System for determining airway patency

Abstract

To provide methods for monitoring a targeted gas being expired or being expelled from an apnoeic or non-spontaneously breathing patient and determining which part of the patient's airway is blocked.SOLUTION: This invention relates to a method or system for providing an indication or establishment of airway patency of a patient comprising: monitoring at least one targeted gas (e.g. CO2, N2 or may be other gases capable of being detected, monitored, and measured) that is being expired or being expelled from an airway of a patient (e.g. an apnoeic or non-spontaneously breathing patient); and based on measurements of the at least one targeted gas for a certain period of time, providing an indicator as to an output of the measurements of the at least one targeted gas for the period of time, or a determination as to airway patency, or a determination as to a location of a blockage or obstruction in the airway, or combinations of these.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure generally relates to methods and / or devices and / or systems for monitoring target gas being exhaled or expired from an apneic or non-spontaneously breathing patient and for determining whether the patient's airway is unblocked or has patency and / or for determining which portions of the patient's airway are blocked based on measurement of a target gas trace. [Background technology]

[0002] Patients may lose respiratory function while under anesthesia or sedation, or more commonly, during some medical procedures. Prior to a medical procedure, patients may be pre-oxygenated by a medical professional to provide a reserve of oxygen saturation, and this pre-oxygenation is typically performed using a bag and face mask. Once under general anesthesia, the patient must be intubated and ventilated. In some cases, intubation can be completed in less than 60 seconds; in other cases, particularly if the patient's airway is difficult to cross (e.g., due to cancer, severe injury, obesity, or spasms of the neck muscles), intubation can take significantly longer. Pre-oxygenation mitigates the loss of oxygen saturation, but prolonged intubation procedures necessitate interrupting the intubation process and reapplying a face mask to raise the patient's oxygen saturation to an appropriate level. Interruptions to the intubation process may occur several times during a difficult intubation process, which is time-consuming and exposes the patient to significant health risks. After approximately three attempts at intubation, the medical procedure is discontinued.

[0003] If a patient's airway becomes obstructed or occluded (e.g., the airway collapses or an item becomes lodged in the airway), respiratory therapy that may be attempted to administer to the patient to assist breathing may be partially or totally ineffective. In such a situation, the safety of the patient is at risk.

[0004] The reference herein to any prior art is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in the field of endeavor in any country throughout the world. Summary of the Invention [Problem to be solved by the invention]

[0005] An object of some embodiments disclosed herein may be to provide methods and / or apparatus that may solve one or more of the problems discussed above, or that may at least go some way toward providing useful options to the general public or medical professionals. [Means for solving the problem]

[0006] A method or system or device as disclosed herein may be associated with a flow therapy or respiratory assistance system or breathing circuit suitable for use with a patient.

[0007] During patient sedation phases (e.g., patients undergoing surgical procedures and who have been sedated to the extent that the patency of their airways may be compromised), humidified gas may be used to allow for comfortable gas delivery. Humidity helps prevent or minimize drying of the airways, and may therefore prevent or minimize damage to the airways, and may also help to increase or maintain patient comfort while receiving a flow of gas being delivered to one or more of the patient's airways. Such humidified gas may also be used with patients in other situations when the patient is apneic or non-breathing for any reason.

[0008] In a first aspect, monitoring at least one target gas being exhaled or expired from the patient's airway; and based on measurements of at least one target gas over a period of time; a determination regarding airway patency, or Determining the location of a blockage or obstruction in the airway; or A combination of i) and ii) To provide indicators regarding The present invention provides a method or system for providing an indication or establishment of airway patency in a patient, comprising:

[0009] Monitoring the at least one target gas may be by measuring or based on variations in the concentration of the at least one target gas.

[0010] Measurements or measurements are measurements taken adjacent to or inside the patient's mouth or oral cavity or oropharyngeal region; measurements taken adjacent or substantially adjacent to the patient's pharynx, or pharyngeal flow; Measurements taken adjacent to or inside the patient's nose or nasal cavity may be obtained from one or more of:

[0011] The determinable location of the airway blockage or obstruction may be in the upper or lower airway.

[0012] The target gas may be CO2, O2, or N2, or a benign medical tracer gas, or a gas that indicates the concentration of carbon dioxide, O2, or N2.

[0013] The target gas may be a tracer gas (or multiple tracer gases), and the target gas may be nitrogen or a mixture of nitrogen and oxygen, or helium or a mixture of helium and oxygen, or any other inert gas, or an inert gas and oxygen as a mixture, or possibly any suitable gas available that is detectable and measurable may be used as the target gas.

[0014] The target gas may be involved in the delivery of gas to the patient's airways as part of a patient's flow therapy or respiratory support.

[0015] A target gas may be delivered to the patient's airways, and the concentration of the target gas may be measured or monitored for a period of time following delivery.

[0016] The exhaled or expired gas, or at least a portion of the exhaled or expired gas, results from cardiogenic activity or results from the patient's heartbeat.

[0017] Gas flow therapy or respiratory support is administered to the patient's airway via a patient interface, which may be of a type including a tight-fitting or non-tight-fitting interface, and may further include a nasal mask, an oral mask, an oronasal mask, a full face mask, a nasal pillows mask, a nasal cannula, a combination of the above, or any other gas-delivering patient interface system.

[0018] The patient interface includes: Gas flow to the patient's airway Target gas into the patient's airway may deliver one or more of:

[0019] The system or method may further comprise: providing or administering flow therapy or respiratory support to the patient's airway for a period of time to increase the patient's oxygen saturation; Removing, stopping, or reducing flow therapy or respiratory support being provided to a patient for a period of time; providing or delivering gas comprising the target gas to the patient's airway for a period of time to restore the provision or delivery of said flow therapy or respiratory support to the patient's airway; Measuring or taking measurements of the concentration of a target gas in gases exhaled or expired by a patient over a period of time may include:

[0020] The oxygen saturation may be greater than about 95 or 96 or 97 or 98%.

[0021] The removal, cessation or reduction of flow therapy or respiratory assistance may be to reduce the pressure exerted by said flow therapy or respiratory assistance on the patient's airways or lungs, or to allow the patient's lungs to partially collapse under reduced flow or pressure conditions compared to the initial flow or pressure conditions of the flow therapy or respiratory assistance previously provided or administered to the patient.

[0022] The gas may be provided or delivered to at least partially re-inflate the patient's lungs with said gas, including said target gas.

[0023] Measuring the concentration or taking the measurement may not substantially deflate the patient's lungs.

[0024] Measuring the concentration or taking measurements thereof may involve monitoring and tracking fluctuations in the concentration of the target gas in gases exhaled or expired by the patient over a period of time.

[0025] A sensor may be placed adjacent to or inside the patient's mouth or oral cavity or oropharyngeal region to obtain measurements of the target gas being exhaled or exhaled from the patient over a period of time.

[0026] The concentration of the target gas measured over time is correlated with the patient's heart rate or cardiogenic action.

[0027] The flow therapy or respiratory support provided or administered to the patient may be from a gas source that provides a portion of oxygen above ambient or air conditions or above about 20.95% oxygen (on a dry weight basis), and the gas source may be a gas of up to about 100% oxygen. One or more gases of the flow therapy or respiratory support may be humidified.

[0028] The gas may comprise a target gas, which may be one or more of a 50:50 mixture of nitrogen and oxygen, a mixture of helium and oxygen, a mixture of one or more inert gases and oxygen, or any suitable gas that is detectable and measurable and that can be mixed with a gas suitable for the patient to breathe.

[0029] Gases provided or delivered to the patient's airways may be humidified.

[0030] Flow therapy or respiratory assistance may be provided or administered to the patient's nares, and pressure may be measured or measurements may be taken in the patient's airway (measuring pressure or taking measurements may use a sensor placed above the larynx), and the pressure of the patient's airway measured above the patient's larynx may contribute to a determination of pharyngeal airway patency.

[0031] Flow therapy or respiratory assistance may be provided or administered via the patient's nares, with a gas sensor placed at or adjacent to or inside the patient's mouth or oral cavity or oropharyngeal region to take measurements of a target gas being exhaled or expired from the patient over a period of time, when the target gas is CO2, and to measure: the concentration of CO2 fluctuates over time, the concentration of CO2 measured by the gas sensor rising from a base concentration to a peak concentration and then substantially returning to said base concentration, said peak concentration being substantially synchronized with the patient's heartbeat or cardiogenic activity (such conditions may indicate that the patient's soft palate or pharyngeal airway is patent or open, and that the patient's trachea is patent or open); the concentration of CO2 fluctuates over time, the concentration of CO2 measured by the gas sensor increases from a first base concentration to a first peak concentration, and the CO2 concentration decreases from the first peak concentration to a second base concentration that is greater than the first base concentration, and over a period of time (two or more patient heartbeats or cardiogenic activity), the subsequent base concentrations returning from the subsequent peak concentrations are greater than the preceding base concentration over time and / or are substantially greater than the first base concentration over time, and the first, second, and subsequent peak concentrations are substantially synchronized with the patient's heartbeat or cardiogenic activity (such conditions may indicate that the patient's soft palate or pharyngeal airway is closed or obstructed or blocked, and that the patient's trachea is patent or open); the concentration of CO2 does not fluctuate over time or is a time-invariant concentration, and the concentration of CO2 measured by the gas sensor remains at a base concentration, which may be asynchronous or synchronous with the patient's heart rate or cardiogenic activity; One or more of the following is measured:

[0032] Flow therapy or respiratory assistance may be provided or administered via the patient's nares, with a gas sensor placed at or inside the patient's mouth or oral cavity or oropharyngeal region to take measurements of a target gas being exhaled or exhaled from the patient for a period of time, and after providing the target gas to the patient, to: the concentration of the target gas fluctuates over time, the concentration of the target gas measured by the gas sensor increasing from a base concentration to a first peak concentration and then substantially returning to said base concentration, with each subsequent peak concentration being substantially less or decreased compared to the immediately preceding peak concentration, each of said peak concentrations being substantially synchronized with the patient's heartbeat or cardiogenic activity (such conditions may indicate that the patient's soft palate or pharyngeal airway is patent or open, and that the patient's trachea is patent or open); the concentration of the target gas fluctuates over time, and the concentration of the target gas measured by the gas sensor increases from a first base concentration to a concentration that substantially matches the concentration of the target gas in the patient's ambient gas (e.g., air or operating room ambient gas conditions) and is exposed to the gas sensor via the patient's oral cavity (such conditions may indicate that the patient's soft palate or pharyngeal airway is closed or obstructed or blocked, and that the patient's trachea is patent or open); the concentration of the target gas decreases from an initial peak concentration to a base concentration, and the concentration of the target gas measured by the gas sensor remains substantially at the base concentration, which may be constant over time or may be asynchronous or synchronous with the patient's heartbeat or cardiogenic activity (such conditions may indicate that the patient's soft palate or pharyngeal airway is patent or open, and that the patient's trachea is closed or obstructed or blocked); One or more of the following is measured:

[0033] Flow therapy or respiratory support may be provided at a constant flow rate.

[0034] The flow of gas may be provided or delivered to the patient's airway.

[0035] The gas flow may be provided or delivered to the patient in an oscillatory flow, or a superimposed oscillation of a positive gas flow to the patient may be delivered.

[0036] The oscillatory flow may be delivered to enhance and / or stimulate exhalation or expiration of at least one target gas, such that measurements of the at least one target gas over a period of time when the patient's airway is unobstructed or patent vary in response to the oscillatory flow.

[0037] The method may include determining a correlation between the delivered flow rate and the measurement value of at least one target gas as a monitoring gas signal, and the indicator may be based on the correlation, and the monitoring gas signal may be based on the concentration of the target gas.

[0038] The flow may be the sum of at least two oscillating waveforms (which may be substantially sinusoidal).

[0039] The flow may be substantially sinusoidal and the flow signal may be based on a sine function.

[0040] The flow has the following signal characteristics: a frequency, which may be substantially repeated over a period of time; amplitude, a wave shape, a waveform that may be substantially repeated over a period of time; phase may have one or more of:

[0041] The correlation is Flow frequency, flow amplitude, a flow waveform, which may be substantially repeating over a period of time; Flow phase, Changes in flow over time (e.g., the decay or driving of the flow) and one or more of the frequency (or frequency range) of the monitored gas signal, the amplitude of the monitored gas signal, the amplitude of the monitored gas signal at a particular frequency, the waveform of the monitoring gas signal; the phase of the monitored gas signal, Changes in monitored gas signals over time The method may be based on a comparison with one or more of:

[0042] The correlation may be based on a comparison of the frequency of the flow with the frequency (or frequency range) of the monitored gas signal.

[0043] The correlation is the edge or transition of the signal in the flow wave shape, local maxima or minima or inflection points of the flow waveform; The gradient of a portion of the flow or the gradient at a discrete point, A number of peaks and / or troughs in flow within a given or predetermined period of time. and one or more of a subsequent signal edge or transition portion of the monitor gas signal waveform, which may be located within a period of time after the signal edge or transition portion of the flow waveform; a subsequent maximum, minimum or inflection point of the waveform of the monitored gas signal, when the subsequent maximum, minimum or inflection point of the waveform of the monitored gas signal may be located within a period of time after an edge or transition portion of the signal of the flow waveform; the slope of a subsequent portion or a discrete point of the waveform of the monitoring gas signal when the slope of a portion or a discrete point of the waveform of the monitoring gas signal may be located within a certain period of time after the slope of a portion or a discrete point of the waveform of the flow; Multiple peaks and / or troughs in the monitored gas signal within a given or predetermined period. The method may be based on a comparison with one or more of:

[0044] The edges of the signal are Rising edge or rising portion Falling edge or falling portion It can be one or more of:

[0045] When the correlation between delivered flow and the monitored gas signal is above a certain threshold, the patient's airway may be determined to be unobstructed or substantially unobstructed.

[0046] When at least one component of the frequency (or frequency range) of the monitored gas signal substantially matches the frequency of the flow, and when said match of frequency is above a certain threshold, the patient's airway may be determined to be unobstructed or substantially unobstructed.

[0047] The level of patency of the patient's airway may be proportional to the strength of the correlation between the delivered flow and the monitored gas signal.

[0048] When the correlation between delivered flow and the monitored target gas falls below a certain threshold, the patient's airway may be determined to be obstructed or substantially obstructed.

[0049] When at least one component of the frequency of the monitored gas signal is not similar to the frequency of the flow and / or the amplitude of the signal at said frequency is similar and below a certain threshold, the patient's airway may be determined to be obstructed or substantially obstructed.

[0050] The monitoring or target gas may be produced as a result of gas exchange in the patient's lungs, and the flow acts to stimulate exhalation or expiration of the monitoring gas (the patient need not be spontaneously breathing) or to enhance or augment gas exchange resulting from cardiogenic pulses occurring within the patient's body.

[0051] The correlation may be determined by one or more of Monte Carlo analysis, and / or spectral analysis, and / or fast Fourier transform. In one form, the correlation may be determined using sequential Monte Carlo analysis, and the correlation is used to determine an index of airway patency.

[0052] The target gas measurements may be instantaneously derived measurements or real-time derived measurements.

[0053] The patient may be an apneic or non-breathing patient.

[0054] A signal or output may be provided, the signal or output being associated individually with any one or combination of the indicators.

[0055] The signal may be used to generate a warning or alarm, whether it is one or a combination of one or more of the following: audible, tactile, visual.

[0056] The method or system may include a sensor configured to detect gases (such as the target gas) exhaled or expired from the patient, which may be a gas sensor or a capnography device.

[0057] A gas analyzer may be provided in communication with the gas sensor.

[0058] An electronic controller may be provided in communication with the gas sensor.

[0059] An electronic controller may determine a correlation between the target gas and the delivered flow rate.

[0060] The electronic controller may process the measurements or one or more outputs of the gas sensor or capnography device to determine the waveform of the exhaled or expired gas.

[0061] The controller may be further configured or adapted to process measurements or one or more outputs of the gas sensor or capnography device, and the controller may be further configured or adapted to apply a correction factor or compensation to account for the particular flow rate of gas being delivered to the patient.

[0062] Flow therapy or respiratory assistance may be delivered to one or more nostrils of a patient (or to a patient's nasal passages).

[0063] The patient interface may be of a type including a tight-fitting or non-tight interface, and may further include a nasal mask, an oral mask, an oronasal mask, a full face mask, a nasal pillow mask, a nasal cannula, a combination of the above, or any other gas-carrying patient interface system.

[0064] Flow therapy or respiratory support may be delivered to the patient's airway at a flow rate of at least about 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, or 150 liters per minute (LPM) or more; or may be selected between any of these values (e.g., about 40 to about 80, about 50 to about 80, about 60 to about 80, about 70 to about 80 LPM); the delivered gas may be delivered in a fully saturated or humidified condition, or the saturated or humidified gas may be blended with other gases (whether target gases or non-target gases) for delivery or delivery to the patient interface or patient, and the target gas may be included in the gas providing flow therapy or respiratory support to the patient.

[0065] Therefore, according to a second aspect disclosed herein, - monitoring at least one target gas (which may be, for example, CO2, N2, or other gas capable of being detected, monitored, and measured) being exhaled or expired from the airway of a patient (e.g., a patient who is apneic or non-spontaneously breathing); and - based on measurements of at least one target gas over a period of time; i. Output of measurements of at least one target gas for that period; or ii. A determination regarding airway patency; or iii. A determination as to the location of a blockage or obstruction in the airway; or iv. a combination of i) and ii), or v. a combination of i) and iii), or vi. a combination of ii) and iii), or vii. Combination of i), ii), and iii) Provides indicators about A method or system for:

[0066] In item i), the output may be a display of the trace of the target gas. Such a trace may be displayed on a user interface such as a screen (e.g., a GUI) and may be updated in real time or at a suitable refresh rate to ensure that the clinician is provided with information regarding the output of said target gas.

[0067] Monitoring the at least one target gas may be by measuring or based on variations in the concentration of the at least one target gas.

[0068] Measuring or measurements are - measurements taken at or inside the patient's mouth or oral cavity or oropharyngeal area, - measurements taken at or substantially adjacent to the pharynx, or the pharyngeal stream; - Measurements taken at or inside the patient's nose or nasal passages may be obtained from one or more of:

[0069] A signal or output may be provided, the signal or output being associated individually with any one of i) to vii), or a combination thereof.

[0070] The signal or output, whether audible, tactile, or visual, or a combination of one or more thereof, may be used to generate a warning or alarm. For example, an audible alarm may be emitted, or the user-wearable device may begin to vibrate, or may be illuminated with a light, or a light may be switched on or off, or an image may be provided in a graphical user interface (GUI). Such a warning or alarm may be used to alert a medical professional or assistant to a change in status of i), ii), or iii) (e.g., the patient's airway may be patent but may collapse, or may become obstructed and lose patency, or the location of the blockage or blockage in the patient's airway may change, which may have implications for medical professionals working on the patient or responsible for assisting the patient's breathing). For example, if a blockage in the patient's airway is determined, an alarm or warning may be emitted to alert or inform persons associated with the patient's care.

