Water shortage alarm determination

Abstract

To provide a system for optimizing alarm criteria selection to minimize a risk of a false alarm.SOLUTION: A method of determining a water shortage condition includes a two-step process including primary determination of a water shortage condition and secondary determination of a water shortage condition. This primary determination is made by a water shortage detection method selected by a controller on the basis of a flow rate and an operation mode of a system. During the secondary determination, the method comprises temporary control over power input of a humidifying part of an apparatus. The secondary determination confirms or denies the primary determination.SELECTED DRAWING: Figure 1a

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 62 / 364250, filed July 19, 2016. The entire contents of U.S. Provisional Patent Application No. 62 / 364250 are incorporated herein by reference.

[0002] The present disclosure relates to a system for humidifying gases delivered to a patient. [Background technology]

[0003] Humidifying gases delivered to patients is beneficial in a variety of applications. These applications include when the gas is intended for patient breathing and when gas is delivered to patients during surgery. In the case of respiratory gases, humidity increases patient comfort, and humidified gases reduce the tendency for tissues in the patient's airway to become dry. In the case of surgical gases, humidified gases reduce drying of exposed tissues, improving postoperative outcomes. Summary of the Invention [Problem to be solved by the invention]

[0004] In gas humidification systems incorporating a humidification chamber for humidifying gas for delivery to a patient, it is important that a certain minimum level of water is maintained in order for the humidifier to have the ability to provide water vapor to the gas stream. It is therefore important that the healthcare professional administering the humidified gas to the patient, or the patient themselves in the case of home administration, check the water level and add more water if necessary. This step is often overlooked, resulting in an interruption to the humidification of the air stream or, in some cases, damage to the respiratory support device.

[0005] While low-water alarms have been incorporated into respiratory humidification devices, the alarms are often prone to false alarms in situations where the chamber is not actually empty. False alarms are often a cause of great concern for non-medical personnel, who are uncertain whether the device is functioning properly. False alarms, if they occur frequently, can also cause medical personnel to ignore true alarms when they occur. [Means for solving the problem]

[0006] The present disclosure provides a system for optimizing the selection of alarm criteria to minimize the risk of false alarms. The present disclosure provides multiple different methods for determining an out-of-water condition and selection criteria based on operating conditions for selecting an advantageous out-of-water determination method.

[0007] It is an object of the present disclosure to provide a breath-assist device that overcomes the above-mentioned drawbacks or that goes some way to at least providing a useful choice for the public or healthcare professionals.

[0008] Accordingly, in a first aspect, the present disclosure can be broadly described as including a respiratory assistance system for humidifying a gas flow, including a humidification chamber including an inlet and an outlet for passing gas through the humidification chamber, the humidification chamber adapted to hold a volume of water, a heater adjacent the humidification chamber, the heater adapted to provide heat to the volume of water in the humidification chamber, a flow sensor disposed in the humidification chamber, a temperature sensor associated with the humidification chamber, and a controller in electronic communication with the heater plate, the flow sensor, and the temperature sensor, the controller configured to determine at least one operating state based on a therapy mode and a flow rate, and to select at least one water outage detection method based on the determined operating state, the operating state being dependent on the flow rate relative to a flow rate threshold.

[0009] The water shortage detection method may include a passive water shortage detection method, an active water shortage detection method, and a combination of a passive water shortage detection method and an active water shortage detection method.

[0010] The respiratory assistance system may also include a user interface configured to allow a person to select a therapy mode from a predetermined list of therapy modes, the predetermined list incorporating an invasive mode, a non-invasive mode, and a high-flow non-sealed therapy mode.

[0011] Those skilled in the art to which this disclosure pertains will suggest themselves numerous structural modifications and widely different embodiments and applications of the present disclosure without departing from the scope of the present disclosure as defined in the appended claims. The present disclosure and the descriptions herein are purely illustrative and are in no way intended to be limiting.

[0012] The term "comprising" as used in the specification and claims means "consisting at least in part of." When interpreting a sentence in the specification and claims containing "comprising," there may be features other than the feature preceded by the term. Related terms such as "comprise" and "comprises" are to be interpreted in the same manner.

[0013] Preferred embodiments of the present disclosure will now be described with reference to the accompanying drawings. [Brief explanation of the drawings]

[0014] [Figure 1a] 1 is a flow chart illustrating an overall process for determining a lack of water in a humidifier chamber according to the present disclosure. [Figure 1b] 10 is a flow chart illustrating another embodiment of an overall process for determining a lack of water in a humidifier chamber according to the present disclosure. [Figure 2] 10 is a flow chart illustrating an overall process for determining a lack of water in a humidifier chamber according to an alternative embodiment of the present disclosure. [Figure 3] 1 is a flow chart illustrating an active water shortage detection method for determining a lack of water in a humidifier chamber according to the present disclosure. [Figure 4a] 1 shows a schematic diagram of a user receiving humidified air, where the user is wearing a nasal mask and receiving air from a modular blower / humidifier breath assist system. [Figure 4b] FIG. 1 shows a schematic diagram of a user receiving humidified air, where the user is wearing nasal prongs and receiving air from a modular blower / humidifier breath assist system. [Figure 5] 1 shows a schematic diagram of a user receiving humidified air, where the user is wearing a nasal mask and receiving air from an integrated blower / humidifier breath assist system. [Figure 6] FIG. 1 shows a schematic diagram of a user wearing nasal prongs and a breath assist system receiving gases from a central source via a wall inlet, which supplies the gases to a control unit which receives humidified air and supplies the gases to a humidifier chamber collocated with and downstream of the control unit. [Figure 7] 10 is a plot of heater plate power, heater plate temperature, filtered water level, and chamber outlet temperature as a function of time from an experiment conducted to test a water shortage detection method using the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0015] This specification provides a respiratory assistance system configured to deliver multiple therapy modes and determine whether the water level in a humidification chamber has reached an acceptable threshold level. The system selects an appropriate water-out detection method based on the system's operating state, which in turn is related to the particular therapy mode and gas flow rate selected by the user. The therapy modes of the system may include an invasive mode, a non-invasive mode, and a high-flow, non-sealing mode, or any other mode known to those skilled in the art. The high-flow, non-sealing therapy mode (referred to herein as the Optiflow® mode) is commercially available as Optiflow® by Fisher and Paykel Healthcare Limited of Auckland, New Zealand.

