Patent Publication Number: US-2020297960-A1

Title: Systems and methods for hypoxic gas delivery for altitude training and athletic conditioning

Description:
This application is a continuation of International Patent Application No. PCT/NZ2018/050136, filed Oct. 5, 2018 entitled SYSTEMS AND METHODS FOR HYPDXIC GAS DELIVERY FOR ALTITUDE TRAINING AND ATHLETIC CONDITIONING, which claims the benefit under 35 U.S.C. § 120 as a nonprovisional application of U.S. Prov. App. No. 62/569,147 filed on Oct. 6, 2017, which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure relates in some aspects to systems and methods for high flow hypoxic gas delivery to a user via a nasal conduit. The gas delivery can be for a wide variety of indications, including but not limited to altitude training and improving cardiovascular conditioning and athletic performance. 
     BACKGROUND 
     Altitude effects can influence athletic performance. Some athletes have found it advantageous to spend time, such as live and/or train, at relatively high altitudes to gain a competitive edge, commonly known as altitude training. Not to be limited by theory, altitude training has several beneficial potential physiological effects. At high altitude the partial pressure of oxygen is reduced due to the reduced barometric pressure, even though the actual concentration of oxygen remains relatively constant. Over the course of multiple weeks, a person&#39;s body may adapt to this relatively low oxygen environment by increasing mass of red blood cells and hemoglobin, and/or by altering muscle metabolism. These physiological changes can be shown to have follow up positive effects, particularly in terms of a raised VO 2  max, which is the maximum rate at which oxygen can be used be consumed by the body. VO 2  max is strongly linked to aerobic capacity, and in turn has effects on speed, strength, endurance and recovery. 
     There can be a large number of variables associated with altitude training, not limited to types of exercise, levels of altitude/oxygen concentration, length of therapy sessions, total length of therapy regime, length of time since leaving altitude, whether or not to remain at altitude for training sessions, whether or not to remain at altitude outside of training sessions, efficacy of simulated altitude, optimum ways to deliver simulated altitude, whether to control to inspired oxygen or blood oxygen saturation, as well as determining the exact underlying mechanism behind the physiological changes. As actually being at altitude poses multiple challenges in terms of cost, inconvenience and difficulty to alter the exact altitude as noted above, methods of generating an artificial high altitude environment have been investigated. As one theory for the effects of altitude training is the reduced partial pressure of oxygen, this could be accurately mimicked by adding one, two, or more hypoxic gases, such as nitrogen or other gases to ambient air, resulting in a gas with a reduced oxygen concentration. Generating a hypoxic environment can be shown to artificially replicate the effects of being at altitude. Systems and methods that can more efficiently, effectively, safely, and conveniently replicate such altitude and other effects are needed. 
     SUMMARY 
     In some configurations, disclosed herein are methods of providing a hypoxic flow of gases to a user. The methods can include providing a hypoxic gas composition. The methods can also include delivering the hypoxic gas composition to the user, such as via an airway such as the nares and/or the mouth. The hypoxic gas composition can be provided to the airway via a nasal cannula or a mask, for example. The flow rate of the hypoxic gas composition to the user can be, for example, less than about, about, or at least about 10 liters/minute. 
     In some configurations, methods of providing a hypoxic flow of gases to a user can include providing a hypoxic gas composition; heating the hypoxic gas composition to a desired temperature, e.g., between about 30° C. and about 45° C.; and delivering the heated, hypoxic gas composition via a user interface in proximity to the airway, e.g., nares or mouth of a user. 
     In some configurations, methods of providing a hypoxic flow of gases to a user can include providing a hypoxic gas composition; humidifying the hypoxic gas composition; and delivering the humidified, hypoxic gas composition via a user interface in proximity to the airway, e.g., nares or mouth of a user. 
     The hypoxic gas composition can include one or more physiologically inert gases, such as nitrogen. The hypoxic gas composition can be delivered continuously at a desired flow rate, such as, for example, about or at least about 10, 20, 30, 40, 50, or more liters/minute. The method can also include delivering (e.g., synchronizing in some cases) the hypoxic gas composition with an inspiratory phase of breathing of the user, for example, at a flow rate of at least about 10 liters/minute during inspiration. Synchronizing can include increasing the flow on inspiration and reducing the flow on expiration. Synchronization of a control signal of the device with a breath cycle of a user can be achieved by identifying a phase of the breath cycle waveform, and iteratively updating a phase of the control signal to achieve a determined phase difference between the control signal and the breath cycle waveform, such that the control signal can be configured to adjust a speed of the blower motor based upon the patient&#39;s inspiration and expiration. Synchronizing can further include phase-shifting the control signal based upon a system delay between the control signal being received by the blower motor and the resulting air flow being sensed by a patient. Synchronizing can also further include phase-shifting the control signal, such that the control signal can pre-empt the breath cycle waveform by a set amount of time. Delivering the hypoxic gas can be sufficient to meet peak inspiratory demand of the user. In some configurations, the method can include synchronizing the hypoxic gas composition with a phase of breathing of the user; delivery of the hypoxic gas composition can be at a flow rate of, for example, less than about 10 liters/minute during at least a portion of expiration. 
     The method can also include heating the hypoxic gas composition prior to reaching the user&#39;s airway (e.g., the nares and/or mouth). Heating can be sufficient to inactivate a pathogen of interest, such as human rhinovirus or influenza, among others. The hypoxic gas composition can be heated to any desired temperature, such as, for example, between about 30° C. and about 45° C., between about 30° C. and about 43° C., between about 37° C. and about 43° C., or about 41° C. The method can also include humidifying the hypoxic gas composition prior to reaching the nares and/or mouth of the user. Humidifying can be to any desired relative humidity, such as about or at least about 80%, 90%, or 95% in some cases. The method can also include mixing ambient air with a source of enriched nitrogen to create the hypoxic gas composition. In some configurations, the peak inspiratory demand of the user can optionally be measured; and the flow rate adjusted based upon the measured peak inspiratory demand. 
     The oxygen concentration of the hypoxic gas composition can be, for example, between about 10% and about 20%, between about 15% and about 20%, between about 10.2% and about 20.9%, between about 11.9% and about 17.4%, between about 13.8% and about 17.4%, or between about 15.7% and about 16.7%. The method can also include sensing the oxygen concentration of the hypoxic gas composition after mixing, and/or measuring at least one physiological parameter of the user; and automatically controlling the delivery of the hypoxic gas composition based on the measured physiological parameter. The measured physiological parameter can be, for example, blood oxygen saturation, heart rate, respiratory rate, heart rate variability, and/or blood pressure. Automatically controlling the delivery of the hypoxic gas composition can include adjusting an amount of hypoxic gas, such as enriched nitrogen, mixed into the hypoxic gas composition. Automatically controlling the delivery of the hypoxic gas can include titrating the composition of the hypoxic gas composition to achieve a predetermined blood oxygen saturation, e.g., of less than about 95%, between about 80% and about 94%, between about 85% and about 92%, between about 87% and about 90%, or between about 80% and about 85%. Titrating the composition of the hypoxic gas composition can include altering a flow rate of nitrogen into the hypoxic gas composition. The sensed oxygen concentration can be outputted, such as in real time, to a display, and/or correlated with an altitude equivalent via a processor, which can also be outputted to a display. The result of one or more sensed physiological parameters can also be outputted to a display. 
     The method can also include notifying the user (e.g., via a visual, auditory, or tactile alarm) when the physiological parameter deviates from a pre-selected range for at least a pre-determined period of time, and/or altering the pre-selected range based upon individual characteristics of the user. The method can be used for a time period sufficient to improve the user&#39;s conditioning at high altitude, and/or stimulate erythropoiesis such that the user&#39;s hemoglobin level increases by at least about 5%, 10%, 15%, 20%, or more compared to before starting the method. 
     Also disclosed herein is a system configured for providing a hypoxic flow of gases to a user. The system can include an apparatus that includes a gas conduit and an ambient air inlet. The system can also include a hypoxic gas source inlet configured to connect to a hypoxic gas source and configured to create a hypoxic gas composition upon mixing of ambient air and the hypoxic gas. The system can also include a user interface comprising a nasal cannula comprising nasal prongs. The system can also include a gas flow generation element configured to deliver the hypoxic gas composition. 
     In some configurations, a system configured for providing a hypoxic flow of gases to a user can include an apparatus that includes a gas conduit and an ambient air inlet, and a hypoxic gas source inlet configured to connect to a hypoxic gas source and configured to create a hypoxic gas composition upon mixing of ambient air and the hypoxic gas; a user interface; a gas flow generation element configured to deliver the hypoxic gas composition to comprising a nasal cannula comprising nasal prongs; and/or a heating element within the gas conduit configured to heat the hypoxic gas composition to a temperature of between about 30° C. and about 45° C. In some configurations, the heating element can comprise a heater plate. In some configurations, the heating element can comprise a heater wire. 
     In some configurations, a system configured for providing a hypoxic flow of gases to a user can include an apparatus that includes a gas conduit and an ambient air inlet, and a hypoxic gas source inlet configured to connect to a hypoxic gas source and configured to create a hypoxic gas composition upon mixing of ambient air and the hypoxic gas; a user interface; a gas flow generation element configured to deliver the hypoxic gas composition to an airway of the user; and a humidification element within the gas conduit configured to humidify the hypoxic gas composition prior to reaching the airway of the user. The humidification element may be a humidification chamber. 
     The hypoxic gas composition can be delivered to the airway, e.g., nares and/or mouth of the user at a predetermined flow rate. The flow rate can be, for example, at least about 10, 20, 30, 40, 50, or more liters/minute. The system can include the hypoxic gas source, such as a hypoxic gas reservoir. The hypoxic gas can be, for example, enriched nitrogen. The gas flow generation element can be configured to deliver the hypoxic gas composition sufficient to meet the inspiratory demand of the user. The system can also include a heating element configured to heat the hypoxic gas composition prior to reaching the nares of the user. In some configurations, the heating element can comprise a heater plate. In some configurations, the heating element can comprise a heater wire. The heating element can be configured, for example, to heat the hypoxic gas composition to a predetermined temperature. The temperature can be, for example, between about 30° C. and about 45° C., between about 30° C. and about 43° C., between about 37° C. and about 43° C., or about 41° C. in some cases. The system can also include a humidification element configured to humidify the hypoxic gas composition prior to reaching the nares of the user, such as to a relative humidity of at least about 80%, 90%, 95%, or more. The humidification element may be a humidification chamber. The system can also include a sensor configured to measure a peak inspiratory demand of the user. The system can be configured to adjust the flow rate based upon the measured peak inspiratory demand. The system can be configured to deliver the hypoxic gas in an oxygen concentration of, for example, between about 10% and about 20%, between about 15% and about 20%, between about 10.2% and about 20.9%, between about 11.9% and about 17.4%, between about 13.8% and about 17.4%, or between about 15.7% and about 16.7%. The system can also include a sensor configured to sense the oxygen concentration of the hypoxic gas composition. The system can also include a sensor configured to measure a physiological parameter of the user. The system can include a controller configured to automatically control the delivery of the hypoxic gas composition based on the measured physiological parameter. The controller can be configured to automatically controlling the delivery of the hypoxic gas composition by adjusting an amount of hypoxic gas, such as enriched nitrogen, mixed into the hypoxic gas composition. The physiological parameter can be, for example, blood oxygen saturation, heart rate, respiratory rate, heart rate variability, and/or blood pressure. 
     The system can also include an alarm (e.g., a visual, auditory, or tactile alarm) configured to notify the user when the physiological parameter deviates from a pre-selected range for at least a pre-determined period of time. The controller can also be configured to titrate the composition of the hypoxic gas composition to achieve a predetermined blood oxygen saturation, e.g., of less than about 95%, between about 80% and about 94%, between about 85% and about 92%, between about 87% and about 90%, or between about 80% and about 85%. The controller can also be configured to alter the flow rate of the hypoxic gas into the hypoxic gas composition. The system can also include a display. The controller can be configured to output the sensed oxygen concentration in real time to the display. The system can also be configured to correlate the sensed oxygen concentration to an altitude equivalent using a processor, and output the altitude equivalent in real time to a display. 
     The above examples are intended to be within the scope of the disclosure herein. These and other examples will become readily apparent to those skilled in the art from the following detailed description having reference to the attached figures, the disclosure not being limited to any particular disclosed example(s). 
     In some configurations, a method of providing a hypoxic flow of gases to a user can include providing a hypoxic gas composition; delivering the hypoxic gas composition to the nares of a user via a nasal cannula at a flow rate of at least about 10 liters/minute; measuring at least one physiological parameter of the user; and automatically controlling the delivery of the hypoxic gas composition based on the measured physiological parameter, wherein the measured physiological parameter can be blood oxygen saturation. 
     In some configurations, the hypoxic gas composition can comprise at least one physiologically inert gas. In some configurations, the hypoxic gas composition can comprise nitrogen. 
     In some configurations, the method can include delivering the hypoxic gas composition continuously at a flow rate of at least about 10 liters/minute. 
     In some configurations, the method can include synchronizing delivering the hypoxic gas composition with an inspiratory phase of breathing of the user, wherein the delivering of the hypoxic gas composition can be at a flow rate of at least about 10 liters/minute during inspiration. 
     In some configurations, synchronizing can comprise increasing the flow rate on inspiration and reducing the flow rate on expiration. 
     In some configurations, delivering the hypoxic gas can be sufficient to meet peak inspiratory demand of the user. 
     In some configurations, the method can include heating the hypoxic gas composition prior to reaching the nares of the user. 
     In some configurations, heating the hypoxic gas composition can be sufficient to inactivate a pathogen of interest. 
     In some configurations, the pathogen of interest can be a human rhinovirus or influenza. 
     In some configurations, heating the hypoxic gas composition can comprise heating the hypoxic gas composition to between about 30° C. and about 43° C. Heating the hypoxic gas composition can comprise heating the hypoxic gas composition to between about 37° C. and about 43° C. Heating the hypoxic gas composition can comprise heating the hypoxic gas composition to about 41° C. 
     In some configurations, the method can include humidifying the hypoxic gas composition prior to reaching the nares of the user. 
     In some configurations, the method can include humidifying and heating the hypoxic gas composition to a dew point temperature between about 30° C. and about 43° C. The method can include humidifying and heating the hypoxic gas composition to a dew point temperature between about 37° C. and about 43° C. The method can include humidifying and heating the hypoxic gas composition to a dew point temperature about 41° C. 
     In some configurations, humidifying the hypoxic gas composition can comprise humidifying the hypoxic gas composition to a relative humidity of at least about 80%. Humidifying the hypoxic gas composition can comprise humidifying the hypoxic gas composition to a relative humidity of at least about 90%. Humidifying the hypoxic gas composition can comprise humidifying the hypoxic gas composition to a relative humidity of at least about 95%. Humidifying the hypoxic gas composition can comprise humidifying the hypoxic gas composition to a relative humidity of at least about 99%. Humidifying the hypoxic gas composition can comprise humidifying the hypoxic gas composition to a relative humidity of at least about 100%. 
     In some configurations, the method can include mixing ambient air with a source of the hypoxic gas to create the hypoxic gas composition. 
     In some configurations, the method can include measuring inspiratory peak demand of the user; and adjusting the flow rate based upon the measured peak inspiratory demand. 
     In some configurations, an oxygen concentration of the hypoxic gas composition can be between about 10% and about 20%. An oxygen concentration of the hypoxic gas composition can be between about 15% and about 20%. An oxygen concentration of the hypoxic gas composition can be between about 10.2% and about 20.9%. An oxygen concentration of the hypoxic gas composition can be between about 11.9% and about 17.4%. An oxygen concentration of the hypoxic gas composition can be between about 13.8% and about 17.4%. An oxygen concentration of the hypoxic gas composition can be between about 15.7% and about 16.7%. 
     In some configurations, the method can include outputting the measured physiological parameter in real time to the display. 
     In some configurations, the measured physiological parameter can further comprise at least one selected from the group consisting of: heart rate, respiratory rate, heart rate variability, and blood pressure. 
     In some configurations, automatically controlling the delivery of the hypoxic gas composition can comprise adjusting an amount of hypoxic gas mixed into the hypoxic gas composition. 
     In some configurations, the method can include notifying the user when the physiological parameter deviates from a pre-selected range for at least a pre-determined period of time. 
     In some configurations, the method can include altering the pre-selected range based upon individual characteristics of the user. 
     In some configurations, notifying the user can comprise activating a visual, auditory, or tactile alarm. 
     In some configurations, automatically controlling the delivery of the hypoxic gas can comprise titrating the composition of the hypoxic gas composition to achieve a blood oxygen saturation of less than about 95%. Automatically controlling the delivery of the hypoxic gas can comprise titrating the composition of the hypoxic gas composition to achieve a blood oxygen saturation of between about 80% and about 94%. Automatically controlling the delivery of the hypoxic gas can comprise titrating the composition of the hypoxic gas composition to achieve a blood oxygen saturation of between about 85% and about 92%. Automatically controlling the delivery of the hypoxic gas can comprise titrating the composition of the hypoxic gas composition to achieve a blood oxygen saturation of between about 87% and about 90%. Automatically controlling the delivery of the hypoxic gas can comprise titrating the composition of the hypoxic gas composition to achieve a blood oxygen saturation of between about 80% and about 85%. 
     In some configurations, the method can include sensing the oxygen concentration of the hypoxic gas composition after mixing. 
     In some configurations, the method can include outputting the sensed oxygen concentration in real time to a display. 
     In some configurations, the method can include correlating the sensed oxygen concentration to an altitude equivalent using a processor, and outputting the altitude equivalent in real time to the display. 
     In some configurations, the method can include obtaining a target oxygen concentration of the hypoxic gas composition based on the blood oxygen saturation. 
     In some configurations, the method can include achieving the target oxygen concentration by controlling a hypoxic gas inlet valve. 
     In some configurations, the method can include achieving the target oxygen concentration based on the sensed oxygen concentration after mixing. 
     In some configurations, automatically controlling the delivery of the hypoxic gas can comprise titrating the composition of the hypoxic gas composition to achieve a simulated altitude. 
     In some configurations, the simulated altitude can be between about 0 m and about 5,950 m. The simulated altitude can be between about 1,000 m and about 5,000 m. The simulated altitude can be between about 1,250 m and about 4,800 m. The simulated altitude can be between about 1,500 m and about 3,500 m. The simulated altitude can be between about 1,600 m and about 3,000 m. The simulated altitude can be between about 2,000 m and about 2,500 m. 
     In some configurations, titrating the composition of the hypoxic gas composition can comprise altering a flow rate of nitrogen into the hypoxic gas composition. 
     In some configurations, the hypoxic gas composition can be delivered to the user at a flow rate of at least about 20 liters/minute. The hypoxic gas composition can be delivered to the user at a flow rate of at least about 30 liters/minute. The hypoxic gas composition can be delivered to the user at a flow rate of at least about 40 liters/minute. The hypoxic gas composition can be delivered to the user at a flow rate of at least about 50 liters/minute. The hypoxic gas composition can be delivered to the user at a flow rate of at least about 60 liters/minute. The hypoxic gas composition can be delivered to the user at a flow rate of at least about 70 liters/minute. 
     In some configurations, the method can be used for a time period sufficient to improve the user&#39;s conditioning at high altitude. 
     In some configurations, the method can be used for a time period sufficient to stimulate erythropoiesis such that the user&#39;s hemoglobin level increases by at least 5% compared to before starting the method. 
     In some configurations, the method can be used for a time period sufficient to stimulate erythropoiesis such that the user&#39;s hemoglobin level increases by at least 10% compared to before starting the method. 
     In some configurations, the method can include controlling the delivery of the hypoxic gas using a mobile device in electrical communication with the device. 
     In some configurations, a system configured for providing a hypoxic flow of gases to a user can include an apparatus comprising a gas flow path, an ambient air inlet, and a hypoxic gas source inlet configured to connect to a hypoxic gas source and configured to create a hypoxic gas composition upon mixing of ambient air and the hypoxic gas; a user interface comprising a nasal cannula comprising nasal prongs; a gas flow generation element configured to deliver the hypoxic gas composition to nares of the user at a predetermined flow rate of at least about 10 liters/minute; a sensor configured to measure a physiological parameter of the user, wherein the physiological parameter is blood oxygen saturation; and a controller configured to automatically control the delivery of the hypoxic gas composition based on the measured physiological parameter. 
     In some configurations, the gas flow generation element can comprise one or more of a blower, a compressor, a pressurized tank, or a gas source in the wall. 
     In some configurations, the system can further include the hypoxic gas source. 
     In some configurations, the hypoxic gas source can comprise a hypoxic gas reservoir. 
     In some configurations, the hypoxic gas can comprise enriched nitrogen. 
     In some configurations, the gas flow generation element can be configured to deliver the hypoxic gas composition sufficient to meet the peak inspiratory demand of the user. 
     In some configurations, the system can further include a heating element configured to heat the hypoxic gas composition prior to reaching the nares of the user. In some configurations, the heating element can comprise a heater plate. In some configurations, the heating element can comprise a heater wire. 
     In some configurations, the heating element can be configured to heat the hypoxic gas composition to between about 30° C. and about 43° C. The heating element can be configured to heat the hypoxic gas composition to between about 37° C. and about 43° C. The heating element can be configured to heat the hypoxic gas composition to about 41° C. 
     In some configurations, the system can further include a humidification element configured to humidify the hypoxic gas composition prior to reaching the nares of the user. The humidification element may be a humidification chamber. 
     In some configurations, the heating element and the humidification element can be configured to heat and humidify the hypoxic gas composition to a dew point temperature between about 30° C. and about 43° C. The heating element and the humidification element can be configured to heat and humidify the hypoxic gas composition to a dew point temperature between about 37° C. and about 43° C. The heating element and the humidification element can be configured to heat and humidify the hypoxic gas composition to a dew point temperature about 41° C. 
