System and method for controlling humidity output in humidifier

Abstract

To provide a humidifier for humidifying a gas flow supplied to a user.SOLUTION: The invention comprises: a humidifier 104 which is used for delivering heated and humidified gas to a patient, and includes a humidification chamber 134 including an inlet 111 and a related sensor 113; a related heater and sensor; an inspiration conduit 106 including the related heater and sensor; and a connection unit 116 for a patient which is not heated, such as a face mask. The humidifier can comprise: a control system 130 which is configured to change, a humidification chamber outlet temperature setting point, including for example, a maximum outlet temperature setting point, or an amount of generated moisture, according to an inlet gas temperature. The control system can maintain substantially consistent humidity in the gas delivered to the patient, and can reduce rainout (namely, condensate), and / or minimize generation of the condensate.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates generally to humidifying gases for medical procedures, such as respiratory humidification, humidification during high flow therapy, and humidification during anesthesia / sedation, or other medical procedures in which humidified gases are delivered to a patient. More specifically, the present disclosure relates to a respiratory assistance system including at least a humidifier and a method of operating the humidifier to control the temperature and / or humidity level of respiratory gases. [Background technology]

[0002] During unassisted inspiration, the upper airway heats and humidifies the inhaled gas to humidity conditions of approximately 100% relative humidity, or approximately 44 mg / L absolute humidity, at body temperature of approximately 37° C. A humidifier operating as part of a respiratory assistance system may be beneficial in heating and humidifying the respiratory gas to a humidity condition such that the respiratory gas reaching the patient's lungs is humidified, thereby mitigating any adverse physiological effects resulting from the delivery of dry gas to the patient's airways. Summary of the Invention [Problem to be solved by the invention]

[0003] Many humidifiers can monitor the amount of humidity added to the incoming gas, for example by controlling the power to the heater plate of the humidifier to control the absolute humidity of the gas being humidified. However, some humidifiers do not necessarily have an integrated hygrometer or other humidity meter to obtain information about the incoming gas, which makes it more difficult to directly detect the humidity of the incoming gas. Humidifiers are often used with a dry gas source, for example a canister or wall gas source, or a ventilator that supplies dry gas (i.e., unhumidified gas). When a humidifier is connected to a room air entrainment ventilator as a gas source, the inability to directly detect the incoming humidity can lead to inaccurate delivered humidity, which can often result in an undesirable amount of condensation formation (aka "rainout") in the inspiratory tubing (i.e., gas delivery conduit) or in the patient connection device due to over-humidification of the gas.

[0004] This undesirable amount of condensation (i.e., rainout) may result from the fact that the humidity of the air entrained by the room air entrainment ventilator is usually higher than the dry gas from the wall source or canister. The humidity difference between the room air and the gas from the wall source or canister may be even more pronounced in more tropical countries and regions. Additionally, room air entrainment ventilators typically use turbines, which may heat the gas.

[0005] Because most humidifiers heat and humidify the incoming gas under the assumption that the incoming gas is dry, high humidity in the incoming air may result in excessive humidity being delivered to the patient. Such humidifiers may add excess humidity to the incoming room air to reach a predetermined set point at the humidification chamber outlet under the assumption that the incoming gas is dry.

[0006] Operating under the above assumptions, the existing humidity from the existing room air can cause the dew point of the gas in the gas flow path to be higher than when dry gas is used as the gas source to the humidifier. Thus, when room air is used as the gas source, the humidity of the gas at the chamber outlet is usually relatively high. When the humidity of the gas at the chamber outlet is relatively high, the temperature of the gas must be maintained above the dew point to prevent condensation. In comparison, when dry gas is used as the gas source, the gas at the chamber outlet may have a relatively low humidity and a relatively low dew point. Thus, the temperature of the gas when dry gas is used as the gas source may be lower due to the relatively low dew point. When the gas flow is cooled along the flow path between the humidification chamber and the patient connection device, the humidity of the gas from the entrainment ventilation device in the room is higher than expected. This narrows the available temperature range to which the gas can be cooled before reaching the dew point, resulting in rainout. Rainout is specifically a problem in the patient connection apparatus at the distal or patient end of the intake tube (i.e., the guide tube), thus causing discomfort and / or inconvenience to the patient. Furthermore, rainout is a greater problem because the patient connection apparatus and its components are not heated, resulting in a relatively rapid drop in temperature compared to the intake tube, which is typically heated. Furthermore, condensation within the tube or the patient connection apparatus can be dangerous to the patient. [Means for solving the problem]

[0007] The present disclosure provides systems and methods for reducing rainout in the inspiratory tract and / or patient interface while still delivering a substantially consistent target humidity to the patient. The present disclosure relates to systems and methods for reducing rainout while humidifying the ambient air and still providing a minimum therapeutic humidity to the patient. The minimum therapeutic humidity reduces dehumidification or drying of the patient's airway, improving patient comfort.

[0008] The humidifier can provide different levels of therapeutic humidity in different therapy applications, such as in a hospital or home health care environment. For example, the humidifier can deliver a desired humidity level of about 44 mg / L BTPS (fully saturated at about 37° C.) for invasive and / or high flow therapy, and / or about 32 mg / L BTPS (fully saturated at about 31° C.) for non-invasive therapy. Other appropriate patient comfort settings can also be delivered for different therapy types.

[0009] The system can output a desired humidity level in the gas delivered to the patient over a range of inlet source conditions, such as a gas source that includes various chamber inlet temperatures (i.e., inlet temperatures) and / or room air entrainment ventilation. Advantageously, the system can reduce rainout, for example, by reducing the humidity output of the humidification chamber below the desired humidity.

[0010] In some examples, the desired humidity of the gas delivered by the humidifier to the patient may be based on one or more assumptions about the incoming gas, such as that the incoming gas is dry. However, such assumptions are not always correct. For example, when the incoming gas, such as ambient air, contains some moisture, the humidity of the gas delivered to the patient may be too high, resulting in rainout. In some systems, rainout may be managed by using a humidity sensor or by otherwise directly measuring the humidity of the incoming gas. However, the system may reduce the humidity output of the humidifier's humidification chamber while maintaining a substantially consistent humidity in the gas delivered to the patient without using a humidity sensor and / or receiving a direct input of the humidity of the incoming gas. For example, the system may determine a parameter of the input gas and use the determined parameter as an indication of the type of input gas and / or the type of gas source.

[0011] Described herein are exemplary systems and methods for reducing excess condensation in a humidifier while still delivering a substantially consistent humidity of the gas delivered to a patient, regardless of the type of gas source (e.g., regardless of the type of ventilator). Certain aspects, advantages, and novel features of the present disclosure are described herein. It is to be understood that not all such advantages may necessarily be achieved in accordance with any particular embodiment of the present disclosure. Thus, the features, aspects, and advantages of the present disclosure may be implemented or performed in a manner that achieves or selects one advantage or group of advantages taught herein without necessarily achieving other advantages that may be taught or suggested herein.

[0012] A humidifier for humidifying a gas flow supplied to a user may comprise a base unit which may include a heater plate; a humidification chamber which may be configured to hold a humidification fluid, the humidification chamber may comprise a conductive base, one or more wall portions which may be configured to be coupled to the base portion, an inlet, and an outlet; at least one inlet temperature sensor disposed within or adjacent to the inlet of the humidification chamber; and at least one outlet temperature sensor disposed within or adjacent to the outlet of the humidification chamber; and a controller which may be configured to output a heater plate control signal to control an amount of power supplied to the heater plate in response to an outlet temperature being measured from a signal received from the outlet temperature sensor; determine an inlet temperature of gas received by the humidification chamber based on the signal received from the inlet temperature sensor; determine when the inlet temperature exceeds a threshold temperature; and reduce a target humidity of gas exiting the outlet of the humidification chamber in response to the inlet temperature exceeding the threshold temperature.

[0013] The humidifier may reduce the target humidity, and the controller may be configured to reduce the amount of power provided to the heater plate in response to the inlet temperature exceeding the threshold temperature. This reduced target humidity is achieved by controlling the power provided to the heater plate. The amount of power provided to the heater plate produces the required target humidity. The target humidity is reduced from the target humidity limit to a relatively low target humidity. In another exemplary implementation, the controller is configured to cap or limit the target humidity to a second humidity if the inlet temperature exceeds the threshold temperature.

[0014] The controller may be configured to reduce the amount of power below a power threshold.

[0015] The power threshold may be set to achieve a minimum dew point of 19°C.

[0016] The power threshold may be set to achieve a minimum humidity output of 15 mg / L.

[0017] The power threshold may be set to achieve a dew point of 25°C.

[0018] The power threshold may be set to achieve a humidity output of 22 mg / L.

[0019] The controller may be configured to control the amount of power supplied to the heater plate in a first mode when the inlet temperature is below a threshold temperature and in a second mode when the inlet temperature is above the threshold temperature.

[0020] In a first mode, the controller may be configured to set a power setpoint, or a chamber exit setpoint, or a heater plate temperature setpoint to achieve a minimum humidity of at least 15 mg / L.In a second mode, the controller may be configured to set a power setpoint, or a chamber exit setpoint, or a heater plate temperature setpoint to achieve a minimum humidity of at least 22 mg / L.

[0021] In a first mode, the controller may be configured to set a power setpoint, or a chamber exit setpoint, or a heater plate temperature setpoint to achieve a minimum dew point of at least 19° C. In a second mode, the controller may be configured to set a power setpoint, or a chamber exit setpoint, or a heater plate temperature setpoint to achieve a minimum dew point of at least 25° C.

[0022] The controller may be configured to control the amount of power supplied to the heater plate power according to a first function that is applied when the inlet temperature is below a threshold temperature.

[0023] The controller may be configured to control the amount of power supplied to the heater plate power according to a second function, which may be different from the first function, that is applied when the inlet temperature exceeds a threshold temperature. The first function and the second function may together define piecewise functions.

[0024] The controller may be configured to lower the target outlet temperature if the inlet temperature exceeds a threshold temperature. If the inlet temperature exceeds a threshold temperature, the target outlet temperature is lowered from a target outlet temperature limit to a lower target outlet temperature. In another example, the controller is configured to limit or cap the target outlet temperature.

[0025] The controller may be configured to lower the target heater plate temperature if the inlet temperature exceeds the threshold temperature. If the inlet temperature exceeds the threshold temperature, the target heater plate temperature is lowered from the target heater plate temperature limit to a lower target heater plate temperature. In another example, the controller is configured to limit or cap the target heater plate temperature.

[0026] The threshold temperature may be between 22°C and 24°C.

[0027] The threshold temperature may be 22°C.

[0028] The threshold temperature may be 24°C.

[0029] This threshold temperature may vary depending on the outlet temperature set point.

[0030] The desired dew point may be selected by the user.

[0031] The humidifier may be operable in one of a number of modes, each mode defining a number of desired dew points, and when operating in any one of the multiple modes, the controller may be configured to reduce the amount of humidity generated based on the inlet temperature exceeding a threshold.

[0032] The multiple modes may include an invasive mode, a non-invasive mode, and a high flow mode.

[0033] The mode may be manually selectable by the user.

[0034] The non-invasive mode may include desired dew points of 31°C, 29°C, 27°C, and 25°C.

[0035] The humidifier may be operable in one of a number of modes, each mode defining a number of outlet temperature set points, and when operating in any one of the multiple modes, the controller may be configured to reduce the amount of humidity generated based on the inlet temperature exceeding a threshold.

[0036] A target humidity for the outlet temperature setpoint may be predetermined when the inlet temperature may fall below a threshold temperature, and if the inlet temperature exceeds the threshold, the amount of humidity generated at that outlet temperature setpoint may be reduced to a relatively low, preset value.

[0037] A humidifier for humidifying a gas flow supplied to a user may comprise a base unit which may include a heater plate; a humidification chamber which may be configured to hold a humidification fluid, the humidification chamber may comprise a conductive base, one or more wall portions which may be configured to be coupled to the base portion, an inlet, and an outlet; at least one inlet temperature sensor disposed within or adjacent to the inlet of the humidification chamber; and at least one outlet temperature sensor disposed within or adjacent to the outlet of the humidification chamber; and an electronic controller which may be configured to output a heater plate control signal to control an amount of power supplied to the heater plate in response to an outlet temperature being measured from a signal received from the outlet temperature sensor; determine an inlet temperature of gas received by the humidification chamber based on the signal received from the inlet temperature sensor; determine whether the inlet temperature exceeds a threshold temperature; and reduce a target humidity of gas exiting the outlet of the humidification chamber in response to the inlet temperature exceeding the threshold temperature.

[0038] The humidifier may reduce the target humidity and the controller may be configured to reduce the amount of power supplied to the heater plate in response to the inlet temperature exceeding the threshold temperature.

[0039] The controller may be configured to reduce the amount of power below a power threshold.

[0040] A decrease in the amount of power delivered to the heater plate below the power threshold decreases the humidity output of the humidifier. The controller is configured to deliver power to the heater plate corresponding to the target humidity. The power delivered to the heater plate of the humidifier causes the humidifier to output a target humidity at or near the target humidity.

[0041] The power threshold may be set to achieve a minimum dew point of 19°C.

[0042] The power threshold may be set to achieve a minimum humidity output of 15 mg / L.

[0043] The power threshold may be set to achieve a dew point of 25°C.

[0044] The power threshold may be set to achieve a humidity output of 22 mg / L.

[0045] The controller may be configured to control the amount of power supplied to the heater plate in a first mode when the inlet temperature is below a threshold temperature and in a second mode when the inlet temperature is above the threshold temperature.

