Method of detecting connection errors in humidification system

Abstract

To provide humidification systems that can detect or automatically detect incorrect connections and alert a user.SOLUTION: A method of detecting a reverse flow in a respiratory humidification system including a gas source, a humidifier including an inlet and an outlet, and an inspiratory conduit comprises the steps of: performing one or more reverse flow detection tests; and outputting an indication when a reverse-flow condition is detected. The step of performing the one or more reverse flow detection tests comprises using a directional flow sensor to directly detect a reverse flow at or near the inlet or outlet of the humidifier.SELECTED DRAWING: Figure 5B

Description

[Technical field]

[0001] This application relates to respiratory humidification systems. In particular, this application relates to detecting errors in connections between components in a humidification system. This application claims priority to U.S. Provisional Patent Application No. 62 / 406,720, filed October 11, 2016, the entire contents of which are incorporated herein by reference. [Background technology]

[0002] A number of methods can be used to provide humidified gas to a patient requiring respiratory assistance. Such humidification systems typically include a source of pressurized gas (or other gas mixture) such as a ventilator, a humidifier including a water source and heating means for vaporizing the water to humidify the gas from the gas source, and a respiratory conduit for conveying the humidified gas to a patient interface, e.g., a mask, nasal cannula, etc. The humidification system can be single or dual limb. In a single limb system, exhaled gas from the patient can be vented to the surrounding air through a vent in the patient interface. In a dual limb system, exhaled gas can be returned from the patient to the gas source through an expiratory conduit.

[0003] For a humidification system to function properly, it is essential that gas flows in the correct or normal direction from the gas source through the humidifier to the patient and that the components of the humidification system are connected correctly. The correct or normal direction may be a forward flow direction. Correct connections and normal flow direction ensure that gas is delivered to the patient at the desired humidity and the desired patient end temperature. Connection errors in a humidification system may occur between various components, such as between two or more of the patient interface, the humidifier, and / or the gas source. Connection errors in a humidification system may be due to setup errors. A caregiver may mistakenly couple conduits having the same type of corresponding end connectors, such as 22 mm male and female medical taper connectors or other standard connectors. A caregiver may reverse connect the humidifier and the gas source. A proprietary connector, such as at the humidifier outlet, may help ameliorate this problem, but it may be complicated to manufacture, increase costs, and / or be confusing to the caregiver or user. Additionally, some connectors may be standardized connectors required by regulation and / or commercial necessity, which may not be conveniently changed to proprietary connectors. Other components of the humidification system may also be misconnected to one another.

[0004] A connection error can cause a backflow condition. A backflow condition can be a condition in which gas flows in the wrong or reverse direction compared to a desired direction, such as a forward flow direction. Misconnection of components can result in gas being delivered to the patient at a higher or lower humidity and / or temperature than desired, which can lead to unsatisfactory treatment, discomfort, and / or adverse reactions in the patient. For example, dry air can be delivered directly from the gas source to the patient, while humidified gas can be delivered to the gas source. In such a case of misconnection, air exhaled from the patient is delivered to the humidifier. A backflow condition can also cause damage by providing moisture to the gas source (e.g., a ventilator or other gas source). Moisture provided to the gas source can cause a pathway that can damage the gas source.

[0005] A backflow condition may indicate a misconnection or incorrect setup by a clinician or nurse. Current humidification systems are unable to directly detect a backflow condition. This may be due to the use of an omnidirectional flow sensor that cannot directly detect the direction of flow and / or humidification systems that do not have an indirect backflow detection method. For example, other types of sensors on current humidification systems, such as humidity sensors and / or infrared temperature sensors, are not configured to detect a backflow condition or a misconnection.

[0006] Some humidification systems can detect whether the patient is exhaling through the inhalation conduit by detecting a higher temperature at the humidifier inlet than the gas source, or by comparing flow rate and / or power loss curves at the humidifier inlet and outlet. These detection features can help identify whether the system is single-limb or dual-limb. However, these detection features are different from the misconnection detection described in this disclosure. Such systems are described in U.S. Provisional Patent Application No. 62 / 280,076, filed January 18, 2016, entitled "HUMIDIFICATION OF RESPIRATORY GASES," and U.S. Provisional Patent Application No. 62 / 362,709, filed July 15, 2016, entitled "HUMIDIFICATION OF RESPIRATORY GASES," each of which is incorporated herein by reference in its entirety.

[0007] Some humidification systems can detect heating or flow anomalies in the system that may be caused by a backflow condition or other type of system malfunction. Anomalies can include when the humidifier inlet temperature exceeds the humidifier outlet temperature by a predetermined threshold. Such a system is described in U.S. Patent Application Serial No. 15 / 021,616, filed March 11, 2016, entitled “HUMIDIFICATION SYSTEM,” which is incorporated herein by reference in its entirety.

[0008] Some humidification systems can minimize component connection errors by having unique end connectors for dedicated tubing and conduits. For example, the intake conduit can have a unique end connector that can only be connected to the outlet of the humidifier. However, these humidification systems cannot detect a backflow condition. Summary of the Invention [Means for solving the problem]

[0009] The disclosed humidification system can detect or automatically detect and alert the user to a misconnection. The system can detect errors in the connections between components in the system, such as the patient interface, the humidifier, and / or the gas source. The disclosed humidification system can detect the presence of a backflow condition / situation resulting in the patient receiving suboptimal humidity and / or temperature. The methods disclosed herein can detect whether gas is flowing in the wrong direction. The wrong direction can be a reverse flow direction. A backflow condition detected by the methods described herein is likely to indicate an error in the connections between the humidifier, the patient interface, and / or the gas source. The disclosure also relates to detecting a misconnection of the expiratory conduit of a dual limb system, such as a system for providing invasive mechanical ventilation, non-invasive mechanical ventilation, neonatal invasive or non-invasive therapy, and / or other therapy. A misconnection can include improper connection and / or disconnection of the expiratory conduit, which can also cause improper connection and / or disconnection of the heat source of the expiratory conduit. Detection of a misconnection of the expiratory conduit may include an alert to the user.

[0010] A method of detecting a misconnection in a respiratory humidification system including a gas source, a humidifier including an inlet and an outlet, and an inhalation conduit may include performing one or more backflow detection tests by comparing an inlet temperature measured by a sensor at the inlet of the humidifier to one or more of an outlet setpoint or an outlet temperature measurement measured by a sensor positioned at the outlet of the humidifier. The method may include outputting an indication of a backflow condition indicative of a misconnection if the inlet temperature is higher than one or more of the outlet setpoint or the outlet temperature measurements. The method may include alerting a user of the indication of the backflow condition. The alerting may include providing one or more audible alarms, text messages, images, or combinations thereof. The alerting may also include providing instructions to eliminate the backflow condition. The humidification system may also include an exhalation conduit.

[0011] The respiratory humidification system with misconnection detection can include a gas source configured to provide a source of gas, a humidifier including an inlet and an outlet, the humidifier configured to humidify air, the humidifier including a humidifier heat source for heating a liquid for humidifying the gas provided by the gas source, and an inhalation conduit configured to provide the humidified gas to a user. The gas source, the humidifier, and the inhalation conduit can form at least a portion of a breathing circuit. The system can include sensors at the humidifier inlet and outlet configured to measure inlet and outlet temperatures, respectively, and a hardware and / or software controller. The hardware and / or software controller can be in electrical communication with the sensor and configured to output an indication of a backflow condition indicative of a misconnection when the inlet temperature is higher than one or more of the outlet setpoint or the outlet temperature. The hardware and / or software controller can be configured to alert the user of the indication of the backflow condition. The alerting can include providing one or more audible alarms, text messages, images, or combinations thereof. The alerting can also include providing instructions to resolve the backflow condition. The humidification system may also include an exhalation conduit.

[0012] A method of detecting a misconnection in a respiratory humidification system including a gas source, a humidifier including an inlet and an outlet, and an inhalation conduit may include performing one or more backflow detection tests by comparing an inlet parameter measured by a first sensor at the inlet of the humidifier with an outlet parameter measured by a second sensor at the outlet of the humidifier. The method may include outputting an indication of a backflow condition if the inlet parameter is higher than the outlet parameter. The parameters may include a flow rate or a power loss value. The method may include alerting a user of the indication of the backflow condition. The alerting may include providing one or more audible alarms, text messages, images, or combinations thereof. The alerting may also include providing instructions to resolve the backflow condition.

[0013] The humidification system with the misconnection detection mechanism may include a gas source configured to provide a source of gas, a humidifier including an inlet and an outlet configured to humidify air, the humidifier including a humidifier heat source, such as a heater plate, for heating a liquid for humidifying the gas provided by the gas source, and an inhalation conduit configured to provide the humidified gas to a user. The gas source, the humidifier, and the inhalation conduit may form at least a portion of a breathing circuit. The system may include sensors at the humidifier inlet and outlet configured to measure inlet and outlet parameters, respectively, and a hardware and / or software controller in electrical communication with the sensors. The hardware and / or software controller may be configured to output an indication of a reflux condition when the inlet parameter is higher than the outlet parameter. The parameters may include a flow rate or a power loss value. The hardware and / or software controller may be configured to alert the user of the indication of the reflux condition. Alerting may include providing one or more audible alarms, text messages, images, or combinations thereof. Alerting may also include providing instructions to resolve the reflux condition. The humidification system may also include an exhalation conduit.

[0014] A method of detecting a misconnection in a respiratory humidification system may include performing one or more backflow detection tests by a hardware and / or software controller of the humidification system. The one or more backflow detection tests may include comparing a patient end temperature measured by a first sensor at a patient end of an inlet conduit of the humidification system to a patient end setpoint, comparing an inlet temperature measured by a second sensor at an inlet of a humidifier of the humidification system to an outlet setpoint or an outlet temperature measured by a third sensor at an outlet of the humidifier if the patient end temperature is higher than the patient end setpoint, and outputting an indication of a backflow condition indicative of a misconnection if the inlet temperature is higher than the outlet setpoint or the outlet temperature. The method may include comparing the inlet temperature to an ambient temperature if the inlet temperature is higher than the outlet setpoint or the outlet temperature, and outputting an indication of a backflow condition if the inlet temperature is higher than the ambient temperature. The method may include alerting a user of the indication of the backflow condition. The alerting may include providing one or more audible alarms, text messages, images, or combinations thereof. The step of alerting may also include the step of providing instructions to resolve the reflux condition.The humidification system may also include an exhalation conduit.

[0015] A humidification system with a misconnection detection mechanism can include a gas source configured to provide a source of gas, a humidifier including an inlet and an outlet, the humidifier configured to humidify air and including a humidifier heat source for heating a liquid for humidifying the gas provided by the gas source, and an inhalation conduit configured to provide humidified gas to a user. The gas source, humidifier, and inhalation conduit can form at least a portion of a breathing circuit. The system can include a first sensor at a patient end of the inhalation conduit configured to measure a patient-end temperature, a second sensor at the humidifier inlet configured to measure an inlet temperature, and a third sensor at the humidifier outlet configured to measure an outlet temperature. The system can include a hardware and / or software controller in electrical communication with the first, second, and third sensors. The hardware and / or software controller can be configured to detect an indication of a backflow condition indicative of a misconnection in the humidification system by comparing the inlet temperature to an outlet setpoint or outlet temperature when the patient-end temperature is higher than a patient-end setpoint, and outputting an indication of a backflow condition when the inlet temperature is higher than the outlet setpoint or outlet temperature. The hardware and / or software controller can be configured to compare the inlet temperature to an ambient temperature when the inlet temperature is higher than an outlet setpoint or outlet temperature, and output an indication of a reflux condition when the inlet temperature is higher than the ambient temperature. The hardware and / or software controller can be configured to alert a user of the indication of the reflux condition. Alerting can include providing one or more audible alarms, text messages, images, or combinations thereof. Alerting can also include providing instructions to resolve the reflux condition. The humidification system can also include an expiratory conduit.

[0016] A method of detecting a misconnection in a respiratory humidification system may include performing one or more backflow detection tests with a hardware and / or software controller of the humidification system. The one or more backflow detection tests may include comparing a patient-end temperature measured by a first sensor at a patient-end of an inhalation conduit of the humidification system to a patient-end setpoint, comparing an outlet temperature measured by a second sensor at an outlet of a humidifier of the humidification system to a patient-end temperature if the patient-end temperature is lower than the patient-end setpoint, and outputting an indication of a backflow condition if the outlet temperature is higher than the patient-end temperature. The method may include alerting a user of the indication of the backflow condition. The alerting may include providing one or more audible alarms, text messages, images, or combinations thereof. The alerting may also include providing instructions to resolve the backflow condition. The humidification system may also include an expiratory conduit.