     In some configurations, the humidification element can be configured to humidify the hypoxic gas composition to a relative humidity of at least about 80%. The humidification element can be configured to humidify the hypoxic gas composition to a relative humidity of at least about 90%. The humidification element can be configured to humidify the hypoxic gas composition to a relative humidity of at least about 95%. The humidification element can be configured to humidify the hypoxic gas composition to a relative humidity of at least about 99%. The humidification element can be configured to humidify the hypoxic gas composition to a relative humidity of at least about 100%. 
     In some configurations, the system can further include a sensor configured to measure a peak inspiratory demand of the user; and the system can be configured to adjust the flow rate based upon the measured peak inspiratory demand. 
     In some configurations, the system can be configured to deliver the hypoxic gas in an oxygen concentration of between about 10% and about 20%. The system can be configured to deliver the hypoxic gas in an oxygen concentration of between about 15% and about 20%. The system can be configured to deliver the hypoxic gas in an oxygen concentration of between about 10.2% and about 20.9%. The system can be configured to deliver the hypoxic gas in an oxygen concentration of between about 11.9% and about 17.4%. The system can be configured to deliver the hypoxic gas in an oxygen concentration of between about 13.8% and about 17.4%. The system can be configured to deliver the hypoxic gas in an oxygen concentration of between about 15.7% and about 16.7%. 
     In some configurations, the controller can be configured to automatically controlling the delivery of the hypoxic gas composition by adjusting an amount of hypoxic gas mixed into the hypoxic gas composition. In some configurations, the controller can be configured to automatically controlling the delivery of the hypoxic gas composition by adjusting an amount of enriched nitrogen mixed into the hypoxic gas composition. 
     In some configurations, the physiological parameter can further comprise at least one selected from the group consisting of: heart rate, respiratory rate, heart rate variability, and blood pressure. 
     In some configurations, the system can further include an alarm configured to notify the user when the physiological parameter deviates from a pre-selected range for at least a pre-determined period of time. 
     In some configurations, the alarm can comprise one of a visual, auditory, or tactile alarm. 
     In some configurations, the controller can be configured to titrate the composition of the hypoxic gas composition to achieve a blood oxygen saturation of the user of less than about 95%. The controller can be configured to titrate the composition of the hypoxic gas composition to achieve a blood oxygen saturation of the user of between about 80% and about 94%. The controller can be configured to titrate the composition of the hypoxic gas composition to achieve a blood oxygen saturation of the user of between about 85% and about 92%. The controller can be configured to titrate the composition of the hypoxic gas composition to achieve a blood oxygen saturation of the user of between about 87% and about 90%. The controller can be configured to titrate the composition of the hypoxic gas composition to achieve a blood oxygen saturation of the user of between about 80% and about 85%. 
     In some configurations, the system can further include a sensor configured to sense the oxygen concentration of the hypoxic gas composition. 
     In some configurations, the system can further include a display, wherein the system is configured to output the sensed oxygen concentration in real time to the display. 
     In some configurations, the system can be further configured to correlate the sensed oxygen concentration to an altitude equivalent using a processor, and outputting the altitude equivalent in real time to the display. 
     In some configurations, the system can be further configured to obtain a target oxygen concentration of the hypoxic gas composition based on the blood oxygen saturation. 
     In some configurations, the system can be further configured to achieve the target oxygen concentration based on the sensed oxygen concentration. 
     In some configurations, the controller can be configured to achieve the target oxygen concentration by controlling a hypoxic gas inlet valve. 
     In some configurations, the controller can be configured to alter a flow rate of the hypoxic gas into the hypoxic gas composition. 
     In some configurations, the gas flow generation element can be configured to deliver the hypoxic gas composition to the nares of the user at a predetermined flow rate of at least about 20 liters/minute. The gas flow generation element can be configured to deliver the hypoxic gas composition to the nares of the user at a predetermined flow rate of at least about 30 liters/minute. The gas flow generation element can be configured to deliver the hypoxic gas composition to the nares of the user at a predetermined flow rate of at least about 40 liters/minute. The gas flow generation element can be configured to deliver the hypoxic gas composition to the nares of the user at a predetermined flow rate of at least about 50 liters/minute. The gas flow generation element can be configured to deliver the hypoxic gas composition to the nares of the user at a predetermined flow rate of at least about 60 liters/minute. The gas flow generation element can be configured to deliver the hypoxic gas composition to the nares of the user at a predetermined flow rate of at least about 70 liters/minute. 
     In some configurations, the nasal cannula can be non-sealed. 
     In some configurations, the system can be a high flow device. 
     In some configurations, the high flow device can be portable. 
     In some configurations, the humidification element can comprise a humidification chamber. 
     In some configurations, the heating element can comprise a heater plate. 
     In some configurations, the heating element can comprise a heater wire. 
     In some configurations, a method of providing a hypoxic flow of gases to a user can include providing a hypoxic gas composition; humidifying and heating the hypoxic gas composition to a dew point temperature of between about 30° C. and about 45° C. prior to reaching the airway of the user; and delivering the heated, humidified hypoxic gas composition via a user interface in proximity to an airway of the user. 
     In some configurations, the method can include delivering the heated, hypoxic gas composition via a nasal cannula to the user&#39;s nares. The method can include delivering the heated, hypoxic gas composition via a nasal cannula to the user&#39;s nares. 
     In some configurations, the hypoxic gas composition can comprise at least one physiologically inert gas. In some configurations, the hypoxic gas composition can comprise nitrogen. 
     In some configurations, the method can include delivering the hypoxic gas composition continuously at a flow rate of at least about 10 liters/minute. 
     In some configurations, the method can include delivering the hypoxic gas composition continuously at a flow rate that meets the user&#39;s inspiratory demand. 
     In some configurations, the method can include synchronizing delivering the hypoxic gas composition with an inspiratory phase of breathing of the user, wherein the delivering of the hypoxic gas composition can be at a flow rate of at least about 10 liters/minute during inspiration. 
     In some configurations, the method can include synchronizing delivering the hypoxic gas composition with an inspiratory phase of breathing of the user, wherein the delivering of the hypoxic gas composition can be at a flow rate that meets the user&#39;s inspiratory demand. 
     In some configurations, synchronizing can comprise increasing the flow rate on inspiration and reducing the flow rate on expiration. 
     In some configurations, the method can include heating the hypoxic gas composition prior to reaching the nares of the user. 
     In some configurations, heating the hypoxic gas composition can be sufficient to inactivate a pathogen of interest. 
     In some configurations, the pathogen of interest can be a human rhinovirus or influenza. 
     In some configurations, humidifying and heating the hypoxic gas composition can comprise humidifying and heating the hypoxic gas composition to a dew point temperature of between about 37° C. and about 45° C. Humidifying and heating the hypoxic gas composition can comprise humidifying and heating the hypoxic gas composition to a dew point temperature of between about 37° C. and about 43° C. Humidifying and heating the hypoxic gas composition can comprise humidifying and heating the hypoxic gas composition to a dew point temperature of between about 43° C. and about 45° C. Humidifying and heating the hypoxic gas composition can comprise humidifying and heating the hypoxic gas composition to a dew point temperature of between about 40° C. and about 43° C. Humidifying and heating the hypoxic gas composition can comprise humidifying and heating the hypoxic gas composition to a dew point temperature of about 41° C. 
     In some configurations, humidifying the hypoxic gas composition can comprise humidifying the hypoxic gas composition to a relative humidity of at least about 80%. Humidifying the hypoxic gas composition can comprise humidifying the hypoxic gas composition to a relative humidity of at least about 90%. Humidifying the hypoxic gas composition can comprise humidifying the hypoxic gas composition to a relative humidity of at least about 95%. Humidifying the hypoxic gas composition can comprise humidifying the hypoxic gas composition to a relative humidity of at least about 99%. Humidifying the hypoxic gas composition can comprise humidifying the hypoxic gas composition to a relative humidity of at least about 100%. 
     In some configurations, the method can include mixing ambient air with a source of enriched nitrogen to create the hypoxic gas composition. 
     In some configurations, the method can include measuring inspiratory peak demand of the user; and adjusting the flow rate based upon the measured peak inspiratory demand. 
     In some configurations, an oxygen concentration of the hypoxic gas composition can be between about 10% and about 20%. An oxygen concentration of the hypoxic gas composition can be between about 15% and about 20%. An oxygen concentration of the hypoxic gas composition can be between about 10.2% and about 20.9%. An oxygen concentration of the hypoxic gas composition can be between about 11.9% and about 17.4%. An oxygen concentration of the hypoxic gas composition can be between about 13.8% and about 17.4%. An oxygen concentration of the hypoxic gas composition can be between about 15.7% and about 16.7%. 
     In some configurations, the method can include measuring at least one physiological parameter of the user; and automatically controlling the delivery of the hypoxic gas composition based on the measured physiological parameter. 
     In some configurations, the method can include outputting the measured physiological parameter in real time to the display. 
     In some configurations, the measured physiological parameter can further comprise at least one selected from the group consisting of: heart rate, respiratory rate, heart rate variability, and blood pressure. 
     In some configurations, automatically controlling the delivery of the hypoxic gas composition can comprise adjusting an amount of hypoxic gas mixed into the hypoxic gas composition. 
     In some configurations, the method can include notifying the user when the physiological parameter deviates from a pre-selected range for at least a pre-determined period of time. 
     In some configurations, the method can include altering the pre-selected range based upon individual characteristics of the user. 
     In some configurations, notifying the user can comprise activating a visual, auditory, or tactile alarm. 
     In some configurations, automatically controlling the delivery of the hypoxic gas can comprise titrating the composition of the hypoxic gas composition to achieve a blood oxygen saturation of less than about 95%. Automatically controlling the delivery of the hypoxic gas can comprise titrating the composition of the hypoxic gas composition to achieve a blood oxygen saturation of between about 80% and about 94%. Automatically controlling the delivery of the hypoxic gas can comprise titrating the composition of the hypoxic gas composition to achieve a blood oxygen saturation of between about 85% and about 92%. Automatically controlling the delivery of the hypoxic gas can comprise titrating the composition of the hypoxic gas composition to achieve a blood oxygen saturation of between about 87% and about 90%. Automatically controlling the delivery of the hypoxic gas can comprise titrating the composition of the hypoxic gas composition to achieve a blood oxygen saturation of between about 80% and about 85%. 
     In some configurations, the method can include sensing the oxygen concentration of the hypoxic gas composition after mixing. 
     In some configurations, the method can include outputting the sensed oxygen concentration in real time to a display. 
     In some configurations, the method can include correlating the sensed oxygen concentration to an altitude equivalent using a processor, and outputting the altitude equivalent in real time to the display. 
     In some configurations, the method can include obtaining a target oxygen saturation of the hypoxic gas composition based on the blood oxygen saturation. 
     In some configurations, the method can include achieving the target oxygen concentration based on the sensed oxygen concentration after mixing. 
     In some configurations, the method can include achieving the target oxygen concentration by controlling a hypoxic gas inlet valve. 
     In some configurations, titrating the composition of the hypoxic gas composition can comprise altering a flow rate of nitrogen into the hypoxic gas composition. 
     In some configurations, the hypoxic gas composition can be delivered to the user at a flow rate of at least about 20 liters/minute. The hypoxic gas composition can be delivered to the user at a flow rate of at least about 30 liters/minute. The hypoxic gas composition can be delivered to the user at a flow rate of at least about 40 liters/minute. The hypoxic gas composition can be delivered to the user at a flow rate of at least about 50 liters/minute. The hypoxic gas composition can be delivered to the user at a flow rate of at least about 60 liters/minute. The hypoxic gas composition can be delivered to the user at a flow rate of at least about 70 liters/minute. 
     In some configurations, the method can be used for a time period sufficient to improve the user&#39;s conditioning at high altitude. 
     In some configurations, the method can be used for a time period sufficient to stimulate erythropoiesis such that the user&#39;s hemoglobin level increases by at least 5% compared to before starting the method. 
     In some configurations, the method can be used for a time period sufficient to stimulate erythropoiesis such that the user&#39;s hemoglobin level increases by at least 10% compared to before starting the method. 
     In some configurations, the user interface can comprise a nasal cannula. 
     In some configurations, the nasal cannula can be non-sealed. 
     In some configurations, a system configured for providing a hypoxic flow of gases to a user can include an apparatus comprising a gas flow path, an ambient air inlet, and a hypoxic gas source inlet configured to connect to a hypoxic gas source and configured to create a hypoxic gas composition upon mixing of ambient air and the hypoxic gas; a gas flow generation element configured to deliver the hypoxic gas composition; a humidification element configured to humidify the hypoxic gas composition prior to reaching the nares of the user; a heating element within the gas flow path, wherein the humidification element and the heating element are configured to heat and humidify the hypoxic gas composition to a dew point temperature of between about 30° C. and about 45° C.; and a user interface. 
     In some configurations, the humidification element can comprise a humidification chamber. 
     In some configurations, the gas flow generation element can comprise one or more of a blower, a compressor, a pressurized tank, or a gas source in the wall. 
     In some configurations, the heating element can comprise a heater plate. 
     In some configurations, the heating element can comprise a heater wire. 
     In some configurations, the user interface can comprise nasal prongs. The user interface can comprise a mask. 
     In some configurations, the gas flow generation element can be configured to deliver the hypoxic gas composition to the user at a predetermined flow rate of at least about 10 liters/minute. 
     In some configurations, the gas flow generation element can be configured to deliver the hypoxic gas composition sufficient to meet the peak inspiratory demand of the user. 
     In some configurations, the system can further include the hypoxic gas source. 
     In some configurations, the hypoxic gas source can comprise a reservoir. 
     In some configurations, the hypoxic gas comprises a physiologically inert gas. The hypoxic gas can comprise enriched nitrogen. 
     In some configurations, the heating element and the humidification element can be configured to heat and humidify the hypoxic gas composition to a dew point temperature of between about 37° C. and about 43° C. The heating element and the humidification element can be configured to heat and humidify the hypoxic gas composition to a dew point temperature of between about 37° C. and about 43° C. The heating element and the humidification element can be configured to heat and humidify the hypoxic gas composition to a dew point temperature of between about 43° C. and about 45° C. The heating element and the humidification element can be configured to heat and humidify the hypoxic gas composition to a dew point temperature of between about 40° C. and about 43° C. The heating element and the humidification element can be configured to heat and humidify the hypoxic gas composition to a dew point temperature of about 41° C. 
     In some configurations, the humidification element can be configured to humidify the hypoxic gas composition to a relative humidity of at least about 80%. The humidification element can be configured to humidify the hypoxic gas composition to a relative humidity of at least about 90%. The humidification element can be configured to humidify the hypoxic gas composition to a relative humidity of at least about 95%. The humidification element can be configured to humidify the hypoxic gas composition to a relative humidity of at least about 99%. The humidification element can be configured to humidify the hypoxic gas composition to a relative humidity of at least about 100%. 
     In some configurations, the system can further include a sensor configured to measure a peak inspiratory demand of the user; and the system can be configured to adjust the flow rate based upon the measured peak inspiratory demand. 
     In some configurations, the system can be configured to deliver the hypoxic gas in an oxygen concentration of between about 10% and about 20%. The system can be configured to deliver the hypoxic gas in an oxygen concentration of between about 15% and about 20%. The system can be configured to deliver the hypoxic gas in an oxygen concentration of between about 10.2% and about 20.9%. The system can be configured to deliver the hypoxic gas in an oxygen concentration of between about 11.9% and about 17.4%. The system can be configured to deliver the hypoxic gas in an oxygen concentration of between about 13.8% and about 17.4%. The system can be configured to deliver the hypoxic gas in an oxygen concentration of between about 15.7% and about 16.7%. 
     In some configurations, the system can further include a sensor configured to measure a physiological parameter of the user; and a controller configured to automatically control the delivery of the hypoxic gas composition based on the measured physiological parameter. 
     In some configurations, the controller can be configured to automatically controlling the delivery of the hypoxic gas composition by adjusting an amount of hypoxic gas mixed into the hypoxic gas composition. In some configurations, the controller can be configured to automatically controlling the delivery of the hypoxic gas composition by adjusting an amount of enriched nitrogen mixed into the hypoxic gas composition. 
     In some configurations, the physiological parameter can be blood oxygen saturation. 
     In some configurations, the physiological parameter can further comprise at least one selected from the group consisting of: heart rate, respiratory rate, heart rate variability, and blood pressure. 
     In some configurations, the system can further include an alarm configured to notify the user when the physiological parameter deviates from a pre-selected range for at least a pre-determined period of time. 
     In some configurations, the alarm can comprise one of a visual, auditory, or tactile alarm. 
     In some configurations, the controller can be configured to titrate the composition of the hypoxic gas composition to achieve a blood oxygen saturation of the user of less than about 95%. The controller can be configured to titrate the composition of the hypoxic gas composition to achieve a blood oxygen saturation of the user of between about 80% and about 94%. The controller can be configured to titrate the composition of the hypoxic gas composition to achieve a blood oxygen saturation of the user of between about 85% and about 92%. The controller can be configured to titrate the composition of the hypoxic gas composition to achieve a blood oxygen saturation of the user of between about 87% and about 90%. The controller can be configured to titrate the composition of the hypoxic gas composition to achieve a blood oxygen saturation of the user of between about 80% and about 85%. 
     In some configurations, the system can further include a sensor configured to sense the oxygen concentration of the hypoxic gas composition. 
     In some configurations, the system can further include a display, wherein the system is configured to output the sensed oxygen concentration in real time to the display. 
     In some configurations, the system can be further configured to correlate the sensed oxygen concentration to an altitude equivalent using a processor, and outputting the altitude equivalent in real time to the display. 
     In some configurations, the system can be further configured to obtain a target oxygen concentration of the hypoxic gas composition based on the blood oxygen saturation. 
     In some configurations, the system can be further configured to achieve the target oxygen concentration based on the sensed oxygen concentration. 
     In some configurations, the system can be further configured to achieve the target oxygen concentration by controlling a hypoxic gas inlet valve. 
     In some configurations, the controller can be configured to alter a flow rate of the hypoxic gas into the hypoxic gas composition. 
     In some configurations, the gas flow generation element can be configured to deliver the hypoxic gas composition to the nares of the user at a predetermined flow rate of at least about 20 liters/minute. The gas flow generation element can be configured to deliver the hypoxic gas composition to the nares of the user at a predetermined flow rate of at least about 30 liters/minute. The gas flow generation element can be configured to deliver the hypoxic gas composition to the nares of the user at a predetermined flow rate of at least about 40 liters/minute. The gas flow generation element can be configured to deliver the hypoxic gas composition to the nares of the user at a predetermined flow rate of at least about 50 liters/minute. The gas flow generation element can be configured to deliver the hypoxic gas composition to the nares of the user at a predetermined flow rate of at least about 60 liters/minute. The gas flow generation element can be configured to deliver the hypoxic gas composition to the nares of the user at a predetermined flow rate of at least about 70 liters/minute. 
     In some configurations, the user interface can comprise a nasal cannula. 
     In some configurations, the nasal cannula can be non-sealed. 
     In some configurations, the system can be a high flow device. 
     In some configurations, the high flow device can be portable. 
     In some configurations, a method of providing altitude or fitness training to a user can include simulating a higher altitude by providing a hypoxic gas composition; humidifying the hypoxic gas composition; and delivering the humidified, hypoxic gas composition via a user interface in proximity to an airway of a user. 
     In some configurations, a method of treating or preventing hypertension, obesity, hyperlipidemia, prediabetes or impaired glucose tolerance, diabetes mellitus type I or type II, metabolic syndrome, mitochondrial regeneration, aging, fatigue, inflammatory diseases, or anemia of a user can include providing a hypoxic gas composition; humidifying the hypoxic gas composition; and delivering the humidified, hypoxic gas composition via a user interface in proximity to an airway of a user so as to treat or prevent hypertension, obesity, hyperlipidemia, prediabetes or impaired glucose tolerance, diabetes mellitus type I or type II, metabolic syndrome, mitochondrial regeneration, aging, fatigue, inflammatory diseases, or anemia. 
     In some configurations, the method can include humidifying the hypoxic gas composition to a relative humidity of at least about 80%. The method can include humidifying the hypoxic gas composition to a relative humidity of at least about 90%. The method can include humidifying the hypoxic gas composition to a relative humidity of at least about 95%. The method can include humidifying the hypoxic gas composition to a relative humidity of at least about 99%. The method can include humidifying the hypoxic gas composition to a relative humidity of at least about 100%. 
     In some configurations, the method can include delivering the humidified, hypoxic gas composition via a nasal cannula to the user&#39;s nares. The method can include delivering the humidified, hypoxic gas composition via a mask. The method can include delivering the humidified, hypoxic gas composition via a mask. 
     In some configurations, the method can include heating the hypoxic gas composition prior to reaching the user. 
     In some configurations, the hypoxic gas composition can comprise at least one physiologically inert gas. In some configurations, the hypoxic gas composition can comprise nitrogen. 
     In some configurations, the method can include delivering the hypoxic gas composition continuously at a flow rate of at least about 10 liters/minute. 