[0016] 4a and 4b are schematic diagrams of a user 2 receiving air from a respiratory assisted breathing unit and humidifier system 1 according to a first exemplary system configuration. System 1 delivers a pressurized flow of heated and humidified gas to user 2 for therapeutic purposes, including, for example, reducing the incidence of obstructive sleep apnea, providing CPAP therapy, providing therapeutic humidification, etc. System 1 is described in more detail below.

[0017] The assisted breathing unit or blower unit 3 has an internal compressor unit, flow generator or fan unit 13 (which may generally be referred to as a flow control mechanism). Air from the atmosphere enters the housing of the blower unit 3 through an atmospheric inlet 40 and is drawn through the fan unit 13. The power output of the fan unit 13 is adjustable and the fan speed is variable. The pressurized gas flow exits the fan unit 13 and blower unit 3 and travels through a connecting conduit 4 to the humidifier chamber 5 and enters the humidifier chamber 5 through an inlet or inlet port 23.

[0018] In alternative embodiments, the assisted breathing unit may include a ventilator. The ventilator may have a fan or turbine configured to generate airflow. In some embodiments, the ventilator may receive gas from a compressed air source, such as a tank. The ventilator may then use a valve to control the delivery of air to the humidification chamber 5.

[0019] The humidifier chamber 5, in use, contains a volume of water 20. In some embodiments, in use, the humidifier chamber 5 is located on a humidifier base unit 21 having a heater plate 12. The heater plate 12 is powered to heat the base of the chamber 5, and therefore the contents of the chamber 5. When the water in the chamber 5 is heated, it evaporates, and the gas within the humidifier chamber 5 (above the surface of the water 20) is heated and humidified. The gas stream entering the humidifier chamber 5 through the inlet port 23 passes over the heated water (or through these heated, humidified gases, as applicable for larger chambers and higher flow rates), becoming heated and humidified as it passes. The gas stream then exits the humidifier chamber 5 through the outlet or exit port 9 and enters the delivery conduit 6.

[0020] In the context of the present disclosure, when reference is made herein to a "humidifier unit," this should be taken to mean at least the chamber 5, and, where appropriate, the base unit 21 and heater plate 12.

[0021] The heated humidified gas passes along the length of a delivery conduit 6 and is delivered to a patient or user 2 through a user interface 7. The conduit 6 may be heated, such as by a heater wire (not shown), to help prevent condensation.

[0022] The user interface 7 shown in FIG. 4a is a nasal mask that surrounds and covers the nose of the user 2. However, it should be noted that a nasal cannula (as shown in FIG. 4b), a full face mask, a tracheostomy fitting, or any other suitable user interface could replace the nasal mask shown. A central controller or control system 8 is located either within the blower casing (controller 8a) or within the humidifier base unit (controller 8b). In this type of modular system, separate blower controller 8a and humidifier controller 8b may be used, and the controllers 8a and 8b may be connected (e.g., by cable) so that they can communicate with each other during use. In some embodiments, the controllers may be independent of each other. The humidifier controller 8b may be a stand-alone unit configured for use with any type of gas source.

[0023] In some embodiments, the blower controller 8a and the humidifier controller 8b have a master-servant relationship, which may generally refer to the ability of one of the controllers to control the functions of the other controller. In other embodiments, the blower controller 8a and the humidifier controller 8b have a peer relationship, which may generally refer to the ability of each controller to function independently of the other.

[0024] In some embodiments, the control system 8 receives user input signals via user controls 11 located on either or both of the humidifier base unit 21 or the blower unit 3. In some embodiments, the controller 8 also receives input from sensors located at various locations throughout the system 1. In another embodiment, the humidifier may include a vertical wall or spine, with the user controls 11 located on the spine. The user controls may be located above the humidification chamber 5 and heater plate 12. This allows the user to interact with the user controls with minimal risk of touching the heater plate 12.

[0025] The sensors and their locations are described in more detail below. In response to user input from the controller 11 and signals received from the sensors, the control system 8, in some embodiments, determines control outputs that send signals to adjust the power to the humidifier chamber heater plate 12 and the speed of the fan 13. The programming that determines how the controller determines the control outputs is described in more detail below.

[0026] A schematic diagram of a user 2 receiving air from an integrated blower / humidifier system 100 according to the second aspect of the present disclosure is shown in FIG. 5. The system operates much like the modular system 1 shown in FIG. 4 and described above, except that the humidifier chamber 105 is integrated with the blower unit 103 to form an integrated unit 110. A pressurized gas flow is provided by a fan unit 113 located inside the casing of the integrated unit 110. Water 120 in the humidifier chamber 105 is heated by a heater plate 112 (which in this embodiment is an integral part of the structure of the blower unit 103). Air enters the humidifier chamber 105 through an inlet port 123 and exits the humidifier chamber 105 through an outlet port 109. The gas flow is provided to the user 2 via a delivery conduit 106 and an interface 107. A controller 108 is housed within the outer shell of the integrated unit 100. In the illustrated embodiment, the controller 108 is a single controller that controls the operation of the heater plate 112 and the blower unit 103 based on one or more sensor inputs. The controller 108 may include separate software or hardware modules for controlling the blower unit 103 and the heater plate 112. User controls 111 are located on the exterior surface of the unit 100.

[0027] A schematic diagram of a user 2 receiving air from yet another form of breath-assist system 200 is shown in Figure 6. The system 200 may generally be characterized as a remote source system, receiving air from a remote source through a wall inlet 1000.

[0028] The wall inlet 1000 is connected via an inlet conduit 201 to a control unit 202 which receives gas from the inlet 1000. The control unit 202 has sensors 250, 260, 280, 290 which measure the humidity, temperature and pressure and flow rate of the input gas stream respectively.

[0029] The gas stream is then provided to the humidifier chamber 205, where it is heated and humidified and provided to the user in a manner similar to that described above. Note that when referring to the "humidifier unit" of a remote source system such as system 200, this should be taken to mean incorporating the control unit 202; i.e., gas from the remote source may be connected either directly to the inlet or via the control unit 202 (such as to reduce pressure), but the control unit and humidifier chamber should be taken to belong to the overall "humidifier unit."

[0030] In some embodiments, the system 200 can provide O2 or an O2 fraction to a user. The system may provide O2 to a user by having a central source as the O2 source. In another embodiment, the system may provide O2 by mixing ambient air with O2 introduced from a central source. Mixing of the ambient air with the introduced O2 may be accomplished by a venturi 90 or the like located within the control unit 202.