[0017] A humidification system with a misconnection detection mechanism may include a gas source configured to provide a source of gas, a humidifier including an inlet and an outlet configured to humidify air, the humidifier including a humidifier heat source for heating a liquid for humidifying the gas provided by the gas source, and an inhalation conduit configured to provide the humidified gas to a user. The gas source, the humidifier, and the inhalation conduit may form at least a portion of a breathing circuit. The system may include a first sensor at a patient end of the inhalation conduit configured to measure a patient-end temperature, and a second sensor at the humidifier outlet configured to measure an outlet temperature. The system may include a hardware and / or software controller in electrical communication with the first and second sensors. The hardware and / or software controller may be configured to detect an indication of a backflow condition indicative of a misconnection in the humidification system by comparing the outlet temperature to the patient-end temperature when the patient-end temperature is lower than a patient-end setpoint, and outputting an indication of a backflow condition when the outlet temperature is higher than the patient-end temperature. The hardware and / or software controller may be configured to alert a user of the indication of the backflow condition. The alerting may include providing one or more audible alarms, text messages, images, or combinations thereof. The alerting may also include providing instructions for resolving the reflux condition. The humidification system may also include an exhalation conduit.

[0018] A method of detecting a misconnection in a respiratory humidification system may include providing a first power to a humidifier heat source in a humidifier of the humidification system, comparing an inlet temperature measured by a first sensor at an inlet of the humidifier of the humidification system to an outlet temperature measured by a second sensor at an outlet of the humidifier, or comparing a change in the inlet temperature to a change in the outlet temperature, and outputting an indication of a backflow condition indicative of a misconnection if the inlet temperature is higher than the outlet temperature, or if the change in the inlet temperature is greater than the change in the outlet temperature. The method may include interrupting a therapy performed in the humidification system. The therapy may include a respiratory / ventilation therapy and / or a humidification therapy. The first power may be a maximum power. The method may include alerting a user of the indication of the backflow condition. The alerting may include providing one or more audible alarms, text messages, images, or combinations thereof. The alerting may also include providing instructions to resolve the backflow condition. The humidification system may also include an expiratory conduit.

[0019] A humidification system with a misconnection detection mechanism may include a gas source configured to provide a source of gas, a humidifier including an inlet and an outlet, the humidifier configured to humidify air and including a humidifier heat source for heating a liquid to humidify the gas provided by the gas source, and an inhalation conduit configured to provide humidified gas to a user. The gas source, humidifier, and inhalation conduit may form at least a portion of a breathing circuit. The system may include a first sensor at the humidifier inlet configured to measure an inlet temperature, a second sensor at the humidifier outlet configured to measure an outlet temperature, and a hardware and / or software controller in electrical communication with the first and second sensors. The hardware and / or software controller may be configured to detect an indication of a reflux condition in the humidification system by providing a first power to the humidifier heat source and outputting an indication of a reflux condition when the inlet temperature is higher than the outlet temperature or when a change in the inlet temperature is greater than a change in the outlet temperature. The hardware and / or software controller may be configured to interrupt a therapy delivered by the humidification system upon detecting an indication of a reflux condition in the humidification system. The therapy can be a respiratory or ventilation therapy and / or a humidification therapy. The first power can be a maximum power. The hardware and / or software controller can be configured to alert a user of the indication of a reflux condition. The alerting can include providing one or more audible alarms, text messages, images, or combinations thereof. The alerting can also include providing instructions to resolve the reflux condition. The humidification system can also include an expiratory conduit.

[0020] A method of detecting a misconnection in a respiratory humidification system may include providing a first power to an inlet conduit heat source in an inlet conduit of the humidification system, comparing a patient end temperature measured by a first sensor at a patient end of the inlet conduit to an outlet temperature measured by a second sensor at an outlet of a humidifier of the humidification system or comparing a change in the patient end temperature to a change in the outlet temperature, and outputting an indication of a reflux condition if the patient end temperature is lower than the outlet temperature or if the change in the patient end temperature is less than the change in the outlet temperature. The method may include interrupting a therapy performed in the humidification system. The therapy may be a respiratory or ventilation therapy and / or a humidification therapy. The first power may be a maximum power. The method may include alerting a user of the indication of the reflux condition. The alerting may include providing one or more audible alarms, text messages, images, or combinations thereof. The alerting may also include providing instructions to resolve the reflux condition. The humidification system may also include an expiratory conduit.

[0021] A humidification system with a misconnection detection mechanism can include a gas source configured to provide a source of gas, a humidifier including an inlet and an outlet configured to humidify air, the humidifier including a humidifier heat source for heating a liquid to humidify the gas provided by the gas source, and an inhalation conduit configured to provide humidified gas to a user. The gas source, humidifier, and inhalation conduit can form at least a portion of a breathing circuit. The system can include a first sensor at a patient end of the inhalation conduit configured to measure a patient-end temperature, a second sensor at the humidifier outlet configured to measure an outlet temperature, and a hardware and / or software controller in electrical communication with the first and second sensors. The hardware and / or software controller can be configured to detect an indication of a reflux condition in the humidification system by providing a first power to the inhalation conduit heat source and outputting an indication of a reflux condition when the patient-end temperature is lower than the outlet temperature or when a change in the patient-end temperature is less than a change in the outlet temperature. The hardware and / or software controller can be configured to interrupt a therapy performed in the humidification system upon detecting an indication of a reflux condition in the humidification system. The therapy can be a respiratory or ventilation therapy and / or a humidification therapy. The first power can be a maximum power. The hardware and / or software controller can be configured to alert a user of the indication of the reflux condition. The alerting can include providing one or more audible alarms, text messages, images, or combinations thereof. The alerting can also include providing instructions to resolve the reflux condition. The humidification system can also include an expiratory conduit.

[0022] A method of detecting backflow in a respiratory humidification system may include using one or more hardware processors of the humidification system to control circuitry configured to power a heating element, providing power to a heating element of the humidification system, the heating system further comprising a gas source, a humidifier including an inlet and an outlet, and an inlet conduit including an inlet conduit heat source, the humidifier further comprising a humidifier heat source, comparing a first temperature gradient measured by a first sensor downstream of the heating element to a second temperature gradient measured by a second sensor upstream of the heating element, the first and second sensors being in electrical communication with the one or more hardware processors, and outputting an indication of a backflow condition on a display of the humidification system if the second temperature gradient is higher than the first temperature gradient. The display may include a screen, such as an LED screen or any other type of screen, an audible arm, and / or any other type of warning method described herein. The method further includes providing separate power to a humidifier heat source of a humidifier of the humidification system, receiving sensor data from a humidifier heat source temperature sensor at or near the humidifier heat source, the humidifier heat source temperature sensor being in electrical communication with one or more hardware processors, comparing a temperature gradient of the humidifier heat source to a threshold temperature gradient, and outputting an indication of a humidifier out-of-water condition on a display of the humidification system if the temperature gradient of the humidifier heat source is higher than the threshold temperature gradient. The threshold temperature gradient may vary based at least in part on the flow rate, the type of humidifier, any other system parameters, and / or any other ambient conditions. The method may be performed from a start-up state.

[0023] The respiratory humidification system with backflow detection from start-up condition includes a gas source configured to provide a source of gas, a humidifier including an inlet and an outlet, the humidifier configured to humidify air, the humidifier further including a humidifier heat source for heating a liquid for humidifying the gas provided by the gas source, an inlet conduit configured to provide humidified gas to a user, the inlet conduit including an inlet conduit heat source, the gas source, the humidifier, and the respiratory conduit forming at least a portion of a respiratory circuit, and a first temperature sensor downstream of the humidification heat source and / or the inlet conduit heat source configured to measure a first temperature. The humidification system may include a first sensor, a second sensor upstream of the humidifier heat source and / or the inlet conduit heat source configured to measure a second temperature, and a hardware and / or software controller configured to detect an indication of a reflux condition in the humidification system by: providing power to the humidifier heat source and / or the inlet conduit heat source in electrical communication with the first and second sensors; comparing a first temperature gradient at the first sensor to a second temperature gradient at the second sensor; and outputting an indication of a reflux condition if the second temperature gradient is higher than the first temperature gradient. The first sensor may be located at the humidifier outlet or the humidifier inlet. The second sensor may be located at the patient end of the inlet conduit or at the humidifier outlet. The hardware and / or software controller may be further configured to detect a humidifier out-of-water condition by providing separate power to the humidifier heat source, receiving sensor data from a humidifier heat source temperature sensor at or near the humidifier heat source, the humidifier heat source temperature sensor in electrical communication with the one or more hardware processors, comparing a temperature gradient at the humidifier heat source to a threshold temperature gradient, and outputting an indication of a humidifier out-of-water condition if the temperature gradient at the humidifier heat source is higher than the threshold temperature gradient. The threshold temperature gradient may vary based, at least in part, on the flow rate, the type of humidifier, any other system parameters, and / or any other ambient conditions. The hardware and / or software controller may be configured to detect an indication of a backflow condition from a start-up condition.

[0024] A method can detect disconnection of an expiratory conduit heat source in a dual limb respiratory humidification system. The system can include an expiratory conduit having an expiratory conduit heat source, an inhalation conduit having a segmented inhalation conduit heat source, a first heat source driver configured to energize the expiratory conduit heat source and at least one segment of the inhalation conduit heat source, and a second heat source driver configured to energize the expiratory conduit heat source and at least one other segment of the inhalation conduit heat source. The method can include providing a voltage to the expiratory and inhalation conduit heat sources using one of the first and second heat source drivers, monitoring a current sensed by the one of the first and second heat source drivers, and outputting an indication of disconnection of the inhalation conduit heat source if the current deviates from an expected value by a predetermined error or exhibits a sudden change above or below a threshold. The method may further include the steps of exiting an ongoing therapy mode, reconnecting the first and second heat source drivers such that one of the first and second drivers is configured to energize the expiratory conduit heat source and the other of the first and second drivers is configured to energize the inspiratory conduit heat source, providing a second voltage to the expiratory conduit heat source using one of the first and second heat source drivers, monitoring a current sensed by one of the first and second heat sources, and outputting an indication of expiratory conduit heat source disconnection if the current is at or near zero. The second voltage may include a low duty cycle or minimum power. Operation of the method may be configured to be adjustable. The method may also detect a disconnection of the expiratory conduit heat source by detecting the presence of a circuit ID register when the hardware and / or software controller applies power to the expiratory conduit heat source. The system may determine that the expiratory conduit heat source is disconnected if the circuit ID register is not detected.

[0025] A dual limb respiratory humidification system with expiratory conduit heat source disconnection detection may include a breathing circuit having a gas source configured to provide a source of gas, a humidifier configured to heat a liquid to humidify gas provided by the gas source, an inspiratory conduit configured to provide humidified gas from the humidifier to a user and including a segmented inspiratory conduit heat source, and an expiratory conduit configured to provide gas expired from the user to the gas source and including an expiratory conduit heat source, a first heat source driver configured to energize the expiratory conduit heat source and at least one segment of the inspiratory conduit heat source, and a second heat source driver configured to energize the expiratory conduit heat source and at least one other segment of the inspiratory conduit heat source, wherein at least one of the first and second heat source drivers is configured to detect an indication of expiratory conduit heat source disconnection by providing a voltage to the expiratory and inspiratory conduit heat sources, detecting a current, and outputting an indication of inspiratory conduit heat source disconnection if the current deviates from an expected value by a predetermined error. The system can be configured to switch the configuration of the first and second heat source drivers such that one of the first and second drivers is configured to energize the expiratory conduit heat source and the other of the first and second drivers is configured to energize the inhalation conduit heat source, and one of the first and second drivers is configured to output an indication of expiratory conduit heat source disconnection when the current is at or near zero. The second voltage can include a low duty cycle or minimum power. The system can be configured to detect the indication of expiratory conduit heat source disconnection at an adjustable interval. The system can also detect the expiratory conduit heat source disconnection by detecting the presence of a circuit ID register when the hardware and / or software controller applies power to the expiratory conduit heat source. The system can identify the expiratory conduit heat source as disconnected if the system fails to detect the circuit ID register.

[0026] A method can detect disconnection of an expiratory conduit heat source in a dual limb respiratory humidification system. The system can include an expiratory conduit having an inhalation conduit heat source, an inhalation conduit having a segmented inhalation conduit heat source, a first heat source driver configured to energize the inhalation conduit heat source, and a second heat source driver configured to energize the inhalation conduit heat source. The method can include providing a voltage to the expiratory conduit heat source using the first heat source driver, monitoring a current sensed by the first heat source driver, and outputting an indication of expiratory conduit heat source disconnection when the current is at or near zero.