     In some configurations, the method can include delivering the hypoxic gas composition continuously at a flow rate that meets the user&#39;s inspiratory demand. 
     In some configurations, the method can include synchronizing delivering the hypoxic gas composition with an inspiratory phase of breathing of the user, wherein the delivering of the hypoxic gas composition can be at a flow rate of at least about 10 liters/minute during inspiration. 
     In some configurations, the method can include synchronizing delivering the hypoxic gas composition with an inspiratory phase of breathing of the user, wherein the delivering of the hypoxic gas composition can be at a flow rate that meets the user&#39;s inspiratory demand. 
     In some configurations, synchronizing can comprise increasing the flow rate on inspiration and reducing the flow rate on expiration. 
     In some configurations, delivering the hypoxic gas can be sufficient to meet peak inspiratory demand of the user. 
     In some configurations, heating the hypoxic gas composition can comprise heating the hypoxic gas composition to a temperature of between about 30° C. and about 45° C. Heating the hypoxic gas composition can comprise heating the hypoxic gas composition to between about 37° C. and about 43° C. Heating the hypoxic gas composition can comprise heating the hypoxic gas composition to about 41° C. 
     In some configurations, the method can include heating and humidifying the hypoxic gas composition to a dew point temperature of between about 30° C. and about 45° C. The method can include heating and humidifying the hypoxic gas composition to a dew point temperature of between about 37° C. and about 45° C. The method can include heating and humidifying the hypoxic gas composition to a dew point temperature of about 41° C. 
     In some configurations, heating the hypoxic gas composition can be sufficient to inactivate a pathogen of interest. 
     In some configurations, the pathogen of interest can be a human rhinovirus or influenza. 
     In some configurations, the method can include mixing ambient air with a source of enriched nitrogen to create the hypoxic gas composition. 
     In some configurations, the method can include measuring inspiratory peak demand of the user; and adjusting the flow rate based upon the measured peak inspiratory demand. 
     In some configurations, an oxygen concentration of the hypoxic gas composition can be between about 10% and about 20%. An oxygen concentration of the hypoxic gas composition can be between about 15% and about 20%. An oxygen concentration of the hypoxic gas composition can be between about 10.2% and about 20.9%. An oxygen concentration of the hypoxic gas composition can be between about 11.9% and about 17.4%. An oxygen concentration of the hypoxic gas composition can be between about 13.8% and about 17.4%. An oxygen concentration of the hypoxic gas composition can be between about 15.7% and about 16.7%. 
     In some configurations, the method can include measuring at least one physiological parameter of the user; and automatically controlling the delivery of the hypoxic gas composition based on the measured physiological parameter. 
     In some configurations, the method can include outputting the measured physiological parameter in real time to the display. 
     In some configurations, the measured physiological parameter can be blood oxygen saturation. 
     In some configurations, the measured physiological parameter can further comprise at least one selected from the group consisting of: heart rate, respiratory rate, heart rate variability, and blood pressure. 
     In some configurations, automatically controlling the delivery of the hypoxic gas composition can comprise adjusting an amount of hypoxic gas mixed into the hypoxic gas composition. 
     In some configurations, the method can include notifying the user when the physiological parameter deviates from a pre-selected range for at least a pre-determined period of time. 
     In some configurations, the method can include altering the pre-selected range based upon individual characteristics of the user. 
     In some configurations, notifying the user can comprise activating a visual, auditory, or tactile alarm. 
     In some configurations, automatically controlling the delivery of the hypoxic gas can comprise titrating the composition of the hypoxic gas composition to achieve a blood oxygen saturation of less than about 95%. Automatically controlling the delivery of the hypoxic gas can comprise titrating the composition of the hypoxic gas composition to achieve a blood oxygen saturation of between about 80% and about 94%. Automatically controlling the delivery of the hypoxic gas can comprise titrating the composition of the hypoxic gas composition to achieve a blood oxygen saturation of between about 85% and about 92%. Automatically controlling the delivery of the hypoxic gas can comprise titrating the composition of the hypoxic gas composition to achieve a blood oxygen saturation of between about 87% and about 90%. Automatically controlling the delivery of the hypoxic gas can comprise titrating the composition of the hypoxic gas composition to achieve a blood oxygen saturation of between about 80% and about 85%. 
     In some configurations, the method can include sensing the oxygen concentration of the hypoxic gas composition after mixing. 
     In some configurations, the method can include outputting the sensed oxygen concentration in real time to a display. 
     In some configurations, the method can include correlating the sensed oxygen concentration to an altitude equivalent using a processor, and outputting the altitude equivalent in real time to the display. 
     In some configurations, the method can include obtaining a target oxygen concentration of the hypoxic gas composition based on the blood oxygen saturation. 
     In some configurations, the method can include achieving the target oxygen concentration based on the sensed oxygen concentration after mixing. 
     In some configurations, the method can include achieving the target oxygen concentration by controlling a hypoxic gas inlet valve. 
     In some configurations, titrating the composition of the hypoxic gas composition can comprise altering a flow rate of nitrogen into the hypoxic gas composition. 
     In some configurations, the hypoxic gas composition can be delivered to the user at a flow rate of at least about 20 liters/minute. The hypoxic gas composition can be delivered to the user at a flow rate of at least about 30 liters/minute. The hypoxic gas composition can be delivered to the user at a flow rate of at least about 40 liters/minute. The hypoxic gas composition can be delivered to the user at a flow rate of at least about 50 liters/minute. The hypoxic gas composition can be delivered to the user at a flow rate of at least about 60 liters/minute. The hypoxic gas composition can be delivered to the user at a flow rate of at least about 70 liters/minute. 
     In some configurations, the method can be used for a time period sufficient to improve the user&#39;s conditioning at high altitude. 
     In some configurations, the method can be used for a time period sufficient to stimulate erythropoiesis such that the user&#39;s hemoglobin level increases by at least 5% compared to before starting the method. 
     In some configurations, the method can be used for a time period sufficient to stimulate erythropoiesis such that the user&#39;s hemoglobin level increases by at least 10% compared to before starting the method. 
     In some configurations, the user interface can comprise a nasal cannula. 
     In some configurations, the nasal cannula can be non-sealed. 
     In some configurations, a system configured for providing altitude or fitness training to a user can include an apparatus comprising a gas flow path, an ambient air inlet, and a hypoxic gas source inlet configured to connect to a hypoxic gas source and configured to create a hypoxic gas composition upon mixing of ambient air and the hypoxic gas; a gas flow generation element configured to deliver the hypoxic gas composition to an airway of the user so as to simulate a higher altitude; a humidification element within the gas flow path configured to humidify the hypoxic gas composition prior to reaching the airway of the user; and a user interface. 
     In some configurations, a system configured for or preventing hypertension, obesity, hyperlipidemia, prediabetes or impaired glucose tolerance, diabetes mellitus type I or type II, metabolic syndrome, mitochondrial regeneration, aging, fatigue, inflammatory diseases, or anemia of a user can include an apparatus comprising a gas flow path, an ambient air inlet, and a hypoxic gas source inlet configured to connect to a hypoxic gas source and configured to create a hypoxic gas composition upon mixing of ambient air and the hypoxic gas; a gas flow generation element configured to deliver the hypoxic gas composition to an airway of the user; a humidification element within the gas flow path configured to humidify the hypoxic gas composition prior to reaching the airway of the user, the gas flow configured to treat or prevent hypertension, obesity, hyperlipidemia, prediabetes or impaired glucose tolerance, diabetes mellitus type I or type II, metabolic syndrome, mitochondrial regeneration, aging, fatigue, inflammatory diseases, or anemia; and a user interface. 
     In some configurations, the humidification element can be configured to humidify the hypoxic gas composition to a relative humidity of at least about 80%. The humidification element can be configured to humidify the hypoxic gas composition to a relative humidity of at least about 90%. The humidification element can be configured to humidify the hypoxic gas composition to a relative humidity of at least about 95%. The humidification element can be configured to humidify the hypoxic gas composition to a relative humidity of at least about 99%. The humidification element can be configured to humidify the hypoxic gas composition to a relative humidity of at least about 100%. 
     In some configurations, the humidification element can comprise a humidification chamber. 
     In some configurations, the gas flow generation element can comprise one or more of a blower, a compressor, a pressurized tank, or a gas source in the wall. 
     In some configurations, the user interface can comprise nasal cannula including nasal prongs. 
     In some configurations, the nasal cannula can be non-sealed. 
     In some configurations, the user interface can comprise a mask. 
     In some configurations, the gas flow generation element can be configured to deliver the hypoxic gas composition to the user at a predetermined flow rate of at least about 10 liters/minute. 
     In some configurations, the gas flow generation element can be configured to deliver the hypoxic gas composition sufficient to meet the peak inspiratory demand of the user. The gas flow generation element can be configured to deliver the hypoxic gas composition sufficient to meet the peak inspiratory demand of the user. 
     In some configurations, the system can further include the hypoxic gas source. 
     In some configurations, the hypoxic gas source can comprise a reservoir. 
     In some configurations, the hypoxic gas comprises a physiologically inert gas. The hypoxic gas can comprise enriched nitrogen. 
     In some configurations, the system can further include a heating element configured to heat the hypoxic gas composition prior to reaching the airway of the user. 
     In some configurations, the heating element can comprise a heater plate. 
     In some configurations, the heating element can comprise a heater wire. 
     In some configurations, the heating element can be configured to heat the hypoxic gas composition to a temperature of between about 30° C. and about 45° C. The heating element can be configured to heat the hypoxic gas composition to between about 30° C. and about 43° C. The heating element can be configured to heat the hypoxic gas composition to between about 37° C. and about 43° C. The heating element can be configured to heat the hypoxic gas composition to about 41° C. 
     In some configurations, the heating element and the humidification element can be configured to heat and humidify the hypoxic gas composition to a dew point temperature of between about 30° C. and about 45° C. The heating element and the humidification element can be configured to heat and humidify the hypoxic gas composition to a dew point temperature of between about 30° C. and about 43° C. The heating element and the humidification element can be configured to heat and humidify the hypoxic gas composition to a dew point temperature of between about 37° C. and about 43° C. The heating element and the humidification element can be configured to heat and humidify the hypoxic gas composition to a dew point temperature of about 41° C. 
     In some configurations, the system can further include a sensor configured to measure a peak inspiratory demand of the user; and the system can be configured to adjust the flow rate based upon the measured peak inspiratory demand. 
     In some configurations, the system can be configured to deliver the hypoxic gas in an oxygen concentration of between about 10% and about 20%. The system can be configured to deliver the hypoxic gas in an oxygen concentration of between about 15% and about 20%. The system can be configured to deliver the hypoxic gas in an oxygen concentration of between about 10.2% and about 20.9%. The system can be configured to deliver the hypoxic gas in an oxygen concentration of between about 11.9% and about 17.4%. The system can be configured to deliver the hypoxic gas in an oxygen concentration of between about 13.8% and about 17.4%. The system can be configured to deliver the hypoxic gas in an oxygen concentration of between about 15.7% and about 16.7%. 
     In some configurations, the system can further include a sensor configured to measure a physiological parameter of the user; and a controller configured to automatically control the delivery of the hypoxic gas composition based on the measured physiological parameter. 
     In some configurations, the controller can be configured to automatically controlling the delivery of the hypoxic gas composition by adjusting an amount of hypoxic gas mixed into the hypoxic gas composition. In some configurations, the controller can be configured to automatically controlling the delivery of the hypoxic gas composition by adjusting an amount of enriched nitrogen mixed into the hypoxic gas composition. 
     In some configurations, the physiological parameter can be blood oxygen saturation. 
     In some configurations, the physiological parameter can further comprise at least one selected from the group consisting of: heart rate, respiratory rate, heart rate variability, and blood pressure. 
     In some configurations, the system can further include an alarm configured to notify the user when the physiological parameter deviates from a pre-selected range for at least a pre-determined period of time. 
     In some configurations, the alarm can comprise one of a visual, auditory, or tactile alarm. 
     In some configurations, the controller can be configured to titrate the composition of the hypoxic gas composition to achieve a blood oxygen saturation of the user of less than about 95%. The controller can be configured to titrate the composition of the hypoxic gas composition to achieve a blood oxygen saturation of the user of between about 80% and about 94%. The controller can be configured to titrate the composition of the hypoxic gas composition to achieve a blood oxygen saturation of the user of between about 85% and about 92%. The controller can be configured to titrate the composition of the hypoxic gas composition to achieve a blood oxygen saturation of the user of between about 87% and about 90%. The controller can be configured to titrate the composition of the hypoxic gas composition to achieve a blood oxygen saturation of the user of between about 80% and about 85%. 
     In some configurations, the system can further include a sensor configured to sense the oxygen concentration of the hypoxic gas composition. 
     In some configurations, the system can further include a display, wherein the system is configured to output the sensed oxygen concentration in real time to the display. 
     In some configurations, the system can be further configured to correlate the sensed oxygen concentration to an altitude equivalent using a processor, and outputting the altitude equivalent in real time to the display. 
     In some configurations, the system can be further configured to obtain a target oxygen concentration of the hypoxic gas composition based on the blood oxygen saturation. 
     In some configurations, the system can be further configured to achieve the target oxygen concentration based on the sensed oxygen concentration. 
     In some configurations, the system can be further configured to achieve the target oxygen concentration by controlling a hypoxic gas inlet valve. 
     In some configurations, the controller can be configured to alter a flow rate of the hypoxic gas into the hypoxic gas composition. 
     In some configurations, the gas flow generation element can be configured to deliver the hypoxic gas composition to the nares of the user at a predetermined flow rate of at least about 20 liters/minute. The gas flow generation element can be configured to deliver the hypoxic gas composition to the nares of the user at a predetermined flow rate of at least about 30 liters/minute. The gas flow generation element can be configured to deliver the hypoxic gas composition to the nares of the user at a predetermined flow rate of at least about 40 liters/minute. The gas flow generation element can be configured to deliver the hypoxic gas composition to the nares of the user at a predetermined flow rate of at least about 50 liters/minute. The gas flow generation element can be configured to deliver the hypoxic gas composition to the nares of the user at a predetermined flow rate of at least about 60 liters/minute. The gas flow generation element can be configured to deliver the hypoxic gas composition to the nares of the user at a predetermined flow rate of at least about 70 liters/minute. 
     In some configurations, the system can be a high flow device. 
     In some configurations, the high flow device can be portable. 
     In some configurations, a method of providing a respiratory training session to a user can include providing a hypoxic gas composition; delivering the hypoxic gas composition via a user interface in proximity to an airway of the user; and varying an oxygen concentration of the hypoxic gas composition after a predetermined period of time. 
     In some configurations, varying can comprise reducing or increasing. 
     In some configurations, varying can comprise reducing followed by increasing the oxygen concentration of the hypoxic gas composition, or increasing followed by reducing the oxygen concentration of the hypoxic gas composition. 
     In some configurations, varying can comprise varying gradually. Varying can comprise varying in a series of step changes. Varying can comprise varying in a step change. 
     In some configurations, the hypoxic gas composition can comprise at least one physiologically inert gas. In some configurations, the hypoxic gas composition can comprise nitrogen. 
     In some configurations, the method can include delivering the hypoxic gas composition continuously at a flow rate of at least about 10 liters/minute. 
     In some configurations, the method can include delivering the hypoxic gas composition continuously at a flow rate that meets the user&#39;s inspiratory demand. 
     In some configurations, providing can comprise simulating a first altitude. 
     In some configurations, varying can comprise simulating a second altitude lower than the first altitude. 
     In some configurations, the method can include providing a gas composition substantially the same as ambient air prior to providing the hypoxic gas composition. 
     In some configurations, varying can be responsive to a change in the user&#39;s SpO 2 . 
     In some configurations, the user interface can comprise a nasal cannula. 
     In some configurations, the nasal cannula can be non-sealed. 
     In some configurations, a system configured for providing a respiratory training session to a user can include an apparatus comprising a gas flow path, an ambient air inlet, and a hypoxic gas source inlet configured to connect to a hypoxic gas source and configured to create a hypoxic gas composition upon mixing of ambient air and the hypoxic gas; a gas flow generation element configured to deliver the hypoxic gas composition; a user interface; and a controller configured to: provide the hypoxic gas composition and vary an oxygen concentration of the hypoxic gas composition after a predetermined period of time. 
     In some configurations, the gas flow generation element can comprise one or more of a blower, a compressor, a pressurized tank, or a gas source in the wall. 
     In some configurations, to vary can comprise to reduce or to increase. 
     In some configurations, the system can include a screen configured to display an altitude equivalent of the altitude or fitness training. 
     In some configurations, the system can include a screen configured to display an SpO 2  of the user. 
     In some configurations, the screen can comprise a touchscreen. 
     In some configurations, the system can include user input devices for the user to select an altitude equivalent of the altitude or fitness training. 
     In some configurations, the altitude equivalent can be based on an oxygen concentration. 
     In some configurations, the oxygen concentration can be an FdO 2  set point or a sensed oxygen concentration. 
     In some configurations, the user input devices can comprise one or more buttons. 
     In some configurations, the user input devices can comprise a touchscreen. 
     In some configurations, to vary can comprise to reduce followed by to increase the oxygen concentration of the hypoxic gas composition, or to increase followed by to reduce the oxygen concentration of the hypoxic gas composition. 
     In some configurations, the controller can be configured to vary the oxygen concentration of the hypoxic gas composition gradually. The controller can be configured to vary the oxygen concentration of the hypoxic gas composition in a series of step changes. The controller can be configured to vary the oxygen concentration of the hypoxic gas composition in a step change. 
     In some configurations, the hypoxic gas composition can comprise at least one physiologically inert gas. In some configurations, the hypoxic gas composition can comprise nitrogen. 
     In some configurations, the gas flow generation element can be configured to deliver the hypoxic gas composition to the user at a predetermined flow rate of at least about 10 liters/minute. 
     In some configurations, the gas flow generation element can be configured to deliver the hypoxic gas composition sufficient to meet the peak inspiratory demand of the user. 
     In some configurations, the controller can be configured to provide the hypoxic gas composition to simulate a first altitude. 
     In some configurations, the controller can be configured to vary the oxygen concentration of the hypoxic gas composition to simulate a second altitude lower than the first altitude. 
     In some configurations, the controller can be configured to provide a gas composition substantially the same as ambient air prior to providing the hypoxic gas composition. 
     In some configurations, the controller can be configured to vary the oxygen concentration of the hypoxic gas composition responsive to a change in the user&#39;s SpO 2 . 
     In some configurations, they system can comprise a sensor configured to measure the user&#39;s SpO 2 . 
     In some configurations, the user interface can comprise a nasal cannula. 
     In some configurations, the nasal cannula can be non-sealed. 
     In some configurations, the system can be a high flow device. 
     In some configurations, the high flow device can be portable. 
     In some configurations, the system can comprise a humidification chamber. 
     In some configurations, the system can comprise a heating element. 
     In some configurations, the heating element can comprise a heater plate. 
     In some configurations, the heating element can comprise a heater wire. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present disclosure are described with reference to the drawings of certain embodiments, which are intended to schematically illustrate certain embodiments and not to limit the disclosure. 
         FIG. 1  shows in diagrammatic form a hypoxic gas composition delivery apparatus in the form of a flow therapy apparatus. 
         FIG. 2  is a front view of the flow therapy apparatus with a humidifier chamber in position and a raised handle/lever. 
         FIG. 3  is a top view corresponding to  FIG. 2 . 
         FIG. 4  is a right side view corresponding to  FIG. 2 . 
         FIG. 5  is a left side view corresponding to  FIG. 2 . 
         FIG. 6  is a rear view corresponding to  FIG. 2 . 
         FIG. 7  is a front left perspective view corresponding to  FIG. 2 . 
         FIG. 8  is a front right perspective view corresponding to  FIG. 2 . 
         FIG. 9  is a bottom view corresponding to  FIG. 2 . 
         FIG. 10  shows a first configuration of an air and nitrogen inlet arrangement of the flow therapy apparatus. 
         FIG. 11  shows a second configuration of an air and nitrogen inlet arrangement of the flow therapy apparatus. 
         FIG. 12  is a transverse sectional view showing further detail of the air and nitrogen inlet arrangement of  FIG. 11 . 
         FIG. 13  is another transverse sectional view showing further detail of the air and nitrogen inlet arrangement of  FIG. 11 . 
         FIG. 14  is a longitudinal sectional view showing further detail of the air and nitrogen inlet arrangement of  FIG. 11 . 
         FIG. 15  is an exploded view of upper and lower chassis components of a main housing of the flow therapy apparatus. 
         FIG. 16  is a front left side perspective view of the lower chassis of the main housing showing a housing for receipt of a motor/sensor module sub-assembly. 
         FIG. 17A  is a first underside perspective view of the main housing of the flow therapy apparatus showing a recess inside the housing for the motor/sensor module sub-assembly. 
         FIG. 17B  is a second underside perspective view of the main housing of the flow therapy apparatus showing the recess for the motor/sensor module sub-assembly. 
         FIGS. 18A-E  illustrate various views of an example flow therapy apparatus. 
         FIG. 19A  illustrates a block diagram of a control system interacting with and/or providing control and direction to components of a respiratory assistance system. 
         FIG. 19B  illustrates a block diagram of an example controller. 
         FIG. 20  illustrates a block diagram of a motor/sensor module. 
         FIG. 21  illustrates a sensing chamber of an example removable motor/sensor module. 
         FIG. 22  illustrates example block diagrams of a closed loop control system. 
     