[0031] The control unit 202 may also include a valve 211 or similar mechanism that functions as a flow control mechanism for regulating the flow rate of gas through the system 200. Additionally, the control unit may also include multiple valves for controlling the flow rate of gas through the system 200. In some embodiments, the operation of the valve 211 may be controlled by the controller 9. In other embodiments, the operation of the valve 211 may be controlled by an additional controller located within the control unit 202.

[0032] Sensor The modular and integrated systems 1, 100 and 200 shown in Figures 4, 5 and 6 have sensors located at points throughout the system, which are described below in connection with the breath-assist system 1.

[0033] In one embodiment, the modular system 1 has at least the following sensors in the following locations as shown in FIG.

[0034] 1) An ambient temperature sensor 60 located in, near or on the blower casing and configured or adapted to measure the temperature of air being introduced from the atmosphere. The temperature sensor 60 may be located in the gas stream after (downstream of) the fan unit 13, as close as possible to the inlet or inlet to the humidifier chamber.

[0035] 2) A humidifier unit outlet port temperature sensor 63 located either at the chamber outlet port 9 or at the device end (opposite the patient end) of the delivery conduit 6. The outlet temperature sensor 63 is configured or adapted to measure the temperature of the gas flow as it exits the chamber 5 (in either configuration, the outlet port temperature sensor 63 can be considered to be proximal to the chamber outlet port 9).

[0036] Similarly, the sensors are located in substantially the same locations in the integrated system 100 shown in FIG. 5 and the system 200 shown in FIG. 6. For example, in the integrated system of FIG. 5, the ambient temperature sensor 160 is located in the gas flow within the blower casing, just prior to (upstream of) the humidifier chamber inlet port 123. The chamber outlet port temperature sensor 163 is located at one of the chamber outlet ports 109 and is configured to measure the temperature of the gas flow as it exits the chamber 105 (in either configuration, the outlet port temperature sensor 163 can be considered to be proximal to the chamber outlet port 109). Alternatively, this sensor can be located at the device end (opposite the patient end) of the delivery conduit 106 in either embodiment. In the breath-assist system shown in FIG. 6, a similar numbering system is used, including the ambient temperature sensor 260, the fan unit 213, and the chamber outlet port temperature sensor 263 located at the chamber outlet port 209.

[0037] In one embodiment, the breath assist system 1 (and 100, 200) includes a heater plate temperature sensor 62 located near the heater plate 12 and configured to measure the temperature of the heater plate. A breath assist system with a heater plate temperature sensor may be used as it provides an immediate indication of the heater plate's status. This sensor should be in the heat path between the heat source and the reservoir. To this end, for example, a sensor on a conductive plate that is in contact with the water chamber on one side and has a heater on the other side may be used.

[0038] In one embodiment, the system includes a flow sensor located upstream of the fan unit 13 and configured to measure gas flow. While the location of the flow sensor can be upstream of the fan unit, the flow sensor can be located downstream of the fan or anywhere else suitable. In some embodiments, the flow sensor can be located at the outlet 9, near the temperature sensor 63. While the flow sensor can form part of the system, it is not essential that the flow sensor be part of the system.

[0039] In one embodiment, the system may include a temperature sensor 63 located at the outlet 9 of the humidification chamber 5. In another embodiment, the temperature sensor 63 may be located at the inlet 23 of the humidification chamber 5. The temperature sensor 63 may also be configured to function as a flow sensor based on the polarity of the voltage applied to the temperature sensor 63 or the level of the voltage applied to the temperature sensor 63.

[0040] The layout and operation of breath assist system 1 will now be described in detail. The operation and layout of systems 100 and 200 are substantially identical and will not be described in detail except where necessary.

[0041] In the breath assist system 1, all sensor readings are fed back to a control system 8. The control system 8 also receives input from a user control 11.

[0042] Further Alternative Sensor Layouts In a variation of the apparatus and method described above, the system (System 1 or System 100 or System 200) also comprises further sensors as described below.

[0043] 3) The patient end temperature sensor 15 (or 115 or 215) is located at the patient end of the delivery conduit 6 (or alternatively, in or on the interface 7), i.e., at or proximate to the patient or delivery point. As interpreted herein, "patient end" or "user end" should be taken to mean either proximate to the user end of the delivery conduit (e.g., delivery conduit 6) or in or on the patient interface 7. This applies unless a specific location is specified. In either configuration, the patient end temperature sensor 15 can be considered to be at or proximate to the user or patient 2.

[0044] Determining the operating state According to some embodiments, the respiratory assistance system incorporates a routine configured to select an appropriate water-out detection method for determining whether the humidification chamber 5 requires additional water based on the system's operating state. The operating state relates to the system's therapy mode and gas flow rate selected by the user. This routine may be performed at any suitable time interval, as described in further detail below. In one embodiment, the routine is performed every 10 minutes, allowing the heater plate to cool appropriately if an active test has already been performed. However, in other embodiments, the routine may be performed every few seconds or milliseconds. The routine is illustrated in Figures 1a and 1b, which show another embodiment of the control of the system in a fourth operating state.

[0045] While the determination steps are described sequentially, the system may similarly perform the steps in a different order or simultaneously. As shown in step 1001, the controller 8 receives information regarding the treatment mode of the system. The controller 8 then proceeds to step 1002 and determines the flow rate of the system. The flow rate may be determined by a flow sensor located in the humidification chamber 5, specifically at either the inlet 23 or outlet port 9. Alternatively, the flow sensor may be located downstream of the fan unit 13 associated with the blower unit 3. The controller 8 uses the received treatment mode and flow rate information to determine the operating state of the system. Based on the system's operating mode and flow rate, the controller 8 selects an appropriate water outage detection method.