[0027] A dual limb respiratory humidification system with expiratory conduit heat source disconnection detection may include a breathing circuit having a gas source configured to provide a source of gas, a humidifier configured to heat a liquid to humidify gas provided by the gas source, an inspiratory conduit configured to provide humidified gas from the humidifier to a user and including an inspiratory conduit heat source, and an expiratory conduit configured to provide gas exhaled from the user to the gas source and including an expiratory conduit heat source, a first heat source driver configured to energize the expiratory conduit heat source, and a second heat source driver configured to energize the inspiratory conduit heat source, wherein the first heat source driver is configured to detect an indication of expiratory conduit heat source disconnection by providing a voltage to the expiratory conduit heat source, detecting a current, and outputting an indication of expiratory conduit heat source disconnection when the current is at or near zero.

[0028] The method may detect backflow in a respiratory humidification system using transient system parameters. The respiratory humidification system may include a gas source, a humidifier including an inlet and an outlet, an inhalation conduit, and a plurality of sensors. The method may include receiving a transient state input from one or more of the plurality of sensors and / or system parameters of the respiratory humidification system, determining a backflow predictor based at least in part on the input and / or the system parameters, and outputting an indication of a backflow condition if the backflow predictor exceeds zero. The plurality of sensors may include more than one of a humidifier inlet temperature and / or flow sensor, a humidifier outlet temperature and / or flow sensor, a patient end temperature sensor, and / or a humidifier heat source temperature sensor. The received input may be from a transient state or from a steady state. The system parameters may include more than one of a humidifier heat source power, a humidifier outlet setpoint temperature, a patient end setpoint temperature, and / or a power of at least one segment of the inhalation conduit heat source. The backflow predictor may be determined at least in part based on the plurality of parameters. The backflow predictor can be determined based at least in part on a humidifier inlet temperature, an absolute difference between the humidifier outlet temperature and the humidifier outlet set point, a ratio of flow rate to humidifier heat source power, a ratio of the humidifier inlet temperature to the humidifier outlet set point, and a ratio of the humidifier inlet temperature to the tube temperature. The backflow predictor can be determined based at least in part on a filtered or unfiltered flow rate, an absolute difference between the humidifier outlet temperature and the humidifier outlet set point, a ratio of the humidifier inlet temperature to the tube temperature, and a ratio of filtered or unfiltered power of a segment of the intake conduit heat source to the humidifier heat source temperature.

[0029] A respiratory humidification system with backflow detection may include a gas source configured to provide a source of gas, a humidifier including an inlet and an outlet, the humidifier configured to humidify air and further including a humidifier heat source for heating a liquid to humidify the gas provided by the gas source, and an inspiratory conduit configured to provide the humidified gas to a user, the gas source, the humidifier, and the inspiratory conduit forming at least a portion of a respiratory circuit, and may also include a plurality of sensors, and a hardware and / or software controller in electrical communication with the plurality of sensors and configured to receive transient state inputs and / or system parameters of the respiratory humidification system from one or more of the plurality of sensors, at least in part, to detect an indication of a backflow condition in the humidification system by identifying a backflow predictive indicator based on the inputs and / or system parameters, and outputting an indication of a backflow condition when the backflow predictive indicator exceeds zero. The plurality of sensors may include one or more of a humidifier inlet temperature and / or flow rate sensor, a humidifier outlet temperature and / or flow rate sensor, a patient end temperature sensor, and / or a humidifier heat source temperature sensor. The received inputs may be from a transient state or from a steady state. The system parameters may include more than one of a humidifier heat source power, a humidifier outlet setpoint temperature, a patient end setpoint temperature, and / or a power of at least one segment of the respiratory conduit heat source. The reflux predictor may be determined based at least in part on a plurality of parameters. The reflux predictor may be determined based at least in part on a humidifier inlet temperature, an absolute value of the difference between the humidifier outlet temperature and the humidifier outlet setpoint, a ratio of flow rate to humidifier heat source power, a ratio of humidifier inlet temperature to humidifier outlet setpoint, and a ratio of humidifier inlet temperature to tubing temperature. The reflux predictor may be determined based at least in part on a filtered or unfiltered flow rate, an absolute value of the difference between the humidifier outlet temperature and the humidifier outlet setpoint, a ratio of humidifier inlet temperature to tubing, or a ratio of filtered or unfiltered power of a segment of the respiratory conduit heat source to humidifier heat source temperature.

[0030] These and other features, aspects, and advantages of the present disclosure will be described with reference to the drawings of specific embodiments which illustrate generally and are not intended to be limiting of the disclosure. [Brief description of the drawings]

[0031] [Figure 1] FIG. 1 shows a schematic diagram of a dual rim humidification system. [Figure 2A] 2 illustrates an example of a backflow condition and / or misconnection in the humidification system of FIG. 1. [Figure 2B] 2 illustrates an example of a backflow condition and / or misconnection in the humidification system of FIG. 1. [Figure 2C] 2 illustrates an example of a backflow condition and / or misconnection in the humidification system of FIG. 1. [Figure 2D] 2 illustrates an example of a backflow condition and / or misconnection in the humidification system of FIG. 1. [Figure 3A] A schematic diagram of a single-rim humidification system is shown. [Figure 3B] 3B illustrates an example of a backflow condition and / or misconnection within the humidification system of FIG. 3A. [Figure 4] 1 illustrates a flow chart of an exemplary respiratory therapy treatment using a humidification system together with a control method for detecting reflux. [Figure 5A] FIG. 1 shows a schematic diagram of a dual rim humidification system with various sensors located within the system. [Figure 5B] 1 shows a flow chart of an exemplary passive backflow detection process. [Figure 6] 13 shows a flow chart of another exemplary passive backflow detection process. [Figure 7A] 1 illustrates a flow chart of an exemplary active backflow detection process. [Figure 7B] 1 illustrates a flow chart of an exemplary active backflow detection process. [Figure 8A] 13 shows a flow chart of another exemplary active backflow detection process. [Figure 8B] 13 shows a flow chart of another exemplary active backflow detection process. [Figure 9A] 1 illustrates components of a humidification system for implementing a particular active backflow detection process. [Figure 9B] 1 illustrates components of a humidification system for implementing a particular active backflow detection process. [Figure 9C] 1 illustrates components of a humidification system for implementing a particular active backflow detection process. [Figure 10] 1 illustrates a flow chart of an exemplary active backflow and water outage detection process. [Figure 11A] 11 illustrates exemplary system temperature parameters for a humidification system implementing the process of FIG. 10 in forward and reverse flow conditions, respectively. [Figure 11B] 11 illustrates exemplary system temperature parameters for a humidification system implementing the process of FIG. 10 in forward and reverse flow conditions, respectively. [Figure 11C] 11 illustrates exemplary system temperature parameters for a humidification system implementing the process of FIG. 10 in forward and reverse flow conditions, respectively. [Figure 11D] 11 illustrates exemplary system temperature parameters for a humidification system implementing the process of FIG. 10 in forward and reverse flow conditions, respectively. [Figure 12A] 11 illustrates an exemplary temperature change detected by a humidifier outlet temperature sensor of a humidification system after activating an inlet conduit heat source in the inlet tube when the process of FIG. 10 is implemented. [Figure 12B] 11 illustrates an exemplary temperature change detected by a patient-end temperature sensor of a humidification system after activating an inlet conduit heat source in the inlet tube when the process of FIG. 10 is implemented. [Figure 13] 11 illustrates an exemplary humidifier heat source temperature change of a heating system after the humidifier heat source is activated when the process of FIG. 10 is implemented. [Figure 14] 13 shows a flow chart of another exemplary passive backflow detection process. [Figure 15A] An example of the outlet temperature change in reverse and forward flow conditions is shown. [Figure 15B]An example of the outlet temperature change in reverse and forward flow conditions is shown. [Figure 16] 1 shows a flow chart of an exemplary passive backflow detection process. [Figure 17A] 1 shows an example of a dual limb humidification system with a segmented breathing conduit. [Figure 17B] 1 shows an example circuit diagram configured to control two segments of an inlet conduit heat source in parallel using an active commutation circuit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] Although specific embodiments and examples are described below, those skilled in the art will recognize that the disclosure does not limit itself to the specifically disclosed embodiments and / or applications, as well as obvious modifications and equivalents thereof, and therefore it is not intended that the scope of the disclosure disclosed herein should be limited by any of the specific embodiments described below.

[0033] Example of a backflow condition in a humidification system FIG. 1 illustrates a schematic diagram of an example dual-limb humidification system 1. The humidification system 1 can include a gas source 10 in fluid communication with a humidifier 20 via a dry-line conduit 30. The humidifier 20 can include various components, including, for example, a water chamber and a heat source. The heat source can include a humidifier heat source. Examples of humidifier heat sources can include chemical heaters, radiant heaters, induction heaters, and others. For example, the heat source can be a heater plate using a resistive heater. The humidifier 20 can also optionally include one or more processors, such as hardware and / or software processors. The gas source can be a one-way gas source, a high-flow gas source, a blower, a ventilator unit, a compressed air tank, a hospital wall-mounted gas source, an oxygen cylinder, or a pressurized gas cylinder. The gas source can also be an airflow source that may provide a flow of air. The gas source may also include a high flow gas source configured to deliver high flow rates of air or gas, for example, greater than 30 L / min and / or up to 150 L / min. The gas provided by the gas source may include any of dry air, ambient air, oxygen, and / or a mixture of therapeutic or respiratory gases. A controller may control the gas source 10 to generate a gas flow of a desired flow rate, temperature, and / or pressure. The gas from the gas source outlet 12 may include dry gas.

[0034] Dry gas may be provided to the humidifier inlet 22 via the dryline conduit 30. The humidifier inlet 22 may include a humidifier inlet temperature sensor and / or a flow sensor. The humidifier 20 may contain a liquid, such as water. The humidifier 20 may have a heat source, such as a heater plate, that vaporizes water to humidify and heat the dry gas from the dryline conduit 30. Water may be provided to the humidifier 20 from a water source. The humidified gas may exit the humidifier outlet 24 and enter the intake conduit 40. The humidifier outlet 24 may include a humidifier outlet temperature sensor and / or a flow sensor.

[0035] The inlet conduit 40 can provide humidified gas to the patient 2. The inlet conduit 40 can be connected to a patient interface. Although the patient 2 is shown wearing a mask in FIGS. 1, 2A-D, and 5A, one skilled in the art will recognize from the disclosure herein that the patient 2 can wear a different type of patient interface than that disclosed herein, such as a nasal cannula. The patient interface can also include an interface tube, which is a short section of unheated tubing, and the inlet conduit 40 can be coupled or connected to the interface tube. The patient interface end of the inlet conduit 40 can include a patient end temperature sensor and / or a flow sensor. The inlet conduit 40 can have an inlet heat source to reduce or prevent the formation of condensation. Examples of inlet conduit heat sources can include heater wire, heating tape, and / or water jacket heating. Condensation can form when the temperature of the humidified gas leaving the humidifier 20 decreases due to heat loss as the gas travels through the unheated expiratory conduit 40. The humidification system 1 can include an expiratory conduit 50. The expiratory conduit 50 can guide gases exhaled from the patient 2 back to the gas source inlet 14. The expiratory conduit 50 can include an expiratory conduit heat source, such as heater wire, heating tape, and / or water jacket heating.

[0036] The sensors can be located in a variety of locations within the humidification system. For example, the sensors can include flow, pressure, temperature, and / or humidity sensors. The sensors can include thermistors. The thermistors can function as temperature sensors and can be switched to function as flow sensors by applying a voltage to the thermistor to heat it. The output of the sensors can be received by a controller to assist the controller in operating the humidification system 1 in a manner that provides optimal therapy. Other sensors that may be used include thermocouples, thermostats, semiconductor sensors, infrared sensors, and resistive temperature devices.

[0037] Examples of backflow conditions and connection errors of the components of the humidification system 1 are described with respect to Figures 2A-D. It should be understood that these are only examples and that other conduit connection errors may occur, such as connecting the conduits in the opposite direction and / or at a different location in the circuit than where they would normally be connected. In error 1 shown in Figure 2A, the connections of the dry line conduit 30 and the expiratory conduit 50 to the gas source 10 are reversed. Specifically, the dry line conduit 30 is incorrectly connected to the gas source inlet 14 and the expiratory conduit 50 is incorrectly connected to the gas source outlet 12. As a result, dry gas may flow directly to the patient 2 in the expiratory conduit 30 and may flow directly to the patient 2 in the expiratory conduit 30 without being humidified or heated because the dry gas does not pass through the humidifier 20. The dry gas may be heated by the expiratory heat source in the expiratory conduit 50, in which case the heating is not properly regulated by the controller. Gases exhaled by the patient 2 may be humidified through a humidifier 30 before being returned to the gas source 10 .