[0046] In a first mode, the controller may be configured to set a power setpoint, or a chamber exit setpoint, or a heater plate temperature setpoint to achieve a minimum humidity of at least 15 mg / L.In a second mode, the controller may be configured to set a power setpoint, or a chamber exit setpoint, or a heater plate temperature setpoint to achieve a minimum humidity of at least 22 mg / L.

[0047] In a first mode, the controller may be configured to set a power setpoint, or a chamber exit setpoint, or a heater plate temperature setpoint to achieve a minimum dew point of at least 19° C. In a second mode, the controller may be configured to set a power setpoint, or a chamber exit setpoint, or a heater plate temperature setpoint to achieve a minimum dew point of at least 25° C.

[0048] The controller may be configured to control the amount of power supplied to the heater plate power according to a first function that is applied when the inlet temperature is below a threshold temperature.

[0049] The controller may be configured to control the amount of power supplied to the heater plate power according to a second function, which may be different from the first function, that is applied when the inlet temperature exceeds a threshold temperature.

[0050] The first function and the second function define a piecewise function. The piecewise function may define a heater plate power. A further piecewise function may define a target humidity. The piecewise function of the target humidity may correspond to or relate to the piecewise function that defines the heater plate power.

[0051] If the inlet temperature exceeds the threshold temperature, the controller may be configured to decrease the target outlet temperature.

[0052] If the inlet temperature exceeds the threshold temperature, the controller may be configured to decrease the target heater plate temperature.

[0053] The threshold temperature may be between 22°C and 24°C.

[0054] The threshold temperature may be 22°C.

[0055] The threshold temperature may be 24°C.

[0056] This threshold temperature may vary depending on the outlet temperature set point.

[0057] The desired dew point may be selected by the user.

[0058] The humidifier may be operable in one of a number of modes, each mode defining a number of desired dew points, and when operating in any one of the multiple modes, the controller may be configured to reduce the amount of humidity generated based on the inlet temperature exceeding a threshold.

[0059] The multiple modes may include an invasive mode, a non-invasive mode, and a high flow mode.

[0060] The mode may be manually selectable by the user.

[0061] The non-invasive mode may include desired dew points of 31°C, 29°C, 27°C, and 25°C.

[0062] The humidifier may be operable in one of a number of modes, each mode defining a number of outlet temperature set points, and when operating in any one of the multiple modes, the controller may be configured to reduce the amount of humidity generated based on the inlet temperature exceeding a threshold.

[0063] A target humidity for the outlet temperature setpoint may be predetermined when the inlet temperature may fall below a threshold temperature, and if the inlet temperature exceeds the threshold, the amount of humidity generated at that outlet temperature setpoint may be reduced to a relatively low, preset value.

[0064] A humidifier for humidifying a gas flow supplied to a user includes a base unit including a heater plate, a removable humidification chamber that may include a conductive base and one or more walls extending from the conductive base, the one or more walls and the conductive base defining a chamber space for holding a humidification fluid, the humidification chamber further including an inlet and an outlet, at least one inlet temperature sensor disposed within or adjacent to the inlet of the humidification chamber, and at least one outlet temperature sensor disposed within or adjacent to the outlet of the humidification chamber. and an electronic controller which may be configured to output a heater plate control signal to control the amount of power supplied to the heater plate in response to an outlet temperature being measured from a signal received from the outlet temperature sensor, to measure an inlet temperature of gas received in the humidification chamber based on a signal received from the inlet temperature sensor, to determine when the inlet temperature exceeds a threshold temperature, to set a first outlet temperature set point if the inlet temperature is below the threshold temperature, and to set a second outlet temperature set point if the gas inlet temperature exceeds or equals the threshold temperature.

[0065] The threshold temperature may be between 22°C and 24°C.

[0066] The first outlet temperature set point may be between 24°C and 32°C.

[0067] The second outlet temperature set point may be between 19°C and 27°C.

[0068] The electronic controller may be configured to control the power delivered to the heater plate based on the chamber outlet temperature set point.

[0069] The electronic controller may be configured to reduce the heater plate power when the inlet temperature exceeds a threshold temperature.

[0070] The electronic controller is configured to control the power delivery such that a first power is delivered to the heater plate when the inlet temperature is below a threshold temperature and a second power is delivered to the heater plate when the inlet temperature exceeds or equals the threshold temperature.

[0071] The electronic controller is configured to cap or limit the amount of power delivered to the heater plate when the inlet temperature exceeds or equals a threshold temperature.

[0072] The electronic controller may be configured to set the first chamber outlet temperature setpoint corresponding to a humidity value between 21 mg / L and 34 mg / L.

[0073] The electronic controller may be configured to set a second chamber outlet temperature setpoint that corresponds to a humidity value between 14 mg / L and 25 mg / L.

[0074] The electronic controller may be configured to reduce the power supplied to the heater plate if the inlet temperature exceeds a temperature threshold.

[0075] The power supplied to the heater plate is reduced from the power limit. In another example, the power supplied to the heater plate may be capped or limited if the inlet temperature exceeds a temperature threshold.

[0076] The electronic controller may be configured to supply heater plate power corresponding to the first or second chamber outlet setpoint temperature so that a desired amount of humidity can be produced.

[0077] A humidifier for humidifying a gas flow supplied to a user may include a base unit including a heater plate, a removable humidification chamber that may include a conductive base and one or more walls extending from the conductive base, the one or more walls and the conductive base defining a chamber space for holding a humidification fluid, the humidification chamber may further include an inlet and an outlet, at least one inlet temperature sensor disposed within or adjacent to the inlet of the humidification chamber and configured to determine an inlet temperature, at least one outlet temperature sensor disposed within or adjacent to the outlet of the humidification chamber and configured to determine an outlet temperature, and an electronic controller configured to determine whether the inlet temperature exceeds a threshold temperature and to set an upper limit on a maximum allowable chamber outlet temperature, heater plate temperature, or allowable heater plate power at a corresponding inlet temperature.

[0078] The maximum allowable chamber exit temperature defined by the second function may be lower than the maximum allowable chamber exit temperature defined by the first function.

[0079] The absolute humidity produced by the first function may be higher than the humidity output produced by the second function.

[0080] The humidifier may include a heater plate, and the controller may be configured to control power supplied to the heater plate based on a maximum allowable outlet temperature.

[0081] The controller may be configured to control power supplied to the heater plate based on the first function or the second function.

[0082] When the gas source may be a low temperature dry gas source, the controller may be configured to use the first function.

[0083] When the gas source may be a room air entrained gas source, the controller may be configured to use a second function.

[0084] A humidifier for humidifying a gas flow supplied to a user may comprise a base unit including a heater plate, a removable humidification chamber that may include a conductive base and one or more walls extending from the conductive base, the one or more walls and the conductive base defining a chamber space for holding a humidification fluid, the humidification chamber may further include an inlet and an outlet, at least one inlet temperature sensor disposed within or adjacent to the inlet of the humidification chamber and configured to measure an inlet temperature, at least one outlet temperature sensor disposed within or adjacent to the outlet of the humidification chamber and configured to measure an outlet temperature, and an electronic controller configured to control to a predefined maximum allowable outlet temperature for a corresponding inlet temperature, the maximum allowable outlet temperature may be related to an inlet temperature defined by a first function, and based on the inlet temperature, apply a second function that defines a new maximum allowable outlet temperature for the corresponding inlet temperature.

[0085] The maximum allowable chamber exit temperature defined by the second function may be lower than the maximum allowable chamber exit temperature defined by the first function.

[0086] The absolute humidity produced by the first function may be higher than the humidity output produced by the second function.

[0087] The humidifier may include a heater plate, and the controller may be configured to control power supplied to the heater plate based on a maximum allowable outlet temperature.

[0088] The controller may be configured to control power supplied to the heater plate based on the first function or the second function.

[0089] When the gas source may be a low temperature dry gas source, the controller may be configured to use the first function.

[0090] When the gas source may be a room air entrained gas source, the controller may be configured to use a second function.

[0091] The controller is configured to use or perform a first function when the inlet temperature is below a threshold temperature, and is further configured to use or perform a second function when the inlet temperature is equal to or greater than the threshold temperature.

[0092] An electronic control device for controlling humidity in a gas stream supplied to a user using a humidifier may include a heater plate in a base unit and a humidification chamber including a conductive base and one or more walls extending from the conductive base, the humidification chamber further including an inlet and an outlet and configured to hold a humidification fluid, and may be configured to: output a heater plate control signal to control the amount of power supplied to the heater plate of the humidifier in response to an outlet temperature of the humidification chamber being measured from a signal received from the outlet temperature sensor; measure an inlet temperature of the gas received in the humidification chamber based on the signal received from the inlet temperature sensor and determine that the inlet temperature exceeds a threshold temperature; and reduce a target humidity of the gas exiting the outlet of the humidification chamber in response to the inlet temperature exceeding the threshold temperature.

[0093] To reduce the target humidity, the controller may be configured to reduce the amount of power supplied to the heater plate in response to the inlet temperature exceeding a threshold temperature.

[0094] The controller may be configured to reduce the amount of power below a power threshold.

[0095] The power threshold may be set to achieve a minimum dew point of 19°C.

[0096] The power threshold may be set to achieve a minimum humidity output of 15 mg / L.

[0097] The power threshold may be set to achieve a dew point of 25°C.

[0098] The power threshold may be set to achieve a humidity output of 22 mg / L.

[0099] The electronic controller may be configured to control the amount of power supplied to the heater plate in a first mode when the inlet temperature may be below a threshold temperature and in a second mode when the inlet temperature exceeds the threshold temperature.

[0100] In a first mode, the controller may be configured to set a power setpoint, or a chamber exit setpoint, or a heater plate temperature setpoint to achieve a minimum humidity of at least 15 mg / L.In a second mode, the controller may be configured to set a power setpoint, or a chamber exit setpoint, or a heater plate temperature setpoint to achieve a minimum humidity of at least 22 mg / L.

[0101] In a first mode, the controller may be configured to set a power setpoint, or a chamber exit setpoint, or a heater plate temperature setpoint to achieve a minimum dew point of at least 19° C. In a second mode, the controller may be configured to set a power setpoint, or a chamber exit setpoint, or a heater plate temperature setpoint to achieve a minimum dew point of at least 25° C.

[0102] The electronic controller may be configured to output a heater plate control signal according to a first function that is applied when the inlet temperature falls below a threshold temperature.

[0103] The electronic controller may be configured to output the heater plate control signal according to a second function, which may be different from the first function, that is applied when the inlet temperature exceeds a threshold temperature.

[0104] In one example, the first function and the second function define a piecewise function.

[0105] If the inlet temperature exceeds the threshold temperature, the electronic controller may be configured to reduce the target outlet temperature.

[0106] If the inlet temperature exceeds the threshold temperature, the electronic controller may be configured to reduce the target heater plate temperature.

[0107] The threshold temperature may be between 22°C and 24°C.

[0108] The threshold temperature may be 22°C.

[0109] The threshold temperature may be 24°C.

[0110] The threshold temperature may vary depending on the desired dew point.

[0111] This desired dew point may be selected by the user.

[0112] The controller may be configured to determine a humidifier mode among a plurality of modes, a mode defining a plurality of desired dew points, and determine a temperature threshold based on the humidifier mode.

[0113] The multiple modes may include an invasive mode, a non-invasive mode, and a high flow mode.

[0114] The mode may be manually selectable by the user.

[0115] The non-invasive mode may include desired dew points of 31°C, 27°C, and 25°C.

[0116] A target humidity for the outlet temperature setpoint may be predetermined when the inlet temperature may fall below a threshold temperature, and if the inlet temperature exceeds the threshold, the amount of humidity generated at that outlet temperature setpoint may be reduced to a relatively low, preset value.

[0117] A method for reducing condensation at an outlet of a humidifier may include receiving an inlet temperature of gas received in the humidifier chamber based on a signal received from an inlet temperature sensor, determining that the inlet temperature exceeds a threshold temperature, and reducing a target humidity of the gas exiting the outlet of the humidifier chamber in response to the inlet temperature exceeding the threshold temperature.

[0118] Reducing the target humidity can include reducing an amount of power supplied to the heater plate in response to the inlet temperature exceeding a threshold temperature. In response to the inlet temperature exceeding the threshold temperature, the amount of power supplied to the heater plate is capped or limited.

[0119] Reducing the amount of power delivered to the heater plate may include reducing the amount of power below a power threshold.

[0120] The power threshold may be set to achieve a minimum dew point of 19°C.

[0121] The power threshold may be set to achieve a minimum humidity output of 15 mg / L.

[0122] The power threshold may be set to achieve a dew point of 25°C.

[0123] The power threshold may be set to achieve a humidity output of 22 mg / L.

[0124] Reducing the amount of power can include controlling the amount of power supplied to the heater plate in a first mode when the inlet temperature may be below a threshold temperature and in a second mode when the inlet temperature exceeds the threshold temperature.

[0125] In a first mode, the power setpoint, or the chamber exit setpoint, or the heater plate temperature setpoint may be set to achieve a minimum humidity of at least 15 mg / L.In a second mode, the power setpoint, or the chamber exit setpoint, or the heater plate temperature setpoint may be set to achieve a minimum humidity of at least 22 mg / L.

[0126] In a first mode, the power setpoint, or the chamber exit setpoint, or the heater plate temperature setpoint may be set to achieve a minimum dew point of at least 19° C. In a second mode, the power setpoint, or the chamber exit setpoint, or the heater plate temperature setpoint may be set to achieve a minimum dew point of at least 25° C.

[0127] Reducing the amount of power can include controlling the amount of power supplied to the heater plate power according to a first function that is applied when the inlet temperature is below the threshold temperature.