    
    
     DETAILED DESCRIPTION 
     Although certain examples are described below, those of skill in the art will appreciate that the disclosure extends beyond the specifically disclosed examples and/or uses and obvious modifications and equivalents thereof. Thus, it is intended that the scope of the disclosure herein disclosed should not be limited by any particular examples described below. 
     In some configurations, systems and methods can reduce the oxygen content of inspired air as a mechanism of simulating being at a higher altitude, improving athletic performance, and other medical and/or wellness benefits. One objective of this is to stimulate the body to produce more red blood cells, and thus oxygen carrying capacity as a way of increasing cardiovascular endurance. In some cases, the systems and methods can be used for a time period sufficient to stimulate erythropoiesis such that the user&#39;s hemoglobin level increases by about or at least about 5%, 10%, 15%, 20%, or more compared with prior to initiation of therapy, or ranges including any two of the aforementioned values. 
     Conventional devices that provide a hypoxic atmosphere within an enclosure can suffer from several disadvantages. Such conventional setups can be quite costly due to the volume of gas that needs to be altered. Many systems are not portable, and the ones that are (such as a tent) can be both difficult to transport as well as quite small, limiting what a user can do while using it. The user can also be prevented/restricted from leaving the enclosure, and others who do not wish to use the device are unable to enter it, thus limiting the ability for interaction between participants and non-participants, especially during extended use. If the user needs to suddenly end the therapy they need to leave the enclosure, which would take significantly longer than simply removing a patient interface, such as a cannula (some devices provide a breathing device with normoxic air for use in an emergency, but this can just further add to the cost). The use of a room would also prevent individually adjusted therapy when used with others, as everyone would be required to breathe the same gas composition. The volume of the room would also make it difficult to make any quick changes to the composition of the gas. As such, it would be advantageous to limit the hypoxic atmosphere to a user interface proximate to, or directly attachable to a user. 
     Devices that use a mask can be disadvantageous in some cases by their obstructive nature. Using a nasal cannula (e.g., as the only conduit to the user) instead of and without using a mask means the user can still talk, eat and drink while the device is attached, making it more viable for longer therapy sessions, as the user would not need to remove it for such tasks. The portability of the cannula can also allow the user to move the device with them as they do various activities throughout the day. These factors combined allow such devices to advantageously implement a wide range of therapy regimes. The user could have a nasal cannula attached and connected to high flow systems as disclosed herein during a majority of day to day tasks, while sleeping, and while exercising on a spot (such as with a treadmill or weight training). The cannula could also be removed and reattached fairly easily, which could be useful if the therapy regime required regularly stopping and starting the administration of the hypoxic gases. The cannula can also be far more comfortable, and does not run the risk of the user developing pressure sores. Users may also in some cases find a mask somewhat claustrophobic due to the amount of their face it covers. A cannula can also be safer than a mask in some cases, as it would not obstruct breathing if the device were to fail, and can be removed more easily if needed. 
     Examples of systems and methods as disclosed herein can advantageously deliver high flow rates (e.g., greater than about 10 liters per minute in adults and/or in excess of peak inspiratory demand in some cases). However, some examples can be configured to deliver lower flow rates as well. Some conventional devices deliver a small dose of pure nitrogen upon inspiration that can mix with additional inspired air through the user&#39;s mouth and/or around the cannula to create the required hypoxic mixture. This method can have several disadvantages in some cases. One disadvantage is that as conventional devices deliver a fixed dose or low flow of nitrogen, the total fraction of inspired oxygen (FiO 2 ) would change as the inspiratory flow rate changes, and would depend on the user&#39;s inspiratory tidal volume, meaning that a change in breath rate or volume would alter the composition being delivered. This could make targeting a specific FiO 2  or SpO 2  very challenging. In contrast, systems and methods as disclosed herein can deliver flow rates in excess of the user&#39;s inspiratory demand, which can advantageously provide a more consistent and controlled hypoxic composition regardless of changes in the user&#39;s breathing. At least two parameters can be used to determine oxygen delivery to the user, FiO 2  and FdO 2 . FiO 2  is the fraction of inspired oxygen, which is the oxygen concentration of the gas that the user is actually breathing in. FdO 2  is the fraction of delivered oxygen, which is the oxygen concentration of the gas flowing out of the cannula. FdO 2  can be directly measured by the flow therapy system, such as by measuring the oxygen concentration of the gas flowing through the system. FiO 2  is dependent on FdO 2  as well as the proportion of ambient air, if any, that is entrained when the user breathes in. While FiO 2  can be a preferred parameter in some cases in assessing the effect of the gas on the user, control of FdO 2  can allow the target FiO 2  be achieved, for example, due to the assumption that those two parameters have the same or substantially the same value in a high flow therapy system. During a high flow therapy session, the oxygen concentration measured in the system, FdO 2,  can be substantially the same as the oxygen concentration the user is breathing, FiO 2,  when the flow rate of gas delivered meets or exceeds the peak inspiratory demand of the user. That is, the volume of gas delivered by the system to the user during inspiration meets, or is in excess of, the volume of gas inspired by the user during inspiration. In that situation, no ambient air is entrained (e.g., around a non-sealed nasal cannula) and hence the value of FdO 2  is equal to the value of FiO 2 . Accordingly, high flow therapies can help to prevent entrainment of ambient air when the user breathes in, as well as to flush the user&#39;s airways of expired gas. Further, systems and methods as disclosed herein can also provide a closed loop control to provide hypoxic composition, such as based on monitoring of the user&#39;s oxygen saturation, SpO 2,  when the flow rate is not meeting the user&#39;s inspiratory demand such that FdO 2  is not equal to FiO 2  due to entrainment of ambient air. 
     While nitrogen is a common hypoxic gas that can be utilized in creating a hypoxic gas mixture, the use of other hypoxic gases are possible in addition to, or instead of nitrogen. In some examples, the hypoxic gas composition can include, or consist entirely of or substantially entirely of physiologically inert gases. Some examples include, but are not limited to nitrogen, heliox, nitric oxide, carbon dioxide, argon, helium, methane, sulfur hexafluoride, and combinations thereof. 
     In some cases, systems and methods as disclosed herein can advantageously not require or perform any detection of when the user breathes in, as a fixed flow rate of gas can be delivered at all times. Systems and methods can also provide a safe, predictable, precise, hypoxic gas composition that avoids the risk of pooling large quantities of nitrogen, such as in situations where the user temporarily breathes through their mouth or the breath synchronization is not used. 
     Conventional systems can also suffer from the disadvantage of at best only being able to control the composition of gas up to the user&#39;s face. The actual composition of gas in the airways of the user would vary based on respiratory volume, respiratory rate, gas exchange rates of the lung, among other factors. Due to the high flow of gas being delivered by some examples as disclosed herein, the user&#39;s airways can be constantly flushed of old expired gas, so when the user inspires, the gas in user&#39;s upper airways would match that being delivered from the device or system, regardless of the aforementioned factors. Nasal high-flow gas delivery systems have been disclosed to enhance oxygen delivery to patients, but not to provide the opposite effect of delivering a hypoxic gas composition for various indications. 
     In some configurations, the use of a nasal system (with or without high flow delivery) to deliver warm and/or humidified hypoxic gas compositions could be beneficial in recovery from physical activity. One current criticism of altitude training is that the hypoxic conditions lead to lower intensity during training and poorer recovery after training, and that these factors have the potential to counteract out the benefits of the body&#39;s acclimatization to altitude. By combining the hot and/or humidified gas delivery of the nasal high flow system with an altitude training program, a user could potentially gain the benefits of natural acclimatization with reduced negative side effects that would otherwise impede performance and reduce overall benefits. In some cases, heated and/or humidified air can prevent or treat infections by various pathogens as discussed elsewhere herein, including via raising the temperature, or creating enough heat energy in the nasal passage, to kill some or all of the pathogens. 
     A schematic representation of a respiratory system or flow therapy apparatus  10  is provided in  FIG. 1 . The apparatus  10  can include a main housing  100 . The main housing  100  can contain a flow generator  11  that can be in the form of a motor/impeller arrangement, an optional humidifier or humidification chamber  12 , a controller  13 , and a user interface  14 . The apparatus  10  can include any suitable gas flow generation element. The gas flow generation element can be used to generate a flow of gas and can include one or more flow generators and/or sources of pressurized gas. Examples of flow generators can include a blower or a compressor. Examples of sources of pressurized gas can include a pressurized tank or a gas source in the wall. The user interface  14  can include a display and input device(s) such as button(s), a touch screen, a combination of a touch screen and button(s), or the like. The controller  13  can include a hardware processor and can be configured or programmed to control the components of the apparatus, including but not limited to operating the flow generator  11  to create a flow of gases (e.g., hypoxic gases) for delivery to a user, operating the humidifier  12  (if present) to humidify and/or heat the gases flow, receiving user input from the user interface  14  for reconfiguration and/or user-defined operation of the apparatus  10 , and outputting information (for example on the display) to the user or healthcare professional or anyone else viewing the apparatus. 
     With continued reference to  FIG. 1 , a user breathing conduit  16  can be coupled to a gases flow outlet  21  in the housing  100  of the flow therapy apparatus  10 , and be coupled to a user interface  17 , which can be a non-sealing interface such as a nasal cannula with a manifold  19  and nasal prongs  18 . The term “non-sealing interface” as used herein can refer to an interface providing a pneumatic link between an airway of a user and a gases flow source (such as from flow generator  11 ) that does not completely occlude the airway of the user. A non-sealed pneumatic link can comprise an occlusion of less than about 95% of the airway of the user. The non-sealed pneumatic link can comprise an occlusion of less than about 90% of the airway of the user. The non-sealed pneumatic link can comprise an occlusion of between about 40% and about 80% of the airway of the user. The airway can include one or more of a nare or mouth of the user. Additionally, or alternatively, the user breathing conduit  16  can be coupled to a face mask, or a tracheostomy interface. The gases flow that is generated by the flow therapy apparatus  10 , and which may be humidified, is delivered to the user via the inspiratory conduit  16  through the cannula  17 . The inspiratory conduit  16  can have a heater wire  16   a  to heat gases flow passing through to the user. The heater wire  16   a  can be under the control of the controller  13 . In some embodiments, the device could include a gas heating mode in which the heater wire  16   a  or another heating element can be utilized to heat the hypoxic gases above the temperature of gases in the user&#39;s airway, and/or provide heat energy sufficient to kill or otherwise inactivate pathogens (e.g. viruses, including human rhinoviruses, influenza, and the like; fungi; and/or bacteria) from the gases flow, and/or pathogens already in the airways or elsewhere within the user. In some embodiments, a heating element can be present within or otherwise associated with a humidifier to raise the actual temperature and/or dew point temperature of the humidified gases stream to create a heated, humidified hypoxic gas composition, as discussed further below. Killing pathogens as both a therapeutic and/or preventative measure could be beneficial especially to athletes, where illness could severely undermine any training regime or competition performance. In some configurations, the gas heating mode can raise the temperature in the user&#39;s nasal passage high enough to provide heat energy for killing some or all of the pathogens, but not to the extent that the gases are too hot and cause other discomfort, airway damage, and other adverse effects. The hypoxic gases delivered could, in some configurations, be heated to at least about 30° C., but not more than about 50° C., 49° C., 48° C., 47° C., 46° C., 45° C., 44° C., or 43° C., such as about 31° C., 32° C., 33° C., 34° C., 35° C., 36° C., 37° C., 38° C., 39° C., 40° C., 41° C., 42° C., 43° C., or ranges incorporating any two of the aforementioned values. In some configurations, the gases can be heated to between about 31° C. and about 50° C., between about 33° C. and about 48° C., between about 35° C. and about 46° C., between about 37° C. and about 44° C., between about 39° C. and about 42° C., between about 40° C. and about 41° C., or about 41° C. In some configurations, the hypoxic gases are delivered at room temperature, such as between about 20° C. and about 25° C., or other higher or lower temperatures, such as between about 15° C. and about 30° C. The gases can also be humidified in some embodiments to prevent evaporation of moisture in the user&#39;s nasal passage and subsequently cool down too much to be effective. Humidified gases, for example, in the temperature ranges specified can in some embodiments carry enough latent heat to not only kill infections and reduce sickness times, but also act as a preventative measure, something which can be advantageous to athletes, among others. The hypoxic gases delivered could, in some configurations, have a dew point temperature of at least about 30° C., but not more than about 50° C., 49° C., 48° C., 47° C., 46° C., 45° C., 44° C., or 43° C., such as about 31° C., 32° C., 33° C., 34° C., 35° C., 36° C., 37° C., 38° C., 39° C., 40° C., 41° C., 42° C., 43° C., or ranges incorporating any two of the aforementioned values. In some configurations, the gases can have a dew point temperature of between about 31° C. and about 50° C., between about 33° C. and about 48° C., between about 35° C. and about 46° C., between about 37° C. and about 44° C., between about 39° C. and about 42° C., between about 40° C. and about 41° C., or about 41° C. In some configurations, the hypoxic gases can have a dew point temperature at room temperature, such as between about 20° C. and about 25° C., or other higher or lower temperatures, such as between about 15° C. and about 30° C. In some embodiments, the relative humidity of the hypoxic gas flow can be, for example, about or at least about 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or more, such as 100% or ranges incorporating any two of the aforementioned values. In some embodiments, the heating and/or humidification is not in an open room setup or configuration, and as such the heating and/or humidification is delivered through the discrete breathing conduit  16  directly connected to the user&#39;s nose and/or mouth. 
     The inspiratory conduit  16  and/or user interface  17  can be considered part of the flow therapy apparatus  10 , or alternatively peripheral to it. The flow therapy apparatus  10 , breathing conduit  16 , and user interface  17  together can form a flow therapy system. 
     General operation of a flow therapy breathing apparatus  10  will now be described. The controller  13  can control the flow generator  11  to generate a gases flow of a desired flow rate, one or more valves to control mixing (e.g., hypoxic mixing) of air and nitrogen or other breathable gas, and/or the humidifier  12 , if present, to humidify the gases flow to an appropriate temperature and/or humidity. In some embodiments, humidification can advantageously prevent the user&#39;s airways from drying out, which can be particularly advantageous during concomitant exercise due to fluid loss from sweating. The flow delivered could be at any desired flow rate. In some embodiments, the flow rate is about or at least about 10 liters/minute. In some embodiments, the flow rate is about, or less than about 10 liters/minute, such as 9, 8, 7, 6, 5, 4, 3, 2, or 1 liter/minute, or ranges incorporating any two of the aforementioned values. 
     As will be described in greater detail below, the apparatus  10  can use ultrasonic or other types of sensing to monitor characteristics of the gases in the flow. For example, the characteristics of the gases flow can include gases concentration, flow rate, or the like. The apparatus  10  can include additional sensors that can be in communication with the hardware processor. These sensors can include a flow rate sensor, a temperature sensor, a humidity sensor, a pressure sensor, or the like. Output of the additional sensors can be used for determining the characteristics of the gases flow, such as temperature, pressure, humidity, and the like. Output of the additional sensors can be used for correcting measurement of the characteristics of the gases flow by ultrasonic sensing. The gases flow can be directed out through the inspiratory conduit  16  and cannula  17  to the user. The cannula  17  may instead be any other user interface, such as a full face mask, nasal mask, nasal pillows mask, tracheostomy interface, or endotracheal tube. The controller  13  can also control a heating element in the humidifier  12  and/or the heating element  16   a  in the inspiratory conduit  16  to heat the gas to a desired temperature that achieves a desired level of therapy and/or level of comfort for the user. The controller  13  can be programmed with or can determine a suitable target temperature of the gases flow using one or more temperature sensors. 
