Gases mixing and measuring for a medical device

A gases humidification system includes a measuring chamber and a mixing chamber. The mixing chamber has one or more mixing elements that improve a mixing of gases before reaching the measuring chamber. Ultrasonic sensing is used to measure gases properties or characteristics within the measuring chamber. A baffle or a vane may be used to control and direct the gases flow through the mixing chamber as the gases flow moves into the measuring chamber.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

BACKGROUND

Field

The present disclosure generally relates to a medical gases delivery system. More particularly, certain features, aspects, and advantages of the present disclosure relate to a respiratory gases delivery system that mixes different respiratory gases and measures properties or characteristics of the mixed gases.

Description of Related Art

A gases delivery system may be used to provide respiratory gases to a patient. The gases delivery system may include a humidification device to condition the gases provided to the patient. The gases may be heated and/or humidified prior to delivery. Gases are delivered to the patient via a tube that is in fluid communication with a patient interface. Gases delivered to patients at 100% relative humidity and 37° C. generally mimic properties of air resulting from the transformation that occurs as air passes through airways from the nose to the lungs. This can promote efficient gases exchange and ventilation in the lungs, aid defense mechanisms in the airways, and increase patient comfort during treatment. In some cases, a gases delivery system used for oxygen therapy may provide oxygen to the patient. The oxygen may be mixed with air to provide a desired or targeted therapy to the patient. In such cases, a gases delivery system may monitor the concentration of oxygen to ensure that the desired or targeted amount is being delivered to the patient and to reduce or prevent wastage of oxygen.

SUMMARY

An aspect of at least one of the embodiments disclosed herein includes the realization that there are problems associated with typical approaches to mixing gases and measuring properties of mixed gases. Typical gases delivery systems may use a combination of gases, such as oxygen and air, but may not mix these sufficiently. Sensors used to measure properties of such a combination of gases may produce unreliable results. Flow rate and gases concentration measurements may both be affected by insufficient gases mixing. A mixing chamber may be used to enable sufficient mixing of gases; however, the size of a typical mixing chamber may cause the gases delivery system to be bulky or undesirably large. Typical mixing chambers may induce turbulence to encourage mixing between gases; however, turbulence may result in an acoustically noisy process and may lead to difficulties when measuring gases properties such as gases flow rate, gases concentration, or the like. Some systems may use ultrasonic sensors to measure a gases property such as concentration by inducing pressure waves that are generally perpendicular to the flow direction of the gases. Some of these systems may position a pair of ultrasonic sensors in close proximity to each other, which may increase the sensitivity of the system. In such systems, one or more additional sensors may be used to determine the gases flow rate.

The gases delivery systems and methods disclosed herein constitute improvements over typical gases delivery systems. A measurement apparatus of a gases delivery system can comprise a measuring chamber positioned within a mixing chamber in a coaxial arrangement. The coaxial chamber arrangement may increase a gases path length through the measurement apparatus while remaining more compact relative to linear or serial chamber arrangements. The mixing chamber can be configured to sufficiently mix gases before the gases move to the measuring chamber. A mixing element within the mixing chamber may induce swirling of the gases to promote mixing, this being accomplished with little or no turbulence. At least one ultrasonic sensor can be located at each end of the measuring chamber to measure gases properties or characteristics along the gases flow. Gases concentration, flow rate, and velocity can be measured using the ultrasonic sensors.

Other embodiments can comprise a mixing chamber comprising a baffle configured to promote turbulent mixing of the gases and a vane configured to linearize the gases to improve measurement of the gases properties in the measuring chamber.

At least one aspect of the present disclosure relates to a gases measurement apparatus comprising a gases measuring chamber, a controller, and first and second ultrasonic sensors. The gases measuring chamber comprises a gases flow path from a first end to a second end of the gases measuring chamber. A downstream direction is defined along the gases flow path from the first end to the second end. An upstream direction is defined along the gases flow path from the second end to the first end. The first ultrasonic sensor is positioned at the first end of the gases measuring chamber. The first ultrasonic sensor is configured to transmit a downstream acoustic pulse train in a first measurement phase. The first ultrasonic sensor is configured to detect an upstream acoustic pulse train in a second measurement phase. The first ultrasonic sensor is configured to send a signal to the controller. The second ultrasonic sensor is positioned at the second end of the gases measuring chamber. The second ultrasonic sensor is configured to transmit the upstream acoustic pulse train in the second measurement phase. The second ultrasonic sensor is configured to detect the downstream acoustic pulse train in the first measurement phase. The second ultrasonic sensor is configured to send a signal to the controller. The controller is configured to determine a characteristic of the gases based at least in part on a signal received from the first ultrasonic sensor and a signal received from the second ultrasonic sensor.

The gases can comprise two gases. The two gases can comprise oxygen and air. The downstream acoustic pulse train can comprise a plurality of acoustic pulses. The upstream acoustic pulse train can comprise a plurality of acoustic pulses. The downstream acoustic pulse train can comprise a single acoustic pulse. The upstream acoustic pulse train can comprise a single acoustic pulse. The characteristic of the gases can comprise at least one of gases concentration, flow rate, or velocity. The first ultrasonic sensor can be configured to be excited at a natural resonant frequency. The second ultrasonic sensor can be configured to be excited at a natural resonant frequency. The controller can be configured to determine a downstream time of flight for the downstream acoustic pulse train. The controller can be configured to determine an upstream time of flight for the upstream acoustic pulse train. The controller can be configured to determine the characteristic of the gases based at least in part on the downstream time of flight and the upstream time of flight.

At least one aspect of the present disclosure relates to a method for determining a characteristic of gases flowing through an apparatus along a gases flow path from a first end to a second end of the apparatus, the apparatus comprising a first ultrasonic sensor positioned at the first end and a second ultrasonic sensor positioned at the second end. A downstream direction is defined along the gases flow path from the first end to the second end. An upstream direction is defined along the gases flow path from the second end to the first end.

The method comprises transmitting a downstream acoustic pulse train from the first ultrasonic sensor. The method comprises detecting the downstream acoustic pulse train at the second ultrasonic sensor. The method comprises determining a downstream time of flight based at least in part on the downstream acoustic pulse train. The method comprises transmitting an upstream acoustic pulse train from the second ultrasonic sensor. The method comprises detecting the upstream acoustic pulse train at the first ultrasonic sensor. The method comprises determining an upstream time of flight based at least in part on the upstream acoustic pulse train. The method comprises determining the characteristic of the gases based at least in part on the downstream time of flight and the upstream time of flight. The downstream acoustic pulse train can comprise a plurality of acoustic pulses. The upstream acoustic pulse train can comprise a plurality of acoustic pulses. The downstream acoustic pulse train can comprise a single acoustic pulse. The upstream acoustic pulse train can comprise a single acoustic pulse.

The method can comprise transmitting a second downstream acoustic pulse train from the first ultrasonic sensor. The method can comprise detecting the second downstream acoustic pulse train at the second ultrasonic sensor. The method can comprise determining the downstream time of flight based at least in part on an average of the downstream acoustic pulse train and the second downstream acoustic pulse train. The method can comprise transmitting a second upstream acoustic pulse train from the second ultrasonic sensor. The method can comprise detecting the second upstream acoustic pulse train at the first ultrasonic sensor. The method can comprise determining the upstream time of flight based at least in part on an average of the upstream acoustic pulse train and the second upstream acoustic pulse train. The characteristic of the gases can comprise at least one of gases concentration, flow rate, or velocity. Transmitting a downstream acoustic pulse train from the first ultrasonic sensor can comprise exciting the first ultrasonic sensor at a natural resonant frequency. Transmitting an upstream acoustic pulse train from the second ultrasonic sensor can comprise exciting the second ultrasonic sensor at the natural resonant frequency.

The gases can comprise oxygen and air. Determining the characteristic of the gases can comprise determining an oxygen concentration as a volume percentage by multiplying the concentration in air of gases other than oxygen with the difference between an average downstream and upstream time of flight for the gases and an average downstream and upstream time of flight for air, dividing that by the difference between an average downstream and upstream time of flight for oxygen and an average downstream and upstream time of flight for air, and then adding to the result the oxygen concentration of air.

Determining the characteristic of the gases can comprise determining a flow rate in liters per minute for a given oxygen concentration by subtracting the downstream time of flight from the upstream time of flight, subtracting from that a calibrated correction for the gases mixture, and then multiplying the result by a constant factor for geometric aspects of the apparatus. The calibrated correction for the gases mixture can be determined by subtracting a calibrated correction for air from a calibrated correction for oxygen, multiplying the result by the difference between the given oxygen concentration and 20.9 (the oxygen concentration of air expressed as a percentage), dividing that result by the concentration as a volume percentage of gases in air other than oxygen, and then adding the calibrated correction for air.

At least one aspect of the present disclosure relates to a gases delivery apparatus comprising a gases mixing chamber and a gases measuring chamber. The gases mixing chamber is configured to receive gases from a gases source. The gases mixing chamber comprises a gases flow path from a first end to a second end of the gases mixing chamber. The gases mixing chamber comprises at least one mixing element situated within the gases flow path. The gases measuring chamber is configured to receive gases from the gases mixing chamber. The gases measuring chamber comprises a gases flow path from a first end to a second end of the gases measuring chamber. The gases measuring chamber is situated coaxially within the gases mixing chamber. The at least one mixing element is configured to mix gases in the gases flow path of the gases mixing chamber before the gases enter the gases flow path of the gases measuring chamber.

The at least one mixing element can comprise a vane that is configured to reduce turbulence in gases that flow from the gases flow path of the gases mixing chamber to the gases flow path of the gases measuring chamber. The at least one mixing element can comprise a baffle that is configured to increase the length of the gases flow path of the gases mixing chamber. The gases mixing chamber can be configured to receive two or more gases. The gases mixing chamber can be configured to mix the received gases. The apparatus can comprise a first ultrasonic sensor positioned at the first end of the gases measuring chamber. The apparatus can comprise a second ultrasonic sensor positioned at the second end of the gases measuring chamber.

DETAILED DESCRIPTION

A gases delivery system can be configured to deliver respiratory gases to a patient. The respiratory gases can be conditioned to have targeted or desirable properties. These properties can be selected to provide therapeutic effects for a patient, to increase comfort of a patient during therapy, or to otherwise improve respiration for the patient. Some gases delivery systems can be configured to provide a mixture of gases to a patient. For example, a gases delivery system can be configured to provide air mixed with oxygen to a patient. The concentration of oxygen in the gases mixture can be measured and maintained by the gases delivery system using a control feedback loop. For example, the gases delivery system can comprise a measurement apparatus configured to measure the concentrations of component gases in the gases mixture and a controller configured to control a valve to regulate the contribution of at least one of the component gases to the gases mixture, based at least in part on the measurements provided by the measurement apparatus. The measurement apparatus can comprise a mixing chamber configured to efficiently mix the component gases prior to entry of the mixed gases into a measuring chamber where the mixed gases can be measured. The accuracy of measurements provided by such a measurement apparatus may be superior to measurements provided by other devices that do not sufficiently mix the gases prior to measurement.

As an example, a gases delivery system can be configured to mix two component gases and control the contribution of at least one of the component gases to the gases mixture via one or more control valves. The gases delivery system can be configured to mix the component gases into a substantially homogeneous binary mixture. The gases delivery system can comprise ultrasonic transducers or sensors configured to generate and detect pressure waves along the flow of gases through a measuring chamber to determine gas concentrations or relative ratios of the component gases. The output of the ultrasonic sensors can be signals indicative of properties or characteristics of the gases. The gases delivery system can comprise a mixing chamber configured to direct the flow of gases along a spiralling gases flow path around the outside of the measuring chamber, the measuring chamber being situated coaxially within the mixing chamber. A coaxial chamber arrangement can provide a relatively long gases flow path to promote efficient mixing of gases as well as a relatively long distance between the ultrasonic sensors to improve measurement accuracy. In some embodiments, the gases delivery system can comprise baffles and/or vanes. The gases delivery system can operate the one or more control valves based at least in part on measurements of concentrations of component gases to maintain a targeted or desired relative ratio of gases in the gases mixture.

Gases Delivery System

FIG. 1illustrates an example gases delivery system1configured to deliver respiratory gases to a patient18. The gases delivery system1comprises a blower assembly2, a humidifier4, a blower conduit12, a patient conduit14, and a patient interface16. The blower assembly2comprises a blower10and a measurement apparatus20. The humidifier4comprises a humidification chamber6and a heating device8configured to heat fluids within the humidification chamber6. In some embodiments, the blower conduit12transports gases from the blower assembly2to the humidifier4and the patient conduit14transports humidified gases from the humidifier4to the patient interface16. In some embodiments, each of the blower conduit12and the patient conduit14may comprise an inspiratory conduit, an expiratory conduit, a dry line, or any other form of conduit, tube, or circuit configured to connect the patient18to a gases source. The patient18receives the humidified gases via the patient interface16.

The blower10as herein described can comprise a gases source, a ventilation device, a flow generator, a fan, or a combination of these or the like. In some embodiments, the blower10is configured to provide air to the measurement apparatus20. In some embodiments, the measurement apparatus20is further configured to receive a second gas or additional gases to mix with the air provided by the blower10.

The patient interface16as herein described can comprise a nasal mask, an oral mask, a full face mask, a nasal cannula, nasal pillows, a tracheal mask, insufflation device, or the like. The systems and methods disclosed herein may be used with invasive or non-invasive therapies, and, in some embodiments, with laparascopic therapies.

The gases delivered to the patient18can comprise air, oxygen, carbon dioxide, nitrous oxide, or a combination of any of the gases listed above. It is to be understood that other gases or combinations of gases may also fall within the scope of the present disclosure. As an example, the measurement apparatus20can be configured to mix two component gases to provide a binary gases mixture to the patient18. Each of the component gases in a binary gases mixture may comprise a pure gas or a mixture of gases. A particular example of a binary gases mixture is a mixture of oxygen and air, where air and oxygen are considered component gases of the binary gases mixture even though air is itself a mixture of gases that includes oxygen. The present disclosure will describe apparatus and systems operating on a binary gases mixture of oxygen and air, but it is to be understood that the apparatus and systems will operate in similar fashion on any binary gases mixture.

The measurement apparatus20can be configured to mix gases from the blower10and/or an additional source of gases to provide a substantially well-mixed gases mixture to the patient18. As used herein, a substantially well-mixed gases mixture can comprise a substantially homogeneous gases mixture. As an example, a substantially homogeneous gases mixture can refer to a gases mixture that is substantially mixed and that has a generally uniform temperature (e.g., a temperature that is sufficiently consistent or uniform such that variations within the mixture are not clinically relevant). As another example, a substantially homogeneous gases mixture can refer to a gases mixture that is substantially uniform with respect to a gases concentration gradient and/or a temperature gradient, such that any differences between high and low measurements of concentration and/or temperature are not clinically relevant. In contrast, a non-homogeneous gases mixture, for example, may display transient changes in gases properties or characteristics (e.g., flow rate or temperature) that may lead to inaccuracies in gases measurements. It may be advantageous for the measurement apparatus20to provide a substantially homogeneous gases mixture because more accurate gases measurements may be achieved more quickly for a substantially homogeneous gases mixture than for a non-homogeneous gases mixture.

In the gases delivery system1, a transient state (e.g., a period of time during which a concentration of gases is changing) may be shorter than for a system without the measurement apparatus20, which may allow for faster sampling rates. Thus, the time it takes to detect changes in the concentration of gases can be similar to the time it takes for the gases to transit through the measurement apparatus20. The time taken for these changes to be detected by the measurement apparatus20may depend, at least in part, on the volume of the measurement apparatus20and the flow rate of gases through the gases delivery system1.

Accuracy of sensing may be improved due at least in part to features of the measurement apparatus20that increase heat transfer from the gases flowing through the measurement apparatus20to a housing of the measurement apparatus20and reduce heat transfer from the gases to the environment, such as but not limited to tracks formed on a surface of a printed circuit board (PCB) or a moulded component, a conductive path assembled into the measurement apparatus20, or the like. This may help to reduce the influence of stem effects on measurement accuracy. High flow rates near a wall of the housing may lead to a high rate of heat transfer between the gases and the housing, which may improve the response time of the materials of the housing to temperature changes and thus ensure that the housing temperature remains generally uniform during a measurement phase. This may be important when determining gases concentration based at least in part on the influence of temperature on the relationship of the actual distance between the sensors and a calibrated distance, which may in turn affect the accuracy of the calculated oxygen concentration. Material properties of the housing can be chosen to reduce or minimize dimensional changes that occur with changes in temperature, which may affect the measurement path length, thereby reducing sensitivity to external parameters.

Oxygen, or other supplementary gases such as but not limited to carbon dioxide, may be supplied to the gases delivery system1from a wall source, a gases bottle, or the like. In some embodiments, the supplementary gases can be supplied to the gases delivery system1through the measurement apparatus20.

The gases delivery system1can comprise a control system9configured to receive measurements or signals from sensors in the gases delivery system1, control delivery of power to the heating device8, receive signals from the measurement apparatus20, control speed or flow rate of the blower10, and the like. The control system9can comprise a controller and data storage device. The controller can comprise one or more microprocessors, application-specific integrated circuits (ASICs), field programmable gate arrays, or the like. The controller can be configured to execute computer executable instructions stored on the data storage device. The data storage device can comprise one or more non-transitory storage devices such as solid state drives, hard disk drives, ROMs, EEPROMs, RAM, and the like. In some embodiments, the control system9can be a part of the humidifier4, part of the blower assembly2, or part of both the humidifier4and the blower assembly2.

Measurement Apparatus

FIG. 2illustrates an example embodiment of the measurement apparatus20configured in a coaxial arrangement. The measurement apparatus20comprises a mixing chamber21that is an outer chamber of the coaxial arrangement. The coaxial arrangement provides a compact design for the measurement apparatus20while allowing for an extended gases flow path which helps to ensure a substantially well-mixed gases mixture. Thus, the measurement apparatus20may be more compact than a measurement apparatus with a non-coaxial arrangement. The mixing chamber21comprises a mixing element24. The mixing element24may extend the length of the gases flow path through the mixing chamber21.

Air enters the mixing chamber21, such as from the blower10, via an air inlet30. Oxygen, or another supplementary gas or combination of gases, enters the mixing chamber21via an oxygen inlet32. The inner diameter of the oxygen inlet32can be substantially smaller than that of the air inlet30. One advantage of such a configuration is that the oxygen will enter the mixing chamber21at a higher velocity than will the air. This can encourage the air to travel along a longer path length, and may also increase the time that the air and the oxygen are in contact with each other, promoting increased mixing of the air and the oxygen. The air inlet30may be positioned such that it is offset from the oxygen inlet32. The oxygen inlet32may be located such that the oxygen does not pass near the air inlet30where it could be redirected towards the blower10, as that may result in a loss of oxygen.

The mixing element24is located in the mixing chamber21of the measurement apparatus20. The mixing element24promotes a swirling flow of the air and the oxygen around the mixing chamber21and towards the measuring chamber22.FIG. 4illustrates the mixing element24apart from the mixing chamber21. A swirling flow promotes gases mixing, which may be important with respect to determining gases properties and for generating predictable measurements, particularly at different flow rates. The swirling flow can also maintain a generally symmetric and stable gases profile, and can reduce or eliminate a varying axial component of the gases flow. The swirling flow may also contribute to an acoustically quieter system.FIG. 3illustrates a wall25that separates the gases in the mixing chamber21from the mixed gases in the measuring chamber22.

In some embodiments, the measuring chamber22is conical in shape. For example, an entrance of the measuring chamber22can be larger than an exit of the measuring chamber22. An inner diameter of the measuring chamber22can decrease along the direction of flow. In certain implementations, an inner wall of the measuring chamber22can form an angle with a longitudinal axis of the measuring chamber22of less than or equal to about 5 degrees, less than or equal to about 4 degrees, less than or equal to about 3 degrees, or less than or equal to about 1.5 degrees. In some implementations, an entrance of the measuring chamber22can be larger than an exit of the measuring chamber22by about 5%, by about 3%, or by about 2%. For example, where an inner wall of the measuring chamber22is substantially conical, gases can enter the measuring chamber22through an entrance that has a radius that is at least about 2-3% larger than a radius of an exit through which gases leave the measuring chamber22. In some embodiments, a cross-sectional width of the measuring chamber22decreases along the direction of flow of gases. The decrease in cross-sectional width is not necessarily linear, but can have any suitable form.

FIG. 5illustrates an example embodiment of a measurement apparatus40. The measurement apparatus40may comprise a mixing chamber41and a measuring chamber22. The mixing chamber41may comprise one or more baffles44a,44b. In some embodiments, the mixing chamber41may comprise a vane46. In some embodiments, the mixing chamber41may comprise the one or more baffles44a,44bcombined with the vane46. Other combinations may also be possible.

As illustrated, the measurement apparatus40comprises two baffles44a,44b, but a different number of baffles may be used, such as but not limited to one, three, or four baffles. The baffle44amay be located at or near the air inlet30to encourage mixing of the air and the oxygen near the entry of the air and/or the oxygen. The baffle44bmay be located further downstream from the baffle44a. The vane46may be a continuation of the baffle44bor may be located further downstream from the baffle44b. The spacing between each of the baffles44a,44band the spacing between the baffle44band the vane46may be affected by the geometry of the mixing chamber41. In some embodiments, the spacing between the baffle44band the vane46can be similar to the spacing between each of the baffles44a,44b. It is to be understood that different variations of spacing between these features may exist. The baffles44a,44bmay increase the path length that the gases travel as they move through the mixing chamber41. The baffles44a,44bmay induce turbulence to encourage mixing between the air and the oxygen. The positioning of the baffles44a,44bcan be configured to enable the gases to be substantially mixed in a relatively small space. The baffles44a,44bcan be orientated perpendicular to the direction of the flow of gases. In some embodiments, the baffles44a,44bcan be orientated non-perpendicular to the direction of the flow of gases while still inducing turbulence to improve mixing of gases.

FIG. 6illustrates that the baffles44a,44bextend at least partially around the measuring chamber22, which may leave respective gaps45a,45baround which the baffles44a,44bdo not extend. The baffle44aand the gap45aare shown inFIG. 6, but it is to be understood that the baffle44band the corresponding gap45bcan be configured in a similar manner. In some embodiments, the baffles44a,44bextend approximately 270° around the mixing chamber41. In some embodiments, the baffles44a,44bextend approximately 180° around the mixing chamber41. The baffles44a,44bmay be configured to extend between 180° and 270° around the mixing chamber41. The baffles44a,44bmay also extend around the mixing chamber41less than 180° or greater than 270°, not including 360°. Each of the baffles44a,44bcan extend differently around the mixing chamber41(e.g., the baffle44acan extend 270° and the baffle44bcan extend 250° around the mixing chamber41). The gaps45a,45bencourage the gases to spiral around the mixing chamber41and are located such that the gases are encouraged to mix along a greater portion of the flow path around the mixing chamber41. The gaps45a,45bcan be offset from one another (e.g., the gaps45a,45bcan be not axially or longitudinally aligned with one another). The baffles44a,44bmay comprise rounded corners to reduce flow separation and to reduce acoustic noise. In some embodiments, the baffles44a,44bmay comprise squared corners.

The vane46can be configured to cause the turbulent, unsteady gases to become more laminar, enabling the gases to be substantially more stable, with fewer fluctuations, by the time they reach the measuring chamber22. The vane46may also reduce pressure-induced acoustic noise in the gases delivery system1by reducing the turbulence of the gases. Due at least in part to the positioning of the baffles44a,44b, the vane46may increase the stability of the gases and may cause the gases to be more laminar, even at relatively high flow rates.

The measuring chamber22may be the inner chamber of a coaxial arrangement. Gases move from the mixing chamber21,41into the measuring chamber22. The measuring chamber22may comprise ultrasonic transducers, transceivers, or sensors26at each end, as shown inFIGS. 2, 3, and 5. In some cases, the ultrasonic sensors26may comprise a pair of sensors or multiple pairs of sensors. The distance between each of the ultrasonic sensors26may enable greater measurement resolution as compared to small changes in gases concentration. An increased distance between each of the ultrasonic sensors26may allow for a longer time period for acoustic signals between each of the ultrasonic sensors26due to the speed of sound relating to the time of flight. The distance may also decrease the sensitivity of the measurement apparatus40with regards to the precision of time measurements, where precision is limited by discretization error.

Ultrasonic Sensing

Each of the ultrasonic sensors26alternately transmits and receives pressure waves along the gases flow path. In a preferred embodiment, a first one of the ultrasonic sensors26, configured as a transmitter, transmits a pulse series in a downstream direction along the gases flow path. A second one of the ultrasonic sensors26, configured as a receiver, detects the transmitted pulses after a first period of time. When the transmission of the pulse series from the first one of the ultrasonic sensors26is complete, the configuration of the ultrasonic sensors26is reversed: the second one of the ultrasonic sensors26transmits a series of pulses in an upstream direction along the gases flow path, and the first one of the ultrasonic sensors26detects the transmitted pulses after a second period of time. A downstream direction is defined as a direction with or following the direction of the flow of gases along the gases flow path. An upstream direction is defined as a direction against or opposite the direction of the flow of gases (and thus opposite the downstream direction) along the gases flow path. The first and second time periods may or may not be of the same length; when they differ, generally the first time period (for the downstream transmission) will be shorter than the second time period (for the upstream transmission). Transmission and detection of pulses along the gases flow path in both directions may reduce the susceptibility of the measurement apparatus20,40to system variations. In some embodiments, it is feasible to transmit only in a single direction.

Sensing along the gases flow path may allow any or all of the following gases properties or characteristics to be measured: velocity, flow rate, and/or oxygen concentration. Sensing along the gases flow path may enable these gases properties to be determined without the need for additional sensors. For redundancy and/or improvement of accuracy purposes, additional sensors, such as but not limited to temperature or humidity sensors, may be incorporated within the gases delivery system1without departing from the scope of the disclosed systems and methods. Sensing along the gases flow path enables the sensing to occur within a closed system. It may be advantageous for the gases delivery system1to be a closed system to improve the capability of the gases delivery system1to contain oxygen (e.g., to reduce the likelihood of oxygen leaks) and to prolong the life of plastic components in the gases delivery system1.

The time an ultrasonic pulse takes to travel from one end of the measuring chamber22to the other, herein referred to as the time of flight, as well as the length and geometry of the measuring chamber22, can be used to determine the velocity of the gases and the gases concentration based on the speed of sound. Changes in gases concentration may predictably affect the time of flight of ultrasonic signals in each direction along the gases flow path. Temperature sensors may be included in the gases delivery system1to enable detection of any temperature changes that may also affect changes to calculations of the speed of sound in the gases mixture.

It is to be understood that various frequencies may be used for the ultrasonic sensing and, thus, the scope of the disclosed systems and methods is not to be limited to a specific value. For purposes of an example only, in some embodiments, a frequency of approximately 25 kHz is used.

Ultrasonic sensing can provide faster responses and redundancy to the measurement apparatus20,40. Measurements in the measurement apparatus20,40and information regarding the flow rate of the gases can be generated quickly relative to other sensing systems. Redundancy may be provided in the form of an in-built verification of measured gases properties. If an unlikely gases flow rate has been detected, this may imply that the oxygen concentration detected is incorrect. Similarly, if an unlikely oxygen concentration is detected, this may indicate that the gases flow rate is incorrect. Such redundancy may help to improve safety factors at the lower and higher extremes for flow rate. The gases that enter the measuring chamber22may be substantially mixed, which may reduce inconsistencies in measurements that may occur from unmixed gases.

A pulse can be defined as a peak of a single cycle associated with the driving frequency of a transducer. A pulse series may use a plurality of cycles and may detect a chosen amount of peaks. A pulse series may be defined by the period of time for which a transducer transmits the desired excitation frequency, such that a desired number of peaks may be transmitted. The number of transmitted cycles, the dispersion characteristics of the ultrasonic transducers26and the physical design of the measurement apparatus20,40may be controlled to reduce or minimize multi-path interference in the measurement apparatus20,40. The time interval between transmission sequences may be configured to be shorter than the time of flight and to not cause significant interference. A single pulse may be less sensitive to the effect of multi-path interference due at least in part to the dispersion characteristics of the ultrasonic transducers26and the effects of the physical design of the measurement apparatus20,40on the received signal.

A pulse series may be used advantageously to transmit a measurement signal that may be higher in amplitude and less sensitive to electronic noise than a single pulse. Use of the pulse series may also enable the ultrasonic sensors26to be excited at the driving frequency and may help to ensure that the acoustic period of the driving frequency is known, thereby removing or reducing issues that may be caused by a resonant response, such as phase delay. The driving frequency may not necessarily equal the natural frequency of the ultrasonic sensors26, which is dependent on temperature, gases concentration, and sensor construction. The time period between when each peak may be determined from the phase shift between the transmitted signal, the received signal, and the measured temperature of the gases mixture. Peak discrimination may be easier at lower frequencies due to larger time intervals between pulses. The pulse series may yield a large sample of readings which can be processed using averaging techniques to improve accuracy.

Calculations of the speed of sound in the mixed gases can be affected by temperature and/or humidity. To improve the accuracy of calculations of the speed of sound, temperature and/or humidity corrections can be made. For example, based on properties of an ideal gas, the speed of sound is proportional to the square root of temperature. Temperature can be measured in the gases delivery system1for use as a correction factor. For example, temperature sensors29may be located at the input of the measuring chamber22and, in some embodiments, at the output of the measurement apparatus20,40as the gases enter the humidification chamber6via the blower conduit12. In some embodiments, measurement methods disclosed herein can be performed without the use of temperature corrections. In some embodiments, systems and methods disclosed herein can maintain the measuring chamber22at or near a targeted temperature, thus allowing calculations of the speed of sound to be performed without the use of temperature corrections.

As another example, changes in humidity may cause changes in the speed of sound of the gases. Thus, it may be desirable to measure humidity in the gases mixture to improve accuracy. These measurements can be used in calculations of the speed of sound in the gas as correction factors. To measure humidity, for example, a humidity sensor27may be positioned at the intake manifold of the blower assembly2to measure the humidity of the air entering the gases delivery system1. In some embodiments, the humidity sensor27may be positioned at the outlet of the measurement apparatus20,40. In some embodiments, a humidity sensor can be placed both at the intake manifold of the blower assembly2and at the outlet of the measurement apparatus20,40. Use of two humidity sensors may provide the additional advantage of helping to determine the presence of a leak.

Pressure sensors31may be located at the oxygen inlet32and at the air inlet30of the measurement apparatus20,40. As a result, the static or dynamic pressure of each of the input gases can be measured as they enter the measurement apparatus20,40. In some embodiments, the static or dynamic pressure of the air inlet30can be approximated by blower speed. This may give an approximation of the ratio of the input gases composition, or the relative fraction of input gases to one another. An additional pressure sensor31may be located at the output of the measurement apparatus20,40as the gases enter the humidification chamber6. The measurement of pressure may provide a secondary gases concentration and a flow rate measurement system, which may be more independent of, or less sensitive to, effects of mixing, carbon dioxide, water vapour, temperature, or altitude changes. The temperature29, humidity29, and pressure31sensors may provide measurement data to improve the accuracy in the measurement of oxygen concentration. This can be achieved through direct calculations or via a lookup table.

Acoustic meta-materials may be chosen to control, manipulate, and/or direct pressure waves to reduce dispersion that may lead to interference. Such materials may be used in conjunction with, or instead of, relying on the positioning of the ultrasonic sensors26with respect to an appropriate aperture diameter for a measurement section that is designed according to the chosen driving frequency.

In some embodiments, the measurement apparatus20,40may be used with a humidification system that is not limited to a gases source comprising a blower but instead may be attached to a ventilator, insufflator, or other gases source. In some embodiments, the measurement apparatus20,40may not be a part of the blower assembly2but may be a separate component of the gases delivery system1that is located between a gases source and a humidification system.

Measurement Methods

The measurement apparatus20,40can be configured to provide electrical signals to a control system that are indicative of characteristics or properties of the gases in the gases delivery system1. The control system can receive electrical signals, determine gases properties or characteristics (e.g., gases concentration, mixing ratios, flow rate, velocity, temperature, or humidity), and control devices or components of the gases delivery system1at least in part in response to the electrical signals.

FIG. 7illustrates a schematic of a measuring chamber700with at least two ultrasonic sensors710a,710bconfigured to measure at least one gases characteristic, where the ultrasonic sensors710a,710bare configured to transmit and receive pressure waves or pulses along the gases flow path. The ultrasonic sensors710a,710bcan be configured to measure, for example and without limitation, gases concentration, flow rate, velocity, or the like. Each ultrasonic sensor710a,710bcan be configured to transmit and receive pressure waves or pulses712. For example, in a first measurement phase the ultrasonic sensor710acan be configured to act as a transmitter to transmit the pulse or pulse train712in a downstream direction (with or following the flow of gases along the gases flow path). In this first measurement phase, the ultrasonic sensor710bcan be configured to act as a receiver to generate an electrical signal in response to the received pulses712. In a second measurement phase, the roles of the ultrasonic sensors can be reversed—the ultrasonic sensor710bcan be switched to act as a transmitter and ultrasonic sensor710acan be switched to act as a receiver. In this second measurement phase, the pressure waves or pulses712are transmitted in an upstream direction (against or opposite the flow of gases, and thus opposite the downstream direction, along the gases flow path).

The ultrasonic sensors710a,710bcan be operably coupled to a control system720. The control system720can comprise a controller, data storage, communication buses, and the like to communicate with the sensors710a,710b, determine gases characteristics based at least in part on signals received from the ultrasonic sensors710a,710b, control components of the gases delivery system1in response to the determined characteristics, and the like. For example, the control system720can be configured to determine gases characteristics by comparing the time of flight (arrival time) of the pulses712in each direction (from each measurement phase). The control system720can determine the flow rate of the gases, for example, based at least in part on the differences in time of flight. The control system720can control a blower, a valve, or other similar component of the gases delivery system1in response to the determined characteristics.

In some embodiments, the ultrasonic sensors710a,710bare configured to transmit and receive the pulses712at a frequency that is at or near a natural operating frequency of the ultrasonic sensors710a,710b. The ultrasonic sensors710a,710bcan be configured to have the same natural operating frequency. This can advantageously reduce distortion from noise. In certain implementations, the natural frequency of the ultrasonic sensors710a,710bis about 25 kHz. In certain implementations, the ultrasonic sensors710a,710bcan transmit and/or receive the pulses712about every 10 ms. The pulse train or pulses712can be a square wave, a sawtooth pattern, a sine wave, or some other shape of pulse. The control system720can be configured to identify or detect the frequency of the pulses712and/or the time of flight of the pulses712. In certain implementations, the control system720can be configured to identify rising or falling edges, maxima or minima, and/or zero crossing points, etc., of the pulses712. In certain implementations, sampling is done in each direction so that about 40 samples are acquired (e.g., 40 samples of rising edges and 40 samples of falling edges). In certain implementations, the sampling rate is set at about 50 Hz. In some embodiments, signals are not filtered.

With a fixed distance between the ultrasonic sensors710a,710b, the signal time of flight between the ultrasonic sensors710a,710bis affected by various characteristics or properties of the gases (e.g., oxygen levels, humidity, and temperature). At a particular temperature, the signal time of flight is expected to fall within a time range bound by the time of flight for air and for a pure oxygen environment. These time of flight boundaries are affected by factors such as gas flow, physical design of the measurement apparatus20,40, and assembly variations and may also be different in the downstream and upstream directions. This is illustrated inFIG. 8A, which shows a plot of a binary gas calibration curve based on example measurements of a binary gas mixture of oxygen and air using a particular embodiment of the measuring chamber700. InFIG. 8A, the measured time of flight of pulses for an unknown mixture of gases in the downstream and upstream directions, Gdand Gurespectively, are plotted against a measured temperature, as is an average time of flight for both directions Gavg. Also shown inFIG. 8Aare time of flight measurements at several temperatures for oxygen in the downstream and upstream directions, Odand Ourespectively, and their average at the measured temperature, Oavg; and time of flight measurements at several temperatures for air in the downstream and upstream directions, Adand Aurespectively, and their average at the measured temperature, Aavg. The averages for air and oxygen represent boundaries of potential time of flight measurements within the gases delivery system1.

To determine an oxygen concentration of a binary gases mixture of oxygen and air, the control system720can be configured to identify peaks in pulse trains received by the ultrasonic sensors710a,710band calculate an average time of flight in each direction based on the number of peaks received and the times of each received peak. At a particular temperature, the oxygen concentration can be calculated as a volume percentage:

Gavg=(Gd+Gu)2Aavg=(Ad+Au)2Oavg=(Od+Ou)2
where Gdrepresents the downstream average time of flight for the binary gases mixture, Gurepresents the upstream average time of flight for the binary gases mixture, and Gavgrepresents the average of Gdand Gu; Ad, Au, and Aavgrepresent the equivalent averages for air (which is 20.9% oxygen); and Od, Ou, and Oavgrepresent the equivalent averages for 100% oxygen. In the graph inFIG. 8B, a linear relationship between the average time of flight Oavgin 100% oxygen and the average time of flight Aavgin an environment where there is 20.9% oxygen (e.g., air) is used to calculate the gases concentration x (e.g., the fraction of oxygen in the binary gases mixture). The line inFIG. 8Bis based on the data inFIG. 8Afor a given temperature (e.g., the measured temperature).

To determine the flow rate of a gases mixture comprising a particular oxygen concentration, the difference between the measured time of flight in each direction is adjusted by an offset referred to as a calibrated correction. The calibrated correction compensates at least in part for asymmetry in the measuring chamber700. For example, even when the flow rate of gases is zero or near zero, there may be a difference in the time of flight for pulses moving in the downstream and upstream directions. As illustrated inFIG. 8C, the calibrated correction fGcan be determined from a time of flight in each direction for the gases mixture based on the concentration x previously determined (e.g., as shown inFIG. 8B). As an example, the flow rate of a mixture of gas and air can be calculated, in liters per minute, as:
F(lpm)=k×[(Gu−Gd)−fG]
where

fG=fA+(fO-fA)⁢(x-20.9)(100-20.9)
where k is a constant representing the influence of the cross sectional area of the measuring chamber700and the distance between the ultrasonic sensors710a,710b, fAis a calibrated correction for air, and fOis a calibrated correction for oxygen. The calibrated correction fGis a linear interpolation between fAand fObased on gas concentration.

Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise,” “comprising,” “having,” “including,” 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”.

It should be noted that various changes and modifications to the embodiments described herein will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the present disclosure and without diminishing its attendant advantages. For instance, various components may be repositioned as desired or various steps in a method may be performed in differing orders. It is therefore intended that such changes and modifications be included within the scope of the present disclosure. Moreover, not all of the features, aspects and advantages are necessarily required to practice the disclosed embodiments. Accordingly, the scope of claimed embodiments is intended to be defined only by the claims that follow and not by any individual embodiment in the present disclosure.