[0038] In error 2 shown in FIG. 2B, there is a backflow condition in the humidifier 20. Specifically, the inspiratory conduit 40 is incorrectly connected to the gas source outlet 12 and the humidifier outlet 24. The expiratory conduit 50 is incorrectly connected to the humidifier inlet port 22 and the patient 2. The dry-line conduit 30 is incorrectly connected to the patient 2 and the gas source inlet 14. The system receives outputs from the patient-end sensor in the inspiratory conduit 40 and the sensors at the humidifier inlet and / or outlet 22, 24 that are not indicative of the actual patient-end temperature and / or inlet / outlet temperature. The humidifier heat source and the inspiratory heat source may not function properly due to the incorrect outputs from the sensors. Gas leaving the humidifier inlet 22 for the patient 2 may not be heated because the expiratory conduit 50 may not have a heating wire, or may be heated by the expiratory conduit heat source in the expiratory conduit 50, in which case the heating is not properly regulated by the controller.

[0039] In error 3 shown in Figure 2C, the connections of the gas source inlet 14 and outlet 12 are reversed. Specifically, the dry line conduit 30 is incorrectly connected to the gas source inlet 14 and the humidifier inlet 22. The expiratory conduit 50 is incorrectly connected to the humidifier outlet 24 and the patient 2. The inhalation conduit 40 is incorrectly connected to the patient 2 and the gas source inlet 12. As a result, dry gas may flow directly to the patient 2 in the expiratory conduit 30 without being humidified or heated because the dry gas does not pass through the humidifier 20. Exhaled gas from the patient 2 may be humidified in the humidifier 30 before flowing to the gas source 10.

[0040] In error 4 shown in FIG. 2D, gas flows in the normal direction, but there is an error in the connection. Specifically, the expiratory conduit 50 is incorrectly connected to the humidifier outlet 24 and the patient 2. The inhalation conduit 40 is incorrectly connected to the gas source inlet 14 and the patient 2. As a result, the patient-end sensor in the inhalation conduit 40 cannot properly measure the temperature of the gas delivered to the patient 2, but rather measures the temperature of the gas exhaled from the patient 2. The gas leaving the humidifier 20 cannot be heated to ensure that the patient-end temperature reaches the patient-end set point. This may be because the expiratory conduit 50 does not have a heat source, or the expiratory conduit heat source is not properly energized by the controller which receives the patient-end temperature input from the sensor in the inhalation conduit 40. The gas reaching the patient 2 may be above or below the patient-end set point as the gas travels through the expiratory conduit 50.

[0041] 3A, the single limb humidification system 301 can have the same features as the dual limb humidification system 1 of FIG. 1A, with the following differences: The single limb humidification system 301 can have a gas source 310, which has an outlet for gas outflow but no inlet for gas inflow. The single limb humidification system 301 may not have an exhalation conduit. Gases exhaled by the patient 302 can exit through a vent in the patient interface and / or through the patient's mouth, as previously described.

[0042] In error 5, shown in FIG. 3B, the flow is reversed throughout the single limb humidification system 301. Specifically, the inlet conduit 340 is incorrectly connected to the gas source 310 and the humidifier outlet 324. The dry line conduit 330 is incorrectly connected to the humidifier inlet 322 and the patient 302. As a result, the system receives outputs from the patient end sensors in the inlet conduit 340 and the humidifier inlets and / or outlets 322, 324 that are not indicative of the actual patient end temperature and / or inlet / outlet temperature. The humidifier heat source and the inlet conduit heat source may not function properly due to the incorrect outputs from the sensors. Dry gas from the gas source 310 may not be properly humidified by the humidifier 320 due to the incorrect sensor output. Gas exiting the humidifier 320 and entering the dry line conduit 330 cannot be heated because the dry line conduit 330 does not have an inlet conduit heat source. The gas reaching the patient 302 may be less than the patient end setting because the gas travels through the unheated dryline conduit 330. There may be condensation formation in the dryline conduit 330.

[0043] Overview of humidification system with backflow detection function The present disclosure relates to methods and systems for detecting reflux conditions and component connection errors within a respiratory humidification system.

[0044] As shown in FIG. 4, a humidification system, such as humidification system 1, 301 of FIGS. 1 and 3A, begins respiratory therapy for a patient by activating the humidification system at 410. The humidification system may need to be assembled by a caregiver, such as a nurse, or by the patient. Setting up the humidification system may include connecting the components of the humidification system to the various conduits described herein. Upon activation, the controller of the humidification system may perform a backflow detection process at step 420 to identify if there is an indication of a backflow condition. Those skilled in the art will appreciate that the backflow detection process may be performed by the controller throughout the course of operation of the humidification system and not necessarily only during the setup phase. An indication of a backflow condition may indicate that there is likely an error in the connection of components within the humidification system. The controller may perform any suitable backflow detection method, such as those described herein or combinations thereof. The controller may also perform an appropriate backflow detection method or process based on the particular therapy mode, which will be described in more detail below.

[0045] Even if the controller identifies an indication of a backflow condition in step 420, it may be difficult to know if a backflow condition exists or if the sensor / probe has been removed. In these systems, the controller may perform a probe-out test before executing the backflow detection process of step 420. The probe-out test may also instruct the controller to heat the system and monitor if the tube temperature increases.

[0046] If indications of backflow and / or incorrect setup / connection and / or disconnected circuit conditions are identified, the humidification system can alert the patient / caregiver (hereinafter "user") at 430. For example, the controller can output an error message, an audible alarm / buzzer, a flashing error indicator light, or other similar method of alerting the user. The message from the controller can also indicate components that may have been connected incorrectly. Text and / or image based messages and / or troubleshooting animations can be displayed to explain possible misconnections. An animation and / or a series of images can be displayed on the screen showing how to correct the error. The animation and / or series of images can be displayed repeatedly until the system detects the correct state and the correct flow direction of gas or until the user inputs that the error has been corrected.

[0047] The controller may optionally include a counter, which may be implemented in hardware and / or software. The counter may increment each time an indication of a backflow condition is identified. The counter may be a timer that may detect the length of time an indication of a backflow condition exists. The counter may be initialized each time an indication of a backflow condition is detected and may be disabled each time a normal flow condition is detected. The counter or timer may be used incrementally up to a threshold whereby the system may alert the user with an alarm as disclosed elsewhere herein when the threshold is reached or exceeded. Alternatively or in addition, a filter may be used, including but not limited to (FIR / IIR) filters.

[0048] After being notified of the reflux condition, the user may reconnect the breathing circuit of the humidification system in the correct configuration. The user may reset the humidification system at 490 after reconnecting the breathing circuit. The controller may also optionally automatically reset upon reconnecting the breathing circuit. The controller may perform the reflux detection process at step 420 on the reconnected breathing circuit. If the controller can still detect an indication of a reflux condition, the controller may output another warning to the user at 430. If the controller can no longer detect an indication of a reflux condition, the controller may proceed to provide respiratory therapy or resume a suspended therapy to the patient at 440.

[0049] Performing a backflow detection process during system setup can allow for detection of connection errors before the patient begins therapy. Correcting connection errors during initial setup can advantageously improve system performance by reducing condensation in the respiratory conduit, providing optimal therapy to the patient, and / or increase patient safety by reducing the likelihood that dry, cold air will be provided directly to the patient, which can cause discomfort and / or more severe adverse reactions in the patient's body.

[0050] Various processes for detecting reflux conditions and / or connection errors are now described. The processes may be based on differential measurements of temperature, flow rate, and / or power loss at various locations in the humidification system. The processes described herein may include active and passive processes. Passive processes may run in the background to identify a reflux condition. Active processes may interrupt respiratory and / or humidification therapy to identify whether a reflux condition exists. The interruption may be brief and / or significant compared to the duration of the respiratory therapy. Active processes may take precedence over normal operation or control of the system. For example, active processes may take precedence over control of the inspiratory and / or expiratory conduit heat sources, and / or the humidifier heat sources, and / or the sensors.

[0051] In this disclosure, the inlet temperature is the temperature measured by the humidifier inlet temperature sensor 23 at or near the humidifier inlet 22 as shown in FIG. 5A. The outlet temperature is the temperature measured by the humidifier outlet temperature sensor 25 at or near the humidifier outlet 24. The tube temperature is the patient end temperature measured by the patient end temperature sensor 42 at or near the patient end of the inhalation conduit 40. The patient end sensor 42 can be incorporated into the inhalation conduit 40 or removably inserted into the gas lumen of the inhalation conduit 40. The humidifier heat source temperature is the temperature measured by the humidifier heat source temperature sensor 21 at or near the humidifier heat source of the humidifier 20. The outlet set point is the set point temperature the system is attempting to achieve at or near the humidifier outlet 24. The tube set point is the set point temperature the system is attempting to achieve at or near the patient end of the inhalation conduit 40. At least one of the humidifier inlet sensor 23, the humidifier outlet sensor 25, and / or the patient end sensor 42 can be a thermistor that can be configured to measure both the temperature and flow rate of the gas flow. The system 1 can have a second humidifier outlet sensor 26, which can be a flow sensor, a pressure sensor, or any other sensor configured to measure a parameter of the gas flow. The system 1 can include other sensors, such as other types of flow sensors, humidity sensors, or the like, at or near the humidity inlet 22, the humidity outlet 24, and / or the patient end of the inlet conduit 40. The humidifier inlet 22, the humidifier outlet 24, and / or the patient end of the inlet conduit 40 can each have one or more sensors disclosed herein. The humidification system 1 can also include one or more sensors elsewhere in the system.

[0052] Temperature-Based Passive and Active Processes The principles behind the temperature-based passive and active processes are now described. In normal operation of the system, cold gas flows into the humidifier inlet. The humidifier heat source of the humidifier is turned on by the controller to warm the gas so that it can exit the humidifier outlet at a higher temperature than the gas flowing into the humidifier inlet. As a result, the inlet temperature can be lower than both the outlet temperature and the outlet set point.

[0053] Additionally, in normal operation of the system, unless the inlet conduit is heated, the gas leaving the humidifier outlet may cool during travel through the inlet conduit. Thus, the system may provide power to an inlet conduit heat source in the inlet conduit to ensure that the tube temperature reaches and remains at the tube set point. There may be a temperature gradient from the humidifier outlet to the patient end of the inlet conduit. The gradient is an ascending temperature gradient from the humidifier outlet to the patient end of the inlet conduit. Thus, the tube temperature may be higher than the outlet temperature, but lower than or equal to the tube set point. Alternatively, the temperature gradient from the humidifier outlet to the patient end is not necessarily an ascending one, but provides enough power to keep the temperature of the gas from dropping below the dew point, causing rain out.

[0054] A temperature-based backflow detection process can utilize temperature differences at various points in the system, as previously described. If the normal flow temperature difference is not observed, the controller can identify indications of a backflow condition, such as the errors shown in Figures 2A-D and 3B. For example, a temperature increase from the patient end to the humidifier outlet may indicate that gas is flowing from the patient end to the humidifier outlet, or that the inspiratory conduit is incorrectly connected. Details of the temperature-based passive and active processes are described with reference to Figures 5B-8B.

[0055] Passive Process - Inlet Overtemperature Test Passive processes can utilize the relationship between the inlet temperature and the set point of the system. Such a process can be configured for use in a non-invasive (NIV) therapy mode, although the process can be configured for use in any therapy mode. In an NIV therapy mode, the tube set point can be set at or below normal human body temperature. For example, the tube set point can be a set point in the range of about 25-37°C, 28-35°C, 30-34°C, or any other suitable range. In other examples, the outlet set point can be a set point in the range of about 22-35°C, 25-33°C, 27-31°C, or any other suitable range. The tube and outlet end set points can correspond to each other. In a non-limiting example, when the tube set point is 34°C, the outlet set point can be about 31°C. Since the body temperature of a patient receiving respiratory therapy in an NIV therapy mode is about 37°C, the exhaled air in this non-limiting example can be 37°C or slightly lower. When a backflow condition exists, exhaled air may be received at the patient end of the inspiratory conduit, causing the tube temperature to be higher than the tube set point. A tube temperature higher than the tube set point may occur, for example, in a backflow condition as shown in Figures 2A and 2C. In a backflow situation, the tube temperature may exceed the tube set point for an extended period of time. For example, the humidification system may further determine whether the period during which the tube temperature exceeds the tube set point is greater than a predetermined threshold time.