     Additional sensors  3   a,    3   b,    3   c,    20 ,  25 , such as flow, temperature, humidity, and/or pressure sensors, can be placed in various locations in the flow therapy apparatus  10  and/or the inspiratory conduit  16  and/or cannula  17 . The controller  13  can receive output from the sensors to assist it in operating the flow therapy apparatus  10  in a manner that provides suitable therapy. Providing suitable therapy can include meeting a user&#39;s peak inspiratory demand in some cases. The apparatus  10  can include a wireless data transmitter and/or receiver, or a transceiver  15  to enable the controller  13  to receive data signals  8  in a wireless manner from the operation sensors and/or to control the various components of the flow therapy apparatus  10 . Additionally, or alternatively, the data transmitter and/or receiver  15  may deliver data to a remote server or enable remote control of the apparatus  10 . The apparatus  10  can include a wired connection, for example, using cables or wires, to enable the controller  13  to receive data signals  8  from the operation sensors and/or to control the various components of the flow therapy apparatus  10 . The transmitter can connect with a mobile device, such as a phone. The display, such as a graphic user interface (GUI) can be replicated on the mobile device&#39;s screen. Once connected to the apparatus  10 , the mobile device can be used to control the device. The apparatus  10  can connect to the mobile device via a wireless connection, such as Bluetooth, WiFi, near field communication (NFC), 2G/3G/4G/5G, or other suitable wireless communications networks. The apparatus  10  can additionally or alternatively connect via a wired connection, such as USB, Ethernet, FireWire, serial port interface, or other suitable data transmission wires. 
     In some embodiments, one or more sensors (e.g., ultrasonic transducers as described herein) can be utilized to measure/verify the hypoxic gas composition (e.g., oxygen concentration) after, for example, nitrogen and ambient air have finished mixing. In some embodiments, at least one sensor on at least two of the ambient air inlet conduit, the nitrogen inlet conduit, and the final delivery conduit can be utilized to determine the flow rate of at least two gases. By inputting the flow rate of both inlet gases or one inlet gas and one total flow rate, along with the assumed oxygen concentrations of the inlet gases (e.g., 20.9% for ambient air, 0% for 100% pure enriched nitrogen), the oxygen concentration of the final gas composition can be calculated. As such, the hypoxic gas composition could include, for example, nitrogen enriched with between about 2% and about 18% oxygen (e.g., FdO 2 ), between about 2% and about 15% of oxygen, between about 10% and about 15% of oxygen, about 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% of oxygen, or ranges incorporating any of the aforementioned values. If inspiratory demand is met by the flow rate delivered to the user, FiO 2  can also be any of the aforementioned values. If inspiratory demand is not met, FiO 2  may be somewhat closer to the oxygen concentration in ambient air, as ambient air would be entrained around the cannula, which may reduce the nitrogen concentration in the gases inspired by the user. 
     In some embodiments, the hypoxic gas source itself could be made of a hypoxic gas of less than 100% purity. For example, the hypoxic gas source (e.g., enriched nitrogen and/or other hypoxic gases) could be at a purity of, for example, between about 82% and about 100%, such as between about 85% and about 90%, or about 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 89%, 99%, 100%, or ranges incorporating any of the aforementioned values. The oxygen concentration of the hypoxic gas source could be in some cases between about 2% and about 18% oxygen, between about 2% and about 15% of oxygen, between about 10% and about 15% of oxygen, about 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% of oxygen, or ranges incorporating any of the aforementioned values. Enriched nitrogen or another hypoxic gas at less than about 100% purity, such as 90% purity (with 10% oxygen), for example, can be advantageous from a safety perspective in preventing the FiO 2  from dipping below 10% (or another desired floor percentage), even in the event of a malfunction when mixing the nitrogen-enriched gas with ambient air. 
     In some embodiments, flow rate sensors can be placed at each location to allow for redundancy and testing that each sensor is working correctly by checking for consistency of readings. Any combination of the above methods, for example, could be implemented together to further allow for checking of consistency of results, along with failsafes if one or more sensors are not working correctly. Further sensors could be included (such as temperature and ambient pressure sensors) as disclosed herein to allow for correction of flow rate and/or gas concentration readings based on other factors. 
     Still referring to  FIG. 1 , one, two, or more physiological sensors  99  can communicate with the data transmitter and/or receiver  15  to communicate data regarding physiological information of the user. The sensors  99  could be, for example, a pulse oximeter for measuring the oxygen saturation of a user&#39;s arterial blood, a heart rate sensor, blood pressure sensor, respiratory rate sensor, tidal volume sensor, ECG, heart rate variability sensor, and the like. Data received from the sensors  99  can also communicate with the controller  13  to be displayed on the user interface  14 . Data from the sensors  99  can also be used by the controller  13  to provide closed loop feedback to modify various parameters of the device including oxygen concentration of the hypoxic gas concentration, flow rate, humidity, temperature, and the like as described in detail elsewhere herein. 
     Overview of Example Flow Therapy Apparatus 
     The flow therapy apparatus may be any suitable type of apparatus, but in some configurations may deliver a high gases flow or high flow therapy (of e.g., air, nitrogen, a hypoxic gas mixture, or some combination thereof) to a user for altitude training, enhanced athletic performance, or other indications such as those discussed elsewhere herein. The gas can be or comprise nitrogen. The gas can comprise ambient air. The gas can comprise a blend of nitrogen and ambient air to create hypoxic gas compositions as noted elsewhere herein. The gas source could be a less than 100% pure enriched hypoxic gas such as a hypoxic mix of nitrogen and oxygen that is mixed with ambient air in the system that can be advantageous from a safety perspective in some cases as mentioned elsewhere herein. “High flow therapy” as used in this disclosure may refer to delivery of gases to a user at a flow rate of greater than or equal to about 10 liters/minute (10 LPM). In some configurations, “high flow” therapy refers to administration of gas to the airways of a patient at a relatively high flow rate. In some configurations, the relatively high flow rate meets or exceeds the peak inspiratory demand of the user. In other configurations, the high flow rate may not meet or exceed the peak inspiratory demand of the user. The flow rates used to achieve “high flow” may be any of the flow rates listed below. For example, in some configurations, for an adult patient “high flow therapy” may refer to the delivery of gases to a user at a flow rate of greater than or equal to about 10 litres per minute (10 LPM), such as between about 10 LPM and about 100 LPM, or between about 15 LPM and about 95 LPM, or between about 20 LPM and about 90 LPM, or between about 25 LPM and about 85 LPM, or between about 30 LPM and about 80 LPM, or between about 35 LPM and about 75 LPM, or between about 40 LPM and about 70 LPM, or between about 45 LPM and about 65 LPM, or between about 50 LPM and about 60 LPM. Gases delivered may comprise a percentage of nitrogen and oxygen. In some configurations, such as when the system is implementing a closed loop control algorithm as disclosed herein, delivery of hypoxic gases may not be limited to a high flow therapy and/or the inspiratory demand of the user may or may not be met by the flow rate. 
     In some embodiments, the device or system can allow for the user to change the flow rate during use, such as through interaction with a control, e.g., a user interface on the device. The flow rate may be varied, for example, by the controller varying the speed of the blower. This could be beneficial as the device could be used in different scenarios that require different flow rates. In some cases, flow rate could also oscillate in synchrony with breathing as long as a peak inspiratory demand of the user is being met. For example, if the user was to use the device while exercising then they could have an increased minute ventilation by way of an increased respiratory rate and/or increased tidal volume, so the flow rate could optionally be raised compared with when using the device at rest in order to meet increased peak inspiratory demand. In some embodiments, the device can allow for the user to change the oxygen concentration of the gases delivered via a control that modulates the flow of a hypoxic gas other than air, such as enriched nitrogen, from a hypoxic gas source into a conduit directly connected to the user, such as the nasal cannula. 
     The percentage of oxygen in the gases delivered may be, in embodiments where hypoxia is desired, such that the percentage of oxygen in the gas composition delivered to the user is less than that of typical room air (e.g., less than about 21%). In some embodiments, the percentage of oxygen in the gas composition is between about 10% and about 20.9%, or between about 11.9% and about 17.4%, or between about 13.8% and about 17.4%, or between about 15.7% and about 16.7%, or between about 15% and about 20%, or between about 13% and about 18%, or about or no more than about 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, 19.5%, 20%, or 20.5%, or any ranges incorporating two of the aforementioned values. The percentage of oxygen in the inspired gas would be the same or greater than the aforementioned values, depending on whether inspiratory demand is met. In some embodiments, the percentage of nitrogen in the hypoxic gas composition is about or at least about 78.2%, 78.5%, 79%, 79.5%, 80%, 80.5%, 81%, 81.5%, 82%, 82.5%, 83%, 83.5%, 84%, 84.5%, 85%, 85.5%, 86%, 86.5%, 87%, 87.5%, 88%, 88.5%, 89%, 89.5%, 90%, or more, or any ranges incorporating two of the aforementioned values. The percentage of nitrogen in the inspired gas would be the same or less than the aforementioned values, depending on whether inspiratory demand is met. In some embodiments, the percentage of inspired or delivered nitrogen, oxygen, and/or other gases could be any of the preceding values or ranges, or others as disclosed elsewhere herein. 
     High flow hypoxic gas therapy can be effective in meeting or exceeding the user&#39;s peak inspiratory demand, delivering nitrogen enriched air (and therefore 02 diminished air) and using a nasal high flow system configured for a variety of medical and non-medical applications, including but not limited to simulated altitude training, enhanced athletic performance, or other indications. Not to be limited by theory, in some embodiments systems and methods as disclosed herein could be used to treat or prevent hypertension, obesity, hyperlipidemia, prediabetes or impaired glucose tolerance, diabetes mellitus type I or type II, metabolic syndrome, mitochondrial regeneration, aging, fatigue, inflammatory diseases, anemia, or other conditions. Additionally, high flow therapy may generate a flushing effect in the nasopharynx such that the anatomical dead space of the upper airways is flushed completely or substantially completely by the high incoming gases flow. This can create a reservoir of fresh gas available of each and every breath of the exact desired composition (e.g., hypoxic composition), and prevent entrainment of ambient air that would alter the composition of the gas as well as minimizing re-breathing of carbon dioxide. These aforementioned features can work together to give increased consistency and control of the hypoxic solution that the user breathes, regardless of factors such as breath rate and volume. 
     The user interface may be in some embodiments a non-sealing interface, which advantageously prevents barotrauma (e.g. tissue damage to the lungs or other organs of the respiratory system due to difference in pressure relative to the atmosphere). The user interface may be a nasal cannula with a manifold and nasal prongs, and/or a face mask, and/or a nasal pillows mask, and/or a nasal mask, and/or a tracheostomy interface, or any other suitable type of user interface. 
     Some examples of the flow therapy apparatus are described herein.  FIGS. 2 to 17B  show an example flow therapy apparatus  10  having a main housing  100 . The main housing  100  has a main housing upper chassis  102  and a main housing lower chassis  202 . 
     The main housing upper chassis  102  has a peripheral wall arrangement  106  (see  FIG. 15 ). The peripheral wall arrangement defines a humidifier or humidification chamber bay  108  for receipt of a removable humidification chamber  300 . The removable humidification chamber  300  contains a suitable liquid such as water for humidifying gases that can be delivered to a user. 
     In the form shown, the peripheral wall arrangement  106  of the main housing upper chassis  102  can include a substantially vertical left side outer wall  110  that is oriented in a front-to-rear direction of the main housing  100 , a substantially vertical left side inner wall  112  that is oriented in a front-to-rear direction of the main housing  100 , and an interconnecting wall  114  that extends between and interconnects the upper ends of the left side inner and outer walls  110 ,  112 . The main housing upper chassis  102  can further include a substantially vertical right side outer wall  116  that is oriented in a front-to-rear direction of the main housing  100 , a substantially vertical right side inner wall  118  that is oriented in a front-to-rear direction of the main housing  100 , and an interconnecting wall  120  that extends between and interconnects the upper ends of the right side inner and outer walls  116 ,  118 . The interconnecting walls  114 ,  120  are angled towards respective outer edges of the main housing  100 , but can alternatively be substantially horizontal or inwardly angled. 
     The main housing upper chassis  102  can further include a substantially vertical rear outer wall  122 . An upper part of the main housing upper chassis  102  can include a forwardly angled surface  124 . The surface  124  can have a recess  126  for receipt of a display and user interface module  14 . The display can be configured to display characteristics of sensed gas(es) in real time, such as the oxygen concentration, temperature, humidity, and/or other characteristics. In some embodiments, the oxygen concentration could be displayed as an altitude above sea level (e.g., in meters or feet) that would result in an equivalent partial pressure of oxygen. Conversions between FiO 2  and equivalent altitude could be done by the device by assuming an ambient oxygen concentration of, for example, about 20.9%. An interconnecting wall  128  can extend between and interconnect the upper end of the rear outer wall  122  and the rear edge of the surface  124 . 
     A substantially vertical wall portion  130  can extend downwardly from a front end of the surface  124 . A substantially horizontal wall portion  132  can extend forwardly from a lower end of the wall portion  130  to form a ledge. A substantially vertical wall portion  134  can extend downwardly from a front end of the wall portion  132  and terminate at a substantially horizontal floor portion  136  of the humidification chamber bay  108 . The left side inner wall  112 , right side inner wall  118 , wall portion  134 , and floor portion  136  together can define the humidification chamber bay  108 . The floor portion  136  of the humidification chamber bay  108  can have a recess  138  to receive a heater arrangement such as a heater plate  140  or other suitable heating element(s) for heating liquid in the humidification chamber  300  for use during a humidification process. 
     The main housing lower chassis  202  can be attachable to the upper chassis  102 , either by suitable fasteners or integrated attachment features such as clips for example. The main housing lower chassis  202  can include a substantially vertical left side outer wall  210  that is oriented in a front-to-rear direction of the main housing  100  and is contiguous with the left side outer wall  110  of the upper chassis  102 , and a substantially vertical right side outer wall  216  that is oriented in a front-to-rear direction of the main housing  100  and is contiguous with the right side outer wall  116  of the upper chassis  102 . The main housing lower chassis  202  can further include a substantially vertical rear outer wall  222  that is contiguous with the rear outer wall  122  of the upper chassis  102 . 
     The lower housing chassis  202  can have a lip  242  that is contiguous with the lip  142  of the upper housing chassis  102 , and also forms part of the recess for receiving the handle portion  506  of the lever  500 . The lower lip  242  can include a forwardly directed protrusion  243  that acts as a retainer for the handle portion  506  of the lever  500 . 
     An underside of the lower housing chassis  202  can include a bottom wall  230 . Respective interconnecting walls  214 ,  220 ,  228  can extend between and interconnect the substantially vertical walls  210 ,  216 ,  222  and the bottom wall  230 . The bottom wall  230  can include a grill  232  comprising a plurality of apertures to enable drainage of liquid in case of leakage from the humidification chamber  300  (e.g. from spills). The bottom wall  230  additionally can include elongated forward-rearward oriented slots  234 . The slots  234  can additionally enable drainage of liquid in case of leakage from the humidification chamber  300 , without the liquid entering the electronics housing. In the illustrated configuration, the slots  234  can be wide and elongate relative to the apertures of the grill  232  to maximize the drainage of liquid. 
     As shown in  FIG. 17A to 17B , the lower chassis  202  can have a motor recess  250  for receipt of a motor/sensor module. The motor/sensor module may be non-removable from the main housing  100 . The motor/sensor module may be removable from the main housing  100 , as illustrated in  FIGS. 17A-17B . A recess opening  251  can be provided in the bottom wall  230  adjacent a rear edge thereof, for receipt of a removable motor/sensor module. A continuous, gas impermeable, unbroken peripheral wall  252  can be integrally formed with the bottom wall  230  of the lower chassis  202  and extend upwardly from the periphery of the opening  251 . A rearward portion  254  of the peripheral wall  252  has a first height, and a forward portion  256  of the peripheral wall  252  has a second height that is greater than the first height. The rearward portion  254  of the peripheral wall  252  terminates at a substantially horizontal step  258 , which in turn terminates at an upper auxiliary rearward portion  260  of the peripheral wall  252 . The forward portion  256  and upper auxiliary rearward portion  260  of the peripheral wall  252  terminate at a ceiling  262 . All of the walls and the ceiling  262  can be continuous, gas impermeable, and unbroken other than the gases flow passage. Therefore, the entire motor recess  250  can be gas impermeable and unbroken, other than the gases flow passage. 
     The motor/sensor module may be insertable into the recess  250  and attachable to the lower chassis  202 . Upon insertion of the motor/sensor module into the lower chassis  202 , the gases flow passage tube  264  can extend through the downward extension tube  133  and be sealed by the soft seal. 
     The humidification chamber  300  can be fluidly coupled to the apparatus  10  in a linear slide-on motion in a rearward direction of the humidification chamber  300  into the chamber bay  108 , from a position at the front of the housing  100  in a direction toward the rear of the housing  100 . A gases outlet port  322  can be in fluid communication with the motor. 
