] Preferably, the step of controlling humidity at a point in the flow path is to achieve a target humidity calculated from the patient's exhaled breath humidity and flow rate, the relationship between the target humidity, the patient's exhaled breath humidity and flow rate being based on a balance between the mass flow rate of water vapour to the mask and the mass flow rate of water vapour from the mask.

[0020] In another aspect, the invention is said to reside in a humidified respiratory apparatus for generating humidified air of a desired humidity proximate to a patient for delivery to the patient, the apparatus comprising an air flow path and a controller for controlling operation of the humidified respiratory apparatus, the controller configured to operate the humidified respiratory apparatus to control the humidity at a point in the flow path to achieve the desired delivered humidity proximate to the patient based on the patient's exhaled humidity and flow rate, and the controller configured to operate the humidified respiratory apparatus to control the temperature at a point in the flow path to achieve the desired delivered temperature proximate to the patient based on the patient's exhaled temperature and flow rate.

[0021] In another aspect, the invention is said to be a method of generating and delivering humidified air of a desired humidity proximate to a patient, the method comprising the steps of operating a humidified respiratory device to control the humidity at a point in the flow path to achieve the desired delivered humidity proximate to the patient based on the patient's exhaled breath humidity and flow rate, and operating the humidified respiratory device to control the temperature at a point in the flow path to achieve the desired delivered temperature proximate to the patient based on the patient's exhaled breath temperature and flow rate.

[0022] In another aspect, the invention is said to reside in a humidified respiratory apparatus for generating and delivering humidified air at a desired temperature proximate to a patient, the apparatus comprising an air flow path and a controller for controlling operation of the humidified respiratory apparatus, the controller being configured to operate the humidified respiratory apparatus to control the temperature at a point in the flow path to achieve the desired delivery temperature proximate to the patient based on the patient's exhaled air temperature and flow rate.

[0023] Preferably, the device further comprises a conduit coupled to the patient interface which forms part of the flow path.

[0024] Preferably, the point in the flow path at which the controller is configured to control the temperature is at or near the patient interface at the end of the conduit.

[0025] Preferably, the patient interface is a mask and the humidifier controls the temperature at a point in the flow path to achieve a target temperature calculated from the patient's exhaled breath temperature and flow rate, the relationship between the target temperature, the patient's exhaled breath temperature and flow rate being based on a balance between the heat flow to and from the mask.

[0026] Preferably, the heat flow is

number

[0027] Preferably, the relationship is: EOH_T =f(A,J B ,M t ,T P ,T A ) (11) wherein: T P is the temperature provided to the mask by the patient (exhaled breath), A is the patient's peak flow rate, J B is the average flow rate (bias flow rate + leakage flow rate), T A is the ambient temperature measured, for example, by a sensor, M t is the mask temperature, EOH_T is the temperature at the end of the hose.

[0028] Preferably, the relationship is:

number

number

[0029] Preferably, the point in the flow path at which the controller is configured to control the temperature is at or near the humidifier outlet.

[0030] Preferably, the apparatus comprises a flow sensor for sensing the flow rate.

[0031] Preferably, the flow rate is average flow velocity, Peak flow velocity, Tidal volume The one or more characteristics of the flow rate are one or more of:

[0032] Preferably, the patient's exhaled breath temperature is Default, A value sensed using a sensor, A value calculated from one or more of the following: BMI, height, weight, body mass, or any other suitable physiological characteristics of the patient. One or more of the following:

[0033] Preferably, the controller is configured to operate the humidifier to control the temperature by controlling energization of a heater in the conduit, or alternatively, by energizing a heater plate arrangement to heat the humidified air being delivered.

[0034] Preferably, the controller is further configured to operate the humidifier to control the temperature based on an input air temperature, optionally the input air temperature being ambient air temperature or a default value.

[0035] Preferably, the controller is further configured to operate the humidified respiratory device to control humidity based on the mask information, optionally the mask information comprising: The internal volume of the mask, The surface area of ​​the mask, Mask Materials One or more of the following:

[0036] In another aspect, the invention is said to be a method of generating and delivering humidified air at a desired temperature proximate to a patient, the method comprising operating a humidified respiratory device to control the temperature at a point in the flow path to achieve the desired delivery temperature proximate to the patient based on the patient's exhaled breath temperature and flow rate.

[0037] Preferably, the temperature at the point in the flow path is to achieve a target temperature calculated from the patient's exhaled breath temperature and flow rate, the relationship between the target temperature, the patient's exhaled breath temperature and flow rate being based on a balance between the heat flow to and from the mask.

[0038] In another aspect, the invention is said to reside in a humidified respiratory apparatus comprising a flow path for delivering humidified air of a desired humidity proximate the patient, the humidifier comprising a controller configured to control humidity at a point in the flow path to achieve the desired delivered humidity proximate the patient based on a contribution made by the patient to the humidity.

[0039] In another aspect, the invention is said to be a method of controlling a humidified respiratory device to deliver a desired humidity to a patient, the method comprising the steps of receiving input relating to a patient's exhaled humidity and flow rate, and operating the humidified respiratory device to provide an output humidity based on the patient's exhaled humidity and flow rate.

[0040] In another aspect, the invention is said to reside in a humidified respiratory device comprising a flow path for delivering humidified air to a patient at a desired temperature proximate the patient, the humidifier comprising a controller configured to control the temperature at a point in the flow path to achieve the desired delivery temperature proximate the patient based on a contribution made by the patient to the temperature.

[0041] In another aspect, the invention is said to reside in a method of controlling a humidified respiratory device to deliver a desired temperature to a patient, the method comprising the steps of receiving input relating to a patient's exhaled breath temperature and flow rate, and operating the humidified respiratory device to provide an output temperature based on the patient's exhaled breath temperature and flow rate.

[0042] Where patents, other external documents or other sources of information are referenced in this specification, this is generally for the purpose of providing a context for discussing features of the present disclosure. Unless specifically stated, the reference to such external documents should not be construed as an admission that such documents or such sources are prior art in any jurisdiction or form part of the common general knowledge in the art.

[0043] The term "comprising" as used in this specification means "consisting at least in part of." In interpreting each statement in this specification that contains the term "comprising," there may be features present other than the one or more prefaced by that term. Related terms such as "comprise" and "comprises" should be interpreted in the same manner.

