ARRANGEMENT AND METHOD FOR MEASURING THE RESPECTIVE CONCENTRATION OF THREE GAS COMPONENTS IN A GAS SAMPLE

Description

[0001] The invention relates to a sensor arrangement and a measuring method for measuring the respective concentration of three gas components of a gas sample.

[0002] The task of measuring the respective concentrations of several gas components in a gas sample arises, for example, during the mechanical ventilation of a patient. A ventilator delivers a breathable gas mixture to a patient-side coupling unit, such as a breathing mask or endotracheal tube, which is connected to the patient. The breathable gas mixture contains oxygen and, in one configuration, at least one anesthetic (anesthetic gas).

[0003] A method and device for measuring oxygen and anesthetic concentrations are described in DE 10 2021 126 106 A1. A magnetic field with an oscillating magnetic field strength is generated in a measuring chamber. The thermal conductivity and the magnetically modulated thermal conductivity of the breathable gas mixture are measured. The fact that oxygen is a paramagnetic gas is utilized. A similar sensor is described in GB 2 355 806 A.

[0004] The invention is based on the objective of providing a sensor arrangement and a measuring method which are able to measure the respective concentration of three gas components of a gas sample with a higher reliability than known sensor arrangements and measuring methods.

[0005] The problem is solved by a sensor arrangement having the features of claim 1 and by a measuring method having the features of claim 6. Advantageous embodiments of the sensor arrangement according to the invention are, where appropriate, also advantageous embodiments of the measuring method according to the invention, and vice versa.

[0006] The sensor arrangement and measuring method according to the invention are capable of measuring the respective concentration (the respective proportion) of three different gas components in a gas sample. Preferably, "concentration" is understood to mean the respective proportion in vol.%; the concentration can also be the proportion in wt.%, i.e., the mass fraction. One gas component of the gas sample is a paramagnetic gas, in particular oxygen.

[0007] Note: A paramagnetic gas has the following properties: The atoms or molecules of the gas possess permanent magnetic properties (a magnetic moment) and align themselves in a magnetic field.

[0008] The respective density and thermal conductivity of each of the three gas components are specified in a computer-readable format. For example, the sensor array has at least temporary read access to a data storage device in which the densities and thermal conductivities are stored.

[0009] The sensor arrangement comprises a measuring chamber, a thermal conductivity sensor, and a density sensor. The measuring chamber is capable of holding a gas sample. The thermal conductivity sensor is capable of measuring the thermal conductivity of the gas sample in the measuring chamber. The density sensor is capable of measuring the density of the gas sample. The measuring method according to the invention is carried out using such a sensor arrangement and comprises the steps of measuring the thermal conductivity and the density of the gas sample.

[0010] Note: The phrase "a sensor measures a physical quantity" means the following: The sensor directly measures the physical quantity or at least one other physical quantity, where the other physical quantity is correlated with the physical quantity being measured. The other physical quantity is thus a measure of the physical quantity being measured.

[0011] The measuring method according to the invention further comprises the following steps, and the sensor arrangement according to the invention is designed to perform the following steps: The gas sample is fed or guided into the measuring chamber. A magnetic field with an oscillating magnetic field strength is applied to the measuring chamber. The magnetically modulated thermal conductivity of the gas sample in the measuring chamber is measured.

[0012] The "magnetically modulated thermal conductivity" of a gas sample refers to the portion of its thermal conductivity that oscillates depending on the magnetic field strength. This magnetically modulated thermal conductivity depends significantly, but usually not exclusively, on the concentration of the paramagnetic gas in the gas sample. It is possible that the thermal conductivity of the gas sample within the measuring chamber is measured as a measure of its (total) thermal conductivity. It is also possible that the same thermal conductivity sensor measures both the thermal conductivity and the magnetically modulated thermal conductivity, thus providing two different signals that can be independent of each other. Alternatively, two different thermal conductivity sensors may be used.

