Method and device for measuring gas samples in bypass, and medical device

Abstract

The invention relates to a method and a device for measuring gas samples in bypass, and to a medical device. According to the invention, the intake rate for taking gas samples from the main flow can be adjusted in such a way that the effective temporal resolution of the measurement of individual gas samples can be significantly increased.

Description

[0001] Method and device for measuring gas samples in the side stream and medical device

[0002] The invention relates to a method for measuring gas samples in a secondary flow, wherein gas samples removed from a main flow are measured by means of at least one suction pump.

[0003] Furthermore, the invention relates to a device for measuring gas samples in the secondary flow, with which gas samples removed from a main flow are measured with the aid of at least one suction pump.

[0004] Furthermore, the invention relates to a medical device comprising a device for measuring gas samples in the side stream.

[0005] In various applications it is of interest to determine the course of certain parameters of a flowing gas or gas mixture, for example the proportion of certain components of a flowing gas mixture, over time or at certain points in time.

[0006] For example, in the course of medical patient monitoring or patient ventilation, the determination of various gas concentrations in both the air supplied to the patient and in the exhaled air is of interest. For example, the carbon dioxide (CO2) or oxygen (O2) concentration is determined using suitable sensors. The determination of the concentration of other gases in the exhaled air, such as VOCs (volatile organic compounds), hydrogen, or anesthetic gases, is also of interest in certain applications. Depending on the application, a high-resolution measurement of the respective gas is required.

[0007] The respiratory cycle of humans and other similarly breathing creatures consists of inspiration and expiration. When ambient air is inhaled, the inspiratory oxygen concentration (fiO2) is approximately 21 vol% and the CO2 concentration (fiCO2) is almost 0 vol%. At the beginning of expiration, the CO2 content typically rises rapidly and reaches a plateau with a lower gradient. At the end of expiration, an end-tidal oxygen concentration (etO2) of approximately 16 vol% remains in the exhaled air, while the CO2 concentration has risen to an end-tidal value (etCO2) of approximately 5 vol%. A respiratory cycle consisting of expiration and inspiration typically lasts between 2 and 5 s in adults. In newborns, the respiratory cycle is significantly shorter at 1 to 2 s (30 to 60 breaths / minute). For special ventilation patterns, significantly higher respiratory rates are used, such as:120 breaths / minute with CCSV (Chest Compression Synchronized Ventilation) or up to 25 breaths / second with HFO ventilation (High Frequency Oscillation).

[0008] In medicine, for example, it is common practice to determine the CO2 content in a patient's exhaled air while they are breathing. Various parts of the measured curve can be relevant. The most important parameter is usually the end-tidal CO2 value (etCO2). However, for diagnostic purposes, the steepness of the curve at the beginning of expiration or during the expiratory plateau can also be relevant. For an O2 measurement, however, not only the end-tidal concentration (etO2) but also the inspiratory concentration (fiO2) would be essential. Whether it is possible to determine the various relevant parameters from the measured respiratory gas curve depends largely on the respiratory rate and the temporal resolution of the measurement. The temporal resolution of the measurement is determined both by the measuring module itself and by the pneumatic design of the system.

[0009] According to the state of the art, there are basically two pneumatic methods for measuring the CO2 content in respiratory air that are used in connection with patient ventilation. The respiratory gas flows through a tube system of the ventilator towards or away from the patient, depending on the breathing phase. In the so-called mainstream method, the patient's entire respiratory gas is analyzed directly in or on this tube system and thus in the mainstream of the respiratory gas. In the sidestream method, in contrast, a sample gas is extracted from the mainstream and analyzed. In the sidestream method, the sample gas is usually taken close to the patient so that both the inhaled and exhaled gas can be analyzed. With the help of a suction pump, the sample gas is fed through a suction tube to the measuring point in the gas analysis module. The gas analysis module is usually located away from the patient in the ventilator or monitoring device.The extraction hose is typically up to three meters long. Mixing of the sample gas in the extraction hose and the various pneumatic components in the bypass flow path limits the slope of the measured CO2 curve, resulting in a lower temporal resolution of the overall system than in a mainstream measurement.

[0010] CO2 sensors based on infrared spectroscopy are often used as gas analysis modules. The rise time t(10%-90%) of these sensors, for example, is approximately 100 ms. O2 sensors suitable for compact ventilators are considerably slower. Electrochemical cells for O2 measurement, for example, provide a rise time of approximately 2 s or more.

[0011] The temporal resolution of the overall system is comprised of the rise time of the measuring module in combination with the pneumatic system that creates mixing of the sample gas. The temporal resolution of the overall system must be sufficiently high to determine the parameters in the CO2 or O2 curve that are relevant for the application. With state-of-the-art systems, for example, using an electrochemical cell, the determination of the etO2 or fiO2 value is not feasible in most applications. With a CO2 sensor based on infrared spectroscopy, the reliable determination of fiCO2 and etCO2 is already possible for standard applications. The temporal resolution of the CO2 measurement becomes critical in neonatology or when using special ventilation patterns. A higher temporal resolution of the CO2 measurement would also be desirable in diagnostics, when, for example, the steepness and duration of the increases are to be determined, and not just fiCO2 and etCO2.

[0012] The state of the art is that the temporal resolution of the measurement is improved by increasing the suction rate. The suction pump is usually operated at a constant suction rate. Simply increasing the suction rate can improve the effects generated by the tubing system, but not increase the temporal resolution of the analysis module itself. Furthermore, a permanent increase in the suction rate is only possible to a limited extent, since too large a suction volume disrupts the operation of the ventilator. Especially in patients with a low tidal volume, usual suction rates are on the order of magnitude of the ventilation flow and therefore cannot be neglected. It is an object of the invention to create a device for measuring gas samples in the sidestream that enables a sectionally improved resolution of the measurement.

[0013] This object is achieved according to the invention by a device according to claim 1.

[0014] Furthermore, it is an object of the invention to provide a medical device that enables a sectionally improved resolution of the measurement.

[0015] This object is achieved according to the invention by a medical device according to patent claim 19.

[0016] It is a further object of the invention to provide a method for measuring gas samples in the side stream, which enables a sectionally improved resolution of the measurement.