[0044] Numerous modifications in structure and widely differing embodiments and applications of the invention will occur to those skilled in the art to which the invention pertains without departing from the scope of the invention as defined in the appended claims. The present disclosure and descriptions herein are merely illustrative and are not intended to be in any sense limiting.

[0045] Where reference is made herein to specific integers that have known equivalents in the art to which this invention pertains, such known equivalents are deemed to be incorporated herein as if individually set forth.

[0046] Embodiments of the present invention will now be described with reference to the following drawings: [Brief description of the drawings]

[0047] [Figure 1A] FIG. 1 is a schematic diagram of a humidified respiratory device that provides humidified air to a patient along a flow path with downstream contributions that modify the humidity and / or temperature of the humidified air. [Figure 1B] FIG. 1 is a schematic diagram showing a typical humidified respirator control. [Diagram 2] FIG. 1 is a detailed schematic diagram of a CPAP device including a humidifier that provides pressurized humidified air to a patient. [Diagram 3] 3 is a high-level schematic generalization of a humidified respiratory device (such as that shown in FIG. 2) that provides humidified air to a patient, according to one embodiment. [Figure 4] FIG. 1 is a schematic diagram of the humidified respirator control. [Diagram 5] FIG. 5 is a schematic diagram of a target temperature and humidity model used in the control shown in FIG. [Figure 6A] FIG. 1 is a schematic diagram showing flow balance in a mask of a humidified respiratory apparatus. [Figure 6B] FIG. 1 is a schematic diagram showing flow balance in a mask of a humidified respiratory apparatus. [Figure 7] 1 shows a sinusoidal approximation of respiratory flow. [Figure 8]FIG. 6 is a schematic diagram of a target humidity model which may form part of the model of FIG. 5. [Figure 9] FIG. 6 is a schematic diagram of a target temperature model which may form part of the model of FIG. 5. [Figure 10] FIG. 1 is a schematic process flow diagram of the overall humidified respirator control. [Figure 11A] FIG. 1 is a schematic diagram showing flow balance in a mask of a humidified respiratory apparatus. [Figure 11B] FIG. 1 is a schematic diagram showing flow balance in a mask of a humidified respiratory apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] The present invention relates to a humidified respiratory device and method of operation thereof for delivering humidified air to a patient, the specification of which is incorporated herein by reference in its entirety. The humidified respiratory device may be a humidifier by itself or in combination with other hardware to provide additional respiratory support, such as a CPAP (Continuous Positive Airway Pressure) device, an auto-titrator, a bi-level device, or other PAP device (operating at 3-20 cmH2O or equivalent) or a high-flow respiratory device with a humidifier. The humidified respiratory device and method of operation thereof produces and delivers humidified air of a desired humidity and / or temperature (which may also mean "at or near" the desired humidity and / or temperature) to a patient. The humidified respiratory device and method of operation thereof aims to achieve the desired humidity and / or temperature of the humidified air that is actually delivered to the patient. That is, the humidified respiratory device and its method of operation control the humidity and / or temperature of the humidified air in the air flow path so that the humidified air nearest / proximal to the patient (i.e., at or near the patient) is at the desired humidity and / or temperature.

[0049] With reference to FIG. 1A, the humidified respiratory device has an air humidification capability (box 10) and includes a humidifier 10a for humidification, a flow generator 10b, and a controller 10c, along with hardware for other capabilities such as CPAP or the like. A flow path 11 conveys humidified air 13 to a patient 12. The flow path is shown separately from the respiratory device box 10, but can be considered part of the respiratory device, and the flow path can include pieces of hardware itself, such as internal ducts and air paths in the humidifier. The patient interface can also be generally considered part of the flow path and the humidified respiratory device. In general terms, the temperature and / or humidity of the humidified air 13 is controlled at some point (target point) 14 of the humidified respiratory device flow path. A model of downstream contributions 15 to humidity and / or temperature provided by components and inputs (e.g., patient inputs) further downstream in the remainder of the flow path (terminating at the patient) is determined, and a target temperature / humidity model is devised and implemented in the controller 10c.

[0050] A target temperature and / or humidity at the target point is determined from the model such that when the target temperature and / or humidity is reached, the remaining contributions to humidity and temperature 15 from downstream influences will cause the actual temperature and / or humidity nearest the patient to be at (or near) the desired value. The humidified respirator and / or any surrounding components (such as fans, heated tubes, masks and the like) are manipulated to control the humidity and / or temperature of the humidified air passing through the humidified respirator flow path such that the target temperature and / or humidity at the target point is achieved and maintained.

[0051] The target temperature and / or humidity of the air in the flow path may be achieved using any of the usual control methods for a humidified respiratory apparatus, such as, for example, using closed loop feedback (using sensors or the like) or using a model or other predictive mechanism.

[0052] With reference to FIG. 1B, a humidified respiratory device control 18 is provided to achieve the required desired temperature and humidity at the patient. The control includes a (parameter) model 16 for determining the relevant values ​​of parameters that must be achieved to deliver the desired temperature and humidity at the patient, and control functionality (e.g., in the form of a model / equation) 17 for operating the humidified device to achieve those parameter values. The model includes a patient contribution / goal parameter model 16, and a humidified respiratory device control model for controlling, for example, the device heater plate temperature and breathing tube heater power. The humidified respiratory device control 18 uses, among other things, ambient temperature 19a, user settings 19b, ambient humidity 19c, and patient feedback (including patient flow rate 19f, patient temperature 19d, patient humidity 19e). Control output parameters 20, signals, or other control mechanisms, such as heater plate temperature 20a and heated breathing tube power 20b, are used to control the operation of the controlled humidified respiratory device to achieve the desired temperature and humidity at the patient.

[0053] When calculating the target temperature / humidity, the relevant model actually takes into account the patient's contribution to the humidity and temperature of the humidified air. The contribution may be due, for example, to the temperature and / or humidity of the patient's breath, as well as the respiratory flow characteristics (also called "flow", "patient flow" or "flow characteristics"). Optionally, other parameters may be used, including those related to the mask type itself. For example, the parameters may include the mask's internal volume, the mask's surface area and / or the mask's material. Using the patient's contribution, the controller 109 (see FIG. 3) can calculate the required target temperature and / or humidity of the air at some other point in the air flow path that, if achieved, will achieve the desired parameters of the humidified air at / delivered to the patient.