[0013] The three gas component concentrations are determined using the following information: the specified densities of the three gas components, the specified thermal conductivities of the three gas components, the measured thermal conductivity of the gas sample, the measured magnetically modulated thermal conductivity of the gas sample and the measured density of the gas sample, optionally additionally the temperature of the gas sample, optionally additionally the temperature in the measuring chamber and optionally additionally the pressure under which the gas sample is located, preferably the pressure in the measuring chamber.

[0014] According to the invention, three different properties of the gas sample are measured: thermal conductivity, magnetically modulated thermal conductivity, and density. These three properties of the gas sample generally depend on the desired concentrations of the three gas components in the sample, but are independent of each other. In particular, these three properties typically change independently of one another. Using these three independent properties of the gas sample, determined by measurements and therefore known, three unknowns can be determined: the three desired concentrations of the three gas components.

[0015] The invention does not require that the gas sample consist only of these three gas components. Rather, the gas sample can include at least one additional gas component. To determine its concentration, the fact that the sum of the concentrations of the gas components, measured in vol.% or wt.%, equals 100% can often be used.

[0016] In some applications, the concentration of the paramagnetic gas, particularly oxygen, is of primary importance. While some known sensor arrangements and measuring methods can also measure the oxygen concentration in a gas sample, they exhibit a relatively high, undesirable cross-sensitivity to other components of the gas sample. Such cross-sensitivity can lead to inaccurate measurements and is therefore undesirable. In contrast, the sensor arrangement and measuring method according to the invention are significantly less cross-sensitive, ideally not cross-sensitive at all, to other gas components in the gas sample.

[0017] Thanks to the invention, in many cases it is not necessary to provide and use a reference gas with a known composition for measurement, while the sensor arrangement and the measuring method measure the gas component concentrations.

[0018] Electrochemical sensors have become well-known. In an electrochemical sensor, a chemical process takes place that depends on the concentration of oxygen and / or another gas component in the gas sample. A detection parameter of the electrochemical sensor measures an electrical detection parameter that correlates with the oxygen concentration being measured. In some cases, such electrochemical sensors have the disadvantage of requiring a chemical that is consumed over time and therefore needs to be replenished periodically. Furthermore, the chemical can be altered or evaporate due to environmental influences, particularly ambient heat. The invention eliminates the need for a chemical and thus avoids these disadvantages.

[0019] In one application, the paramagnetic gas component is oxygen. The two other gas components, whose concentrations are measured according to the invention, are, in this application, an anesthetic (an anesthetic gas) or carbon dioxide, and argon. The noble gas argon occurs in ambient air at a known concentration. However, the concentration of argon in the gas sample is often higher than the known concentration of argon in ambient air. This situation occurs particularly in the following application: The gas sample originates from a breathable gas mixture used for the artificial ventilation of a patient. The gas mixture is produced using ambient air but has a higher oxygen content than ambient air. A so-called concentrator is used to generate the gas mixture from ambient air.If a gas mixture with a higher oxygen content than ambient air is generated by means of a concentrator, the generated gas mixture typically also has a higher concentration of argon than ambient air. This higher concentration is measured in the application of the invention just described.

[0020] Preferably, the sensor arrangement is capable of simultaneously measuring both the thermal conductivity and the magnetically modulated thermal conductivity of a gas sample in the same measuring chamber. In one embodiment, the sensor arrangement includes a heating element and is capable of heating the heating element, in particular by applying an electrical voltage to the heating element, causing an electric current to flow through an electrical heating wire of the heating element. When the heating element is heated, it transfers thermal energy to a gas sample in the measuring chamber. Preferably, this heating element does not chemically react with the gas sample in the measuring chamber.

[0021] According to the invention, a magnetic field with an oscillating magnetic field strength is applied to the measuring chamber. The thermal conductivity and the magnetically modulated thermal conductivity of the gas sample are measured in the measuring chamber. Preferably, an electrical detection quantity is measured. This electrical detection quantity correlates with the thermal conductivity of the gas sample in the measuring chamber. Electrical or electronic filtering of the electrical detection quantity is performed. This filtering yields two signals: an oscillating signal and another signal. The oscillating signal oscillates depending on the oscillating magnetic field strength. Ideally, the time course of the other signal does not depend on the oscillating magnetic field strength. The oscillating signal is used as a measure of the magnetically modulated thermal conductivity.The oscillating signal correlates with the concentration of the paramagnetic gas in the gas sample. The other signal is used as a measure of the thermal conductivity of the gas sample. It correlates with the thermal conductivity of the gas sample.