[0071] A warning or alarm or indication may be issued regarding the patency of a patient's airway, for example, if an obstruction or clog or occlusion of the airway is detected or if the patency of said patient's airway is compromised. Different warnings or alarms or indications may be provided in relation to different locations of such obstruction or clog or occlusion, for example, if the upper airway is obstructed or clogged or occluded there may be a warning or alarm or indication such as a first audible or first tactile or first visual output, and if the lower airway is obstructed or clogged or occluded there may be a second warning or alarm or indication such as a second audible or second tactile or second visual output.

[0072] The determinable location of the blockage or obstruction or obstruction in the airway may be in the upper airway or the lower airway.

[0073] A determination may be made of additional or different locations of blockage or obstruction or occlusion based on processing of the output of the target gas or tracer gas.

[0074] The target gas may be CO or N or a benign medical tracer gas (e.g., argon), or another gas or gases that can be detected and measured over a period of time to determine a signature of the target gas. Any suitable inert gas, such as helium, argon, or neon, may be used as the tracer gas, provided that the gas is non-toxic, and such gases may remain in the lungs because they are not very dense. A suitable target gas may be delivered as a mixture of O and an inert gas.

[0075] The target gas may be a tracer gas (or multiple tracer gases) such as nitrogen (e.g., a mixture of nitrogen and oxygen) or helium (e.g., a mixture of helium and oxygen), or any other inert gas (e.g., such an inert gas and oxygen as a mixture). Alternatively, any suitable gas available that is detectable and measurable may be used as the target gas.

[0076] The target gas may be involved in the delivery of gas to the patient's airways as part of flow therapy or respiratory support to the patient.

[0077] A target gas may be delivered to the patient's airway, and the concentration of the target gas may be measured or monitored for a period of time following delivery, which may be the entire period during which the patient is receiving flow therapy or respiratory assistance, or the entire period during which the patient is apneic or non-spontaneously breathing.

[0078] The concentration of the target gas over a period of time can be analyzed, and based on the analysis, a determination can be made regarding the location of airway patency and / or the location of a blockage or obstruction within the airway can be determined.

[0079] The method or system may include a sensor, which may be configured to detect gases (e.g., the target gas) exhaled or expired by the patient. The sensor may be a gas sensor or a capnography device.

[0080] A gas analyzer may be provided in communication with the gas sensor.

[0081] A controller may be provided in communication with the gas sensor.

[0082] The controller may process the measurements or one or more outputs of the gas sensor or capnography device to determine the waveform of the exhaled or expired gas.

[0083] A controller may be further configured or adapted to process measurements or one or more outputs of the gas sensor or capnography device, and the controller may be further configured or adapted to apply a correction factor or compensation to account for the particular flow rate of gas being delivered to the patient. For example, the particular flow rate of gas being delivered to the patient, if sufficiently high, may interfere with or add "noise" to the signal or output generated by the sensor in response to sensing or detecting gas being exhaled or expired from the patient.

[0084] The method or system may provide compensation to account for interference with or addition of noise to the measurement or sensing of gas exhaled or expired from the patient (e.g., target gas) to compensate for the flow rate of gas being delivered to the patient's airway.

[0085] The exhaled or expired gas may result from cardiogenic activity or may result from the patient's heartbeat.

[0086] A flow of gas for flow therapy or respiratory assistance may be delivered to the patient's airway.

[0087] The target gas may be delivered to the patient's airway via a patient interface as part of a flow therapy or respiratory assist gas flow being delivered to the patient's airway.

[0088] The flow therapy or respiratory support may be administered to one or more of the patient's nostrils (or the patient's nasal passages). Alternatively or additionally, the flow therapy or respiratory support may be administered to the patient's oral cavity.

[0089] The patient interface may include a tight-fitting or non-tight interface and may include a nasal mask, an oral mask, an oronasal mask, a full face mask, a nasal pillows mask, a nasal cannula, a combination of the above, or some other gas delivery system.

[0090] The flow therapy or respiratory support administered to the patient's airway can be at a flow rate of at least about 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, or 150 liters per minute (LPM) or greater; or can be selected between any of these values (e.g., about 40 to about 80, about 50 to about 80, about 60 to about 80, or about 70 to about 80 LPM). The gas delivered can be delivered in a fully saturated or humidified condition, or the saturated or humidified gas can be blended with other gases (whether targeted or non-targeted) for delivery to the patient interface or patient. The targeted gas can be included in the gases used to provide flow therapy or respiratory support to the patient.

[0091] With respect to the methods or systems disclosed herein, the flow rate of gas provided by flow therapy or respiratory assistance may be a constant flow rate, or alternatively, an oscillating or circulating flow may be provided.

[0092] The method or system comprises: - providing or administering flow therapy or respiratory support to the patient's airway for a period of time to increase the patient's oxygen saturation (which may be to an oxygen saturation of greater than about 95 or 96 or 97 or 98%); - removing, ceasing or reducing flow therapy or respiratory assistance being provided to the patient for a period of time (which may be to reduce the pressure exerted by said flow therapy or respiratory assistance on the patient's airways or lungs, or to allow the patient's lungs to partially collapse under conditions of reduced flow or pressure relative to the initial flow or pressure conditions of the flow therapy or respiratory assistance previously provided or delivered to the patient); - providing or delivering gas comprising a target gas to the patient's airways for a period of time, optionally to at least partially re-inflate the patient's lungs with said gas comprising said target gas; - restoring the provision or delivery of said flow therapy or respiratory support to the patient's airway (which may not substantially allow said patient's lungs to collapse); - measuring or taking measurements of the concentration of the target gas in gases exhaled or expired by the patient over a period of time (which may include monitoring and tracking variations in the concentration of the target gas in gases exhaled or expired by the patient over a period of time); may include:

[0093] The sensor may be placed at or inside the patient's mouth or oral cavity or oropharyngeal region to take measurements of the target gas being exhaled or exhaled by the patient over a period of time.

[0094] The concentration of the target gas measured over time can be correlated with the patient's heart rate or cardiogenic activity.

[0095] The flow therapy or respiratory support provided or administered to the patient may be from a gas source providing an amount of oxygen of about 90% or more, or the gas source may be air. The gas source may be supplemented with additional oxygen. One or more gases of the flow therapy or respiratory support may be humidified.

[0096] The gas, including the target gas, may be a 50:50 mixture of nitrogen and oxygen. Alternatively, it may be a mixture of helium and oxygen, or any other inert gas and oxygen. Alternatively, any suitable detectable and measurable gas may be used, which may be mixed with a gas suitable for the patient to breathe. Alternatively, the target gas may be a mixture comprising less than about 50% O, with a minimum of about 5% O. The gas, including the target gas, may be humidified.

[0097] Flow therapy or respiratory assistance may be provided or administered to the patient's nares and may measure or take measurements of the pressure in the patient's airway (which may be measured or taken using a sensor placed above the larynx). The pressure in the patient's airway measured above the patient's larynx may contribute to determining the patency of the pharyngeal airway.

[0098] Flow therapy or respiratory assistance may be provided or administered via the patient's nares, and a gas sensor may be placed at or inside the patient's mouth or oral cavity or oropharyngeal region to take measurements of a target gas being exhaled or expired from the patient over a period of time, when the target gas is CO2, and - the concentration of CO2 fluctuates over time, the concentration of CO2 measured by the gas sensor rising from a base concentration to a peak concentration and then substantially returning to said base concentration, said peak concentration being substantially synchronized with the patient's heartbeat or cardiogenic activity (such conditions may indicate that the patient's soft palate or pharyngeal airway is patent or open, and that the patient's trachea is patent or open); - the concentration of CO2 fluctuates over time, the concentration of CO2 measured by the gas sensor increasing from a first base concentration to a first peak concentration, and said CO2 concentration decreasing from said first peak concentration to a second base concentration that is greater than the first base concentration, and over a period of time (two or more patient heartbeats or cardiogenic activity), the subsequent base concentrations returning from the subsequent peak concentrations are greater than the preceding base concentrations over time and / or are substantially greater than the first base concentration over time, and said first, second and subsequent peak concentrations are substantially synchronized with the patient's heartbeat or cardiogenic activity (such conditions may indicate that the patient's soft palate or pharyngeal airway is closed or obstructed or blocked, and that the patient's trachea is patent or open); - the concentration of CO2 does not fluctuate over time or is a constant concentration over time, and the concentration of CO2 measured by the gas sensor remains at a base concentration, which may be asynchronous or non-synchronous with the patient's heartbeat or cardiogenic activity (such conditions may indicate that the patient's soft palate or pharyngeal airway is patent or open, and that the patient's trachea is closed or obstructed or blocked); One or more of the following is measured:

[0099] The target gas may be a gas that is not consumed by the patient or the patient's respiratory system.

[0100] Flow therapy or respiratory assistance may be provided or administered via the patient's nares, and a gas sensor may be placed at or inside the patient's mouth or oral cavity or oropharyngeal region to take measurements of a target gas being exhaled or exhaled from the patient for a period of time, and after providing the target gas to the patient, the gas sensor may measure: - the concentration of the target gas fluctuates over time, the concentration of the target gas measured by the gas sensor increasing from a base concentration to a first peak concentration and then substantially returning to said base concentration, and each subsequent peak concentration being substantially less or decreased compared to the immediately preceding peak concentration, each of said peak concentrations being substantially synchronized with the patient's heartbeat or cardiogenic activity (such conditions may indicate that the patient's soft palate or pharyngeal airway is patent or open, and that the patient's trachea is patent or open); - the concentration of the target gas fluctuates over time, and the concentration of the target gas measured by the gas sensor increases from a first base concentration to a concentration that substantially matches the concentration of the target gas in the patient's ambient gas (e.g., air or operating room ambient gas conditions) and that is exposed to the gas sensor via the patient's oral cavity (such conditions may indicate that the patient's soft palate or pharyngeal airway is closed or obstructed or occluded, and that the patient's trachea is patent or open). - the concentration of the target gas decreases from an initial peak concentration to a base concentration, and the concentration of the target gas measured by the gas sensor remains substantially at the base concentration, said base concentration being constant over time or being asynchronous or synchronous with the patient's heartbeat or cardiogenic activity (such conditions may indicate that the patient's soft palate or pharyngeal airway is patent or open, and that the patient's trachea is closed or obstructed or occluded); One or more of the following is measured:

[0101] Flow therapy or respiratory support may be delivered at a constant flow rate. Alternatively, flow therapy or respiratory support may be delivered to the patient at an oscillatory (actual) flow rate or with superimposed oscillations. Oscillatory flow may also be delivered to augment exhalation of CO2 or tracer gas.

[0102] According to the present disclosure herein, high-flow gas delivered by a high-flow therapy or respiratory support method or device can be generated to include various components with one or more parameters (e.g., flow rate) that can be adjusted, including oscillating. Each parameter can be adjusted independently or dependently on other parameters, thereby providing a fluctuating gas flow (variable gas flow parameter). The fluctuating gas flow (with oscillation) can aid in the removal of gases (e.g., exhaled or exhaled CO2 or other gases, including, for example, removal of target gases or benign tracer gases) and can aid in oxygen administration or the provision or delivery of other gases (e.g., target gases or benign tracer gases) to the patient's airway or respiratory system. By way of example, the gas flow can include a non-oscillating base flow component combined with one or more oscillating flow components, each at a different frequency, thereby generating a fluctuating overall gas flow waveform. The flow therapy device can be controlled through valves, blower controllers, and / or other modulation devices to generate the flow components. PCT Application No. PCT / IB2016 / 051820 describes the use of oscillatory components and is incorporated herein by reference in its entirety.

[0103] The method or system may include a high flow gas source, a proportional valve that produces an oscillating waveform, or an oscillator arrangement. The system may further include a controller for controlling the proportional valve or the gas source or the humidifier.

[0104] Because relatively high gas delivery flow rates may be used in the embodiments or configurations described herein, the gas being delivered or delivered to a user or patient may be delivered to different portions of the user's or patient's airway, and the gas being delivered may reach the patient's lungs or any portion of the respiratory system.

[0105] For example, according to various embodiments described herein, the flow rate of gas supplied or provided to an interface or via a system, such as to provide flow therapy or respiratory assistance, can include, but is not limited to, flows of at least about 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, or 150 liters per minute (LPM) or more, and a useful range can be selected between any of these values (e.g., about 40 to about 80, about 50 to about 80, about 60 to about 80, about 70 to about 80 LPM). The supplied gas can be delivered in a fully saturated or humidified condition, or the saturated or humidified gas can be blended with other gases for supply or delivery to the patient interface or patient.

[0106] Such relatively high flow rates of gas may assist in providing the supplied gas to a user's airway or to different portions of a user's airway, for example, such flow rates may enable delivery of such gas to upper or lower respiratory tract regions. The upper respiratory tract region generally includes the nasal cavity, pharynx, and larynx, while the lower respiratory tract region generally includes the trachea, primary bronchi, and lungs.

[0107] The flow of gas may be an oscillatory flow of gas, with the trailing edge (or trailing flow rate) of the oscillatory flow causing a drop in pressure in the patient's airway; and If the patient's airway is at least partially patent, the target gas is exhaled from the patient's airway or the target gas is detected in gas exhaled from the patient's airway; If the patient's airway is patent, then substantially no target gas is exhaled from the patient's airway, or no target gas is detected exhaled from the patient's airway.

[0108] The amplitude, or rise time (or slope of the rise), or fall time (or slope of the fall) of the target gas concentration corresponds to the degree to which the patient's airways are patent.

[0109] The method or system includes measuring the concentration of the target gas, and the patient's airway is determined to be at least partially patent when the concentration of the gas increases after the falling edge (or falling flow rate or falling pressure).

[0110] The concentration of the target gas can be measured in the period between two flow peaks of the oscillatory flow (or oscillatory pressure?).

[0111] The concentration of the target gas may be measured between subsequent pairs of flow (or pressure) peaks of said oscillatory flow (or oscillatory pressure).

[0112] The provided or delivered oscillatory (real) flow rate (or flow pressure) is determined by the following oscillatory characteristics: amplitude, frequency (or period), wavelength may have one or more of:

[0113] The vibration characteristics may vary over time.

[0114] The determination of airway patency may be based on a correlation factor, which is based on a comparison of oscillatory characteristics of the oscillatory flow with characteristics of one or more target gases.

[0115] The property of the target gas may relate to the concentration (or an indicator thereof) of the target gas.

[0116] The one or more target gas properties may be measured instantaneously or are real-time measurements.

[0117] One or more target gas properties may be measured at a time corresponding to a trough of the oscillatory flow rate (or oscillatory pressure of the delivered flow) or at a point between two peaks.

[0118] One or more properties of the target gas may be measured over a period of time.

[0119] The properties of the target gas may change over time.

[0120] The target gas characteristics are: amplitude, frequency (or period), wavelength, phase It can be one or more of:

[0121] The tracer gas may be introduced into the oscillating flow for a first period of time, after which the introduction of the tracer gas is discontinued and the concentration of the tracer gas is measured over a second period of time.

[0122] Determination of airway patency is - comparing or correlating (possibly over said second time period) said oscillatory characteristics of said oscillatory flow (or oscillatory pressure of the delivered flow) with target gas characteristics of said target gas. - a rate of decay of the concentration of the target gas over said second period of time. The method may be based on one or more of the following:

[0123] In a third aspect of the present invention there is provided a method of determining the status of an airway in a patient, the method comprising: delivering a flow (or possibly a pressure) of gas to the patient, said flow of gas being delivered in accordance with a flow signal; and monitoring the concentration of at least one gas being exhaled or expired from the patient's airway as a monitored gas signal, and determining a correlation between the delivered flow signal and the monitored gas signal; and characterizing a condition of the patient's airway based on said correlation. Includes:

[0124] The flow may be an oscillatory flow.

[0125] The flow may vary over time.

[0126] The flow may include a flow offset or bias.

[0127] The flow signal may be delivered with a first shape or profile (which shape or profile may be repeated), and the correlation is based on a comparison of the first shape or profile of the flow signal with a second shape or profile (or subsequent shape or profile) of the monitored gas signal.

[0128] The correlation may be based on a comparison of waveform characteristics of the flow signal and waveform characteristics of the monitor gas signal.

[0129] The flow may be configured to enhance or augment gas exchange resulting from cardiogenic pulses occurring within the patient.

[0130] The flow signal may be the sum of at least two oscillatory waveforms (which may be substantially sinusoidal).

[0131] The flow signal may be substantially sinusoidal, and the flow signal may be based on a sine function.

[0132] The flow signal has the following signal characteristics: a frequency, which may be substantially repeated over a period of time; amplitude, a waveform, which may be substantially repeating over a period of time; phase may have one or more of:

[0133] The correlation is the frequency of the flow signal, the amplitude of the flow signal, a flow signal waveform, which may be substantially repeating over a period of time; the phase of the flow signal, Changes in the flow signal over time (e.g., attenuation or promotion of the signal) and one or more of the frequency (or frequency range) of the monitored gas signal, the amplitude of the monitored gas signal, the amplitude of the monitored gas signal at a particular frequency, the waveform of the monitoring gas signal; the phase of the monitored gas signal, Changes in monitored gas signals over time The method may be based on a comparison of one or more of:

[0134] The correlation is signal edges or transitions in the waveform of the flow signal; the maximum or minimum or inflection point of the flow signal waveform; The slope of a portion of the flow signal or the slope at a discrete point, A number of peaks and / or troughs in the flow signal over a given or predetermined period of time. and one or more of a subsequent signal edge or transition portion of the monitor gas signal waveform, which may be located within a period of time after the signal edge or transition portion of the flow waveform; a subsequent maximum, minimum or inflection point of the waveform of the monitored gas signal, when the subsequent maximum, minimum or inflection point of the waveform of the monitored gas signal may be located within a period of time after an edge or transition portion of the signal of the flow waveform; the slope of a subsequent portion or a discrete point of the waveform of the monitoring gas signal when the slope of a portion or a discrete point of the waveform of the monitoring gas signal may be located within a certain period of time after the slope of a portion or a discrete point of the waveform of the flow; Multiple peaks and / or troughs in the monitored gas signal within a given or predetermined period. The method may be based on a comparison with one or more of:

[0135] The edges of the signal are Rising edge or rising portion Falling edge or falling portion It can be one or more of:

[0136] The patient's airway may be determined to be unobstructed or substantially unobstructed when the correlation between delivered flow and the monitored gas signal is above a certain threshold.

[0137] The patient's airway may be determined to be unobstructed or substantially unobstructed when at least one component of the frequency (or frequency range) of the monitored gas signal is similar to the frequency (or frequency range) of the flow signal, and when the amplitude of the flow signal at said frequency is above a certain threshold.