[0054] 1. First embodiment of the present invention 1.1 Overview 2-4, a possible non-limiting embodiment of a humidified respiratory device is shown, in this case a CPAP device 1 with an integrated humidifier as shown in Figure 2. It will be appreciated that any type of respiratory device that provides humidification can be used, including a flow therapy device with humidification capabilities or even a humidifier alone.

[0055] FIG. 2 shows a block diagram illustrating one embodiment of a humidified respiratory apparatus 1 comprising a PAP device 100 for delivering a supply of respiratory gas, a respiratory conduit 101 with a heater, and a patient interface 102.

[0056] A breathing conduit 101 (also called a "hose" or "tube") extends from the outlet of the PAP device 100 to a patient interface 102. The patient interface can be any suitable sealed patient interface (such as a full face mask, nasal mask, direct nasal mask, oral mask or the like) with bias flow holes with a bias flow rate that is kept constant by maintaining a constant pressure in the mask during both the inhalation and exhalation phases.

[0057] The PAP device includes a blower 103. Preferably, the blower includes a fan driven by an electric motor. Air is drawn into the PAP device by the fan through an inlet 104. Pressurized air exits the fan for delivery to the patient. Alternatively, a controllable flow generator can direct a high pressure gas source and regulate the flow rate of gas from the high pressure source.

[0058] The PAP device includes a humidifier 115. In alternative embodiments, the humidifier 115 can be separate from the PAP device and from parts of the PAP device. The humidifier 115 shown is a pass-over type humidifier where air passing through the humidifier picks up a large amount of water vapor from a water reservoir 107. The water reservoir is heated by a heater 108. The humidifier is preferably integrated into the housing of the PAP device. Alternatively, the humidifier may be a separate component in the housing of the PAP device or separate from the PAP device with a conduit connected between the PAP device and the humidifier. Other types of humidifiers besides the pass-over type can also be used. In some forms, multiple humidifiers can be used. The humidified air exits the heated end of the breathing tube 101 (later referred to as the end of the hose EOH), mixes with the patient's exhaled air, and then exits through a bias hole on the nasal, full face or oral mask 102. In some embodiments, a non-heated breathing tube can be used instead.

[0059] The PAP device includes a controller 109. The controller 109 is used to control the humidified breathing device, including the PAP device, the tube heater 101a, and other peripherals. The controller 109 also operates the model of the present invention. The controller receives input from a user interface (UI) 113 and sensors. The user interface can be in the form of any suitable user interface, such as a knob, a number of buttons, a screen, or any combination thereof. The user interface allows the PAP device to display information to the user and also allows the user to input information into the PAP device (or, more specifically, into the controller). The controller can also be provided with an interface 114 for connecting to an external data source.

[0060] The controller includes inputs (112, 110, 201, 111, 117, 119, etc., as shown) for receiving inputs from one or more sensors, which may include temperature, flow, humidity and / or pressure sensors upstream or downstream of the fan or external to the device. As shown, the flow sensors determine the flow characteristics (such as volume, speed or phase) of the gas delivered to the patient or user. The flow sensors may be located upstream 110 or downstream 111, 112 of the fan. Ambient temperature and humidity sensors 201, 110 may also be used, which may be located at the blower inlet, humidifier inlet or any other suitable location. Optionally, temperature and / or humidity sensors at the end of the hose 112 and / or mask 117 may be used as needed. Optionally, a heater plate temperature sensor 119 is used. The sensors shown are one configuration of sensors that may be used. Any other configuration of sensors and any other type of sensors may also be used. There may be fewer or more sensors than shown. Sensors may be provided at any suitable location to sense flow, humidity, temperature and / or pressure, the like of the patient (e.g., the patient's exhaled air flow measured at the mask or any other suitable point), or either humidified or unhumidified flow at any point in the flow path, the surrounding environment, or any other point in the device or surrounding components. The device is powered by a power source.

[0061] The humidified respiratory apparatus comprises an air flow path 30, which may comprise any part through which the air 13 flow travels. The humidified respiratory apparatus may comprise a blower inlet, a blower 103, a duct 118 to the humidifier, a flow path 115 through the water chamber, an exhaust tube from the water chamber, a conduit 101 and a patient interface 102. In this embodiment, the desired temperature and humidity is that of the mask near the patient's nose / mouth, and this is the temperature and humidity that is transmitted to the patient. The target point is a suitable point in the air flow path, in this embodiment the end of the conduit (called the "end of the hose" 31, see FIG. 3), because that is the point in the flow path where the humidity and / or temperature can be controlled to a target value. The patient interface is a full face, nasal or oral mask. The mask 102 itself and the patient provide a contribution such that the humidity and / or temperature at the end of the conduit is different from that closest to the patient (i.e., at the mask and near the mouth / nose). For example, due to heat loss from the end of the hose to the mask, and due to the addition of humidity and heat from the patient's exhaled breath to the mask space, the relative humidity of the air at the mask may be much higher than at the end of the hose, which can cause condensation in the mask if the relative humidity exceeds 100%.

[0062] With reference to Figure 3, the humidification device of Figure 2 is modeled as a device with an air flow path 30 and downstream patient / mask contributions that affect the humidity and temperature of the airflow. The patient contribution (and / or, optionally, the mask contribution) is used to derive a model (based on inputs) that determines the target temperature and / or humidity at the end of the conduit that results in the desired mask temperature and humidity. With reference to Figure 4, which is an embodiment of the general case shown in Figure 1B, the controller implements a model 40 (among other functionalities) as part of an overall humidifier control program 41 to determine the target temperature and / or humidity at the target point 31 (to achieve the desired temperature and humidity at the mask) and control the heater plate 108 and breathing tube power 101a to achieve / maintain the target temperature and / or humidity at the target point 31. The desired temperature and humidity (i.e., mask humidity and temperature) are taken as inputs 42d, 42e (desired mask temperature and humidity) to the model. Also taken as inputs may be one or more of ambient temperature 19a, ambient humidity 19c, average flow rate 42a, patient peak flow rate or tidal volume 42b, and optionally mask type 42c, patient temperature 19d, patient humidity 19e, and the like.

[0063] The target temperature and / or humidity of the air in the flow path may be achieved using any of the usual control methods for a humidified respiratory device, for example using closed loop feedback (using sensors or the like) or using a model or other predictive mechanism. The target temperature and / or humidity is achieved in this embodiment using the heater plate temperature setting and the heated breathing tube power setting, which are described below with reference to FIG. 10.

[0064] In this embodiment, the controller is configured to determine both the target temperature and the target humidity, and configured to achieve / maintain both at the target point. However, in alternative embodiments, the controller may be programmed to determine and achieve only the target temperature, or only the target humidity, instead of both. If both the target temperature and the target humidity are required, the controller may be configured with a single model to determine and control both of them, or separate models (as in this embodiment) to determine and control each of them separately. If only one of the target temperature or the target humidity is required, separate models are used.

[0065] 1.2 Detailed Description of the First Embodiment The embodiment will now be described in more detail with reference to FIGS.

[0066] 1.2.1 General Description of Target Temperature and Humidity Model This embodiment uses separate models to determine the target temperature and humidity, so that these parameters can be determined and controlled in separate implementations. However, first, for overview purposes and to support the discussion of how the models are derived, a brief description of the combined target temperature and humidity model is described with reference to Figures 5, 6A, and 6B (Figure 5 is a simplified version of the model shown in Figure 4 as part of the overall control). This is followed by a detailed description of the separate models for determining the target temperature and humidity. However, this description is provided for illustrative purposes only and should not be considered limiting.

[0067] As previously mentioned, in this embodiment, the desired temperature is the temperature at the mask, referred to as the "mask temperature (M t ) or (Mask_T). The desired humidity is the humidity at the mask, called the "Mask (absolute) humidity (M h) or (mask_AH) which may be specified by patient / physician settings, or determined using measured parameters, or a combination of both. The determination of these parameters is described below. Referring to FIG. 5, once determined, M h , M t are known parameters that are inputs 42d, 42e to a target humidity and temperature model 50 based on a ("inverse") patient contribution model for humidity and temperature, along with other inputs to generate the (target) humidity (EOH_AH) 44b and temperature (EOH_T) 44a at the end of the conduit (hose). Inputs to the model 50 also optionally include patient temperature 19d and patient absolute humidity (AH) 19e, which are the temperature and humidity of the air exhaled by the patient. Rather than direct inputs, these can be inherently included in the model (as in FIG. 5), but still be considered model inputs. As an example, average values ​​obtained from the literature (e.g., 34° C., 85%, 32 mg / L) can be used. Mask type or mask parameters can also be inputs to the model, with the mask type detected by the CPAP or input by the user. However, in an alternative implementation, an average mask type is used to simplify the model. Alternatively, values ​​can be calculated using physiological patient characteristics / parameters such as height, weight, age, BMI, inspiratory temperature or humidity, tidal volume, nasal or mouth breathing, lung disease (e.g., COPD), rhinitis / cold, bronchial blood flow, hydration level, etc.

[0068] The model 50 is based on the following: In a balanced system, the flow provided by the CPAP breathing device is equal to the negative sum of the patient flow and the average / bias flow. This is shown in Figures 6A, 6B. There is a CPAP flow into the mask and a flow out of the bias hole at a constant rate. Figures 6A, 6B show the airflow during the inhalation and exhalation process considering the mask as the control volume. The patient flow can be approximated by a sine curve for the purpose of the model. The CPAP flow waveform is shown in Figure 7. The average flow can be assumed to be constant.

[0069] According to conservation of mass, and assuming the density remains the same, the volumetric flow rate of the system can be expressed by the following equation: V CPAP +V patient +V bias =0 (16)

[0070] This is equivalent to Equation 13 below.

[0071] CPAP flow has a positive sign most of the time, representing the flow into the system, while bias flow should always have a negative sign, representing the flow out of the system. Patient flow has a positive sign during exhalation and a negative sign during inhalation. However, with particularly large exhalations, the CPAP flow may reverse direction and backflow into the device, resulting in a negative flow.

[0072] The EOH air temperature and humidity levels can be considered as known input parameters in this particular analysis. Also, real-time CPAP flow rate and bias flow rate sensor measurements available from the controller can also be taken as input parameters (flow characteristics). Another input element is the ambient room conditions, which are assumed to be constant for the analysis. The average patient's exhaled breath composition depends primarily on the patient in question and varies considerably from individual to individual. Most of the studies conducted to date suggest that a temperature of 34-35 degrees Celsius and a humidity level of 75-95% at exhalation are generally acceptable values. Rather than assuming an average breathing pattern for the patient, the average flow and amplitude (or peak flow) are calculated based on the detected CPAP and bias flow rates and the breathing pattern is modeled using an appropriate function such as sine / cosine. Some of the model inputs can be determined from using the CPAP flow waveform. For example, the average flow can be obtained by calculating a moving average of the dynamic flow over 749 or more samples (15 seconds with 10 ms sensor sampling). The peak flow for each breath can be obtained by calculating the difference between the maximum flow and the average flow for each breath. A running average of this peak flow can be calculated over 15 breaths or over a set period of time to obtain the average peak flow, which can also be calculated from physiological parameters such as those mentioned above.

[0073] The above combined target temperature and humidity model is provided as an overview, where the model of this embodiment is described in detail below as a separate model.

[0074] 1.2.2 Target Humidity Model Referring to FIG. 8, once determined, M h is a known parameter that is input to a target humidity model based on the ("inverse") patient contribution model for humidity, along with other inputs to generate the (target) humidity at the end of the conduit (hose) (EOH_AH) 44b.

[0075] The patient contribution model for humidity can generally be defined as the following function: M h =f(flow characteristic,h C ,h P ) (1) During the ceremony, h C is the humidity provided to the mask by the CPAP device (in this case the humidity at the end of the hose (also EOH_AH)), h P is the humidity provided to the mask by the patient (exhaled breath), The flow characteristics represent one or more respiratory flow characteristics of the patient.