     A gases inlet port  340  (humidified gases return) as shown in  FIG. 8  can include a removable L-shaped elbow. The removable elbow can further include a user outlet port  344  for coupling to the inspiratory conduit  16  to deliver gases to the user interface  17 . The gases outlet port  322 , gases inlet port  340 , and user outlet port  344  each can have soft seals such as  0 -ring seals or T-seals to provide a sealed gases passageway between the apparatus  10 , the humidification chamber  300 , and the inspiratory conduit  16 . 
     The humidification chamber gases inlet port  306  can be complementary with the gases outlet port  322 , and the humidification chamber gases outlet port  308  can be complementary with the gases inlet port  340 . The axes of those ports can be parallel to each other to enable the humidification chamber  300  to be inserted into the chamber bay  108  in a linear movement. 
     The apparatus  10  can have air and nitrogen (or alternative auxiliary gas) inlets in fluid communication with the motor to enable the motor to deliver air, nitrogen-enhanced air to form a hypoxic mixture, or a suitable mixture thereof to the humidification chamber  300  and thereby to the user. As shown in  FIG. 10 , the apparatus  10  may have a combined air/nitrogen (or alternative auxiliary gas) inlet arrangement  350 . This arrangement can include a combined air/nitrogen port  352  into the housing  100 , a filter  354 , and a cover  356  with a hinge  358 . In other embodiments, a gases tube can extend laterally or in another appropriate direction and be in fluid communication with a nitrogen source. The port  352  can be fluidly coupled with the motor  402 . For example, the port  352  may be coupled with the motor/sensor module  400  via a gases flow passage between the port  352  and an inlet aperture or port in the motor/sensor module  400 , which in turn would lead to the motor. 
     The apparatus  10  may have the arrangement shown in  FIGS. 11 to 14  to enable the motor to deliver air, nitrogen (or alternative auxiliary gas), or a suitable mixture thereof to the humidification chamber  300  and thereby to the user. This arrangement can include an air inlet  356 ′ in the rear wall  222  of the lower chassis  202  of the housing  100 . The air inlet  356 ′ comprises a rigid plate with a suitable grill arrangement of apertures and/or slots. Sound dampening foam may be provided adjacent the plate on the interior side of the plate. An air filter box  354 ′ can be positioned adjacent the air inlet  356 ′ internally in the main housing  100 , and include an air outlet port  360  to deliver filtered air to the motor via an air inlet port  404  in the motor/sensor module  400 . The air filter box  354 ′ may include a filter configured to remove particulates (e.g. dust) and/or pathogens (e.g. viruses, fungi, or bacteria) from the gases flow. A soft seal such as an  0 -ring seal can be provided between the air outlet port  360  and air inlet port  404  to seal between the components. The apparatus  10  can include a separate nitrogen inlet port  358 ′ positioned adjacent one side of the housing  100  at a rear end thereof, the nitrogen port  358 ′ for receipt of nitrogen from a nitrogen source such as a tank or source of piped nitrogen. The nitrogen inlet port  358 ′ can optionally be in fluid communication with a valve  362 . The valve  362  can suitably be a solenoid valve that enables the control of the amount of nitrogen that is added to the gases flow that is delivered to the humidification chamber  300 . The nitrogen port  358 ′ and valve  362  may be used with other (e.g., other than nitrogen) auxiliary gases to control the addition of other auxiliary gases to the gases flow. The other auxiliary gases may include any one or more of a number of gases useful for gas therapy, including but not limited to heliox, oxygen, nitrogen, nitric oxide, carbon dioxide, argon, helium, methane, sulfur hexafluoride, and combinations thereof. In some embodiments a valve need not be present, and nitrogen flow can be manually controlled at the nitrogen source. The oxygen concentration of the hypoxic gases flow can be read from the user interface, and the amount of nitrogen titrated at the nitrogen source accordingly depending on the desired result. 
     As shown in  FIGS. 13 to 16 , the lower housing chassis  202  can include suitable electronics boards  272 , such as sensing circuit boards. The electronics boards can be positioned adjacent respective outer side walls  210 ,  216  of the lower housing chassis  202 . The electronics boards  272  can contain, or can be in electrical communication with, suitable electrical or electronics components, such as but not limited to microprocessors, capacitors, resistors, diodes, operational amplifiers, comparators, and switches. Sensors may be used with the electronic boards  272 . Components of the electronics boards  272  (such as but not limited to one or more microprocessors) can act as the controller  13  of the apparatus. 
     One or both of the electronics boards  272  can be in electrical communication with the electrical components of the apparatus  10 , including the display unit and user interface  14 , motor, valve  362 , and the heater plate  140  to operate the motor to provide the desired flow rate of gases, operate the humidifier  12  to humidify and heat the gases flow to an appropriate level, and supply appropriate quantities of nitrogen (or quantities of an alternative auxiliary gas) to the gases flow. 
     The electronics boards  272  can be in electrical communication with a connector arrangement  274  projecting from the rear wall  122  of the upper housing chassis  102 . The connector arrangement  274  may be coupled to an audible, visual, tactile, or other alarm, pulse oximetry port, and/or other suitable accessories. The electronics boards  272  can also be in electrical communication with an electrical connector  276  that can also be provided in the rear wall  122  of the upper housing chassis  102  to provide mains or battery power to the components of the apparatus  10 . 
     As mentioned above, operation sensors, such as flow, temperature, humidity, and/or pressure sensors can be placed in various locations in the flow therapy apparatus  10  and/or the inspiratory conduit  16  and/or cannula  17 . The electronics boards  272  can be in electrical communication with those sensors. Output from the sensors can be received by the controller  13 , to assist the controller  13  to operate the flow therapy apparatus  10  in a manner that provides optimal therapy, including optionally meeting peak inspiratory demand. 
     As outlined above, the electronics boards  272  and other electrical and electronic components can be pneumatically isolated from the gases flow path to improve safety. The sealing also prevents water ingress. 
       FIGS. 18A-E  illustrate another flow therapy apparatus  3010  including a main housing having a main housing upper chassis  3102  and a main housing lower chassis  3202 . The flow therapy apparatus  3010  can further include a humidification chamber bay  3108  for receipt of a removable humidification chamber. The flow therapy apparatus  3010  may have any of the features and/or functionality described herein in relation to the flow therapy apparatus  10 , but those features are not repeated here for simplicity. Similarly, the features and/or functionality of the flow therapy apparatus  3010  may be used in the other apparatus described herein. 
     The flow therapy apparatus  3010  can have a single-sided handle/lever  4500 . That is, only one side of the handle/lever  4500  is movably connected relative to the main housing of the flow therapy apparatus  3010 , whereas there is no pivot connection of the other side of the handle/lever  4500  to the main housing. As shown in  FIG. 18D , a left side of the handle/lever  4500  is pivotally connected relative to the main housing. However, it is possible to have only the right side pivotally connected to the main housing. The handle/lever  4500  is pivotally and translationally connected to the main housing, so that the handle/lever  4500  moves on a path having a varying radius relative to the main housing. 
     A terminal part of the handle/lever  4500  can have a cross-member handle portion  4506  that interconnects forward ends of a left side arm  4502  and a right side member  4504  and forms an engagement region for grasping by a user&#39;s fingers. When the handle  4500  is in the raised position as shown in  FIG. 18D  for example, the cross-member  4506  can act as a carrying handle for the flow therapy apparatus  3010 . When the handle is in the fully raised position, the cross member  4506  can be positioned generally above and generally in line with the centre of gravity of the flow therapy apparatus  3010  (including the liquid chamber). The liquid chamber can be inserted into or removed from the humidification chamber bay  3108  when the handle/lever  4500  is raised. When the handle/lever  4500  is in the lowered position, it can inhibit or prevent removal of the liquid chamber from the humidification chamber bay  108 . 
       FIG. 18E  illustrates the flow therapy apparatus  3010  without the handle/lever. As shown in  FIG. 18E , a removable gases flow tube in the form of a removable elbow  1342  can be used in the flow therapy apparatus  3010 . The elbow  1342  can receive humidified gases from the liquid chamber at an inlet port  1340  and direct the humidified gases to an outlet port  1344  toward the user interface through the user breathing conduit. 
     Similar to the flow therapy apparatus  10 , the lower chassis  3202  of the flow therapy apparatus  3010  can have a motor recess for receiving a motor/sensor module. The motor/sensor module can include a blower, which entrains room air to deliver to a user. The gases can be mixed prior to entering the sensor module. The blower can be a mixer for mixing the gases before the gases enter a sensing chamber of the sensor module. The apparatus can include an integrated or separate gas mixer in some cases. The separate gas mixer can be positioned before or after the blower. Nitrogen can be entrained after the blower and the separate gas mixer can be used to mix the nitrogen and air following entrainment. The controller can increase or decrease a flow rate of the gases flowing through the flow therapy apparatus by controlling a motor speed of the blower. 
     Control System 
       FIG. 19A  illustrates a block diagram  900  of an example control system  920  that can detect user conditions and control operation of the flow therapy apparatus including the gas source. The control system  920  can manage a flow rate of the gas flowing through the flow therapy apparatus as it is delivered to a user. For example, the control system  920  can increase or decrease the flow rate by controlling an output of a motor speed of the blower (hereinafter also referred to as a “blower motor”)  930  or an output of a valve  932  in a blender. The control system  920  can automatically determine a set value or a personalized value of the flow rate for a particular user as discussed below. The flow rate can be optimized by the control system  920  to improve user comfort and therapy. 
     The control system  920  can also generate audio and/or display/visual outputs  938 ,  939 . For example, the flow therapy apparatus can include a display and/or a speaker. The display can indicate to the user, physician, trainer, or other party any warnings or alarms generated by the control system  920 . The display can also indicate control parameters that can be adjusted by the user or other individual. For example, the control system  920  can automatically recommend a flow rate for a particular user. The control system  920  can also determine a respiratory state of the user, including but not limited to generating a respiratory rate of the user, and send it to the display. 
     In some embodiments, a physiological parameter, such as SpO 2  of a user for example, could additionally or alternatively be fed into an alarm system. The alarm system could monitor the user&#39;s SpO 2 , and have set responses if it were to fall below a certain level. The device could additionally or alternatively have alarms for FiO 2  values, assuming that the user&#39;s inspiratory demand is met, and that FdO 2  is equal to FiO 2 . As described above, if the user&#39;s inspiratory demand is not met, the actual FiO 2  value would be higher than the assumed value. The alarms would be on the basis of the measured oxygen concentration in the unit, which is FdO 2 . The device would alarm on the basis of FdO 2  and assume that the parameter being measured is FiO 2 . This could affect therapy, but not affect safety. Responses from the system could include visual and/or audible alarms, reducing the nitrogen being supplied, setting the nitrogen flow to a predetermined value, setting the nitrogen flow to achieve a specific FiO 2  or SpO 2,  completely shutting off the nitrogen supply, shutting off all flow completely or any combination of these responses. 
     The system could have multiple thresholds, where different responses or sets of responses are triggered at different SpO 2  and/or FiO 2  readings. As subsequent thresholds are crossed, different responses could occur in place of the previous responses, in addition to the previous responses, and/or act as a variation of a previous response (e.g. an audible alarm changes in volume or tone). 
     In some embodiments, the device could alarm for at least the FiO 2  when controlling SpO 2,  and vice versa, as this could mean the user is prevented from reaching dangerous levels of both SpO 2  and FiO 2,  as one is bound by the control limits of the device and the other is bound by alarm limits. It would also have added safety through redundancy in the event of a faulty reading of one of the SpO 2  or FiO 2  sensors. 
     Alarm thresholds could include time factors. These would allow for the device to not be triggered by brief false readings, such as requiring a threshold to be about or at least about 5, 10, 15, 20, 25, 30, or more seconds for example. They could also allow for escalation in response of the device based on length of time at a certain value (for example, going from a visual to audible alarm, or a louder or more prominent alarm). They could also allow for alarms to be set off after a set amount of time (for example, alarming at SpO 2  readings that are safe for a short exposure but become dangerous after a longer duration of exposure, such as, for example, at about or at least about 30, 45, 60, 75, 90, 120, 150, 180, 240, 300 seconds, or more). 
     Some non-limiting examples of values at which an SpO 2  reading could trigger an alarm could include below about 94% (as this is the lower limit of what is considered a healthy SpO 2  reading at sea level), and/or below about 85% (as this is typically the value below which negative side effects begin to occur), and/or below about 80% (as this is the value that is typically regarded as the point where altitude training becomes dangerous), and/or below about 75% (as this is the point where therapy should be stopped immediately), and/or below about 65% (as this is the point where the user would likely have impaired mental function and judgement), and/or below about 55% (as this is the point where the user would likely lose consciousness). 
     Some values at which FiO 2/ equivalent altitude readings could trigger a response from the system could include about 15.7% (that is, about 2500 m) as this is typically the upper altitude limit of an extended exposure therapy program, and/or about 13.8% (that is, about 3500 m) as this is typically the upper altitude limit of any therapy program, and/or about 11.9% (that is, about 4800 m) as this is the limit of what is typically considered safe without medical supervision, and/or about 10.2% (that is, about 5950m) as this represents the highest recorded permanently tolerable altitude, and/or about 7.7% (that is, about 8000 m) as this is commonly referred to as the “death zone” where the oxygen concentration is insufficient to sustain human life. 
     The device could additionally or alternatively have one or more alarm limits for SpO 2  and/or FiO 2  that change in response to one or more inputs. The one or more inputs could include an FiO 2  reading, an SpO 2  reading, a heart rate measurement, a respiratory rate measurement, an input by the user of their desired therapy program, a sensed or user input indication that the user is exercising, an amount of time the user has been using the device, and/or one or more user characteristics (this could include age, height, weight, gender, activity/fitness level, experience with altitude training). The indication of user exercise in particular could come from one or a combination of the other inputs listed, and could be transmitted as qualitative signal (e.g., either exercising or not exercising) or as a quantitative signal (e.g., exercise intensity level). 
     The relationship between one or more alarm limits and one or more inputs could be one that changes dynamically (e.g., as age increases the alarm trigger threshold for FiO 2  steadily increases). Additionally, or alternatively, one or more alarm limits could change by a set amount in response to one or more inputs. The change in one or more limits could occur at one or more thresholds of a quantitative signal (e.g., the alarm threshold for SpO 2  increases by a certain amount after a specific amount of time that user has been using the device) and/or in response to a qualitative signal (e.g., the FiO 2  alarm threshold jumps to a higher value when the user indicates that they are beginning exercise). 
     Having alarm limits that vary on a range of conditions can allow the user to safely employ a training regime that allows them to reach their maximum potential. While alarm limits can be applied in a blanket “one fit all” approach in some embodiments, this may not be desirable in some implementations because in order for the system to be safe for all or most users in all or most scenarios the device may become overly safe (or not challenging enough) for others, to the point where certain users are not able to gain maximum benefit from the device. The system would also be able to provide alarms for readings, particularly SpO 2  readings, that while potentially safe are abnormal given the current parameters provided. For example, if a user had an SpO 2  reading of less than 94% while at rest and breathing normoxic gas, then the device could alarm to tell the user that his or her resting SpO 2  is abnormally low, and the user should consult a medical professional before commencing with an altitude training program. 
     In some embodiments, any alarms that are capable of changing based off various inputs would be coupled with one or more fixed alarms (such as the ones listed above) that provide absolute limits regardless of any input. 
     A similar methodology to the above could be additionally or alternatively applied in a similar way to the ranges for FiO 2  and/or SpO 2  that the user can attempt to control to. As above, this could allow the user to use the device in a way that is individually tailored to be both optimally effective and safe based on the parameters provided. It could allow for access to a greater range of training levels while avoiding potentially dangerous misuse by the user. Optionally, a fixed upper limit for the device could be coupled with a variable lower limit, or vice versa. The device could have one or more variable limits paired with a fixed limit that the variable limit could not exceed. 
     Table 1 below lists various non-limiting flow rates of nitrogen to illustrate what would roughly be required to achieve various oxygen concentrations. Preferably a value for total flow would be selected, and this would remain constant regardless of changes to nitrogen flow rate and/or FiO 2,  unless a new total flow rate is selected. If the total flow rate in the device is adjusted, a proportional change in the nitrogen flow rate would be required to maintain the same FiO 2 . 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Nitrogen flowrate 
                 FiO 2  (assuming inspiratory 
               