[0138] The patient's airway may be determined to be unobstructed or substantially unobstructed when at least one component of the frequency (or frequency range) of the monitored gas signal substantially matches the frequency of the flow signal, and when said match of frequency is above a certain threshold. The level of patency of the patient's airway may be proportional to the strength of correlation between the delivered flow signal and said monitored gas signal.

[0139] A patient's airway may be determined to be obstructed or substantially obstructed when the correlation between delivered flow and the monitored target gas falls below a certain threshold.

[0140] The patient's airway may be determined to be unobstructed or substantially unobstructed when at least one component of the frequency of the monitored gas signal is similar to the frequency of the flow signal, and when the amplitude of the signal at said frequency is above a certain threshold.

[0141] The monitored gas signal may be measured instantaneously, in real time, or sampled (possibly at regular intervals).

[0142] The flow may be configured to cause a flow of gas from the patient to facilitate exhalation or expiration of the gas.

[0143] The flow parameters may be selected to optimize or increase the exhalation or expiration of the gas from the patient.

[0144] The monitor gas signal may be based on the concentration (or an indicator thereof) of the monitor gas.

[0145] The patient's airway status is Determination of airway patency, and / or Determining the location of the blockage or obstruction in the airway One or more of the following:

[0146] The determinable location of the airway blockage or obstruction may be in the upper or lower airway.

[0147] The monitor gas may be one of CO2 or O2, or a gas that indicates the concentration of carbon dioxide or O2.

[0148] The monitored gas signal is measurements taken at or inside the patient's mouth or oral cavity or oropharyngeal region; measurements taken at or substantially adjacent to the patient's pharynx or pharyngeal stream; Measurements taken at or inside the patient's nose or nasal cavity may be obtained from one or more of:

[0149] A monitoring gas (eg, target gas) is generated as a result of gas exchange in the patient's lungs, and the flow acts to stimulate exhalation or expiration of the monitoring gas (the patient does not have to be spontaneously breathing).

[0150] The flow may be delivered via a patient interface.

[0151] The patient interface may be of a type including a tight-fitting or non-tight interface.

[0152] The patient interface may include a nasal mask, an oral mask, an oronasal mask, a full face mask, a nasal pillows mask, a nasal cannula, a combination of the above, or any other gas-carrying patient interface system.

[0153] The flow therapy or respiratory support administered to the patient's airway can be an average flow rate of at least about 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, or 150 liters per minute (LPM) or more; or can be selected between any of these values (e.g., about 40 to about 80, about 50 to about 80, about 60 to about 80, about 70 to about 80 LPM);

[0154] The supplied gas may be delivered in a fully saturated or humidified condition, or the saturated or humidified gas may be blended with other gases (whether targeted or non-targeted) for supply or delivery to the patient interface or patient, and medical gases may be included among the gases that provide flow therapy or respiratory assistance to the patient.

[0155] The correlation may be determined by one or more of Monte Carlo analysis and / or spectral analysis. In one form, a sequential Monte Carlo method may be used.

[0156] In a fourth aspect of the present invention, there is provided an apparatus, the apparatus comprising: a flow generator that provides a flow (which may be an oscillating flow) of gas delivered to the patient in accordance with a flow signal; a gas sensor (or sampling device) configured to monitor or detect at least one parameter (which may be a concentration) of a target gas (which may be, for example, CO, N, or other gas that can be detected, monitored, and measured) being exhaled or expired from the airway of a patient (e.g., a patient who is apneic or non-spontaneously breathing) as a monitored gas signal; and a controller (which may include a processor) for determining a correlation between the delivered flow signal and the monitored gas signal and for characterizing the patient's airway condition based on the correlation; may include:

[0157] The indicator may be based on measurements of at least one target gas over a period of time (or instantaneously).

[0158] The sensor may be a gas sensor or a capnography device.

[0159] The apparatus may further include a gas analyzer disposed in communication with the gas sensor.

[0160] An electronic controller may be provided in communication with the gas sensor.

[0161] The electronic controller may process the measurements or one or more outputs of the gas sensor or capnography device to determine the waveform of the exhaled or expired gas.

[0162] The controller may be further configured or adapted to process measurements or one or more outputs of the gas sensor or capnography device, and the controller may be further configured or adapted to apply a correction factor or compensation to account for the particular flow rate of gas being delivered to the patient.

[0163] The gas sensor or sampling device may be part of the patient interface arrangement.

[0164] The sampling device may include a sampling tip for sampling the gas, the sampling tip in communication with the gas sensor.

[0165] The device may further include a capnography device or unit and / or said gas sensor.

[0166] In a fifth aspect, there may be provided a device (or device assembly) for determining airway patency, the device comprising: a flow generator for providing a flow of gas delivered to a patient, said flow of gas being delivered in accordance with a flow signal; a gas sensor configured to monitor the concentration of at least one gas and provide a monitor gas signal; determining a correlation between the delivered flow signal and the monitor gas signal; characterizing the patient's airway condition based on the correlation; a controller (which may include a processor) for Includes.

[0167] The sensor may be a gas sensor or a capnography device.

[0168] A gas analyzer may be provided in communication with the gas sensor.

[0169] An electronic controller may be provided in communication with the gas sensor.

[0170] The electronic controller may process the measurements or one or more outputs of the gas sensor or capnography device to determine the waveform of the exhaled or expired gas.

[0171] The controller may be further configured or adapted to process measurements or one or more outputs of the gas sensor or capnography device, and the controller may be further configured or adapted to apply a correction factor or compensation to account for the particular flow rate of gas being delivered to the patient.

[0172] The gas sensor or sampling device may be part of the patient interface arrangement.

[0173] The sampling device may include a sampling tip for sampling the gas, the sampling tip in communication with the gas sensor.

[0174] The device may further include a capnography device or unit and / or said gas sensor.

[0175] For both the fourth and fifth aspects, the following options are provided:

[0176] In particular, with respect to the apparatus described herein with respect to the fourth and fifth aspects, the options described below are provided for:

[0177] The controller may monitor at least one target gas by measuring or measuring variations in the concentration of the at least one target gas, which may be done by sampling equipment (which may include a gas sensor).

[0178] The sampling equipment is measurements taken adjacent to or inside the patient's mouth or oral cavity or oropharyngeal region; measurements taken adjacent or substantially adjacent to the patient's pharynx, or pharyngeal flow; Measurements taken adjacent to or inside the patient's nose or nasal cavity One or more measurements of:

[0179] The controller may determine the location of the blockage or obstruction in the airway, which may be the upper airway or the lower airway.

[0180] The target gas is CO2, O2, or N2, or a benign medical tracer gas, or a gas that exhibits a concentration of carbon dioxide, O2, or N2.

[0181] The target gas may be added to the gas provided by the flow generator to the patient's airway as part of flow therapy or respiratory support to the patient.

[0182] A target gas may be delivered to the patient's airway by a patient interface, and the concentration of the target gas is measured or monitored for a period of time following delivery by a sampling device.

[0183] The exhaled or expired gas, or at least a portion of the exhaled or expired gas, may result from cardiogenic activity or may result from the patient's heartbeat.

[0184] The flow of gas for flow therapy or respiratory assistance may be delivered to the patient's airway via a patient interface, which may be of a type including a tight-fitting or non-tight-fitting interface, and may further include a nasal mask, an oral mask, an oronasal mask, a full face mask, a nasal pillows mask, a nasal cannula, a combination of the above, or any other gas-carrying patient interface system.

[0185] The patient interface includes: Gas flow to the patient's airway Target gas into the patient's airway may deliver one or more of:

[0186] The controller Controlling a flow generator to provide or administer flow therapy or respiratory support to a patient's airway for a period of time to increase the patient's oxygen saturation. Remove, stop, or reduce flow therapy or respiratory support being provided to a patient for a period of time. Controlling a flow generator to provide or deliver gas containing a target gas to the patient's airway for a period of time. controlling a flow generator to restore delivery or administration of said flow therapy or respiratory assistance to the patient's airway; Measuring or providing a measurement of the concentration of a target gas in gases exhaled or expired by a patient over a period of time. It can be configured as follows.

[0187] The controller may be configured to correlate the measured concentration of the target gas over time with the patient's heart rate or cardiogenic activity.

[0188] The device may be configured to administer flow therapy or respiratory assistance via the patient's nares, wherein the gas sensor (which may be part of the sampling device) is placed at or inside the patient's mouth or oral cavity or oropharyngeal region for a period of time to take measurements of a target gas being exhaled or expired from the patient, when the target gas is CO2, and the controller performs the following: the concentration of CO2 fluctuates over time, the concentration of CO2 measured by the gas sensor rising from a base concentration to a peak concentration and then substantially returning to said base concentration, said peak concentration being substantially synchronized with the patient's heart rate or cardiogenic activity; the concentration of CO2 fluctuates over time, the concentration of CO2 measured by the gas sensor increases from a first base concentration to a first peak concentration, and the CO2 concentration decreases from the first peak concentration to a second base concentration that is greater than the first base concentration, and over a period of time (two or more patient heartbeats or cardiogenic activity), subsequent base concentrations returning from subsequent peak concentrations are greater than the preceding base concentration over time and / or are substantially greater than the first base concentration over time, and the first, second, and subsequent peak concentrations are substantially synchronized with the patient's heartbeat or cardiogenic activity; The concentration of CO2 does not fluctuate over time or is a constant concentration over time, and the concentration of CO2 measured by the gas sensor remains at the base concentration. The signal may be configured to detect one or more of:

[0189] Flow therapy or respiratory assistance may be provided or administered via the patient's nares, and a gas sensor (which may be part of the sampling device) is placed at or inside the patient's mouth or oral cavity or oropharyngeal region to take measurements of a target gas being exhaled or expired from the patient for a period of time, and after providing the target gas to the patient, the controller performs the following: the concentration of the target gas fluctuates over time, the concentration of the target gas measured by the gas sensor increasing from a base concentration to a first peak concentration and then substantially returning to said base concentration, and each subsequent peak concentration being substantially less or decreased compared to the immediately preceding peak concentration, each of said peak concentrations being substantially synchronized with the patient's heartbeat or cardiogenic activity; the concentration of the target gas fluctuates over time, and the concentration of the target gas measured by the gas sensor increases from a first base concentration to a concentration that substantially matches the concentration of the target gas in the gas surrounding the patient (e.g., air or operating room ambient gas conditions), and which is exposed to the gas sensor via the patient's oral cavity; The concentration of the target gas is reduced from an initial peak concentration to a base concentration, and the concentration of the target gas measured by the gas sensor remains substantially at the base concentration, which may be constant over time or may be asynchronous or synchronous with the patient's heartbeat or cardiac activity. The signal may be configured to detect one or more of:

[0190] The flow of gas is provided or delivered to the patient's airway by a patient interface.

[0191] The flow generator may be configured to provide an oscillatory flow of gas to the patient, or a superimposed oscillation of the actual gas flow to the patient may be delivered.

[0192] The flow generator may be configured to provide an oscillatory flow delivered to enhance and / or encourage exhalation or expiration of at least one target gas, wherein a measurement of the at least one target gas over a period of time varies in response to the oscillatory flow when the patient's airway is unobstructed or patent.

[0193] The method may include determining a correlation between a delivered flow rate and the measurement of at least one target gas as a monitored gas signal, the indicator being based on the correlation.

[0194] The flow generator may be configured to provide a flow based on a flow signal provided by the controller, the flow being determined based on the following signal characteristics: a frequency, which may be substantially repeated over a period of time; amplitude, a waveform, which may be substantially repeating over a period of time; phase It has one or more of the following.

[0195] The controller Flow frequency, flow amplitude, a flow waveform, which may be substantially repeating over a period of time; Flow phase, Changes in flow over time (e.g., the decay or promotion of said flow) and one or more of the frequency (or frequency range) of the monitored gas signal, the amplitude of the monitored gas signal, the amplitude of the monitored gas signal at a particular frequency, the waveform of the monitoring gas signal; the phase of the monitored gas signal, Changes in monitored gas signals over time The method may be configured to determine a correlation based on a comparison with one or more of:

[0196] The controller may be configured to determine a correlation based on a comparison of the frequency of the flow and the frequency (or frequency range) of the monitored gas signal.

[0197] The controller Edges or transitions of the flow waveform signal; local maxima or minima or inflection points of the flow waveform; The gradient of a portion of the flow or the gradient at a discrete point, A number of peaks and / or troughs in flow within a given or predetermined period of time. and one or more of a subsequent signal edge or transition portion of the monitor gas signal waveform, which may be located within a period of time after the signal edge or transition portion of the flow waveform; a subsequent maximum, minimum or inflection point of the waveform of the monitored gas signal, when the subsequent maximum, minimum or inflection point of the waveform of the monitored gas signal may be located within a period of time after an edge or transition portion of the signal of the flow waveform; the slope of a subsequent portion or a discrete point of the waveform of the monitoring gas signal when the slope of a portion or a discrete point of the waveform of the monitoring gas signal may be located within a certain period of time after the slope of a portion or a discrete point of the waveform of the flow; Multiple peaks and / or troughs in the monitored gas signal within a given or predetermined period. The method may be configured to determine a correlation based on a comparison with one or more of:

[0198] The controller may determine that the patient's airway is not obstructed or substantially not obstructed when the correlation between the delivered flow and the monitored gas signal is above a certain threshold.

[0199] The controller may determine that the patient's airway is not obstructed or substantially not obstructed when at least one component of the frequency (or frequency range) of the monitored gas signal substantially matches the frequency of the flow, and when said matching of frequency is above a certain threshold.

[0200] A controller can determine a level of patency of the patient's airway, said level being proportional to the strength of correlation between delivered flow and said monitored gas signal.

[0201] The controller may determine that the patient's airway is obstructed or substantially obstructed when the correlation between the delivered flow and the monitored target gas falls below a certain threshold.

[0202] The controller may determine that the patient's airway is obstructed or substantially obstructed when at least one component of the frequency of the monitored gas signal is not similar or different or not sufficiently similar to the frequency of the flow, and / or when the amplitude of the signal at said frequency is similar and below a certain threshold.

[0203] The monitoring or target gas is produced as a result of gas exchange in the patient's lungs, and the flow provided by the flow generator acts to encourage exhalation or expiration of the monitoring gas (the patient need not be spontaneously breathing) or to enhance or augment gas exchange resulting from cardiogenic pulses occurring within the patient's body.

[0204] The controller may determine the correlation by one or more of Monte Carlo analysis, and / or spectral analysis, and / or fast Fourier transform.

[0205] It will be understood that the apparatus of the fourth and fifth aspects may carry out the method of any of the first to third aspects, and as such, any of the alternatives as described with respect to the first to third aspects are applicable to the fourth and fifth aspects.

[0206] In a sixth aspect, Providing or delivering flow to a patient; monitoring at least one target gas (which may be, for example, CO, N, or other gas capable of being detected, monitored, and measured) being exhaled or expired from the airway of a patient (e.g., a patient who is apneic or non-spontaneously breathing); and determining a correlation between the delivered flow rate and the monitored gas signal; and providing an indicator for a determination regarding airway patency based on a correlation of at least one target gas over a period of time; A method or system is provided for providing an indication or confirmation of airway patency in a patient, comprising:

[0207] It will be appreciated that the alternatives discussed in relation to the first, second and third aspects above are applicable to the sixth aspect.

[0208] According to the disclosed methods and / or systems and / or devices, the high-flow or flow therapy or respiratory support providing gas may contain a significant proportion of O2 (or perhaps the majority of the gas). This may be particularly important given the patient's condition of being non-ventilating or apneic. As such, it is beneficial to increase the amount of O2 being provided or delivered to patients with these conditions to assist with oxygenation. The therapeutic gas provided may be a portion of the high-flow gas containing at least about 90% or more O2.

[0209] It would be desirable to provide a system, and tubing for such a system, in which the humidity and temperature of the gas reach ideal gas conditions, eg, about 37° C. and about 44 mg / L, as quickly as possible.

[0210] For example, according to various embodiments and configurations thereof, the flow rate of gas supplied or provided to the interface or through the system, e.g., through a breathing circuit, may include, but is not limited to, flows as defined by the high gas delivery flow rates previously described herein.

[0211] Such relatively high flow rates of gas may assist in providing the supplied gas to the patient's airway or to different portions of the patient's airway. For example, such flow rates may enable delivery of such gas to the upper or lower respiratory tract regions. The upper respiratory tract region generally includes the nasal cavity, pharynx, and larynx, while the lower respiratory tract region generally includes the trachea, primary bronchi, and lungs.

[0212] Some features, aspects, and advantages of some configurations of the present disclosure have been described with respect to a respiratory breathing circuit for use in parallel with or in conjunction with an anesthesia breathing circuit, however, some features, aspects, and advantages of the configurations as described may be advantageously used with other respiratory systems.

[0213] As used herein, the term "comprising" means "consisting at least in part of." When interpreting each sentence in this specification containing the term "comprising," features other than those preceded by this term may also be present. Related words such as "comprise" and "comprises" are to be interpreted in the same manner.

[0214] The present invention may also be broadly said to consist of the parts, elements and features referred to or shown in the specification of this application, individually or collectively, and all combinations of any or any two or more of said parts, elements, or features, and where a specific integer having a known equivalent in the art relevant to the invention is set forth herein, such known equivalent is deemed to be incorporated herein as if individually set forth.

[0215] The present invention contemplates the structures constructed above and also given below by way of example only.

