Respiratory Gas Sensing

Abstract

In an embodiment, an apparatus 100 is described. The apparatus includes an infrared IR generating system 102. The IR generating system has a first IR source 104 configured to generate IR radiation to form a first IR beam 106 in a first spectral band. The IR generating system further has a second IR source 108 configured to generate IR radiation to form a second IR beam 110 in a second spectral band. The apparatus further includes a beam steering system 112 configured to combine beam paths of the first IR beam and the second IR beam and direct the first IR beam and the second IR beam along the beam paths through a gas sample region 114. The apparatus further includes an IR detection system 116 configured to detect intensities of the first and second IR beams after passing through the gas sample region. The IR detection system is configured to generate a signal 118 from which an indication of a concentration of a target gas in the gas sample region can be derived.

Description

[Technical field]

[0001] The present invention relates to an apparatus, method and respiratory monitoring system for gas sensing. [Background technology]

[0002] Some infrared (IR) sensors used to detect the partial pressure (or concentration) of a target gas component (e.g., carbon dioxide) in a gas sample operate by measuring the percentage of absorbed IR radiation of the gas sample at certain wavelengths within the absorption spectrum of the target gas that is characteristic of the target gas and not another gas component (e.g., water vapor). Some absorption bands of carbon dioxide have absorption peaks centered around the following wavelengths: 2 μm (microns), 2.7 μm, and 4.3 μm. By comparison, some absorption bands of water vapor have absorption peaks centered around the following wavelengths: 1.38 μm, 1.87 μm, and 2.7 μm. Appropriate selection of wavelengths used in such IR sensors facilitates the measurement of the partial pressure of the target gas in a gas sample, such as that obtained from a subject in a clinical setting or in environmental monitoring applications.

[0003] In capnography, such IR sensors are used to measure the partial pressure (and therefore concentration) of carbon dioxide in the gas exhaled by a subject during the subject's breathing cycle. Such carbon dioxide measurements are indicative of the subject's health status and are used in a variety of clinical and emergency scenarios. Certain clinical and emergency scenarios require rapid and accurate measurement of a subject's carbon dioxide profile during its breathing cycle. There are scenarios where such measurements need to be captured within a wide range of ambient temperatures encountered in different clinical scenarios.

[0004] In some examples, the source of IR radiation in some IR sensors includes an electrically-powered broadband IR radiation source, such as an incandescent lamp or a gas discharge lamp. In some examples, two or more IR detectors are used to measure the absorption of IR radiation at different wavelengths by target gas components in the gas sample volume. The signal generated by the IR detector is indicative of the partial pressure of the target gas.

[0005] However, the spectral power of the IR radiation output by the IR source and the spectral responsivity of the IR detector may vary due to various factors, such as changes in ambient temperature. Certain techniques are used to reduce the effect of such factors on the accuracy of measurements used to determine the partial pressure of a target gas. For example, the IR source is appropriately controlled by providing power at an appropriate rate to ensure that the spectral output power and system temperature are maintained within an acceptable range. In another example, the IR detector is temperature controlled (e.g., by heating and / or cooling) to ensure that its spectral responsivity is maintained within an acceptable range. In another example, the IR source and / or the IR detector are recalibrated when necessary, such as when the ambient temperature drifts outside the acceptable range. In another example, measurements captured by the IR detector are corrected based on an analysis of previously obtained measurements. The implementation of such control and / or correction involves trade-offs in terms of power consumption, number of components used, size, weight, cost, complexity, and / or functionality of the IR sensor. Summary of the Invention [Problem to be solved by the invention]

[0006] Aspects or embodiments described herein relate to improving the implementation and / or deployment of gas sensing apparatus, methods, and systems that obviate one or more problems associated with gas sensing in different scenarios and / or hardware used for such gas sensing. [Means for solving the problem]

[0007] In a first aspect of the present invention, an apparatus is described.

[0008] The apparatus includes an infrared IR generating system. The IR generating system has a first IR source configured to generate IR radiation to form a first IR beam in a first spectral band. The IR generating system further has a second IR source configured to generate IR radiation to form a second IR beam in a second spectral band. The first spectral band is associated with a first attenuation coefficient of the target gas. The second spectral band is associated with a second attenuation coefficient of the target gas. The second attenuation coefficient is higher than the first attenuation coefficient. An intensity of the IR radiation generated by the first IR source is modulatable in time in response to a modulation of power for operating the first IR source. An intensity of the IR radiation generated by the second IR source is modulatable in time in response to a modulation of power for operating the second IR source. An intensity of the IR radiation generated by the first IR source is modulatable independently of an intensity of the IR radiation generated by the second IR source.

[0009] The apparatus further includes a beam steering system configured to combine beam paths of the first IR beam and the second IR beam and direct the first IR beam and the second IR beam along the beam paths through the gas sample region.

[0010] The apparatus further includes an IR detection system configured to detect the intensities of the first and second IR beams after passing through the gas sample region. The IR detection system is configured to generate a signal. The signal is indicative of a detected intensity by the first IR beam, and a first parameter derived from a first time interval of the signal is indicative of a level of attenuation of the first IR beam in the gas sample region. The signal is further indicative of a detected intensity by the second IR beam, and a second parameter derived from a second time interval of the signal is indicative of a level of attenuation of the second IR beam in the gas sample region. A comparison of the second parameter to the first parameter is indicative of a concentration of the target gas in the gas sample region.

[0011] Several embodiments relating to the first and other aspects are described below.

[0012] In some embodiments, the gas of interest is at least one component of a gas for inhalation by the subject and / or at least one component of a gas exhaled by the subject, and the device is configured to obtain an indication of a concentration of the at least one component in a gas sample obtained from the gas for inhalation by the subject and / or from the gas exhaled by the subject.

[0013] In some embodiments, the signal includes a convolution of a first signal component corresponding to the detected intensity by the first IR beam and a second signal component corresponding to the detected intensity by the second IR beam. A first parameter is derivable from the signal based on a deconvolution of the first and second signal components over a first time interval. A second parameter is derivable from the signal based on a deconvolution of the first and second signal components over a second time interval.

[0014] In some embodiments, the intensity of the IR radiation generated by the first and second IR sources can be modulated such that the intensity of the IR radiation generated by the first IR source is modulated at the same frequency, but out of phase, with the intensity of the IR radiation generated by the second IR source.

[0015] In some embodiments, the intensity of the IR radiation generated by the first and second IR sources can be modulated such that the intensity of the IR radiation generated by the first IR source is modulated at a different frequency than the intensity of the IR radiation generated by the second IR source.

[0016] In some embodiments, the intensity of the IR radiation generated by the first and second IR sources can be modulated such that during a first time interval, the intensity of the IR radiation generated by the first IR source has a higher intensity than the IR radiation generated by the second IR source.

[0017] In some embodiments, the intensity of the IR radiation generated by the first and second IR sources can be modulated such that during the second time interval, the intensity of the IR radiation generated by the second IR source has a higher intensity than the IR radiation generated by the first IR source.

[0018] In some embodiments, the intensity of the IR radiation generated by the first and second IR sources can be modulated such that the IR radiation generated by the second IR source is generated continuously or repeatedly over a period of time. The signal generated by the IR detection system over the period of time is indicative of multiple values ​​for a second parameter. The multiple values ​​for the second parameter are indicative of a level of attenuation of the second IR beam in the gas sample region over the period of time. The multiple values ​​for the second parameter are indicative of any variation in concentration of the target gas over the period of time.

[0019] In some embodiments, the intensity of the IR radiation generated by the first and second IR sources can be modulated such that the IR radiation generated by the first IR source is generated at least once before, during, and / or after the time period. The signal generated by the IR detection system at least once before, during, and / or after the time period is indicative of at least one value for a first parameter. The at least one value for the first parameter is indicative of a level of attenuation of the first IR beam in the gas sample region.

[0020] In some embodiments, the time period corresponds to a phase of a respiratory cycle.

[0021] In some embodiments, the beam steering system is configured to combine beam paths of the first IR beam and the second IR beam through the gas sample region such that the optical axes of the first IR beam and the second IR beam are collinear at the gas sample region.

[0022] In some embodiments, the apparatus further comprises a control system for modulating power for operating the first and second IR sources to individually modulate an intensity of IR radiation generated by the first IR source and an intensity of IR radiation generated by the second IR source.

[0023] In some embodiments, the control system is configured to modulate an intensity of IR radiation generated by the first IR source and an intensity of IR radiation generated by the second IR source such that, in response to receiving an indication as to whether the first and / or second parameters should be determined, the IR detection system generates a signal indicative of the first and / or second parameters.

[0024] In some embodiments, the apparatus further includes a processing system configured to derive first and second parameters from the signal and / or perform a comparison of the second parameter to the first parameter to obtain an indication of the concentration of the target gas in the gas sample volume.

[0025] In some embodiments, the processing system is configured to determine a first parameter from the signal based on a range of signal values ​​obtained during a first time interval.

[0026] In some embodiments, the processing system is configured to determine a second parameter from the signal based on a range of signal values ​​obtained during a second time interval.

[0027] In some embodiments, the processing system is configured to deconvolve a first signal component corresponding to the detected intensity by the first IR beam from a second signal component corresponding to the detected intensity by the second IR beam based on the indicated timing of the modulated intensity of the IR radiation generated by the first IR source and the modulated intensity of the IR radiation generated by the second IR source. The processing system is further configured to derive a first parameter from the first signal component and a second parameter from the second signal component.

[0028] In some embodiments, the IR detection system includes an IR detector that includes an IR-sensitive detection area positioned to detect both the first and second IR beams using the same detection area.