[0046] Cold start operation state In step 1003, controller 8 determines whether the system is in a cold start operating state. After startup, the system is determined to be in a cold start operating state until (i) the heater plate temperature exceeds a predetermined temperature threshold, (ii) a predetermined time threshold is met since system startup, (iii) the chamber outlet temperature exceeds a predetermined temperature threshold, and / or (iv) the patient end temperature exceeds a predetermined temperature threshold. The heater plate temperature, chamber outlet temperature, and patient end temperature may be determined by their respective temperature sensors, such as temperature sensors 62, 63, and 15. The predetermined temperature thresholds for the heater plate, chamber outlet, and patient end may be, for example, temperatures above 30 degrees Celsius, such as 35 degrees Celsius, 37 degrees Celsius, 40 degrees Celsius, 42 degrees Celsius, and / or another predetermined temperature that is sufficient for each component after system startup. Each predetermined temperature threshold for the heater plate, chamber outlet, and patient end may be defined separately. For example, in a preferred embodiment, the heater plate temperature threshold is 40 degrees Celsius, the chamber outlet temperature threshold is 37 degrees Celsius, and the patient end temperature threshold is 40 degrees Celsius. In some embodiments, the chamber outlet of the system includes a predetermined flow rate threshold and a temperature threshold. The flow rate threshold can be any non-zero flow rate, such as about or greater than 0.5 L / min, about or greater than 3 L / min, or another non-zero flow rate. For example, the chamber outlet temperature threshold can be 37 degrees Celsius and the flow rate threshold can be 3 L / min. The predetermined time threshold, measured from system startup, can be 2 minutes, 5 minutes, 10 minutes, 20 minutes, and / or any other predetermined time frame that provides sufficient time for the heater plate to heat up after system startup. The cold start operating condition is independent of the therapy mode or flow rate. In other embodiments, the cold start operating condition can depend at least in part on the flow rate.

[0047] If the controller 8 determines that the system meets the criteria for the cold start operating state, the controller 8 proceeds to the active water out detection method in step 1004. If the active water out detection method returns to the water out state, an alarm is activated with a setup error and / or water out alarm. If the controller 8 determines that the system does not meet the criteria for the cold start operating state, the controller 8 proceeds to step 1005. In some embodiments, the default operating state after system startup is the cold start operating state. The system remains in the cold start operating state until one of the criteria for exiting the cold start operating mode is met. For example, the system remains in the cold start operating mode until a time threshold is met or until one of the heater plate, chamber outlet, or patient inlet temperatures exceeds their respective temperature thresholds.

[0048] First operating state In step 1005, the controller 8 determines whether the system is in a first operating state. The system is determined to be in the first operating state (or "no flow" state) if the flow rate of any selected therapy mode is between 0 and 3 L / min. If the controller 8 determines that the system meets the criteria for the first operating state, the water out alarm is disabled in step 1006. False alarms may be common at low flow rates because the water level does not decrease as rapidly during this low flow state. The alarm can be disabled without major issues. Once the alarm is disabled, the controller 8 may return to step 1001. However, if the controller 8 determines that the system does not meet the criteria for the first operating state, the controller 8 proceeds to step 1007.

[0049] Second operating state In step 1007, the controller 8 determines whether the system is in a second operating state. The system is determined to be in a second operating state if the system is in either an invasive or Optiflow® treatment mode, and the flow rate is determined to be medium or high. The flow rate level is based on a threshold provided to the system.

[0050] If the controller 8 determines that the system meets the criteria for the second operating state, the controller 8 proceeds to the passive water out detection method in step 1008. If the passive water out detection method returns to the out of water state, an alarm is activated without performing the active water out detection method. However, if the controller 8 determines that the system does not meet the criteria for the second operating state, the controller 8 proceeds to the next step.

[0051] Third operating state In step 1009, the controller 8 determines whether the system is in a third operating state. The system is determined to be in the third operating state if the system is in either an invasive treatment mode or an Optiflow® treatment mode, and the flow rate is determined to be medium or low.

[0052] If the controller 8 determines that the system meets the criteria for a third operating state, the controller 8 proceeds to the passive water out detection method at step 1010. The passive water out detection method determines whether a water out condition exists at step 1011. If the passive water out detection method returns to a water out condition, the controller proceeds to the active water out detection method at step 1012. As described in more detail below, the active water out detection method is performed in conjunction with the passive water out detection method to reduce the likelihood of a false positive alarm in the low setpoint treatment mode. If the active water out detection method returns to a water out condition, an alarm is activated. However, if the active water out detection method does not return to a water out condition, the controller 8 ends the sequence and restarts the routine at an appropriate time interval.

[0053] Additionally, if the controller 8 determines that the system does not meet the third operating condition criterion, the controller 8 proceeds to the next step.

[0054] Fourth operating state In step 1013, the controller 8 determines whether the system is in a fourth operating state. The system is determined to be in the fourth operating state if the system is in a non-invasive treatment mode.

[0055] If the controller 8 determines that the system meets the criteria for a fourth operating state, the controller 8 proceeds to the passive water out detection method at step 1010. If the passive water out detection method returns to the water out state, the controller 8 proceeds to the active water out detection method at step 1012. If the active water out detection method returns to the water out state, an alarm is activated.

[0056] However, if the active water out detection method does not return to the water out state, or if the controller 8 determines that the system does not meet the criteria for the fourth operating state, the controller 8 terminates the sequence and restarts the routine at an appropriate time interval.

[0057] Referring now to FIG. 1b, another embodiment of the fourth operating state is shown. In FIG. 1b, if the controller 8 determines that the system meets the criteria for the fourth operating state, the controller 8 proceeds to a time-based active water outage detection method in step 1014. In step 1014, the controller 8 determines whether a predetermined time period has elapsed since the previous active water outage detection method was activated or since the system entered a non-invasive treatment mode. If the controller 8 determines that the predetermined time period has elapsed, the controller 8 proceeds to the active water outage detection method in step 1012. The predetermined time period may be any predetermined time interval, such as, for example, 15 minutes, 20 minutes, 30 minutes, 1 hour, etc. If the time period has not elapsed, the controller 8 may return to step 1001. In some embodiments, the controller 8 continues to perform the active water outage detection method at each predetermined time interval.

[0058] Step 1001 may represent the continuous receipt of information regarding the system's therapy mode due to system conditions. This continuous process is intended to ensure that the humidification chamber 5 contains enough water to maintain the delivered gas temperature and humidity at or near the desired levels. As a continuous process, the routine monitors for a possible water out-of-water condition. However, it should be noted that the routine need not continuously monitor for a possible water out-of-water condition. The routine may be performed at appropriate intervals depending on system requirements.

[0059] Alternative Routine Embodiments As described in more detail below, in some embodiments, the passive out-of-water detection method may be performed continuously because the detection method involves calculations based on sensor data collected during the course of normal operation, and therefore does not affect the operation of the humidifier.

[0060] 2, the initiation of the routine in step 2002 may be triggered based on a first out-of-water condition detected by a continuously running passive out-of-water detection method as shown in step 2001. The system may then initiate a routine to select an appropriate method that can accurately determine whether the humidification chamber 5 is empty based on the operating state of the system similar to the previous embodiment described above.