[0216] Specific embodiments and modifications thereof will become apparent to those skilled in the art from the detailed description herein, which refers to the drawings. [Brief explanation of the drawings]

[0217] [Figure 1] 1 illustrates a respiratory therapy support system including an exemplary breathing circuit that may be combined with a patient interface to provide or administer a desired flow therapy to a patient. [Figure 2] 1 shows a patient and different portions of the patient's airway, and portions of the airway referred to in the accompanying description. [Figure 3] An example of cardiac oscillation (COS) during the inspiratory phase of a patient, where the COS is synchronized with the cardiac cycle (ECG). [Figure 4] 1 illustrates components of a system for practicing the methods as disclosed herein using a gas source and a sensor in the form of a nasal patient interface and a gas analysis sensor. [Figure 5A-B] FIG. 5(A) shows the indicative ratio of gas flow exiting the patient's mouth to the gas flow being provided or delivered to the patient interface for the patient, and FIG. 5(B) is a linear plot of 5(A) which is then used to determine a correction or compensation factor. [Figure 6A-C] (A) shows different gas concentration traces (CO2) over time depending on whether the soft palate is open and the trachea is open; (B) whether the soft palate is closed and the trachea is open; (C) whether the soft palate is open and the trachea is closed. [Figure 7] 1 illustrates a further configuration of a system for practicing the methods as disclosed herein, in which a sensor in the form of a gas analysis sensor is provided inside the patient's mouth or oral cavity, and the target gas is provided via a second gas source. [Figure 8A-C] 7 shows the traces of the concentration of a different gas (N2) over time when the configuration of FIG. 7 is performed, depending on (A) the soft palate open and the trachea open; (B) the soft palate closed and the trachea open; (C) the soft palate open and the trachea closed. [Figure 9] 10 illustrates a further configuration of a system for practicing the methods as disclosed herein, in which a sensor in the form of a gas pressure sensor is provided inside the patient's mouth or oral cavity. [Figure 10] 1 is a plot of how the pressure in the airway varies approximately as the square of the cannula flow. [Figure 11] 10 illustrates a further configuration of a system for practicing the method as disclosed herein, wherein a sensor in the form of a gas analysis sensor is provided inside the patient's mouth or oral cavity, and a processing unit or controller receives data relating to the concentration of gas being exhaled or exhaled from the patient's mouth, ECG data, the flow rate of flow therapy or respiratory support provided to the patient, and the ability to display warnings or alarms as a result of processing such data / measurements. [Figure 12] 1 illustrates the effect of flow application on a patient's airway. [Figure 13A]1 shows plots of oscillatory flow rates applied to a patient and corresponding CO2 and tracheal flow measurements. [Figure 13B] 1 shows plots of oscillatory flow rates applied to a patient and corresponding CO2 and tracheal flow measurements. [Figure 13C] 1 shows plots of oscillatory flow rates applied to a patient and corresponding CO2 and tracheal flow measurements. [Figure 14] A block diagram of the device is shown. DETAILED DESCRIPTION OF THE INVENTION

[0218] FIG. 2 illustrates a typical airway of a person or patient and includes arrows showing how a relatively high flow rate of gas delivered to the person or patient can be used to effectively push or force the delivered gas further or deeper into the patient's airway than when the patient is in a normal or typical self-driven breathing state. The use of high-flow gas delivery can help push the gas flow, and therefore O2, deeper into the patient's airway. High-flow gas also aids in airway flushing and CO2 flushing, which can also help push O2 / respiratory gas deeper into the airway. In some situations, high-flow gas delivery can be used when the patient is not spontaneously breathing, i.e., when the patient is apneic.

[0219] The methods, systems, or devices described herein may be used in respiratory care or therapy systems, in high-flow therapy, or with sealed or non-sealing interfaces, for example, in hospital respiratory management systems. The methods, systems, or devices may also be used to provide nasal high-flow therapy. A particular application relates to measuring or detecting a gas or gases as they are exhaled or exhaled from a patient's airway, and, based on such measurements or detections, providing an indication of the patency of the patient's airway and / or of potential locations of obstruction, blockage, or closure (i.e., non-patency) in the patient's airway. As described below, the described methods, systems, or devices are also useful for determining airway patency when the patient is already apneic or has reduced respiratory drive, i.e., is not breathing spontaneously. In these situations, it is necessary to detect whether respiratory gases are reaching the patient's lungs, as opposed to attempting to determine whether the patient is breathing.

[0220] FIG. 1 illustrates a humidified respiratory assistance system and humidified breathing circuit. A patient P receives humidified and pressurized gas through a nasal cannula assembly of a patient interface 601, which is operably connected to a humidified gas delivery pathway or inspiratory conduit 401 via a filter 501. The inspiratory conduit 401 is then connected to a humidifier 200 (including a humidifier chamber 251) that is supplied with gas from a blower 15 or other suitable gas supply via a gas delivery conduit 301. The gas delivery conduit is a "dry" conduit; i.e., it is positioned upstream of the humidifier. Headgear 620 is provided to support and hold the patient interface against the patient's face. It will be appreciated that while a humidifier may be provided, including humidified gas may be preferable due to benefits to the patient's airway. Although a filter may be provided, it will be appreciated that providing such an in-line filter is beneficial (e.g., a circuit component upstream of the filter may be used to provide flow therapy or respiratory assistance to multiple patients, as there is less likelihood of contamination of the circuit component upstream by a component (provided downstream of the filter) by a patient receiving flow therapy or respiratory assistance).

[0221] If a humidifier is used, the inhalation conduit 401 may be connected to the outlet 257 of the humidifier chamber 251, which contains a quantity of liquid, such as water. The humidifier chamber 251 may be formed from a plastic material and may have a highly thermally conductive base 259 (e.g., an aluminum base) that is in direct contact with the heating plate 203 of the humidifier 200.

[0222] The humidifier 200 may include a control means or electronic control unit 205, which may include a microprocessor-based controller executing computer software instructions stored in associated memory. Gases flowing through the inspiratory conduit 401 are passed to the patient by a filter 501 (optional) and a patient interface 601.

[0223] The controller 205 can receive input from an input source, such as a user input means or dial 207, by which a user of the device can set, for example, a therapy mode. As part of this therapy mode, the device user of the controller can automatically set the gas flow rate, gas humidity, or temperature delivered to the patient P to a predetermined required value (preset value). In response to the therapy mode set by the user (or any other input), the user interface (e.g., dial 207, or touchscreen interface, or one or more buttons), and other possible inputs such as internal sensors sensing gas flow or temperature, or by parameters calculated in the controller, the controller 205 can determine when (or to what level) to activate the heating plate 203 to heat the water in the humidifier chamber 251. As the volume of water in the humidifier chamber 251 is heated, water vapor begins to fill the volume of the chamber above the water level and is expelled from the outlet port 257 of the humidifier chamber 251 along with the flow of gas (e.g., air) provided by the gas supply means or blower 15 that enters the chamber through the gas inlet port 255. It should be noted that it is possible to obtain a relationship between the humidity of the gas in the humidifier chamber 251 and the temperature of the heater plate 203. Thus, the temperature of the heater plate can be used in an algorithm or look-up table to determine the humidity of the gas.

[0224] Blower 15 may include a variable speed pump or fan 22 that draws air or other gas through blower inlet 17. The speed of variable speed pump or fan 22 may be controlled by a further control means or electronic control device 18 in response to input from controller 205 and predetermined required values (presets) of pressure or fan speed or flow rate set by the user via dial 19 or other input device (or, alternatively, the functions of this controller 18 may be performed by another controller 205). Additionally, a touch screen or other input device or interface may be used to set the flow rate. Alternatively, gas may be provided from a wall supply; i.e., a wall gas port GP in wall W.

[0225] The blower housing 16 is provided with an outlet port 20. The inlet port 303 of the gas delivery conduit 301 and the outlet port 20 of the blower are provided with complementary mating features to connect the outlet port 20 with the inlet port 303 and provide a gas flow path therethrough. The complementary mating features may be provided in part by an adapter insert (not shown), for example, an adapter insert that provides suitable connection features that allow a conduit or other component to be connected or mated with the adapter insert and, accordingly, provide a suitable air connection.

[0226] The system may also include (or be connectable to) a sampling device, or a device including a sensor, such as a gas sensing head, may be placed in the patient's airway (e.g., the mouth / oropharyngeal region). The sampling device may sense a parameter of the target or monitoring gas. The sensed parameter of the target or monitoring gas may be communicated to the system's controller and used in the airway patency determination methodology described herein.

[0227] In some configurations, the flow generator can be configured to provide an oscillatory flow. The flow signal can include an oscillatory flow signal to provide the oscillatory flow. The flow signal can include one or more frequencies. The flow signal can include a base gas flow component and one or more oscillatory gas flow components.

[0228] In some configurations, the flow generator may include one or more valves in a manifold arrangement. Additionally, the manifold arrangement may further include at least one proportional valve controlled by an associated controller 18. The valves may be used to deliver a desired flow rate or a desired flow signal. In some configurations, the manifold includes at least one pressure relief valve configured to open if the pressure within the manifold exceeds a maximum pressure.

[0229] In one exemplary configuration, the flow generator is controlled to deliver an oscillatory flow that includes multiple oscillatory flow components that combine to form a composite oscillatory flow. Each oscillatory flow component may have a different frequency than the other components. Alternatively, multiple oscillatory flow components may be present.

[0230] In some configurations, there are at least three oscillatory components: a first component at a frequency substantially similar to a person's resting heartbeat; a second component at a low frequency configured to provide for moving gas from the patient's airway; and a third component at a high frequency. The three components are combined to produce a composite signal that is output from the flow generator (e.g., generated by a manifold).

[0231] By way of example, the oscillating component may have a maximum flow rate of about 375 liters / minute to about 0.5 liters / minute (or about 270 liters / minute to about 0.25 liters / minute for the base component), or preferably about 270 liters / minute to about 15 liters / minute (or about 120 liters / minute to about 0.5 liters / minute for the base component), or more preferably about 150 liters / minute to about 30 liters / minute (or about 60 liters / minute to about 10 liters / minute for the base component). The oscillating component may have a minimum flow rate of about 370 liters / minute to about 0.5 liters / minute (or about 270 liters / minute to about 0.25 liters / minute for the base component), or preferably about 240 liters / minute to about 15 liters / minute (or about 120 liters / minute to about 5 liters / minute for the base component), or more preferably about 150 liters / minute to about 30 liters / minute (or about 60 liters / minute to about 10 liters / minute for the base component).

[0232] In some configurations, the frequency of the oscillatory component may be altered based on one or more parameters sensed from one or more sensors, such as O2 saturation, respiratory rate, respiratory phase, flow rate, CO2 concentration, heart rate.

[0233] Fluctuating gas flow with gas flow oscillation is useful when a patient's respiratory drive is impaired or at least reduced, whether this is before, during, or after a medical procedure, or in any other situation. Fluctuating gas flow with an oscillatory component primarily assists in removing CO2 from a breathing patient. CO2 removal can be useful when a patient is apneic or when the patient's respiratory function is impaired, such as during sedation or anesthesia. During these events, the patient's respiratory function may not be in a good enough state to fully clear CO2 without assistance.

[0234] In some configurations, the gas flow may be obtained from some other gas source or sources rather than using a blower 15. For example, in some configurations, the gas source or sources may include one or more containers of compressed air and / or another gas and one or more valve devices adapted to control the rate at which the gas exits the one or more containers. As another example, in some configurations, the gas may be obtained from an oxygen concentrator. The system may also include a supplemental gas source to provide a mixture of air and a supplemental gas. For example, the supplemental gas may be O2. In some configurations, the device may be adapted to perform high-flow therapy. In this disclosure, "high-flow therapy" may refer to the delivery of gas to a patient at a flow rate of about 5 or 10 liters per minute (5 or 10 LPM) or greater.

[0235] In some configurations, "high flow therapy" may refer to the delivery of gas to a patient at a flow rate of from about 5 or 10 LPM to about 150 LPM, or from about 15 LPM to about 95 LPM, or from about 20 LPM to about 90 LPM, or from about 25 LPM to about 85 LPM, or from about 30 LPM to about 80 LPM, or from about 35 LPM to about 75 LPM, or from about 40 LPM to about 70 LPM, or from about 45 LPM to about 65 LPM, or from about 50 LPM to about 60 LPM. For example, according to various embodiments and configurations thereof described herein, the flow rate of gas supplied or provided to an interface or through a flow path or otherwise through the system may include, but is not limited to, flows of at least about 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150 L / min or more, and a useful range may be selected between any of these values (e.g., about 40 to about 80, about 50 to about 80, about 60 to about 80, about 70 to about 100 L / min, about 70 to 80 L / min).

[0236] The delivered gas may include a percentage of oxygen. In some configurations, the percentage of oxygen in the delivered gas may be between about 20% and about 100%, or between about 30% and about 100%, or between about 40% and about 100%, or between about 50% and about 100%, or between about 60% and about 100%, or between about 70% and about 100%, or between about 80% and about 100%, or between about 90% and about 100%, or about 100%, or 100%.

[0237] High-flow therapy has been shown to be effective in meeting or exceeding a patient's normal actual inspiratory demand to increase the patient's oxygen delivery and / or reduce the work of breathing. Furthermore, high-flow therapy can create a flushing effect in the nasopharynx, allowing the anatomical dead space of the upper airway to be flushed with a high flow of incoming gas. This can create a reservoir of fresh gas available for each breath while minimizing rebreathing of carbon dioxide, nitrogen, etc.

[0238] The humidifier 200 may have a humidifier base including a housing 201 with a heater 203, a controller 205 coupled to the heater, and a user input device 207 that allows a user to turn the humidifier on and off and select a desired temperature to be provided by the heater. The user input device 207 may be, for example, a button, a switch, or a touchscreen display. The heater 203 may include one or more heating elements.

[0239] The humidifier base may be configured to receive a humidifier chamber 251. The humidifier chamber 251 includes a housing 253 defining an internal liquid reservoir 254, an upstream gas inlet port 255 in fluid / air communication with the reservoir, a downstream gas outlet port 257 in fluid / air communication with the reservoir, and a base 259. The base 259 may be arranged to be positioned on or above the heater 203 to heat the liquid in the reservoir. The base may include a flange 261 projecting outward from an adjacent portion of the housing 253 to aid in seating the humidifier chamber in place on the humidifier base.

[0240] The gas inlet port 255, the liquid reservoir 254, and the gas outlet port 257 are in fluid / air communication to provide a gas flow path from the gas inlet port 255 through or past the liquid reservoir to the gas outlet port 257, heating and humidifying gas traveling along the gas flow path.

[0241] The humidifier chamber 251 may be any suitable chamber that holds a liquid suitable for use in humidifying gases, such as water. The humidifier chamber 251 may be a manually filled chamber and may be filled through a liquid inlet port 263. Alternatively, the humidifier chamber 251 may be an automatically filled chamber, and liquid may be supplied to the humidifier chamber from a liquid container, bag, or other liquid source. The humidifier chamber may include a float valve in a liquid reservoir, the float valve configured to control the flow of liquid from the liquid container to the liquid reservoir.

[0242] The gas delivery conduit 301 may be located upstream of the humidifier chamber 251. Such gas delivery conduit 301 may be in fluid / air communication with the humidifier chamber 251 or configured to be placed in fluid / air communication with the humidifier chamber upstream of the humidifier chamber; i.e., downstream of the gas conduit 301. The gas delivery conduit 301 may be configured to receive one or more gases from a gas source and deliver one or more gases to the gas inlet port 255 of the humidifier chamber.

[0243] The gas delivery conduit 301 has an upstream gas inlet port 303 at one end of the conduit and a downstream gas outlet port 305 at the opposite end of the conduit. The gas inlet port 303 and the gas outlet port 305 are in fluid / air communication to provide a gas flow path from the gas inlet port 303 through the gas delivery conduit to the gas outlet port 305. The gas outlet port 305 of the gas delivery conduit and the gas inlet port 255 of the humidifier chamber 251 may include complementary mating features to couple the gas delivery conduit 301 to the humidifier and enable fluid / air communication between the gas delivery conduit 301 and the humidifier chamber 251. The complementary mating features of the gas outlet port 305 of the gas delivery conduit 301 and the gas inlet port 255 of the humidifier chamber 251 may be disconnected from each other, allowing the gas delivery conduit 251 to be disconnected from the humidifier chamber 251. Alternatively, the complementary binding features may be permanently or semi-permanently bonded.

[0244] With regard to complementary mating features, at least some of them may be provided by an adapter insert, for example an adapter insert (not shown) that includes one or more suitable mating features.

[0245] The gas inlet port 303 of the gas delivery conduit may include one or more coupling features to allow the gas delivery conduit to be coupled to a gas source.

[0246] The inhalation conduit 401 extends from the humidifier chamber 251 and connects the humidifier to the patient interface 601 via an in-line filter 501. The inhalation conduit 401 may include a conduit heater 403 adapted to heat gas passing through the conduit 401. The heater 403 helps minimize or prevent the formation of condensation within the inhalation conduit, which may otherwise occur due to temperature differences between the inner and outer surfaces of the conduit wall. In other configurations, the conduit heater 403 may not be present. The inhalation conduit 401 includes an upstream gas inlet port 409 at one end of the conduit and a downstream gas outlet port 405 at the opposite end of the conduit, the conduit defining a gas flow path from the gas inlet port 409 to the gas outlet port 405.

[0247] The humidifier chamber 251 is configured to be disposed in fluid / air communication with the inhalation conduit 401 upstream of the inhalation conduit 401, or in fluid / air communication with the inhalation conduit 401 upstream of the inhalation conduit; i.e., an inhalation conduit positioned downstream of the humidifier chamber 251. The gas outlet port 257 of the humidifier chamber 251 and the gas inlet port 409 of the inhalation conduit 401 may include complementary coupling features to allow the inhalation conduit to be coupled to the humidifier, thereby providing fluid / air communication between the humidifier chamber 251 and the inhalation conduit 401. The complementary coupling features of the gas outlet port 257 of the humidifier chamber 251 and the gas inlet port 409 of the inhalation conduit 401 may be disconnectable from each other, allowing the inhalation conduit 401 to be disconnected from the humidifier chamber 251. Alternatively, the complementary coupling features may be permanently or semi-permanently coupled. The humidifier outlet port 257 and inlet port 255 may be standard medical taper connections, such as ISO 22 mm medical taper connections. Alternatively, other connections are contemplated, such as proprietary connections, for at least the humidifier outlet port 257.

[0248] The inhalation conduit 401 is generally longer than the gas delivery conduit 301 .

[0249] The filter 501 may be of any suitable type, for example, but may include a generally cylindrical filter housing 503 with an enlarged central body portion. The leading edge of the enlarged central body portion includes a tapered wall terminating in an upstream gas inlet port 505, and the trailing edge of the enlarged central body portion terminates in a downstream gas outlet port 507. The gas inlet port 505 and the gas outlet port 507 are in fluid / air communication through the central body portion. The filter may be a high-efficiency particulate arrestance (HEPA) filter. The enlarged central portion of the filter housing contains a suitable filter material. For example, the filter material may include pleated paper, nanofiber, or any other suitable filter material, including a sock filter, a stacked disc filter, a spiral filter, one or more blocks of filter material, or one or more discs of filter material where the stream of filter material flows freely relative to the discs with the fluid flow. The filter traps particulates, bacteria and / or other infectious agents and prevents them from passing downstream through the filter from the inhalation conduit to the patient, and also traps bacteria and / or other infectious agents and prevents them from passing upstream through the filter from the patient to the inhalation conduit.

[0250] The inhalation conduit 401 may be in fluid / air communication with such a filter 501 upstream of the filter, or may be configured to be placed in fluid / air communication with a filter upstream of the filter; i.e., with a filter located downstream of the inhalation conduit. The gas inlet port 505 of the filter 501 and the gas outlet port 405 of the inhalation conduit 401 may include complementary coupling features that allow the inhalation conduit to be coupled to the filter, providing fluid / air communication between the inhalation conduit and the filter. The complementary coupling features of the gas inlet port 505 of the filter and the gas outlet port 405 of the inhalation conduit can be disconnected from each other, allowing the inhalation conduit 401 to be disconnected from the filter 501.

[0251] In one configuration, the complementary mating feature between the gas outlet port 405 of the inhalation conduit 401 and the gas inlet port 505 of the filter comprises a 22mm medical connection or a 22mm medical tapered connection.