[0029] In some embodiments, the IR generating system further comprises a third IR source configured to generate IR radiation to form a third IR beam in a third spectral band. The third spectral band is associated with a third attenuation coefficient of the second target gas. The third attenuation coefficient is higher than the first attenuation coefficient. The intensity of the IR radiation generated by the third IR source is modulatable in time in response to modulation of power for operating the third IR source. The intensity of the IR radiation generated by the third source is modulatable independently of the intensity of the IR radiation generated by the first and second IR sources. The beam steering system is configured to combine beam paths of the first, second, and third IR beams and direct the first, second, and third IR beams along the beam paths through the gas sample region. The IR detection system is configured to detect the intensity of the first, second, and third IR beams after passing through the gas sample region. The signal generated by the IR detection system is further indicative of the detected intensity of the third IR beam. A third parameter derived from a third time interval of the signal indicates a level of attenuation of the third IR beam in the gas sample region. A comparison of the third parameter to the first parameter indicates a concentration of the second target gas in the gas sample region.

[0030] In a second aspect of the present invention, a respiratory monitoring system is described. The respiratory monitoring system includes a respiratory gas sampling system. The respiratory gas sampling system is configured to acquire a respiratory gas sample. The respiratory monitoring system further includes an apparatus according to the first aspect or any related embodiment. The respiratory gas sampling system is configured to provide an acquired respiratory gas sample into a gas sampling region of the apparatus. The apparatus is further configured to generate an indication of a concentration of a gas of interest in the acquired respiratory gas sample.

[0031] In a third aspect of the present invention, a method is described.

[0032] The method includes generating, with a first IR source, IR radiation to form a first IR beam in a first spectral band.

[0033] The method further includes generating a second IR beam in a second spectral band with a second IR source.

[0034] The first spectral band is associated with a first attenuation coefficient of the target gas. The second spectral band is associated with a second attenuation coefficient of the target gas. The second attenuation coefficient is higher than the first attenuation coefficient. The intensity of the IR radiation generated by the first IR source is modulatable in time in response to a modulation of power for operating the first IR source. The intensity of the IR radiation generated by the second IR source is modulatable in time in response to a modulation of power for operating the second IR source. The intensity of the IR radiation generated by the first IR source is modulatable independently of the intensity of the IR radiation generated by the second IR source.

[0035] The method further includes combining beam paths of the first IR beam and the second IR beam with the beam steering system and directing the first IR beam and the second IR beam along the beam paths through the gas sample region.

[0036] The method further includes detecting, with an IR detection system, the intensity of the first and second IR beams after passing through the gas sample region.

[0037] The method further includes generating a signal with the IR detection system. The signal is indicative of a detected intensity of the first IR beam. A first parameter derived from a first time interval of the signal is indicative of a level of attenuation of the first IR beam at the gas sample region. The signal is further indicative of a detected intensity of a second IR beam. A second parameter derived from a second time interval of the signal is indicative of a level of attenuation of the second IR beam at the gas sample region. A comparison of the second parameter to the first parameter is indicative of a concentration of the target gas at the gas sample region.

[0038] According to certain embodiments described herein, at least two individually modulated IR beams are multiplexed by combining the IR beams to facilitate measuring the attenuation of the IR beams by the target gas with reduced or minimized temperature dependence. Certain embodiments allow signals from an IR detection system to be demultiplexed based on synchronization with the IR radiation output profile of each IR source (e.g., based on a model of the IR source resistance and / or knowledge of the type of IR source) to detect the intensity of the at least two IR beams. Certain embodiments allow fast and / or accurate signal demultiplexing from the IR detection system. Certain embodiments provide a device that can operate at relatively low power (e.g., due to a reduced number of components and / or individual modulation of the IR sources) in a compact and / or robust package, while still providing accurate measurements over a relatively wide ambient temperature range. Certain embodiments are deployed for multi-gas sensing applications. Certain embodiments relate to devices that are deployable in a range of scenarios, such as clinical and / or emergency scenarios, while still providing fast and accurate measurements (e.g., for capnography applications).

[0039] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0040] Exemplary embodiments of the invention will now be described, by way of example only, with reference to the following drawings, in which: [Brief description of the drawings]

[0041] [Figure 1] 1 is a schematic diagram of an apparatus for gas sensing, according to an embodiment. [Diagram 2] FIG. 1 is a schematic diagram of a system for gas sensing, according to an embodiment. [Diagram 3] 1 is a graph depicting data representative of the sensed concentration of carbon dioxide during a respiratory cycle. [Figure 4] 1 is a graph depicting data representative of absorption of IR radiation in a first spectral band detected by a single IR detector channel. [Diagram 5] 1 is a graph depicting data representative of absorption of IR radiation in first and second spectral bands detected by a single IR detector channel, according to an embodiment. [Figure 6] 1 is a schematic diagram of an apparatus for gas sensing, according to an embodiment. [Figure 7] 1 is a schematic diagram of an apparatus for gas sensing, according to an embodiment. [Figure 8] FIG. 1 is a diagram of a method of gas sensing, according to an embodiment. [Figure 9] 1 is a schematic diagram of a machine-readable medium for facilitating gas sensing, according to an embodiment. [Figure 10] 1 is a schematic diagram of an apparatus for facilitating gas sensing, according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] As noted above, changes in ambient temperature affect the operation of IR sources and / or IR detectors, such as those used in certain gas sensing applications. In some cases, changes in ambient temperature can lead to inaccurate measurements of IR absorption by the target gas, resulting in erroneous estimates of the partial pressure (and therefore concentration) of the target gas in the gas sample. While some applications may tolerate a certain level of inaccuracy for some measurements, certain applications, such as capnography, require that measurements be obtained according to an acceptable precision.

[0043] An exemplary method for reducing the risk of obtaining an inaccurate measurement of the partial pressure of a gas is to control the operating temperature of components such as the IR source and / or the IR detector.

[0044] For example, a powered IR source is sometimes supplied with power that is modulated such that the temperature of the IR source is maintained within an acceptable range. If the IR source is an incandescent lamp, appropriate modulation of the power supplied to the IR source prevents overheating and / or underheating such that the spectral power (i.e., power output at each portion of the illuminated spectrum) of the IR source is maintained within an acceptable range. If the IR source is a gas discharge lamp, appropriate modulation of the power supplied to the gas discharge lamp provides control of the spectral power output of the gas discharge lamp. Other types of powered IR sources include solid-state (i.e., semiconductor-based) IR emitters such as IR light emitting diodes (LEDs) or laser diodes. The relationship between the spectral power output (and other performance characteristics) of these different types of IR sources is affected by the temperature at which the IR source is operating, which depends on both the ambient temperature and self-heating due to operation of the IR source.

[0045] As highlighted above, controls (e.g., temperature control by heating or cooling) are used to control the performance (e.g., spectral power) of the IR source. However, such controls require additional hardware (e.g., power supply modulation, dedicated cooling equipment, thermoelectric cooling, heating, temperature measurement, etc.) of the IR sensor to implement the temperature control, which increases power consumption, number of components used, size, weight, cost, complexity, and / or functionality.

[0046] While the spectral responsivity of some IR detectors is not significantly affected by temperature variations, as experienced in some scenarios, the spectral responsivity of some other IR detectors is more significantly affected by temperature variations to the extent that measurements by such IR detectors may be erroneous. In some cases, this temperature sensitivity depends not only on the type of IR detector being used, but also on how the IR detector is being operated. As an example, lead selenide (PbSe)-based IR detectors and / or indium antimonide arsenide (InAsSb)-based IR detectors exhibit good responsivity in the wavelength range of 2 to 5 microns. However, such materials are highly temperature sensitive in that the responsivity at certain wavelengths changes by a large factor within the temperature operating range of the IR detector. For example, the responsivity changes by a factor of 8 (eight) for an ambient temperature change of 0° C. to 60° C., which is an example of a reasonable ambient temperature range in which IR sensors are used in capnography.

[0047] As already mentioned, additional hardware is provided to maintain a constant temperature for such IR sensors. However, such additional hardware involves tradeoffs such as additional power usage and latency to reach a particular temperature. The tradeoff between power consumption, time to accuracy, and temperature swings is problematic for clinical and emergency applications that require fast, accurate measurements.

[0048] Additionally, as highlighted in the above examples, recalibration of the hardware environment (e.g., periodically or whenever a change in temperature exceeds a predetermined threshold) helps reduce errors in the measurements. In another example, correction techniques are applied to newly acquired measurements based on analysis of previously acquired measurements (e.g., within different temperature ranges) to account for factors that affect the measurements, such as changes in temperature (e.g., based on application of the ideal gas law).

[0049] Although it is possible to calibrate and / or correct the temperature sensitivity of an IR detector, this process may be difficult for end users to perform and / or may not necessarily result in sufficiently accurate measurement results in various deployment scenarios (e.g., when the ambient temperature varies) if such calibration and / or correction is based on different deployment scenarios (e.g., where the calibration / correction measurements are obtained in a particular ambient temperature range).

[0050] Certain embodiments described herein facilitate the deployment and / or implementation of gas sensing in various scenarios. Certain embodiments described herein reduce the need for additional components of IR sensors used in gas sensing. Certain embodiments described herein reduce the need for calibration of such IR sensors and / or reduce or avoid the need to correct for various factors that otherwise affect the accuracy and / or reliability of such IR sensors.

[0051] 1 is a schematic diagram of an apparatus 100 for gas sensing according to an embodiment. The apparatus 100 implements the functionality of an IR sensor and is deployed in various scenarios requiring gas sensing. For example, the apparatus 100 is used for gas sensing in clinical scenarios (e.g., for measuring partial pressure / concentration of carbon dioxide and / or other gases of interest such as anesthetic gases such as nitrous oxide). In another example, the apparatus 100 is used in environmental monitoring applications.