[0017] This object is achieved according to the invention by a method according to patent claim 21.

[0018] Advantageous embodiments of the invention are claimed in the dependent claims.

[0019] The features of a device for measuring gas samples in the side stream, a medical device and a method for measuring gas samples in the side stream disclosed below are part of the invention both individually and in all executable combinations.

[0020] Fundamental to the invention is the temporary increase of the suction rate for extracting gas samples from a gas stream in order to increase the effective resolution of the measurement of these gas samples.

[0021] A device according to the invention for measuring gas samples in the bypass flow has at least one gas storage device, at least one measuring device and at least one suction pump.

[0022] In embodiments of the invention, the at least one gas reservoir, the at least one measuring device, and the at least one suction pump are connected in series or correspondingly interconnected. In other embodiments of the invention, parallel connections of one or more of the gas reservoir, measuring device, and suction pump components are provided.

[0023] For example, the invention allows for a parallel connection of entire strings consisting of a gas reservoir, a measuring device, and an extraction pump, or for a parallel connection of several measuring devices with a shared gas reservoir and a shared extraction pump, or individually assigned extraction pumps. By sequentially timing the high-resolution sections from parallel measuring strings, in corresponding embodiments of the invention, a high-resolution measurement can be realized over the entire course of a main flow by combining the high-resolution sections of the individual strings.

[0024] In embodiments of the invention, the gas storage is at least partially realized by a hose line that connects a sampling point on the main stream to the measuring device.

[0025] The measuring device has at least one measuring cell and, in embodiments of the invention, is designed to detect a gas in a gas sample and / or to measure the proportion of at least one gas in a gas sample. In principle, however, in corresponding embodiments of the invention, any property of the gas sample that can be measured using a corresponding measuring device can be measured.

[0026] In embodiments of the invention, the at least one measuring device is designed to detect and / or determine the proportion of CO2, O2, N2O, argon, N2, CO, water vapor, volatile organic components (VCO), and / or an anesthetic gas in the gas mixture of a gas sample. Depending on the application, however, other gases are also conceivable.

[0027] The measuring device has a specific sampling rate and a specific rise time for each measured variable.

[0028] In embodiments of the invention, the measuring device comprises a CO2 sensor and / or an O2 sensor.

[0029] A CO2 sensor can, for example, be implemented using infrared spectroscopy and, in some embodiments, have a sampling rate of 40 Hz and / or a rise time of 100 ms. An O2 sensor can, for example, be implemented as an electrochemical cell and, in some embodiments, have a rise time of approximately 2 to 10 s.

[0030] According to the invention, the suction rate can be adjusted either by switching between at least two suction pumps using at least one valve, wherein the different suction pumps are set to at least two different suction rates, or by adjusting the suction rate of at least one suction pump.

[0031] The adjustment of the suction rate can be carried out continuously or gradually in some embodiments and abruptly in other embodiments of the invention.

[0032] The at least one suction pump is designed to suck gas samples from the main flow through the gas storage and into the at least one measuring cell of the at least one measuring device.

[0033] In corresponding embodiments, at least one suction pump has an adjustable suction rate.

[0034] In preferred embodiments of the invention, the suction rate of at least one suction pump can be quickly adjusted. A rapid adjustment of the suction rate within the meaning of this document is an adjustment of the suction rate from 50 ml / min to 100 ml / min in 0.5 s, and in particularly preferred embodiments of the invention, from 0 ml / min to 300 ml / min in a maximum of 0.2 s.

[0035] Depending on the specific application, it is crucial that the suction rate of the respective suction pump can be varied quickly enough and precisely depending on the duration of individual segments in the main flow to be measured. For example, in an application in neonatal ventilation technology with a respiratory cycle of approximately 1 second, the suction rate must also be adjustable quickly enough between at least two different values ​​within this respiratory cycle.

[0036] In embodiments of the invention, particularly in applications in ventilation technology, the at least one suction pump has a suction rate adjustable between 0 ml / min and at least 300 ml / min, particularly preferably between 0 ml / min and 1 L / min. This allows suitable suction rates to be set for different patient types (newborns, infants, adults) while taking into account the respective expected ventilation flow. Accordingly, the rapid adaptability of the suction rate in corresponding embodiments also applies to adjusting the suction rate by switching between at least two suction pumps with different suction rates using at least one controllable valve or switching valve.

[0037] In embodiments of the invention, the extraction rate is generally set to a first value W1 and can be temporarily increased to a value W2 to increase the effective resolution of the gas sample measurement. W2 is thus a higher extraction rate than W1.

[0038] In embodiments of the invention, W1 > 0, so that gas samples are continuously extracted from the main stream. In corresponding embodiments of the invention, continuous measurement of gas samples from the main stream is possible.

[0039] In embodiments of the invention, more than two different discrete values ​​for the suction rate can be set or the suction rate can be continuously varied.

[0040] In embodiments of the invention, the suction rate is adjustable at least between a first value W1 from a first value range (low value range) and at least a second higher value W2 from a second value range (high value range), wherein W1 is smaller than W2.

[0041] In embodiments of the invention, the smallest value of the second value range is greater than the highest value of the first value range.

[0042] In embodiments of the invention, the extraction rate is adjustable between at least two different high values ​​W2.1 and W2.2 from the second value range and at least one low value W1 from the first value range.

[0043] In embodiments of the invention, at least three different value ranges are defined, from each of which at least one value for the suction rate can be set.

[0044] In embodiments of the invention, particularly in applications in ventilation technology, the value W2 or a high value for the suction rate is selected to be greater than 70 ml / min, and the value W1 or a low value is selected to be less than or equal to 70 ml / min. In preferred embodiments, particularly in applications in ventilation technology, the value W2 or a high value for the suction rate is in a range from approximately 200 ml / min to 1 L / min (second value range).

[0045] In embodiments of the invention, the smallest value of the first value range is selected as 0 ml / min (no volume flow). In other embodiments of the invention, the smallest value of the first value range is greater than 0 ml / min.

[0046] In embodiments of the invention for applications in ventilation technology, the parameter range for the W2 value or a high value for the suction rate is categorized according to patient type. Patient types can include, for example, newborns, infants, and adults.

