METHOD FOR OPERATING A BREATHING GAS ANALYSIS DEVICE WITH AT LEAST ONE GAS SENSOR

Description

[0001] The present invention relates to a method for operating a respiratory gas analyzer with at least one gas sensor, wherein the respiratory gas analyzer comprises at least one humidity-regulating system element arranged in a switchable, parallel air guide path. Furthermore, the invention relates to the use of a humidity-regulating system element arranged in a switchable, parallel air guide path of a respiratory gas analyzer with at least one gas sensor for checking the humidity state of the gas sensor, as well as to a correspondingly configured respiratory gas analyzer. State of the art

[0002] The air exhaled by a person (exhaled air) contains various substances (biomarkers) of medical and, in particular, diagnostic interest. For example, the nitrogen monoxide content in exhaled air can be examined to detect inflammatory processes or chronic pulmonary diseases, such as bronchial asthma. Exhaled air can be analyzed using respiratory gas analyzers equipped with appropriate sensors, particularly gas sensors. NO and / or NO2 sensors are primarily used for this purpose, which are used to measure the concentration of these substances in exhaled air. Such gas sensors are generally sensitive to cross-influences, meaning that, for example, variations in ambient humidity and temperature can affect measurement accuracy.This can also lead to storage effects on gas sensors, whereby the sensitivity of the sensor changes with prolonged storage depending on the storage conditions and affects the measurement signal. In this context, the humidity that develops at the sensor plays a particularly important role.

[0003] JP2019184571 discloses a respiratory gas analyzer with gas sensors and a humidity sensor as well as a humidity regulating element, wherein gas samples are guided via an air guide path with the humidity regulating element and via an air guide path without the humidity regulating element. Disclosure of the invention Advantages of the invention

[0004] The proposed method serves to operate a respiratory gas analyzer with at least one gas sensor, wherein the humidity state of the gas sensor is checked. For this purpose, the respiratory gas analyzer is equipped with at least one humidity-regulating system element arranged in a switchable, parallel air duct path. A switchable, parallel air duct path here means that an additional air duct path is provided that does not run via the humidity-regulating system element. The air duct for the actual gas analytical measurement at the gas sensor generally runs via this additional air duct path. Such a respiratory gas analyzer can, for example, be configured for the analysis of nitrogen species and, in particular, be equipped with NO / NO2 sensors. The gas sensor can, for example, be an electrochemical gas sensor or a sensor based on field-effect transistors (FETs).

[0005] To check the humidity state of the gas sensor according to the proposed method, a measurable difference is evaluated when air is circulated via the parallel air duct path with the humidity-regulating system element compared to air is circulated via the air duct path without the humidity-regulating element. This method solves the problem that an unknown humidity state at the gas sensor can influence the measurement accuracy of the gas sensor to such an extent that inaccurate or even incorrect measurement results occur. The proposed method can determine the state of the gas sensor(s), and in particular their humidity state, so that, based on these results, measures can be initiated to restore a specific sensor state or, if necessary, for example, to computationally compensate for the cross-influences that can be detected in this way.Using the proposed method eliminates the need for complex structural solutions to shield the gas sensor(s) from environmental interference, particularly humidity. In this context, existing breath gas analyzers, for example, utilize Nafion tubes that adapt the humidity of the gas sample to the ambient humidity. Such complex solutions, which are generally difficult to miniaturize, can be dispensed with using the proposed method, since the proposed method allows the breath gas analyzer to more or less independently detect the potentially variable humidity state of the gas sensor, allowing measures to be derived to correct the sensor state or, if necessary, compensate for interference.