[0022] This design often results in a particularly compact sensor arrangement. In the same measuring chamber, two independent properties of the gas sample are measured using the same magnetic field generator and the same heated heating element: thermal conductivity and magnetically modulated thermal conductivity.

[0023] Several configurations are possible for measuring the density of a gas sample. One configuration uses a mechanical or electronic flexural resonator. This resonator comprises a vibrating body. In the case of a mechanical flexural resonator, this vibrating body is or comprises a movably mounted fluid guidance unit. A "fluid guidance unit" is understood to be a component that guides a fluid along a trajectory, the trajectory being defined by the component's design and arrangement. A corrugated hose, a smooth hose, and a tube are examples of a fluid guidance unit. The fluid guidance unit does not necessarily include a conveying unit. In the case of an electronic flexural resonator, this vibrating body is preferably a quartz crystal oscillator.

[0024] The gas sample is passed through the fluid guide unit of the bending resonator or past the quartz crystal. The bending resonator is able to set the oscillating body (fluid guide unit or quartz crystal) into vibration while a portion of the gas sample is located within the fluid guide unit, passed by the oscillating body, or surrounds it. The natural frequency of the vibrating body is measured. This measured natural frequency correlates with the mass of the gas sample.

[0025] In the case of a mechanical oscillating beam, the natural frequency correlates with the mass of the filled fluid guide unit. This mass is typically the sum of the mass of the empty fluid guide unit and the mass of the gas sample within it. The mass of the empty fluid guide unit is known due to the design of the oscillating beam and does not change during measurement. The volume of the fluid guide unit is also known due to its design and remains constant. From the measured natural frequency, as well as the mass and volume of the empty fluid guide unit, the density of the gas sample can be derived.

[0026] The principle of such a bending oscillator has been known for a long time, and reliable bending oscillators for density measurement are available.

[0027] In one embodiment, the concentration of at least one fourth gas component of the gas sample is measured directly. The respective concentration of this fourth gas component is then used to determine the concentrations of the three gas components. This embodiment often increases the reliability with which the concentrations of the three gas components are determined.

[0028] In one implementation of this design, the concentration of one or at least one fourth gas component is measured by a photoelectric sensor that applies the following well-known principle: A radiation source emits electromagnetic radiation, sound, or ultrasound into a measuring section or chamber, with a sufficiently broadband frequency. The gas sample flows through this measuring section or is located within this measuring chamber. The measuring chamber can be the one just described with the specified magnetic field strength, or a spatially separated measuring section or chamber. The electromagnetic radiation or sound penetrates the measuring section or chamber. At least a portion of it reaches a detector. The gas sample in the measuring section or chamber absorbs some of the radiation or sound. This reduces the intensity of the radiation or sound within a specific wavelength range. A detector measures the intensity of the incident radiation or sound. This intensity correlates with the desired concentration of the fourth gas component.The detector generates a signal depending on the measured intensity. This signal contains information about the intensity and therefore also about the concentration of the fourth gas component.

[0029] Many gases exhibit a characteristic spectral absorption profile, meaning that the absorptivity depends on the wavelength of the electromagnetic radiation or sound passing through the gas. The concentration of the fourth gas component can usually be measured independently of the concentrations of the three other gas components.

[0030] According to the invention, three properties of the gas sample are measured to determine values ​​for three unknowns, wherein the three unknowns are the three desired concentrations of the three gas components in the gas sample. In one embodiment, three functional relationships, three distance measures, and an objective function are specified. Preferably, the sensor arrangement according to the invention has at least temporary read access to a data storage device in which the objective function, the distance measures, and the functional relationships are stored in a computer-evaluable form.

[0031] The first functional relationship describes the thermal conductivity of the gas sample as a function of the three unknown gas component concentrations. The second functional relationship describes the magnetically modulated thermal conductivity of the gas sample as a function of the three gas component concentrations. The third functional relationship describes the density of the gas sample as a function of the three gas component concentrations. All three functional relationships therefore depend on the three unknown gas component concentrations.

[0032] The first distance measure describes a measure of the difference between the measured thermal conductivity of the gas sample and the thermal conductivity derived using the first functional relationship. The second distance measure describes a measure of the difference between the measured magnetically modulated thermal conductivity of the gas sample and the magnetically modulated thermal conductivity derived using the second functional relationship. The third distance measure describes a measure of the difference between the measured density of the gas sample and the density derived using the third functional relationship. Preferably, each distance measure is the square of the respective difference, alternatively the absolute value of the difference, or some other function that increases with the magnitude of the difference.

[0033] The objective function is an aggregation of these three distance measures. Preferably, the objective function is a weighted average of the three distance measures. The weighting factors compensate, for example, for different orders of magnitude of the three properties: thermal conductivity, magnetically modulated thermal conductivity, and density. It is also possible that the weighting factors additionally or instead take into account different accuracy requirements for the desired gas component concentrations.

[0034] The three measured values ​​for the gas sample—the measured thermal conductivity, the magnetically modulated thermal conductivity, and the density of the gas sample—are inserted into the objective function. After insertion, the objective function depends on three unknowns: the three concentrations of the gas components that are being sought. The objective function is minimized numerically. This means that various sets of three values ​​for the three gas component concentrations are trial-based and inserted into the objective function. Each set of three values ​​assigns a value to each of the three concentrations. The set of three values ​​that results in a minimum value for the objective function yields the three desired gas component concentrations. Ideally, the minimizing set of three values ​​results in a value of zero for the objective function. In practice, a discrepancy always arises between the measured property and the property predicted according to the functional relationship.An iterative minimization method is preferably used. It is possible that the objective function has multiple minima.

[0035] It is possible that the concentration of a fourth gas component occurs in at least one functional context. In one implementation, a sensor directly measures the concentration of this fourth gas component, for example, using the photoelectric measurement principle described above, comprising a radiation source and a detector. In another implementation, a standard value is specified for the concentration of the fourth gas component. It is also possible that there is a further, i.e., a fifth, gas component whose concentration is measured or for which a standard value is specified.

[0036] The invention further relates to a ventilation arrangement and a ventilation method for the artificial ventilation of a patient. The ventilation arrangement comprises a medical device, in particular a ventilator, a patient-side coupling unit, a ventilator control unit and a sensor arrangement according to the invention.

[0037] The ventilation procedure is performed using such a ventilation setup.

[0038] The patient is connected to the patient-side coupling unit or can at least be temporarily connected to one. The patient-side coupling unit includes, in particular, a breathing mask and / or an endotracheal tube and / or a catheter. The ventilation system is capable of conveying and / or pumping a breathable gas mixture from the medical device to the patient-side coupling unit. The gas mixture contains oxygen and, in one configuration, at least one anesthetic and / or a medication. A ventilation circuit may be established. The gas mixture exhaled by the patient flows back to the medical device in the ventilation circuit.

[0039] The concentration of at least one gas component of the breathable gas mixture, in particular the concentration of oxygen, should be within a specified target range. This target range may vary over time. It is also possible that a target range is specified for at least two gas components.

[0040] The ventilation setup is designed to perform the following steps, and the ventilation procedure includes the following steps: A gas sample is taken from the gas mixture that is conveyed to the patient-side coupling unit. This sample is then directed to the sensor array. The sensor array measures at least the concentration of each gas component for which a target range is specified in the sample, and optionally the concentration of at least one other gas component.

[0041] The ventilator control unit performs either closed-loop control or open-loop control. The controlled variable is the actual concentration of at least one gas component in the gas mixture supplied to the patient-side coupling unit. The control gain is the objective of ensuring that the controlled variable, i.e., the actual gas component concentration, remains within the predefined target range. For this control, the ventilator control unit uses the gas component concentration in the diverted gas sample, which is measured by the sensor array.