[0047] In embodiments of the invention, the maximum value of the suction rate for newborns is about 300 ml / min, not exceeding an average suction rate of about 70 ml / min, for infants about 500 ml / min, not exceeding an average suction rate of about 90 ml / min, and for adults about 1 L / min, not exceeding an average suction rate of about 170 ml / min.

[0048] Furthermore, the maximum possible suction rate in ventilation applications depends on the respective breathing phase, because, as in all applications, the suction rate is ultimately limited by the mainstream flow. At the end of expiration, for example, a patient's expiratory flow is relatively low, and the sidestream cannot suction more than the mainstream.

[0049] Adjusting the extraction rate means that more gas mixture is extracted from the main flow in a time period with a higher extraction rate than in a time period with a lower extraction rate. In the gas storage device, which is usually implemented primarily in the form of a hose, the gas samples extracted from the main flow at a specific time are temporarily stored chronologically one after the other, neglecting a certain amount of mixing. A gas sample extracted at a high extraction rate therefore stays in the hose for a disproportionately long time in relation to the actual course in the main flow compared to a gas sample extracted at a lower extraction rate. With a temporally constant sampling of the respective gas sample in the measuring cell, this means an increase in the number of actual samples of the gas sample extracted at the higher extraction rate if it is conveyed through the measuring cell at a lower volume flow.According to the invention, the effective resolution of the measurement is thereby improved for gas samples extracted at a higher extraction rate.

[0050] In advantageous embodiments of the invention, for an undistorted representation of the measurement signal of the at least one measuring device, the time-dependent output signal can be compensated taking into account the extraction rate of the respective gas sample.

[0051] In preferred embodiments of the invention, the setting of the extraction rate is coordinated with the storage volume of the associated gas storage device such that the extraction rate can be set to a value W1, or a value from the first low value range, when a gas sample extracted with the value W2, or a higher extraction rate selected from the second value range, has reached the area of ​​at least one measuring cell of the measuring device. This extends the time during which the respective gas sample is sampled in the measuring cell, thus improving the effective resolution of the measurement of the respective gas samples.

[0052] In embodiments of the invention, the volume of the gas storage is at least half as large as the total volume of the gas samples extracted over one (breathing) cycle.

[0053] In embodiments of the invention, the device for measuring gas samples in the secondary flow comprises a synchronization device for synchronizing the extraction rate with at least one parameter with respect to the main flow (main flow parameter).

[0054] In embodiments of the invention, the main flow parameter is defined as a pressure value, volume flow value, temperature value or as a proportion of a specific gas in the gas mixture of the main flow.

[0055] In alternative embodiments, the main current parameter can also be given by indirect values / measurement signals that allow a corresponding conclusion to be drawn about the main current.

[0056] For example, pressure or volume flow measurements from the sidestream, predefined operating parameters of a mainstream device that influence the gas flow in the mainstream, or a (trigger) signal from a separate detection device arranged in the area of ​​the mainstream are suitable for this purpose. In ventilation technology applications, the ventilator is such a mainstream device that influences the gas flow in the mainstream, for example, through the parameters of the predefined ventilation pressure and / or the volume flow for ventilation. A detection device in the area of ​​the mainstream can be a spontaneous breathing trigger in such applications. Control signals from a ventilator that indicate, for example, the start or end of the inspiration or expiration phase, can also be used accordingly in embodiments of the invention.

[0057] In embodiments of the invention, at least two of the above-mentioned parameters are combined with each other or at least one of the above-mentioned parameters is combined with at least one further parameter for synchronizing the suction rate using the synchronization device.

[0058] In embodiments of the invention, the synchronization device is designed to detect a relevant section in the main flow by evaluating at least one main flow parameter, wherein the suction rate upon detection of a relevant section in the main flow can be set to a suction rate with the value W2, or a suction rate selected from the second high value range.

[0059] In embodiments of the invention, the suction rate can be set to the suction rate W1 or to a suction rate selected from the low value range after the detection of the end of a relevant section or after the expiration of a predetermined time.

[0060] In embodiments of the invention, the occurrence of a relevant and / or an irrelevant section in the main stream can be predicted, so that the suction rate can be adjusted accordingly.

[0061] In embodiments of the invention, the extraction rate can be synchronized with the aid of the synchronization device with regard to at least one relevant section in a cyclical main flow in such a way that in the at least one relevant section of the cycle the extraction rate can be set to a higher value W2, or a value selected from the second value range, and in the at least one remaining section of the cycle to a value W1, or a value selected from the first lower value range, while the gas sample or gas samples of the relevant section is or are extracted from the main flow. In embodiments of the invention, it is thus possible to define a plurality of relevant sections for sampling from the main flow, which sections can be detected and / or predicted accordingly with the aid of the synchronization device, such that the extraction rate for the relevant sections can be set to a value W2, ora higher value selected from the second value range, or to values ​​from the high value range that differ for the individual relevant sections.

[0062] In embodiments of the invention, the extraction rate can be set to a corresponding value W2 or a value selected from the second value range depending on the expected dynamics of the at least one measured value to be recorded in a relevant section of a possibly cyclical main flow and taking into account the rise time of the measuring device, so that a measurement of the at least one measured value with a sufficiently effective temporal resolution is possible.

[0063] In embodiments of the invention in which one part of the cycle of the main flow is relevant (e.g. expiration in a breathing cycle) and the other part of the cycle (e.g. inspiration in a breathing cycle) is irrelevant, the relevant gas sample can be extracted from the main flow at an extraction rate W2 or a high extraction rate selected from the second value range and measured in the measuring device at an extraction rate W1 or a low extraction rate selected from the first value range. Conversely, the irrelevant gas sample can be extracted at a low extraction rate and measured at a high extraction rate. The extraction rates for the relevant and irrelevant parts of the cycle are preferably selected such that the extracted volume of the gas samples for the relevant part is the same as the extracted volume of the gas samples for the irrelevant part.In a setup with a serial arrangement of gas storage, measuring device and suction pump, it is ensured that the respective setting of the suction rate remains constant for the entire length of the measurement of the gas sample(s).

[0064] In preferred embodiments of the invention, in which switching takes place between two discrete values ​​W1 and W2 for the extraction rate, the relationships apply that the quotient of the duration of the irrelevant and the relevant main flow section (tjrrelevant / t_relevant) is equal to the quotient of the extraction rates W2 and W1 (W2 / W1) and that the product of the extraction rate and the duration of the main flow section extracted thereby is equal to the extracted sample volume in the gas reservoir. Here, W2 > W1 and preferably tjrrelevant > t_relevant. The two extraction rates are selected in embodiments of the invention such that, at the resulting average extraction rate, the flow time of a gas sample through the gas reservoir from the sampling point to the measuring device corresponds approximately to (N+1 / 2) times the main flow period (breathing period), where N is a natural number.The edge steepness and sampling rate of the relevant cycle half are thus increased at the expense of the edge steepness and sampling rate of the irrelevant cycle half.

[0065] In embodiments of the invention in which two relevant sections (e.g., the expiratory rise and the etCO2 value at the end of expiration) are defined in each main flow cycle (e.g., respiratory cycle), and the two sections in between are irrelevant, the flow time cannot correspond to (N+1 / 2) times the main flow period (e.g., respiratory period), as in the first example, because then the first relevant sample would potentially be measured with higher temporal resolution at the expense of the second relevant sample. In this case, the extraction rates in embodiments of the invention are selected such that the flow time of a gas sample through the gas reservoir corresponds approximately to (N+1 / 4) times the main flow period (e.g., respiratory period).

[0066] In a further embodiment, the cycle of the periodically varied extraction rate is n times the main flow cycle (e.g., the breathing period), where n is a natural number. Then, at least one relevant gas sample is analyzed with increased resolution only every n main flow cycles. This allows the resolution enhancement factor to be increased.

[0067] In embodiments of the invention, the suction rate is synchronized to relevant sections in a breathing cycle by means of the synchronization device, wherein the main flow is provided by the breathing gas flowing through a breathing tube during the ventilation of a patient.

[0068] In the corresponding embodiments of the invention, the hose line of the gas storage device serves to transport a gas sample from the sampling point in the main stream to the measuring device. In this way, a certain amount of mixing of a gas sample with neighboring gas samples in the hose line is unavoidable, so that the measurement of each gas sample is distorted by neighboring gas samples with different gas fractions.

[0069] This problem is also addressed by the inventive increase in the extraction rate for gas samples from relevant sections of the main flow by increasing the volume of the relevant gas sample in the gas reservoir compared to a constant extraction rate. For a hose with a specific inner diameter, the length of the relevant gas samples in the hose is thus extended, so that they predominantly only mix with neighboring gas samples in the peripheral areas. When measuring the entire gas sample, a higher degree of realism can be achieved.

[0070] In embodiments of the invention, the mixing of adjacent gas samples is further reduced by the tubing having the smallest possible inner diameter.

[0071] In ventilation technology applications, an inner diameter of the hose line is selected in a range of approximately 1 mm to 2 mm, particularly preferably approximately 1.5 mm.

[0072] Depending on the application of the invention and the implemented embodiment, certain requirements may apply to the minimum volume of the gas storage device and thus also of the hose line.

[0073] In embodiments of the invention for applications in ventilation technology in which at least one relevant range of the cyclic respiratory air flow is to be measured with increased resolution, the volume of the gas reservoir is at least half of the sample gas extracted from the main flow in one breathing cycle in order to be able to implement a synchronization of the extraction rate such that a gas sample extracted at a high extraction rate can be conveyed through the measuring cell of the corresponding measuring device at a low extraction rate.

[0074] In embodiments of the invention, the volume of the gas storage is approximately 2 ml to 10 ml.

[0075] For a typical configuration in ventilation technology, with an average suction rate of 100 ml / min and a breathing cycle length of 2 s, the minimum volume of the gas storage device is approximately 3 ml. With a hose length of 2 m (typically about 2 to 3 m), this results in a value of approximately 1.4 mm as the minimum inner diameter of the hose line.

[0076] In embodiments of the invention, the device for measuring gas samples in the bypass stream comprises further pneumatic components such as a water trap.

[0077] In embodiments of the invention, the device for measuring gas samples in the bypass flow comprises at least one switching valve in the region of at least one measuring device, with which the suction in the region of the measuring device can be at least temporarily deactivated. This allows individual gas samples to be measured for a longer period.

[0078] In embodiments of the invention, the device for measuring gas samples in the bypass flow has at least one switching valve in the region of at least one measuring device, with which the extracted gas flow can be switched back and forth between at least two different measuring devices or at least one measuring device and an exhaust air duct, so that it can be guided into a respective measuring device depending on the valve position.

[0079] In embodiments of the invention, at least two switching valves are used, which are arranged in such a way that the same gas sample can be measured successively in different measuring devices and / or different gas samples can be measured independently of one another in parallel-connected measuring devices.

[0080] In an application example in ventilation technology, the values ​​for fiO2, etO2, and etCO2 are to be measured. The other temporal profiles (between the fi and et values) of the concentration values ​​are irrelevant for oxygen, but relevant for CO2.

[0081] In embodiments of the invention, the device for measuring gas samples in the bypass flow comprises a communication device for communicating with a main flow device. This allows operating parameters of the main flow device to be synchronized with measured values ​​of the device for measuring gas samples in the bypass flow and / or allows the extraction rate of the device for measuring gas samples in the bypass flow to be taken into account for the main flow device.

[0082] A medical device according to the invention has at least one device according to the invention for measuring gas samples in the side stream.

[0083] In embodiments of the medical device according to the invention, at least the measuring device and / or the suction pump of the device for measuring gas samples in the secondary flow are integrated into the housing of the medical device.

[0084] In embodiments of the medical device according to the invention, it is connected to the at least one measuring device and / or the synchronization device for transmitting data.

[0085] In embodiments of the invention, the medical device is designed as a ventilator, a patient monitor, or a defibrillator with a monitoring function. In embodiments of the ventilator according to the invention, the current suction rate of the device for measuring gas samples in the sidestream can be retrieved from the ventilator and used to compensate for the volume or flow measurement and / or the ventilation volume.

[0086] A method according to the invention for measuring gas samples in the side stream comprises at least the following method steps:

[0087] - Suction of gas samples from a main stream by means of at least one suction pump through at least one gas storage device, measuring the gas samples by means of at least one measuring device, setting the suction rate to a value W2 for at least one time period of the measurement in order to take at least one gas sample, setting the suction rate of the suction rate to a second value W1 for at least one other time period of the measurement in order to take at least one further gas sample and / or to measure a gas sample sucked out at the suction rate W2, where W1 is less than W2.

[0088] In embodiments of the invention, the suction rate is adjusted by setting the suction rate of at least one suction pump and / or switching at least one controllable valve or a switching valve between at least two suction pumps with different suction rates.

[0089] In embodiments of the invention, the adjustment of the suction rate occurs abruptly or continuously or smoothly.

[0090] In embodiments, the value W1 for the extraction rate is selected from a first value range and the value W2 from a second value range.

[0091] In embodiments of the invention, the highest value of the first value range is smaller than the lowest value of the second value range.

[0092] In advantageous embodiments of the method according to the invention, the extraction rate is adjusted such that a gas sample extracted from the main flow at an extraction rate W2 is conveyed through the at least one measuring device at an extraction rate less than W2. In particularly advantageous embodiments of the method according to the invention, the extraction rate is adjusted such that a gas sample extracted from the main flow at an extraction rate W2 is conveyed through the at least one measuring device at an extraction rate W1.

[0093] In embodiments of the invention, the extraction rate is adjusted between at least two different high values ​​W2.1 and W2.2 from the second value range and at least one low value W1 from the first value range.

[0094] In embodiments of the invention, at least three different value ranges are defined, from each of which at least one value for the suction rate is set.

[0095] In embodiments of the invention, in particular in applications in ventilation technology, the value W2 or a high value for the suction rate is selected to be greater than 70 ml / min and the value W1 or a low value less than or equal to 70 ml / min.

[0096] In embodiments of the method according to the invention, the adjustment of the suction rate is carried out by means of a synchronization device taking into account at least one main flow parameter such that at least a relevant section of the main flow is suctioned with a suction rate W2, or a suction rate selected from the second value range.

[0097] In embodiments of the invention, synchronization using the synchronization device is carried out by detecting or receiving at least one main flow parameter, analyzing the at least one main flow parameter with regard to the presence of a first decision criterion corresponding to the presence of a relevant section in the main flow, and setting the suction rate to a value W2, or to a value selected from the second value range if the first decision criterion is present.

[0098] Depending on the dependencies between the at least one main flow parameter or the occurrence of the respective decision criterion with regard to the at least one main flow parameter and the relevant section of the main flow, the extraction rate is set to the value W2, or to a value from the second value range, in embodiments of the invention with a specific time delay. This allows for any existing delays between the at least one evaluated main flow parameter and a section of the main flow relevant for the measurement to be taken into account, whether caused by design influences, such as the arrangement of a sensor detecting the main flow parameter and the sampling point on the main flow, or by properties of the main flow itself.

[0099] In embodiments of the invention, the average extraction rate is determined as a function of the gas storage volume and a cycle length of the main flow.

[0100] If necessary, the gas storage volume and / or cycle length are determined in advance. In ventilation applications, this can be done, for example, by the following steps:

[0101] 1. Switch off the extraction system

[0102] 2. Recording the ventilation cycle, e.g. using a pressure sensor

[0103] 3. Start the extraction with a known constant extraction rate

[0104] 4. Evaluation of the first measured values ​​recorded using at least one measuring device

[0105] 5. Determine the length or volume of the gas storage (e.g. the hose) from the running time of the gas through the gas storage from the sampling point to the measuring device

[0106] In embodiments of the invention, the tube length is determined by utilizing a known change in the gas composition or the concentration of a specific gas component. For example, in applications in ventilation technology, suction starts with a detected inspiration, so that the CO2 concentration in the corresponding gas sample in the tube is very low. For example, by detecting a pressure change, the change between inspiration and expiration and vice versa can be detected, allowing it to be determined how long the gas sample from a known breathing phase takes to pass through the gas reservoir into the measuring device at a known suction rate.

[0107] In embodiments of the invention, the measured values ​​of the respective gas samples recorded by means of the at least one measuring device are computationally equalized over time, taking into account the respective extraction rates, in order to realistically represent the temporal progression.

[0108] In embodiments of the invention, the measured values ​​of the respective gas samples acquired using the at least one measuring device are output and / or displayed in a distorted or preferably corrected state. In embodiments of the invention, at least one characteristic value (e.g., fiO2, fiCO2, etO2, or etCO2) is determined from the corrected curve of the measured values.

[0109] In embodiments of the method according to the invention, the suction rate is synchronized to relevant sections in a breathing cycle by means of a synchronization device, wherein the main flow is provided by the respiratory gas flowing through a ventilation tube during the ventilation of a patient.

[0110] In embodiments of the method according to the invention for measuring gas samples in the side stream, a device according to the invention for measuring gas samples in the side stream or a medical device according to the invention is used.

[0111] In embodiments of the method according to the invention, the current suction rate of the at least one suction pump is retrieved from the ventilator and used to compensate for the volume or flow measurement and / or the ventilation volume.

[0112] In embodiments of the method according to the invention, the features disclosed with regard to the device according to the invention for measuring gas samples in the side stream in the various disclosed embodiments are implemented / used accordingly.

[0113] Among other things, the invention can be used in the following application examples from ventilation technology.

[0114] According to the invention, the etO2 value can be determined in an e.t.O. measurement using a commercially available O.t.O. module, e.g., an electrochemical cell, which is actually too slow for a breath-resolved measurement. The relevant gas sample, or the relevant segment of the mainstream, in this case is the end of expiration. The remainder of the respiratory cycle is less relevant and can therefore be aspirated at a lower aspiration rate.

[0115] For example, in an application for an ET O2 measurement in an adult patient, the key parameters might be a tube length of 3 m, a tube diameter of 1.5 mm, a respiratory rate of 15 / min (corresponding to a respiratory period of 4 s), and an expiratory plateau length of approximately 1.5 s. In this example, the O2 measurement is performed using a chemical cell measuring device with a 2 s rise time. In addition, there is the rise time caused by the tube system, which is approximately 250 ms at a suction rate of 100 ml / min.

[0116] Measuring the eTO2 value is therefore not possible using the traditional sidestream method with a constant suction rate, as the rise time of the O2 sensor, including the tubing system (2 s + 0.25 s), is longer than the expiratory plateau (1.5 s), and thus the eTO2 value is not reached. Measuring the eTO2 value is only possible if the total rise time of the measuring device and the tubing system or gas reservoir is a maximum of 1.5 s.

[0117] The relevant gas sample in this example, within the meaning of the invention, is the entire expiratory plateau. Therefore, the entire expiratory plateau must be measured with increased effective resolution so that the etO2 value at the end of the plateau is achieved. In this example, an increase in resolution by a factor of 1.7 is desired. To this end, the suction rate for taking the relevant gas sample is set to 133 ml / min. While the relevant gas sample is in the measuring device for measurement, the suction rate is set to 80 ml / min. The sensor's rise time can thus be effectively reduced to 2 s / 133 * 80 = 1.2 s for the relevant gas sample. The rise time of the tubing system is reduced to approximately 0.25 s / 133 * 100 = 0.19 s due to the increased suction rate (previously 100 ml / min, now 133 ml / min). Overall, this results in a total rise time that is shorter than the length of the expiratory plateau (1.5 s).The etO2 value at the end of the expiratory plateau can thus be realistically reflected by the inventive implementation of the measurement.

[0118] Another application example is etCO2 measurement in neonatology. Infants, especially premature or newborn babies, have respiratory rates of up to 60 breaths / min. At 60 breaths per minute, the expiratory plateau is only approximately 250 ms long. For accurate determination of the etCO2 value, the temporal resolution of the measurement must be less than 250 ms. Due to the module's measurement speed in combination with the mixing of the sample gas in the supply line, a rise time of 250 ms may not be guaranteed with a traditional sidestream CO2 measurement. Using the invention, the temporal resolution during the expiratory plateau can be increased. The rest of the respiratory cycle is less relevant and is displayed with lower resolution.

[0119] Another application example is CO2 measurement for diagnostics. For example, in pulmonary function diagnostics and ergospirometry, the steepness of the expiratory rise as well as the gradient during the plateau are relevant. With traditional sidestream CO2 measurement, sufficient temporal resolution may not be ensured to realistically reflect, in particular, the steepness of the expiratory rise. The relevant section of the mainstream within the meaning of this invention is then the expiratory rise. In this section, the temporal resolution is increased, while the remainder of the respiratory cycle is measured at a lower resolution.

[0120] In another application example in CO2 measurement for diagnostics, another relevant section in the respiratory cycle is defined, e.g. the fiCO2 value.

[0121] In another application example in CO2 measurement for diagnostics, the relevant section is enlarged so that it also captures the fiCO2 value and / or the etCO2 value. In extreme cases, the entire range from fiCO2 to etCO2 is defined as the relevant section in the mainstream within the meaning of this invention. Only the inspiratory decline of the CO2 curve and the inspiratory O plateau would then be irrelevant.

[0122] The following figures serve to illustrate the invention by way of example. They show:

[0123] Figure 1: A schematic representation of a device according to the invention in a

[0124] Ventilation application,

[0125] Figure 2: Two schematic representations of the volume distribution of gas samples in corresponding measuring systems FIG.2(a) with constant extraction rate and FIG.2(b) with variable extraction rate,

[0126] Figures 3 - 9: Schematic representations of further embodiments of a device according to the invention and

[0127] Figure 10: A representation of the course of CO2 concentration over the respiratory cycle of an adult human.

[0128] Figure 1 shows a schematic block diagram of an inventive device for measuring gas samples in a secondary flow (1). The illustrated embodiment of the invention comprises a gas reservoir (3) designed as a suction hose, which is connected to a main flow (2) at a sampling point for taking gas samples. Furthermore, the device for measuring a gas sample in a secondary flow (1) comprises a measuring device M (4) and a suction pump P (5) with an adjustable suction rate.

[0129] With the aid of the suction pump (5), gas samples can be sucked from the main stream (2) through the gas reservoir (3) into the measuring device (4).

[0130] Furthermore, the illustrated device for measuring gas samples in the secondary flow (1) comprises a synchronization device S (6) with which the suction rate of the suction pump (5) can be synchronized with at least one main flow parameter. To detect a main flow parameter, the device (1) comprises a detection device (7), which is designed, for example, as a sensor for detecting measured values ​​in the main flow (2).

[0131] The detection device (7) can be a component of the device (1) or a separate module that transmits corresponding values ​​of the at least one main current parameter directly or indirectly to the synchronization device (6).

[0132] Furthermore, the illustrated device (1) comprises a communication device K (8) configured for communication with a main flow device (9). In the illustrated embodiment, the main flow device (9) is configured as a ventilator B, and the main flow (2) is formed by the breathing gas flowing through a ventilation tube.

[0133] The communication device (8) is designed to receive and / or transmit data, for example measured values ​​of the measuring device (9), the suction rate of the suction pump (5), data of the synchronization device (6) or a detection device (7) and / or from a main power device (9).

[0134] In embodiments of the invention, the communication device (8) is at least partially integrated into the synchronization device (6), so that the latter is designed for independent communication, for example with a main power device (9).

[0135] In Figure 2, the lengths of gas samples in the gas reservoir (3) of a device for measuring gas samples in the secondary flow (1) are shown according to the prior art in FIG. 2(a) and according to the invention in FIG. 2(b). The basic structure of the device shown for measuring gas samples in the secondary flow (1) is identical in both cases and comprises a gas reservoir (3) connected to the main flow (2), a measuring device (4), and a suction pump (5).

[0136] In both representations, relevant sections (11) and irrelevant sections (12) are marked in the main stream (2). The relevant gas samples (13) and irrelevant gas samples (14) extracted into the gas reservoir (3), which is designed as a suction hose, are shown accordingly. A relevant gas sample (13) is taken from the main stream (2), while a relevant section (11) flows past the sampling point. The lower part of the representation schematically represents individual volumes of the gas samples (13, 14), which are spaced apart from one another according to the scanning by the measuring device (4).

[0137] If the gas samples (13, 14) are taken according to the prior art with a constant suction rate of the suction pump (5), the ratio of the volumes of the gas samples (13, 14), or the length of the gas samples for a defined hose diameter, corresponds to the lengths of the respective sections (11, 12) in the main flow (2). This can be seen in FIG. 2(a). Taking into account the discrete measurement volumes from the lower part of the diagram, it can be seen that these are arranged equidistantly because the suction rate and sampling rate are constant.

[0138] However, if the gas samples (13, 14) are taken according to the invention at a higher extraction rate when a relevant section (11) of the main stream (2) flows past the sampling point and at a lower extraction rate when an irrelevant section (12) of the main stream (2) flows past the sampling point, disproportionately large volumes or lengths of the relevant gas samples (13) can be realized in comparison to the irrelevant gas samples (14).

[0139] If such a relevant gas sample (13) is additionally conveyed through the measuring device (4) at a lower suction rate during the measurement, a significantly increased effective resolution of the measurement of the relevant gas sample (13) results, depending on the selected suction rates. This occurs at the expense of the resolution of the irrelevant gas samples (14), which, however, is harmless in the corresponding applications. The higher temporal resolution of the measurement of the relevant gas samples (13) in comparison with the irrelevant gas samples (14) can also be seen in the lower part of the illustration. The discrete volumes of the relevant gas samples (13) are close together, while those of the irrelevant gas samples (14) are further apart. Figures 3 to 9 show alternative embodiments of the device according to the invention for measuring gas samples in the secondary flow (1).

[0140] The embodiment according to Figure 3 has a switching valve (15) between the measuring device (4) and two suction pumps (5). The suction pumps (5) preferably have two differently set suction rates, so that the suction rate of the device (1) can be adjusted by switching between the suction pumps (5) using the switching valve (15). Preferably, the suction rate of one suction pump (5) is set to the value W1 (measuring pump for relevant gas samples) and the suction rate of the other suction pump (5) is set to the value W2 (extraction pump for relevant gas samples).

[0141] According to the embodiment shown in Figure 4, the two suction pumps (5) can be switched back and forth between the measuring line with the measuring device (4) and an auxiliary channel (16) by means of the switching valve (15).

[0142] Figures 5 and 6 each show an embodiment with two parallel-connected measuring devices (4). For example, two possibly different measured variables can be determined in parallel, e.g., the O2 and CO2 content of the gas mixture. The embodiment shown in Figure 6 also has two parallel gas reservoirs (3).

[0143] Figures 7 and 8 show embodiments with parallel measuring lines, each having its own gas reservoir (3), a measuring device (4), and a suction pump (4). In these embodiments, it is possible, for example, to carry out the measurements in the individual lines independently of each other over time. The same or different measurement variables can be measured in the measuring lines. For example, one line can determine the eO2 value and the fiO2 value in the other line, or the O2 content of the gas mixture can be measured in the first line and the CO2 content in the second line.

[0144] In the exemplary embodiment according to Figure 9, the device for measuring gas samples in the bypass flow (1) has two parallel gas reservoirs (3) and a measuring device (4), wherein the gas reservoirs (3) can be alternately connected to the measuring device (4) using a switching valve (15). Furthermore, the gas reservoir (3) not connected to the measuring device (4) is connected to a waste channel (17). An extraction pump (5) is arranged both in the line of the measuring device (4) and in the waste channel (17). In one exemplary embodiment, the extraction pumps are each set to constant extraction rates W1 (first extraction pump) and W2 (second extraction pump). A relevant gas sample is pumped into the first gas reservoir G1 by means of the extraction pump (extraction rate W2).During this time and during the subsequent irrelevant phase in the main flow, the relevant gas sample is pumped from the second gas reservoir G2 through the measuring device (4) by means of the measuring pump (extraction rate W1). The valve (15) is then switched, and the process is repeated in reverse.

[0145] The gas sample of the irrelevant phase in the main stream is not passed through the measuring cell (4), but exits the system through the waste channel (17). This allows more time to measure the gas sample of the relevant phase. A continuous, high-resolution curve is recorded for the relevant gas sample; no measured values ​​are recorded for the irrelevant sample.

[0146] Figure 10 shows the CO2 concentration curve in mmHg over the respiratory cycle of an adult (time in s). The inspiratory phase is shown from 0 to 1 s. The expiratory plateau extends from a steep rise shortly after 1 s in a CO2 concentration range between 30 and 40 mmHg to a steep decline shortly before about 3 s.

[0147] It is clear that, depending on the application, only certain, possibly very short, sections of the cycle are relevant for recording certain values ​​(e.g., etCO2). However, determining these values ​​requires a high temporal resolution of the measurement in the relevant section of the cycle, which can be achieved either by using fast and therefore usually more expensive (or large) measurement technology or, with the help of the invention, by using cheaper and / or smaller measurement technology.