               
                 Total flow L/min 
                 (L/min) 
                 demand is met) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 30 
                 0 
                 21.0% 
               
               
                 30 
                 1 
                 20.2% 
               
               
                 30 
                 2 
                 19.4% 
               
               
                 30 
                 3 
                 18.7% 
               
               
                 30 
                 4 
                 17.9% 
               
               
                 30 
                 5 
                 17.1% 
               
               
                 30 
                 6 
                 16.3% 
               
               
                 30 
                 7 
                 15.6% 
               
               
                 30 
                 8 
                 14.8% 
               
               
                 30 
                 9 
                 14.0% 
               
               
                 30 
                 10 
                 13.2% 
               
               
                   
               
            
           
         
       
     
     The control system  920  can change heater control outputs to control one or more of the heating elements (for example, to maintain a temperature set point of the gas delivered to the user). The control system  920  can also change the operation or duty cycle of the heating elements. The heater control outputs can include heater plate control output(s)  934  and heated breathing tube control output(s)  936 . 
     The control system  920  can determine the outputs  930 - 939  based on one or more received inputs  901 - 916 . The inputs  901 - 916  can correspond to sensor measurements received automatically by the controller  600  (shown in  FIG. 19B ). The control system  920  can receive sensor inputs including but not limited to temperature sensor(s) inputs  901 , flow rate sensor(s) inputs  902 , motor speed inputs  903 , pressure sensor(s) inputs  904 , gas(s) fraction sensor(s) inputs  905 , humidity sensor(s) inputs  906 , pulse oximeter (for example, SpO 2 ) sensor(s) inputs  907 , stored or user parameter(s)  908 , duty cycle or pulse width modulation (PWM) inputs  909 , voltage(s) inputs  910 , current(s) inputs  911 , acoustic sensor(s) inputs  912 , power(s) inputs  913 , resistance(s) inputs  914 , CO 2  sensor(s) inputs  915 , and/or spirometer inputs  916 . The control system  920  can receive inputs from the user or stored parameter values in a memory  624  (shown in  FIG. 19B ). The control system  920  can dynamically adjust flow rate for a user over the time of their therapy. The control system  920  can continuously detect system parameters and user parameters. A person of ordinary skill in the art will appreciate based on the disclosure herein that any other suitable inputs and/or outputs can be used with the control system  920 . 
     In some embodiments, a target oxygen concentration could be selected, and the difference between this and the measured oxygen concentration could be fed into a controller for the valve, which would open and close to alter the supply of nitrogen until the measured oxygen concentration matches the target oxygen concentration. In some embodiments, the target oxygen concentration and/or the measured oxygen concentration could be displayed on the device and/or an ancillary device, such as the user&#39;s smartphone, smartwatch, or the like. Alternatively, the device could control to the user&#39;s blood oxygen saturation (SpO 2 ) instead of inspired oxygen concentration (FiO 2 ). This could utilize at least one sensor (such as a pulse oximeter) to measure SpO 2  at a point on the user&#39;s body (for example, their finger). This reading could then be displayed somewhere, potentially on the device or the sensor. The user, or the control system could then alter the FiO 2  being delivered using any of the above methods to reach a target SpO 2 . In some setups, the FiO 2  or equivalent altitude could be displayed. Additionally, the display could display the altitude equivalent of the current FiO 2 . The user may be able to change the target altitude via controls on the display or elsewhere. This target altitude would be converted to a target FiO 2  value by the device controller, which can be used to control the valve. The ability of allowing users to vary the altitude would be desirable for a user who wishes to simulate specific altitudes, instead of targeting specific FiO 2  values. 
     With reference to  FIG. 22 , a schematic diagram of the closed loop control system is illustrated. The closed loop control system may utilize two control loops. The first control loop may be implemented by the SpO 2  controller. The SpO 2  controller can determine a target oxygen concentration, such as FdO 2 . Where the gases flow is being delivered as nasal high flow through a non-sealed cannula, assuming the user&#39;s inspiratory demand is met, FdO 2  would be substantially equivalent to FiO 2 . The determined target oxygen concentration is based at least in part on the target SpO 2  and/or the measured SpO 2 . The target SpO 2  value can be a single value or a range of acceptable values. The value(s) could be pre-set, chosen by a user, or determined automatically based on user characteristics. Generally, target SpO 2  values are received or determined before or at the beginning of a therapy session, though target SpO 2  values may be received at any time during the therapy session. During a therapy session, the SpO 2  controller can also receive as inputs: measured FdO 2  reading(s) from a gases composition sensor, and measured SpO 2  reading(s) and a signal quality reading(s) from the physiological sensor. In some configurations, the SpO 2  controller can receive target FdO 2  as an input. In such a case, the output of the SpO 2  controller may be provided directly back to the SpO 2  controller as the input. Based at least in part on the inputs, the SpO 2  controller can output a target FdO 2  to the second control loop. 
     The second control loop may be implemented by the FdO 2  controller. The FdO 2  controller can receive inputs of measured FdO 2  and target FdO 2 . The FdO 2  controller can then output a hypoxic gas inlet valve control signal to control the operation of the hypoxic gas valve based on a difference between these measured FdO 2  and target FdO 2  values. The FdO 2  controller may receive the target FdO 2  value that is output from the first control loop when the flow therapy apparatus is controlling to a target SpO 2 . In some configurations, the control signal of the FdO 2  controller may set the current of the hypoxic gas valve in order to control operation of the hypoxic gas valve. Additionally, or alternatively, the FdO 2  controller could detect changes to the measured FdO 2  and alter the position of the valve accordingly. In some configurations, the user manually sets a target SpO 2  or oxygen concentration, and the second control loop can operate independently without receiving the target FdO 2  from the first control loop. Rather, the target FdO 2  can be received from user input or a default value. 
     The FiO 2  could be controlled within a set of limits, such as pre-determined limits programmed into a memory of device that can be user-customizable in some cases. If the device allows for the supply of nitrogen to be suddenly blocked such that the device returns to delivery of normoxic gas, then such a function could be considered separate and unrestricted by any of the following limits. With each set of limits, an altitude e.g., in meters or feet, can be provided that roughly corresponds to an equivalent partial pressure of oxygen, as this could be displayed alternatively or in addition to the FiO 2  reading. The following FiO 2  limits serve as examples of possible ranges, but the FiO 2  range could be between any two values, including a lower limit from one range and an upper limit from another.
         FiO 2  could be limited between about 20.9% (i.e., about Om) which represents sea level, and about 10.2% (i.e., about 5950 m altitude) which represents the highest recorded permanently tolerable altitude.   FiO 2  could be limited or between about 17.4% (i.e., about 1600 m) which represents approximately the lowest simulated altitude at which the effects of high altitude begin to take effect, and about 11.9% (i.e., about 4800 m altitude) as lower oxygen concentrations in some cases could require monitoring by a healthcare professional.   FiO 2  could be limited between about 17.4% (i.e., about 1600 m) for reasons given above, and about 13.8% (i.e., about 3500 m altitude) as this is the limit of the “high altitude” region, and higher simulated altitudes may begin to have overly negative effects on training, recovery, sleep quality, appetite, etc. that result in loss of efficacy of the therapy.   FiO 2  could be limited between about 16.7% (i.e., about 2000 m) and about 15.7% (i.e., about 2500 m altitude), which in some cases has been shown to have both benefit and safety advantages.   FiO 2  could also be limited to other height/altitude equivalents, such as about 500 m, about 750 m, about 1,000 m, about 1,250 m, about 1,500 m, about 1,750 m, about 2,000 m, about 2,250 m, about 2,500 m, about 2,750 m, about 3,000 m, about 3,250 m, about 3,500 m, about 3,750 m, about 4,000 m, or any ranges between the aforementioned values.       

     In some embodiments, the device could operate based upon a target SpO 2  measurement. One advantage of controlling the hypoxic gas delivery based on SpO 2  is that it allows the device to adjust the FiO 2  (and equivalent altitude) with the exercise intensity. For example, if the user begins exercising at a higher level of intensity, the user&#39;s SpO 2  may begin to drop. In response, the device would increase the FiO 2  in order to maintain the target SpO 2 . In this situation, the device would effectively be raising the FiO 2  in response to increased exercise intensity. The target SpO 2  could be a pre-set value, a selected value, a pre-set range, a selected range, or a value that changes over time based on a selected therapy program. The SpO 2  reading could be directly fed into the device, and the difference between the target SpO 2  and measured SpO 2  could be used to control a proportional valve on the nitrogen inlet, and therefore the oxygen content of the gas delivered (FiO 2 ), similar to the one discussed above. As described above, the device controls FiO 2  by changing FdO 2,  and assumes inspiratory demand is met, and therefore in such a scenario FiO 2  is equal to FdO 2 . If inspiratory demand is not met, the device can still control FdO 2  according to a target SpO 2,  as the controller would continue to change FdO 2  (and in turn assumed FiO 2 ) until the target SpO 2  is achieved. By constantly using feedback from the SpO 2  sensor to control the nitrogen inflow, the target SpO 2  can be reached by altering the oxygen content of the gas. In some embodiments, the measured SpO 2,  target SpO 2,  and/or FiO 2  can be displayed. The device could include limits on the amount of nitrogen that the valve can allow through and/or a valve position so that an overly dangerous hypoxic composition is not delivered. Additionally, the device could be configured to allow for control of SpO 2  when an SpO 2  sensor is used, but to then default back to one of the earlier FiO 2  control methods when the SpO 2  is not present. Additionally or alternatively, the system can use feedback from other proxy measurements of exertion, such as heart rate, blood pressure, respiratory rate, or heart rate variability to adjust the FiO 2  (and equivalent altitude). 
     SpO 2  can in some embodiments be controlled between a set of pre-set or other limits. The following are a few non-limiting examples of possible limits, in practice SpO 2  could be limited between any two values, including any reasonable combination of a lower value from one range and an upper value from another.
         SpO 2  could be limited between about 80% (the absolute lower limit of what is considered a safe SpO 2  reading in some cases) and about 99% or about 100% (the upper limit of what is considered a safe SpO 2  reading in some cases).   SpO 2  could be limited between about 80% and about 94% (the lower limit of a healthy SpO 2  reading at sea level, and therefore the upper limit of what can be considered altitude training in some cases).   SpO 2  could be limited between about 85% (the lower limit of safe extended exposure without medical supervision in some cases) and about 92% (a typical SpO 2  reading at the lower range of high altitude, i.e. about 1600 m), in some cases for extended use.   SpO 2  could be limited between about 87% and about 90% (a more specific range of SpO 2  that can be both safe and effective in some cases), such as for extended use.   SpO 2  could be limited between about 80% and about 85% (the lowest range that can be considered safe in some cases), such as for intermittent use.       