[0056] Since the tube temperature may be higher than the tube set point in a reverse flow condition, the controller may cause the inlet conduit heat source in the inlet conduit to have a 0% or very low duty cycle. Gas moving in the wrong way through the inlet conduit may be cooled because the inlet conduit heat source is not heating the gas flowing through the inlet conduit. When the cooled gas reaches the humidifier outlet, the outlet temperature sensor may detect an outlet temperature lower than the outlet set point. This may cause the humidifier heat source to have a first duty cycle to heat the gas in the humidifier. The first duty cycle may be any duty cycle that is large enough to cause a temperature change at the humidifier inlet and outlet. The first duty cycle may be a maximum duty cycle or near a maximum duty cycle. A duty cycle less than the maximum duty cycle may still change the temperature, but it may take longer for the change to be measurable, and therefore other suitable duty cycles may be used. Application of the first duty cycle may result in the inlet temperature exceeding both the outlet temperature and the set point under reverse flow conditions.

[0057] The process can instruct the controller to directly compare the inlet temperature to the outlet temperature in NIV therapy mode. In normal operation, the inlet temperature is lower than the outlet temperature because the humidifier heat source temperature is high enough that the gas is heated as it travels from the inlet to the outlet. Thus, if the inlet temperature is higher than the outlet temperature, an indication of a reflux condition can be provided to the user.

[0058] A multi-step passive process 520 as shown in FIG. 5B can also be implemented. As shown in FIG. 5B, after the controller starts executing the backflow detection process 520 at 522, the controller can determine at step 524 whether the tube temperature is higher than the tube set point. If the tube temperature is lower than the tube set point, the controller can determine at step 540 that there is no backflow condition. The system can output an indication that a backflow condition was not detected at step 540, output no indication, and / or initiate ventilation and / or humidification therapy, or continue its current ventilation and / or humidification therapy. If the tube temperature is higher than the tube set point, which indicates that the inlet conduit heat source is not heating the inlet conduit and that the humidifier heat source may be heating the gas in the humidifier, the controller can check at step 526 whether the inlet temperature is higher than the outlet temperature or higher than the outlet set point. Under normal flow conditions, the inlet temperature is lower than the outlet temperature because the gas is heated as it leaves the humidifier outlet. If the inlet temperature does not exceed either the outlet temperature or the outlet setpoint, the system may avoid outputting an indication of a reflux condition at step 540. The system may initiate respiratory therapy or continue its current respiratory therapy.

[0059] 5B, if the inlet temperature exceeds the outlet temperature or the outlet set point, the system can further optionally determine whether the inlet temperature is greater than the ambient temperature in step 528 as a further confirmation that a backflow condition may exist. Specifically, the inlet temperature is approximately equal to or less than the ambient temperature in a forward flow condition, since most gas sources provide either ambient air or gas from a gas tank. In either case, the temperature of the gas provided by the gas source, as indicated by the inlet temperature, is unlikely to exceed the ambient temperature. The ambient temperature can also be measured by an optional ambient sensor, manually entered by a user, or received from the gas source.

[0060] After either determining in step 526 that the inlet temperature is greater than the outlet temperature or the set point, or after determining in step 528 that the inlet temperature is also greater than the ambient temperature, the controller can output an indication of a backflow condition in step 530. Process 520 can also check whether the inlet temperature is greater than the ambient temperature in step 528 and then check whether the inlet temperature is also greater than the outlet temperature or the outlet set point in step 526. Process 520 can also check whether the inlet temperature is greater than both the outlet temperature and the set point in step 526. Process 520 can optionally check whether the inlet temperature is greater than the outlet temperature, the set point, and the ambient temperature in any order. Additionally, the controller can determine that there may be a backflow condition in the humidifier. The system can alert the user in a manner described herein.

[0061] Passive Process - Tube Overtemperature Test Passive processes can also utilize the tube temperature as a reference point. Such processes can be configured for use in an invasive or high-flow therapy mode, although the process can be configured for use in either therapy mode. In an invasive or high-flow therapy mode, the tube set point can be approximately normal human body temperature or higher. In an invasive therapy mode, the tube set point can be approximately 40° C. and the outlet set point can be approximately 37° C. In a high-flow therapy mode, the tube set point can be approximately 36-40° C. and the outlet set point can be approximately 33-37° C. The body temperature of a patient receiving respiratory therapy can be approximately 37° C., so the exhaled air can be 37° C. or slightly higher. If there is a reflux condition, the exhaled air can be received at the patient end of the inspiratory conduit, resulting in a tube temperature lower than the tube set point. A tube temperature lower than the tube set point can occur, for example, in a reflux condition as shown in FIGS. 2A and 2D.

[0062] When exhaled gas flows in a reverse flow condition from the patient to the humidifier, the inlet conduit heat source can heat the gas up to a first inlet conduit heat source duty cycle. The first inlet conduit heat source duty cycle can be at or near a maximum duty cycle. The inlet conduit heat source can be activated because the controller is programmed to power the inlet conduit heat source when the tube temperature is below a tube set point. The controller is configured to cause the tube temperature to reach the set point even in a reverse flow condition because controllers in existing humidification systems are not configured to directly or indirectly detect a reverse flow condition.

[0063] 6 illustrates an example passive "tube temperature overshoot" process 620 for detecting an indication of a reflux condition using tubing temperature as a reference point. After the controller begins executing process 620 at 622, the controller can determine whether the tubing temperature is below the tubing set point at step 624. A tubing temperature below the tubing set point can be interpreted by the controller at step 640 as not indicating a reflux condition. The system can output an indication that a reflux condition was not detected at step 640, not output any indication, and / or initiate ventilation and / or humidification therapy or continue its current ventilation and / or humidification therapy.

[0064] If the tube temperature is lower than the tube set point, the controller can check whether the outlet temperature is higher than the tube temperature in step 626. Because the tube temperature is lower than the tube set point, the inspiratory conduit heat source may be heating the inspiratory conduit to force the gas moving in the inspiratory conduit to reach the tube set point. Under normal flow conditions, the gas exiting the humidifier outlet may be at a lower temperature than the gas at the patient end of the inspiratory conduit. A thermal gradient may rise from the outlet to the patient end when the inspiratory conduit heat source is turned on. If the outlet temperature is not higher than the tube temperature, the controller can interpret that result as not indicating a reflux condition. The system can output an indication that a reflux condition is not detected in step 640, not output any indication, and / or initiate ventilation and / or humidification therapy or continue its current ventilation / humidification therapy.

[0065] 6, if the tube temperature is lower than the outlet temperature, the controller can output an indication of a backflow condition at step 630. The controller can identify that the inspiratory conduit may be improperly connected since cooler exhaled gas may be flowing in the reverse direction from the patient end to the humidifier outlet. The system can alert the user in a manner described herein.

[0066] The passive backflow detection process described herein may be advantageous because the respiratory or ventilation therapy and / or humidification therapy being provided to the patient is not interrupted, thereby making it more convenient for the patient, while detecting a backflow condition and / or incorrect connection ensures patient safety. To run the passive process in the background, the inlet conduit heat source or the humidifier heat source do not need to be heated outside of a therapy mode, and therefore no additional processing is required by the controller. The control of the inlet conduit heat source and the humidifier heat source can function normally. Furthermore, no waiting time is required for the inlet conduit heat source or the humidifier heat source to reach a steady state or a specific temperature before running the passive process.

[0067] Active Process - Humidifier Heat Source High Duty Cycle (or Power) Test The passive processes described herein are controller dependent. In order for a passive process to function, it must be incorporated into the setup of the controller of the system. A passive process may be effective when the operation of the controller is known, such as when a user presets the operation of the controller. In contrast, an active process may be independent of a controller, such as a humidification heat source controller, an inlet conduit heat source controller, and / or others. An active process may be effective when the operation of the controller is not known.

[0068] 7A-B show example active processes 720, 721. As shown in FIG. 7A-B, the controller may first actively increase the humidifier heat source duty cycle to a first duty cycle in step 722. The first duty cycle may be approximately 100%. The active processes 720, 721 may advantageously be executed independent of the humidifier heat source controller. The controller may interrupt a therapy running in the system when executing the active processes 720, 721. The therapy may be a respiratory or ventilation therapy and / or a humidification therapy. As with the passive process 500, the outlet temperature is expected to be higher than the inlet temperature under normal flow conditions because the gas may be heated by the humidifier heat source at the first duty cycle as it flows from the humidifier inlet to the humidifier outlet. The first duty cycle is large enough to heat the humidifier heat source and change the temperature at the humidifier inlet and outlet. If there is a backflow condition, the gas can heat from the outlet to the inlet instead. As shown in Figure 7A, the controller can determine whether the inlet temperature is greater than the outlet temperature, step 724. As shown in Figure 7B, the controller can determine whether the change in inlet temperature is greater than the change in outlet temperature, step 725.

[0069] If the inlet temperature is lower than the outlet temperature or the inlet temperature change is less than the outlet temperature change, the controller may interpret the result as not indicating a reflux condition at step 740. The system may output an indication that a reflux condition is not detected, output no indication, and / or initiate ventilation and / or humidification therapy or continue its current ventilation and / or humidification therapy at step 740. If the inlet temperature is higher than the outlet temperature or the inlet temperature change is greater than the outlet temperature change, the system may output an indication of a reflux condition at step 730. Additionally, the controller may identify that a connection to the humidifier may be incorrect. The controller may also compare both absolute temperature and temperature change at the humidifier inlet and outlet in either order. The system may alert the user of the incorrect connection in a manner described herein. The system may not resume a paused therapy until the user corrects the reflux condition in the system.

[0070] Active Process - Inlet Conduit Heat Source High Duty Cycle (or Power) Test 8A-B show example active processes 820, 821. As shown in FIG. 8A-B, the controller may first actively increase the inhalation conduit heat source duty cycle to a first duty cycle in step 822. The first duty cycle may be approximately 100%. The first duty cycle is large enough to heat the inhalation conduit heat source so that it causes a temperature change at the humidifier outlet and the patient end of the inhalation conduit. The active processes 820, 821 may advantageously be executed independent of the inhalation conduit heat source controller. The controller may suspend any therapy running in the system when executing the active processes 820, 821. The therapy may be a respiratory or ventilation therapy and / or a humidification therapy. As with the passive process 600, the tube temperature is expected to be higher than the outlet temperature under normal flow conditions due to a heating gradient in the inhalation conduit. When a backflow condition exists, unheated gas enters the patient end of the inspiratory conduit and can heat up as the gas reaches the humidifier outlet, resulting in a tube temperature lower than the outlet temperature. As shown in Figure 8A, the controller can determine whether the tube temperature is lower than the outlet temperature, step 824. As shown in Figure 8B, the controller can determine whether the change in tube temperature is greater than the change in outlet temperature, step 825.

[0071] If the tube temperature is higher than the outlet temperature or the tube temperature change is less than the outlet temperature change, the controller may interpret the result as not indicating a reflux condition, step 840. The system may output an indication that a reflux condition is not detected, output no indication, and / or initiate ventilation and / or humidification therapy or continue its current ventilation and / or humidification therapy, step 840. If the tube temperature is lower than the outlet temperature or the tube temperature change is greater than the outlet temperature change, the system may output an indication of a reflux condition, step 830. Additionally, the controller may identify that a connection to the inspiratory conduit may be incorrect. The controller may also compare both absolute temperature and temperature change at the patient end and the humidifier outlet, in either order. The system may alert the user of the incorrect connection, in a manner described herein. The system may not resume a paused therapy until the user corrects the reflux condition in the system.

[0072] In addition to being independent of the humidifier heat source / wire controller, the active process 720, 721, 820, 821 advantageously allows for more easily detectable temperature differences in steps 724, 725, 824, 825, resulting in higher heating capacity for the inlet conduit heat source or humidifier heat source. The higher heating capacity can be at maximum or substantially maximum duty cycle.

[0073] Active Processes - Upstream and Downstream Temperature Gradient Testing 9A-C show a combination 910, 920, 930 of a sensor and heater in a humidification system that can perform an active backflow detection process that compares upstream and downstream temperature gradients. The process can be performed from an initial "cold" and / or unheated start-up condition. The process can be performed by providing a heating pattern after start-up, for example during normal operation of the humidification system. The temperature gradient at the sensor location can be the rate of change of the temperature sensor reading. When the heater in the humidification system is heated from an initial unheated condition, the temperature gradient seen at the downstream temperature sensor is expected to be greater than the temperature gradient seen at the upstream temperature sensor under normal flow conditions. This is because under normal flow conditions, the gas flow is heated as the gas flows from the gas source through the humidifier and inspiratory conduit to the patient interface.