[0128] Reducing the amount of power can include controlling the amount of power supplied to the heater plate power according to a second function, which may be different from the first function, that is applied when the inlet temperature exceeds a threshold temperature.

[0129] Reducing the target outlet temperature if the inlet temperature exceeds a threshold temperature.

[0130] Decreasing the target heater plate temperature if the inlet temperature exceeds a threshold temperature.

[0131] The threshold temperature may be between 22°C and 24°C.

[0132] The threshold temperature may be 22°C.

[0133] The threshold temperature may be 24°C.

[0134] The threshold temperature may vary depending on the desired dew point.

[0135] This desired dew point may be selected by the user.

[0136] The method may further include determining a humidifier mode among a plurality of modes, a mode defining a plurality of desired dew points, and determining a temperature threshold based on the humidifier mode.

[0137] The multiple modes may include an invasive mode, a non-invasive mode, and a high flow mode.

[0138] This mode may be manually selectable by the user.

[0139] The non-invasive mode may include desired dew points of 31°C, 29°C, 27°C, and 25°C.

[0140] A target humidity for the outlet temperature setpoint may be predetermined when the inlet temperature may fall below a threshold temperature, and if the inlet temperature exceeds the threshold, the amount of humidity generated at that outlet temperature setpoint may be reduced to a relatively low, preset value.

[0141] A controller for operating the humidifier may be configured to receive an inlet temperature of gas received in the humidifier chamber based on a signal received from the inlet temperature sensor, determine that the inlet temperature exceeds a threshold temperature, and reduce a target heater plate power or a target heater plate temperature of gas exiting an outlet of the humidifier chamber in response to the inlet temperature exceeding the threshold temperature.

[0142] To reduce the amount of power delivered to the heater plate, the controller may be configured to reduce this amount of power below a power threshold.

[0143] The power threshold may be set to achieve a minimum dew point of 19°C.

[0144] The power threshold may be set to achieve a minimum humidity output of 15 mg / L.

[0145] The power threshold may be set to achieve a dew point of 25°C.

[0146] The power threshold may be set to achieve a humidity output of 22 mg / L.

[0147] To reduce the amount of power, the controller may be configured to control the amount of power supplied to the heater plate in a first mode when the inlet temperature is below a threshold temperature and in a second mode when the inlet temperature is above the threshold temperature.

[0148] In a first mode, the controller may be configured to set a power setpoint, or a chamber exit setpoint, or a heater plate temperature setpoint to achieve a minimum humidity of at least 15 mg / L.In a second mode, the controller may be configured to set a power setpoint, or a chamber exit setpoint, or a heater plate temperature setpoint to achieve a minimum humidity of at least 22 mg / L.

[0149] In a first mode, the controller may be configured to set a power setpoint, or a chamber exit setpoint, or a heater plate temperature setpoint to achieve a minimum dew point of at least 19° C. In a second mode, the controller may be configured to set a power setpoint, or a chamber exit setpoint, or a heater plate temperature setpoint to achieve a minimum dew point of at least 25° C.

[0150] To reduce the amount of power, the controller may be configured to control the amount of power supplied to the heater plate power according to a first function that is applied when the inlet temperature falls below a threshold temperature.

[0151] To reduce the amount of power, the controller may be configured to control reducing the amount of power supplied to the heater plate power according to a second function, which may be different from the first function, that is applied when the inlet temperature exceeds a threshold temperature.

[0152] The threshold temperature may be between 22°C and 24°C.

[0153] The threshold temperature may be 22°C.

[0154] The threshold temperature may be 24°C.

[0155] The threshold temperature may vary depending on the desired dew point.

[0156] This desired dew point may be selected by the user.

[0157] The controller may be configured to determine a humidifier mode among a plurality of modes, a mode defining a plurality of desired dew points, and determine a temperature threshold based on the humidifier mode.

[0158] The multiple modes may include an invasive mode, a non-invasive mode, and a high flow mode.

[0159] This mode may be manually selectable by the user.

[0160] The non-invasive mode may include desired dew points of 31°C, 29°C, 27°C, and 25°C.

[0161] A target humidity for the outlet temperature setpoint may be predetermined when the inlet temperature may fall below a threshold temperature, and if the inlet temperature exceeds the threshold, the amount of humidity generated at that outlet temperature setpoint may be reduced to a relatively low, preset value.

[0162] In a further aspect, a humidifier for humidifying a gas flow supplied to a user is disclosed, the humidifier comprising: a base unit including a heater plate; A humidification chamber configured to hold a humidification fluid, Conductive base, one or more wall portions configured to be coupled to the base portion; Entrance, and Exit a humidification chamber comprising: at least one inlet temperature sensor disposed within or adjacent to an inlet of the humidification chamber; at least one outlet temperature sensor located in or adjacent to an outlet of the humidification chamber; outputting a heater plate control signal to control an amount of power provided to the heater plate based at least in part on a function of the outlet temperature measured from a signal received from the outlet temperature sensor; determining an inlet temperature of the gas received by the humidification chamber based on a signal received from the inlet temperature sensor; It is determined that the inlet temperature exceeds a threshold temperature; In response to the inlet temperature exceeding a threshold temperature, reducing the maximum target humidity of the gas exiting the outlet of the humidification chamber. An electronic control device configured as follows: The controller is configured to calculate an amount of power provided to the heater plate based on a function of the outlet temperature. The controller is configured to cap a maximum allowable heater plate power based on a maximum allowable chamber outlet temperature set point.

[0163] The terms conduit and tube are used interchangeably herein. [Brief description of the drawings]

[0164] [Figure 1] 1 shows a diagram of an exemplary respiratory assistance system. [Figure 2A] A block diagram of an exemplary control system that interacts with and / or controls and directs components of the respiratory assistance system is shown. [Figure 2B]FIG. 2 illustrates a block diagram of an exemplary control device. [Diagram 3] 1 shows the potential gas types at the inlet of the humidification chamber. [Figure 4A] 1 shows an exemplary graph of actual humidity in outlet gas as a function of inlet temperature in a room air entrainment ventilation system. [Figure 4B] 1 shows an exemplary graph of actual humidity in outlet gas as a function of inlet temperature in a room air entrainment ventilation system for various non-invasive user settings of the humidifier. [Figure 5A] 1 is a graph showing an exemplary effect of additional room air humidity at an inlet temperature of 36° C. [Figure 5B] 1 is a graph showing an exemplary effect of additional room air humidity at an inlet temperature of 26° C. [Figure 5C] 1 is a graph showing an exemplary effect of additional room air humidity at an inlet temperature of 21° C. [Figure 6A] 1 illustrates an exemplary process for setting a maximum chamber outlet set point based on an inlet temperature. [Figure 6B] 13 illustrates another exemplary process for setting the maximum chamber outlet set point based on the inlet temperature. [Figure 7] 4 shows exemplary improved outlet humidity levels for gas conditions at the inlet to the humidifier. [Figure 8] 13 shows exemplary maximum chamber outlet temperature limits as a function of chamber inlet temperature at various exemplary user settings for the humidifier. [Figure 9A] 4 shows an example of humidity added by an exemplary humidifier as a function of inlet temperature and humidity added by the humidifier. [Figure 9B] 4 shows an example of humidity added by an exemplary humidifier as a function of inlet temperature and humidity added by the humidifier. [Figure 10A] 13 is a graph illustrating an exemplary operation of an exemplary humidity delivery control system in non-invasive mode at an inlet temperature of 36° C. [Figure 10B]13 is a graph illustrating an exemplary operation of an exemplary humidity delivery control system in non-invasive mode at an inlet temperature of 26° C. [Figure 10C] 13 is a graph illustrating an exemplary operation of an exemplary humidity delivery control system in non-invasive mode at an inlet temperature of 21° C. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0165] Summary A respiratory assistance system for delivering heated and humidified gas to a patient may include a patient connection device configured to deliver a flow of respiratory gas received from a gas source, and an inhalation conduit configured to fluidly connect with the patient connection device and the gas source via a humidifier. The humidifier may include a humidification chamber having at least one wall defining the chamber such that the chamber can hold a liquid, a chamber inlet, a chamber outlet, and a gas flow path between the chamber inlet and the chamber outlet. The chamber inlet may be configured to be fluidly connected with the gas source, and the chamber outlet may be configured to be fluidly connected with the inhalation conduit. The humidification chamber may hold a quantity of liquid (e.g., water). The humidifier may include a heater plate configured to heat a quantity of liquid and the flow of respiratory gas in the gas flow path in the humidification chamber to heat and humidify the flow of respiratory gas. The humidifier may also include a controller having one or more hardware processors configured to control an amount of power provided to the heater plate.

[0166] An example of a humidifier disclosed herein may include a controller configured to vary the outlet temperature setpoint of the humidification chamber as a function of the chamber inlet temperature. For example, the controller may be configured to detect the inlet gas temperature. If the chamber inlet temperature increases, the controller may reduce the desired humidity level at the outlet to a relatively low level (such as a relatively low therapeutic level) to allow and take into account additional humidity that may be added in the case of a room air entrainment ventilation system that is a gas source connected to the humidifier. The controller may decrease the desired humidity level by optionally changing the heater plate power setpoint or the heater plate temperature setpoint. These two parameters may be used in addition to or instead of the chamber outlet setpoint. The controller may be configured to limit or cap the chamber outlet temperature setpoint so that the amount of humidity generated by the humidifier is capped if the inlet temperature exceeds a threshold value to take into account the increased humidity in the ambient air. The capped chamber outlet temperature setpoint may define the maximum allowable temperature setpoint. The humidifier controller is configured to stay below a capped chamber outlet temperature set point (i.e., maximum allowable temperature set point). Additionally or alternatively, the power provided to the heater plate may be capped or limited if the inlet gas temperature exceeds a threshold to define a maximum allowable heater plate power set point. If the inlet gas temperature exceeds the threshold, the controller may also cap or limit the heater plate temperature set point. The capped heater plate temperature set point defines the maximum allowable heater plate temperature set point in the state (i.e., mode) when the inlet gas temperature exceeds the threshold. This threshold may be a temperature threshold. This process may enable the humidifier to maintain and / or deliver therapeutic levels of humidity while reducing condensation that may occur on the inlet tubing and / or patient connection as a result of adding humidity in the incoming gas.Thus, the systems and methods described herein can take into account various inlet humidity levels within a respiratory assistance system and can improve patient comfort by reducing rainout when the humidity of the inlet gas is higher than that of dry gas.

[0167] The humidifier and / or humidifier controller disclosed herein may be configured to control the humidifier to operate in two modes, a first mode being a relatively cool and / or low humidity inlet gas mode and a second mode being a relatively warm and / or high humidity inlet gas mode, e.g., ambient air. The controlled operating mode may be based on the temperature of the inlet gas. If the temperature of the inlet gas (or inlet temperature) is below a threshold, the humidifier functions in the first mode. If the temperature of the inlet gas exceeds a threshold (i.e., the inlet temperature, i.e., the inlet gas temperature exceeds a threshold), the controller operates in the second mode. The second mode reduces the humidity output of the humidifier. This may be achieved by capping or limiting the chamber outlet temperature set point to reduce the amount of humidity generated by the humidifier. In other words, the chamber outlet temperature set point may be limited or capped based on the inlet temperature of the gas to define a maximum allowable chamber outlet set point. The humidifier controller is configured to modify the maximum allowable chamber outlet set point based on the determined inlet temperature. The controller is configured to control the heater plate power to ensure that the gas temperature is below the maximum allowable chamber outlet set point. Additionally or alternatively, the controller may cap or limit the heater plate temperature set point or heater plate power to reduce or cap or further reduce or cap the humidity generated in the second mode compared to the first mode. Thus, the second mode can compensate for humidity present in the inlet gas (e.g., when the inlet gas is relatively humid ambient air).

[0168] The humidifiers and methods of use described herein can be used to achieve high-flow, non-invasive, invasive, and / or other therapies. The humidifiers can be operated in invasive, non-invasive, high-flow, or other modes. The humidifiers can be operated with a variety of patient connection devices, such as, for example, an endotracheal tube (ET tube), a full face mask, a nasal mask, a nasal cannula, nasal pillows, sealing prongs, or any other connection device. Other desired humidity levels may be achievable and other types of therapy systems may be used. The chamber outlet temperature set point can be adjusted depending on the therapy provided and the desired humidity level.

[0169] Exemplary Humidifier 1 shows a schematic diagram of an exemplary respiratory assistance system 100. As shown, the respiratory assistance system 100 includes a humidifier 104, a gas source 102, a patient connection device 116, and an inhalation conduit 106 configured to transport respiratory gas from the humidifier 104 to the patient connection device 116. The gas source 102 and the humidifier 104 may be in separate housings or may be located adjacent to each other in the same housing and / or may be included in a single device. The respiratory assistance system 100 includes an optional exhalation conduit 120 configured to transport gas from the patient connection device 116 to the gas source 102, and an optional Y-piece 114 configured to connect the inhalation conduit 106 and the exhalation conduit 120 to the patient connection device 116. The respiratory assistance system 100 may not include an exhalation conduit 120 or may include an exhalation port. Depending on whether an expiratory conduit or an expiratory port is included, the operating parameters of the respiratory assistance system 100 may have to be adjusted. In one example, the humidifier is configured to operate with multiple operating parameters that are modifiable to allow the humidifier to operate in various configurations, for example, a single lobe configuration (i.e., only an inhalation conduit) or a dual lobe configuration (i.e., an inhalation conduit and an expiratory conduit).