[0061] Water shortage detection method Various out-of-water detection methods that can be used to determine whether an out-of-water condition exists are described below. Each method is used under specific conditions, and the system routine selects the most appropriate out-of-water detection method based on the system's operating conditions, as described in more detail above. Once the appropriate out-of-water detection method is selected, the system determines the presence or absence of an out-of-water condition using one of the methods described below.

[0062] Passive water shortage detection method In accordance with the present disclosure, a passive water outage detection method determines whether a water outage condition exists. Referring to FIG. 2, in one embodiment, controller 8 continuously evaluates the heater plate power, heater plate temperature, and chamber outlet temperature functions during normal use of the device. The passive water outage detection method does not affect the operation of the humidifier and therefore runs continuously. The passive water outage detection method performs an estimated water level calculation based on sensor data collected during the normal course of operation.

[0063] The controller 8 determines a possible out-of-water condition when the result of the following function differs from a baseline threshold level: The function is the ratio of the chamber outlet temperature from sensor 63 (or 163 or 263) to the heater plate power as indicated by the heater plate duty cycle.

[0064] The passive water out detection method uses at least the heater plate power, heater plate temperature, and chamber outlet temperature to estimate the current water level. In some embodiments, no coefficients or weighting factors are used. The passive water out detection method estimates the water level according to the following formula:

[0065]

number

[0066] When the humidification chamber 5 is empty, the amount of power required to maintain the same chamber outlet temperature is reduced. This is useful for detecting an out-of-water condition. If the estimated water level falls below a pre-defined threshold for a period of time, an out-of-water alarm is triggered.

[0067] The threshold value is flow rate dependent and can be determined experimentally. With water in the chamber, the system is allowed to reach steady state for a flow rate within the operating range. The system is then tested at the same flow rate without water in the chamber. The result is two values: a water value and an out-of-water value. In some embodiments, the threshold value is set halfway between these two values. As the user selects a different treatment mode, the threshold value can be adjusted according to the specific settings of the selected treatment mode.

[0068] Since the estimated water level is based on heater plate power, which can vary due to pulsatile flow, controller stability, etc., some embodiments use a timer to wait for the estimated water level to remain below a threshold for a set period of time before activating an alarm. In one embodiment, this is set to 15 minutes at low flow rates and 10 minutes at higher flow rates. There is also a separate settling timer to prevent false triggers due to setpoint changes, flow rate changes, etc. In some embodiments, this is set to 20 minutes.

[0069] In some embodiments, if the humidification chamber 5 is refilled with water after an out-of-water condition alert, the alert will cease when the estimated water level rises above a threshold.

[0070] Active water shortage detection According to the present disclosure, an active method of detecting a water outage condition is performed in response to a passive method of detecting a water outage condition under certain circumstances. According to some embodiments, during the active method of detecting a water outage, the controller 8 controls the power input to the humidifier, adjusts the heater plate power input, and observes the temperature response of the heater plate 12. This active method of detecting a water outage is performed to confirm the water outage condition under certain circumstances when the passive method of detecting a water outage returns a possible water outage condition.

[0071] In some embodiments, passive water out detection methods may be used without active testing, although this may sacrifice some accuracy at low flow rates. In other embodiments, active testing may be used without passive testing, although this may further interfere with the delivery of therapy and the execution of other modules such as low temperature alarms.

[0072] In some embodiments, an active water out detection method may be used to confirm a water out condition because a passive water out detection method may erroneously determine a water out condition under certain operating conditions. These conditions include the third and fourth operating conditions, as described above. As described above, the likelihood of the passive water out detection method returning a false positive increases at low setpoints because the denominator of the estimated water level ratio becomes too close to zero. This occurs because the heater plate temperature also decreases, bringing the ranges of the two denominator values ​​closer. This occurs because both the heater plate temperature and the chamber outlet temperature are closer to ambient temperature. Therefore, the heater plate does not need to operate as hard to achieve the target chamber outlet temperature.

[0073] According to the present disclosure, after the passive water out detection method determines a water out condition, the controller 8 begins to implement the active water out detection method when the system is in the third or fourth operating state.

[0074] During an active test, the controller 8 controls the heater plate's feedback mode and duty cycle calculation according to the routine described below. As shown in Figure 3, the active water out detection method involves briefly pulsing a fixed power to the heater plate 12 and observing the increase in heater plate 12 temperature. When the humidification chamber 5 is empty, the heater plate's effective heat capacity is reduced and a higher maximum heater plate temperature is expected. Upon completion of the active water out detection method, the controller 8 transitions to step 3001 and control of the heater plate's feedback mode and duty cycle calculation then reverts to the standard heater plate control algorithm and PI controller.

[0075] As shown in FIG. 3, the controller 8 follows a routine to implement the following active water shortage detection method described below.

[0076] While the system is in the third or fourth operating state, it waits for a trigger resulting from the passive water out detection method to return to the water out state, as shown in step 3001. In this state, the heater plate control mode is standard, using chamber outlet feedback. If the system receives a water out state trigger, as shown in step 3002, the system will perform an active water out detection test and proceed to the next step.

[0077] In step 3003, the controller 8 controls the heater plate temperature to a baseline so that the starting conditions for the test are controlled. To achieve the baseline, the system is turned off, the power supplied is reduced, or a constant power is supplied to the heater plate 12 at a level low enough to achieve the desired baseline level. The heater plate temperature must then remain within 0.1°C for 15 seconds before the controller 8 moves to the next step.

[0078] In step 3004, the controller 8 adjusts the heater plate duty cycle to apply 150 W to the heater plate 12 for 10 seconds. The controller 8 then proceeds to the next step.

[0079] In step 3005, the controller 8 turns off the heater plate power and monitors the temperature of the heater plate 12 via the heater plate sensor for the maximum heater plate temperature. The temperature curve is monitored until the maximum temperature is reached.

[0080] In step 3006, the maximum heater plate temperature is determined by any suitable method. One way to determine the maximum temperature is by taking the first derivative of the temperature signal, where the derivative equals zero indicates the maximum temperature. Alternatively, the system can wait until there is a temperature drop and use the measurement just before the drop as the maximum temperature. Once the maximum heater plate temperature is reached, the system moves to the next step.