[0074] The various sensors can be upstream or downstream temperature sensors. The sensors can include a humidifier outlet temperature sensor, a humidifier inlet temperature sensor, and / or a patient end temperature sensor. Various heaters can be heated for active processes. The heaters can include a humidifier heat source and / or an inlet conduit heat source. As shown in FIG. 9A, an active process can utilize a combination 910 that includes a humidifier outlet temperature sensor as an upstream sensor 912, an inlet conduit heater as a heater 914, and a patient end temperature sensor as a downstream sensor 916. The humidifier heat source can be deactivated. As shown in FIG. 9B, an active process can utilize a combination 920 that includes a humidifier inlet temperature sensor as an upstream sensor 922, a humidifier heat source and an inlet conduit heat source as heaters 924, and a patient end temperature sensor as a downstream sensor 926. 9C, an active process can utilize a combination 930 that includes a humidifier inlet temperature sensor as an upstream sensor 932, a humidifier heat source as a heater 934, and a humidifier outlet temperature sensor as a downstream sensor 936. The inlet conduit heat source can be deactivated.

[0075] Figure 10 shows an example active detection manager 1000 utilizing combination 910 of Figure 10A. A humidifier outlet temperature sensor for detecting the humidifier outlet temperature can be an upstream sensor. A patient end temperature sensor for detecting the patient end temperature can be a downstream sensor. The active detection manager 1000 can also utilize other combinations such as combinations 920, 930 of Figures 10B and 10C.

[0076] At step 1004, the active detection manager 1000 may be in an idle state. In the idle state, the active detection manager 1000 may wait for a system self-test to complete. The system self-test may check for hardware disconnects and / or failures and / or may include a probe-out test. Some sensors may not be available during the self-test. For example, a flow sensor may need to be warmed up before a flow detection sensor is available. The controller may not be able to perform heating control during the self-test. The active detection manager 1000 may also wait for a gas flow to be detected at step 1004.

[0077] After completing the self-test, the active detection manager 1000 may energize the inhalation conduit heat source in the inhalation conduit at step 1008. The active detection manager 1000 may provide 100% duty cycle or power until the tube temperature detected by the patient end temperature sensor reaches or is maintained for a pre-set threshold temperature or maximum limit for a pre-defined duration. The power may be constant or variable power in a known pattern that may be a pulsed or wave pattern or other. The maximum limit may be approximately 40° C. The humidifier heat source may be deactivated. The active detection manager 1000 may de-energize the inhalation conduit heat source if the tube temperature or humidifier heat source temperature exceeds a threshold. The threshold may be a safe maximum temperature limit. The tube or humidifier heat source temperature may exceed the threshold due to a warm start or due to the inhalation conduit being temporarily disconnected from the humidifier. A warm start may occur by starting the system before it has cooled down to ambient temperature.

[0078] The active sensing manager 1000 can monitor and compare the temperature gradients measured by the patient-end and humidifier outlet temperature sensors at step 1008. As shown in FIGS. 12A and 12B, which show the area enclosed by the dashed lines in FIGS. 11A-11D, when gas flow is in the forward direction for a certain amount of time after activating the inlet conduit heat source, the temperature detected at the patient-end will be higher than the humidifier outlet. In the example shown, this amount of time is approximately 200 seconds, but one of ordinary skill in the art will recognize that this amount of time depends on many factors, such as the ambient temperature conditions, the flow rate, and the power applied to the inlet conduit heat source. The amount of time may be in the range of approximately 5 seconds to 10 minutes, 10 seconds to 4 minutes, 10 seconds to 3 minutes, 10 seconds to 200 seconds, 10 seconds to 100 seconds, and / or 50 seconds to 100 seconds. At the humidifier outlet, gas is not heated because the humidifier heat source is deactivated. At the patient end of the inspiratory conduit, the gas can be heated as the inspiratory conduit heat source is energized with normal flow. The inspiratory conduit heat source can be energized to maximum duty cycle or constant power, or with variable power in a known pattern, which can be a pulsed or wave pattern, or other.

[0079] As shown in Figures 12A-12B, when gas flow is reversed for a length of time after activating the inhalation conduit heat source, the temperature gradient detected at the humidifier outlet is greater than at the patient end. In the example shown in the figures, this length of time is approximately 200 seconds, but one skilled in the art would recognize that this length of time depends on many factors, such as ambient temperature conditions, flow rate, and power applied to the inhalation conduit heat source. The length of time may be in the range of approximately 5 seconds to 10 minutes, 10 seconds to 4 minutes, 10 seconds to 3 minutes, 10 seconds to 200 seconds, 10 seconds to 100 seconds, and / or 50 seconds to 100 seconds. The gas arriving at the humidifier outlet has been heated by the inhalation conduit heat source, which causes the temperature to spike at the humidifier outlet. The gas arriving at the patient end of the inhalation conduit may not be heated. The temperature gradient at the patient end may exist due to the flow of exhaled gas from the heated expiratory conduit moving into the heated inhalation conduit. The temperature gradients at the patient end and at the humidifier outlet can have similar trends when the humidifier has water in it or when the humidifier is out of water.

[0080] As previously discussed, the active detection manager 1000 can energize different heaters to detect a backflow condition. The active detection manager 1000 can energize the humidifier heat source or a combination of the humidifier heat source and the inlet conduit heat source in step 1008. The active detection manager 1000 can monitor the temperature gradient detected by the different temperature sensors. The humidifier inlet temperature sensor can be an upstream sensor and a patient end temperature sensor, or the humidifier outlet temperature sensor can be a downstream sensor.

[0081] If the ramp manager 1000 detects a backflow condition based on the difference in temperature gradients of the upstream and downstream temperature sensors as described above, the active detection manager 1000 can output a backflow setup error in step 1012. The output of the backflow error can trigger an alarm message. The message can be in the form of video, text, pictures, or a combination thereof. The message can include instructions regarding corrective action. Upon detecting the error, the active detection manager 1000 can de-energize the inlet conduit heat source or other active heaters.

[0082] If the ramp manager 1000 determines that the gas flow is in the forward direction, the active detection manager 1000 proceeds to step 1016. In step 1016, the active detection manager 1000 may energize the humidifier heat source to detect a water-out condition. The water-out condition may indicate that the humidifier is empty (zero water level) or that the water level in the humidifier is below a minimum threshold. The minimum threshold may be any suitable threshold, such as within the range of 10 mm, 9 mm, 8 mm, 7 mm, 6 mm, 5 mm, 4 mm, 3 mm, 2 mm, and / or less than 1 mm. The threshold may vary based, at least in part, on the flow rate, the type of humidifier, any other system parameters, and / or any other ambient conditions. The active detection manager 1000 may energize the humidifier heat source for a set time or to a set temperature. The humidifier heat source may be energized at a constant power or with variable power in a known pattern, which may be a pulse or wave pattern or other. The constant or variable power may be any suitable power, and one skilled in the art will recognize that higher power may produce faster results but with the possible risk of overheating, and lower power may produce slower results, with less risk of overheating, but may be more susceptible to ambient conditions. The low or variable power may be a power in the range of approximately 10-250W, 50-200W, 25-175W, 50-150W, 75-125W, 100W, and / or 150W. The active detection manager 1000 may de-energize the humidifier heat source if it exceeds a threshold value. The threshold value may be a safe maximum temperature limit. In step 1016, the active detection manager 1000 can energize the humidifier heat source or both the humidifier heat source and the inlet conduit heat source. If both the inlet conduit heat source and the humidifier heat source are energized, the humidifier heat source can be supplied with constant power or with variable power in a known pattern, as previously described.

[0083] The active detection manager 1000 can monitor the temperature gradient at the humidifier heat source at step 1016. As shown in FIG. 13, the temperature gradient at the humidifier heat source is greater when the humidifier is out of water than when the humidifier water level is zero or above a minimum threshold for a period of time after the humidifier heat source is turned on. In the example shown, the period of time is approximately 150 seconds, but one skilled in the art would recognize that this period of time depends on many factors, such as the ambient temperature conditions, the flow rate, and the power applied to the inlet conduit heat source. The period of time may be within the range of approximately 5 seconds to 10 minutes, 10 seconds to 4 minutes, 10 seconds to 3 minutes, 10 seconds to 200 seconds, 10 seconds to 100 seconds, 50 seconds to 150 seconds, and / or 50 seconds to 100 seconds. In both forward and reverse flow conditions, the temperature gradient at the humidifier heat source is greater when the humidifier is out of water than when the humidifier is not out of water. The temperature of the humidifier heat source may rise more quickly if there is insufficient water to act as a heat sink to absorb heat from the humidifier heat source. The active detection manager 1000 may compare the temperature gradient at the humidifier heat source to a predetermined threshold temperature gradient. The humidifier may be out of water if the temperature gradient exceeds the threshold.

[0084] If the start-up manager 1000 detects an out-of-water condition as described above, the active detection manager 1000 can output a setup error in step 1020. The output of the out-of-water error can trigger an alarm message. The message can be in the form of video, text, pictures, or a combination thereof. The message can include instructions regarding corrective action. Upon detecting the error, the active detection manager 1000 can de-energize the humidifier heat source or other energized heaters.

[0085] If the start-up manager 1000 determines that the humidifier contains water or that the water level in the humidifier is above a minimum threshold, the active detection manager 1000 may proceed to step 1024. At step 1024, the active detection manager 1000 may be energized and the controller may begin normal operation of the humidification system.

[0086] The humidification system active detection manager 1000 may be enabled to facilitate detection of backflow conditions, detection of humidifier dry conditions, and / or minimization of condensation in the unheated portion of the inlet tube. The active detection manager 1000 may provide predictable control independent of the humidifier heat source and / or the inlet conduit heat source to aid in fault detection.

[0087] Passive processes based on power loss and / or flow rate A backflow condition can be detected based on parameters other than temperature. For example, FIG. 14 illustrates a passive backflow detection process 1420 based on flow measurements. As previously described, the humidification system can include thermistors at the humidifier inlet and / or outlet. After initiating the backflow detection process at 1422, the controller can cause the thermistor to act as a flow sensor by first applying a voltage to the thermistor to heat it up and indirectly measure the flow rate based on the power loss of the thermistor. The controller can receive determined flow rate inputs from thermistor flow sensors at the humidifier inlet and outlet at step 1423. The humidification system may not be able to directly detect a backflow condition since these thermistor flow sensors are omnidirectional flow sensors. There may also be dedicated direction-specific and / or non-directional flow sensors, both of which may not require heating at the humidifier inlet and / or outlet. A backflow condition can be detected by monitoring changes in flow rate measurements at different locations in the system. The different locations can include, for example, at or near the humidifier inlet and outlet. Flow measurements can vary throughout the system and deviate from the flow setpoint for systems with different geometries.

[0088] As shown in FIG. 14, the controller can compare the measured inlet and outlet flow rates in step 1425. For example, the flow waveforms of the humidifier inlet and humidifier outlet can be compared. During normal operation of the system, the measured flow rate is higher at the humidifier outlet than at the humidifier inlet. This is because the shape of the humidifier outlet can act as a nozzle and the shape of the humidifier inlet can act as a diffuser if the gas flows in the correct direction. As a result, gas can move through a diffuser at the humidifier inlet and gas can move through a nozzle at the humidifier outlet. The difference in the shape of the humidifier inlet and outlet can cause a change in the velocity of the gas, resulting in a lower velocity at the humidifier inlet and a higher velocity at the humidifier outlet. If the inlet flow rate is less than the outlet flow rate, the controller can interpret the result in step 1440 as not indicating a backflow condition. The system may output an indication that no backflow condition was detected, output no indication, and / or initiate ventilation and / or humidification therapy or continue its current ventilation and / or humidification therapy, at step 1440. If a backflow condition exists as shown in FIGS. 2A-C and 3B, the flow rate at the humidifier outlet may be lower than the flow rate at the humidifier inlet. The system may output an indication of a backflow condition, at step 1430. The system may also output an indication that the connection to the humidifier may be incorrect, at step 1430. The system may stop the therapy, at step 1430. The system may alert the user of the incorrect condition, according to methods described herein. The system may resume the interrupted therapy or not start a new therapy until the user corrects the backflow condition in the system.

[0089] As another example, the controller may include, in step 1425, power loss curves of thermistor flow sensors at the humidifier inlet and humidifier outlet. Similar to the flow-based process 1420, the controller must first apply voltage to heat the thermistor. The power loss scheme may depend on the type of gas source and may need to identify the phases of breathing and compare these phases in power loss values ​​at the humidifier inlet and outlet separately. For example, a higher value on the waveform may identify the exhalation phase and a lower value may identify the inspiration phase. The power loss at the outlet sensor may be lower than that of the inlet sensor in normal flow conditions because the gases are being heated by the humidifier heat source as they exit the humidifier outlet. The power loss through the outlet sensor may be higher in reverse flow conditions because cooler gases may be moving through the outlet sensor compared to the inlet sensor. Additional details regarding the use of power loss curves at the humidifier inlet and outlet to detect reverse flow conditions are described in U.S. Provisional Patent Application No. 62 / 362,709.

[0090] The controller can also compare both the flow rate and power loss at the humidifier inlet and outlet in either order. One of the backflow detection processes can be used to cross-check the accuracy of the other backflow detection process.

[0091] The flow sensor can be calibrated to a zero point reference prior to the backflow detection process 1420. The flow sensor can be calibrated to zero scale when there is no gas flow. In a humidification system, no gas flow can occur if the port cap is still attached to the humidifier inlet or when the humidifier system commands the user to calibrate the flow sensor and the user blocks at least the inlet port of the humidifier. Alternatively, the user or the port cap may block both the inlet and outlet. The user may also manually block one or more ports. The system can provide instructions for calibration with prompts on a display screen.

[0092] Some humidification systems may include one or more directional flow sensors to directly detect a reverse flow condition. Detection of a reverse flow condition by one or more directional flow sensors may prompt the humidification system to output an alert of a possible misconnection. Possible misconnections may include when the humidifier inlet and outlet are swapped or mixed up during setup of the humidification system, or when the ventilator inlet and outlet are swapped or mixed up during setup of the humidification system. Although a directional sensor may indicate whether gas is flowing in a direction opposite to the preferred direction, the sensor may not indicate whether any conduits are installed incorrectly as in FIGS. 2B and 2D.

[0093] Passive processes using sensor measurements and / or system parameters The above-described backflow condition detection process can be configured to occur when the humidification system reaches a steady state. The humidification system may be in a steady state when readings from one or more sensors in the humidification system are substantially stable. The passive process may also be performed during a transient state before the readings from the one or more sensors are substantially stable. Although the examples below are described in the context of transient sensor measurements and / or other parameters, the above-described process may also apply to steady state sensor readings and / or other parameters for detecting a backflow condition.

[0094] In transient conditions, the sensor inputs may be increasing, decreasing, and / or fluctuating. The monitored system parameters may include raw values, raw sensor data, and / or derived or differential values. The raw values ​​may include heating power, sensor measurements, mode of therapy, and / or others. Heating power may be, for example, from a humidifier heat source and / or from various portions of the inlet conduit heat source, such as HW1 and HW2 described below. The sensor measurements may be, for example, inlet temperature, humidifier heat source temperature, outlet temperature, tubing temperature, flow rate, and / or filtered or unfiltered flow rate. The humidifier and / or breathing mode of therapy may include, for example, invasive, mask, non-invasive, high flow, Optiflow™, neonatal, anesthesia, or other therapy modes. Derivative or differential values ​​may include errors between measurements and setpoints, filtered or unfiltered values, differences between parameter values, ratios between parameters, Boolean conditions, slopes, and / or integers, mathematical functions, and / or combinations thereof. Setpoint values ​​may include, for example, a humidifier heat source setpoint, an outlet setpoint, or a tube setpoint. Differences between parameter values ​​may include, for example, the difference between two temperature and / or flow sensor readings. Ratios between parameter values ​​may include, for example, the ratio between different sensor readings. Boolean conditions may include, for example, whether a parameter is higher or lower than a threshold. Slopes and / or integers may include, for example, the parameter data being monitored in the near past. Mathematical functions may include, for example, the exponent of the parameter value.

[0095] The humidification system controller may also optionally observe various system parameters as they progress toward a steady state. The controller may predict what the steady state values ​​are likely to be. The prediction may be performed using a model to predict the trajectory of the parameters or other prediction modes. The controller may perform one or more of the passive backflow detection processes described above on the predicted steady state values ​​to predict the likelihood of a backflow condition.

[0096] The controller may also optionally first detect whether external conditions have stabilized. An example of an external condition may include gas flow. The controller may perform a passive transient backflow detection process by looking for patterns in changing and / or unstable system parameters. The system parameters may be one or more of the parameters mentioned above. The controller may use different algorithms for different therapy modes, different flow ranges, and / or other parameters. The humidification system may include a memory that stores a look-up table that includes a set of known behaviors that may distinguish between backflow and forward flow conditions. The controller may be configured to identify whether the current condition is closer to a backflow or forward flow behavior in the table. For conditions not in the table, the controller may make an inference based on the table. The controller may predict the likelihood that a backflow condition exists.

[0097] The table below provides example parameters at steady state for reverse and forward flow conditions, and shows that these example parameters may be useful in an algorithm for identifying a reverse flow or setup error condition, because the difference in values ​​at steady state for reverse and forward flow conditions is large enough to suggest with reasonable confidence that they may be due to some setup error and / or reverse flow condition, rather than all being due to normal measurement error, therapy conditions, flow rate, and / or ambient conditions.

[0098] [Table 1]

[0099] 15A-15B show examples of patterns of changing and / or unstable system parameters. As shown in Figs. 15A and 15B, the temperature at the humidifier outlet approaches and eventually reaches the outlet setpoint temperature in forward flow. The temperature at the humidifier outlet does not reach or approach the outlet setpoint temperature in reverse flow. This may be due to gas flowing from a source other than expected. For example, the tube temperature may be lower than its setpoint temperature when gas flows from the gas source rather than from the humidifier during reverse flow, or from the patient's exhalation. This may also be because the gas is heated by a heater downstream of the sensor rather than upstream, resulting in a temperature higher or lower than the setpoint temperature, e.g., the upstream temperature may be higher than the setpoint because gas is heated by a respiratory conduit heat source during reverse flow.

[0100] If the system detects a backflow condition based on a pattern of unstable parameters, the system may output a backflow error alarm in the manner described above. The controller may be configured to check for a sudden change in flow rate when a backflow condition is detected and / or a backflow error alarm is issued. The controller may disable operation of the alarm if conditions external to the system become unstable. For example, the controller may disable operation of the alarm when a sudden change in flow is detected. The controller may optionally wait until the flow and / or other unstable external conditions stabilize. The controller may resume the passive backflow detection process described above.

[0101] 16 illustrates an example passive backflow detection process 1620 based on one or more detected parameters during a transient state. Once the backflow detection process is initiated at 1622, the controller may receive transient state inputs from various sensors and / or system parameters as described herein at step 1623. Example monitored parameters may include, for example, humidifier inlet temperature, humidifier outlet temperature, humidifier outlet set point, flow rate, humidifier heat source power, and / or tube temperature.

[0102] In step 1624, the controller may combine various sensor inputs and / or system parameters using a specific algorithm to calculate a backflow prediction number. The process may advantageously increase the reliability of the backflow prediction by combining parameters that individually may predict a backflow condition less reliably.

[0103] The process may evaluate, for example, the humidifier inlet temperature, the absolute value of the humidifier outlet temperature error (the difference between the measured humidifier outlet temperature and the set point), the ratio of flow rate to humidifier heat source power, the ratio of the measured humidifier inlet temperature to the humidifier outlet set point, and the ratio of the measured humidifier inlet temperature to the measured tube temperature. Those skilled in the art will recognize from the disclosure herein that other ratios may be used. One example algorithm may include, for example, * Humidifier inlet temperature +B * Humidifier outlet temperature - Humidifier outlet set point +C * (Flow rate ÷ Humidifier heat source power) + D * (humidifier inlet temperature ÷ humidifier outlet set point) + E * A backflow prediction number can be obtained by calculating (Humidifier Inlet Temperature / Tube Temperature)+F, where A, B, C, D, E, and F can be coefficients. The coefficients can be estimated empirically, experimentally, and / or otherwise using the learning software. For example, the learning software can estimate one or more of the coefficients from multiple backflow data sets and multiple forward flow data sets. The reverse and / or forward data sets can include different external conditions, e.g., flow rate, ambient temperature, or other. The coefficients can vary depending on the parameters and / or data sets provided to the learning software.

[0104] The process may also evaluate, for example, filtered or unfiltered flow rate, the absolute value of the humidifier outlet temperature error (the difference between the measured humidifier outlet temperature and the set point), the ratio of the measured humidifier inlet temperature to the measured tube temperature, and the ratio of the filtered or unfiltered power to at least a portion of the inlet conduit heat source ("inlet conduit heat source power") to the humidifier heat source temperature. Those skilled in the art will recognize from the disclosure herein that other ratios may be used. An example algorithm may be, for example, G * Filtered or unfiltered flow rate + H * |Humidifier outlet temperature - Humidifier outlet set point|+I * (Humidifier inlet temperature / Tube temperature) + J * A backflow prediction number can be obtained by calculating (filtered or unfiltered inlet conduit heat source power / humidifier heat source temperature), where G, H, I, J are coefficients that can be empirically estimated. For example, G, H, I, and J can be estimated in a similar manner as A, B, C, D, E, and F described above.

[0105] At step 1625, the controller can determine whether the predicted number is greater than zero. If the predicted number is greater than zero, the controller can output an indication that a reflux condition exists at step 1630. If the predicted number does not exceed zero, reflux is not detected at step 1640. The system can output an indication that a reflux condition is not detected at step 1640, output no indication, and / or initiate ventilation and / or humidification therapy or continue its current ventilation and / or humidification therapy. Different thresholds can be used to indicate a reflux condition other than a predicted number greater than zero. For example, a number equal to or less than zero can indicate forward flow. Any number between 0 and 100 can indicate a possible reflux condition, with higher numbers indicating a more likely reflux condition. Additionally, a counter and / or cumulative value over time can be used to build confidence. In one example, the system may require the predicted number to exceed a threshold for a period of time to trigger a reflux alarm.

[0106] In other instances, reflux may be detected by monitoring only one parameter, for example, if the flow sensor reading is significantly higher than expected, a reflux condition may be present.

[0107] Although the passive and active processes are described herein with respect to a backflow condition in a humidifier and / or inlet conduit, such as the humidifier 20 and / or inlet conduit 40 as shown in Figures 2A-D, the processes can be used in various embodiments to detect backflow conditions and connection errors at various locations in the humidification system. Additionally, one process can be used to verify whether the other process has correctly identified an indication of a backflow condition. The system can switch between passive and active detection processes and / or between various processes when the system is in a passive or active detection mode.

[0108] Other sensors may alternatively or additionally be used to detect backflow, such as using the directional flow sensors mentioned above, differential pressure sensors, laser Dopplers, ultrasonic transducers, inlet and / or outlet humidity sensors, and / or mechanical sensors such as flaps, levers, or turbines.

[0109] If the humidification system detects multiple errors, the system can first output a backflow alarm. The multiple errors can include a backflow error and a water out error. The backflow condition may need to be corrected before other errors, such as a water out error, can be detected more reliably. The system can improve the speed of alarm recovery by disabling alarm action when a sudden change in flow rate is detected.

[0110] Detecting incorrect connection of expiratory tube In respiratory therapies requiring a dual limb humidification system, it is important to monitor for disconnection of the expiratory conduit heat source in the expiratory conduit. As previously mentioned, dual limb humidification systems can be used in substantially all invasive therapies, approximately half of non-invasive adult therapies, approximately half of neonatal therapies, and possibly some pediatric therapies. Disconnection of the inspiratory conduit heat source in the expiratory conduit can occur during setup and / or during use. Disconnection can be due to improper and / or incomplete connection of the expiratory conduit to the patient interface, or misuse of the expiratory conduit by the user during setup. Disconnection during use can be due to accidental disconnection or user misuse.

[0111] For certain therapy modes, the inhalation conduit heat sources on the inhalation and exhalation conduits are each heated as a single wire ("single-zone heating"). For example, non-invasive adult therapy can be performed with single-zone heating of the inhalation conduit. The humidification system can have two heat source drivers. Each driver can be configured to energize one of the two inhalation conduit heat sources. The two inhalation conduit heat sources can be energized with a low duty cycle and / or minimum power, which one skilled in the art will understand to be any duty cycle high enough to provide power to generate a detectable current when the inhalation conduit heat sources are connected. Low power may be preferred as it is safer and minimizes therapy interruption. This interruption may be shortened by providing power only for a short period of time. The low duty cycle may be within the range of approximately 1-50%, 1-25%, 1-10%, 2-15%, 3-10%, 4-9%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any other suitable duty cycle. A driver for heating the expiratory conduit heat source may apply a voltage to the expiratory conduit heat source. The driver may monitor the current in the electrical circuit. If the current is at or near zero, the driver may output an expiratory conduit heat source disconnection alarm. The alarm may be by the methods described above. If the current is not at or near zero, the expiratory conduit heat source is connected to the circuit. The system may also detect a disconnection of the expiratory conduit heat source by detecting the presence of a circuit ID register when the hardware and / or software controller applies power to the expiratory conduit heat source. If the system cannot detect the circuit ID register, the system may identify the expiratory conduit heat source as disconnected.