[0252] When used, the filter 501 may be in fluid / pneumatic communication with the patient interface 601 upstream of the patient interface 601 or is configured to be placed in fluid / pneumatic communication with the patient interface 601 upstream of the patient interface 601; i.e., with a patient interface located downstream of the filter. In one example configuration, the filter 501 is coupled to the patient interface 601 or is configured to be coupled to the patient interface 601.

[0253] The patient interface 601 may include a patient interface gas conduit 603 with an upstream gas inlet port 605 at one end of the conduit. The opposing downstream end of the patient interface gas conduit 603 is in fluid / pneumatic communication with the patient cannula 30 / 607 for delivering gas from the patient interface gas conduit 603 to the patient P.

[0254] In one configuration, the gas outlet port 507 of the filter 501 and the gas inlet port 605 of the patient interface gas conduit include complementary mating features to allow the filter 501 to be mated to the patient interface 601, providing fluid / air communication between the filter and the patient interface gas conduit, with the filter aligned with the gas flow path through the patient interface gas conduit. The complementary mating features are disconnectable from each other, allowing the filter to be disconnected from the patient interface gas tubing of the patient interface. Alternatively, the complementary mating features may be permanently or semi-permanently coupled.

[0255] While the patient interface 601 is shown as being a nasal cannula, it should be understood that in some configurations, other patient interfaces may be suitable. For example, in some configurations, the patient interface may include a tight-fitting or non-tight-fitting interface and may include a nasal mask, oral mask, oronasal mask, full face mask, nasal pillow mask, nasal cannula, combinations of the above, or some other gas delivery system. It is understood that other interfaces that extend at least partially into the patient's airway may also be used as part of the contemplated system. In embodiments, the patient interface 601 includes a non-tight-fitting interface, such as a nasal cannula, which allows gas to be exchanged with the environment. For example, a non-tight-fitting cannula can remove and / or clear carbon dioxide from the patient's airway while the patient is receiving flow therapy from the system. Furthermore, in embodiments, the patient interface is in the form of a nasal interface, preventing the system from interfering with other oral airway equipment and / or devices, such as a tracheal tube, during an intubation procedure. Thus, the patient may continue to receive flow therapy throughout the intubation procedure.

[0256] The patient interface gas conduit 603 forms a first gas lumen defined by a tubular wall adapted to receive gas from the respiratory therapy system via the inhalation conduit 401 and filter 501 shown in FIG.

[0257] As shown, in one example, the patient interface 601 may include two nasal delivery elements adapted to be positioned one in each of the patient's nostrils. Each nasal delivery element may be shaped or angled to extend inward toward the patient's nasal septum. The gases inlet conduit 603 may include unheated breathable tubing configured to reduce the formation of condensation within the gases conduit 603.

[0258] Additionally, each nasal delivery element may be shaped or angled such that the tip of each nasal delivery element points towards the back of the patient P's head during use.

[0259] In other embodiments, each nasal delivery element may have different characteristics, for example, one nasal delivery element of a pair may be relatively long and the other nasal delivery element may be relatively short.

[0260] In some embodiments, the flow manifold can be configured to accept flow from two sides of the flow manifold (e.g., from the "left" and "right" sides of the flow manifold, e.g., as shown in FIG. 1 , when instead of just the "left" side or just the "right" side of the flow manifold).

[0261] In some such embodiments, multiple gas lumens may be used to provide pneumatic communication between the flow manifold and the respiratory therapy system.

[0262] In some embodiments, the flow manifold can be configured to accept flow from a non-side of the flow manifold (eg, from the "bottom" or "top" of the patient interface).

[0263] In other embodiments, the flow manifold may be a separate, attachable component that is attached to the body of a patient interface, such as a nasal cannula or nasal mask. Such a manifold may be an entirely separate component that can be removed from its attachment to the interface, or it may be de-attached or disconnected from its operating position to allow for re-orientation of the manifold (and associated supply conduits) relative to the interface. For example, the manifold may have a push-fit arrangement that presses it into connection with the interface body, or it may have a swivel-type connection with the body of the interface that allows for re-orientation of the manifold. Re-orientation allows for positioning of the supply conduits on the left or right side of the interface (and thus from one side of the patient to another). This may improve the convenience or arrangement of the components of the system that delivers gas to the patient. For example, if those assisting in a medical procedure need to access the patient from a specific side, the manifold can be re-oriented and the supply tubes repositioned to extend from a different side of the patient. Such an arrangement allows for relatively unobtrusive application of the patient interface and its associated components away from medical professionals.

[0264] When the patient interface is in the form of a nasal cannula, it may use headgear in the form of straps that may be bifurcated (i.e., may have lines of weakness or other split arrangements) to allow the headgear or its straps to be reconfigured from a single strap arrangement to a bifurcated strap arrangement.

[0265] When the patient interface is in the form of a nasal cannula, it may employ a pair of side arms extending from the main body (to which the manifold is connected) that may include features that allow the gas delivery tube to be held or secured or positioned therein (to prevent the gas delivery tube from moving around uncontrollably).

[0266] The patient interface 601 may further include mounts and / or supports, e.g., cheek supports, for attaching and / or supporting the gas lumen 603 and / or cannula 30 / 607 to the patient's face. For example, a releasable connection system may be used to position or place the interface on the patient's face, but allow for relatively quick removal or repositioning of the interface if needed.

[0267] Thus, when pneumatically coupled to the circuit, the assembled patient interface can be used to deliver gas to a patient while the patient is under anesthesia and / or during pre-oxygenation once the patient has become anesthetized (i.e., during the apneic window). For example, the device can be used to deliver heated, humidified, high-flow gas at 5 L / min to 200 L / min, conveniently at least about 70 L / min, but can also be at least about 50 L / min, once the patient is under anesthesia. Once the patient becomes anesthetized, the patient's respiratory urge decreases, and the patient does not breathe spontaneously. The high flow maintains the patient's oxygen levels at a safe level, thereby providing a useful alternative to masks and bags typically used to artificially ventilate patients.

[0268] The system may include a wall source instead of the blower, or the blower may be a wall source.

[0269] Additionally or alternatively, the method may be used when a patient is being pre-oxygenated before being placed under anesthesia, while the patient is breathing spontaneously, and the pre-oxygenation is performed to increase the oxygen concentration in the patient's lungs.

[0270] In either case, the temperature of the gas delivered to the patient may conveniently be about 37°C and the humidity about 44 mg / l H2O.

[0271] Nasal cannulae as patient interfaces may provide a patient with a suitable patient interface for delivering a high airflow, high humidity gas flow to the patient's nasal passages.

[0272] Nasal cannulas can be useful from an anesthesia perspective or for patients who are apneic or non-spontaneously breathing because the cannula has a relatively small footprint and is positioned on the upper lip, freeing the mouth and throat to allow a surgeon or other medical professional to insert additional instruments or perform procedures on the mouth / throat with minimal obstruction or interference.

[0273] However, in some embodiments, the patient interface may be of a type that includes a tight-fitting or non-tight interface, and may further include a nasal mask, an oral mask, an oronasal mask, a full face mask, a nasal pillows mask, a nasal cannula, a combination of the above, or some other gas-carrying patient interface system.

[0274] One form of nasal cannula assembly 30 / 607 may be provided with a facial attachment portion including a pair of tubular nasal prongs either integrally molded or removably attached, and a gas flow manifold portion either integrally molded or attached to the tube 603, as described above.

[0275] As described above, the nasal cannula may include a removably attachable manifold for delivering gas flow to the interface, which can be oriented to place the gas supply connection on either the left or right side of the interface (or the patient). One or a pair of side arms or cheek supports of such a nasal cannula may enable positioning of the interface on the patient's face and may include a relatively soft outer material or overmolded material on at least the patient-contacting surface. In one embodiment, the cheek supports are rigid and are also overmolded with a relatively soft material, such as silicone or TPE.

[0276] The removable manifold may be reoriented as previously described, and such reorientation may be performed manually by the user or a person assisting the patient / user.

[0277] Headgear as disclosed herein may be provided in combination with a nasal cannula and may include at least one strap that is bifurcable (i.e., may have a line of weakness or other predefined zone that allows the user to separate the strap into two portions).

[0278] The body of the nasal cannula may include a barrel-shaped portion into which the manifold is inserted and may be removed therefrom to allow side swapping. Additionally or optionally, the nasal cannula may include a headgear connector for connecting to one or both side arms.

[0279] The face mount portion and prongs may be molded from silicone or other flexible materials as known in the art of cannula construction. The gas flow manifold portion may be made from a hard plastic material, but may also be manufactured from other suitable materials.

[0280] The face mount may be integrally molded with the prongs and may be shaped to generally follow the contours of the patient's face around the upper lip area.

[0281] The gas flow manifold section may be generally tubular in shape with a substantially circular inlet (not shown) on one side that curves around an elongated oval outlet. The circular inlet receives the end of a conduit or tube 603 so that gas can be supplied to the gas flow manifold section and flow through the inlet and out the outlet. The tube 603 may be permanently fixed to the manifold section or may be releasably attachable.

[0282] The elongated and oval-shaped outlets may fit into the elongated recesses in a friction-fit or snap-fit engagement with the manifold, and significant force may be required to remove the manifold section from such elongated recesses. Furthermore, because the face mount section may be flexible and the manifold section may be made from a harder plastic material, the manifold section outlets may be relatively easier to push or force into such elongated recesses. Once the manifold section is engaged with the face mount section, and during use, gas flows from the tube 603 through the gas flow manifold section and out its outlets 29, into each of the oval recesses, into each of the prongs, and into the patient's nares.

[0283] The elongated recess of the face mount portion and the outlet of the manifold portion may be symmetrical in shape and configuration, so that the manifold portion can be switched or inverted so that the tubing 603 extends from either the left or right side of the patient's nostril. This means that the nasal cannula assembly and associated tubing 603 are relatively unobtrusive, as the cannula 20 only requires a single horizontal side inlet rather than two inlets.

[0284] The nasal cannula assembly as generally described may be more comfortable to wear because it rests below the nasal septum and supports two nasal prongs, which are made from a single molding of a soft material such as silicone, making them easy to insert into the patient's nostrils and comfortable for the patient.

[0285] The gas used in the embodiments described herein in connection with administering or providing flow therapy or respiratory support is generally oxygen, or the gas may be air or another suitable gas or gases, or a mixture of air with supplemental oxygen or other gases suitable for the patient.

[0286] The liquid used in the above arrangements for humidification is generally water, or the liquid may be one or more other liquids suitable for the humidification process.

[0287] More specifically, for some surgical procedures, it is desirable to have unobstructed access to elements of a patient's airway, such as the vocal cords, glottis, or trachea, while the patient is anesthetized and the patient's respiratory system is paralyzed.

[0288] In paralyzed patients, an endotracheal tube is typically used to secure the airway and provide a route for applying artificial ventilation, but the use of an endotracheal tube may be undesirable in these situations because the tube not only completely obstructs the lower airway but also significantly impedes access to the airway elements above the inflated cuff of such an endotracheal tube configuration. Similarly, a laryngeal mask also substantially obstructs access to the airway and therefore is generally not suitable for use during this type of procedure.

[0289] Until recently, physicians or clinicians may have used various forms of jet ventilation, using oxygen delivered via a thin catheter (e.g., a Hunsaker catheter) introduced into the trachea via the mouth to provide some ventilation and gas exchange. However, the catheter still must be delivered via a tube extending down the airway, which, while less invasive, still limits access. Clinicians also need to be aware of the potential fire and injury risks when introducing plastic tubes down the airway in an oxygen-rich atmosphere, as some procedures, such as laser ablation and cauterization, may be performed.

[0290] High-flow gas (e.g., O2 or oxygenated gas) delivered via the patient's nostrils (e.g., a nasal interface), or high-flow gas therapy or respiratory assistance, provides the ability to ventilate paralyzed patients using high flows of humidified oxygen or gas delivered, for example, via a nasal cannula or other form of patient interface. As the delivered gas (e.g., containing oxygen) passes through the patient interface (e.g., via the nasal prongs of a nasal cannula) into the nose and out the mouth, it can cause significant turbulent flushing of the pharyngeal cavity. Such gas flow may be capable of being humidified. Such high flow creates a relatively small positive pressure in the trachea and lungs, effectively splinting the airways and expanding the alveoli—partially alleviating atelectasis. As oxygen is consumed in the alveoli, fresh gas is naturally drawn down the trachea, allowing it to cross the alveolar membrane and be absorbed.

[0291] At the same time, carbon dioxide is produced in the body and carried through the bloodstream to the lungs, where it accumulates in the alveoli and diffuses into the bronchi.

[0292] As the heart beats, it creates cyclical pressure fluctuations in the arterial system, and these pressure fluctuations are transmitted to the lungs via the arteries surrounding them. Furthermore, the heart is in partial contact with the lungs and, thereby, also exerts cyclical pressure fluctuations on the lung tissue. The pressure fluctuations exerted on the lungs cause slight cyclical lung volume fluctuations, which—in paralyzed or non-ventilating patients—cyclically squeeze gas accumulated in the bronchi into the trachea and toward the pharynx (when the heart causes a net compression of the lungs) and cyclically inhale gas from the pharynx toward the lungs (on the other half of the heart cycle when the net compressive force is released).

[0293] The cyclical flow in the trachea caused by cardiac action is commonly called "cardiac oscillation." In most patients, the lung volume displaced by cardiac action is sufficient to carry a small amount of gas (including CO2) from the lungs to the pharynx during the expiratory portion of each cardiogenic cycle, and then to return gas (including O2) from the pharynx to the lungs during the inspiratory portion of the cycle.

[0294] During the expiratory portion of the cardiogenic cycle, when CO2-containing gas reaches the pharynx, it is almost immediately swept out of the mouth by a relatively high flow of gas provided by flow therapy or a patient interface providing respiratory support (e.g., from a nasal cannula).

[0295] Similarly, the inspiratory portion of the cardiogenic cycle substantially enhances the transport of oxygen-containing gases from the pharynx toward the lungs—in addition to the flow resulting from the net consumption of oxygen in the alveoli.

[0296] It is worth noting that in the absence of flow from a patient interface (e.g., a nasal cannula), cardiogenic action alone may not be of sufficient amplitude to transport significant amounts of gas, including CO2, from the lungs through the tracheal and pharyngeal dead space and out the patient's airway (e.g., the patient's mouth). Adequate clearance of gas, including CO2, can occur only if the pharyngeal dead space is flushed.

[0297] In various instances, for example, at high nasal gas flows, cardiac oscillation therefore acts as a pump, transporting gas from the lungs to the pharynx where it is flushed, and enhancing gas transport from the pharynx back to the lungs. This is shown in Figure 2.

[0298] FIG. 2 illustrates a ventilation system for apnea due to cardiogenic action. A patient P is shown having a flow of gas provided or delivered to one or more nostrils of the patient's nose via a patient interface 2 as flow therapy or respiratory support. The provided or delivered gas enters the nasal passages and the patient's airways. The gas may be transported down the upper airways and into the patient's lower airways toward the lungs L. The lungs L may experience some oscillatory pressure on the lungs caused by pulsatile blowflow from the heart, helping to induce cardiogenic action, as indicated by arrows 6. The gas flow may be exhaled or exhaled (or expelled) through the patient's mouth 5.

[0299] Flow therapy or respiratory assistance may be provided or administered to a patient at a constant flow rate, but oscillations may be applied to the flow. Oscillatory flow of gas in the patient's trachea may be due to the cardiogenic effect of the patient's heartbeat. Flow therapy or respiratory assistance at a relatively high flow rate provided or delivered to a patient via the nose may assist in flushing of exhaled or expired gas from the patient's lungs in response to this oscillatory flow of gas in the trachea. Gas and flushing may be expelled through the patient's mouth or oral cavity when receiving flow therapy or respiratory assistance administered via the nose. Examples of applications of oscillatory flow rates are described in detail below.

[0300] For apneic ventilation to work effectively, it is important that there be a patent airway between the lungs and pharynx. Obstruction or blockage of the trachea or vocal cords disrupts cardiogenic pumping, preventing the ability to provide flow therapy or respiratory support (including oxygen administration) to the patient, as well as preventing clearance of expired or exhaled gases from the patient, e.g., CO2 clearance or flushing.

[0301] It would therefore be particularly beneficial to clinicians (and to the safety and health of patients) if the patency of a patient's airway could be more efficiently monitored and / or determined.

[0302] It is also important that gas flow be able to travel unobstructed from a patient interface providing flow therapy or respiratory assistance in the nose (e.g., a nasal cannula), through the oropharynx, and out the mouth. If this flow path is blocked, occluded, or otherwise obstructed, the pharynx will not flush properly, and CO2 will build up in the alveoli and trachea, displacing oxygen and ultimately causing both a decrease in blood O2 saturation and hypercapnia.

[0303] Sensing concentration fluctuations of target gases (e.g., CO2) in the pharynx / mouth The lungs continuously produce CO2, which is exhaled or expelled through the trachea and mouth in a series of pulses by cardiogenic action in non-ventilating or apneic patients.

[0304] Therefore, by monitoring the variation in CO2 concentration over time in the pharynx / mouth, it is possible to check whether CO2 is being sent from the lungs to the trachea and also whether it is being swept away by relatively high flow therapy or respiratory assistance (e.g., gases that may contain oxygen) being provided or administered via the patient's nose, for example, from a nasal patient interface (e.g., a nasal cannula).

[0305] Amount of target gas (e.g., CO2) cleared per cardiogenic cycle during apneic ventilation and oral concentration Figure 3 shows a plot of the flow out of the mouth due to cardiac oscillation. Cardiogenic flow volume over the expiratory portion of the cardiogenic cycle varies from person to person but is generally in the range of 20-60 ml.

[0306] In one example, model experiments have shown that at cardiogenic flow rates in this range, gas exchange between the lungs and pharynx of approximately 5 to 30 ml per cycle can be achieved. Assuming a partial pressure of CO2 in the lungs of approximately 40 mmHg, a cardiogenic pump can clear approximately 0.27 to 1.59 ml of CO2 into the pharynx per cardiogenic cycle. As shown, cardiac oscillations in gas flow can be mapped to the patient's heart rate.

[0307] Gases cleared from the lungs may mix with the relatively high flow of gases passing through the pharynx (provided or delivered as flow therapy or respiratory support), which significantly dilutes the CO2 (and other gases simultaneously exhaled or exhaled).

[0308] In one example, if the oxygen flow through the pharynx is 70 l / min and the expiratory portion of the cardiogenic cycle lasts 0.4 seconds, the concentration of CO2 exiting the mouth during each cardiogenic pulse will be approximately 570-3405 ppm (0.057-0.34%, corresponding to a partial pressure of 0.43-2.58 mmHg).