[0052] The apparatus includes an infrared IR generating system 102 .

[0053] The IR generating system 102 includes a first IR source 104. The first IR source 104 is configured to generate IR radiation to form a first IR beam 106 in a first spectral band.

[0054] The IR generating system 102 further includes a second IR source 108. The second IR source 108 is configured to generate IR radiation to form a second IR beam 110 in a second spectral band.

[0055] The manner in which the IR radiation is generated and how the respective IR beams 106, 110 are formed depends on the type of IR sources 104, 108 and / or how the IR radiation is provided in the first and second spectral bands. Certain embodiments described below further provide details regarding the implementation of the IR sources 104, 108 and how the respective IR beams 106, 110 are formed.

[0056] Some further details of the implementation of the device 100 according to the present embodiment are described below.

[0057] A first part of the implementation will now be described, referring to the attenuation of the first and second spectral bands by the target gas.

[0058] According to a first portion of the implementation, the first spectral band is associated with a first attenuation coefficient of the target gas, and the second spectral band is associated with a second attenuation coefficient of the target gas, the second attenuation coefficient being higher than the first attenuation coefficient.

[0059] The attenuation coefficient of a target gas refers to the proportion of IR radiation that is absorbed, scattered, and / or otherwise attenuated by the target gas. As described above, each of the first and second attenuation coefficients has a first and second spectral band associated therewith. Thus, the level of attenuation is different for each of the first and second spectral bands. In particular, IR radiation in the second spectral band (i.e., of the second IR beam) is attenuated more by the target gas than IR radiation in the first spectral band (i.e., of the first IR beam).

[0060] With reference to the example given above regarding carbon dioxide absorption bands, when the target gas is carbon dioxide, the first spectral band includes wavelengths that do not include the absorption peak wavelength of carbon dioxide (and thus the first spectral band is associated with a "first extinction coefficient") (i.e., the first spectral band does not include or does not substantially overlap with this wavelength, or other wavelengths associated with absorption by carbon dioxide), such as 4.3 microns (μm).

[0061] The second spectral band includes wavelengths that include a (e.g., at least one) absorption peak wavelength of carbon dioxide, such as 4.3 μm (i.e., the second spectral band includes (substantially overlaps with) this wavelength, or other wavelengths associated with absorption by carbon dioxide) (and thus the second spectral band is associated with a "second extinction coefficient").

[0062] Because the attenuation coefficient associated with the second spectral band is higher than the attenuation coefficient associated with the first spectral band, if the IR radiation in the second spectral band is attenuated (after the gas sample has passed) to a greater extent than the IR radiation in the first spectral band is attenuated, this indicates that the target gas is present in the measured gas sample. However, if the IR radiation in the second spectral band is attenuated to the same extent (or not) as the IR radiation in the first spectral band, this indicates that the target gas is not present, or is present in small amounts, in the gas sample.

[0063] Next, a second part of the implementation will be described, referring to modulating the intensity of the IR radiation.

[0064] According to a second portion of the implementation, the intensity of the IR radiation generated by the first IR source 104 can be modulated in time (i.e., the intensity can be modulated in time) in response to modulation of the power for operating the first IR source 104. Furthermore, the intensity of the IR radiation generated by the second IR source 108 can be modulated in time in response to modulation of the power for operating the second IR source 108. Furthermore, the intensity of the IR radiation generated by the first IR source 104 can be modulated independently of the intensity of the IR radiation generated by the second IR source 108.

[0065] Thus, as described in further detail below, the first IR source 104 can be operated independently of the second IR source 108 such that the intensities of the first and second IR beams 106, 110 can be modulated at the appropriate time and when necessary.

[0066] Further details of the device 100 are described below.

[0067] The apparatus 100 further includes a beam steering system 112 configured to combine beam paths of the first IR beam 106 and the second IR beam 110 and direct the first IR beam 106 and the second IR beam 110 along the beam paths through a gas sample volume 114.

[0068] In some cases, the first and second IR beams 106, 110 are not generated simultaneously (because the intensities of the IR beams 106, 110 are modulated in time). Thus, the beam steering system 112 combines the two IR beams 106, 110 to direct them along substantially the same beam path (e.g., including the gas sample region 114), but this does not necessarily mean that the two IR beams 106, 110 are directed along the beam path at the same time (unless there is a time overlap when both the first and second IR sources 104, 108 are generating IR radiation). The beam paths of the first and second IR beams 106, 110 are the same or at least substantially similar (e.g., at least a portion of the beam paths of the first and second IR beams 106, 110 follow substantially the same beam path within the gas sample region). Further details of the beam steering system 112 and the gas sample region 114 are described in more detail in connection with certain embodiments described below.

[0069] The apparatus 100 further includes an IR detection system 116. The IR detection system 116 is configured to detect the intensity of the first and second IR beams 106, 110 after passing through the gas sample volume 114. As described in more detail below, the IR detection system 116 is configured to generate a signal 118 (e.g., an electrical signal) indicative of certain information about the target gas.

[0070] Signal 118 is indicative of the detected intensity of first IR beam 106. A first parameter derived from a first time interval of signal 118 (such as amplitude and / or difference between a peak / maximum intensity value and a trough / minimum intensity value) is indicative of a level of attenuation of first IR beam 106 in gas sample region 114. In some cases, the beginning and end points of the first time interval correspond to intensity values ​​used to calculate the first parameter. For example, a trough / minimum intensity value is observed at the beginning point and a peak / maximum intensity value is observed at the end point of the first time interval. The first parameter is indicative of attenuation of first IR beam 106 in gas sample region 114. In an example, the difference between the two intensity values ​​is proportional to the attenuation of first IR beam 106 in gas sample region 114.

[0071] Signal 118 is further indicative of the detected intensity of second IR beam 110. A second parameter derived from a second time interval of signal 118 is indicative of a level of attenuation of second IR beam 110 in gas sample region 114. The second parameter is derived from the second time interval in the same manner as the first parameter is derived from the first time interval. The second parameter is indicative of the attenuation of second IR beam 110 in gas sample region 114. In an example, the difference between the peak intensity value and the trough intensity value derived from the second time interval is proportional to the attenuation of second IR beam 110 in gas sample region 114.

[0072] The first and second time intervals may be of the same or different duration. The first and second time intervals may at least partially overlap or may not overlap at all. If the first and second time intervals completely overlap, it is difficult to extract the first and / or second parameters in the overlapping time intervals (although it is easier to extract the first and / or second parameters in different time intervals). However, if the first and second time intervals partially overlap or do not overlap, it is relatively easy to extract the first and / or second parameters.

[0073] A comparison of the second parameter to the first parameter is indicative of the concentration (or partial pressure) of the target gas in the gas sample volume 114. Because the attenuation of the second IR beam 110 is due to the presence of the target gas in the gas sample volume 114 (e.g., because the second spectral band is associated with a higher attenuation coefficient associated with the target gas) and the attenuation of the first IR beam 106 is not due to the presence of the target gas, a comparison of the first parameter to the second parameter is indicative of the concentration of the target gas. Certain embodiments described below relate to how the comparison is made.

[0074] Thus, the signal 118 generated by the device 100 is used to estimate or determine the change in concentration (or partial pressure) of the target gas within the gas sample volume 114. This change in concentration is used to infer the actual concentration of the target gas. As discussed above, determining the concentration of the target gas is useful in a variety of applications, such as capnography or environmental monitoring.

[0075] Thus, the apparatus 100 facilitates time and wavelength multiplexing of the IR radiation generated by the first and second IR sources 104, 108. The first and second spectral bands are selected to have different (potentially narrowband) wavelengths to enable individual modulation and / or power efficient operation of each channel associated with the first and second IR beams 106, 110.

[0076] In some cases, such multiplexing facilitates individual modulation of the intensity of the IR radiation generated by the first and second IR sources 104, 108. Each IR channel (i.e., a first channel associated with the first IR beam 106 and a second channel associated with the second IR beam 110) is individually monitored using the same IR detection system 116. In some cases, such a setup facilitates power-efficient operation by only having the first and second IR sources 104, 108 generate IR radiation when necessary. The multiplexed setup further avoids the need to use additional components to detect the intensity of both the first and second IR beams, e.g., simultaneously. Instead, the IR detection system 116 is configured to detect the intensity of the first and second IR beams 106, 110 as and when the first and second IR sources 104, 108 generate IR radiation to form the first and second IR beams 106, 110. The multiplexed configuration facilitates flexible operation of the device 100 such that certain components, such as the first and second IR sources 104, 108, are used when needed.

[0077] In some cases, the device 100 operates to generate accurate measurements of the intensities of the first and second IR beams 106, 110 with reduced or minimal delay after start-up (e.g., the device 100 is ready for use when needed). The use of individually modulated first and second IR beams 106, 110 facilitates a measurement of the concentration of the target gas that is unrelated to ambient temperature, since the measurement of the intensity of the first IR beam 106 after passing through the gas sample region 114 serves as a "reference" signal representative of attenuation not due to the target gas. The "comparison" allows the effects of such other factors (e.g., temperature variations, scattering particles, etc. that cause attenuation of both the first and second IR beams 106, 110) to be taken into account, so that the measurement of the intensity of the second IR beam 110 represents attenuation due to the target gas (and not any other constituent gases or components of the gas sample).

[0078] In some cases, the production of IR radiation by the first and second IR sources 104, 108 is monitored (e.g., based on measurements of the electrical resistance of the IR sources 104, 108, which is indicative of the intensity level of the IR radiation produced by the IR sources 104, 108). As explained in more detail below, such monitoring of the first and second IR sources 104, 108 is useful for decoupling the signal 118 due to the first IR beam 106 (after attenuation, if any attenuation occurs) from the signal 118 due to the second IR beam 110 (after attenuation due to the presence of the target gas).

[0079] Thus, the independent operation and modulation of the first and second IR sources 104, 108 is useful for obtaining a representative, rapid, and accurate indicative measurement result of the concentration of the target gas, taking into account the effect of certain factors (e.g., temperature variations, scattering particles, etc.) Furthermore, the independent operation and modulation of the first and second IR sources 104, 108 is useful for decoupling the two channels associated with the first and second IR sources 104, 108 and establishing the contribution by each channel, thus facilitating a representative, rapid, and accurate indicative measurement of the concentration of the target gas.

[0080] In some cases, device 100 is operated under an extended ambient temperature range, which is useful for deploying device 100 in various scenarios (e.g., clinical and / or emergency scenarios) while ensuring accuracy of measurements so that the concentration of the target gas can be indicated with a certain level of confidence.

[0081] In some cases, the design of device 100 is such that device 100 can have a relatively compact size, low weight, simple optical architecture, simple design (by virtue of avoiding the use of certain components that would otherwise increase the size of device 100), and / or is energy efficient (e.g., by virtue of the separate operation of first and second IR sources 104, 108 and the use of the same IR detection system 116 to detect the intensity of first and second IR beams 106, 110). In some cases, device 100 is portable / body worn by virtue of its compact size and potential compatibility with battery-powered operation.

[0082] Thus, the device 100 can be deployed in a variety of scenarios and can provide an accurate indication of the concentration of a target gas in such scenarios.

[0083] 2 is a schematic diagram of a respiratory monitoring system 200 for respiratory gas sensing, according to an embodiment. The respiratory monitoring system 200 includes a respiratory gas sampling system 202. In this embodiment, the respiratory gas sampling system 202 is configured to obtain respiratory gas samples including gases inhaled (e.g., oxygen, anesthetic gases, etc.) and / or exhaled (e.g., carbon dioxide, water vapor) by a subject, such as a patient. For example, the respiratory gas sampling system 202 may be part of a ventilator (not shown) or otherwise deployed for respiratory monitoring purposes. The respiratory gas sampling system 202 includes infrastructure (not shown), such as tubing, a removable sample chamber, etc., for capturing gas samples from the inhaled and / or exhaled gases.

[0084] The respiratory monitoring system 200 further includes a device 204 according to any embodiment described herein, such as device 100, or certain other devices described below. With reference to device 100 in FIG. 1, respiratory gas sampling system 202 is configured to provide an acquired respiratory gas sample into a gas sample region 206 of device 204 (i.e., gas sample region 114 in FIG. 1). Device 100 is configured to generate an indication (e.g., via signal 118) of the concentration of the target gas in the acquired respiratory gas sample. In some cases, the gas sample is passed through gas sample region 206 (e.g., repeatedly or when needed). In this case, gas sample region 206 has a gas inlet and outlet (not shown) that allows the gas sample to flow through gas sample region 206. In some cases, the gas sample is stored in a sample chamber (not shown) that can be positioned in gas sample region 206 when needed (i.e., the sample chamber can be replaced whenever a gas sample is acquired).

[0085] FIG. 3 shows a graph depicting data representative of the sensed concentration of carbon dioxide during a respiratory cycle.

[0086] Graph (a) is a capnogram representing the partial pressure of carbon dioxide (CO2) (in millimeters of mercury mmHg) in a respiratory gas sample taken over three respiratory cycles. The capnogram shows the level of carbon dioxide in the inhaled and exhaled gas sample. The capnogram profile is indicative of the subject's health condition. For example, the capnogram profile may indicate a particular health problem.

[0087] Graph (b) shows decoupled channels (C1, C2) derived from the signal 118. The decoupling of the channels is described in more detail below. The first channel C1 refers to the detected intensity of the first IR beam 106 after passing through the gas sample region 114. The second channel C2 refers to the detected intensity of the second IR beam 110 after passing through the gas sample region 114. As depicted by graph (b), the intensity of the first IR beam 106 (represented by channel C1) does not vary significantly over time because the IR radiation in the first spectral band is used for reference purposes and is not substantially attenuated by the presence of carbon dioxide (the concentration of carbon dioxide varies over time during the respiratory cycle). However, because the attenuation coefficient associated with the second spectral band is higher than the attenuation coefficient associated with the first spectral band, the variation in the concentration of carbon dioxide results in an attenuation of the second IR beam 110 over time (represented by the second channel C2). A comparison (such as a difference or ratiometric calculation) of channels C1 and C2 is used to generate the capnogram of graph (a).

[0088] FIG. 4 is a graph depicting data representative of the attenuation (if any such absorption occurs) of IR radiation in a first spectral band detected by a single IR detector channel. In this case, the IR radiation generated by a single IR source is modulated by supplying power to the IR source. As depicted in the graph, periodically, the detected intensity increases (when power is supplied or increased) and then decreases (when power is not supplied or decreased). The profile of detected intensity shown by the graph represents the type of IR source. For example, an incandescent lamp continues to generate IR radiation even when power is no longer supplied because it cools down slowly. Thus, the depicted decrease (downward slope) of the detected IR radiation represents the continuous generation of IR radiation by the IR source. With reference to FIGS. 1 and 3, FIG. 4 represents a measured signal 118 obtained by operating only the first channel C1.

[0089] FIG. 5 is a graph depicting data representing the attenuation of IR radiation in both the first and second spectral bands (as depicted by the device 100) detected by a single IR detector channel according to an embodiment. Reference is made to the features and functions of the device 100. In this case, the modulation of the first and second IR sources is out of phase, so that the first IR source 104 is powered such that the peak IR irradiation occurs at approximately 20 milliseconds (ms) and 120 ms (through the example depicted by FIG. 4), and the second IR source 108 is powered such that the peak IR irradiation occurs at approximately 70 ms and 170 ms. In other words, FIG. 5 shows the addition of the second channel C2 to the data depicted by FIG. 4. Thus, the contributions of both the first and second channels C1 and C2 are depicted in the graph of FIG. 5. As shown by the graph, the second channel C2 records a lower peak intensity than the first channel C1. This is because the second IR beam 110 experienced a greater level of attenuation (due to the presence of the target gas) than the first IR beam 106. The data illustrated by Figure 5 is an example of a "raw" signal 118 acquired by the IR detection system 116. This signal 118 is then used to derive channels C1 and C2 and the associated capnogram shown by Figure 3.

[0090] FIG. 5 further depicts the intensity values ​​and the time intervals used to determine the first and second parameters.

[0091] The first parameter is determined by calculating the difference between the peak / maximum intensity (Rp) and the trough / minimum intensity (Rv) (i.e., the amplitude A1). Thus, the first time interval refers to the time between when Rv and Rp are obtained (i.e., not only between 0 and 20 ms, but also between 100 and 120 ms, as shown in FIG. 5).

[0092] The second parameter is determined by calculating the difference (i.e., amplitude A2) between the peak / maximum intensity (Dp) and the trough / minimum intensity (Dv). The second time interval therefore refers to the time between when Dv and Dp are obtained (i.e., between 150 and 170 ms as well as between 50 and 70 ms as shown in FIG. 5).

[0093] It can be seen that the amplitude A1 associated with the first IR beam 106 (channel C1) is greater than the amplitude A2 associated with the second IR beam 110 (channel C2) because the second IR beam 110 was attenuated by the presence of the target gas in the gas sample volume 114. A comparison of the amplitude A1 to the amplitude D2 (e.g., the difference or ratiometric calculation A2 / A1) indicates the concentration of the target gas in the gas sample volume 114.

[0094] Several embodiments of the device 100, as well as other embodiments, are described below. Any selected combination of the embodiments described below may be implemented by the device 100 and other devices described below, where appropriate. In the description of the embodiments below, reference is made to the above-mentioned drawings.

[0095] In some embodiments, the gas of interest is at least one component of a gas for inhalation by the subject and / or at least one component of a gas exhaled by the subject. In this regard, the device 100 is configured to obtain an indication of the concentration of at least one component in a gas sample obtained from the gas for inhalation by the subject and / or from the gas exhaled by the subject. Thus, when the device 100 is used to monitor gas inhaled and / or exhaled by a subject, such as a patient, the device 100 is configured to obtain an indication of the concentration of at least one selected gas of interest (e.g., carbon dioxide, anaesthetic gas, etc.).

[0096] In some embodiments, the signal 118 includes a convolution of a first signal component corresponding to the detected intensity by the first IR beam 106 and a second signal component corresponding to the detected intensity by the second IR beam 110 (e.g., because the same IR detection system 116 is used to detect the intensity of both IR channels). A first parameter (e.g., "A1") can be derived from the signal 118 based on a deconvolution of the first and second signal components in a first time interval. A second parameter (e.g., "A2") can be derived from the signal 118 based on a deconvolution of the first and second signal components in a second time interval.

[0097] The modulation of the first and second IR sources 104, 108 can be performed in various ways, as mentioned in the embodiments described below. The choice of which modulation scheme to use depends, for example, on the settings of the device 100 and / or on whether measurements need to be obtained continuously from one or both IR channels. Any combination of modulation schemes can be performed simultaneously, if possible, or at different times, if appropriate.

[0098] In some embodiments, the intensity of the IR radiation generated by the first and second IR sources 104, 108 can be modulated such that (i) the intensity of the IR radiation generated by the first IR source 104 is modulated at the same frequency, but out of phase, with the intensity of the IR radiation generated by the second IR source 110. This embodiment is depicted by FIG. 5, where the peak powers of the first and second IR sources 104, 108 are 180 degrees out of phase with each other. Other phase differences are possible, such as 90 degrees (the choice of phase difference is arbitrary). As described below, it is difficult to extract the first and second parameters when the phase difference is 0 degrees within a particular time interval, even though it is easier to extract the first and second parameters in other time intervals.

[0099] In some embodiments, the intensity of the IR radiation generated by the first and second IR sources 104, 108 can be modulated such that (ii) the intensity of the IR radiation generated by the first IR source 104 is modulated at a different frequency than the intensity of the IR radiation generated by the second IR source 108. In this case, the first and second channels C1 and C2 corresponding to the output of the first and second IR sources 104, 108 proceed in phase and out of phase over the sampling time period. Thus, an indication of the concentration of the target gas is obtained when possible over the sampling time period.

[0100] In some embodiments, the intensity of the IR radiation generated by the first and second IR sources 104, 108 can be modulated such that (iii) during a first time interval, the intensity of the IR radiation generated by the first IR source has a higher intensity than the IR radiation generated by the second IR source. In some embodiments, the intensity of the IR radiation generated by the first and second IR sources 104, 108 can be modulated such that (iv) during a second time interval, the intensity of the IR radiation generated by the second IR source has a higher intensity than the IR radiation generated by the first IR source. These embodiments are similar to those described above, where there is a phase difference with respect to the peak powers of the first and second IR sources 104, 108.

[0101] Certain types of IR sources 104, 108 continue to emit IR radiation even after power is no longer provided to the IR sources 104, 108 (or if less power is provided for a particular time interval). Thus, if more power is provided to the first IR source 104 than to the second IR source 108 (or no power is provided to the second IR source 108) during a "first time interval" such that the peak IR output of the first IR source 104 occurs during the first time interval, then both the first and second IR beams 106, 110 will be "on" simultaneously. Similarly, if more power is provided to the second IR source 108 than to the first IR source 104 (or no power is provided to the first IR source 104) during a "second time interval" such that the peak IR output of the second IR source 108 occurs during the second time interval, then both the first and second IR beams 106, 110 will be "on" simultaneously. As depicted by comparing Figures 4 and 5, the emission of IR radiation by the first and second IR sources 104, 108 occurs simultaneously such that there is a contribution to the signal 118 by both simultaneous IR sources 104, 108. However, the peak intensity of the first IR beam 106 (e.g., time = 20 ms) is out of phase with the peak intensity of the second IR beam 110 (e.g., time = 70 ms), so that the effect of the ongoing emission of IR radiation by the "off" or "low power" IR sources 104, 108 during each respective time interval can be decoupled. Certain types of IR sources do not produce IR radiation when powered off (e.g., laser diodes), or the production of IR radiation tapers off over a different time scale and / or at a different rate than depicted in Figures 4 and 5.

[0102] In some embodiments, the intensity of the IR radiation generated by the first and second IR sources 104, 108 can be modulated such that (v) the IR radiation generated by the second IR source 108 is generated continuously or repeatedly over a period of time. The signal 118 generated by the IR detection system 116 over that period of time indicates multiple values ​​for a second parameter (e.g., "A2"). The multiple values ​​for the second parameter indicate a level of attenuation of the second IR beam 110 in the gas sample volume 114 over that period of time. The multiple values ​​for the second parameter indicate any variation in the concentration of the target gas over that period of time. In other words, repeated measurements of the attenuation of the second IR beam 110 are obtained over any period of time (e.g., including multiple "second" time intervals).

[0103] In some embodiments, the intensity of the IR radiation generated by the first and second IR sources 104, 108 can be modulated such that (vi) the IR radiation generated by the first IR source 104 is generated at least once before, during, and / or after the time period. The signal 118 generated by the IR detection system 116 at least once before, during, and / or after the time period is indicative of at least one value for a first parameter (e.g., “A1”). The at least one value for the first parameter is indicative of a level of attenuation of the first IR beam 106 in the gas sample region 114.

[0104] In other words, at least one value for the first parameter is obtained during a time period during which multiple values ​​for the second parameter are obtained (see embodiment (v)). If the first parameter indicates a "reference" level of attenuation and the second parameter indicates the concentration of the target gas, then fewer measurements of the attenuation of the first IR beam 106 are required if it can be assumed that the reference level of attenuation does not change significantly over that time period. Thus, in some cases, the first parameter needs to be obtained only when necessary. In an example scenario, the second IR source 108 is modulated at a frequency of 100 Hz (e.g., to obtain the second parameter every 100 ms) and the first IR source 104 is modulated to generate IR radiation every 5 minutes (e.g., over a time interval of 100 ms), so that a reference measurement of the first parameter can be obtained. However, if greater accuracy is required, the values ​​for the first parameter are obtained more regularly, such as the same number of times as the values ​​for the second parameter within that time interval.

[0105] As highlighted above, a time period is defined as a time period for taking a certain number of measurements. In some embodiments, the time period corresponds to a phase of a respiratory cycle, such as an inhalation phase, an exhalation phase, or a full respiratory cycle of inhalation and exhalation. In one example, if the time period is 5 seconds (typical for an exhalation phase) and the modulation frequency is 100 ms, 50 measurements are obtained during this time period. In one example, one measurement is made using the first IR beam 106 and the remaining 49 measurements are made using the second IR beam 110 (for one value of the first parameter and 49 values ​​of the second parameter). In another example, 25 measurements are made using the first IR beam 106 and the remaining 25 measurements are made using the second IR beam 110 (for 25 values ​​of the first parameter and 25 values ​​of the second parameter).

[0106] FIG. 6 is a schematic diagram of an apparatus 600 for gas sensing according to an embodiment. The apparatus 600 includes features of the apparatus 100 of FIG. 1 and is used in the same applications as described above. In this regard, such features of the apparatus 600 have reference numbers increased by 500 compared to FIG. 1. Various embodiments are described with respect to FIG. 6, and FIG. 6 is used to assist in explaining the features associated with these embodiments. Not all features are present in a particular variant of the apparatus 600. For example, a feature described for any of the embodiments described below may be omitted in a particular variant. In other words, FIG. 6 represents possible combinations of features for one variant of the apparatus 600. However, any selected combination of features according to the embodiments described below may be provided in another variant of the apparatus 600.

[0107] Some details of the beam steering system 612 according to an embodiment are described below.

[0108] The beam steering system 612 includes a first collector lens 630 configured to collect the first IR beam 606. The first collector lens 630 collimates or at least reduces the divergence of the first IR beam 606. The beam steering system 612 further includes a first filter 632 (e.g., a long-pass, band-pass, or short-pass filter) for spectrally filtering the IR radiation generated by the first IR source 604 (of the IR generating system 602) such that the first IR beam 606 has a “first spectral content” after being filtered by the first filter 632.

[0109] The beam steering system 612 further includes a second collector lens 634 configured to collect the second IR beam 610. The second collector lens 634 collimates or at least reduces the divergence of the second IR beam 610. The beam steering system 612 further includes a second filter 636 (e.g., a long-pass, band-pass, or short-pass filter) for spectrally filtering the IR radiation generated by the second IR source 608 (of the IR generating system 602) such that the second IR beam 610 has a “second spectral content” after being filtered by the second filter 636.

[0110] In an example implementation of apparatus 600, the second filter 636 is configured to pass IR radiation at approximately 4.3 microns, which is absorbed by carbon dioxide, such that the detected intensity of the second IR beam 610 is indicative of the concentration of carbon dioxide in the gas sample volume 614. The first filter 632 is configured to pass IR radiation of a different wavelength that is not absorbed by carbon dioxide, to provide a reference measurement of background attenuation (e.g., due to the presence of water vapor, scattering particles, etc.).

[0111] The beam steering system 612 further includes a beam combiner 638 configured to transmit the first beam 606 and reflect the second IR beam 610 (or reflect the first beam 606 and transmit the second IR beam 610) to combine the first and second IR beams 606, 610 to have the same beam path (or substantially the same beam path). Due to the arrangement of the first and second IR sources 604, 608 relative to the beam steering system 612, the first and second IR beams 606, 610 are directed through the gas sample volume 614 along the same (or similar) beam path.

[0112] In some embodiments, as described in further detail below, the beam steering system 612 further includes a focusing lens 640 to focus (or further collimate) the combined first and second IR beams 606, 610 onto the IR detection system 616.

[0113] In some embodiments, the beam steering system 612 is configured to combine the beam paths of the first and second IR beams 606, 610 through the gas sample volume 614 such that the optical axes 642 of the first and second IR beams 606, 610 are collinear within the gas sample volume 614. In other words, the first and second IR beams 606, 610 have overlapping or substantially overlapping beam paths (including optical axes at 0 degrees or a small angle to each other) at the gas sample volume 614.

[0114] The apparatus 600 further includes a control system 644 for modulating the power (e.g., electrical power) for operating the first and second IR sources 604, 608 to individually modulate the intensity of the IR radiation generated by the first IR source 604 and the intensity of the IR radiation generated by the second IR source 608. The control system 644 controls the electrical power supplied to the first and second IR sources 604, 608 via separate power supply lines, as depicted in FIG. 6. The control system 644 is depicted as being part of the apparatus 600 itself. In other embodiments, the functions of the control system 644 are performed by at least one external device (not shown), such as an individually controllable external power supply for each of the first and second IR sources 604, 608.

[0115] In some embodiments, the control system 644 is configured to modulate the intensity of the IR radiation generated by the first IR source 604 and the intensity of the IR radiation generated by the second IR source 608 in response to receiving an indication as to whether the first parameter and / or the second parameter should be determined, such that the IR detection system generates a signal 618 indicative of the first and / or second parameters. Thus, when the first parameter needs to be determined, the control system 644 operates the first and second IR sources 604, 608 such that the first parameter can be measured (e.g., during a first time interval) and the second parameter can be measured (e.g., during a second time interval). As previously highlighted, the first and second parameters can be measured as and when needed. Thus, the "indication" causes the control system 644 to operate the first and second IR sources 604, 608 depending on when IR radiation needs to be generated so that the first and / or second parameters can be obtained. In an example, the “indication” may be triggering a command from another device or system, or a predefined command stored in the control system 644, to supply power to either the first IR source 104 or the second IR source 108 for a specific time interval.

[0116] In some embodiments, the apparatus 600 further includes a processing system 646 configured to derive first and second parameters from the signal 618 and / or perform a comparison of the second parameter to the first parameter to obtain an indication of the concentration of the target gas in the gas sample region 614. The processing system 646 is depicted as being part of the apparatus 600 itself. In other embodiments, the functions of the processing system 646 are performed by at least one external device (not shown), such as a user computer for analyzing the signal 618. In some embodiments, the functions of the processing system 646 and the control system 644 are performed by the same device (e.g., at least one processor for executing instructions stored on a machine-readable medium for performing the functions of the processing system 464 and / or the control system 644).

[0117] There are various ways to "compare" a first parameter with a second parameter to obtain an indication of the concentration (or partial pressure) of the target gas. In some embodiments, the indication of concentration is obtained by calculating a ratio between the second parameter and the first parameter (i.e., a "ratiometric" calculation). In some embodiments, the indication of the calculation is obtained based on a difference between the first parameter and the second parameter, or some other comparison of the first parameter and the second parameter.

[0118] In some embodiments, the processing system 646 is configured to determine a first parameter from the signal 618 based on a range of signal values ​​obtained during a first time interval. In some embodiments, the processing system 646 is configured to determine a second parameter from the signal based on a range of signal values ​​obtained during a second time interval.

[0119] In some embodiments, the processing system 646 is configured to deconvolve a first signal component corresponding to the detected intensity by the first IR beam 606 from a second signal component corresponding to the detected intensity by the second IR beam 610 based on an indicated timing of the modulated intensity of the IR radiation generated by the first IR source 604 and the modulated intensity of the IR radiation generated by the second IR source 608. The "indicated timing" relates to the phase difference, frequency, etc. of the modulated first and second IR sources 604, 608. For example, if the phase difference, frequency, other synchronization information, etc. are known or can be determined by the processing system 646, the processing system 646 can deconvolve the first and second signal components from each other. In an example, a measurement of the electrical resistance across the first and second IR sources 604, 608 (as obtained by the control system 644) indicates the timing of the modulated intensity of the IR radiation generated by each IR source 604, 608. Based on the indicated timing, it can be determined which portions of the signal 618 correspond to the first and second time intervals. In an example implementation, the processing system 646 obtains the indicated timing from the control system 644. In another example implementation, the processing system 646 sends an indication to the control system 644 as to whether the first parameter and / or the second parameter should be determined, as described above. In either example, the control system 644 and the processing system 646 are synchronized with each other to enable extraction of the first and second parameters within the appropriate time intervals.

[0120] After the convolution has taken place, the processing system 646 is configured to derive a first parameter from the first signal component and a second parameter from the second signal component.

[0121] In some embodiments, the deconvolution of the first signal component from the second signal component is performed as described below.

[0122] The processing system 646 determines the contribution to the detected intensity by the first IR beam 606 during the first and / or second time intervals. The processing system 646 further determines the contribution to the detected intensity by the second IR beam 610 during the first and / or second time intervals.

[0123] The contribution is determined by accounting for the contribution to the detected intensity due to the first IR beam 606 during the second time interval and / or due to the second IR beam 610 during the first time interval based on a model of the level of IR radiation expected to be generated by the first and second IR sources 604, 608 over time due to the modulated power used to operate the first and second IR sources during the first and second time intervals. In other words, the "model" indicates how much IR radiation is expected to be generated by the first and second IR sources 604, 608 over time even when the power provided is reduced or turned off. Thus, the model can take into account the contribution to the detected intensity due to the second IR beam 610 being present during the first time interval. The model can further take into account the contribution to the detected intensity due to the first IR beam 606 being present during the second time interval. The model is based on knowledge or previous measurements of the IR radiation output by the first and second IR sources 606, 610. The model depends on the type of source used. For example, laser diodes only produce IR radiation when powered, whereas incandescent lamps, when hot, continue to produce IR radiation even when unpowered, and so on.

[0124] Once the contributions have been determined and their effects taken into account in each of the first and second time intervals, a first signal component is extracted from the determined contribution to the detected intensity due to the first IR beam 606 (i.e., in the first time interval), and a second signal component is extracted from the determined contribution to the detected intensity due to the second IR beam 610 (i.e., in the second time interval).

[0125] In some embodiments, the IR detection system 616 further includes an IR detector 648 including an IR-sensitive detection area positioned to detect both the first and second IR beams 606, 610 using the same detection area. As depicted by FIG. 6, both the first and second IR beams 606, 610 are combined and follow the same beam path and are directed to the same detection area in the IR detection system 616. In this case, the same IR detector 648 is configured to detect the intensity of the first and second IR beams 606, 610 (and thus generate a signal 618 corresponding to the combined intensity of the first and / or second IR beams 606, 610). In some cases, the IR detector 648 includes a single detection area or multiple detection areas aligned with the first and second IR beams 606, 610. In some cases, the IR detection system 616 includes multiple such IR detectors 648, all of which are aligned with both the first and second IR beams 606, 610.

[0126] In contrast to the exemplary approach of using one IR source and two or more detection channels with one common mode of modulation, the depicted implementation of the device 600 utilizes two IR sources 604, 608 and a common IR detection system 616. According to the exemplary implementation of the device 600, the two (or more) channels C1 and C2 are time multiplexed for detection of the intensity of IR radiation in each channel and demultiplexed for comparison (e.g., ratiometric calculation) of the level of attenuation of IR radiation for the first channel (i.e., the “reference channel”) to the level of attenuation of IR radiation (i.e., due to the presence of a gas component of interest such as carbon dioxide) for the second channel.

[0127] In an exemplary implementation of the device 600, the IR detection system 616 includes an IR detector 648 based on PbSe or InAsSb technology (responsive to IR radiation in the wavelength range 2.5 to 10 μm). Any suitable IR detection technology may be utilized, such as based on solid-state technology (e.g., in the case of PbSe or InAsSb technology) or another type of technology, such as pyroelectric IR detection. Such IR detection technology provides fast response times suitable for certain applications, such as capnography. An exemplary response time is, for example, less than 10 ms with a sampling rate of 100 Hz. Another exemplary response time is less than 1 ms. In an exemplary implementation, the response time is such that the IR detection system 616 is configured to obtain multiple measurements of the intensity of the first and / or second IR beams 606, 610 over a period of time corresponding to a phase of the respiratory cycle. In other words, the response time is the time such that sufficient measurements (e.g., 50 measurements if the time period is 5 seconds and a sampling rate of 100 Hz is utilized) can be obtained over an appropriate time period.

[0128] Some IR detection technologies have strong temperature sensitivity that can result in uncalibrated or unreliable measurements of the detected intensity as the ambient temperature changes. However, the embodiments described herein take into account any variations such as temperature changes so that measurements made using reference channel C1 can obtain accurate measurements of channel C2, reducing or eliminating the need to perform calibrations / corrections when the temperature changes.

[0129] FIG. 7 is a schematic diagram of an apparatus 700 for gas sensing, in particular for multi-gas sensing, according to an embodiment. The apparatus 700 is used in the same or similar applications as described above, but with the additional functionality for multi-gas sensing. The apparatus 700 represents a possible variant of the apparatus 100 or 600. For example, the features of the apparatus 700 can be implemented in or combined with any of the embodiments or variants described in connection with the apparatus 100, 600, and vice versa. The apparatus 700 has the same features as the apparatus 100. In this regard, the features of the apparatus 700 have reference numbers that are increased by 600 compared to FIG. 1 or increased by 100 compared to FIG. 6. Further features of the apparatus 700 are described below.

[0130] The IR generating system 702 further includes a third IR source 750 configured to generate IR radiation in a third spectral band to form a third IR beam 752. The operation of the third IR source 750 is similar to the operation of the second IR source 708, as described below.

[0131] The third spectral band is associated with a third attenuation coefficient of a second target gas (eg, for multi-gas sensing).

[0132] The third damping coefficient is higher than the first damping coefficient, and thus the third damping coefficient may be higher than the second damping coefficient, lower than the second damping coefficient, or the same as the second damping coefficient.

[0133] The intensity of the IR radiation generated by the third IR source 750 can be modulated in time in response to modulation of the power for operating the third IR source 750 .

[0134] The intensity of the IR radiation generated by the third source 750 can be modulated independently of the intensity of the IR radiation generated by the first and second IR sources 704,708.

[0135] The beam steering system 712 is configured to combine the beam paths of the first, second, and third IR beams 706, 710, 752 and direct the first, second, and third IR beams 706, 710, 752 along the beam paths through the gas sample region 714.

[0136] 6, the beam steering system 712 further includes a third collector lens 754 configured to collect the third IR beam 752. The third collector lens 754 collimates or at least reduces the divergence of the third IR beam 752. The beam steering system 712 further includes a third filter 756 (e.g., a long-pass, band-pass, or short-pass filter) for spectrally filtering the IR radiation generated by the third IR source 750 such that the third IR beam 752 has a “third spectral content” after being filtered by the third filter 756.

[0137] 6, the beam steering system 712 further includes an additional beam combiner 758 (arranged similarly to the beam combiner 638 of FIG. 6) configured to transmit the first beam 706 (and the second IR beam 710) and reflect the third IR beam 752 (or reflect the first and second IR beams 706, 710 and transmit the third IR beam 752, etc.) to combine the first, second, and third IR beams 706, 710, 752 to have the same beam path (or substantially the same beam path). By virtue of the arrangement of the first, second, and third IR sources 704, 708, 750 relative to the beam steering system 712, the first, second, and third IR beams 706, 710, 752 are directed through the gas sample volume 614 along the same (or similar) beam path.

[0138] The IR detection system 716 is configured to detect the intensity of the first, second, and third IR beams 706, 710, 752 after passing through the gas sample region 714. The signal generated by the IR detection system 716 is further indicative of the detected intensity of the third IR beam 752. A third parameter derived from a third time interval of the signal (which may or may not overlap with the first and / or second time intervals) is indicative of the level of attenuation of the third IR beam 752 in the gas sample region 714. A comparison (e.g., ratiometric calculation, difference, etc.) of the third parameter to the first parameter is indicative of the concentration of the second target gas in the gas sample region 714.

[0139] The device 700 is used for multi-gas sensing. For example, the (first) target gas is one particular gas component in a gas sample (such as carbon dioxide) and the second target gas is another gas component in the gas sample (such as an anesthetic gas). Such a device 700 provides accurate measurements of the concentrations of different gas components over a relatively wide operating temperature range in a compact / robust package with relatively low power consumption.

[0140] 8 relates to a method 800 of gas sensing, according to an embodiment. In this embodiment, the method 800 performs the functions of the apparatus 100. In other embodiments, corresponding methods perform the functions of other apparatuses described herein, such as the apparatus 600 and related embodiments. In the description of the method 800, reference is made to the apparatus 100.

[0141] The method 800 includes, at block 802, generating IR radiation with a first IR source 104 to form a first IR beam 106 in a first spectral band.

[0142] The method 800 includes, at block 804, generating a second IR beam 110 in a second spectral band with a second IR source 108.

[0143] The first spectral band is associated with a first attenuation coefficient of the target gas.

[0144] The second spectral band is associated with a second attenuation coefficient of the target gas.

[0145] The second damping coefficient is higher than the first damping coefficient.

[0146] The intensity of the IR radiation generated by the first IR source 104 can be modulated in time in response to modulation of the power for operating the first IR source 104 .

[0147] The intensity of the IR radiation generated by the second IR source 108 can be modulated in time in response to modulation of the power for operating the second IR source 108 .

[0148] The intensity of the IR radiation generated by the first IR source 104 can be modulated independently of the intensity of the IR radiation generated by the second IR source 108 .

[0149] The method 800 further includes, at block 806, combining beam paths of the first IR beam 106 and the second IR beam 110 using the beam steering system 112 and directing the first IR beam 106 and the second IR beam 110 along the beam paths through the gas sample region 114.

[0150] The method 800 further includes detecting, at block 808 , with the IR detection system 116 the intensity of the first and second IR beams 106 , 110 after passing through the gas sample volume 114 .

[0151] Method 800 further includes, at block 810, generating a signal 118 with IR detection system 116. Signal 118 is indicative of a detected intensity due to first IR beam 106. A first parameter derived from a first time interval of signal 118 is indicative of a level of attenuation of first IR beam 106 at gas sample region 114. Signal 118 is also indicative of a detected intensity due to second IR beam 110. A second parameter derived from a second time interval of signal 118 is indicative of a level of attenuation of second IR beam 110 at gas sample region 114.

[0152] A comparison of the second parameter to the first parameter is indicative of the concentration of the target gas in the gas sample volume 114 .

[0153] According to certain embodiments described herein, the apparatus 100, 600, 700, related embodiments, and related methods multiplex at least two individually modulated IR beams 606, 610 by combining the IR beams 606, 610 to facilitate measurement of the attenuation of the IR beams 606, 610 by the target gas with reduced or minimal temperature dependence. Certain embodiments allow signals 118, 618 from the IR detection system 616 to be demultiplexed based on synchronization with the IR radiation output profile of each IR source 604, 608 (e.g., based on a model of the IR source 604, 608 resistance and / or based on knowledge of the type of IR source 604, 608) to detect the intensity of the at least two IR beams 606, 610. Certain embodiments allow for fast and / or accurate signal 618 demultiplexing from the IR detection system 616. Certain embodiments provide devices 100, 600 that can operate at relatively low power (e.g., due to low component count and / or separate modulation of IR sources 604, 608) in a compact and / or robust package while still providing accurate measurements over a relatively wide ambient temperature range. Certain embodiments, such as device 700, are deployed for multi-gas sensing applications. Certain embodiments relate to devices 100, 600, 700 and methods 700 that are deployable in a range of scenarios, such as clinical and / or emergency scenarios, while still providing rapid and accurate measurements (e.g., for capnography applications).

[0154] 9 illustrates a non-transitory machine-readable medium 900 for facilitating gas sensing, according to an embodiment. The non-transitory machine-readable medium 900 includes instructions 902 that, when executed on at least one processor 904, cause the at least one processor 904 to perform certain methods associated with the operation of the apparatus 100, 600, 700 and / or with the operation of an implementation of the method 700. In some embodiments, the non-transitory machine-readable medium 900 is implemented by the control system 644 and / or the processing system 646 (e.g., to facilitate synchronization of the systems 644, 646 or to otherwise facilitate the operation of any of the embodiments described herein).

[0155] 10 illustrates an apparatus 1000 for facilitating gas sensing, according to an embodiment. The apparatus 1000 includes at least one processor 1002 (e.g., implemented by a computing device such as the control system 644 and / or the processing system 646). The at least one processor 1002 is communicatively coupled to an interface 1004 for communicating data (e.g., exchanging synchronization information such as "indicated timing," receiving raw data signals 118, 618, and / or transmitting an indication of the concentration of a target gas).

[0156] The apparatus 1000 further includes a non-transitory machine-readable medium 1006 that stores instructions 1008 readable and executable by at least one processor 1002 to perform a method corresponding to a particular method as implemented by the control system 644 and / or the processing system 646 (e.g., to facilitate synchronization of the systems 644, 646 or to otherwise facilitate the operation of any of the embodiments described herein).

[0157] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive, and the invention is not limited to the disclosed embodiments.

[0158] One or more features described in one embodiment may be combined with or substituted for features described in another embodiment.

[0159] Embodiments of the present disclosure may be provided as a method, a system, or a combination of machine-readable instructions and processing circuitry. Such machine-readable instructions may be contained on a non-transitory machine (e.g., computer) readable storage medium (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) having computer-readable program code therein or thereon.

[0160] The present disclosure will be described with reference to flowcharts and block diagrams of methods, devices, and systems according to embodiments of the present disclosure. Although the above flowcharts show a specific order of execution, the order of execution may vary depending on what is depicted. Blocks described for one flowchart can be combined with blocks of another flowchart. It will be understood that each block in the flowcharts and / or block diagrams, and combinations of blocks in the flowcharts and / or block diagrams, can be realized by machine-readable instructions.

[0161] The machine-readable instructions are executed by, for example, a processor of a general purpose computer, a special purpose computer, an embedded processor, or other programmable data processing device to implement the functions described and illustrated in the figures. In particular, a processor or processing circuit, or modules thereof, executes the machine-readable instructions. Thus, the functional modules of the apparatus and other devices described herein are implemented by a processor that executes machine-readable instructions stored in a memory, or that operates according to instructions embedded in logic circuits. The term "processor" should be interpreted broadly to include a CPU, a processing unit, an ASIC, a logic unit, or a programmable gate array, etc. All the methods and functional modules are executed by a single processor or are divided among several processors.

[0162] Such machine-readable instructions, which can direct a computer or other programmable data processing device to operate in a particular mode, are further stored within the computer-readable storage.

[0163] Such machine-readable instructions can then be loaded onto a computer or other programmable data processing device such that the computer or other programmable data processing device performs a sequence of operations to generate computer-implemented processes whereby the instructions executed on the computer or other programmable device implement the functions specified by the blocks in the flowcharts and / or block diagrams.

[0164] Furthermore, the teachings herein may be implemented in the form of a computer program product, the computer program product being stored on a storage medium and including a plurality of instructions for causing a computing device to perform the methods described in the embodiments of the present disclosure.

[0165] An element or step described for one embodiment may be combined with or substituted for an element or step described for another embodiment. Other variations to the disclosed embodiments can be understood and achieved by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprises" does not exclude other elements or steps, and the singular elements do not exclude a plurality. A single processor or other unit performs the functions of several items recited in the claims. The mere fact that certain methods are recited in mutually different dependent claims does not indicate that a combination of these methods cannot be used to advantage. A computer program is stored or distributed on a suitable medium, such as an optical storage medium or a solid-state medium, provided together with or as part of other hardware, but also distributed in other forms, such as via the Internet or other wired or wireless communication systems. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A method for detecting infrared radiation comprising: a first infrared (IR) source generating IR radiation to form a first IR beam in a first spectral band; a second IR source generating IR radiation to form a second IR beam in a second spectral band, an intensity of the IR radiation generated by the first IR source is modulatable in time in response to modulation of power for operating the first IR source; an intensity of the IR radiation generated by the second IR source is modulatable in time in response to modulation of power for operating the second IR source; an IR generating system, wherein the intensity of the IR radiation generated by the first IR source is modulatable independently of the intensity of the IR radiation generated by the second IR source; a beam steering system that combines beam paths of the first IR beam and the second IR beam and directs the first IR beam and the second IR beam along the beam paths through a gas sample volume; an IR detection system that detects the intensity of the first IR beam and the second IR beam after passing through the gas sample region; An apparatus comprising: The IR detection system comprises: a detected intensity of the first IR beam, where a first parameter derived from a first time interval of the signal indicates a level of attenuation of the first IR beam in the gas sample volume; and a detected intensity of the second IR beam, where a second parameter derived from a second time interval of the signal indicates a level of attenuation of the second IR beam in the gas sample region; and generating said signal indicative of the signal includes a convolution of a first signal component corresponding to the detected intensity due to the first IR beam and a second signal component corresponding to the detected intensity due to the second IR beam; the first parameter is derivable from the signal based on a deconvolution of first and second signal components in the first time interval; the second parameter is derivable from the signal based on deconvolution of first and second signal components during the second time interval; The concentration of the target gas in the gas sample volume is indicated by comparing the second parameter to the first parameter.

2. the target gas is at least one component of a gas inhaled by the subject and / or at least one component of a gas exhaled by the subject; 10. The apparatus of claim 1, wherein the apparatus obtains an indication of the concentration of the at least one component in a gas sample obtained from the gas inhaled by the subject and / or obtained from the gas exhaled by the subject.

3. The intensity of the IR radiation generated by the first IR source and the second IR source is (i) the intensity of the IR radiation generated by the first IR source is modulated at the same frequency but out of phase with the intensity of the IR radiation generated by the second IR source; (ii) the intensity of the IR radiation generated by the first IR source is modulated at a different frequency than the intensity of the IR radiation generated by the second IR source; (iii) during the first time interval, the intensity of the IR radiation generated by the first IR source has a higher intensity than the IR radiation generated by the second IR source; (iv) during the second time interval, the intensity of the IR radiation generated by the second IR source has a higher intensity than the IR radiation generated by the first IR source; (v) the IR radiation generated by the second IR source is generated continuously or repeatedly over a period of time, and the signal generated by the IR detection system over the period of time indicates a plurality of values ​​for the second parameter, the plurality of values ​​for the second parameter indicating a level of attenuation of the second IR beam in the gas sample volume over the period of time, and the plurality of values ​​for the second parameter indicating any variation in the concentration of the target gas over the period of time; or (vi) the IR radiation generated by the first IR source is generated at least once before, during, and / or after the certain time period, and the signal generated by the IR detection system at least once before, during, and / or after the certain time period is indicative of at least one value for the first parameter, the at least one value for the first parameter being indicative of the level of attenuation of the first IR beam in the gas sample volume. The apparatus of claim 1 , wherein the at least one of the modulation modes is modulatable as follows:

4. The apparatus of claim 3 , wherein the period of time corresponds to a phase of a respiratory cycle.

5. 2. The apparatus of claim 1 , wherein the beam steering system combines the beam paths of the first IR beam and the second IR beam through the gas sample volume such that optical axes of the first IR beam and the second IR beam are collinear at the gas sample volume.

6. 10. The apparatus of claim 1, further comprising a control system that modulates the power to operate the first IR source and the second IR source to individually modulate the intensity of the IR radiation generated by the first IR source and the intensity of the IR radiation generated by the second IR source.

7. 7. The apparatus of claim 6, wherein the control system, in response to receiving an indication as to whether the first parameter and / or the second parameter should be determined, modulates the intensity of the IR radiation generated by the first IR source and the intensity of the IR radiation generated by the second IR source such that the IR detection system generates the signal indicative of the first parameter and / or the second parameter.

8. 2. The apparatus of claim 1, further comprising a processing system that derives the first parameter and the second parameter from the signal and / or performs the comparison of the second parameter to the first parameter to obtain an indication of the concentration of the target gas in the gas sample region.

9. The processing system includes: determining the first parameter from the signal based on a range of signal values ​​obtained during the first time interval; and / or The apparatus of claim 8 , further comprising: determining the second parameter from the signal based on a range of signal values ​​obtained during the second time interval.

10. The processing system includes: deconvolving the first signal component corresponding to the detected intensity by the first IR beam from the second signal component corresponding to the detected intensity by the second IR beam based on an indicated timing of the modulated intensity of the IR radiation generated by the first IR source and the modulated intensity of the IR radiation generated by the second IR source; 9. The apparatus of claim 8, further comprising: a first parameter derived from the first signal component; and a second parameter derived from the second signal component.

11. 2. The apparatus of claim 1, wherein the IR detection system comprises an IR detector including an IR-sensitive detection area positioned to detect both the first IR beam and the second IR beam with a same detection area.

12. the IR generating system further includes a third IR source generating IR radiation in a third spectral band to form a third IR beam; an intensity of the IR radiation generated by the third IR source is modulatable in time in response to modulation of power for operating the third IR source; the intensity of the IR radiation generated by the third IR source is modulatable independently of the intensities of the IR radiation generated by the first IR source and the second IR source; the beam steering system combines beam paths of the first IR beam, the second IR beam, and the third IR beam and directs the first IR beam, the second IR beam, and the third IR beam along the beam paths through the gas sample volume; the IR detection system detects an intensity of the first IR beam, the second IR beam, and the third IR beam after passing through the gas sample region; 2. The apparatus of claim 1, wherein the signal generated by the IR detection system is further indicative of the detected intensity of the third IR beam, a third parameter derived from a third time interval of the signal is indicative of a level of attenuation of the third IR beam in the gas sample region, and the concentration of a second target gas in the gas sample region is further indicated by a comparison of the third parameter to the first parameter.

13. a respiratory gas sampling system for obtaining a respiratory gas sample; The device according to claim 1 . A respiratory monitoring system comprising: A respiratory monitoring system, wherein the respiratory gas sampling system provides an acquired respiratory gas sample into the gas sample region of the device, and an indication of the concentration of the target gas in the acquired respiratory gas sample is generated.

14. generating, with a first infrared (IR) source, IR radiation to form a first IR beam in a first spectral band associated with a first attenuation coefficient of the target gas; and generating a second IR beam in a second spectral band associated with a second attenuation coefficient of the target gas using a second IR source, the second damping coefficient is higher than the first damping coefficient; an intensity of the IR radiation generated by the first IR source is modulatable in time in response to modulation of power for operating the first IR source; an intensity of the IR radiation generated by the second IR source is modulatable in time in response to modulation of power for operating the second IR source; the intensity of the IR radiation generated by the first IR source is modulatable independently of the intensity of the IR radiation generated by the second IR source; The method further comprises: combining beam paths of the first IR beam and the second IR beam with a beam steering system to direct the first IR beam and the second IR beam along the beam paths through a gas sample region; detecting an intensity of the first IR beam and the second IR beam after passing through the gas sample region with an IR detection system; Using the IR detection system the detected intensity by the first IR beam, where a first parameter derived from a first time interval of a signal indicates a level of attenuation of the first IR beam in the gas sample volume; and generating a signal indicative of the detected intensity of the second IR beam, where a second parameter derived from a second time interval of the signal is indicative of a level of attenuation of the second IR beam in the gas sample volume; the signal includes a convolution of a first signal component corresponding to the detected intensity due to the first IR beam and a second signal component corresponding to the detected intensity due to the second IR beam; the first parameter is derivable from the signal based on a deconvolution of first and second signal components in the first time interval; the second parameter is derivable from the signal based on deconvolution of first and second signal components during the second time interval; The method further comprises: determining a concentration of the target gas in the gas sample volume by comparing the second parameter to the first parameter.

15. An infrared (IR) generating system including a first IR source generating IR radiation to form a first IR beam in a first spectral band, and a second IR source generating IR radiation to form a second IR beam in a second spectral band; a beam steering system that combines beam paths of the first IR beam and the second IR beam and directs the first IR beam and the second IR beam along the beam paths through a gas sample volume; a control system for modulating power to operate the first IR source to modulate in time the intensity of the IR radiation generated by the first IR source and for independently modulating in time the intensity of the IR radiation generated by the second IR source; an IR detection system for detecting intensities of the first IR beam and the second IR beam after passing through the gas sample volume, the IR detection system generating a signal indicative of a detected intensity by the first IR beam and a detected intensity by the second IR beam, the signal including a convolution of a first signal component corresponding to the detected intensity by the first IR beam and a second signal component corresponding to the detected intensity by the second IR beam; deriving a first parameter from the signal based on deconvolution of the first signal component and the second signal component during a first time interval of the signal indicative of a level of attenuation of the first IR beam at the gas sample volume; deriving a second parameter from the signal based on deconvolution of the first signal component and the second signal component during a second time interval of the signal indicative of a level of attenuation of the second IR beam at the gas sample volume; performing a comparison between the second parameter and the first parameter, the comparison being indicative of a concentration of the target gas in the gas sample volume; Processing system and An apparatus comprising:

16. The device described in claim 15, wherein the target gas is at least one component of a gas inhaled by the subject and / or at least one component of a gas exhaled by the subject.

17. The control system further comprising: (i) the intensity of the IR radiation generated by the first IR source is modulated at the same frequency and out of phase with the intensity of the IR radiation generated by the second IR source; (ii) the intensity of the IR radiation generated by the first IR source is modulated at a different frequency than the intensity of the IR radiation generated by the second IR source; (iii) during the first time interval, the intensity of the IR radiation generated by the first IR source has a higher intensity than the IR radiation generated by the second IR source; or (iv) during the second time interval, the intensity of the IR radiation generated by the second IR source has a higher intensity than the IR radiation generated by the first IR source; 16. The apparatus of claim 15, wherein the modulation is at least one of:

18. The apparatus of claim 15, wherein the beam steering system further combines the beam paths of the first IR beam and the second IR beam through the gas sample region so that the optical axes of the first IR beam and the second IR beam are collinear in the gas sample region.

19. The processing system further comprising: determining the first parameter from the signal based on a range of signal values ​​obtained during the first time interval; and / or The apparatus of claim 15 , further comprising: determining the second parameter from the signal based on a range of signal values ​​obtained during the second time interval.

20. The apparatus of claim 15, wherein the IR detection system has an IR detector including an IR-sensitive detection area positioned to detect the first IR beam and the second IR beam using the same detection area.

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