[0112] For certain therapy modes, such as neonatal therapy or other forms of therapy, the expiratory conduit heat source may have more than a single zone heating. FIG. 17A illustrates an example neonatal therapy humidification system 1700. The respiratory humidification system 1700 may include a respiratory circuit 1701, which includes a segmented inspiratory conduit 1702 and an expiratory conduit 1710. The expiratory conduit 1710 may include an expiratory heater wire 1712. The segmented inspiratory conduit 1702 may include first and second segments 1702a and 1702b. The first segment 1702a may include a first inspiratory heater wire 1706a. The second segment 1702b may include a second inspiratory heater wire 1706b.

[0113] The segments 1702a, 1702b of the intake rim can be interconnected to form one conduit for gas delivery. The first segment 1702a can be the portion of the intake conduit 1602 that is outside the incubator 1708, and the second segment 1702b, or incubator extension, can be the portion of the intake conduit 1702 that is within the incubator 1708. The incubator 1708 can create different temperatures along different segments of the intake conduit 1702, such as in the case of a radiant warmer. The first and second intake heater wires 1706a, 1706b can provide different levels of heat to different segments 1702a, 1702b of the intake conduit 1702 to reduce or prevent condensation and / or control the temperature of the gas delivered to the user.

[0114] The controller 1722 can be configured to switch between controlling the first inhalation heater wire 1706a ("HW1") and controlling the first and second inhalation heater wires 1706a and 1706b ("HW2"). ​​FIG. 17B shows an example circuit diagram 1750 for switching heating of HW1 and HW2 by varying the switching of the inhalation heater wire 1712, HW1, and HW2. The system 1700 can have two drivers for driving the exhalation heater wires 1712, HW1, and HW2. The first driver can energize HW1 and the exhalation heater wire 1712 in parallel. The second driver can energize HW2 and the exhalation heater wire 1712 in parallel. This method of disclosure is useful in situations where the system includes more heater wires than the battery wire drivers.

[0115] To detect disconnection of an expiratory heater wire during use, at least one of the inhalation heater wire drivers can monitor the current in the electrical circuit. The heater wire can have a known resistance or a known resistance with an error. When one of the drivers is activated to apply a voltage to the inhalation heater wire, the active driver can monitor the current in the electrical circuit. The driver can apply a voltage to the expiratory heater wire and HW1 or to the expiratory heater wire and HW2. If the current is not at or near the expected value based on the known voltage and / or if there is an abrupt change in current, one or more of the inhalation heater wires may be disconnected. If the current differs from the expected value by a predetermined error, the current may not be at or near the expected value based on the known voltage. An abrupt change may occur when the change in current exceeds a threshold. The current through the inhalation heater wire may be lower when the expiratory heater wire is properly connected to the circuit than when the expiratory heater wire is disconnected. This may be because a properly connected exhalation heater wire lowers the overall resistance of the circuit.

[0116] If the controller observes a current flow different than expected and / or a sudden change in current (and therefore resistance), the controller can exit the therapy mode. The controller can output an indication that the therapy mode has been exited. The controller can proceed to use the one inlet heater wire per driver detection process described above as if the inlet heater wire provided single-zone heating. Specifically, the controller can switch to a configuration where it reconnects the heater wire drivers to one heater wire per driver and observes the current through the expiratory heater wire.

[0117] The humidification system may have an exhalation conduit heat source disconnection alarm setting, e.g., the exhalation heater wire of FIG. 17A, that is adjustable based on therapy mode. The exhalation conduit heat source disconnection alarm may remain activated in therapies that use a dual limb system substantially all the time. The alarm may remain activated by default in some, e.g., dual limb systems for invasive therapies. The exhalation conduit heat source disconnection alarm may be activated at predetermined intervals and / or may remain deactivated in therapies that do not use a dual limb system most of the time. The intervals may be preprogrammed and / or user determined. The alarm may remain deactivated by default in some systems, e.g., non-invasive adult therapies or neonatal therapies.

[0118] Although the present disclosure has been described with respect to specific embodiments and examples, those skilled in the art will appreciate that the disclosure extends beyond the specifically disclosed embodiments, and to other alternative embodiments and / or applications, as well as obvious improvements and equivalents thereof. In addition, while several variations of the disclosed embodiments have been shown and described in detail, other improvements are within the scope of the disclosure and will be readily apparent to those skilled in the art. It is also contemplated that various combinations or subcombinations of specific features of the embodiments and aspects of the disclosure may be made and still fall within the scope of the disclosure. For example, features described above in relation to one embodiment may also be used in different embodiments described herein, and such combinations will still fall within the scope of the disclosure. It should be understood that various features and aspects of the disclosed embodiments may be combined with or substituted for each other to form different modes of the disclosed embodiments. It is therefore intended that the scope of the disclosure herein should not be limited by the specific embodiments described above. Thus, unless otherwise specified or clearly contradicted, each embodiment of the present invention may include, in addition to its basic features described herein, one or more features described herein from each of the other embodiments of the present invention disclosed herein.

[0119] It should be understood that features, materials, properties, or groups described in connection with a particular aspect, embodiment, or example also apply to any other aspect, embodiment, or example described in this section or elsewhere in this specification, unless inconsistent therewith. All of the features disclosed in this specification (including all of the accompanying claims, abstract, and drawings) and / or all of the steps of any method or process so disclosed may be combined in any combination, unless at least some of those features and / or steps are mutually exclusive. Protection is not limited to the details of any of the above-described embodiments. Protection extends to any novel one, or any novel combination, of the features disclosed in this specification (including all of the accompanying claims, abstract, and drawings) or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0120] Moreover, certain features described in the present disclosure in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Furthermore, although features may be described above as functioning in a particular combination, one or more features in a claimed combination can, in some cases, be deleted from the combination, and the combination may be claimed as a subcombination or a variation of the subcombination.

[0121] Additionally, although operations may be illustrated or described herein in a particular order, such operations need not be performed in the particular order illustrated or sequential order, or all operations need not be performed, to achieve desired results. Other operations not illustrated or described may be incorporated into the example method or process. For example, one or more additional operations may be performed before, after, simultaneously with, or during any of the described operations. Additionally, operations may be arranged or ordered differently in other implementations. Those skilled in the art will appreciate that in some embodiments, the actual steps taken in the illustrated and / or disclosed processes may differ from those shown in the drawings. Depending on the embodiment, certain of the steps described above may be omitted and others may be added. Additionally, the features and attributes of certain embodiments disclosed above may be combined in other ways to form other embodiments, all of which are within the scope of the present disclosure. Additionally, the separation of various system components in the above implementations should not be understood as requiring such separation in all embodiments, and it should be understood that the components and systems described may generally be integrated into a single product or packaged into multiple products.

[0122] For purposes of this disclosure, certain aspects, advantages, and novel features have been described herein. Not all of these advantages may be achieved in accordance with any particular embodiment. Thus, for example, a person skilled in the art will recognize that the present disclosure may be implemented or carried out in a manner that achieves one advantage or set of advantages taught herein, but does not necessarily achieve other advantages that may be taught or suggested herein.

[0123] Conditional statements such as "can," "could," "might," or "may" are generally intended to convey that a particular embodiment includes certain features, elements, and / or steps, and other embodiments do not, unless expressly stated otherwise or understood otherwise in the context in which they are used. Thus, such conditional statements are not generally intended to imply that those features, elements, and / or steps are in any way required by one or more embodiments, or that one or more embodiments necessarily include logic for determining whether or not those features, elements, and / or steps should be included or performed in any particular embodiment, with or without user input or prompting.

[0124] As used herein, degree words such as "approximately," "about," "generally," and "substantially" refer to a value, amount, or characteristic that is close to the stated value, amount, or characteristic and still performs a desired function or achieves a desired result. For example, the terms "approximately," "about," "generally," and "substantially" may refer to an amount that is within 10%, within 5%, within 1%, within 0.1%, and within 0.01% of the stated amount. In addition, as used herein, "gradually" has its ordinary meaning and is distinct from a discontinuous change, such as a step change.

[0125] The scope of the present disclosure is not intended to be limited by the specific disclosure of preferred embodiments in this section or elsewhere herein, but may be defined by the claims presented or presented in the future in this section or elsewhere herein. The claim language is to be interpreted broadly based on the language used in the claims, and is not to be limited to the examples described in this specification or during the prosecution of this application, which examples are to be construed as non-exclusive.

Claims

1. 1. A method for detecting reflux in a respiratory humidification system, comprising: using one or more hardware and / or software controllers of the respiratory humidification system to control circuitry configured to supply power to a heating element of the respiratory humidification system to provide a first power to the heating element, the respiratory humidification system further comprising a gas source, a humidifier including an inlet and an outlet, and an inlet conduit including an inlet conduit heat source, the humidifier further comprising a humidifier heat source; comparing a first temperature gradient measured by a first sensor downstream of the heating element with a second temperature gradient measured by a second sensor upstream of the heating element, the first and second sensors being in electrical communication with the one or more hardware and / or software controllers; outputting an indication of a reflux condition on a display of the respiratory humidification system when the second temperature gradient is greater than the first temperature gradient. A method comprising:

2. The method of claim 1 , wherein the heating element comprises the inlet conduit heat source and / or the humidifier heat source.

3. providing second power to the humidifier heat source of the humidifier of the respiratory humidification system when the one or more hardware and / or software controllers provide the first power to at least a heating element separate from the humidifier heat source; receiving sensor data from a humidifier heat source temperature sensor at or near the humidifier heat source, the humidifier heat source temperature sensor being in electrical communication with the one or more hardware and / or software controllers; comparing the temperature gradient at the humidifier heat source to a threshold temperature gradient; outputting an indication of a humidifier out-of-water condition on a display of the respiratory humidification system when the temperature gradient at the humidifier heat source is greater than the threshold temperature gradient.

3. The method of claim 1 or 2, further comprising:

4. 4. The method of claim 1, further comprising controlling a duty cycle to the intake conduit heat source when the one or more hardware and / or software controllers provide the first power to at least the intake conduit heat source before comparing the first temperature gradient to the second temperature gradient.

5. The method of claim 4 further comprising controlling the duty cycle to the intake conduit heat source to 100%.

6. 3. The method of claim 1, further comprising controlling a duty cycle to the humidifier heat source when the one or more hardware and / or software controllers provide the first power to at least the humidifier heat source before comparing the first temperature gradient with the second temperature gradient.

7. The method of claim 6 further comprising deactivating the humidifier heat source.

8. 8. The method of claim 1, further comprising: discontinuing a therapy being performed on the respiratory humidification system when indicating a reflux condition in the respiratory humidification system, the therapy being a respiratory or ventilation therapy or a humidification therapy.

9. 10. The method of claim 8, further comprising outputting an indication of the reflux condition and resuming the therapy after correcting the reflux condition.

10. 9. The method of claim 1, further comprising alerting a user to the indication of the reflux condition.

11. The method of claim 10 , wherein the alerting comprises providing one or more audible alarms, text messages, images, or combinations thereof.

12. The method of claim 10 , wherein the alerting includes providing instructions to resolve the reflux condition.

13. 13. The method of any one of claims 1 to 12, wherein the respiratory humidification system comprises an expiratory conduit.

14. 14. The method of claim 1, further comprising checking for sudden changes in flow rate when outputting the indication of a reflux condition.

15. 15. The method of any one of claims 1 to 14, further comprising checking for a sudden change in flow rate when a backflow error alarm is issued.

16. 16. The method of claim 14 or 15, further comprising disabling the indication of the reflux condition if a sudden change in the flow rate is detected.

17. A respiratory humidification system comprising one or more hardware and / or software controllers according to any one of claims 1 to 16, said controllers executing a method according to any one of claims 1 to 16.

18. 18. A respiratory humidification system according to claim 17, further comprising the humidifier and the inlet conduit.

19. 19. A respiratory humidification system according to claim 17 or 18, wherein the first sensor is located at the outlet of the humidifier and the second sensor is located at the inlet of the humidifier.

20. 19. A respiratory humidification system according to claim 17 or 18, wherein the first sensor is located at the patient end of the inspiratory conduit and the second sensor is located at the outlet of the humidifier.

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