[0081] In step 3007, the system determines whether the maximum heater plate temperature exceeds a predetermined threshold. The threshold is set midway between the estimated heater plate temperature rise when the chamber is full and the estimated heater plate temperature rise when the chamber is empty. The formula for calculating the threshold is included below. Heater Plate Temperature Threshold = 0.5 * Estimated heater plate temperature when chamber is full + (1-0.5) * Estimated heater plate temperature when chamber is empty Estimated heater plate temperature when the chamber is full =5.377-0.052*Heater plate temperature baseline-0.017*Filtration flow rate Estimated heater plate temperature when the chamber is empty = 6.970 - 0.040 * heater plate temperature baseline - 0.017 * filtration flow rate

[0082] The thresholds may be adjusted for room temperature conditions and flow rate, among other parameters. In other embodiments, the system may automatically adjust the thresholds based on changes in other parameters. Alternatively, the system may have a preset number of stored thresholds for various environmental parameters.

[0083] If the maximum heater plate temperature or the measured temperature after 10 seconds does not exceed the threshold level, the controller 8 determines that the water is not out of water. The controller 8 proceeds to step 3001 and waits for the next request for an active water out detection test. In some embodiments, the controller 8 may do nothing before proceeding to step 3001. Alternatively, the controller 8 may send a message to the user indicating that there is enough water before returning to step 3001.

[0084] As soon as the maximum heater plate temperature or the measured temperature after 10 seconds exceeds the threshold level, the controller 8 activates an alarm in step 3008. The alarm may be a visual alarm, a message, an animation, or an audible alarm. After the alarm is activated, the controller 8 may proceed to step 3001 and wait for the next request for an active water shortage detection test.

[0085] An example of this monitoring function is shown in Figure 7. The graph shows data captured during a routine test to select an appropriate water-out detection method. Moving from left to right in time, the heater plate power (shown as HP Power) spikes during system startup and then settles to a steady state, as do the heater plate temperature, chamber outlet temperature, and filtered water level, referred to above as Estimated Water Level.

[0086] Stage 1 is reached when the water in the humidification chamber 5 is depleted. At this point, the base plate is dry, but the chamber outlet temperature sensor is still wet from condensation. The temperature sensor returns to a lower value even though the gas temperature has not decreased. This occurs because the wet temperature sensor measuring the dry gas introduces an error. The heater plate power increases, compensating for the decrease in temperature value. As a result, the heater plate temperature also increases, but faster than usual due to the lack of water on the base plate. The filtered water level begins to decrease due to this change in ratio.

[0087] Stage 2 is reached when the temperature sensor dries out and the error is no longer present. The heater plate power also decreases, but the heater plate temperature continues to rise because the air above the base plate does not absorb as much heat as the water does. This causes the filtered water level to drop even more rapidly as the heater plate power and heater plate temperature continue to increase.

[0088] The third stage is reached when the filtered water level drops below the water out threshold. In this example, the therapy mode is set to non-invasive or the flow rate is low to medium, which initiates the active water out detection method. Each spike in heater plate power indicates the execution of a test (i.e., the state machine moves to step 3004). After the third spike, water is replenished into the humidification chamber 5, significantly reducing the heater plate temperature. This, in turn, increases the heater plate power, heating the additional cold water.

[0089] System Treatment Mode In accordance with the present disclosure, the respiratory assistance system may be placed into one of several therapy modes. When controller 8 determines the appropriate water outage detection method, certain settings and thresholds may be altered depending on the selected therapy mode. In particular, certain gas flow rates for the system may be altered depending on the therapy mode.

[0090] In some embodiments, the treatment mode may be selected from one of either an invasive mode, a non-invasive mode, or an Optiflow® mode, which is used when the application requires a high flow rate through a non-sealing interface.

[0091] As noted, each treatment mode has a personalized setting. In some embodiments, the non-invasive mode may include settings of 31 degrees Celsius, 29 degrees Celsius, and 27 degrees Celsius. The Optiflow® mode may include settings of 37 degrees Celsius, 35 degrees Celsius, and 33 degrees Celsius. The invasive mode may include a setting of 37 degrees Celsius.

[0092] In some embodiments, the system may include a user interface configured to allow a user to select each treatment mode.

[0093] Gas flow rate In accordance with the present disclosure, a respiratory assistance system may also be configured to provide various gas flow rates, with the selected flow rate altering the system's determination of an appropriate water outage detection method, and in particular, the flow rate may alter the system's particular operating state.

[0094] In some embodiments, the flow rate may be selected from one of: no flow rate, low flow rate, medium flow rate, or high flow rate. As noted, each flow rate has a distinct classification range. In some embodiments, no flow rate may include flow rates between 0 L / min and 3.5 L / min. Low flow rate may include flow rates between 3 L / min and 7 L / min. Medium-low flow rate may include flow rates between 5 L / min and 15 L / min. Medium-high flow rate may include flow rates between 13 L / min and 35 L / min. High flow rate may include flow rates above 30 L / min.

[0095] The ranges for each flow rate category can overlap with other categories. To move from one flow rate category to the next, the flow rate must exceed the category's upper limit or fall below the category's lower limit. For example, if the current flow rate is in the low flow rate category, the flow rate must exceed 7 L / min to move to the medium-low category. Similarly, once in the medium-low category, the flow rate must drop below 5 L / min to return to the low category. Overlapping ranges can be useful to avoid constantly switching categories for flow rates that fluctuate near thresholds.

[0096] Design considerations Baseline temperature Because the heater plate temperature increase depends on the baseline temperature, the test range for the threshold design should include the lowest and highest expected heater plate temperatures within the intended operating range. To minimize the impact on passive alarms and therapy delivery, the baseline temperature should be close to the heater plate operating temperature. If enthalpy is a concern, the baseline temperature should be lower than the heater plate operating temperature, although this may increase the test cycle time.

[0097] flow rate The same analysis as described for baseline temperature applies to flow rate. The test range should include the expected operating range.

[0098] Open Loop Duty Cycle An open loop duty cycle is applied which gives a nice square pulse of power and is not influenced by the controller 8. The duty cycle is based on the power supply voltage measured by the PMIC, the measured heater plate resistance, and the desired power.

[0099] Applied power In some embodiments, 150 W is chosen because the heater plate can still provide 150 W if the power supply voltage drops by 10% (assuming a nominal heater plate power of 200 W). If the power supply were higher, the heater plate might not be able to provide the same power when connected to a lower power supply voltage. If the power supply were lower, the heater plate might experience a reduced temperature rise, potentially increasing the likelihood of false alarms.

[0100] Power application time In some embodiments, 10 seconds is chosen to reduce the impact of timing jitter while minimizing the possibility of generating excessive humidity. (Note: If the timer implementation changes and affects the duration of the pulse, the threshold value will need to be re-determined.)

[0101] Detection Criteria The maximum heater plate temperature is used as the sensing metric due to its consistency, good signal-to-noise ratio between the dry and wet chambers, low computational complexity, and short test cycle time.

[0102] Minimum time for step 3005 Due to the delay between the application of power and the heater plate temperature response, the controller 8 stays in step 3005 long enough to allow the heater plate temperature to increase before terminating if the temperature falls below the maximum temperature.

[0103] Possible interruption Because the test takes a non-negligible amount of time to complete, external events may affect the results. Possible events include water refills, changes in flow rate or pattern, changes in therapy mode, setpoint changes (by user or humidity compensation), inspiratory circuit or sensor cartridge disconnection, and power on or off.

[0104] In the case of water replenishment, the heater plate temperature will drop, however this is appropriate as the drop in temperature indicates the presence of water.

[0105] Interaction with low temperature alarms The active water out detection method interrupts normal heating and therefore affects heater plate and chamber outlet temperatures. Routine attempts to minimize this effect by setting the baseline temperature close to the current heater plate operating temperature. The active water out detection method is expected to complete well within 10 minutes, so the low temperature alarm (which can take 10-60 minutes to trigger depending on treatment and setpoint) should not trigger a false alarm.

[0106] Timeout and return to default state If the system fails to meet the conditions for the state transition, a timeout occurs and the state returns to step 3001. In one embodiment of the device, the timeout value may be: Step 3003 timeout = 15 minutes Step 3004 timeout = 15 seconds Step 3005 timeout = 5 minutes

[0107] Not enough energy is supplied Due to timing or a lower-than-expected power supply voltage, the system may not deliver the required power over time. Power measurements made by the PMIC are recorded to evaluate the energy pulses delivered during the active test phase. In some embodiments, if too little or too much power is delivered, the system retries three times. If all retries fail, the system stops the active water out detection method (because the active water out detection method affects the passive water out detection method) and reverts to the passive water out detection method.

[0108] Test duration To reduce disruption to normal therapy, test duration is minimized by allowing the active water out detection method to begin at different baseline heater plate temperatures.

[0109] Examples of respiratory humidification systems and related components and methods have been described with reference to the figures. The figures illustrate various systems and modules and the connections between them. The various modules and systems can be combined in various configurations, and the connections between the various modules and systems may represent physical or logical links. The representations in the figures, intended to clearly illustrate the principles and details of module or system division, are provided for ease of explanation rather than attempting to detail separate physical embodiments. The examples and illustrations are for illustrative purposes and do not limit the scope of the inventions described herein. For example, the principles herein may be applied to respiratory humidifiers as well as other types of humidification systems, including surgical humidifiers. The principles herein may be applied to respiratory applications as well as other situations in which water is determined to be available in a respiratory system.

[0110] As used herein, the term "processor" broadly refers to any suitable device, logic block, module, circuit, or combination of elements for executing instructions. For example, controller 8 may include any conventional general-purpose single-chip or multi-chip microprocessor, such as a Pentium® processor, a MIPS® processor, a Power PC® processor, an AMD® processor, an ARM® processor, or an ALPHA® processor. In addition, controller 122 may include any conventional special-purpose microprocessor, such as a digital signal processor or a microcontroller. The various exemplary logic blocks, modules, and circuits described in conjunction with the embodiments disclosed herein may be implemented or performed by 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, or may be pure software within a main processor. For example, logic module 504 may be a functional block implemented in software without any additional and / or specialized hardware elements. The controller 8 may be implemented as a combination of computing devices, for example, a combination of a DSP and a microprocessor, a combination of a microcontroller and a microprocessor, multiple microprocessors, one or more microprocessors in combination with a DSP core, or any other such configuration.

[0111] Data storage may refer to electronic circuitry that stores data and enables retrieval by a processor. Data storage may refer to external devices or systems, such as disk drives or solid-state drives. Data storage may also refer to high-speed semiconductor storage (chips) connected to a communication bus or directly to the controller 8, such as random access memory (RAM) or various forms of read-only memory (ROM). Other types of data storage include bubble memory and core memory. Data storage may be physical hardware configured to store data on a non-transitory medium.

[0112] Although specific embodiments and examples have been disclosed herein, the subject matter extends to other alternative embodiments and / or uses other than those specifically disclosed, as well as modifications and equivalents thereof. Accordingly, the scope of the claims or the embodiments appended hereto is not limited by any of the specific embodiments described herein. For example, in any method or process disclosed herein, the acts or operations of the method or process may be performed in any suitable order and are not necessarily limited to any particular order disclosed. Various operations may be described sequentially as multiple separate operations to aid in understanding particular embodiments, but the order of description should not be construed to imply that these operations are order dependent. In addition, structures described herein may be embodied as integrated or separate components. For purposes of comparing various embodiments, certain aspects and advantages of these embodiments are described. Not necessarily all such aspects or advantages are achieved by any particular embodiment. Thus, for example, various embodiments may be implemented to achieve or optimize one advantage or group of advantages as taught herein, without necessarily achieving other aspects or advantages that may also be taught or suggested herein.

[0113] As used herein, conditional language, particularly "can," "could," "might," "may," "eg," and the like, unless expressly stated otherwise or understood within the context in which it is used, is generally intended to convey that certain embodiments include certain features, elements, and / or conditions, while other embodiments do not. Thus, such conditional language is not generally intended to imply that features, elements, and / or conditions are more or less required for one or more embodiments. As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having," or any other variation thereof, are intended to include a non-exclusive inclusion. For example, a process, method, article, or apparatus that includes a list of elements is not necessarily limited to only those elements and may include other elements not specifically listed or inherent in such process, method, article, or apparatus. Also, the term "or" is used in its inclusive sense (rather than its exclusive sense), so that, for example, when used to connect a list of elements, the term "or" means one, some, or all of the elements in the list. Connective language such as the phrase "at least one of X, Y, and Z" is generally understood by context to be used to convey that an article, term, etc. can be either X, Y, or Z, unless expressly stated otherwise. Thus, such connective language does not generally imply that a particular embodiment requires that at least one X, at least one Y, and at least one Z are present, respectively. As used herein, the words "about" or "approximately" can mean that a value is within ±10%, ±5%, or ±1% of the stated value.

[0114] The methods and processes described herein may be embodied in software code modules executed by one or more general-purpose and / or special-purpose computers, and may thereby be partially or fully automated. The term "module" refers to logic embodied in hardware and / or firmware, or a collection of software instructions, possibly having entry and exit points, written in a programming language such as C or C++. A software module may be compiled and linked into an executable program, installed in a dynamically linked library, or written in an interpreted programming language such as BASIC, Perl, or Python. It will be understood that a software module may be callable by other modules or itself and / or may be invoked in response to a detected event or interrupt. Software instructions may be embodied in firmware, such as an erasable programmable read-only memory (EPROM). It will be further understood that software instructions may include connected logic units, such as gates and flip-flops, and / or may include programmable units, such as programmable gate arrays, application-specific integrated circuits, and / or processors. The modules described herein may be implemented as software modules, but may also be manifested in hardware and / or firmware. Furthermore, while in some embodiments a module may be separately compiled, in other embodiments a module may represent a subset of instructions of a separately compiled program and may not have an interface available to other logical program units.

[0115] In particular embodiments, code modules may be embodied in and / or stored on any type of computer-readable medium or other computer storage device. In some systems, data (and / or metadata) input to, generated by, and / or used by the system may be stored in any type of computer data repository, such as a relational database and / or a flat file system. Any of the systems, methods, and processes described herein may include interfaces configured to enable interaction with users, operators, other systems, components, programs, etc.

[0116] It should be emphasized that many variations and modifications may be made to the embodiments described herein, and that the elements are understood to be within the permissible examples. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims. Moreover, nothing in the foregoing disclosure implies that any particular component, feature, or process step is required or essential.

Claims

1. 1. A method for determining a water outage condition in a respiratory assistance system, the method comprising: operating the respiratory assistance system in a selected therapy mode; receiving data related to the operation of the selected treatment mode; receiving flow data; determining an operating state of the system based on at least one of: a heater temperature; a humidification chamber outlet temperature; the selected treatment mode; and a gas flow rate; selecting a water shortage detection method from a plurality of water shortage detection methods based on the determined operating state of the system, the water shortage detection method being one of a passive water shortage detection method and an active water shortage detection method; operating the respiratory assistance system with the selected water outage detection method; A method comprising:

2. the operating state of the system is based on the selected treatment mode and gas flow rate; 10. A method for determining a water outage condition in a respiratory assistance system according to claim 1.

3. the operating state is based on a temperature setpoint and a gas flow rate, the temperature setpoint being based on the selected treatment mode; 10. A method for determining a water outage condition in a respiratory assistance system according to claim 1.

4. determining the operating state includes a predetermined relationship between a treatment mode and a gas flow rate; 10. A method for determining a water outage condition in a respiratory assistance system according to claim 1.

5. detecting a flow rate of the gas with a flow sensor; receiving data related to the selected treatment mode from a user interface; associating the temperature setpoint with a temperature sensor located in a humidification chamber, a conduit, or both the humidification chamber and the conduit; Including, A method for determining a water-out condition of a respiratory assistance system according to any one of claims 1 to 4.

6. The selected treatment mode is: Invasive mode and A non-invasive mode, High flow non-sealed mode and selected from a predetermined list containing the high-flow non-sealing mode includes a high flow rate through the non-sealing interface; A method for determining a water-out condition of a respiratory assistance system according to any one of claims 1 to 5.

7. The method of claim 6 , wherein the selected treatment mode includes a plurality of settings.

8. the non-invasive mode includes settings of 31 degrees Celsius, 29 degrees Celsius, and 27 degrees Celsius; the high flow non-sealed mode includes setpoints of 37 degrees Celsius, 35 degrees Celsius, and 33 degrees Celsius; the invasive mode includes a set point of 37 degrees Celsius; 8. The method for determining a water outage condition according to claim 7.

9. The operating state is a start-up operating condition associated with the temperature of the heater being below a predetermined heater temperature threshold or the temperature at the outlet of the humidification chamber being below a predetermined outlet temperature threshold; a first operating state associated with no or low flow; a second operating state associated with a therapy mode having a high set point and a high flow rate; a third operating state associated with a therapy mode having a low setting; a fourth operating state associated with a therapy mode having a high setting and a low or medium flow rate; A method for determining a water-out state according to any one of claims 1 to 8.

10. 10. The method of claim 9, wherein the high set point comprises a temperature above 31 degrees Celsius and the low set point comprises a temperature between 25 degrees Celsius and 31 degrees Celsius.

11. 11. The method of claim 9 or 10, wherein the predetermined temperature threshold of the heater is greater than or equal to 30 degrees Celsius.

12. A method for determining an out-of-water condition according to any one of claims 9 to 11, wherein the predetermined temperature threshold at the outlet of the humidification chamber is greater than or equal to 30 degrees Celsius.

13. The no flow rate has a flow rate of 0 L / min to 3.5 L / min, the low flow rate has a flow rate of 3 liters / min to 7 liters / min; The medium flow rate has a flow rate of 5 L / min to 15 L / min, The high flow rate has a flow rate of 13 l / min to 35 l / min. A method for determining a water-out state according to any one of claims 9 to 12.

14. A method for determining an out-of-water condition according to any one of claims 9 to 13, wherein the passive out-of-water detection method is performed at predetermined intervals to constantly check for an out-of-water condition.

15. The passive water shortage detection method includes: Calculating the water level; comparing the water level to a threshold; determining a water-out condition if the calculated water level is less than the threshold; Including, A method for determining a water-out state according to any one of claims 1 to 14.

16. 16. The method of determining a water outage condition of claim 15, wherein calculating the water level comprises dividing a ratio of an amount of power supplied to the heater by the difference between the temperature of the heater minus the temperature of the humidified gas.

17. 17. The method of claim 16, wherein the amount of power supplied to the heater is determined by a heater plate power sensor and / or decreases as the humidification chamber dries out.

18. The active water shortage detection method includes: controlling the temperature of the heater relative to a baseline; supplying an amount of power to the heater until a target is achieved; monitoring the heater temperature of the heater until a maximum temperature is reached; comparing the maximum heater temperature to a threshold value; determining a positive test result if the heater maximum temperature exceeds the threshold; Including, A method for determining a water-out state according to any one of claims 1 to 17.

19. The treatment mode is associated with a mode value and / or is selected by a user. A method for determining a water-out state according to any one of claims 1 to 18.

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