     The device could be for extended use, for example, all the time (e.g., 24 hours a day); using the device only when awake; using the device only when sleeping; using the device only when exercising; using the device only when not exercising; using the device for a set amount of time, e.g., about, at least about, or no more than about 30 minutes, 45 minutes, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 16 hours, 20 hours, or 24 hours a day; or any logical combination of the above (e.g., only when awake and not exercising). 
     Intermittent use could entail using the device for a set amount of time, such as for example, shorter than about 4, 3, 2, or 1 hour, or using the device for short bursts of about or less than about 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 minute interspaced with similar short recovery periods of about or less than about 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 minute, or only using the device while exercising, or any logical combination of the above (e.g., short bursts with interspaced recovery only during exercise). 
     In some embodiments, the use can be done once a week, or for 2, 3, 4, 5, 6, or 7 days out of a week, 2 weeks, or month for example. 
     In some embodiments, the use can be continued for a total period of time depending on the desired clinical result. The device can be used over a time period of, for example, about, at least about, or no more than about 1 week, 2 weeks, 3 weeks, 1 month, 2 months, 3 months, 4 months, 5 months, 6 months, 9 months, 12 months, or more or less. 
     The device could be used in a therapy program that contains treatment periods that could be considered extended use as well as other periods that could be considered intermittent use, and could use different SpO 2  target ranges appropriate for both. For example, the device could be used in a lower SpO 2  target range while exercising, as well as a higher SpO 2  target range when not exercising for the rest of the day. 
     In some embodiments, personalized training methods and altitude equivalent oxygen concentrations for therapy can determined by observing how different individuals acclimatize at different rates. In general, less than about 1250 meters above sea level is commonly described as “low altitude”, as noticeable effects generally begin to take place at about 1500 meters. From about 1500 meters to about 3500 meters is often referred to as the “high altitude” region, with regions over about 3500 meters being the “very high altitude”, and can be potentially dangerous to train at in some cases, especially if not given the proper time to acclimatize. High altitude training tends to occur in the region about 2000 meters to about 2500 meters, although this varies with training regimes, particularly the activity performed in the high altitude region and the length of time spent there. Some activity regimes include:
         Live high/train high: This is likely the simplest form of altitude training, as it simply consists of remaining at altitude (e.g., breathing an altitude-equivalent oxygen concentration of the hypoxic gas composition) for the entire length of the therapy, including at training times.   Live high/train low: This involves exposing oneself to altitude (e.g. &gt;2000 m meters) (e.g., breathing an altitude-equivalent oxygen concentration of the hypoxic gas composition) during non-training periods, but returning to a low altitude environment (i.e., less than about 1250 meters) (e.g., breathing an altitude-equivalent oxygen concentration of the hypoxic gas composition) for exercise. In some embodiments, the low altitude environment can be achieved by utilizing systems and methods as disclosed herein with supplemental oxygen during non-training periods (e.g., non-hypoxic gas compositions with oxygen concentrations of at least about 21%, 22%, 23%, 24%, 25%, 30%, 35%, 40%, 45%, 50%, or more, or ranges encompassing two or more of the aforementioned values). This is thought to allow for the benefits of acclimatization while still maintaining the same exercise intensity. A study using these altitude ranges showed improvements in speed, strength, endurance and recovery.   Live low/train high: This involves athletes training at high altitude (e.g., breathing an altitude-equivalent oxygen concentration of the hypoxic gas composition) and spending the remaining non-training periods in a low oxygen environment. The idea is increase the strain on the user&#39;s cardiovascular system while allowing them to recover in a normoxic environment. This has the added benefit of reducing the time needed to be spent in hypoxia.   Repeated sprints in hypoxia: This involves the athlete performing a high intensity exercise (e.g., sprinting) for a short period followed by a rest period, and then repeating the cycle, all in hypoxic conditions. In some embodiments, the high intensity exercise could be performed for, for example, between about 15 seconds and about 180 seconds, such as about 15, 30, 60, 75, 90, 105, 120, 150, or 180 seconds, or ranges incorporating any two of the aforementioned values. In some embodiments, the rest period can be, for example, about, at least about, or no more than about 1, 1.5×, 2×, 2.5×, 3×, 3.5×, 4×, 4.5×, 5× the exercise period or ranges incorporating any two of the aforementioned values. As one non-limiting example, high intensity exercise is performed for about 30 seconds, and then a rest period for about or no more than about 120 seconds, followed by additional cycles of high intensity exercise and rest. In some embodiments, the user can perform between about 2 cycles and about 20 cycles under this protocol, such as between about 2 cycles and about 12 cycles, between about 5 cycles and about 10 cycles, or about 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 cycles, or ranges incorporating any two of the aforementioned values. While this can be seen as a variation on live low/train high, the underlying mechanisms are theorized to achieve different results. This was tested on athletes who were able to complete 9-10 sprints before total exhaustion. The athletes were split into two groups that performed the above exercises, however one group did it in hypoxia and the other in normoxia. After 4 weeks the athletes who performed the sprints in hypoxia could manage 13 before total exhaustion, while the normoxic group had shown no improvement.   In some configurations, an exercise program can include varying FiO 2  (or FdO 2 ) by increasing or decreasing FiO 2  (or FdO 2 ) during a training session based on a pre-set sequence. For example, the FiO 2  could start at or near 21% and slowly drop to a specific hypoxic value, and then slowly ramp back up to around 21% near the end of the session, or vice versa. The varying of FiO 2  (or FdO 2 ) can be performed gradually, in a series of step changes, and/or in one step change. The varying of FiO 2  (or FdO 2 ) can be repeated during the training session. This could be done to simulate rising from sea level to high altitude, followed by descending back to sea level. The FiO 2  could also be varied based on other determined exercise regimes. For example, an exercise session could involve high and low intensity phases, with the FiO 2  programmed to coordinate with these phases. This could involve lower FiO 2  values being set for periods of low exercise intensity, with the FiO 2  being raised for periods of high intensity. The device could also assess exercise intensity level and automatically adjust the FiO 2  based on the determined exercise intensity level. Assessing intensity level could be done by monitoring one or more physiological parameters, such as heart rate, respiratory rate, blood pressure, heart rate variability, and/or the like. When performing the pre-set exercise programs, the user&#39;s SpO 2  could be monitored (e.g., by a pulse oximeter or otherwise) to ensure that the user&#39;s SpO 2  does not drop below a predetermined value. When the user&#39;s SpO 2  drops below a predetermined value, the device or system can manually override the target FiO 2  value or target altitude equivalent value.       

     Controller 
       FIG. 19B  illustrates a block diagram of an embodiment of a controller  600 . The controller  600  can include programming instructions for detection of input conditions and control of output conditions. The programming instructions can be stored in a memory  624  of the controller  600 . The programming instructions can correspond to the methods, processes and functions described herein. The programming instructions can be executed by one or more hardware processors  622  of the controller  600 . The programming instructions can be implemented in C, C++, JAVA, or any other suitable programming languages. Some or all of the portions of the programming instructions can be implemented in application specific circuitry  628  such as ASICs and FPGAs. 
     The controller  600  can also include circuits  628  for receiving sensor signals. The controller  600  can further include a display  630  for transmitting status of the user and the respiratory assistance system. The display  630  can also show warnings. The display  630  can be configured to display characteristics of sensed gas(es) in real time. The controller  600  can also receive user inputs via the user interface such as display  630 . The user interface may alternatively or additionally comprise buttons or a dial. The user interface may alternatively or additionally comprise a touch screen. 
     Motor/Sensor Module 
     Any of the features of the flow therapy apparatus described herein, including but not limited to the humidifier, the flow generator, the user interface, the controller, and the user breathing conduit configured to couple the gases flow outlet of the respiratory system to the user interface, can be combined with any of the sensor modules described herein. 
       FIG. 20  illustrates a block diagram of the motor/sensor module  2000 , which is received by the recess  250  in the flow therapy apparatus (shown in  FIGS. 17A and 17B ). The motor/sensor module can include a blower  2001 , which entrains room air to deliver to a user. The blower  2001  can be a centrifugal blower. 
     Room air can enter an ambient/room air inlet  2002 , which enters the blower  2001  through an inlet port  2003 . The inlet port  2003  can include a valve  2004  through which a pressurized gas may enter the blower  2001 . The valve  2004  can control a flow of nitrogen or other auxiliary gas into the blower  2001 . The valve  2004  can be any type of valve, including a proportional valve or a binary valve. In some embodiments, the valve can be on the nitrogen supply line, e.g., a nitrogen source bottle or other reservoir, and manually or automatically adjusted to alter the amount of nitrogen being delivered. In some embodiments, the inlet port does not include a valve. 
     The blower  2001  can operate at a motor speed of greater than 1,000 RPM and less than 30,000 RPM, greater than 2,000 RPM and less than 21,000 RPM, or between any of the foregoing values. Operation of the blower  2001  mixes the gases entering the blower  2001  through the inlet port  2003 . Using the blower  2001  as the mixer can decrease the pressure drop that would otherwise occur in a system with a separate mixer, such as a static mixer comprising baffles, because mixing requires energy. 
     The mixed air can exit the blower  2001  through a conduit  2005  and enters the flow path  2006  in the sensor chamber  2007 . A sensing circuit board with sensors  2008  can positioned in the sensor chamber  2007  such that the sensing circuit board is at least partially immersed in the gases flow. At least some of the sensors  2008  on the sensing circuit board can be positioned within the gases flow to measure gas properties within the flow. After passing through the flow path  2006  in the sensor chamber  2007 , the gases can exit  2009  to the humidification chamber. 
     Positioning sensors  2008  downstream of the combined blower and mixer  2001  can increase accuracy of measurements, such as the measurement of gases fraction concentration, including nitrogen and/or oxygen concentration, over systems that position the sensors upstream of the blower and/or the mixer. Such a positioning can give a repeatable flow profile. Further, positioning the sensors downstream of the combined blower and mixer avoids the pressure drop that would otherwise occur, as where sensing occurs prior to the blower, a separate mixer, such as a static mixer with baffles, is required between the inlet and the sensing system. The mixer can introduce a pressure drop across the mixer. Positioning the sensing after the blower can allow the blower to be a mixer, and while a static mixer would lower pressure, in contrast, a blower increases pressure. Also, immersing at least part of the sensing circuit board and sensors  2008  in the flow path can increase the accuracy of measurements because the sensors being immersed in the flow means they are more likely to be user to the same conditions, such as temperature and pressure, as the gases flow and therefore provide a better representation of the gas characteristics. 
     Turning to  FIG. 21 , the gases exiting the blower can enter a flow path  402  in the sensor chamber  400 , which can be positioned within the motor and/or sensor module. The flow path  402  can have a curved shape. The flow path  402  can be configured to have a curved shape with no sharp turns. The flow path  402  can have curved ends with a straighter section between the curved ends. A curved flow path shape can reduce pressure drop in a gases flow without reducing the sensitivity of flow measurements by partially coinciding a measuring region with the flow path to form a measurement portion of the flow path. 
     A sensing circuit board  404  with sensors, such as ultrasonic transmitters, receivers, humidity sensor, temperature sensor, flow rate sensor, and the like, can be positioned in the sensor chamber  400  such that the sensing circuit board  404  is at least partially immersed in the flow path  402 . Immersing at least part of the sensing circuit board and sensors in the flow path can increase the accuracy of measurements because the sensors immersed in the flow are more likely to be user to the same conditions, such as temperature and pressure, as the gases flow, and therefore provide a better representation of the characteristics of the gases flow. After passing through the flow path  402  in the sensor chamber  400 , the gases can exit to the humidification chamber. 
     With continued reference to  FIG. 21 , openings  406  of the sensor chamber  400  can hold acoustic transmitters, such as ultrasonic transducers which form an acoustic axis along at least a portion of the flow path  402  to measure properties or characteristics of the gases within the flow. The ultrasonic transducers can act as both transmitters and receivers. 
     EXAMPLE 1 
     A human user performed a 3 km trial run on a gravel track and recorded a time of 10 minutes and 54 seconds. The user&#39;s best time over recent years has been 10 minutes and 38 seconds. 2 weeks later, the user commenced use of a high flow device, such as a high flow device coupled to a nasal cannula patient interface as disclosed herein with delivery of a hypoxic gas composition including enriched nitrogen at an altitude equivalent of about 2,000 m (about 16.7% oxygen concentration in the hypoxic gas composition) for 2-3 hours a night, 5 days a week, for a total of three weeks. During this time, the user typically maintained the hypoxic gas flow rate at between about 5 liters/minute and about 8 liters/minute, and occasionally raised the hypoxic gas flow rate to at least 15 liters/minute for a couple minutes to verify its effects on his blood saturation, and using a pulse oximeter was able to observe his blood oxygen saturation dropping below 90%. After three weeks of the therapy, the user took a week off with no therapy, and then ran a 3 km trial run on a grass track (which typically produces much slower times than gravel) and recorded a much faster time of 10 minutes and 15 seconds. The user attributed the surprising and unexpected improvement in his run time to use of the high flow device disclosed herein. 
     Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like, are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense, that is to say, in the sense of “including, but not limited to”. 
     Although this disclosure has been described in the context of certain embodiments and examples, it will be understood by those skilled in the art that the disclosure extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses and obvious modifications and equivalents thereof. In addition, while several variations of the embodiments of the disclosure have been shown and described in detail, other modifications, which are within the scope of this disclosure, will be readily apparent to those of skill in the art. It is also contemplated that various combinations or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the disclosure. For example, features described above in connection with one embodiment can be used with a different embodiment described herein and the combination still fall within the scope of the disclosure. It should be understood that various features and aspects of the disclosed embodiments can be combined with, or substituted for, one another in order to form varying modes of the embodiments of the disclosure. Thus, it is intended that the scope of the disclosure herein should not be limited by the particular embodiments described above. Accordingly, unless otherwise stated, or unless clearly incompatible, each embodiment of this invention may comprise, additional to its essential features described herein, one or more features as described herein from each other embodiment of the invention disclosed herein. 
     Features, materials, characteristics, or groups described in conjunction with a particular aspect, embodiment, or example are to be understood to be applicable to any other aspect, embodiment or example described in this section or elsewhere in this specification unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The protection is not restricted to the details of any foregoing embodiments. The protection extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. 
     Furthermore, certain features that are described in this disclosure in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations, one or more features from a claimed combination can, in some cases, be excised from the combination, and the combination may be claimed as a subcombination or variation of a subcombination. 
     Moreover, while operations may be depicted in the drawings or described in the specification in a particular order, such operations need not be performed in the particular order shown or in sequential order, or that all operations be performed, to achieve desirable results. Other operations that are not depicted or described can be incorporated in the example methods and processes. For example, one or more additional operations can be performed before, after, simultaneously, or between any of the described operations. Further, the operations may be rearranged or reordered in other implementations. Those skilled in the art will appreciate that in some embodiments, the actual steps taken in the processes illustrated and/or disclosed may differ from those shown in the figures. Depending on the embodiment, certain of the steps described above may be removed, others may be added. Furthermore, the features and attributes of the specific embodiments disclosed above may be combined in different ways to form additional embodiments, all of which fall within the scope of the present disclosure. Also, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described components and systems can generally be integrated together in a single product or packaged into multiple products. 
     For purposes of this disclosure, certain aspects, advantages, and novel features are described herein. Not necessarily all such advantages may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the disclosure may be embodied or carried out in a manner that achieves one advantage or a group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein. 
     Conditional language, such as “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements, and/or steps. Thus, such conditional language is not generally intended to imply that features, elements, and/or steps are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without user input or prompting, whether these features, elements, and/or steps are included or are to be performed in any particular embodiment. 
     Language of degree used herein, such as the terms “approximately,” “about,” “generally,” and “substantially” as used herein represent a value, amount, or characteristic close to the stated value, amount, or characteristic that still performs a desired function or achieves a desired result. For example, the terms “approximately”, “about”, “generally,” and “substantially” may refer to an amount that is within less than 10% of, within less than 5% of, within less than 1% of, within less than 0.1% of, and within less than 0.01% of the stated amount. 
     The scope of the present disclosure is not intended to be limited by the specific disclosures of embodiments in this section or elsewhere in this specification, and may be defined by claims as presented in this section or elsewhere in this specification or as presented in the future. The language of the claims is to be interpreted broadly based on the language employed in the claims and not limited to the examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive.