An ergospirometry mask for measuring the composition of breath

Field of the Invention

The present teaching relates to an ergospirometry mask for measuring the composition of breath. In particular but not limited to, the present teaching is directed to an ergospirometry mask for measuring metabolic and other physiological responses to activity based on the flow and composition of breath. The disclosure also relates to an ergospirometry mask for monitoring the well being of living animals by measuring the flow and composition of exhaled and/or inhaled breath. Background

Ergosirometry is a procedure to continuously measure respiration and gas metabolism during ergometer exercise. It enables judgement of function and performance capacity of the cardiopulmonary system and metabolism. Determinaton of 0 ₂ consumption (V0 ₂ ) via sensing of inhaled and exhaled air flow, 0 ₂ and C0 ₂ concentrations is the principle method of indirect calorimetry employed in exercise physiology. Further, the maximal rate of 0 ₂ consumption (V0 ₂ max) is the criterion measure of a person's

cardiorespiratory fitness. Assessment of V0 ₂ max for the purpose of monitoring adaptation to exercise training and for the purpose of prescription of exercise training to athletes and cardiac rehabilitation patients occurs routinely in exercise science laboratories worldwide. Exercise prescription is optimally expressed in terms of proportions of V0 ₂ max or V0 ₂ reserve.

In addition, the concentration of volatile organic compounds contained in exhaled breath yields further physiologically relevant information about the condition of the person. For example, breath acetone and ammonia concentrations relate to the metabolism of lipids and proteins respectively.

Currently equipment described in the prior art for the purpose of ergospirometry such as those described in Patent Applications Nos. CN002102092; EP0196396A1 ; WO0134022A1 ; WO0147417A1 requires components, which may include gas sensors, a sample mixing chamber, pumps, telemetry and power source, to be contained in embodiments that are additional to the mask or mouth piece, and which are typically mounted on the body of the user. The reasons for inclusion of such embodiments are that they reduce the number of components embeded within the mask/mouthpiece and therefore the weight of mask/mouth piece; they enable the use of a mixing chamber to integrate gas concentrations over time; they facilitate drying of exhaled air through drying sample tubing prior to gas sensing, which prolongs the life of gas sensors and enhances their sensing performance. However, embodiments mounted on the body of the user can be bulky and impede natural athletic movement, consequently contributing to an observer effect whereby the measurement outcome is altered by the measurement process itself. Further, their effect on natural athletic movement deters their routine use by athlete end users for the purpose of self monitoring and are consequently the preserve of exercise scientists.

The prior art in ergospirometry devices such as those described in Patent Applications CN002102092; EP0196396A1 ; WO0134022A1 ; WO0147417A1 describes methods for measuring inhaled or exhaled airflow by means of pneumotachograph, hot wire (thermal anemometry), and turbine or fly. Yet while various methods are described, practice prefers the use of pneumotachograph or turbine over thermal anemometry, due to greater accuracy of these methods compared to thermal anemometry through a single port. Pneumotachograph or turbine aneomoeters measure the enitre flow through a tube, while thermal anemometers are surface based and therefore depend on assumptons about the nature of the flow. However, both pneumotachograph and turbine are necessarily substantially large and weighty by comparison with thermal anemometers. The prior art for portable ergospirometry devices such as those described in Patent Appications CN002102092; EP0196396A1 ; WO0134022A1 ; WO0147417A1 relies on a mixing chamber or bag collection to measure the exhaled air. This method is in effect a measure of the long term integration of the exhaled air. It does not offer fine temporal resolution, but time- averaged fluctuations in exhaled gases. The prior art for portable ergospirometry devices (CN002102092; EP0196396A1 ; WO0134022A1 ; WO0147417A1) exclusively considers the measurement of the 0 ₂ and C0 ₂ components of exhaled breath and thereby limits the capacity for physiological monitoring through breath analysis. For example, exhaled acetone concentration is relevant in the assessment of lipid metabolism. The prior art relating to the sensing of volatile organic compounds in exhaled breath describes a handheld protable device for single breath analysis (WO0126547A1 ; O2009020647A1 ) or a stationary device for continuous monitroing (WO2013090999A1) as opposed to a wearable device for continuous monitoring. There is therefore a need for an ergospirometry mask which addresses at least some of the drawbacks of the prior art.

Summary

The present teaching relates to an ergospirometry mask for measuring a composition of exhaled breath. All the components are located on the mask thereby removing the need to have any components located on a torso of the mask wearer which could impede movement. In particular, the present teaching is directed to an ergospirometry mask for measuring metabolic and other physiological responses to activity based on the composition of exhaled breath.

Conventionally air flow is a measurement of inhaled or exhaled air passing through a single port. Accordingly, the present teaching relates to a mask for measuring the composition of exhaled breath with multiple ports, as detailed in claim 1. Furthermore, the present teaching relates to a method for measuring physiological responses to exercise based on the composition of exhaled breath.

In one aspect an ergospirometry mask for measuring a composition of exhaled breath is provided, the mask comprising:

a plurality of inhalation ports through which air can be inhaled,

a plurality of exhaust ports through which exhaled breath can exit the mask, an exhaled air-flow channel for accommodating the flow of exhaled breath, and a first sensing means for sensing one or more consituents in the exhaled breath.

In another aspect, there is provided a dehumidifying means for dehumidifying exhaled breath within the mask. In one example, the dehumidifying means comprises a dehumidifying membrane. Advantageously, the dehumidifying membrane comprises a sulfonated tetrafluoroethylene based fluoropolymer-copolymer. In one example, the dehumidifying means comprises Nation.

In one aspect, the dehumidifying means is located between the exhalation port and the first sensing means such that the exhaled breath is dehumidified prior to be being sensed by the first sensing means.

In another aspect a second sensing means is in communication with the inhalation, exhalation or both types of ports for monitoring air characteristics. Advantageously, the second sensing means comprises mutliple air flow meters, with one or more on each port. Preferably, the second sensing means comprises at least one temperature sensor. Ideally, the second sensing means comprises at least one humidity sensor. In a further aspect, the first sensing means comprises an oxygen sensor.

Advantageously, the first sensing means comprises a carbon dioxide sensor. Ideally, the first sensing means comprises an air flow meter, with one or more for each port. In one example, the first sensing means comprises a plurality of sensors located adjacent an airflow channel.

In one aspect a battery is provided for powering the first sensing means and the second sensing means. In another aspect the battery is located in the mask neckband for weight distribution. In an exemplary arrangement, one or more mask membranes define an exhalation channel. Advantageously, an exhalation port is in fluid communication with the exhalation channel. Ideally, one or more mask membranes are configured to enclose one or more exhalation cavities of an individual. Preferably, an inner and outer mask membrane is provided which together define the exhalation channel.

In a further aspect, a section of one or more membranes defining an exhalation channel are composed of Nation or other drying material, to enable dehumidification of exhaled air prior to gas analysis. In another aspect, a communication module is in communication with the first sensing means. Advantageously, the communication module is operable for transmitting sensed or post-processed data to a remote computing means for analysis or simple consideration thereof. In one aspect, the first sensing means is operable for measuring ammonia concentration in the exhaled breath. Advantageously, the first sensing means is operable for measuring acetone concentration in the exhaled breath. Ideally, the first sensing means is operable for measuring nitric oxide concentration in the exhaled breath. In one example, the first sensing means is operable for measuring isoprene concentration in the exhaled breath. In one example the first sensing means is operable for measuring the concentration of any VOC or combination thereof in the exhaled breath. In another aspect, two or more secondary air flow channels extend between the exhaled air-flow channel and the exhaust ports. Advantageously, each secondary air flow channels is in fluid communication with the exhaled air-flow channel and with a corresponding one of the exhaust ports.

The present teaching also relates to a method of montoring physiological responses of an individual to physical exercise; the method comprising:

the individual wearing the mask for measuring a composition of exhaled breath while exercising, and

using the mask to measure one or more gases in the exhaled breath and/or inhaled breath of the individual.

Advantageously, the one or more gases include at least one of oxygen, carbon dioxide, and ammonia, acetone, nitric oxide, volatile trace gases and isoprene. Advantageously, a combination of gases are measured simultaneously.

The present teaching further relates to a mask for measuring a composition of exhaled and/or inhaled breath, the mask comprising:

multiple ports through which air is inhaled,

multiple ports through which exhaled breath exits the mask,

an exhaled air-flow channel for accommodating the flow of exhaled breath, and a sensing means for sensing one or more consituents in the exhaled and/or inhaled breath.

Brief Description of the Drawings

The present teaching will now be described with reference to Figure 1 which is a perspective view of an ergospirometry mask in accordance with the present teaching;

Detailed Description of the Drawings

The present teaching will now be described with reference to an exemplary ergospirometry mask for measuring the composition of exhaled breath and/or inhaled. It will be understood that the exemplary ergospirometry mask is provided to assist in an understanding of the present teaching and is not to be construed as limiting in any fashion. Furthermore, features or elements that are described with reference to Figure 1 may be interchanged with equivalent elements without departing from the spirit of the present teaching. Referring to Figure 1 there is provided a ergospirometry mask 100 for measuring the composition of breath. The ergospirometry mask 100 is configured for measuring metabolic and other physiological responses of an individual to exercise based on the composition of exhaled breath. The ergospirometry mask 100 may also be constructed such as to be used for monitoring the well-being of living mammals by measuring the composition of exhaled and/or inhaled breath. The ergospirometry mask 100 consists of a combination of miniature sensors incorporated into an ergonomic design to be worn about the face over the mouth and nose. The mask 100 has a sensor array that can detect the presence and quantity of selected gases and/or volatile organic compounds (VOC) in the exhaled air. Analysis of the primary respiratory gases such as oxygen (0 ₂ ) and/or carbon dioxide (C0 ₂ ) is the mainstay of exercise physiology, as fluctuations in these gasses reflect changes in metabolism resulting from variation in exercise intensity and/or fuel (carbohydrate/fat) utilisation. Furthermore, individual exhaled VOCs and/or the pattern of VOC in the exhaled air serve as additional biomarkers for relevant metabolic processes and as potentially sensitive indicators of fluctuation in pulmonary blood flow and respiratory air flow.

In an exemplary embodiment, the mask 100 comprises multiple inhalation ports 105 through which air is inhaled by an individual 110. In the exemplary embodiment the inhalation ports 105 are unidirectional. The first sensing element on each port may include one or more air mass flow sensor 134. An air-flow channel 1 15 extends between an exhalation port 120 and exhaust ports 125. The exhalation port 120 is located adjacent to the individual's 1 10 nose and mouth so that air exhaled by the individual 1 10 flows into the exhalation port 120 and along the air-flow channel 1 15 and exits the mask 100 through the exhaust port 125. The exhalation port 120 may comprise an air filter and a unidirectional valve. A first sensing means is located in the air-flow channel 130 for sensing metabolic and other physiological responses as the individual exercises based on the composition of the exhaled breath. The first sensing means may include primary sensors 135 such as an oxygen sensor 135A, a carbon dioxide sensor 135B, a trace gas sensor 135C and an air mass flow sensor 135D. The trace gas sensor 135C may comprise a single sensor or a sensor array, such as an electronic nose. These sensors are provided by way of example only; it is not intended to limit the present teaching to these particular sensors as other sensors may also be included if desired. The primary sensors 135 may be distributed in the air flow channel 130 or on a panel 140, which is mounted in the exhaust air path, such as adjacent to the air-flow channel 130 so that the primary sensors 135A, 135B and 135C are in fluid communication with the air as it is being exhaled by the individual 110. The direction of flow of the exhaled breath is indicated by arrow Ά'. A second sensing means is arranged to be in communication with the inhalation ports 105 and/or air flow channel 115. The second sensing means may include secondary sensors 145A, 145B such a temperature sensor, a humidity sensor, a pressure sensor.

The mask 100 includes one or more mask membranes for enclosing one or more exhalation cavities (nose/mouth) of the individual 110. In the exemplary embodiment, an inner mask membrane 150 together with an outer mask membrane 155 define an exhalation channel 160 for capturing exhaled air from the exhalation cavities of the individual 10. The outer mask 155 membrane may comprise in part a Nafion, or other gas drying material, section 165 in the vicinity of the exhalation channel 130 for drying/dehumidifying the exhaled air. Nafion is a sulfonated tetrafluoroethylene based fluoropolymer-copolymer and the presence of exposed sulfonic acid groups in Nafion gives it a high water absorbing capacity and diffusivity constant (~10 ^~6 cm ² .s ^"1 ). Water diffusion across a Nafion membrane follows essentially Fick diffusion principles, but with a very small impact of membrane thickness on water flux. This enables the use of thicker membranes 165 to achieve structural integrity, while not compromising on drying/dehumidifying efficiency. The opening to channel 130 is a small circular bore that extends into a large flat cavity in the vicinity of the Nafion membrane. This has the advantage of increasing the surface area to volume ratio of Nafion to humid air, thereby maximising the drying efficiency of the Nafion membrane 165. The exhalation channel 160 is in fluid communication with the exhalation air-flow channels 115 and 130. As the individual exhales the exhaled air flows into the exhalation channel 160 and into the air-flow channels 115 and 130 and exits the mask 100 via the exhaust ports 125. The primary sensors 135 measure the composition of the exhaled air which may include levels of gases such as oxygen/carbon dioxide and/or volatile organic compounds. The secondary sensors 145 measure the composition of the inhaled and/or exhaled air which may include levels of gases such as oxygen/carbon dioxide and/or volatile organic compounds. Data which is sensed by the primary and/or secondary sensors 135, 145 may be analysed locally or transmitted by a communication module 170 to a remote computer for analysis. A circuit 180 electrically couples the primary and secondary sensors 135, 145 to the communication module 170. A power supply in the form of a battery 190 is configured to power the circuit 180. Thus the battery 190 electrically powers the primary and secondary sensors 135, 145 as well as the communication module 170. The battery 190 may be located in the mask neckband for facilitating weight distribution. The circuit 180 may also include an atmospheric pressure meter for measuring atmospheric pressure. By incorporating a battery into the mask 100 allows an athlete to wear the mask 100 when participating in a field sport such as soccer, football, hurling, basket ball, hockey, etc. Weighted importance can be assigned to sensor readings for measuring metabolic and other physiological responses to exercise based on the composition of the individuals 110 exhaled breath. Adaptive pattern recognition may be used when implementing continuous analysis of the VOC in real-time.

The primary and secondary multiple sensors 135, 145 determine respiratory parameters by measuring inhaled, exhaled or both inhaled and exhaled air flow, and the exhaled fractions of oxygen and carbon dioxide. Temperature and pressure gauges enable corrections to volume/flow measurements according to the gas laws. This raw data enables real-time, breath-by-breath and time-averaged determination of the following respiratory variables both at rest and during exercise: · Minute rate of oxygen consumption (V0 ₂ ).

«> Metabolic rate or rate of energy expenditure (EE).

• Inhaled minute ventilation (V; the volume of air inhaled each minute).

• Exhaled minute ventilation (V _E ; the volume of air exhaled each minute).

• Minute rate of carbon dioxide production (VC0 ₂ ).

· Respiratory exchange ratio (VC0 ₂ /V0 ₂ ; this measure reflects the relative use of carbohydrates and lipids during exercise).

• Ventilatory equivalent for oxygen (V _E /V0 ₂ ).

• Ventilatory equivalent for carbon dioxide (this value, together with the V _E /V0 ₂ can be used to determine the ventilatory threshold (V _T ), a threshold exercise intensity above which exercise cannot be sustained for prolonged durations (V _E /VC0 ₂ ).

• Cardiac output estimated according to the Fick method.

In addition to these continuous respiratory measures, the mask 100 may be configued for use in pulmonary function testing. Standard protocols may be used for determining the following:

• Forced vital capacity (FVC)

• Slow vital capacity (SVC)

• Forced expiratory volume in one second (FEV^

· Flow/volume loops The mask 100 may be linked with other external inputs to enable simultaneous monitoring of blood pressure, blood 0 ₂ saturation, heart electrical activity (ECG) and galvanic skin response, each of which contributes additional clinically relevant information during exercise. The communication module 170 will wirelessly interface with mobile devices and/or smart glasses or any wireless compatible device to provide real-time biofeedback in a usable and actionable way. Through interfacing with such mobile devices on 4G and Wi-Fi networks it will be possible to upload live data to a cloud server which can then enable real-time remote monitoring by and interaction with coaches, physiologists or clinicians.

The advantages of the present teaching are many. The mask is light-weight and does not require additional embodiments beyond the mask itself as are required in the ergospirometry devices cited in the prior art (CN002102092; EP0196396A1 ; WO0134022A1 ; WO0147417A1). This is achieved through a number of mechanisms: small and light-wieght air mass flow meters can be used in place of larger and heavier devices by means of incorporating multiple small air flow channels in place of a single large channel; drying of an exhaled air sample is achieved passing the sample through an air flow channel within mask which is defined by a Nation (or other drying material) membrane; an exhaled sample mixing chamber is replaced by mathematical integration of gas concentrations over time. This approach can integrate air-flow measurements over time using either in-mask or remote processing. The multiple ports facilitate air passage against lower back pressure without compromising on air-flow accuracy because of the deployment of air-flow sensors on each port. In addition, the use of multiple small ports enables greater mask 100 design flexibility, thereby creating the possibility for mask customisation, a more comfortable fit to the individual 110 and an overall more ergonomic mask 100. The mask 100 provides the ability to detect trace gases in exhaled breath, thus enabling greater scope for metabolic analysis. It facilitates real-time monitoring of standard respiratory parameters (including respiratory frequency, ventilation (VE), V0 ₂ , VC0 _2> respiratory exchange ratio (RER), ventilatory equivalents for 0 ₂ and C0 ₂ ) during a variety of activities. For example, ammonia concentration in exhaled air reflects changes in exercise intensity and is closely related to the lactate threshold. The detection of acetone in exhaled breath provides an indication of lipid metabolism (especially relevant for diabetes and ultra-endurance exercise). The detection of nitric oxide in exhaled breath provides an indication of respiratory airway response to exercise (especially relevant for asthma). The detection of isoprene in exhaled breath reflects cholesterol/lipid metabolism. The primary sensors 135 are operable to measure one or more gases in the exhaled breath. The gases may include at least one of oxygen, carbon dioxide, acetone, nitric oxide and isoprene. Advantageously, a combination of gases in the exhaled breath may be measured simultaneously.The communication module 170 allows data from the sensors to be presented directly to the end-user and third parties in a real-time through interaction with the latest mobile technologies. The mask 100 has an ergonomic design that is comfortable to wear, enabling high quality measurements to be obtained in a range of field environments and during a wide range of different activities.

Multiple small ports are superior to a single larger port as the air flow will be more laminar flow due to the smaller bore, compared with larger ports, which are therefore more difficult to accurately estimate with surface sensors. It will be appreciated by those skilled in the art that the present invention does not employ a mixing chamber, but relies on accurate measurement of the exhaled gases on a breath-by-breath basis. Measuring the exhaled 0 ₂ and C0 ₂ is further complicated by the presence of dead space air, which appears in the early phase of the exhaled breath. The desired physiological information lies in the steady state value arrived at once the dead space air has passed. Breath-by-breath measurement of the exhaled air can be therefore greatly improved by synchronising the measurements to the inhaled or exhaled air or both. This will ensure measurement in the breath region which contains no dead space air. The mask 100 may be used for monitoring the performance of athletes in a variety of sports for whom physical fitness and/or body composition/nutrition are critical components of their performance. The mask 100 may be used to monitoring patients, for example, cardiovascular, metabolic and respiratory disease patients, for whom exercise is a recommended component of their rehabilitation process. Weight loss exercisers who aim to achieve weight loss through a systematic and scientific method can wear the mask 100 while exercising. Firefighters and other emergency response personnel who operate in threatening environments can wear the mask to monitor their respiratory health. The mask 100 may comprise an insert 175 for facilitating hygenic use by multiple subjects. For example, in a team sport environment it is desireable that the mask may be worn by multiple users on different occasions. In particular, the insert 175 may be configured to isolate bodily fluid such as salvia from contaminating other portions of the mask 100. The insert 175 may be releasably replacable so that each team member when using the mask 100 can use their own specific insert 175. In an exemplary arrangement, the insert 175 is a filter for locating adjacent the nose and/or mouth region in the mask 100.

While the present teaching has been described with reference to exemplary arrangements, it will be understood that it is not intended to limit the teaching of the present teaching to such arrangements as modifications may be made without departing from the spirit and scope of the present invention. It will be appreciated that gas sensors may also be provided for facilitating analysing inhaled breath. In one exemplary arrangement the difference between inhaled and exhaled gas concentrations are measured. Furthermore, sensors may be provided on the mask for measuring gas concentrations in the atmospheric air. While the mask 00 has been described as being worn by a person during exercise, it is not intended to limit the mask to be solely used by humans. It will be appreciated by those skilled in the art that the mask could be tailored in its construction to be worn by high performance animal athletes such as race horses, camels or greyhounds. While the sensors have been described for sensing particular gases, it is not intended to limit the teaching to these gases as alternative gases may also be measured using the mask as will be appreciated by thoses skilled in the art.

In this way it will be understood that the present teaching is to be limited only insofar as is deemed necessary in the light of the appended claims.

Similarly the words comprises/comprising when used in the specification are used to specify the presence of stated features, integers, steps or components but do not preclude the presence or addition of one or more additional features, integers, steps, components or groups thereof.