[0170] As shown, the gas source 102 includes a ventilator 124, which may include a blower or alternatively a turbine. The gas source 102 may also include other mechanisms for delivering or pumping the flow of breathing gas to the humidifier 104, such as a valve arrangement or a pump. The gas source 102 in FIG. 1 is an exemplary room entrainment ventilator or an ambient air entrainment ventilator. The gas source 102 may include an inlet 122, for example, through which ambient air is drawn into the gas source 102 by the ventilator 124. The gas source 102 may include a controller 126 configured to control the operation of the ventilator 124. The gas source 102 may include a user interface 132 that may present information about user input to the controller 126. The controller 126 may control the operation of the ventilator 124 based on information presented by the user interface 132 and / or based on other information, such as feedback from the ventilator 124, such as, but not limited to, from a sensor associated with the ventilator 124. Instead of drawing in ambient air, the inlet 122 can be connected to a source of dry gas, such as a gas cylinder or tank. This type of ventilator is sometimes referred to as a non-entrained ventilator and may be controlled by one or more valves, such as proportional valves. The valves may be controlled by a controller, such as controller 126.

[0171] The humidifier 104 may include a base unit, a humidification chamber 134, and a heater plate 136. The heater plate 136 is disposed on the base unit. The humidification chamber 134 may be configured to hold a quantity of water W or other suitable liquid. The humidification chamber 134 is disposed on the base unit and in contact with the heater plate 136. The chamber 134 is removable from the base unit. The heater plate 136 may be configured to heat the quantity of water W and breathing gas in the humidification chamber 134, which may increase the temperature of the breathing gas and may generate steam from the quantity of water W entrained by the breathing gas. The heater plate 136 is a plate-shaped member. In one example, the heater plate 136 includes a metal plate and a heating element disposed in contact with the heating element. The heating element is disposed within the metal plate. The heating element includes a substrate with an electrical wire wound around the substrate. The humidification chamber 134 may comprise a chamber inlet 111 and a chamber outlet 112. The inhalation conduit 106 may be configured to be connected to the chamber outlet 112 such that the heated and humidified breathing gas may be transported from the humidification chamber 134 to the patient connection device 116 by the inhalation conduit 106 and then delivered to the patient P. Gas exhaled by the patient P into the patient connection device 116 may be returned to the gas source 102 by the exhalation conduit 120. The respiratory assistance system 100 may not comprise an exhalation conduit 120, and thus gas exhaled by the patient P into the patient connection device 116 may be vented to the atmosphere, such as directly or optionally through an exhalation port.

[0172] The humidifier 104 may include a controller 130 that may control, for example, but not limited to, the operation of the heater plate 136. The controller 130 is preferably located in the base unit. When the humidifier 104 and the gas source 102 form an integrated device, the controllers 126, 130 may be the same hardware processor, or separate processors. In one example, the controller 130 may be a microprocessor. The humidifier 104 may also include a user interface 140 for providing and / or receiving information regarding user input to and / or from the controller 130. The user interface 140 may be located in the base unit. The humidifier 104 further includes an inlet temperature sensor 113. The inlet temperature sensor 113 may be configured to detect the temperature of the gas entering the humidifier. The inlet temperature sensor 113 may measure a property of the ambient air proximate the location of the inlet temperature sensor 113, such as the temperature of the ambient air. The inlet temperature sensor 113 may also be a temperature sensor located at or near the chamber inlet 111. A temperature sensor at the chamber inlet 111 may be capable of measuring both the temperature and flow rate of the air entering from the gas source 102. This measurement may be indicative of ambient conditions. In one example, the inlet temperature sensor 113 may be a thermistor. Additionally and / or alternatively, the respiratory assistance system 100 may include two or more sensors located at or near the chamber inlet 111. The inlet sensor may include a temperature sensor and a separate flow rate sensor. The inlet sensor or sensors may be located anywhere from the gas source 102 to the humidification chamber 134. The outlet sensor or sensors 110 and the inlet sensor or sensors may be integrated with the humidification chamber 134. The controller 130 may receive information from the inlet temperature sensor 113 about the characteristics of the ambient air proximate to the location of the inlet temperature sensor 113.The controller 130 may be configured to control the operation of the heater plate 136 based on information presented by the user interface 140, based on information presented by the inlet temperature sensor 113, and / or based on other information, such as feedback from the heater plate 136, such as, but not limited to, from a temperature sensor 146 disposed at or near the heater plate 136. The controller 130 may be configured to determine an amount of power or a power duty cycle to supply to the heater plate 136 such that the heater plate 136 delivers a desired amount of heat to the breathing gas and to a volume of water W in the humidification chamber 134. In the illustrated example, the humidifier does not include a hygrometer, but only temperature sensors at the inlet, outlet, and heater plate, and an optional flow sensor at the outlet. The lack of a hygrometer may make the humidifier cheaper than a humidifier that includes one or more hygrometers, since temperature sensors may be relatively inexpensive.

[0173] The respiratory assistance system 100 may include one or more outlet sensors 110 associated with the chamber outlet location 112. The one or more outlet sensors 110 may also be located at or near the chamber outlet 112. The outlet sensor 110 may include two sensors: a temperature sensor and a flow sensor. The temperature sensor may be a thermistor (such as a heated thermistor). The thermistor may also be used as a flow sensor. Thus, a single sensor 110 may be present at or near the chamber outlet 112. Other types of temperature and flow sensors that may operate with the respiratory assistance system 100 may also be used. The outlet sensor 110 may be located at the chamber outlet 112, in the inhalation conduit 106 near the connection between the chamber outlet 112 and the inhalation conduit 106, or in another suitable location downstream of the humidification chamber 134. The controller 130 may receive information from the outlet sensor 110 regarding the characteristics of the respiratory gas flowing through the location of the outlet sensor 110. The controller 130 may be configured to control operation of the heater plate 136 based on information provided by the outlet sensor 110 instead of, or in addition to, other sources of information such as those discussed above.

[0174] The outlet sensor 110 may be integrated into the heater base (i.e., base unit) or may be located on any cartridge that can be removably attached to a vertical portion of the heater base (i.e., base unit). When the chamber 134 is placed in an operating position on the heater base, the sensors may be insertable into the inlet and outlet ports. The chamber inlet and outlet may include openings to accommodate and receive the inlet temperature sensor 113 and the outlet sensor 110. The sensor openings in the chamber may include a polymer cover configured to cover the sensor tip when the sensors are inserted into the gas path, so that the sensors do not actually come into contact with the gas and do not need to be (re)sterilized.

[0175] Respiratory gas flowing through the inhalation conduit 106 may lose heat through the walls of the inhalation conduit 106, thereby reducing the temperature of the respiratory gas and causing condensation within the inhalation conduit 106. The inhalation conduit 106 may include a conduit heater 144 configured to heat the inhalation conduit 106 to reduce or prevent this heat loss. As discussed above, the controller 130 may be configured to control the operation of the conduit heater 144 based on one or several sources of information. In particular, the controller 130 may be configured to determine an amount of power or a power duty cycle to supply to the conduit heater 144 such that the conduit heater 144 delivers a desired amount of heat to the inhalation conduit 106. The conduit heater may be disposed within the wall of the conduit or may be disposed within the lumen of the conduit.

[0176] The respiratory assistance system 100 may include one or more conduit sensors 142 disposed in the inhalation conduit 106. The conduit sensor 142 may be disposed in the inhalation conduit 106 near the connection between the inhalation conduit 106 and the wye piece 114, at the connection between the inhalation conduit 106 and the patient connection device 116 if the inhalation conduit 106 is directly connected to the patient connection device 116, or at the wye piece 114 or the patient connection device 116. The conduit sensor 142 may measure a characteristic of the respiratory gas flowing through the location of the conduit sensor 142, such as the temperature of the respiratory gas. The conduit sensor 142 may include a temperature sensor. The conduit sensor 142 may also include a separate flow sensor. As described herein, the conduit sensor 142 may include an integrated flow and temperature sensor capable of measuring both temperature and flow rate. The controller 130 may receive information from the conduit sensor 142 regarding the characteristic of the respiratory gas flowing through the location of the conduit sensor 142. Controller 130 may determine the flow rate of breathing gas flowing through conduit sensor 142. Controller 130 may be configured to control operation of conduit heater 144 and / or heater plate 136 based on information received from conduit sensor 142 instead of or in addition to other sources of information, such as those discussed above. The conduit sensor may be integrated into the conduit or may extend within the gas path defined by the conduit. Additionally, the wire of the conduit sensor may be integrated into the wall of the conduit or may extend along the conduit.

[0177] The breathing gas may also lose heat through the walls of the patient connection device 116, the Y-piece 114, and / or any other breathing system components that may connect the patient connection device 116 to the inhalation conduit 106. One or more of the patient connection device 116, the Y-piece 114, and any other breathing system components that may connect the patient connection device 116 to the inhalation conduit 106 may include an associated heater and / or an associated sensor. The controller 130 may receive information from such associated sensors regarding the characteristics of the breathing gas flowing through the location of the sensor. The controller 130 may use the information received from such associated sensors to control the operation of the respective associated heaters.

[0178] One or more of the patient connection device 116, the Y-piece 114, and any other breathing system components that may connect the patient connection device 116 to the inhalation conduit 106 may not have associated heaters and / or associated sensors. The controller 130 may use an estimate of the heat lost by the breathing gas flowing through the non-heated breathing system components to control other heaters associated with the humidifier 104, such as the heater plate 136 and / or the conduit heater 144. The controller 130 may calculate such estimates of heat loss for the non-heated breathing system components based on other information received, for example, but not limited to, information received from the outlet sensor 110, the conduit sensor 142, the inlet temperature sensor 113, and / or the user interface 140, and / or based on information retrieved from a data storage device that may be located within the controller. Data received from each sensor described herein may also be stored in the data storage device.

[0179] The humidifier 104 may be used in the respiratory assistance system 100 to deliver heated and humidified respiratory gas to the patient P for multiple types of respiratory therapy, including, but not limited to, invasive ventilation, non-invasive ventilation, high-flow therapy, BiPaP therapy, continuous positive airway pressure therapy, or other respiratory assistance therapy. The humidity condition of the respiratory gas supplied by the gas source 102 to the humidifier 104 may vary. For example, the type of gas source 102 used in the respiratory assistance system 100 may depend on the type of respiratory therapy, the configuration of the breathing system, the location of use (e.g., home or hospital), or the availability of various gas sources. Gas from various sources may have different characteristics, including temperature and humidity. Ambient air, particularly ambient air in tropical weather and / or ambient air in summer, may be more humid than gas obtained from a tank or bottle of compressed gas. For example, it may be beneficial to adjust the operating parameters of the respiratory assistance system 100 using the control system 220 (described below) to reduce and / or minimize rainout on the inspiratory tract and / or patient connection apparatus to provide a comfortable medical experience to the patient while still receiving adequately humidified gas despite varying supply gas characteristics. The control system may be capable of automatically adjusting the operating parameters based on an inference of whether the supply gas is dry or ambient. The operating parameters may include certain temperature set points, described below. Additionally or alternatively, the operating parameters may be dew point, humidity output of a humidifier, or other suitable parameters.

[0180] FIG. 2A illustrates an exemplary control system 220 for detecting input conditions of the gas source 102 and automatically controlling the aforementioned components of the respiratory assistance system 100 to change the output state of the gas delivered to the patient. The control system 220 can generate outputs configured to control the operation of the components of the respiratory assistance system 100 based on the inputs received. The control system can generate a heater element output 230 to change the temperature set point of one of the heating elements, such as the heater plate 136, to control the output state of the gas delivered to the patient. The control system 220 can also change the operation or duty cycle of the heater plate. The control system 220 may not require direct communication between the humidifier 104 and the gas source 102 to determine the input conditions. The control system 220 can also generate other outputs, such as a flow control output to change the flow rate of the gas, and / or generate an output 234 to a display device. The user input 210 can be received, for example, via a user interface, such as a touch screen. The user input may be a selection of a particular mode corresponding to a type of therapy (e.g., invasive ventilation, non-invasive ventilation, or a high-flow therapy such as Fisher & Paykel Healthcare's Optiflow therapy). A further user input may specify a desired dew point, i.e., a desired humidity value, to be delivered to the patient. For example, each mode may include a number of pre-set desired dew point values ​​(e.g., 31° C., 29° C., 27° C., or other) from which the user may select. This selected dew point enables the controller to control the heater plate and / or heater wires in the inhalation conduit to deliver saturated gas at the selected temperature (i.e., the selected dew point).

[0181] The control system 220 may include programming instructions as described herein to detect input conditions and control output conditions. As shown in FIG. 2B, the programming instructions may be stored in the memory 924 of the controller 126, 130. The programming instructions may include instructions corresponding to the processes and functions described herein. The control system 220 may be executed by a hardware processor 922 of the controller 126, 130. The programming instructions may be implemented in C, C++, JAVA, or any other suitable programming language. Some or all of the portions of the control system 220 may be implemented in application specific circuitry 928, such as ASICs and FPGAs.

[0182] As shown in Figure 2A, the control system 220 can receive inputs from multiple components of the respiratory assistance system 100. Other types of inputs may also be present. A humidity sensor may or may not be included. The controller may also receive inputs from various sensors in the system. Additionally or alternatively, the humidifier may receive signals or inputs from a user device, such as a cell phone or tablet.

[0183] Excessive humidity in indoor entrained air In FIG. 3, the potential possible gas conditions at the inlet of the humidification chamber are shown. Without knowing the inlet humidity condition, the humidifier can deliver humidity close to the desired humidity level in at least three of four types of gas conditions, namely, cool high humidity (QI), cool low humidity (QII), and hot low humidity (QIV), as shown in FIG. 3. "Cold" may correspond to a temperature lower than the ambient temperature, which may be approximately 24° C., and "hot" may correspond to a temperature higher than the ambient temperature. In the example shown in FIG. 3, cold is considered to be below 24° C., and hot is considered to be 24° C. or higher. In some examples, the inlet temperature above 24° C. may be caused by heat generated by the turbine in the indoor air entrainment ventilation device. The ambient air passing through the turbine of the indoor air entrainment ventilation device is heated above the ambient temperature due to the turbine rotating the gas. In some examples, the generated heat may be added to the high ambient temperature. Compressed air (e.g., from a gas tank) is generally considered to be cool and dry because it is not humidified (e.g., the humidity is lower than ambient) and is generally below 24°C (e.g., the temperature may be 18°C).

[0184] The humidifiers described herein can modify the maximum amount of added humidity, i.e., the humidifiers described can modify the amount of humidity added based on the inlet temperature of the gas. In some examples, when the inlet temperature is low (i.e., when the gas is cold as shown in quadrants I and II in FIG. 3), the relative humidity (RH) of the gas at the chamber outlet may be close to saturation regardless of the inlet gas humidity level. This is because the heater plate of the humidifier may heat and add moisture to the gas. In other words, the temperature difference between the inlet temperature and the outlet temperature must be large enough so that the humidifier can add enough humidity to saturate the gas.

[0185] On the other hand, in instances where the chamber inlet temperature is high or well above ambient conditions (i.e., the gas is hot as shown in quadrants III and IV of FIG. 3), the RH level at the chamber outlet may be reduced. This is because the heater plate may have a safety temperature limit such that it cannot heat beyond a certain temperature. Thus, the heater plate may have a relatively small buffer or range for heating and adding humidity before reaching the maximum allowable chamber outlet temperature set point. An example of the maximum allowable chamber outlet temperature set point may be approximately 36° C.

[0186] Additionally, or alternatively, at higher temperatures with the same humidity level, water may evaporate less from the water surface due to increased vapor pressure of moist gases at the water surface. Thus, different inlet humidity levels may have different effects on the outlet humidity levels.

[0187] In another example, the delivery of hot, (relatively) dry gas to a patient may cause irreversible damage to the patient's airways. Therefore, to help prevent this problem, the system may avoid the delivery of hot, dry gas when the humidity of the incoming hot, dry gas is low by effectively treating the incoming hot, dry gas to a cool, dry state. If this assumption holds true, the humidity can be increased as the incoming gas is heated by the heater plate as it passes through the humidification chamber.

[0188] Humidifiers generally add more heat and humidity to the incoming gas. Depending on the temperature and humidity of the incoming gas, in some cases this may result in excessive humidification and / or overheating. For example, air taken in by an entrained air ventilator may contain some humidity. The humidity of the indoor air may be higher than that from a compressed gas source such as a gas bottle or wall-fed gas. Furthermore, as mentioned above, an entrained air ventilator typically uses a blower or turbine, which may unfortunately heat the gas. This excess heat causes the entrained air to be further humidified before entering the humidification chamber, as the temperature of the gas may increase, raising the dew point.

[0189] FIG. 4A shows an exemplary graph of the dew point of the outlet gas as a function of the inlet temperature of the room air entrainment ventilation device when the humidifier assumes that all incoming gases are dry. This dew point corresponds to an absolute humidity value. Specifically, FIG. 4A shows how the humidifier may add unnecessary humidity in the case of room entrained air, since the humidifier may not take into account the humidity already present in the room entrained air. As mentioned above, the humidifier may use a gas source to reliably deliver the desired humidity level over a range of different chamber inlet temperatures. The solid black line in FIG. 4A is the humidity added by the chamber, which represents the humidity added by the chamber when a cold dry gas is used. The double black line in FIG. 4A shows the cumulative humidity when ambient air is entrained (specifically, the chamber humidity plus the ambient humidity). Under dry air source conditions, the desired humidity level may be approximately the same as the level of humidity added by the humidifier. However, when used in conjunction with a room air entrainment ventilation system, the additional humidity from the room air can cause the humidifier to deliver more than the desired or target humidity level, increasing the level of condensation, as shown in FIG. 4A.

[0190] Based on the desired humidity level, over-humidification may occur at various chamber inlet temperatures for the entrained room air. FIG. 4B shows an exemplary graph of outlet gas humidity as a function of inlet temperature at various user settings of the entrained room air ventilation system. For example, as shown in FIG. 4B, the 31° C. humidifier mode (shown as the desired humidity level for mask 31) may begin to over-humidify at a chamber inlet temperature of about 20° C. The 29° C. humidifier mode (shown as the desired humidity level for mask 29) may begin to over-humidify at a chamber inlet temperature of about 22° C. The 27° C. humidifier mode (shown as the desired humidity level for mask 27) may begin to over-humidify at a chamber inlet temperature of about 24° C. The solid lines in FIG. 4B represent the humidity (or dew point) delivered to the patient. The lines for mask 31, mask 29, and mask 27 represent the desired dew point delivered to the patient in “mask mode.” The desired dew point corresponds to the amount of humidity delivered to the patient. Mask mode refers to a non-invasive therapy. More specifically, "mask mode" refers to a respiratory therapy delivered using a sealing mask, e.g., a full mask. Mask mode refers to both pressurized, e.g., bilevel pressurized or continuous positive airway pressure (CPAP), or other non-invasive ventilation modes. The excess humidification curve (lighter double line) shows the excess humidification caused by the additional humidity, i.e., ambient humidity, when ambient air is used in mask mode at three different set points. The upward line represents an increase in the dew point of the gas, i.e., the gas delivered at a relatively high desired humidity. The controller in the first mode operates under the assumption that dry gas is being delivered, and therefore excess humidification often occurs when ambient air is used in this first mode. Each system disclosed herein operates the humidifier in a second mode when the inlet temperature exceeds a threshold to reduce excess humidification.

[0191] 5A-5C depict three different use cases of the humidifier at three different inlet gas temperatures. FIG. 5A is a graph showing the effect of additional room air humidity at an inlet temperature of 36° C. (i.e., actual inlet gas temperature is 36° C.). As shown in FIG. 5A, the inlet gas temperature 510 may be relatively higher than ambient. For example, the ambient temperature may be 24° C. and the inlet gas temperature may be 36° C. (i.e., hot inlet gas). To attempt to achieve a desired humidity level using a dry gas source, the humidifier may set a maximum chamber outlet set point at a target humidity corresponding to, for example, a dew point of 31° C., as shown by line 514. Line 514 may be a first function (i.e., first mode) of operation, when the humidifier assumes that the inlet gas is a dry gas. In standard operation of the humidifier, the hot, dry inlet gas, as it passes over the evaporative water surface in the humidification chamber, may attain a desired level of humidity corresponding to a chamber outlet temperature corresponding to a desired dew point at the patient side, for example, of 31° C. The exemplary value of 31° C. represents a desired dew point at the patient. This desired dew point can be used to calculate and / or set the chamber outlet set point temperature and / or the patient side set point temperature. Additionally, the chamber outlet set point can be used to control the heating / power of the heater plate to achieve the chamber outlet set point. However, when the humidifier is used with a room air entrainment ventilation system, the hot incoming gas already contains more moisture than the dry gas and may be over-humidified, as shown by line 512, because it gains humidity in the humidification chamber with an actual humidity equivalent to a 36° C. dew point. This over-humidification may result in unwanted condensation at the patient connection and may result in condensation in the conduits.

[0192] Condensation may occur as the temperature of the gas drops below the actual dew point of the gas. For example, condensation may occur because the actual dew point of the gas in the respiratory support system may be higher than the desired humidity level (such as line 514, which corresponds to a dew point of 31° C. in this example) due to additional room air humidity. In the example shown in FIG. 5A, the actual dew point at the chamber outlet may be, for example, 36° C. as shown by line 512. The duty cycle of the inspiratory wire in the respiratory support system may be controlled to allow the gas to cool from the chamber outlet temperature (e.g., 36° C. as shown in FIG. 5A) to the patient side temperature (e.g., 34° C. as shown in FIG. 5A). Once the gas has cooled to the patient side temperature, the water vapor that can no longer be contained in the gas with a relatively low dew point, e.g., 34° C. in this example, will condense into liquid. This condensation is represented by the grey area in FIG. 5A. In FIG. 5A, a first mode of operation (i.e., standard operation assuming that dry gas is used) is shown. A desired patient-side dew point of 31° C. may be used to define the temperature at the patient-side sensor and the chamber outlet set point. In this mode, the humidifier may be controlled to achieve an exemplary dew point of 34° C. at the patient side. The gas outlet temperature may be 36° C. Since this outlet temperature is higher than the chamber outlet temperature set point and / or the desired temperature at the patient side, which in this example is 34° C., the system will be configured to cool the gas as it travels from the chamber outlet to the patient side, as shown by line 510 between the chamber outlet and the patient side. However, the gas dew point may also correspond to 36° C. at the chamber outlet. The gas dew point cannot be higher than the actual temperature of the gas. Thus, as the gas cools between the chamber outlet and the patient side, the gas dew point will also decrease and may be comparable to line 510 but not exceed it. As previously mentioned, the water vapor that can no longer be contained in the gas at its relatively low dew point of 34° C. condenses into liquid. This condensation is represented by the grey area in FIG. 5A. FIG. 5A also illustrates the additional cooling that may occur in the patient interface area, which may be any area beyond the distal end of the intake tube.Such areas may include connection devices to the patient, such as an endotracheal tube for invasive respiratory therapy or a full face mask for non-invasive therapy.

[0193] When operating with bottled or dry gas, the patient side temperature can be calculated and targeted to be above the dew point corresponding to the desired humidity level. For example, a patient side temperature of 34° C. may be targeted, which is 3° C. above the desired dew point temperature of 31° C. This targeting takes into account the temperature drop as the gas moves through the patient connection. Typically, the patient connection is not heated, so the gas generally cools throughout the patient connection. A temperature drop of 3° C. may be calculated during operation of the respiratory support system, but any suitable temperature drop may be used. As shown in FIG. 5A, since the gas is below the actual dew point, more condensation forms in the patient connection as the gas further cools to 31° C. throughout the patient connection. This causes discomfort to the patient and may cause treatment to be interrupted as the patient disconnects the patient connection and / or the inspiratory tube to deal with the condensation. Additionally, further condensation may also be a safety risk, as condensation inside the patient connection may increase the risk of drowning for the patient or cause discomfort to the patient.

[0194] 5B-5C show the effect of additional room air humidity for inlet temperatures of 26° C. and 21° C., respectively. As shown in FIG. 5B, for a gas inlet temperature of 26° C. (gas temperature shown by line 520), the actual dew point at the chamber outlet may be 33° C., as shown by line 522, and the desired dew point at the chamber outlet may be 31° C., as shown by line 524. In such a case, condensation may form at the patient connection, as shown by the shaded area in FIG. 5B. As shown in FIG. 5C, for a gas inlet temperature of 21° C. (gas temperature shown by line 530), the actual dew point at the chamber outlet (line 534) and the desired dew point (line 532) may be 31° C. In such a case, as previously discussed, condensation may not form in the inlet tube or in the patient connection, because the inlet gas is not hot relative to the ambient air, and therefore the relative humidity of the gas at the chamber outlet may be close to saturation, regardless of the humidity level of the inlet gas. In the case shown in Figure 5C, the temperature of the gas exceeds the dew point and therefore no condensation occurs, where the dew points of the dry and wet inlets remain substantially constant between the chamber outlet and the patient interface outlet.

[0195] Controlling outlet humidity as a function of inlet temperature The control system described herein can minimize or at least reduce condensation levels and improve moisture delivery to the patient through the process of monitoring the chamber inlet temperature. The described control system for a humidifier is configured to control the heater plate power delivered and / or modify the chamber outlet temperature or humidity setpoint, or the heater plate power or temperature setpoint, based on the monitored chamber inlet temperature to reduce condensation in the conduit and / or in the patient connection device and / or in the downstream unheated section of the conduit. For example, the chamber outlet temperature and / or humidity behavior can operate as a function of the chamber inlet temperature. For example, the chamber outlet temperature setpoint may be capped (i.e., limited) based on the gas inlet temperature. In another example, the humidity setpoint or heater plate temperature setpoint or heater plate power setpoint may be capped based on the gas inlet temperature. The control system may use this functional association to help ensure that excessive moisture is not added to the gas via the humidifier. Specifically, this functional association may assume that an inlet gas that exceeds a threshold temperature is likely to contain excessive moisture. Thus, the control system may adjust the target humidity so that the humidifier adds relatively less humidity to the incoming gas. For example, in a given treatment mode of the humidifier, if the chamber inlet temperature is below a threshold, a desired humidity level range may be delivered to the patient. If the chamber inlet temperature is above a threshold, the delivered humidity may be reduced to a humidity level range lower than the original desired humidity level range. The humidity level may be controlled by controlling the chamber outlet temperature set point, the heater plate temperature set point, or the heater plate power. For example, as shown in the flow diagram in FIG. 6A and the schematic diagram in FIG. 7, the chamber outlet temperature set point may be limited or capped based on the gas inlet temperature. The illustrated example is based on controlling the chamber outlet temperature set point by capping the chamber outlet temperature set point.Additionally or alternatively, if the inlet temperature exceeds a threshold, the heater plate set point or heater plate power may be capped or limited to reduce the humidity output of the humidifier. Additionally or alternatively, the humidity level may be controlled by lowering the maximum chamber outlet temperature set point (i.e., maximum allowable chamber outlet temperature set point), as shown in the flow diagram of FIG. 6B and the schematic diagram of FIG. 7. A maximum chamber outlet temperature set point may be established after which power to the heater plate is disabled. If the chamber outlet temperature exceeds the maximum allowable chamber outlet temperature set point, the controller is configured to disable or shut down the heater plate. In one example, the heater plate power may be limited or capped to define a maximum allowable heater plate power based at least in part on the gas inlet temperature. In a non-limiting example, the controller is configured to modify the maximum allowable heater plate power based at least in part on the determined inlet temperature. The controller is configured to control the heater plate power up to the maximum allowable heater plate power. The controller is configured to control the heater plate power to any heater plate power that may be calculated to be less than or equal to the maximum allowable heater plate power. In a further example, the heater plate temperature setpoint may be limited or capped to define a maximum allowable heater plate temperature setpoint based at least in part on the gas inlet temperature. In a non-limiting example, the controller is configured to modify the maximum allowable heater plate temperature setpoint based at least in part on the determined inlet temperature. The controller is configured to control the heater plate power to the maximum allowable heater plate temperature setpoint. The controller is configured to control the heater plate power to any heater plate temperature setpoint that may be calculated to be less than or equal to the maximum allowable heater plate temperature setpoint.

[0196] The humidifier may include a second mode of operation that sets the humidity output or other parameters of the humidifier based on, for example, the inlet temperature. In this second mode, the humidifier may control either the chamber outlet setpoint, the heater plate temperature setpoint, or the heater plate power based on the inlet temperature. In the second mode of operation, the power to the heater plate may be capped based on the gas inlet temperature. The second mode may be activated if the inlet temperature exceeds a temperature threshold. In some examples, the temperature threshold may be a predetermined threshold. In one example, the temperature threshold is 24° C. In one example, in the second mode, the chamber outlet setpoint may be capped (i.e., limited) if the gas inlet temperature exceeds the temperature threshold. In a further example, the heater plate temperature setpoint may be capped (i.e., limited) if the gas inlet temperature exceeds the temperature threshold. The chamber outlet temperature setpoint may be capped at a maximum allowable chamber outlet if the gas inlet temperature exceeds the temperature threshold. If the inlet temperature exceeds the temperature threshold, the heater plate temperature setpoint may be capped at the maximum allowable heater plate temperature setpoint. If the inlet temperature exceeds the temperature threshold, the heater plate power may be capped to the maximum allowable heater plate. The capped chamber outlet temperature setpoint, or heater plate temperature setpoint, or heater plate power may be adjusted (i.e., modified) based on the gas inlet temperature. For example, when the inlet temperature exceeds the temperature threshold, such maximum allowable setpoint may be modified as a function of the inlet temperature in the second mode.

[0197] Advantageously, using the method described herein, the humidifier control device does not need to directly determine the humidity of the input gas, nor does it need to adjust control parameters if a room air entrainment ventilation device is detected. The described humidifier control method (and humidifier) ​​also does not require any specific sensor configuration or detection method to determine the type of ventilation device or gas source connected to the humidifier. Furthermore, the humidifier does not require complex and expensive humidity sensors (e.g., hygrometers). Thus, the control system and method can provide a relatively simple and cost-effective solution for reducing condensation levels during operation of a humidifier using room entrained air, at least since it does not require a humidity sensor upstream of the humidification chamber.

[0198] FIG. 6A illustrates an exemplary process 600 for setting a maximum allowable chamber outlet temperature set point using an inlet gas temperature threshold. For example, the process 600 may include step 610, where the system measures the gas temperature of the gas at or near the inlet to the humidification chamber, or anywhere in the gas flow path upstream of the humidification chamber. The system may then determine in decision block 612 whether the measured gas temperature exceeds the temperature threshold. If the gas temperature exceeds the threshold, the system may reduce the maximum chamber outlet temperature set point in step 616. When the inlet temperature falls below the temperature threshold, the maximum allowable chamber outlet temperature set point is reduced to a lower value compared to the maximum allowable chamber outlet temperature set point. In other words, if the gas temperature (i.e., the inlet gas temperature) does not exceed the threshold, the system may continue under standard operation under step 614, for example, by maintaining a predetermined chamber outlet set point and / or a predetermined power or duty cycle of the heater plate. Step 614 may correspond to a first, i.e., standard, mode of operation. Step 616 may correspond to a second mode of operation in which the humidity at the outlet is capped or limited. This may be achieved by capping or further capping the chamber outlet set point, capping the heater plate temperature (i.e., heater plate temperature set point), or capping the heater plate power. The capped values ​​are capped based on the inlet temperature exceeding a threshold, e.g., a temperature threshold. The capped chamber outlet temperature set point defines the highest allowable chamber outlet temperature set point. The capped heater plate temperature (i.e., heater plate temperature set point) defines the highest allowable heater plate temperature set point. The capped heater plate power (i.e., heater plate power set point) is the maximum allowable heater plate power (i.e., maximum allowable heater plate power set point). The capped values ​​may be adjusted by the controller as a function of the inlet temperature. The capped value defines the maximum allowable value in the second mode, ie when the gas inlet temperature exceeds the temperature threshold.In one example, the maximum allowable set point in the second mode may be lower than the maximum set point in the first mode.

[0199] FIG. 6B illustrates an exemplary process 601 for setting a maximum chamber outlet temperature set point (i.e., a maximum allowable chamber outlet temperature set point) using an inlet gas temperature threshold. For example, the process 601 may include step 620, where the system measures the temperature of the gas at or near the inlet to the humidification chamber, or anywhere in the gas flow path upstream of the humidification chamber. The system may then determine a chamber outlet temperature set point based on the inlet gas temperature in step 620. In addition to the inlet gas temperature, other inputs may be used to define the chamber outlet temperature set point. Then, in decision block 612, the system may determine whether the measured inlet gas temperature exceeds a temperature threshold. If the inlet gas temperature does not exceed the threshold, the system may control the heater plate in step 630 up to the chamber outlet temperature set point determined in step 620. In one example, the chamber outlet temperature set point determined in step 620 may define a maximum allowable chamber outlet temperature set point, i.e., may define an upper limit on the chamber outlet temperature. If the inlet gas temperature exceeds the threshold, the system may cap or limit the maximum allowable chamber outlet temperature setpoint based on the inlet gas temperature in step 626, i.e., cap or limit the allowable temperature of the gas at the chamber outlet. Once the system caps or limits the maximum allowable chamber outlet temperature setpoint in step 626, a new chamber outlet setpoint temperature may be set in step 628. Once a new chamber outlet setpoint temperature is set in step 628, the system (i.e., the humidifier controller) is configured to control the heater plate in step 630 up to the chamber outlet temperature setpoint determined in step 628. The controller may be configured to adjust the chamber outlet temperature setpoint determined in 628 based on at least the inlet temperature and flow rate to achieve the desired humidity level. The controller is configured to control the chamber outlet temperature setpoint such that it does not exceed the maximum allowable temperature setpoint determined in step 626.The controller is further configured to control the heater plate power based on feedback from a chamber exit temperature sensor (e.g., sensor 110) such that the temperature of the gas does not exceed the maximum allowable chamber exit temperature sensor.

[0200] The chamber outlet temperature determined in step 620 may be unlimited in some circumstances. For example, the chamber outlet temperature in "standard operation" (or in the first function / mode) may be allowed to go up to about 36°C without being limited. The maximum value of 36°C may be a hard limit, meaning that if the gas temperature at the chamber outlet exceeds 36°C, the heater plate is powered off, either by a software shutoff or a hardware shutoff, or a combination thereof. The chamber outlet set point may be based on some combination of the inlet temperature, the heater plate temperature, and / or input from one or more other sensors (e.g., an ambient temperature sensor and / or a flow rate). In step 626, the chamber outlet set point may be capped or limited. For example, in "new operation" (i.e. in the second function / mode), the maximum outlet temperature achievable at a given inlet temperature may be limited / capped (i.e. capped to define the maximum allowable chamber outlet temperature), so that the amount of moisture generated is limited at that particular inlet temperature.

[0201] As previously described, the system may measure the gas temperature in step 610 using an inlet temperature sensor. The inlet gas sensor may be an inlet gas temperature sensor that may be used at the inlet. The inlet temperature sensor may be coupled to the inlet to the humidification chamber so that the temperature of the gas in the inlet can be measured. The temperature sensor may be any sensor configured to measure the temperature of the gas, such as a thermistor or a probe sensor. However, the temperature sensor need not be directly attached to the inlet, but may be near the inlet, or on or within the inlet. The gas in the inlet may be any gas entering the humidification chamber that has not yet been humidified by the humidification chamber. Such gas may include dry gas, such as bottled gas, or gas containing excess humidity, such as room-entrained gas.

[0202] The temperature thresholds may include a single temperature threshold or multiple temperature thresholds, for example, in the case of multiple thresholds, the system may determine if the inlet gas temperature exceeds a first temperature threshold to set a first chamber outlet set point and determine if the inlet gas temperature exceeds a second temperature threshold to set a second chamber outlet set point.

[0203] Additionally or alternatively, in step 612, the system may determine whether the inlet temperature passes a different humidity scale. For example, the system may use a functional relationship between inlet gas heat and humidity to determine whether to reduce the maximum chamber outlet set point in steps 616, 626, or 628, or to continue standard control in steps 614 or 630. This functional relationship may take into account factors other than the current inlet temperature. If the ambient air pressure reading is above, below, or within a threshold range, this pressure value may be used to cap the maximum chamber outlet temperature and / or define the chamber outlet temperature.

[0204] The threshold value in step 612 may include a predetermined temperature threshold or set of temperature thresholds. Predetermined means that the temperature threshold is preprogrammed into the controller. In the alternative, the temperature threshold may not be predetermined, but instead may be dynamically calculated based on one or more of the chamber outlet setpoint, the heater plate temperature setpoint, the flow rate, or the target humidity. The temperature threshold may be calculated by the controller based on other factors, such as the patient side temperature setpoint or the desired (i.e., selected) patient side dew point. The temperature threshold may correspond to several temperatures. For example, the temperature threshold may be between 19°C and 26°C. Throughout this disclosure, a temperature range between a first temperature and a second temperature includes both the first temperature and the second temperature. For example, the threshold temperature may preferably be between 22°C and 24°C. The predetermined temperature threshold may vary depending on the outlet temperature setpoint of the humidifier. The predetermined temperature threshold may also vary depending on the target humidity value of the gas after it has passed through the humidification chamber. The target humidity may vary for various modes of the humidifier. For example, the humidifier may have different operating modes, such as invasive or non-invasive modes, that deliver different temperature and humidity conditions of the gas to the patient based on the need for treatment. Each operating mode may include multiple desired dew points, or modes, for delivery to the patient. For example, the non-invasive mode (i.e., corresponding to non-invasive ventilation delivery) may include a desired dew point mode of 27° C., a mode of 29° C., and a mode of 31° C., or other temperature mode. Each desired dew point, or mode, may correspond to a target humidity of the gas. Each desired dew point may have a corresponding temperature threshold, shared or unique. For example, the 27° C. mode may have a corresponding temperature threshold of 22° C., and both the 29° C. and 31° C. modes may have corresponding temperature thresholds of 24° C. In addition to or instead of the desired dew point modes, the operating modes may include multiple chamber outlet set points.

[0205] Table 1 shows some exemplary associated ranges for the maximum allowable chamber outlet temperature setpoint and corresponding chamber inlet temperature threshold for the non-invasive treatment mode. As can be seen, the humidity level is defined both as mg / L as well as the dew point temperature. The dew point temperature can correspond to the required temperature of the gas at the chamber outlet. The "chamber inlet threshold" refers to the chamber inlet temperature that instructs the controller when to reduce the desired humidity level output by the humidifier and incorporated into the incoming gas to a relatively lower humidity level. The "dry humidity level range when chamber inlet is below threshold" refers to the desired humidity level that the humidifier delivers when the inlet gas temperature is below the chamber inlet temperature threshold. This can correspond to what the humidifier does during standard operating conditions in step 614 of FIG. 6A or under step 630 of FIG. 6B if the gas inlet temperature does not exceed the threshold temperature at decision block 612. The "dry humidity level range when chamber inlet is above threshold" refers to the reduced humidity level that the humidifier delivers when the chamber inlet temperature is above threshold. This range may correspond to the minimum allowable tolerance for humidity levels.

[0206] [Table 1]

[0207] In other examples, there may be other ranges of acceptable chamber outlet temperature set points for other therapy modes. For example, in an invasive therapy mode (corresponding to invasive ventilation therapy), the dry humidity level range when the chamber inlet temperature exceeds the threshold may include 36-40 mg / L, which may equate to a dew point of 33-35° C. in the 37° C. mode. In another example, in a high flow mode (corresponding to delivery of a humidified high flow therapy), the dry humidity level range when the chamber inlet temperature exceeds the threshold may include 36-40 mg / L, which may equate to a dew point of 33-35° C. in the 37° C. mode, which may include 26-34 mg / L, which may equate to a dew point of 28° C. in the 35° C. mode, and / or the threshold may include 22-20 mg / L, which may equate to a dew point of 26° C. in the 33° C. mode.

[0208] The system may control the amount of power provided to a heater in the humidifier to achieve a chamber outlet temperature set point. The heater may be a heater plate in the humidifier. For example, the system may control the amount of power to the heater plate to achieve the chamber outlet set point. The system may use a closed loop system that uses feedback from an actual measured temperature at the chamber outlet to control the amount of power to the heater plate. An error value between the measured chamber outlet temperature and the chamber outlet set point may be used to increase or decrease the power provided to the heater plate. The system may control the power by controlling a PWM module that provides a voltage to the power. The system may reduce the amount of power provided to the heater. For example, the system may set a power threshold or limit. The power threshold or limit may correspond to a dew point and / or a target humidity of the gas. For example, the power threshold may correspond to a dew point at 19° C. In another example, the power threshold may correspond to a humidity output of 15.3 mg / L. Additionally or alternatively, the system may reduce the amount of power by limiting the power by a function or set of functions. For example, the system may cause the heater to output an amount of power according to a first function when the inlet temperature does or does not exceed a threshold temperature, and may cause the heater to output an amount of power according to a second function when the inlet temperature does or does not exceed a second threshold temperature. The first function may operate to control the amount of power to the heater plate, where the power may be capped by a maximum allowed power when the temperature (i.e., gas inlet temperature) is below a threshold. The maximum allowed power may correspond to a safety limit on the power supplied to the heater plate. The second function may cap a maximum allowed heater plate power at a given inlet temperature when the gas inlet temperature exceeds a threshold. That is, the second function may operate to control the amount of power to the heater plate, where the power is further limited to be below the maximum allowed power to the heater plate when the inlet temperature exceeds a threshold. The first and second functions may correspond to several functions.In the second function, the controller is configured to define a second maximum allowable power to the heater plate. The second maximum allowable power defines a new limit. The second maximum allowable power to the heater plate may be below the maximum allowable power defined by the first function (i.e., the first maximum allowable heater plate power). The second maximum allowable power to the heater plate is a reduced value. The second maximum allowable power may correspond to a maximum allowable chamber outlet set point when the gas inlet temperature exceeds a temperature threshold. The relatively lower second allowable heater plate power places an upper limit on the output humidity of the humidifier. This upper limit setting reduces the possibility of over-humidifying the gas and helps to take into account humidity in the gas resulting from an air-entraining gas source, for example an air-entraining ventilation system. The maximum allowable heater plate power may be defined in a piecewise function. This piecewise function may be similar to, or at least correspond to, the piecewise function defining the maximum allowable chamber outlet temperature set point. For example, the first function and the second function may operate together or separately as piecewise functions.

[0209] FIG. 7 shows an exemplary improved exit humidity level for gas conditions at the inlet of the humidifier chamber. As described with respect to FIG. 3, without knowledge of the inlet humidity conditions, the humidifier can deliver humidity close to the desired humidity level in three of the four types of gas conditions, namely, cold and humid (QI), cold and humid (QII), and hot and humid (QIV). However, at least when the inlet gas is hot and humid (QIII), excessive rainout may occur in the intake tube and / or the patient connection device. Using the processes 600 and 601 shown in FIG. 6A and FIG. 6B, the system can more effectively deliver the desired humidity levels in quadrants I, II, and III and therapeutic humidity levels in quadrant IV, even when used with turbine-driven ventilators or room-entrained gas. Since hot inlet gas conditions are typically associated with room-air entrained ventilators with turbines that generate heat, hot and humid inlet gas conditions are less common. Thus, the gas is typically "dry" and may have significantly higher humidity levels relative to compressed bottle gas or wall gas. In this less common case of hot, low humidity inlet gas conditions, the delivered humidity level can be reduced while still delivering therapeutic levels of humidity to the patient.

[0210] FIG. 8 illustrates exemplary different outlet set points or exemplary maximum chamber outlet temperature set points as a function of chamber inlet temperature in user modes (shown as mask 27, mask 29, and mask 31 modes) for a humidifier operating as part of a non-invasive respiratory assistance system. The humidifier is operating in a non-invasive mode, which may be selected by a graphical user interface, such as a touch screen located on the humidifier's base unit. The system may modify existing temperature and humidity control algorithms to set the chamber outlet temperature set point to an appropriate value below the curve shown in FIG. 8 based on the temperature threshold of each outlet set point or user mode, such as in step 616 of FIG. 6A. Line 810 represents a first mode / function in which the chamber outlet temperature set point is not limited and the only limit is the high temperature limit (or temperature safety limit), and a first system operation when the inlet temperature is below the threshold temperature. In the first mode (i.e., first function), the maximum allowable chamber outlet temperature set point is defined as 36° C., as defined by line 810. As can be seen in FIG. 8, the actual chamber outlet temperature set point used to control power to the heater plate corresponds to the selected dew point, i.e., 27° C. or 29° C. or 31° C., according to lines 812, 814, 816. Such chamber outlet set point may vary depending on gas conditions, e.g., flow rate, but such chamber outlet temperature set point will not exceed the maximum allowable limit defined by line 810 when in the first mode (i.e., when the inlet temperature is below the temperature threshold). Line 810 may correspond to a temperature safety limit. Under the first mode / function, the system may set the chamber outlet temperature set point anywhere below line 810, which may correspond to a temperature below 36° C., for example, which may act as a temperature safety limit. That is, under a first mode / function, which may occur with an inlet temperature below the threshold temperature, the system may cap the maximum chamber outlet temperature set point at a predetermined value, and the system may adjust the chamber outlet temperature set point to any value up to 36°C to achieve the desired humidity.Lines 812, 814, and 816 represent a second mode / function where the chamber outlet temperature set point is capped and along each line it will not exceed the maximum chamber outlet temperature set point, and a second system operation when the inlet temperature exceeds a threshold temperature. The chamber outlet temperature set point is set below the curved line of lines 812, 814, and 816 when the inlet temperature exceeds the threshold. Each line 812, 814, and 816 may correspond to a temperature difference between the inlet temperature and the chamber outlet temperature. This difference may be sufficient to achieve a desired therapeutic humidity level (according to Table 1). Lines 812, 814, and 816 define the maximum allowable chamber outlet temperature set point in the second mode or function (i.e., when the gas inlet temperature exceeds the temperature threshold). Lines 812, 814, and 816 show the chamber outlet set points in both the first and second modes. In the second mode, i.e., when the inlet temperature exceeds the temperature threshold, lines 812, 814, 816 define the maximum allowable chamber outlet temperature set point. This maximum allowable set point is less than the first maximum allowable set point in the first mode (i.e., when the inlet temperature is below the temperature threshold), as defined by line 810. Line 810 together with any one of lines 812, 814, 816 represents a piecewise function that defines the maximum allowable chamber outlet temperature set point. In the first mode, i.e., in the first part of the piecewise function, the maximum allowable set point is defined by line 810. In the second part of the piecewise function, the maximum allowable set point is defined by lines 812 or 814 or 816, respectively (depending on the dew point selected by the user). As can be seen in FIG. 8, in the second mode, when the inlet temperature exceeds the second temperature threshold, the maximum allowable chamber outlet temperature set point reaches and remains at 36° C. The second temperature threshold corresponds to an inlet temperature exceeding the required minimum temperature difference. The second temperature threshold may be a single temperature value or a range of temperature values. Each mode, e.g., 27 degrees, 29 degrees, or 31 degrees, may have its own second temperature threshold. As can be seen in FIG. 8, the controller attempts to maintain a temperature difference between the chamber exit set point and the gas inlet temperature. This temperature difference is used to define the chamber exit temperature set point.The temperature difference depends at least on the flow rate and may be further dependent on the ambient temperature and the heater plate temperature. As shown in Figure 8, when the gas inlet temperature exceeds a second temperature threshold, the chamber outlet temperature set point is set to the maximum allowable chamber outlet temperature set point of 36°C. As shown in Figure 8, lines 812, 814, and 816 flatten out at 36°C when the temperature difference between the inlet temperature and the chamber outlet set point falls below the difference threshold.

[0211] 9A shows an example of humidity added by an exemplary humidifier depending on the inlet temperature and the humidity added when the inlet gas is dry. For example, when the chamber inlet temperature is low (e.g., below a threshold of 24° C.), the humidifier can deliver a desired humidity level to the incoming gas under standard operating conditions (e.g., when the gas inlet temperature does not exceed the threshold temperature at decision block 612, as shown in step 614 of FIG. 6A and below step 630 of FIG. 6B). When the chamber inlet temperature rises above about 24° C., the system can reduce the humidity level to a relatively low desired humidity level for the incoming gas (e.g., when the gas inlet temperature exceeds the threshold temperature at decision block 612, as shown in step 616 of FIG. 6A and below step 630 of FIG. 6B, the system performs steps 626 and 628). As discussed above, when this algorithm is used with dry gas that exceeds the temperature threshold (i.e., hot, dry gas as shown in FIG. 7), but with the same inlet temperature, the humidity level delivered to the patient will be relatively lower, but still therapeutic. When this algorithm is used with a room air entrainment ventilation system (i.e., generating hot, dry gas as shown in FIG. 7), the humidity level delivered to the patient or user will be the relatively lower desired humidity level plus the humidity from the room air. That is, this relatively lower humidity level takes into account the room entrained humidity, as shown in FIG. 4A-4B and FIG. 5A-5B, in this case, the room air humidity that is not taken into account can raise the dew point to a relatively high undesirable level and minimize problems that would result in condensation (such as excessive condensation causing discomfort to the patient and / or interruption of therapy to clean the patient connection device and / or the inlet tube). In other words, as shown in FIG. 9A, when the inlet temperature threshold is exceeded, the controller may control the heater plate to generate a relatively lower absolute humidity to take into account the increased amount of humidity from the ambient air. The relatively low absolute humidity values ​​and humidity from the incoming air can result in an absolute humidity that is at or above therapeutic values, reducing or minimizing condensation in tubing or patient connection devices.

[0212] FIG. 9B shows an example of humidity added by an exemplary humidifier depending on the inlet temperature and the humidity added when the inlet gas is dry for different exemplary user settings or outlet temperature set points. Specifically, FIG. 9B shows the effect of a relatively low humidity level for the non-invasive operation mode of the humidifier, with different user settings or chamber outlet temperature set points of 27° C., 29° C., and 31° C. corresponding to mask 27, mask 29, and mask 31, respectively. Additionally or alternatively, the maximum chamber outlet temperature set point may be set at a reduced level to minimize condensation (e.g., 25° C., 27° C., and 29° C. corresponding to mask 27, mask 29, and mask 31, respectively). For the high flow mode, a similar approach may be adopted by the controller. Alternatively, the maximum allowable humidity may not change in the high flow mode. During the invasive mode, humidity is maximized and does not change over the full range of inlet temperatures.

[0213] Exemplary Humidity Delivery Control System 10A-10C are illustrative overlays of FIGS. 5A-5C that provide a solution to the condensation that may form under standard operation as shown in FIGS. 5A-5C.

[0214] FIG. 10A is a graph showing an exemplary effect of an exemplary humidity delivery control system at an inlet temperature of 36° C. Specifically, FIG. 10A shows a comparison between operating a humidifier under standard operating conditions where the target or desired humidity corresponds to a dew point of 31° C. (e.g., as shown in FIG. 5A) and operating a humidifier with a reduced maximum chamber outlet set point corresponding to a dew point of 29° C. An exemplary actual gas temperature as the gas passes through the humidifier is shown by line 1010. The gas temperature may decrease from the outlet temperature shown as 36° C. in FIG. 10A to a target temperature at the patient interface outlet, shown as 31° C. in FIG. 10A, for example. When gas is entrained in the room, the gas may contain excess moisture. When gas is not entrained in the room, the gas may be considered “dry.” Under process 601 shown in FIG. 6A or process 600 shown in FIG. 6B, the target or desired humidity level (line 1014A) represented by the dry inlet humidity (i.e., dry gas) may be reduced to a relatively lower desired humidity level (line 1014B) corresponding to a dew point of, for example, 29° C. Line 1014A may represent the dew point when the system does not cap the chamber outlet set point if the inlet gas temperature threshold is not exceeded. Line 1014B may represent the dew point that results from lowering the chamber outlet set point when the temperature threshold is exceeded. In the case of room entrained gas, the effective target humidity of the outlet gas may be reduced from line 1012A to line 1012B. Line 1012A may represent the dew point of the ambient gas humidity in addition to the chamber humidity (shown in FIG. 5A). Line 1012B may represent the resulting dew point of ambient gas humidity in addition to chamber humidity when a temperature threshold is exceeded and the chamber outlet temperature set point is lowered (i.e., the maximum allowable chamber outlet temperature set point is capped). Lines 1012B and 1014B may represent the change in dew point due to the chamber outlet set point being lowered, for example, by capping the chamber outlet temperature set point. Lines 1012B and 1014B may represent the decrease in dew point due to the reduced amount of humidity added to the gas by the humidifier when the chamber outlet set point is reduced.When the inlet temperature threshold is exceeded, the controller may cap the chamber outlet temperature setpoint (or heater plate power setpoint or heater plate temperature setpoint or humidity setpoint) to a lower chamber outlet setpoint (or lower heater plate power setpoint or heater plate temperature setpoint or lower humidity setpoint) compared to standard control (shown by line 1014A). In addition to or as an alternative to capping the chamber outlet temperature setpoint, the heater plate setpoint temperature may be capped or the heater plate power setpoint may be capped. A lower chamber outlet temperature setpoint may result in a lower dew point and a lower absolute humidity output by the humidifier. If the humidifier is connected to a room air entrainment ventilation system, less condensation may form as the dew point decreases from 1012A to 1012B, as shown by the shaded triangles. This is accomplished by capping the chamber outlet temperature setpoint (or capping the heater plate power setpoint or heater plate temperature setpoint) to reduce the humidity produced. The capped chamber outlet temperature setpoint (or capped heater plate power setpoint or heater plate temperature setpoint) corresponds to the maximum allowable setpoint. In the second mode (i.e., when the inlet temperature is equal to or exceeds the temperature range), the capped setpoint is less than the maximum setpoint in the first mode (i.e., when the inlet temperature is below the temperature threshold). Although some condensation may still occur due to the high inlet temperature, as shown in FIG. 5A, the condensation in FIG. 10A may be significantly reduced compared to the condensation level of gas during normal operation of the humidifier. As previously mentioned, lines 1012A, 1012B, 1014A, and 1014B are shown as horizontal straight lines representing estimated dew points for illustrative purposes to indicate one or more points at which condensation may occur in the humidifier or respiratory support system.

[0215] FIG. 10B is a graph showing an exemplary effect of an exemplary humidity delivery control system at an inlet temperature of 26° C. In particular, FIG. 10B shows a comparison between operating a humidifier under standard operating conditions where the target humidity corresponds to a dew point of 31° C. (e.g., as shown in FIG. 5B) and operating a humidifier with a reduced maximum chamber outlet set point corresponding to a dew point of 29° C. An exemplary gas temperature as the gas passes through the humidifier is shown by line 1030. Under process 600, the target humidity level represented by the dry inlet humidity (line 1013A) may be reduced to a relatively lower desired humidity level (line 1034B), for example, corresponding to a dew point of 29° C. Line 1034A may represent the dew point at the chamber outlet when the system does not further cap the chamber outlet temperature set point when the inlet gas temperature threshold is exceeded. Line 1034B may represent the dew point at the chamber outlet resulting from reducing (i.e., capping) the chamber outlet temperature set point when the temperature threshold is exceeded. The chamber outlet temperature set point is capped at the highest allowable chamber outlet temperature set point. In the case of room entrained gas, the effective target humidity of the outlet gas may be reduced from line 1032A to line 1032B. Line 1032A may represent the dew point at the chamber outlet (shown in FIG. 5B). The outlet temperature of the gas may be 33° C. As this outlet temperature is lower than the chamber outlet temperature set point and / or the desired temperature at the patient side, which is 34° C. in this example, as shown by line 1030 between the chamber outlet and the patient side sensor, the system will be configured to heat the gas as it travels from the chamber outlet to the patient side. The gas will then cool as it travels through the patient interface, where it is not heated to about 31° C. at the patient interface outlet, as shown by line 1030 between the patient side sensor and the patient interface outlet. As the gas cools between the patient side and the patient interface outlet, the dew point of the gas will also decrease. As previously mentioned, the water vapor that can no longer be contained in the gas with its relatively low dew point of 31° C. will condense into liquid. This condensation is represented by the gray area in FIG. 10B. Line 1032B may represent the resulting dew point at the chamber outlet when the inlet temperature threshold is exceeded and the chamber outlet set point is reduced.Lines 1032B and 1034B may represent the change in dew point due to a lowering of the chamber outlet set point, for example, by capping the chamber outlet set point. Lines 1032B and 1034B may represent the decrease in dew point due to a reduction in the amount of humidity added to the gas by the humidifier when the chamber outlet set point is reduced (i.e., the maximum allowable chamber outlet set point is capped). When the inlet temperature threshold is exceeded, the controller may cap the chamber outlet set point (or heater plate power set point or heater plate temperature set point) to a relatively lower chamber outlet set point compared to standard control (represented by line 1014A). In addition to or as an alternative to capping the chamber outlet set point, the heater plate set point temperature may be capped or the heater plate power set point may be capped. A relatively lower chamber outlet set point may result in a relatively lower dew point and a relatively lower absolute humidity. The relatively low or capped chamber outlet set point corresponds to the maximum allowable chamber set point in the second mode (i.e., when the inlet gas temperature exceeds the temperature threshold). The maximum allowable chamber set point may vary with respect to changes in the inlet gas temperature. Condensation, for example, represented by the shaded area, may be avoided by lowering the desired humidity dew point, also referred to as the actual dew point. For example, reduced condensation may be achieved by capping the chamber outlet temperature set point (or capping the heater plate temperature set point or heater plate power set point) when the inlet gas temperature exceeds the temperature threshold. As previously mentioned, lines 1032A, 1032B, 1034A, and 1034B are shown as horizontal lines representing estimated dew points for illustrative purposes to indicate one or more points at which condensation may occur in the humidifier or respiratory support system.

[0216] FIG. 10C is a graph showing an exemplary effect of an exemplary humidity delivery control system at an inlet temperature of 21° C., which is below a threshold temperature of 24° C. An exemplary gas temperature as the gas passes through the humidifier is shown by line 1040. The target humidity dew point may remain at line 1042A rather than decreasing because the inlet temperature threshold is not exceeded. In the example shown in FIG. 10C, the humidifier may heat and humidify the gas until it saturates at a reduced humidity level, regardless of the inlet humidity resulting from the low inlet temperature (i.e., lower than the ambient temperature). This is shown by merging the dry inlet and wet inlet humidity lines (i.e., lines 1042A and 1044A are the same after the gas leaves the chamber outlet). Lines 1042A and 1044A are shown as horizontal straight lines representing estimated dew points for illustrative purposes to show one or more points at which condensation may occur in the humidifier or respiratory support system.

[0217] In an alternative configuration, the humidifier may include a humidity sensor at the outlet of the humidifier instead of the temperature sensor. The controller is configured to control the power supplied to the heater plate based on the measured inlet temperature. The controller may be configured to operate in a first mode when the gas inlet temperature is below a threshold temperature and in a second mode when the gas inlet temperature exceeds the temperature threshold. The controller may be configured to define a first maximum allowable humidity value in the first mode and a second maximum allowable humidity in the second mode. The second allowable humidity is below the first maximum allowable humidity. The controller determines the humidity of the gas based on the outlet humidity sensor. The controller is configured to control the power to the heater plate to achieve a desired humidity output at the chamber outlet. In the second mode, the power level of the heater plate is controlled to ensure that the output humidity at the chamber outlet is below the second maximum allowable humidity. The humidity set point may be defined by a piecewise function. A first part of the piecewise function defines a first maximum allowable humidity output when the gas inlet temperature is below the temperature threshold. A second portion of the segmental function defines a second humidity output. The humidity set point may be adjusted by the controller in the second mode based on at least the inlet temperature and flow rate readings. However, the maximum allowable humidity corresponds to a second maximum allowable humidity. The humidity set point may be adjusted to be lower than the second maximum allowable humidity corresponding to a desired humidity input by the user. However, in the second mode (i.e., when the gas inlet temperature exceeds the temperature threshold), the humidity output does not exceed the second maximum allowable humidity. If the humidity output exceeds the second maximum allowable humidity, the heater plate power is turned off by the controller. The relatively low humidity when the inlet temperature exceeds the temperature threshold reduces condensation in the tubing and / or the patient connection device. The relatively low humidity output helps prevent excessive humidification of gases, particularly gases received from an air entrainment ventilator. In a further alternative configuration, the system may operate with a humidity sensor that measures the inlet gas to determine if the gas is hot and humid or hot and humid. The system may use this additional information to modify or refine the outlet temperature setpoint.Additionally or alternatively, the system may operate with a pressure sensor measuring the inlet gas configured to determine the ambient air pressure, which may be used to determine the indicated humidity of the inlet gas.

[0218] Terminology Many other variations beyond those described herein will be apparent from the present disclosure. For example, depending on the embodiment, certain acts, events, or functions of any algorithm described herein may be performed in a different order, added, combined, or omitted altogether (e.g., not all acts or events described are necessary to execute an algorithm). Furthermore, in certain embodiments, acts or events may be performed simultaneously, rather than sequentially, for example, by multi-threading, interrupt handling, or multiple processors or processor cores, or in other parallel architectures. Furthermore, various tasks or processes may be performed by various machines and / or computing systems that can function together.

[0219] The various exemplary logic blocks, modules, and algorithmic steps described in conjunction with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or a combination of both. To clearly illustrate this interchangeability of hardware and software, the various exemplary components, blocks, modules, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends on the particular application and design constraints imposed on the overall system. The described functionality may be implemented in various ways for each particular application, and such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.

[0220] For example, the various illustrative logic blocks and modules described in conjunction with the embodiments disclosed herein may be implemented or executed by a machine such as a hardware processor comprising digital logic circuitry, a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but alternatively the processor may be a controller, a microcontroller, or a state machine, combinations thereof, and the like. A processor may comprise electrical circuitry configured to process computer-executable instructions. In another embodiment, the processor comprises an FPGA, or other programmable device that performs logical operations without processing computer-executable instructions. A processor may also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in combination with a DSP core, or any other such configuration. The computing environment may comprise any type of computer system, including, but not limited to, a computer system based on a computing engine within a microprocessor, a mainframe computer, a digital signal processor, a portable computing device, a device controller, or an appliance, to name a few.

[0221] Each step of the method, process, or algorithm described in conjunction with each embodiment disclosed herein may be implemented directly in hardware, in a software module stored in one or more memory devices and executed by one or more processors, or in a combination of the two. The software module may be in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of persistent computer readable storage medium, medium, or physical computer storage device known to one skilled in the art. An exemplary storage medium may be coupled to the processor such that the processor can read information from and write information to the storage medium. In another alternative, the storage medium may be integrated with the processor. The storage medium may be volatile or non-volatile. The processor and the storage medium may be in an ASIC.

[0222] Unless otherwise indicated or understood otherwise within the context of use, conditional language used herein, such as "can," "might," "may," "eg," among others, is generally intended to convey that certain embodiments include certain features, elements, and / or conditions, while other embodiments do not. Thus, such conditional language does not generally imply that each feature, element, and / or condition is required in any way in one or more embodiments, or that one or more embodiments necessarily include logic for determining whether such features, elements, and / or conditions are included or should be performed in any particular embodiment, with or without author input or direction. Terms such as "comprising," "including," "having," and the like, are synonymous and used interchangeably inclusively and do not exclude additional elements, features, acts, operations, etc. The term "or" is also used in its inclusive sense (rather than its exclusive sense), and thus the term "or," for example, when used to connect elements in a sequence, may mean one, some, or all of the elements in the sequence. Furthermore, the term "each" as used herein, in addition to having its inherent meaning, can refer to any portion of the set of elements to which the term "each" applies.

[0223] For example, disjunctive language such as the phrase "at least one of X, Y, and Z" should be understood with the context in which it is generally used to convey whether an item, term, etc. may be X, Y, or Z, or combinations thereof, unless otherwise indicated. Thus, such disjunctive language does not generally imply that a particular embodiment requires that at least one X, at least one Y, and at least one Z, respectively, be present.

[0224] Unless expressly stated otherwise, articles such as "a" or "an" should generally be construed to include one or more of the listed items. Thus, a phrase such as "an apparatus configured to" is intended to include one or more of the listed apparatuses. Such one or more of the listed apparatuses may also be collectively configured to perform the recited and recited items. For example, "a processor configured to perform the recited items A, B, and C" may include a first processor configured to perform the recited item A working with a second processor configured to perform the recited items B and C.

[0225] Although detailed descriptions have been shown and described above, and novel features applicable to various embodiments have been pointed out, it will be understood that various omissions, substitutions, and changes may be made in the form and details of the illustrated apparatus or algorithms without departing from the spirit of the disclosure. It will be recognized that certain embodiments of the invention described herein may be implemented within a form that does not provide all of the features and advantages set forth herein, since some of the features may be used or may be practiced separately from other features.

Claims

1. 1. A humidifier for humidifying a gas flow supplied to a user in a humidification chamber, comprising: a base unit including a heater plate; An electronic control device, outputting a heater plate control signal to the heater plate based on a heater plate temperature setpoint or a heater plate power setpoint; determining an inlet temperature of the gas received by the humidification chamber based on a signal received from an inlet temperature sensor; determining that the inlet temperature exceeds a threshold temperature; determining an upper limit for the heater plate temperature setpoint or the heater plate power setpoint based on the inlet temperature exceeding the threshold temperature; and an electronic control device configured as follows: A humidifier comprising:

2. 10. The humidifier of claim 1, wherein the controller is configured to reduce the amount of power supplied to the heater plate in response to an upper limit on the heater plate temperature setpoint or the heater plate power setpoint.

3. 3. The humidifier of claim 2, wherein the heater plate temperature setpoint or the heater plate power setpoint is set to achieve a minimum dew point of 19°C.

4. 4. The humidifier of claim 1, wherein the control device is configured to control the heater plate temperature setpoint or the heater plate power setpoint in a first mode when the inlet temperature is below the threshold temperature and in a second mode when the inlet temperature is above the threshold temperature.

5. A humidifier according to any one of claims 1 to 4, wherein the threshold temperature is between 22°C and 24°C.

6. A humidifier according to any one of claims 1 to 5, wherein the desired dew point is selected by the user.

7. 6. The humidifier of claim 1, wherein the humidifier is operable in one of a plurality of modes, each mode defining a plurality of desired dew points, and the controller is configured to impose an upper limit on the heater plate temperature setpoint or the heater plate power setpoint when operating in any one of the plurality of modes.

8. 8. The humidifier of claim 7, wherein the plurality of modes includes an invasive mode, a non-invasive mode, and a high flow mode.

9. 9. The humidifier of claim 8, wherein the controller is configured to limit humidity added to the input gas when operating in a non-invasive mode.

10. 10. A humidifier according to claim 8 or 9, wherein the mode is manually selectable by a user.

11. The humidifier of any one of claims 8 to 10, wherein the non-invasive mode includes desired dew points of 29°C, 27°C, and 25°C.

12. The humidifier of any one of claims 8 to 10, wherein the non-invasive mode includes desired dew points of 27°C, 25°C, and 23°C.

13. 13. A humidifier as claimed in any preceding claim, wherein a target humidity at the outlet temperature setpoint is predetermined when the inlet temperature is below the threshold temperature, and wherein the amount of humidity produced at the outlet temperature setpoint is reduced to a relatively low, predetermined value when the inlet temperature exceeds the threshold.

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