[0076] The patient contribution model is reconstructed into the following function that defines the target humidity model 50: EOH_AH=f(flow characteristic,M h ,h P, ) (2)

[0077] In one embodiment, the functional definition of the patient contribution model that specifies the actual flow characteristics is as follows: M h =f(A,J B ,h C ,h P ) (3) During the ceremony, A is the patient's peak flow rate, J B is the average flow rate (bias flow rate + leakage flow rate).

[0078] Additionally, the mask type can also be used as an input, although this is not required; an average over the mask can be used instead and is inherently included in the function.

[0079] An example of this function, such as based on a water vapor mass balance, is AH mask V mask +AH CPAP V CPAP +AH patient Vpatient =AH mixture V total (4a).

[0080] Because the mask volume is constantly flushed with incoming air, the remaining term (AH mask V mask )=0. So the equation becomes: AH CPAP V CPAP +AH patient V patient =AH mixture V total (4b)

[0081] To determine the (absolute) humidity at the end of the hose, the functional definition of the patient contribution model (3) specifying the actual flow characteristics is: EOH_AH = f(A,J B ,M h ,h p ) (5) (as shown in FIG. 8).

[0082] A specific example of the function of equation (5) can be implemented by the following equation: EOH_AH=(Mask_AH-(A / (J B * p)) * Patient_AH) / (lA / (J B * p)) (6) During the ceremony, A is the patient's peak flow rate, J B is the average flow rate, Patient_T and Patient_AH are the temperature and humidity of the air exhaled by the patient.

[0083] Thus, equation (6) is one implementation of a target humidity model for determining the target humidity at the target point at the end of the hose.

[0084] 1.2.3 Target Temperature Model Referring to FIG. 9, once determined, M t are known parameters that are input to a target temperature model based on a ("inverse") patient contribution model for temperature, along with other inputs to generate the end of conduit (hose) (target) temperature (EOH_T) 44a.

[0085] The patient contribution model for temperature can generally be defined as follows: M t =f(flow characteristic,T C ,T P ) (7) During the ceremony, T C is the temperature provided to the mask by the CPAP device (in this case the end of hose temperature (EOH_T) 44a), T P is the temperature provided to the mask by the patient (exhaled breath), The flow characteristics represent one or more respiratory flow characteristics of the patient.

[0086] The patient contribution model is reconstructed into the following function that defines the target temperature model 50: EOH_T = f(flow characteristic, M t ,T P ) (8)

[0087] In one embodiment, the functional definition of the patient contribution model that specifies the actual flow characteristics is as follows: M t =f(A,J B ,T C ,T P ,T A ) (9) During the ceremony, A is the patient's peak flow rate, J B is the average flow rate (bias flow rate + leakage flow rate), T A is, for example, the ambient temperature measured by a sensor.

[0088] Additionally, the mask type can also be used as an input, although this is not required; an average over the mask can be used instead and is inherently included in the function.

[0089] An example of this function based on the energy balance equation is:

number

[0090] At steady state, the change in energy of the air in the mask, Δ(m mask C p T mask ) becomes 0. Therefore, the equation becomes:

number

[0091] To determine the end-of-hose temperature, the functional definition of the patient contribution model (9) specifying the actual flow characteristics is: EOH_T = f(A,J B ,M t ,T P ,T A ) (11) can be reconstructed into

[0092] A particular example of this function can be implemented by the following equation:

number

number

[0093] Therefore, equation (12) is one implementation of a target temperature model for determining the target humidity at the target point at the end of the hose.

[0094] Thus, equation (6) can be used to determine the target humidity and equation (12) can be used to determine the target temperature, which can then be achieved using a control method programmed into the controller. Alternatively, a neural network can be used to determine the target humidity and temperature using the inputs described above.

[0095] 1.2.4 Derivation of the target humidity and temperature model Here, the derivation of the patient contribution, target temperature and target humidity models is described.

[0096] 1.2.4.1 Background definition The following abbreviations are used: Index: "C" - "CPAP", "P" - "Patient", "B" - "Bias (flow)", "M" - On Mask (mixed), "A" - "Ambient", J X,X=C,P,B -Volume flow rate, h X,X=C,P,M - Absolute Humidity (mgH2OL -1 in air), T X,X=C,P,M -Temperature (℃), V LUNG is the ventilation per breath, br_period is the breathing time, and RF is the breathing rate.

[0097] Referring to FIGS. 6A and 6B, according to the law of conservation of mass, and assuming the density remains the same, the system shown can be written as follows: J C (t)+J P (t)-J B =0 (13)

[0098] When exhaust pressure is constant (atmospheric), J B is also constant. For illustrative purposes, the sinusoidal time dependence of the flow to / from the lungs on the patient flow is P = Asin(ωt), where A is the amplitude or peak flow of the patient.

[0099] With reference to Fig. 11a, if we consider the mask 90 as an open system or control volume, the thermodynamic interactions involved are mainly the mixing of different fluids. During the exhalation phase, the remaining air 91 inside the mask (i.e. the mixture from the last breathing cycle) mixes with the inflowing CPAP air 92 and the patient's exhaled air 93, while during the inhalation phase, the remaining air inside the mask is largely flushed out by the large volume of inflowing CPAP air. This is the mass convection and diffusion process shown in Fig. 11a.

[0100] In most CPAP device operating environments, the room has a lower temperature than the air inside the mask, resulting in heat exchange from inside the system to the outside. The breathing cycle can be considered as a thermodynamic circulatory process, with each exhalation being relatively similar, and it is assumed that the remaining air in the mask is flushed out by the inflowing CPAP air during inspiration, restoring the mask state to the initial state. Therefore, the average air temperature inside the mask averaged over each cycle of the inhalation and exhalation process should remain approximately constant. For this reason, a steady-state heat transfer process involving convection 95a, 95b and conduction 94 is considered as shown in FIG. 11b.

[0101] The thermodynamic process in the occlusive mask referred to above is likely to be turbulent mixing due to the nature of rapid fluctuations in velocity in a small space. Turbulence is an effective aid in the molecular mixing process because flow creates a large interfacial surface area that promotes the diffusion process.

[0102] Turbulent mixing is usually classified into three levels: (1) passive mixing, such as mixing of density-matched fluids; (2) dynamics-coupled mixing, such as Rayleigh-Taylor instability flows for fluids of different densities in an acceleration field; and (3) mixing that alters the flow, such as pressure rise. Air mixing inside a mask falls into the first category because the fluids involved (i.e., air) are of similar density. For such mixing processes, no mixing analysis is required to describe the flow dynamics. Therefore, there is no need to consider changes in the flow pattern during each respiratory cycle due to the mixing process.

[0103] 1.2.4.2 Derivation of the target humidity model The water vapor mass (m) rate balance averaged over one breathing cycle is

number

number

number

number

[0104] Due to the complexity of the form, simplifications can be made. A scalar conservation of mass of water vapor at some discrete point during the breathing cycle applies. This assumes that the incoming CPAP air is well mixed with the exhaled air and the remaining air inside the mask before exiting through the bias hole. The mathematical expression is as follows (mass inflow of water vapor into the mask equals mass outflow of water vapor): AH mask V mask +AH CPAP V CPAP +AH patient V patient =AH mixture V total (4a)

[0105] Because the mask volume is constantly flushed with incoming air, the remaining term (AH mask V mask )=0. So the equation becomes: AH CPAP V CPAP +AH patient V patient =AH mixture V total (4b)

[0106] From the above equation, the average humidity of the air in the mask is: Mask humidity = function(A,J B ,h C ,h P ) (3) It can be written as follows.

[0107] Solving the above equation for the target humidity gives us EOH_AH = f(A,J B ,M h ,h p ) (5) and, as mentioned before, EOH_AH=(Mask_AH-(A / (J B * p)) * Patient_AH) / (lA / (J B * p)) (6) It is.

[0108] 1.2.4.3 Derivation of the target temperature model Using the same approach for temperature, the thermal energy balance equation for the mask system can be written as:

number

[0109] The air mixing process is assumed to be completed before the air exits the system through the bias holes during both inspiration and expiration. The expiration phase is the process during which the mixed air gains additional heat and humidity.

[0110] 1. The mask temperature obtained from the previous step is used to calculate the mask temperature in the current step, thus obtaining the iterative model represented by the following equation:

[0111] 2. The model output gives the mask air temperature as a function of time during each respiratory cycle, and the average value is calculated and compared with the experimental measurements. However, the results showed errors mostly in one direction.

[0112] From the second law of thermodynamics, it is known that heat flows from a hotter object to a cooler object. In most CPAP operating environments, the air inside the mask is likely to have a temperature higher than the surrounding room temperature, and there will be heat lost from inside the mask to the atmosphere.

[0113] The energy balance equation including heat losses is:

number

[0114] At steady state, the change in energy of the air in the mask, Δ(m mask C p T mask ) becomes 0. Therefore, the equation becomes:

number

[0115] Using the concept of thermal resistance,

number

[0116] Due to the complex geometry of the mask, it is very difficult to theoretically calculate these thermal resistances, therefore an experimental approach was taken to obtain a statistical relationship to the thermal resistances using experimental measurements.

[0117] Solving the above equation for the mask temperature gives the average temperature of the air at the mask: Mask temperature = f(A,J B ,T C ,T P ,T A ) (9) It can be written as follows.

[0118] Solving the above equation for the target temperature gives: EOH_T = f(A,J B ,M t ,T P ,T A ) (11) and, as mentioned before,

number

[0119] 1.2.5 Humidified respirator control The controller is configured to implement the above model using equations (6) and (12) to determine target temperature and humidity at the end of the hose. Once those targets have been determined, the controller is also configured to operate the humidified breathing apparatus to achieve those targets at the target point (the end of the hose). This is shown generally in Figure 4, and a detailed example of the overall device control (implemented by the controller) for this embodiment is shown in Figure 10.

[0120] With reference to those figures, a user or physician inputs preferred temperature and / or humidity settings into the humidified respiratory device via a user input control interface 114. An ambient temperature 19a is also received as an input to the controller, for example from a temperature sensor located outside the respiratory device. The controller 109 includes a lookup table or similar implementation that uses the ambient temperature 19a and user settings 19b to determine the desired mask humidity 42e and temperature 42d. For example, the mask relative humidity (Mask_RH), mask temperature (Mask_T) 42d and mask absolute humidity (Mask_AH) 42e are pre-determined for each comfort setting of ambient temperatures between 5°C and 35°C, and these are programmed into the lookup table of the controller. These values ​​are defined based on feedback from patient trials or other empirical methods. The desired Mask_T 42d and Mask_AH 42e can be determined using two lookup tables in the unit memory for each user setting and different ambient temperatures.

[0121] The controller 109 then uses the desired mask humidity 42e and temperature 42d as inputs to equations (6), (12) which implement the target temperature and humidity model 50. The controller 109 also uses the average flow rate 42a, peak flow rate 42b and ambient temperature 19a as inputs to those equations when received from the appropriate sensors / inputs. The target temperature and humidity model 50 then outputs the target end of hose humidity (EOH_AH) 44b and temperature (EOH_T) 44a as previously described.

[0122] The controller 109 then operates the humidified respirator to achieve and maintain the target humidity and temperature. In this embodiment, the controller does this by controlling the heater plate (HP) 108 to control the target humidity and the breathing tube heater (HBT) 101a to control the target temperature. To control the heater plate 108 to achieve the target humidity, the controller 109 uses the target humidity (end of hose temperature 44a) along with the ambient temperature 19a, ambient humidity 19c (measured by a sensor or determined through a model) and average flow rate 42a as inputs to a neural network model or equation 120 that outputs a target heater plate temperature 43a that achieves the target end of hose humidity 44b. The controller 109 also optionally uses an end of hose humidity sensor 122 that reads the inputs to the model 120 as feedback. Similarly, to control the heated breathing tube to achieve a target temperature (end of hose temperature 44a), the controller 109 uses the target temperature along with the ambient temperature 19a, average flow rate 42a and heater plate temperature 43a as inputs to a neural network model or equation 121 which outputs a target power 43b to the heated breathing tube 101 to achieve the target end of hose temperature 44a. The controller 109 also optionally or alternatively uses an end of hose temperature sensor 123 which reads as feedback an input to the model 121. Based on the heater plate target temperature 43a and the HBT target power 43b, the controller 109 generates and delivers control voltages to the heater plate 108 and breathing tube heater 101a, respectively, to control them to achieve and maintain the target heater plate temperature 43a and breathing tube power 43b and achieve the target temperature / humidity at the end of the hose 44a, 44b.