Claims

Patent claims Device for measuring gas samples in the secondary flow (1), comprising at least one gas reservoir (3), at least one measuring device (4) and at least one suction pump (5), wherein the at least one suction pump (5) is designed to suction a gas sample from a main flow (2) through the gas reservoir (3) and into the at least one measuring device (4), characterized in that the suction rate with which the gas samples can be suctioned from the main flow (2) is adjustable, wherein the suction rate is adjustable at least between a first value W1 and at least one second value W2 and wherein W1 is smaller than W2.Device (1) according to claim 1, characterized in that the suction rate can be adjusted by setting the suction rate of at least one suction pump (5) and / or by switching between at least two suction pumps (5) with different set suction rates using at least one controllable valve or a switching valve (15). Device (1) according to claim 1 or 2, characterized in that the gas reservoir (3) is at least partially realized by a hose line that connects a withdrawal point on the main stream (2) to at least one measuring device (4). Device (1) according to claim 3, characterized in that the inner diameter of the hose line is selected in a range from approximately 1 mm to 2 mm. Device (1) according to one of the preceding claims, characterized in that the measuring device (4) has at least one measuring cell and is designed to measure the proportion of at least one gas in a gas sample. Device (1) according to one of the preceding claims, characterized in that the measuring device (4) has a CO2 sensor and / or an O2 sensor for determining the proportion of the respective gas in the gas mixture. Device (1) according to one of the preceding claims, characterized in that the suction rate can be adjusted from 50 ml / min to 100 ml / min in a maximum of 0.5 s. Device (1) according to one of the preceding claims, characterized in that the suction rate can be adjusted from 0 ml / min to 300 ml / min in a maximum of 0.2 s.Device (1) according to one of the preceding claims, characterized in that at least one time-dependent output signal of the measuring device (4) can be compensated taking into account the extraction rate of the respective gas sample. Device (1) according to one of the preceding claims, characterized in that the extraction rate can be set to a value W1, or a value selected from the first value range, when a gas sample extracted from the main stream (2) with a value W2, or a higher extraction rate selected from the second value range, has reached the region of the at least one measuring device (4). Device (1) according to claim 10, characterized in that the values ​​of the extraction rates are selected such that, with the resulting average extraction rate as a function of the volume of the gas reservoir (3), a corresponding flow time of the gas sample through the gas reservoir (3) is realized.Device (1) according to one of the preceding claims, characterized in that the main flow (2) has a substantially cyclical course and that the volume of the gas reservoir (3) corresponds to at least half of the sample gas extracted from the main flow (2) in one main flow cycle. Device (1) according to one of the preceding claims, characterized in that the extraction rate is adjustable such that the volume of the gas reservoir (3) corresponds to the (N + 1)-. times the sample gas extracted from the main flow (2) in one main flow cycle, where N is a natural number. Device (1) according to one of the preceding claims, characterized in that it comprises a synchronization device (6) for synchronizing the extraction rate of at least one extraction pump (5) with at least one main flow parameter. Device (1) according to claim 14, characterized in that the Synchronization device (6) using the evaluation of at least one Main flow parameter for detecting a relevant section (11) in the main flow (2), wherein the suction rate upon detection of a relevant section (11) in the main flow (2) is adjustable to a suction rate W2 or to a suction rate selected from the second high value range. Device (1) according to one of the preceding claims, characterized in that the second value range has a lower limit of the suction rate of 70 ml / min. Device (1) according to one of claims 1 to 15, characterized in that the second value range has a lower limit of the suction rate of 200 ml / min. Device (1) according to one of the preceding claims, characterized in that W1 or the smallest value of the suction rate of the first value range is greater than 0 ml / min. Medical device comprising at least one device for measuring gas samples in the secondary flow (1) according to one of the preceding claims.A medical device according to claim 19, characterized in that it is designed as a ventilator, and in that the current suction rate of the device (1) can be retrieved from the ventilator and used for compensation in the volume or flow measurement and / or the ventilation volume. A method for measuring gas samples in the sidestream, comprising the following method steps: • Extracting gas samples from a main stream using at least one extraction pump through at least one gas storage device, • Measuring the gas samples using at least one measuring device, • Setting the extraction rate to a value W2 for at least one period of the measurement to take at least one gas sample, • Setting the extraction rate to a second value W1 for at least one other time period of the measurement for taking at least one further gas sample and / or for measuring a gas sample extracted at the extraction rate W2, where W1 is less than W2, characterized in that the extraction rate is adjusted in such a way that a gas sample (13) which was extracted from the main stream (2) at an extraction rate W2 or an extraction rate selected from the second value range is conveyed through the at least one measuring device (4) and measured at an extraction rate less than W2. Method according to claim 21, characterized in that the extraction rate is adjusted in such a way that a gas sample (13) which was extracted from the main stream (2) at an extraction rate W2 or an extraction rate selected from the second value range is conveyed through the at least one measuring device (4) and measured at the extraction rate W1 ora suction rate selected from the first value range is conveyed through the at least one measuring device (4) and measured. Method according to one of claims 21 and 22, characterized in that the adjustment of the suction rate is carried out with the aid of a synchronization device (6) taking into account at least one main flow parameter such that at least one relevant section (11) of the main flow (2) is suctioned at the suction rate W2 or a suction rate selected from the second value range. Method according to claim 23, characterized in that the synchronization with the aid of the synchronization device (6) is carried out by detecting or receiving at least one main flow parameter, an analysis of the at least one main flow parameter with regard to the presence of a first decision criterion which corresponds to the presence of a relevant section (11) in the main flow (2), and an adjustment of the suction rate to the value W2 orto a value selected from the second value range when the first decision criterion is met. Method according to claim 24, characterized in that the setting of the suction rate to a value selected from the first value range is carried out with a temporal Delay after detection of the presence of a first decision criterion occurs in such a way that an existing delay between the at least one evaluated main flow parameter or the occurrence of the corresponding decision criterion and a section (11) of the main flow (2) relevant for the measurement is taken into account. Method according to one of claims 23 to 25, characterized in that the suction rate is synchronized with the aid of the synchronization device (6) to relevant sections (11) in a patient's respiratory cycle, wherein the main flow (2) is determined by the respiratory gas flowing through a ventilation tube during ventilation of a patient using a ventilator.Method according to one of claims 21 to 26, characterized in that the measured values ​​of the respective gas samples (13, 14) recorded with the aid of the at least one measuring device (4) are computationally equalized in time, taking into account the respective suction rates. Method according to one of claims 21 to 27, characterized in that a device according to the invention for measuring gas samples in the sidestream (1) according to one of claims 1 to 18 or a medical device according to the invention according to one of claims 19 and 20 is used. Method according to one of claims 21 to 28, characterized in that the current suction rate is retrieved from a ventilator and used to compensate for the volume or flow measurement of the ventilation volume.Method according to one of claims 21 to 29, characterized in that the adjustment of the suction rate is carried out by setting the suction rate of at least one suction pump (5) and / or by switching between at least two suction pumps (5) with different set suction rates by means of at least one controllable valve or a switching valve (15).

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