[0309] To monitor the CO2 pulse exiting the mouth (or moving through the pharynx) during cardiogenic exhalation, it is desirable to have a gas sensor capable of measuring concentrations that are approximately 1 / 10 of these values, allowing for tracking of the concentration pulse waveform. This corresponds to a sensitivity of approximately 57–340 ppm or 0.04–0.26 mmHg, with a time response of 0.2 seconds or less.

[0310] The implementation and use of sensitive CO2 sensing technology in the methods, systems and devices disclosed herein allows for the monitoring of CO2 concentration fluctuations in the pharyngeal flow due to the cardiogenic pumping of CO2 from the lungs.

[0311] An alternative to capnography with cardiogenically cleared target gas (e.g., CO2) for assessing airway patency during apneic ventilation As a further example, the concentration of CO2 in the lungs is relatively low—about 5% of the arterial CO2 level of 40 mmHg. This low concentration of CO2 is further substantially reduced when the CO2 pumped from the lungs is diluted, for example, in the pharynx, with the high flushing flow of flow therapy or respiratory assistance delivered or provided to the patient—and this contributes to the aforementioned challenge of being able to efficiently and accurately measure the concentration of gas being exhaled or expired by a patient.

[0312] Due to such challenges, when under apneic ventilation, a patient may be supplied with a high concentration of oxygen (which may include, but is not limited to, 100% oxygen). As such, it is possible to effectively flood the lungs with a high concentration of a benign tracer gas (which is the target gas that is then detected and measured) for a short period of time, and then monitor the cardiogenic pumping of the target gas from the patient's pulmonary system. This allows for effective monitoring of the patient's airway patency.

[0313] Under normal spontaneous breathing conditions, patients breathe air that is approximately 80% nitrogen and 20% oxygen. In light of this, a method, system, or device as disclosed herein facilitates the ability to briefly fill the lungs of an apneically ventilated patient with substantially (or fully) oxygenated 50:50 nitrogen / oxygen mixture (or other mixture of gases containing the gas being targeted, detected, and measured), followed by clearance of nitrogen (or other target gas) through cardiogenic action. While incurring only a small additional risk of desaturating the patient, such an approach offers significant benefits by providing clinicians with information regarding the monitoring of target gases, such as nitrogen, and their clearance at relatively high concentrations.

[0314] Therefore, in one particular embodiment of the present disclosure, it is provided to fill the patient's lungs with a mixed gas (e.g., a nitrogen / oxygen mixture) so that airway patency can be monitored. A particular procedure may be provided as follows: 1. A relatively high flow of gas (delivered via a nasal interface) is used to ensure that the patient is substantially oxygenated (or at least the patient's oxygen saturation level is increased) (oxygen saturation above about 98% may be achieved), the gas flow including oxygen (which may be humidified oxygen), the gas flow being at least 70 l / min and a pharyngeal splinting pressure of about 1 cm H2O. 2. Remove or substantially reduce gas flow for a relatively short period of time (e.g., remove or reduce humidified oxygen supply for approximately 1-2 seconds), thereby removing or reducing effective airway splinting pressure and slightly deflat- ing the lungs. 3. Apply gas containing a target gas (e.g., a humidified nitrogen / oxygen mixture) at a flow rate (e.g., a relatively high flow rate, e.g., about 70 L / min or more, depending on the flow therapy or respiratory support required for a particular patient) for a period of time (e.g., about 1-3 seconds). Here, the gas flow provided during step 3 may at least partially re-inflate the lungs, but the lungs are at least partially re-inflated using gas containing the target gas (e.g., a nitrogen / oxygen mixture) to ensure that the gas containing the target gas reaches the lungs. 4. Resume the flow therapy or respiratory support provided from step 1 (e.g., providing humidified oxygen) without potentially reducing the pressure applied to the patient's airway to prevent the lungs from collapsing. 5. Monitor the variation in the concentration of the target gas (e.g., nitrogen) in the mouth / pharynx over time as it is pushed from the lungs by cardiogenic action and swept out of the mouth by the flow of gas provided by flow therapy or respiratory support (e.g., relatively high flow humidified oxygen).

[0315] If a 50:50 nitrogen / oxygen gas mixture is used in step (3) above, the concentration of nitrogen is initially about 10 times that of CO2, which may provide significant advantages in clearance monitoring. It is understood that alternative gas mixtures may be used in this procedure, and different gases may be used to detect, measure, and monitor the target gas.

[0316] It should be noted that if a deflation / inflation procedure is not performed and instead high flow oxygen is simply replaced with a high flow mixed gas, e.g., a nitrogen / oxygen mixture, it is not possible to ensure that the physiological dead space will be filled with the mixed gas (e.g., nitrogen / oxygen mixture) or that the target gas (e.g., nitrogen) will reach the lungs.

[0317] Monitoring airway pressure to ensure sufficient flow to support and relieve atelectasis A relatively high flow of gas provided to a patient, for example, via the patient's nose, by, for example, flow therapy or respiratory assistance (e.g., the gas may be oxygenated or contain supplemental oxygen to increase the oxygen concentration above that of air alone), can help create or provide a small sprinting pressure within the patient's airways (which may be, but is not limited to, approximately 0.5-5 cmH2O). This pressure, although relatively small, can help expand the alveoli and assist in reducing atelectasis. This extra pressure can be particularly important in obese patients and other patients prone to atelectasis.

[0318] If the nasal pharyngeal airway becomes partially obstructed, the splinting pressure may be substantially reduced, thereby placing the patient at increased risk for airway collapse, atelectasis, and / or desaturation.

[0319] Therefore, the methods or systems and devices disclosed herein may also provide for monitoring of splinting pressure in the airway by a pressure sensor or probe that may be placed just above the larynx, which may provide additional information that allows a clinician to further assess the patency of the pharyngeal airway, or the pressure data signal or output from such a sensor or probe may contribute to determining the patency of the patient's airway.

[0320] Sensing fluctuations in concentration of a target gas (e.g., CO2) in the pharynx / mouth to assess airway patency FIG. 4 shows an example of a system for assessing airway patency by monitoring a target gas, such as CO 2 , exhaled or expired from the lungs of a patient P due to cardiogenic action.

[0321] The anesthetized and / or paralyzed respiratory system of a patient is apnea-ventilated by providing or implementing flow therapy respiratory support using, for example, a relatively high flow of gas (e.g., humidified oxygen) delivered via a nasal patient interface (e.g., nasal cannula). The flow rate of the delivered or provided gas is sufficiently high to achieve at least some sprinting pressure to alleviate atelectasis and ensure sufficient absorption of the delivered gas (e.g., oxygen) by the lungs to address and avoid desaturation conditions.

[0322] Precautions may be taken to avoid or reduce the possibility of patient barotrauma (e.g., safety valves or other pressure relief valves or vents to relieve or reduce pressure within the circuit or patient interface providing flow therapy or respiratory assistance).

[0323] As shown in FIG. 4, the patient's mouth is open and gas flow in flow therapy or respiratory assistance is provided or delivered through the nose and can travel through the pharynx and out the mouth.

[0324] A sampling instrument or device including a sensor, such as a gas sensing head, may be placed within the patient's mouth / oropharynx region. The sensor may be positioned anywhere between positions (a) and (b) along the floor of the mouth / oropharynx, as shown in Figure 4.

[0325] The sampling device or apparatus may be a separate device, or may be incorporated into the nasal cannula, or may be removably connectable to the nasal cannula.

[0326] Position (a) is shown as being at or near the bottom of the mouth entrance between the teeth, and position (b) is shown as being at or near the entrance to the trachea. The sensor head should not be placed in the valley, as this presents a risk of blocking gas flow into the sensor, and therefore should not be placed directly in the gas stream coming from the trachea. A range of different positions for placing the sensor gives the clinician flexibility to avoid obscuring the surgical site, depending on the procedure being performed. The range of positions is possible so that the patient is apneic and reduces the possibility of causing irritation or discomfort to the patient.

[0327] In some configurations, gas may be sampled from both the patient's mouth and nose.

[0328] Alternatively or additionally, the sampling device / apparatus may include a sampling tip. The tip may be designed to maximize CO2 collection and prevent / reduce the introduction of saliva into the sampling device / apparatus. The sampling device / apparatus may include a hollow tube coupled to a gas sensor located remotely from the patient, for example, in the flow generator. The sampling tip may be a malleable tip that can maintain the position of the sampling tip when manipulated into the operable position.

[0329] The sensor may be connected to a sensitive sidestream gas (e.g., CO, N, helium) sensor that draws a sample of gas from the mouth / oropharyngeal region at a relatively low flow rate. The flow rate drawn into the sensor should be less than about 200 ml / min (one-fifth the peak expected for cardiogenically-induced gas flow in the trachea).

[0330] If necessary, precautions can be taken to avoid aspiration of fluids and water vapor into the sensor, such as using a water trap or filter in conjunction with semi-permeable tubing (such as a material called NAFION). These are not shown in the drawings. In accordance with the above embodiments, the sampling tip can be shaped or include wall arrangements, such as castellations, to prevent fluids from being aspirated.

[0331] The sensor (e.g., a gas analyzer-type sensor) may provide a signal or output that can be processed by a processing device or controller, and a corrected or compensated output or signal of the detected and measured target gas concentration may be provided via an output (e.g., a GUI) or other information display. Alarms or other warnings may be issued or emitted depending on the variation in the concentration of the target gas measured over time.

[0332] Similarly, the input of the patient's heart rate or cardiogenic activity may be correlated or related to the sensed concentration of the target gas to provide an informational output to the clinician.

[0333] Similarly, the input of the flow rate of gas provided or delivered to the patient (i.e., the flow rate of flow therapy or respiratory support provided to the patient) may be sensed or measured by the flow meter device, and such input provided to be correlated or related to the sensed concentration of the target gas to provide an information output to the clinician.

[0334] As described above, the flow of gas may be provided or delivered to the patient in an oscillatory flow or may be delivered in an oscillatory flow superimposed on the actual flow of gas to the patient. The flow may help to enhance or augment gas exchange from the patient's airway. Additionally or alternatively, the flow may help to enhance or augment gas exchange resulting from cardiogenic pulses occurring within the patient's body.

[0335] The flow may be the sum of one or more oscillatory waveforms. The oscillatory flow or each oscillatory waveform may be substantially sinusoidal (i.e., generated based on a sine function). In one embodiment, the flow is the sum of two or three oscillatory waveforms. In one embodiment, the flow may include oscillatory waveforms with frequency characteristics similar to the patient's heartbeat or cardiogenic pulsing.

[0336] The flow of gas may be delivered in accordance with a flow signal. The flow signal (and thus delivered) may include one or more of the following signal characteristics or parameters: frequency, amplitude, waveform, and / or phase. The frequency is substantially repeating over a period of time. Further, the waveform is substantially repeating over a period of time.

[0337] Flow parameters can be selected to optimize or increase exhalation or expiration of the gas from the patient. Oscillatory flow can have one or more frequency components to improve exhalation of gas due to cardiogenic mechanisms. Alternatively or additionally, flow parameters can be selected (e.g., oscillation amplitude or duration) to maximize exhalation of a target gas.

[0338] The terms target gas and monitor gas may be used interchangeably: the signal measured by a sensor in the system may be a target gas signal or a monitor gas signal, respectively.

[0339] The flow of gas delivered to the patient may enhance and / or encourage the exhalation or expiration of at least one target gas. In this manner, measurements of at least one target or monitored gas may vary in response to the delivered flow when the patient's airway is unobstructed or patent for a period of time.

[0340] A correlation between the delivered flow rate and a measurement of at least one target or monitoring gas as a monitoring gas signal may be determined, and an indication of the patient's airway patency may be based on this correlation.

[0341] The monitor or target gas may be CO2 or O2, or a gas that indicates the concentration of carbon dioxide or O2. Additionally, the monitor gas may be any of the target gases described above.

[0342] In an embodiment, the target gas is CO2 because CO2 is exhaled from the lungs. As such, CO2 provides a particularly good indicator of airway patency when 100% O2 is being delivered to patients who are not spontaneously breathing or who have a very low respiratory drive.

[0343] The physiology of how the correlation enables airway patency to be determined is described below with respect to a nasal cannula interface and oscillatory flow, although it is envisioned that other interfaces may be utilized (whether or not the flow profile actually varies). When flow is applied through a nasal cannula (e.g., via a flow generator including a proportional valve as described above) and the patient's upper airway is patent, a significant portion of the flow passes through the nasopharyngeal passage and exits through the mouth. In normal adults, when a flow rate of 70 l / min (or up to 100 l / min when the patient is apneic or has a reduced respiratory urge) is applied through the cannula, the pressure generated in the pharynx is typically 0.5-5 cm.

[0344] If the lower airways (e.g., larynx / trachea) are patent in addition to the upper airways, this flow or pressure is delivered to the lungs. An increase or decrease in the provided oscillatory flow rate results in a corresponding increase or decrease in pressure in the pharynx (at a rate approximately proportional to the square of the flow rate). Because a patient's lungs are generally compliant, they expand when pressure is applied to the airways. Therefore, when the flow applied through the interface increases, the lungs expand due to the increased pressure created in the airways, and at least a portion of the gas flow passes through the airways from the pharynx to the lungs. Conversely, when the flow applied through the cannula decreases, the airway pressure decreases. Therefore, the lungs contract, and some of the gas in the lungs is forced up the trachea, entering the turbulent flow in the pharynx, where it mixes with the gas stream expelled from the mouth. Furthermore, CO2 also occurs as part of cardiogenic pulsing (as discussed above) and is a component of the gas forced up the trachea.

[0345] When gas exchange occurs in the lungs (e.g., by either cardiogenic pulsing or normal gas exchange), the lungs contain CO2, and when gas is forced up the trachea (i.e., a decrease in the applied flow rate), this is manifested as a transient increase in CO2 concentration in the gas leaving the mouth due to the reduced flow applied to the cannula. This transient increase in CO2 concentration is only seen if both the upper and lower airways are patent (i.e., flow can move from the nose to the pharynx and exert pressure there, and gas can pass up and down the trachea between the lungs and pharynx).

[0346] The relationship between applied flow rate, lung volume and airway pressure is shown in Figure 12. Figure 12 shows a patient P being provided with a flow of gas from interface 2. The graph shows that as the flow rate increases from A' to D', the lung volume also increases and a flow 10 is generated into the patient's lungs L.

[0347] As can be appreciated, application of an oscillatory or otherwise variable flow rate is preferred when the patient is not spontaneously breathing, since there is otherwise no flow from the patient's lungs (or at least very minimal flow due to cardiogenic pulsing). However, when the patient may be spontaneously breathing, both oscillatory or otherwise variable flow and constant flow rates may be used, and the concentration of CO or other target gas is used to determine airway patency.

[0348] Correlation of delivered flow rate with target or monitor gas The correlation may be based on the flow rate of the gas (as a flow signal) with the concentration of the target gas. Other properties of the target gas may also be correlated with the flow signal, such as flow rate.

[0349] The correlation may be based on a comparison of waveform characteristics of the gas flow with waveform characteristics of the monitored gas signal. The waveform characteristics may be any characteristic of a wave. Some non-limiting examples of waveform characteristics are frequency, amplitude, phase, shape, and slope.

[0350] Additionally or alternatively, the correlation may be based on a comparison of a first shape or profile of the delivered flow with a second shape or profile (or the shape of a subsequent profile) of the monitored gas signal. The first shape or profile of the delivered flow may be at least partially repeated. By way of example, the first shape or profile may be a peak or trough of the delivered flow, and the second shape or profile may be a similar or substantially identical waveform shape or profile in the monitored gas signal.

[0351] Additionally or alternatively, the correlation may be based on a comparison of one or more of the frequency of the flow, the amplitude of the flow, the waveform of the flow, the phase of the flow, and the change in the flow over time (e.g., the damping or driving of the flow) with one or more of the frequency (or frequency range) of the monitored gas signal, the amplitude of the monitored gas signal, the amplitude of the monitored gas signal at a particular frequency, the waveform of the monitored gas signal, the phase of the monitored gas signal, and the change in the monitored gas signal over time.

[0352] One particular method of correlation as described above is a comparison of the frequency (or frequency range) of the flow (or flow signal) with the frequency (or frequency range) of the monitor gas signal.

[0353] Alternatively or additionally, the correlation may be performed using one or more of an edge or transition portion of the signal of the flow waveform, a local maximum or minimum or inflection point of the flow waveform, a slope of a portion of the flow or a slope at a discrete point, a number of peaks and / or troughs of the flow within a given period or a predetermined period, and a subsequent edge or transition portion of the signal of the monitoring gas signal waveform when the subsequent edge or transition portion of the signal of the monitoring gas signal waveform is located within a period after the edge or transition portion of the signal of the flow waveform. The comparison may be based on a comparison of a subsequent maximum, minimum or inflection point of the waveform of the monitored gas signal within a certain period of time, the slope of a subsequent portion or discrete point of the waveform of the monitored gas signal within a certain period of time, the slope of a subsequent portion or discrete point of the waveform of the monitored gas signal within a certain period of time, the slope of a subsequent portion or discrete point of the waveform of the monitored gas signal within a certain period of time, or one or more of a number of peaks and / or troughs of the monitored gas signal within a given period or a predetermined period of time.

[0354] An edge of a signal as described above may be a rising edge or a rising portion of the signal. Additionally or alternatively, an edge of a signal may be a falling edge or a falling portion of the signal.

[0355] Use of correlation to determine airway patency A correlation indicative of a non-obstructed or substantially non-obstructed airway condition may be based on any one or combination of the correlation bases described above that are above (or within) a set threshold or margin. Conversely, a correlation indicative of an obstructed or substantially obstructed airway condition may be based on any of the correlation bases described above that are below (or not within) a set threshold or margin.

[0356] Additionally or alternatively, the strength of the correlation is proportional to the degree to which the patient's airway is patent.

[0357] Again, reference is made to a particular correlation based on a comparison of the frequency of the flow (or flow signal) with the frequency (or frequency range) of the monitored gas signal. When at least one component of the frequency (or frequency range) of the monitored gas signal is similar to the frequency (or frequency range) of the flow, and when the amplitude of the flow at said frequency is above a certain threshold, the patient's airway is determined to be unobstructed or substantially unobstructed.

[0358] FIG. 13A shows the delivered flow rate versus time waveform W. FIG. 13B shows the measured monitored gas (CO2 in this case). As shown in FIG. 13A, the measured monitored gas is a filtered signal to remove noise. It can be observed that a decrease in the delivered flow to the patient (indicated by section A in FIG. 13A) produces a corresponding peak in the monitored gas (indicated by section A in FIG. 13B). This is due to a drop in pressure, causing a flow of gas containing CO2 from the patient's lungs. Furthermore, in section B of FIG. 13A, the flow rate decreases, and during this section, there is no gas flow from the patient's lungs; therefore, no CO2 is measured in section B of FIG. 13B. The frequency of the monitored gas signal W' is the same as the frequency of the delivered flow signal W. Therefore, a frequency-based correlation between the two shows a strong correlation between the monitored gas signal W' and the delivered flow signal W at the frequency of the delivered flow signal (in this case, the delivered flow frequency is approximately 3 Hz). The oscillatory flow rate shown in Figure 13A assists in oxygenation of the patient and aids in CO2 clearance by flushing. Oscillatory flow is described in more detail above.

[0359] In some embodiments, the measured monitored gas and / or gas flow rate may be displayed on a user interface, as described in more detail above, as shown in Figures 13B and 13A, respectively.

[0360] Similar to above, the patient's airway is determined to be obstructed or substantially obstructed when at least one component of the frequency of the monitored gas signal is not similar or different or not sufficiently similar to the frequency of the flow, and / or when the amplitude of the signal at said frequency is similar and below a certain threshold.

[0361] Furthermore, gas monitoring can be instantaneous or real-time as a monitored gas signal. The monitored gas signal may be sampled periodically or at regular intervals. Additionally or alternatively, the monitored gas signal can be monitored over a set period of time, for example, for a procedure (such as surgery or pre-oxygenation procedure) or portion thereof.

[0362] The determination of airway patency may be based on real-time measurements of the monitored gas, or measurements may be made of the monitored gas over a period of time and subsequently analyzed to derive a waveform and / or determine airway patency.

[0363] The correlation can be determined by one of the methods known in the art. Possible methods for determining the correlation are Monte Carlo, spectral analysis, or Fourier transform. In one example, a sequential Monte Carlo method can be used.

[0364] In some configurations, a sequential Monte Carlo method may be used. In a sequential Monte Carlo method, multiple estimates corresponding to different airway conditions are generated. The estimates are kept in the controller's memory and updated at each time step based on a determined model of the system. Such a model may be based on various factors of the airway or other physiological parameters of the patient. The monitored gas is then measured and compared to the updated estimates—estimates that are closer to the actual measurement are given more weight than estimates that are further away. Over multiple time steps, the estimates are reweighted (based on how close they are to the actual measurement). The weight of the estimate corresponds to the confidence that a particular estimate is correct.

[0365] The above-mentioned correlation method may be implemented by the above-mentioned apparatus, which may include a flow generator for generating and / or providing a flow rate (which may be oscillating) and delivering the flow rate to the patient, a gas sampler (or sampling instrument or device) configured to monitor or detect at least one target (or monitored gas) being exhaled or expired from the patient's airway, and a controller (which may include a processor) for determining a correlation between the delivered flow rate and the monitored gas and determining one or more indicators of airway patency or a location of a blockage or obstruction in the airway based on said correlation.

[0366] The apparatus may be configured to perform any of the methods described above or to include any of the features described above.

[0367] Correction for the dilution effect of flow from a nasal cannula on the concentration of a target gas (e.g., CO2) measured in the mouth / pharynx To reliably estimate the concentration of a target gas (e.g., CO2) exiting the mouth during a cardiogenic-induced expiratory pulse, it is necessary to provide a correction or compensation to account for dilution of the target gas (e.g., CO2) by high-flow O2 exiting the mouth or by gas being provided or delivered to the patient by flow therapy or respiratory assistance (e.g., relatively high-flow humidified oxygen) from high-flow gas therapy or respiratory assistance. This flow rate can be estimated by measuring the flow rate of gas (e.g., oxygen) entering a patient interface (e.g., nasal cannula) delivering flow therapy or respiratory assistance, and then applying a correction factor or compensation to account for bypass leakage from the patient's nares, leaving the flow exiting through the mouth unchanged. The relationship between the flow entering a patient interface (e.g., nasal cannula) and the flow being exhaled or exhaled (i.e., exiting the mouth) is shown in Figure 5. That is, Figure 5 shows the ratio of mouth flow to nasal cannula flow as a function of cannula flow rate.

[0368] In particular, regarding Figure 5(A), 1. At relatively low gas flows (i.e., up to about 10 l / min), a significant portion of the gas flow entering a patient interface (e.g., a nasal interface, e.g., a nasal cannula) exits the nose by leaking back through the nares, with virtually no flow from the interface passing through the pharynx and exiting the mouth. 2. At relatively moderate flows (i.e., from about 10 l / min to about 30 l / min), an increased proportion or percentage of the gas flow entering the patient interface exits via the mouth, proportionally reducing leakage back into the nose via the nostrils. 3. Above about 30 l / min, the ratio of gas flow out of the mouth to gas flow into the patient interface is substantially or nearly constant. The ratio depends on the relative sizes of the nostrils and the gas delivery elements of the patient interface to the patient's airway (e.g., the cannula prongs of a nasal cannula) and therefore may vary from patient to patient. The average value may be about 0.4.

[0369] Correcting for the dilution effect of flow from a patient interface (e.g., nasal cannula) on CO measurements made through the mouth may be sufficient to approximate the curve in FIG. 5(A) by three straight lines as shown in FIG. 5(B).

[0370] With respect to FIG. 5(B), and in the first horizontal segment of the line from about 0 to 10 L / min, the dilution factor may be about 1 (i.e., there is substantially no flow exiting the patient via the mouth, and CO2 entering the mouth due to cardiogenic effects is not diluted). If F<10 l / min: dilution factor = 1 where F is the flow rate of the cannula.

[0371] In the second rising segment of the line (from about 10 l / min to 30 l / min), the ratio of flow from the mouth to flow into the patient interface increases linearly from about 0 to 0.4 with patient interface flow rate F. If this ratio is designated as R, then the equation for the variation of R with patient interface flow rate is: When 10 l / min < F < 30 l / min: R = 0.4(F - 10) / 20 Where: R is the ratio of the flow out of the mouth to the flow into the cannula. The dilution factor for flows in this range can be expressed as follows. When 10 l / min < F < 30 l / min, dilution factor = 1 + 0.4F(F - 10) / (20PCF) Where: F = the flow rate (l / min) of the patient interface (e.g., nasal cannula) PCF = the peak cardiogenic flow rate (in l / min units - typically 2 l / min) For flows of the patient interface (e.g., nasal cannula) above 30 l / min, the ratio of the flow from the mouth to the flow into the patient interface remains approximately 0.4. Therefore, the dilution factor for flows above 30 l / min is as follows. When F > 30 l / min: dilution factor = 1 + 0.4F / PCF

[0372] Constants: 10 l / min, 30 l / min, and 0.4 are given only as examples and are based on measurements made only for an exemplary nasal cannula. It should be noted that for different cannula sizes or different patient interfaces, different empirically determined constants may be used to determine the dilution factor. The dilution factor can be determined by empirical testing or modeling and can be programmed into the controller.

[0373] The CO2 concentration measured at the mouth / pharynx using the configuration shown in Figure 6 can be corrected for dilution by multiplying it by the dilution factor determined according to the flow rate of the cannula as described above, resulting in a corrected CO2 concentration, which is used in the determination of airway patency described below.

[0374] The step - by - step procedure for starting the correction is as follows. 1. The flow rate F of the patient interface (e.g., nasal cannula) is measured using a flow meter in the patient interface supply conduit or line. The flow meter signal is transmitted to a signal processing device. 2. The dilution factor used for correcting the CO2 sensor signal is calculated as follows. When F < 10 l / min: Dilution factor = 1 When 10 l / min < F < 30 l / min: Dilution factor = 1 + 0.4F(F - 10) / (20 - PCF) When F > 30 l / min: Dilution factor = 1 + 0.4F / PCF

[0375] Note that these types of dilution factors are only illustrative, and other dilution factors may be determined for other supply flows.

[0376] The dilution factor can be used by the controller to account for the flow rate of the gas delivered by the supplied high-flow therapy or respiratory assistance. The controller may include a flow sensor to determine the flow during supply, and thus the controller can automatically determine the dilution factor.

[0377] When PCF is the peak flow rate induced by cardiac generation, generally 2 l / min, and usually in the range of 1 l / min to 6 l / min. The value of PCF used by the processing device is predetermined from measurements for a range of typical subjects. 1. The CO2 level in the mouth / pharynx is detected over time by a sensitive high-speed CO2 sensor with a sensitivity better than 0.05% and a response time < 0.2 seconds. 2. The measured CO2 signal is multiplied by the dilution factor to give a corrected CO2 level. 3. The corrected CO2 level is displayed over time on the display unit.

[0378] Figure 6 shows the trace of CO2 concentration (before correction) over time that would be expected from a gas sensor providing gas concentration analysis under various airway conditions. Note that the values given in Figure 6 are only indicative or approximations and will vary substantially from patient to patient, depending on the position of the sensor's sensing head and the flow rate of gas (such as oxygen) delivered through the patient's nose. It is not an absolute value, but a qualitative feature of the trace that is used to assess airway patency.

[0379] Plot (A) of Figure 6 shows the expected signature in a patient in which both the pharyngeal airway and trachea are patent and CO2 is substantially cleared by apneic ventilation. It has the following characteristics: The CO2 concentration pulse occurs in synchronization with the patient's heart rate or cardiogenic activity. The baseline CO2 level is zero (or close to zero) because substantially all of the CO2 delivered to the pharynx during the expiratory portion of the cardiogenic cycle is flushed out of the mouth by the relatively high flow of gas (e.g., oxygen) being delivered or provided to the patient (e.g., via the nose) while flow therapy or respiratory support is being provided to the patient. · Baseline CO2 levels do not increase over time.

[0380] Note that the peak value of the CO2 concentration pulses may vary over time depending on variations in CO2 production by the patient (likely as a result of metabolic variations due to the surgical procedure). The peak value of the CO2 concentration pulses, and their duration, also vary with the flow rate of oxygen delivered to the patient via the nose. Higher flow rates give lower peak values and shorter pulses.

[0381] Plot (B) of Figure 6 shows the expected trace in a patient with a patent trachea but a blocked nasopharyngeal airway. This may be due, for example, to the soft palate dropping into the airway and obstructing it. In this case, the flushing flow does not reach the mouth / oropharynx, and the trace has the following characteristics: Early in the blockage, CO2 is still being produced by the lungs and is being sent to the mouth / oropharynx by cardiogenic action, so a pulse of CO2 concentration is seen. The pulse is synchronized with the patient's heartbeat. Gas reaching the oropharynx or mouth from the trachea is not cleared through the mouth by flushing flow. The only mechanisms available to clear this are dilution, auxiliary air movement outside the mouth causing residual flow / turbulence inside the mouth, and patient movement. Generally, these clearance mechanisms are not sufficient to substantially clear all CO2 from the oropharynx, so baseline CO2 levels rise over time. Note that the rate of rise can vary depending on the patient's metabolic rate, tracheal resistance to cardiogenically induced flow, and the level of residual flushing from external air movement or patient movement. The CO2 concentration in the oropharynx, or mouth, rises as it fills with gases pumped from the lungs by cardiogenic action. Eventually, it can reach the CO2 concentration in the lungs themselves. Therefore, without residual clearance from air movement outside of the patient, the amplitude of the concentration pulse is expected to decrease as the baseline concentration of CO2 in the pharynx reaches that of the lungs. Note that even when the baseline concentration of CO2 in the oropharynx reaches that of the lungs, the baseline level is still expected to rise slowly over time as the partial pressure of CO2 builds in the blood due to ongoing metabolic action (hence its concentration in the lungs increasing over time).

[0382] It should be noted that only a small flow from the nose is required to sufficiently clear CO2 from the oropharynx, and this signature would not be expected in a partial obstruction of the pharyngeal airway, which still allows for flow from nose to mouth at rates in excess of 1-5 l / min. In such a situation, measurement of the splinting pressure in the airway is required, and this forms part of a separate patent claim.

[0383] Plot (C) of Figure 6 shows the expected trace in a patient with a blocked trachea and a patent pharyngeal airway. CO2 is not driven to the oropharynx by cardiogenic action, but flushing with oxygen occurs. The trace remains essentially zero or at baseline concentrations.

[0384] In traditional ventilation practices, clinicians visually monitor the capnographic signature to gain comfort that the patient is being cleared of CO. In the present application, a gas sensor with a suitable controller can be implemented that can recognize the characteristics of the signature described above and issue or generate a warning or alarm if conditions (B) or (C) are detected.

[0385] The following is an example of such a software process for distinguishing between conditions (A) and (B), and (A) and (C).

[0386] To distinguish between signals (A) and (B), note that when both the soft palate and trachea are open, signal (A) consists of a regular series of pulses of CO2 concentration synchronized with the patient's heartbeat. Between each pulse, the CO2 concentration in the mouth / pharynx drops to zero because the pharynx is flushed with high-flow pure oxygen from the nasal cannula. However, when the soft palate is closed, the CO2 level in the mouth / pharynx rises to above 1000 ppm. Therefore, CO2 levels continuously above 1000 ppm for a period of several heartbeats indicate a problem with the soft palate.

[0387] It is understood that the following routines or procedures may be implemented or performed by one or more programmable devices based on computer-readable instructions, software logic, or hardware logic. Suitable programmable devices may include, but are not limited to, a microcontroller, a microprocessor, a CPU, an ASIC (application-specific integrated circuit), or hardware or any other programmable hardware device, system, or platform. It is also understood that the described routines and procedures may be implemented by a controller of the flow rate delivered for high-flow therapy or the flow rate for respiratory assistance.

[0388] An example of a process or routine or procedure (which may be implemented by software, for example) for determining condition (B) may be as follows. 1. The signal processor continuously monitors the gas concentration level (e.g., CO2 concentration level) from the sensor. 2. If the gas concentration level rises above a threshold (e.g., 1500 ppm) (this is a typical value, but other ranges of values may be used, e.g., from about 100 ppm to about 4000 ppm when 100% pure oxygen is delivered to the patient interface), a software flag is set and a counter is started. The counter counts heartbeat pulses from a plethysmograph sensor (oxygen saturation sensor) attached to the patient. Alternatively, the counter may also be configured to count heartbeats in a signal from an ECG attached to the patient. 3. A flag is reset. This flag or counter may be implemented as a software flag or counter. If the gas concentration (e.g., CO2 concentration) level subsequently drops below a threshold (e.g., the 1500 ppm mentioned above), the counter is stopped and set to zero. 4. Each time the counter is incremented, its value is checked, and if the value exceeds a set threshold (a typical value setting is 30, but could be in the range of 10-120), an alarm or warning or other indicator may be generated or emitted to indicate condition (B) (i.e., the soft palate is closed and the trachea is open).

[0389] The same routine can be used or implemented to detect soft palate closure or obstruction or blockage when injection of a target gas, such as a benign tracer gas or other target gas, is used. In such a situation, a software flag is set for the concentration of target gas (such as a benign medical gas or otherwise tracer gas) provided to the patient, e.g., a 10% initial concentration of target gas (e.g., a benign medical tracer gas).

[0390] An example of a process or routine or procedure (eg, by software) for determining condition (C) may be as follows. 1. The signal processor continuously monitors the target gas concentration (e.g., CO2) level from the sensor. 2. A counter, for example a software counter, is provided which is zeroed at the start of treatment or when a reset button is pressed or activated by the clinician. 3. Each time the target gas concentration (e.g., CO2) level rises above an upper threshold (e.g., 250 ppm) and then falls below a lower threshold (e.g., 200 ppm), a software counter is decremented. 4. At the same time, pulses from the plethysmograph sensor (oxygen saturation sensor) are fed to the signal processor. 5. Each time a plethysmograph pulse occurs, a software counter is incremented and its value is monitored. 6. If the value of the software counter exceeds a certain threshold (a typical value setting is about 30, but may be in the range of about 10-120), an alarm or warning or other indication may be issued or provided to indicate condition (C) (trachea closed).

[0391] The same software routine or algorithm may be used to detect tracheal closure when injection of a target gas, such as a benign tracer-type gas or other target gas, is used. In such a situation, pulses of the target gas tracer gas are detected by setting thresholds at 1% of the concentration of the tracer gas injected into the patient (for the rising edge of the tracer cardiogenic pulse) and at 0.75% of the concentration of the tracer gas injected into the patient (for the falling edge of the tracer cardiogenic pulse).

[0392] It should be noted that the counter used to determine condition (B) is a different counter than that used to determine condition (C).

[0393] Monitoring tracer gas clearance to assess airway patency FIG. 7 shows an example of a system for assessing airway patency by monitoring the clearance of a target gas (e.g., a benign tracer gas) being exhaled or expired from the lungs by cardiogenic action.

[0394] A paralyzed patient P under anesthesia is apnea-ventilated using a relatively high flow of gas (e.g., humidified oxygen) delivered via a patient interface (e.g., nasal cannula 2). The flow rate provided or delivered to the patient by such flow therapy or respiratory support is sufficiently high to achieve at least some or necessary sprinting pressure to alleviate atelectasis and to ensure sufficient capacity of the lungs to absorb oxygen and help avoid desaturation.

[0395] The gas flow may be delivered at a constant rate. Alternatively, flow therapy or respiratory support may be delivered to the patient at an oscillatory (actual) flow rate or with superimposed oscillations. Oscillatory flow may be delivered to augment exhalation of CO2 or tracer gas.

[0396] When high-flow gas is delivered to a patient via a high-flow therapy or respiratory assistance method or device, such flow rate can be generated to include various components with one or more parameters (e.g., flow rate) that can be adjusted, including oscillating. Each parameter can be adjusted independently or dependently on other parameters, thereby providing a varying gas flow (variable gas flow parameter). The varying gas flow (with oscillation) can aid in the removal of gases (e.g., exhaled or exhaled CO2 or other gases, including target gases or benign tracer gases) and can aid in the provision or delivery of oxygen or other gases (e.g., target gases or benign tracer gases) to the patient's airway or respiratory system. By way of example, the gas flow can include a non-oscillating base flow component combined with one or more oscillating flow components, each at a different frequency, thereby generating a varying overall gas flow waveform. The flow therapy device can be controlled by a valve, blower controller, and / or other modulation device to generate the flow components. PCT Application No. PCT / IB2016 / 051820 describes the use of oscillatory components and is incorporated herein by reference in its entirety.

[0397] The supply system to the patient interface may incorporate a proportional or switching valve 14 to allow flow to the patient interface to be controlled and to switch from a first gas source 1 (such as an oxygenated gas source) to a source of gas 13 containing the target gas (e.g., a mixture of oxygen and a benign tracer gas). In this example, a 50:50 nitrogen / oxygen mixture is used, but the relative concentrations of oxygen and tracer gas may be varied and different tracer gases may be used, provided that this does not endanger the patient or compromise the procedure in the operating room.

[0398] The proportional or switching valve 13 may be configured to switch flow from one source to another without interrupting the net flow to the patient interface (e.g., nasal cannula 2) and thus without causing a drop in airway splinting pressure resulting from flow delivered through the patient interface.

[0399] The flow of the nitrogen / oxygen mixture may be independently controlled by a second valve between zero and a maximum flow rate limited by the risk of barotrauma to the patient. As previously described herein, precautions to avoid barotrauma (e.g., a safety valve to relieve pressure in the nasal cannula) may be implemented. These are not shown in the drawings.

[0400] The patient's mouth is open so that the flushing flow entering through the nose can travel through the pharynx and exit through the mouth.

[0401] A sensor, such as gas sensing head 4, may be placed within the patient's mouth / oropharynx region. The gas sensing head may be part of or attached to a gas sensor (not shown). There is considerable latitude in positioning the head along the floor of the mouth / oropharynx, to be placed anywhere between positions (a) and (b) as shown in the drawing. Position (a) is at the bottom of the mouth entrance between the teeth, and position (b) is at the entrance to the trachea. Note that the sensor head should not be placed in a valley, as this would risk blocking gas flow to the sensor and would also not be directly in the gas stream coming from the trachea. The range of sensing heads allows flexibility for the clinician to avoid obscuring the surgical site, depending on the procedure being performed. The sensor may be part of a sampling instrument or device, as described above.

[0402] The sensing head is connected to a sensitive sidestream nitrogen sensor that aspirates a sample of gas from the mouth / oropharyngeal region at a low flow rate. The flow rate aspirated into the sensor should generally be less than 200 ml / min (one-fifth the expected peak of tracheal cardiogenic evoked flow). Standard precautions should be taken, such as using a water trap or filter in conjunction with semi-permeable tubing of a material such as NAFION, to avoid aspirating fluid and water vapor into the sensor head, if necessary. These are not shown in the drawings.

[0403] The clinician assesses airway patency by performing the following measurement procedures: 1. The patient is initially adequately oxygenated (above 98% saturation) using a high nasal flow of humidified oxygen at least 70 l / min and either a pharyngeal splinting pressure of 1 cm H2O or bag and mask ventilation (or a combination of these). 2. The humidified oxygen supply via the nasal cannula is then removed for a second or two, which relieves the splinting pressure and allows the lungs to contract slightly. 3. A high flow (70 l / min or more) of humidified nitrogen / oxygen gas is then applied for a few seconds, which partially re-inflates the lungs with the nitrogen / oxygen gas, ensuring that the gas mixture reaches the lungs. 4. Humidified oxygen supply is restored without constricting the lungs. 5. Fluctuations in nitrogen concentration in the mouth / pharynx are monitored over time as it is pumped from the lungs by cardiogenic action and cleared from the mouth by high oxygen flow.

[0404] Figure 11 illustrates a further configuration including a correction or compensation system similar to that disclosed in Figure 7. The system includes a processing unit 33 having at least one data input for reading data from various other components of the system and at least one data output for transmitting data to various other components.

[0405] A flow meter 31 is disposed in the gas delivery conduit between the gas source (1, 13) and the nasal cannula 2. The gas sources may be as described above, such as a first gas source 1 (such as an oxygenated gas source) and a gas source 13 containing a target gas (such as a mixture of oxygen and a benign tracer gas). The flow meter measures the flow rate of gas provided by the gas source (1, 13) through the valve 14. The flow meter may measure a mass flow rate, or a volumetric flow rate, or any other signal proportional to the flow rate of gas into the nasal cannula 2. Data from the flow meter is provided to a processing unit 23.

[0406] A gas sensor 32 is provided in the gas sensing head 4, which may be similar to that described in relation to Figure 7. The output of the gas sensor 32 and the gas sensing head 4 is provided to the processing unit 23.

[0407] The processing unit may also be provided with a signal indicative of a patient parameter from a plethysmograph sensor or an electrocardiogram (ECG).

[0408] The processing device may use the above-described inputs to calculate or apply a correction or compensation factor. The compensation factor may compensate for gas dilution resulting from the provision of flow therapy or respiratory assistance provided or administered to the patient P (e.g., from flow sources 1, 13 and via a patient interface, e.g., a nasal interface), as described above. The flow therapy may dilute the target gas or may dilute other gases that may be measured (e.g., CO2). The processing device may also determine or estimate airway patency; for example, the processing device may analyze information from relevant components (e.g., gas sensor 32, flow meter 31, and ECG 34) to determine airway patency and, for example, any of conditions (A), (B), and (C) as described above.

[0409] A display 36 is provided to display at least the data output 36 from the processing unit 33. The data output 36 may relate to any of conditions (A), (B), and (C) as described above, and / or may be raw data measured from any of the components attached to or connected to the processing unit. In some embodiments, the display serves to display the concentration or partial pressure of CO2 over time as it is being measured by the gas sensor 32 and / or the gas sensing head 4. The display 36 allows a clinician to directly monitor system variables or measurements.

[0410] The processing unit may take inputs from at least one or more, or even all, of the components described above and provide an alarm output 37. The alarm output may include one or more alarm signals 39. The one or more alarm signals 39 may be related to conditions (A), (B), and (C), or various other conditions of airway patency. The alarms may be audible or visual, or may be otherwise indicated to the clinician.

[0411] Figure 8 shows the expected nitrogen concentration signature from the sensor over time under various airway conditions. Note that the values given in the chart are only approximations and will vary substantially from patient to patient, depending on the position of the sensing head and the flow rate of oxygen delivered through the nose. It is not an absolute value, but a qualitative feature of the signature that is used to assess airway patency.

[0412] Plot (A) in Figure 8 shows the expected trace when both the pharyngeal airway and trachea are patent. A 50:50 nitrogen / oxygen gas mixture is applied to the patient interface (e.g., nasal cannula) while the nitrogen concentration is increased to 50%. When the flow is switched back to oxygen only, any remaining nitrogen in the pharynx is quickly flushed through the mouth. Nitrogen is then pumped from the lungs to the pharynx in pulses by cardiogenic action. Oxygen is also directed to the lungs, diluting the remaining nitrogen there, so the amplitude of the nitrogen concentration pulse decreases over time, eventually reaching zero when all the nitrogen has been pumped out of the lungs.

[0413] Note that the pulse size is exaggerated in the figure for illustrative purposes. Nitrogen coming from the lungs is substantially diluted when flow is switched back to oxygen only, and peak concentrations of approximately 0.57-3.4% are expected in the first pulse if a 50:50 nitrogen / oxygen mix is used.

[0414] The pulse of nitrogen concentration is synchronized with the patient's heart rate or cardiogenic activity.

[0415] Plot (B) in Figure 8 shows the expected signature when the pharyngeal airway is obstructed but the trachea is open. In this case, nitrogen from the patient interface (e.g., nasal cannula) does not pass through the oropharynx, so there is no flushing flow. Instead, as soon as oxygen administration is stopped, air enters the oropharynx via the open mouth, due to a combination of diffusion induced by the gas sensing head and slow flow. The nitrogen concentration rises to that of air (80%).

[0416] Plot (C) of Figure 8 shows the concentration trace as it fluctuates over time, as would be expected if the trachea were obstructed but the pharyngeal airway were open. When a 50:50 nitrogen / oxygen mixture is introduced via the cannula, the nitrogen concentration in the oropharynx immediately rises to 50%. When the flow is switched back to oxygen only, the oropharynx quickly flushes and the nitrogen concentration drops to zero. Because the trachea is obstructed, nitrogen may not be introduced into the lungs, and nitrogen may not be transported to the trachea due to cardiogenic effects. After the flow is switched back to oxygen only, a cyclical fluctuation in nitrogen concentration can be observed.

[0417] If the pharyngeal airway is partially obstructed and the trachea is open, small amounts of nitrogen may reach the lungs when a 50:50 nitrogen / oxygen mixture is applied via a nasal cannula. In this case, several small residual pulses of nitrogen concentration may be observed, along with a longer oropharyngeal flushing time, after the flow is switched to oxygen only. This condition may be checked to eliminate possible misinterpretation of the trace by monitoring the airway pressure—the subject of another patent claim.

[0418] The algorithm for determining the above-mentioned "fault" conditions (B) and (C) associated with FIG. 8 is described above in connection with monitoring CO2 to determine airway patency. When a target gas, such as a benign tracer gas, is used, it is certainly the concentration threshold of that tracer gas, rather than the CO2 threshold, that is used to trigger the software counter. Note also that the threshold is different for the tracer gas than for CO2 due to the initial concentration of the tracer gas in the lungs being much higher than that of CO2. The algorithm may be stored as computer-readable and executable instructions in a memory device associated with the controller (as described above). The controller is configured to read and execute the algorithm to cause the electronic control unit to determine airway patency based on measurements of the target gas it processes.

[0419] All thresholds are given as examples only and to illustrate methods or systems that may be implemented.

[0420] Monitoring airway pressure to ensure sufficient flow to support and relieve atelectasis High flow of gas (e.g., oxygen) offered or delivered via the nose creates a small sprinting pressure in the airways (typically 0.5-5 cmH2O). Although this pressure is small, it helps to expand the alveoli, thereby reducing atelectasis. This can be particularly important in obese patients.

[0421] If the nasal pharyngeal airway is partially obstructed, splinting pressure can be substantially reduced. Thus, monitoring the pressure in the patient's airway provides the clinician with a means of confirming obstruction of the pharyngeal airway, which may be suspected from CO or tracer gas measurements as described above.

[0422] A system for measuring airway pressure that allows this confirmation is shown in FIG.

[0423] A pressure transducer 12 is introduced into the airway of an apneic patient P to measure pressure just above the larynx but out of the main gas flow from the patient interface 2 exiting the mouth. It should be located deeper in the airway than the gas sensing head sensor described above. This may be necessary to minimize disturbances in the pressure measurement due to dynamic effects from high flow. The pressure transducer 12 may have a range of approximately -10 to +10 cmH2O, with a sensitivity of 0.2 cmH2O or better. The transducer may have a response time of better than 0.1 seconds.

[0424] The patient's mouth must be open for this measurement: a closed mouth can give a false indication that the pharyngeal airway is open when in fact it is only partially closed.

[0425] The nasal patient interface (e.g., nasal cannula 2) attached to the nose needs to be the perfect size for the patient's nostrils. A cannula that is too large may give a false indication that the pharyngeal airway is open when it is actually only partially closed. A cannula that is too small may give a false indication that the pharyngeal airway is partially obstructed when it is actually open within the normal range for the patient.

[0426] When the pharyngeal airway is normally open, the pressure within the airway varies approximately as the square of the cannula flow. In normal adults, the pressure at a cannula flow rate of 70 l / min may be in the range of approximately 0.5 to 2 cmH2O (see, e.g., Figure 10). Pressures below 0.5 cmH2O indicate that the pharyngeal airway is partially obstructed and that the sprinting pressure may be substantially lower than that required to relieve atelectasis. Low airway pressures are of particular concern in obese patients, e.g., with a body mass index (BMI) of 30 or greater.

[0427] Further confirmation of low flow rates from the patient interface (e.g., nasal cannula) through the pharyngeal airway can be obtained by measuring turbulent pressure fluctuations at the sensor, which occur on a time scale of 0.1 to 0.5 seconds. Pressure fluctuations of 0.2 cmH2O or greater indicate flows of 60 L / min or greater. Under normal conditions, pressure fluctuations less than this indicate that flow to the pharynx is not optimal for supporting the airways and alveoli.

[0428] The system may also include a display 3, and flow sources 1, 13 and valves 14 (all of which are described in connection with Figures 7 and 11 above).

[0429] It is envisioned that a system such as that shown in FIG. 9 may be combined with the systems of FIG. 7 and / or FIG.

[0430] Unless the context clearly dictates otherwise, throughout the description and claims, the words "comprise," "comprising," and the like, are to be construed in the inclusive sense, i.e., "including but not limited to," as opposed to exclusive or exhaustive.

[0431] Reference to a range of numerical values disclosed herein (e.g., 1 to 10) is also intended to include reference to all rational numbers within that range (e.g., 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9, and 10) and also to any range of rational numbers within that range (e.g., 2 to 8, 1.5 to 5.5, and 3.1 to 4.7); therefore, all subranges of all ranges expressly disclosed herein are hereby expressly disclosed. These are only examples of what is specifically intended, and all possible combinations of numerical values between the lowest and highest values recited are considered to be expressly set forth in this application as well.

[0432] As used herein, the term "one or more" followed by a noun refers to the plural and / or the singular of that noun.

[0433] As used herein, the term "and / or" means "and" or "or," or both, where the context allows.

[0434] As used herein, the term "configured to" may instead be replaced with the term "disposed to" or "adapted to."

[0435] Where the above description refers to components having wholes or their known equivalents, those wholes are incorporated herein as if individually set forth.

[0436] The present disclosure may also be broadly said to consist of the parts, elements and features referred to or shown in the specification of this application, individually or collectively, and any or all combinations of two or more of said parts, elements and features.

[0437] The reference herein to any prior art is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in the field of endeavor in any country throughout the world.

[0438] Some features, aspects, and advantages of some configurations of the present disclosure have been described with reference to the use of a gas humidification system with a respiratory therapy system. However, some features, aspects, and advantages of the use of a gas humidification system as described may be advantageously used in other therapeutic or non-therapeutic systems requiring humidification of gases. Some features, aspects, and advantages of the methods and apparatus of the present disclosure may be equally applicable for use in other systems.

[0439] Although the present disclosure has been described with respect to several embodiments, other embodiments apparent to those skilled in the art are also within the scope of the present disclosure. Accordingly, various changes and modifications may be made without departing from the spirit and scope of the present disclosure. For example, various components may be rearranged as desired. Features from any of the above-described configurations may be combined with each other and / or with a respiratory assistance system, or a humidifier may include one or more of the above-described configurations. Furthermore, not all features, aspects, and advantages are necessarily required to practice the present disclosure. Accordingly, the scope of the present disclosure is to be defined solely by the following claims.

Claims

1. 1. A system for determining a patient's airway status, comprising: a non-close-fitting nose interface; a flow generator that provides a flow of gas delivered to the patient's airway through the non-sealing nasal interface in accordance with a flow signal; a gas sensor configured to monitor or detect a parameter of a target gas being exhaled or expired from a patient's airway as a monitored gas signal, the target gas being carbon dioxide, O2, or a gas indicative of a concentration of carbon dioxide or O2; a controller for determining a correlation between the flow signal and the monitor gas signal; The system determines that the patient's airway condition is obstructed or substantially obstructed if the correlation between the delivered flow and the monitored target gas is below a threshold.

2. The system of claim 1 , wherein the controller monitors the target gas by measuring changes in concentration of at least one of the target gases.

3. A system as described in claim 1 or 2, wherein the gas sensor performs measurements adjacent to or within the patient's mouth or oral cavity or oropharyngeal region, or adjacent to or within the patient's nose or nasal cavity.

4. A system described in any one of claims 1 to 3, wherein the target gas comprises N2, or a benign medical tracer gas, or a gas exhibiting a concentration of N2.

5. 5. The system of claim 1, wherein the gas flow is oscillating or time-varying.

6. 6. The system of claim 1, wherein the flow signal is transmitted in a first shape or profile, and the correlation is based on a comparison of the first shape or profile of the flow signal with a second shape or profile of the monitored gas signal.

7. The system of claim 1 , wherein the correlation is based on a comparison of waveform characteristics of the flow signal and waveform characteristics of the monitor gas signal.

8. 8. The system of claim 1, wherein the flow signal is a sum of at least two oscillatory waveforms.

9. 9. The system of claim 1, wherein the flow signal is substantially sinusoidal.

10. The flow signal has the following signal characteristics: a frequency, which may be substantially repeated over a period of time; amplitude, a waveform, which may be substantially repeating over a period of time; phase 10. The system of claim 1, wherein the system comprises one or more of:

11. The correlation is the frequency of the flow signal; the amplitude of the flow signal; a flow waveform of the flow signal, which may be substantially repeating over a period of time; the phase of the flow signal; Changes in the flow signal over time and one or more of the frequency of the monitor gas signal; the amplitude of the monitored gas signal; the amplitude of the monitor gas signal at a particular frequency; the waveform of the monitored gas signal; the phase of the monitored gas signal; Changes in the monitored gas signal over time The system of claim 1 , wherein the comparison is based on a comparison with one or more of:

12. The correlation is a signal edge or transition portion of the waveform of the flow signal; a maximum value, a minimum value, or an inflection point of the waveform of the flow signal; the slope of a portion of the flow signal or the slope at a discrete point; A number of peaks and / or troughs in the flow signal within a given or predetermined period. and one or more of a subsequent signal edge or transition portion of the monitor gas signal waveform, which may be located within a period of time after the signal edge or transition portion of the flow signal waveform; a subsequent maximum or minimum or inflection point of the waveform of the monitor gas signal, when the subsequent maximum or minimum of the waveform of the monitor gas signal may be located within a period of time after a signal edge or transition portion of the waveform of the flow signal; the slope of a subsequent portion or a discrete point of the waveform of the monitoring gas signal, when the slope of a subsequent portion or a discrete point of the waveform of the monitoring gas signal may be located within a period of time after the slope of a portion or a discrete point of the waveform of the flow signal; the number of peaks and / or troughs in the monitored gas signal within a given or predetermined period; The system of claim 1 , wherein the comparison is based on a comparison with one or more of:

13. A system described in any one of claims 1 to 12, wherein the condition of the patient's airway is determined to be unobstructed or substantially unobstructed when the correlation between the delivered flow and the monitored gas signal is greater than or equal to a threshold value.

14. 14. The system of claim 1, wherein the patient's airway is determined to be unobstructed or substantially unobstructed when at least one component of the frequency of the monitored gas signal is similar to the frequency of the flow signal and the amplitude of the flow signal at said frequency is equal to or greater than a threshold.

15. 14. The system of claim 1, wherein the condition of the patient's airway is determined to be unobstructed or substantially unobstructed when at least one component of the frequency of the monitored gas signal substantially matches the frequency of the flow signal and the frequency match is greater than or equal to a threshold value.

16. 16. The system of claim 1, wherein the condition of the patient's airway is determined to be unobstructed or substantially unobstructed when at least one component of the frequency of the monitored gas signal is similar to the frequency of the flow signal and the amplitude of the signal at said frequency is equal to or greater than a threshold value.

17. 17. The system of any one of claims 1 to 16, wherein the flow of gas delivered to the patient's airway is an average flow of at least about 20-90 liters per minute.

18. 18. The system of claim 1, comprising a humidifier for humidifying the gas flow.

19. 19. The system of claim 1, wherein the correlation is determined by one or more of Monte Carlo analysis and / or spectral analysis.

20. 20. The system of claim 1, wherein the controller determines a level of patency of the patient's airway, the level being proportional to the strength of correlation between the delivered flow and the monitored gas signal.

21. 21. The system of claim 1, wherein the controller determines that the patient's airway is obstructed or substantially obstructed if at least one component of the frequency of the monitored gas signal is similar to, different from, or not sufficiently similar to, the frequency of the flow, and / or if the amplitude of the signal at said frequency is similar and below a threshold.

22. A system described in any one of claims 1 to 21, wherein the gas sensor or sampling device may be part of a patient interface arrangement.

23. 23. The system of claim 22, wherein the sampling device comprises a sampling tip for sampling the gas, the sampling tip in communication with the gas sensor.

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