[0123] The above embodiment can be run as an open loop system where there are no sensors to measure the output humidity and temperature. Optionally, however, there may be sensors to measure the humidity and / or temperature at the end of the mask or hose. If sensors are present, the following occurs:

[0124] If a sensor 117 is implemented to measure the temperature of the mask 102, then according to a feedback control loop, the HBT power 43b is adjusted to maintain the target mask temperature 42d, bypassing the target temperature model (T) 50 and the neural network model (HBT) 121. In this case, only the target humidity model 50 for the heater plate 108 and the neural network model 120 will be used.

[0125] Similarly, if the sensor 117 is implemented to measure the humidity (AH or RH) of the mask 102, then according to a feedback control loop, the HP temperature / power 43a is adjusted to maintain the target mask humidity 42e, bypassing the target humidity model (AH) 50 and the neural network model (HP) 120. In this case, only the target temperature model 50 for the breathing tube heater and the neural network model 121 will be used.

[0126] If a sensor 123 is implemented to measure the temperature at the end of the hose, then according to a feedback control loop, the HBT power 43b is adjusted to maintain the target EOH T 44a, in this case bypassing the neural network model (HBT) 121. However, the patient contribution model (T) 50 will still be used to calculate the EOH T 44a from the mask temperature target 42a.

[0127] If a sensor 122 is implemented to measure humidity at the end of the hose, then according to a feedback control loop, the HP temperature / power 43a is adjusted to maintain the target EOH humidity 44b, bypassing the neural network model (HP) 120. However, the patient contribution model (AH) 50 will still be used to calculate the EOH AH 44b from the mask AH target 42e.

[0128] The illustrated humidity control model 120 can be a machine learning algorithm such as a neural network model or a set of equations. The neural network model can be implemented in a controller to predict the HP 43a and HBT settings 43b under different conditions to achieve the EOH targets (AH and T) 44b, 44a. The model 120 is trained using known input and output parameters from experimental data to mimic the relationships of a physical system. The model 120 is then implemented in a controller to predict the required settings output using different sets of inputs. Preferably, the HP model 120 is started first. This model determines the HP temperature 43a to maintain the target EOH AH 44b under different conditions (ambient T, ambient AH and flow rate). The HBT model 121 takes the HP setting 43a as an input and controls the HBT power 43b to compensate for the remaining EOH_T 44a requirements under different conditions (ambient T and flow rate).

[0129] The model may optionally include additional functionality to take other effects into account. If the water level in the water chamber decreases overnight due to the shape of the water chamber, the moisture absorption capacity and therefore the humidity level delivered will also decrease. By compensating for the decrease in water level, a constant level of humidity can be maintained throughout the night.

[0130] This is done using the following steps:

[0131] Step 1 - Calculate Water Level Estimate The water level estimate is calculated using the following inputs: ambient absolute humidity (Amb_AH), output humidity at the end of the target hose (EOH_AH), average flow rate (L / min) and nightly CPAP runtime. - The initial WL (water level at the start of treatment) can be assumed to be the total water chamber volume. - Units AH = EOH_AH - Amb_AH [AH added by CPAP (mg / L)] - Evaporation rate = AH units * Average flow rate [evaporation rate (mg / min)] - Water evaporated (mg) = evaporation rate * Runtime (hours) * 60 - Water level (mg or ml) = initial WL - evaporated water

[0132] Step 2 - Calculate HP Settings The mathematical model was described above with reference to FIG. 10, which relates the output humidity (or moisture absorption) as a function of the heater plate temperature, the ambient temperature, the input humidity and the flow rate. The water level is also added as an input to the model. By rearranging this equation, the heater plate temperature setting can be obtained. Alternatively, the water level can be added as an input to a neural network model.

[0133] 1.2.6 Humidity and Temperature Control Model Here, examples of the mathematical HP 120 and HBT 121 models are described in more detail. The models are divided into two subsystems: the humidity model (mainly the humidifier chamber) 120 and the temperature model 121 (mainly the heated breathing tube). The models described below relate to a specific humidified breathing apparatus configuration. If the configuration is changed, the equations will change. Returning to Figure 2, the respirator configuration has a water chamber that holds approximately 400 ml of water on top of a heater plate for evaporation of the water in the water chamber. The temperature of the heater plate (T HPLThere is a sensor to measure the current (P) 119 in the tube. The incoming air flows over the water surface and picks up humidity. This humidity is transported through the hose 101, which is heated over its entire surface using HBT (Heater in Breathing Tube) 101a to prevent rainout due to temperature drop. The power (P HBT ) is controlled to obtain the desired temperature 44a at the end of the hose as previously described.

[0134] 1.3 Alternative Embodiments The above is one embodiment. Many other embodiments will be considered by those skilled in the art. Different implementations of the target temperature and humidity model 50 (different equations defining the target temperature and humidity model 50) can be considered, along with different heater plate 120 and heated breathing tube 121 control models and implementations. Moreover, the above embodiment uses the end of the hose as the target point, and the model used relates to the patient contribution, which affects the humidity and temperature of the mask contribution. Other target points in the respiratory device flow path can be used, and appropriate models are used to compensate for the contribution to humidity and temperature made by downstream parts of the respiratory device. For example, the humidifier outlet can be used as the target point, and the model will take into account the patient and breathing tube contributions.

[0135] In an alternative embodiment, there is an unheated breathing tube (i.e., no heating) and the only controlled parameter is the heater plate temperature 119. This means that the AH 42e and temperature 42d at the mask cannot be controlled independently since they are both determined by the heater plate setting. An equation can be used to determine the HP setting for a particular ambient temperature, ambient humidity, average flow rate, and desired mask_RH or EOH_RH.

[0136] Although the embodiments described herein refer to the mask humidity and mask temperature as the desired temperature / humidity closest to the patient, this should not be considered limiting - models can be created to achieve the desired temperature / humidity at other points in the flow path.

[0137] In further embodiments, it is possible to estimate parameters (such as the patient's exhaled air humidity and temperature and tidal volume) based on further information about the patient (such as height, weight, lung volume, age, sex, BMI, etc.) or the environment (such as ambient temperature, inhaled air temperature, etc.), or whether the patient is a nose or mouth breather.

[0138] Another way to express the average humidity and temperature at the mask when the patient's breathing cannot be assumed to be sinusoidal is Mask humidity = function(V LUNG ,RF,J B ,h C ,h P ) Mask temperature = function(V LUNG ,RF,J B ,T C ,T P ,T A ) where RF=respiratory rate.

[0139] An empirical relationship can be devised for tidal volume through body surface area (BSA), weight (W) and height (H), so that V in the above function LUNG These can be substituted instead of

[0140] Also, RF in the above functions can be replaced with br_period.

[0141] List of parameters Throughout this specification, various parameters are used. In some instances, the same parameters are represented by different symbols or acronyms in different equations. For clarity, the set of parameters used in the equations and their symbols are listed below. The desired absolute humidity at the mask is Mask_AH, M h , h M , Mask Humidity, AH mixture , A.H. mask It is called. The desired relative humidity at the mask is called Mask_RH. The desired temperature at the mask is Mask_T, M t , T M , mask temperature, T mask It is called. The absolute humidity of the air at the end of the patient's breathing tube is EOH_AH, h C , A.H. CPAP It is called. The relative humidity of the air at the end of the patient's respiratory tract is called EOH_RH. The temperature of the air at the end of the patient's breathing tube is EOH_T, T C , T CPAP It is called. The absolute humidity of the patient's breath is Patient_AH, h P , patient humidity, AH Patient It is called. The temperature of the patient's breath is Patient_T, T P , patient temperature, T Patient The generally constant flow rate exiting the mask bias hole (and leaking through the mask) is called the average flow rate, Avg Flow, J B , called av.Flow. The amplitude of the assumed sinusoidal patient flow velocity is called the peak flow, A. Ambient temperature is Amb_T, T A , Amb.Temperature, ambient temperature, T amb It is called. The ambient humidity is called Amb_AH, ambient humidity. The specific heat and (average) density of air at a constant (average) process pressure are, respectively, C p and is called ρ. The effective thermal conductivity through the mask is k eff It is called. The surface area of ​​the mask is called S. The heater plate is called HP. The breathing tube heater is called the HBT. The temperature of the heater plate is T HPL It is called. The power of the heating tube is P HBT It is called. Neural networks are referred to as NNs. The ventilation volume per breath is V LUNG It is called. The breathing period is called br_period. The respiratory rate is called RF. The volumetric flow rate of CPAP is V CPAP ,J C It is called. The flow rate of the patient's respiratory volume is V patient ,J P It is called. The volumetric flow rate through the bias hole is V bias ,J B ,V total It is called. The volume of the mask is V mask It is called. The absolute humidity of the air in the mask is AH mask It is called. The heat lost to the atmosphere through the mask is Q lost It is called. The forced convection resistance inside the mask is R in It is called. The conduction resistance through the mask is R cond It is called. The natural convection resistance from the mask to the surroundings is R out It is called. The temperature of the inner surface of the mask is T inWall It is called. The temperature of the outer surface of the mask is T outWall It is called.

Claims

1. 1. A humidified respiratory device for generating and delivering humidified air to a patient, comprising: a humidifier for use with an air delivery conduit and a patient interface, the humidifier, the air delivery conduit and the patient interface forming an air flow path in use, the humidifier having a heater plate; The humidified breathing apparatus includes a controller for controlling an operation of the humidified breathing apparatus; The controller is configured to model a mass flow rate of water vapor for the patient interface according to an equation that defines a balance between a mass of water vapor to the patient interface and a mass of water vapor from the patient interface; In the model, a mass of water vapor to the patient interface includes a mass of water vapor delivered from the air delivery conduit to the patient interface and a mass of water vapor flowing into the patient interface by the patient's breathing, and in the water vapor mass flow equation, the mass of water vapor delivered from the air delivery conduit to the patient interface is calculated based on a target absolute humidity and a delivered flow rate, and the mass of water vapor flowing into the patient interface by the patient's breathing is calculated using the target absolute humidity and the flow rate and absolute humidity of the patient's breathing, a mass of water vapor from the patient interface including a mass of water vapor carried by air flowing through the bias hole of the patient interface, and in an equation for mass flow rate of water vapor, the mass of water vapor carried by air flowing through the bias hole of the patient interface is calculated using the flow rate and absolute humidity of air flowing through the bias hole; In the water vapor mass flow equation, reflecting steady state, the mass of water vapor into the patient interface is equal to the mass of water vapor out of the patient interface; The controller may include the following parameters: (i) a desired absolute humidity at the patient interface input by a user into the humidified respiratory device; and (ii) the patient's respiratory flow rate and absolute humidity estimated based on information about the patient; and (iii) the flow rate and absolute humidity of air exiting through the bias hole of the patient interface as determined by a flow sensor and the desired absolute humidity; and and determining the target absolute humidity at the end of the air transmission conduit downstream of the heater plate in the model according to the water vapor mass flow rate equation using the above-mentioned parameter, the target absolute humidity determined by the above-mentioned parameter being the target absolute humidity for maintaining the steady state in the water vapor mass flow rate equation; The controller is configured to control the heater plate to evaporate water to provide a mass of water vapor in the air flow path to achieve and maintain the target absolute humidity.

2. 2. The humidified respiratory apparatus of claim 1, wherein the controller is configured to use a neural network to control the heater plate to achieve and maintain the target absolute humidity.

3. 3. The humidified respiratory apparatus of claim 2, wherein the neural network uses as inputs a target absolute humidity, an ambient temperature, an ambient absolute humidity, and an average flow rate of air flowing through the bias hole, and the neural network outputs a target heater plate temperature that achieves the target absolute humidity.

4. 4. A humidified respiratory apparatus as claimed in claim 3, wherein the neural network uses an absolute humidity sensor reading at the end of a hose as an input.

5. 2. The humidified respiratory apparatus of claim 1, wherein the controller is configured to control the heater plate using a feedback control loop and using an absolute humidity sensor at the end of a hose as an input to achieve and maintain the target absolute humidity.

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