[0006] The proposed method generates a signal based on a difference in humidity between airflow with and without humidity regulation. The humidity level at the sensor is determined indirectly by passing a gas sample through the humidity-regulating system element (humidity regulator) before it reaches the gas sensor. The gas properties altered by the humidity-regulating system element serve to generate signals or characteristics that provide information about the humidity level in the sensor area. Thus, the humidity level of the sensor is not measured directly, which would generally be very difficult when using gas-sensitive layers, for example, in the range of a few 100 nm thick.Rather, the humidity state of the gas sensor is determined based on the properties of the humidity regulator, whereby a correlation between the absorption capacity of the humidity-regulating system element (e.g., activated carbon) and the humidity state of the sensor is used for the purposes of the invention. If, for example, the respiratory gas analyzer was stored in a very humid environment before measurement, the humidity-regulating system element releases moisture into the gas sample. If the respiratory gas analyzer was stored in a dry environment before measurement, the humidity-regulating system element removes moisture from the gas sample. Depending on the moisture content of the gas sample and the humidity state of the humidity-regulating system element, the humidity of the gas sample is influenced to a greater or lesser extent.This effect can be measured directly or indirectly by comparing it with an air flow without humidity control. If the gas sample is temporarily routed through the humidity-regulating system element and temporarily not through the humidity-regulating system element, the difference in the different influence of the humidity-regulating system element on the gas sample can be detected. Depending on which air flow path is switched, a different humidity X is established at the gas sensor. At the moment of switching, a humidity jump of amplitude ΔX occurs, which can be used to determine the humidity level in the area of ​​the gas sensor.

[0007] Switching between the air flow path with a humidity-regulating system element and the air flow path without a humidity-regulating system element can be achieved, for example, by selectively switching corresponding valves or pumps. Corresponding arrangements are known in principle in the prior art, with such parallel air flow paths conventionally being used to eliminate interference by appropriate system elements and, for example, to remove certain substances from the gas sample and partially purify the gas. The proposed method, however, uses the parallel air flow paths to enable indirect measurement of the humidity at the gas sensor and thus compensate for its influence on measurement accuracy or to initiate other measures.

[0008] In a preferred embodiment of the proposed method, an element containing activated carbon is provided as the humidity-regulating system element. In addition to the humidity-regulating effect of activated carbon, the activated carbon usually also has a gas-filtering function. This gas-filtering function of activated carbon is already used in conventional breath gas analyzers for partial gas purification. For example, in conventional breath gas analyzers, the activated carbon is used to pass an initial fraction of the exhaled air, which is usually contaminated, over the activated carbon, thereby purifying it so that the gas sensor is not contaminated. As a rule, this initial, contaminated fraction of the exhaled gas is discarded for the actual breath gas analysis, and only subsequent fractions are actually measured.

[0009] In preferred embodiments, the measurable difference in air flow with and without humidity regulation can be detected based on measurements from the gas sensor. According to the invention, the respiratory gas analyzer is equipped with a separate humidity sensor, which can, for example, be connected upstream and / or downstream of the gas sensor. If necessary, multiple humidity sensors can also be provided. The humidity sensor(s) can, for example, be a capacitive humidity sensor. In embodiments, the measurable difference can be measured directly via the humidity sensor(s). Furthermore, the measurable difference can, for example, also be detected using both the gas sensor and one or more humidity sensors.

[0010] In particularly preferred embodiments of the proposed method, measures are initiated if necessary to regulate the humidity level and / or to compensate for it during gas analysis measurements. Such measures can, for example, be initiated automatically, or the user can be alerted to the need for such measures with an appropriate signal or display.

[0011] The measures that may need to be initiated may, for example, include blocking the respiratory gas analyzer for further measurements and / or recalibrating the respiratory gas analyzer and / or drying the gas sensor in particular and / or drying the humidity-regulating system element and / or correcting the measured value of a respiratory gas analysis measurement. Depending on the mathematical evaluation method, the initiation of such measures can, for example, be made dependent on the measurable difference exceeding or falling below a certain threshold. Exceeding or falling below a predefined threshold for the measurable difference then indicates that a certain level of humidity is present in the area of ​​the gas sensor, which is influencing the measurement signal, so that sufficient measurement accuracy or, in some cases, even the full functionality of the gas sensor can no longer be assumed.If necessary, the evaluation may also stipulate that the measurable difference must lie between two predefined threshold values ​​in order to demonstrate a humidity level that ensures sufficient measurement accuracy.

[0012] The proposed method is expediently implemented in such a way that the humidity level is checked regularly. For example, specific time intervals can be specified to ensure operational readiness with sufficient measurement accuracy at all times. For example, it can also be planned to perform a check regularly after a certain storage period of the respiratory gas analyzer.

[0013] The humidity level can be checked, for example, during or at the beginning of a regular respiratory gas measurement, whereby the subject's exhaled air is temporarily guided via the parallel air guide path with the humidity-regulating system element and temporarily via the air guide path without the humidity-regulating system element, and the measurable difference is evaluated accordingly. It can also be provided that the humidity level is checked during a so-called pseudo-measurement, in particular by sucking in ambient air and directing it via the corresponding air guide paths according to the proposed method. In general, a pseudo-measurement is understood to be a measurement with the respiratory gas analyzer in which ambient air, rather than the subject's exhaled air, is introduced into the respiratory gas analyzer.

[0014] Finally, the invention comprises a respiratory gas analyzer with at least one gas sensor and at least one humidity sensor, as well as at least one humidity-regulating system element, which is arranged in a switchable, parallel air guide path. This respiratory gas analyzer is characterized in that the respiratory gas analyzer is configured to carry out the described method. In particular, the respiratory gas analyzer is equipped with a corresponding control system that allows the gas sample to be guided via the air guide path with the humidity-regulating system element and, before or after this, the gas sample to be guided via the air guide path without the humidity-regulating system element. In principle, it is also possible for the gas sample to be guided in parallel via both air guide paths, at least temporarily.Furthermore, a corresponding evaluation of the measurable difference is provided in the manner described above, whereby this difference is based on measurements of the gas sensor or on measurements of the humidity sensor provided in the device during air flow with and without humidity regulation.

[0015] Further features and advantages of the invention will become apparent from the following description of embodiments in conjunction with the drawings.

[0016] The drawings show: Fig. 1: Block diagram of the gas flow and involved system components in a respiratory gas analyzer; Fig. 2: Representation of the humidity profile and the humidity jump ΔX when switching between the air flow paths with and without humidity regulation of a respiratory gas analyzer; and Fig. 3: Exemplary flow diagram of the implementation of the proposed method. Description of implementation examples

[0017] Fig. 1 shows an exemplary block diagram for the gas flow in a respiratory gas analyzer with the system components involved in implementing the proposed method. Arrow 1 indicates the subject's exhaled air, which is introduced into the respiratory gas analyzer via an optional mouthpiece 2. Such a mouthpiece 2 is usually provided in respiratory gas analyzers to make exhaling into the respiratory gas analyzer more comfortable. Furthermore, the mouthpiece is often a disposable item that is replaced before each use of the respiratory gas analyzer for hygienic reasons or is used only for a specific subject.

[0018] Within the respiratory gas analyzer, the gas flow branches into an air guide path 11 containing a humidity regulating system element 3 (humidity regulator), which in particular contains activated carbon, and into an air guide path 12 without such a humidity regulating system element.

[0019] The air guide path 12 without a humidity-regulating element is, in particular, the actual measuring path for the gas sample, via which the gas sample is guided for gas analytical testing at the gas sensor 4. The gas sensor 4 can be, for example, an electrochemical gas sensor or a sensor based on field-effect transistors (FETs). Switching back and forth between the air guide paths 11 and 12 can be carried out using means not shown in detail here, for example, via appropriately switchable valves or pumps. After a subsequent reunion of the air guide paths 11 and 12, the gas sample reaches the gas sensor 4, where the analytes in the gas sample are measured. In this exemplary embodiment, the humidity sensor 5 is connected upstream of the gas sensor 4. The humidity sensor 5 can, for example, be a capacitive humidity sensor.In other embodiments, the humidity sensor can be connected downstream of the gas sensor 4. In other embodiments, no humidity sensor is provided.

[0020] To carry out the proposed method with checking the humidity level, the gas sample is first fed to the breath gas analyzer in a known manner. The gas sample can be fed to the device by active exhalation by the test subject, which may be pump-assisted. In a so-called pseudo-measurement, which can also be used for the purposes of the invention, the gas sample is fed by pump-assisted suction of ambient air. As the gas sample enters the device, its chemical and / or physical properties can first be modified using the optional mouthpiece 2, which is equipped, for example, with filters and / or converters (for example, for converting NO to NO2). Depending on the design, purpose, and function of the breath gas analyzer, the sample can, for example, be dried or humidified and / or oxidized or reduced.In addition to humidity, other factors can...

[0021] Properties of the gas sample, such as temperature, pressure, or similar, are determined using suitable sensors as it enters the device. It can be particularly advantageous to use the measured humidity to check whether the desired dehumidification performance of a mouthpiece in use is sufficient. If the measured dehumidification performance is insufficient, for example, the user can be prompted to change the mouthpiece.

[0022] In a second step, the gas sample is passed through the humidity-regulating system element 3 to check the humidity level at the gas sensor. For this purpose, the gas sample is passed through path 11 via the humidity-regulating system element 3 by appropriately switching valves or pumps. This influences the moisture content of the gas sample. The humidity-regulating system element is preferably a humidity regulator with activated carbon, which, in addition to humidity regulation, also has a gas-filtering function that can also be used for other purposes. If the device was stored in a very humid environment before the measurement, the activated carbon will release moisture into the gas sample. If the device was stored in a dry environment before the measurement, the activated carbon will remove moisture from the gas sample.Depending on the moisture content of the gas sample and the moisture content of the activated carbon, the moisture content of the gas sample is influenced to a greater or lesser extent. The moisture content of the gas sample upon arrival at gas sensor 4 is measured in the . Fig. 1 indicated by X and can usually be specified as relative or absolute humidity. To carry out the proposed method, in this second stage the gas sample is temporarily passed along path 11 and temporarily along path 12, the actual measurement path without humidity regulation. It is particularly useful to first pass the gas sample along path 11 and then along path 12 so that there is no need to switch again for the actual gas analytical measurement at gas sensor 4. As a rule, it is sufficient if the gas sample is passed first along path 11 and then along path 12 for a few seconds. This can therefore also be done during the test subject's exhalation (unless a pseudo-measurement is already planned for this process). In principle, however, it is also possible to first pass the gas sample along path 12 and then along path 11 in order to generate a measurable difference.Furthermore, it is possible to switch back and forth between paths 11 and 12 several times within a measurement in order to evaluate multiple humidity jumps. Depending on which path is controlled—i.e., path 11 via humidity regulator 3 or path 12 without humidity regulator—a different humidity X is established in the area of ​​gas sensor 4. Fig. 2 represents this progression of humidity X over time. In the first phase 21, the air is guided via path 11. In this case, humidity X is relatively low. After switching to the further air guide path 12 in phase 22, the gas sample is guided past humidity regulator 3, resulting in a humidity jump of amplitude ΔX. The humidity state of the gas sensor can be deduced from ΔX. In the example shown here, humidity X rises suddenly to a higher value when switching to path 12. From this, it can be concluded that the device was stored in a dry place because the humidity regulator was able to remove the moisture from the gas sample. How the humidity jump is actually evaluated depends on the switching direction of the air guide paths and the mathematical evaluation method.In general, it can be assumed that when the device is stored in a dry environment, the humidity regulator is at its full capacity, and therefore a significant humidity jump can be expected when switching between the airflow paths. In this case, the humidity level at the gas sensor is normal due to the dry storage conditions.

[0023] In a third stage, the actual determination of the humidity state at the gas sensor takes place. To evaluate the sensor state, the humidity jump ΔX is preferably analyzed as a feature in the gas sensor's sensor signal and converted into a humidity state Z = f(ΔX). This can be done, for example, using a transient analysis or a Fourier transformation of the signal. In order for such an analysis of the gas sensor's sensor signal to be possible, a gas sensor with cross-sensitivity to humidity and a short response time should be used. In other embodiments, the humidity state of the sensor can also be determined in particular using a dedicated humidity sensor 5, wherein the humidity sensor 5 can be connected upstream or downstream of the gas sensor 4. Depending on the evaluation method, the humidity sensor can measure either the humidity X directly or the humidity jump ΔX.

[0024] In a fourth stage, any necessary corrective and / or compensation measures can be initiated if the humidity level falls outside specified limits. If predefined limits for the humidity level are exceeded or undershot, for example, the device can be blocked for further measurements, a request for recalibration of the device can be issued, the gas sensor can be dried, for example, by actively heating it using an integrated heating element (if provided), or the measured value of a breath gas analysis measurement can be corrected depending on the humidity level of the gas sensor.

[0025] Fig. 3 illustrates, by way of example, a flowchart for detecting and correcting the humidity status of the gas sensor in a respiratory gas analyzer. After switching on 101 the respiratory gas analyzer, an initial check 102 of the device is performed, checking in particular whether a maximum tolerable storage time has been exceeded, whether the time is set and whether a battery change should be carried out, or whether other parameters indicate that the device was stored under unfavorable environmental conditions. Step 102 serves to check whether the device has not been used for a long time and could therefore be in a changed and / or critical humidity status. Based on this check 102, step 103 queries whether a humidity check or a check of the humidity status of the gas sensor is required. If this is not the case, the device is ready for measurement (step 104).If query 103 indicates that a moisture check is required, the actual moisture check is started with step 105. The start of the moisture check 105 is shown in the lower part of the flow chart. Fig. 3shown again separately. After the start of the test 105, in a first phase in this embodiment a pseudo measurement 106 is carried out by sucking in air from the environment. Here the current device status is checked in step 107. In a second phase 108 the mouthpiece status is checked in step 109 and in step 110 it is determined whether a new mouthpiece is required. If this is the case, after replacing the mouthpiece a return to step 106 occurs. If this is not the case, the program proceeds to the third phase 111. If necessary it is possible to proceed directly from step 109 to the third phase 111. In the third phase 111, in step 112 it is analyzed based on ΔX in the manner described above whether the humidity status of the gas sensor exceeds or falls below predeterminable limit values.Based on this evaluation, step 113 queries whether any derivable measures are required, such as baking out the sensor. If this is not the case, the normal gas analytical measurement cycle can take place in step 114. If the query in step 113 reveals that measures are required, step 115 can involve, for example, cleaning the gas sensor to remove the interfering moisture or baking out the sensor. As an alternative to such moisture-regenerating measures, the measured value can be corrected to compensate for the influence of moisture in a subsequent measurement, or recalibration or, if necessary, blocking the respiratory gas analyzer for further measurements. Phases 106, 108, and 111 can be repeated as a cycle for checking the sensor status, for example, to check the effectiveness of cleaning the sensor in step 115.

Claims

1. Method for operating a respiratory gas analyser after prolonged storage, the respiratory gas analyser comprising at least one gas sensor (4) and at least one humidity sensor (5) and at least one humidity-regulating system element (3) that is arranged in an air conduction path (11), characterized in that the humidity state of the gas sensor (4) is checked, with a humidity of a gas sample in the respiratory gas analyser being determined using the humidity sensor (5) and by virtue of evaluating a measured difference in the different influences on the humidity of its gas sample in air conduction via the air conduction path (11) with the humidity-regulating system element (3) in comparison with air conduction via a humidity-regulating-element-free air conduction path (12) which is in parallel with the air conduction path (11) and via which the air flow is guided in a gas analytical measurement.

2. Method according to Claim 1, characterized in that the humidity-regulating system element (3) contains activated carbon.

3. Method according to Claim 1 or Claim 2, characterized in that the difference is acquired on the basis of measurements taken by the gas sensor (4).

4. Method according to any of the preceding claims, characterized in that the humidity sensor (5) is disposed upstream and / or downstream of the gas sensor (4).

5. Method according to Claim 4, characterized in that the difference is acquired on the basis of measurements taken by the humidity sensor (5).

6. Method according to any of the preceding claims, characterized in that measures for regulating the humidity state and / or for compensating for said humidity state in measurements for respiratory gas analysis are optionally initiated.

7. Method according to Claim 6, characterized in that the measures to be optionally initiated comprise at least one of the following measures: - blocking the respiratory gas analyser from taking further measurements, - recalibrating the respiratory gas analyser, - drying the gas sensor (4), - drying the humidity-regulating system element (3) and - correcting the measured value of a respiratory gas analytical measurement.

8. Method according to any of the preceding claims, characterized in that the humidity state is checked regularly.

9. Method according to any of the preceding claims, characterized in that the humidity state is checked during a regular respiratory gas measurement.

10. Method according to any of the preceding claims, characterized in that the humidity state is checked during a pseudo-measurement.

11. Respiratory gas analyser having at least one gas sensor (4) and at least one humidity sensor (5) and at least one humidity-regulating system element (3) that is arranged in a preferably switchable air conduction path (11), characterized in that the respiratory gas analyser is configured to perform a method according to any of Claims 1 to 10.