[0042] The invention is described below using an exemplary embodiment. Here, it is shown that... Figure 1 schematically shows a ventilation circuit for the artificial ventilation of a patient; Figure 2 schematically shows a first embodiment of a sensor capable of measuring the concentration of oxygen and another gas; Figure 3 schematically shows a second embodiment of such a sensor; Figure 4 shows the measuring unit of the sensor. Figure 3 Figure 5 shows an exemplary evaluation circuit of the sensor from Figure 2 and from Figure 3 Figure 6 shows a mechanical bending oscillator used to measure the density of the gas sample; Figure 7 shows an electronic bending oscillator in the form of a quartz crystal used to measure the density of the gas sample; Figure 8 shows, by way of example, the magnetically modulated thermal conductivity λ 2f of a gas mixture as a function of the oxygen concentration.

[0043] In the exemplary embodiment, the sensor arrangement according to the invention is used for the artificial ventilation of a patient. The patient is supplied with a breathable gas mixture comprising oxygen and at least one anesthetic agent. The patient is therefore anesthetized or at least sedated.

[0044] Figure 1 Figure 1 schematically shows a ventilation setup 200 with a schematically shown ventilator 1, wherein the ventilation setup 200 is capable of artificially ventilating a patient P. Only the patient P's face is shown schematically. In the example shown, the ventilator 1 maintains a ventilation circuit 40. In the example shown, the ventilator 1 is configured as an anesthesia machine, and the patient P is anesthetized or at least sedated.

[0045] In the ventilation circuit 40, a breathable gas mixture Gg is supplied to the patient P. In the exemplary embodiment, this gas mixture Gg comprises oxygen (O₂), at least one anesthetic agent, and optionally a carrier gas for an anesthetic agent, e.g., nitrous oxide (N₂O), and optionally also a medication. An anesthetic metering device 31 generates a fluid flow 28 containing vaporous anesthetic agent and a carrier gas. The fluid flow 28 is fed into the ventilation circuit 40. In addition, a fluid flow 27 of fresh air or other fresh gas is introduced at least intermittently. At least as long as there is no excessive overpressure in the ventilation circuit 40, the gas mixture exhaled by the patient P remains in the ventilation circuit 40, so that no anesthetic agent escapes into the environment.

[0046] The gas mixture At, which is exhaled by the patient P and flows through the ventilation circuit 40, necessarily contains carbon dioxide (CO₂). A carbon dioxide absorber (CO₂ absorber) 25a is able to absorb carbon dioxide from the ventilation circuit 40. Furthermore, the breathable gas mixture Gg may contain other components that also occur in ambient air, although possibly at a different concentration.

[0047] The invention can also be used in an application where no ventilation circuit is implemented. The gas mixture At exhaled by the patient P passes through an expiratory line 33 into the environment.

[0048] A patient-side coupling unit 21, shown only schematically, for example a mouthpiece, a breathing mask or a tube, connects the patient P to the ventilation circuit 40. A tube near the patient connects the patient-side coupling unit 21 to the base of a Y-piece 22. One leg of the Y-piece 22 is connected to an inspiratory line 32 for inhalation (inspiration), the other leg to an expiratory line 33 for exhalation (expiration).

[0049] A fluid delivery unit 24a draws in gas and generates a continuous flow of breathable gas mixture Gg through the inspiratory line 32 to the Y-piece 22 and to the patient-side coupling unit 21, and thus to the patient P. The ventilation circuit 40 is maintained by the fluid delivery unit 24a and optionally by a breathing bag 26, which can be manually operated. The fluid delivery unit 24a can be implemented, in particular, as a blower, a pump, or a piston-cylinder unit.

[0050] A non-return valve 23a allows gas to flow through the inspiratory line 32 to the Y-piece 22 and prevents gas flow in the opposite direction. A non-return valve 23b allows gas to flow through the expiratory line 33 away from the Y-piece 22 and prevents gas flow in the opposite direction.

[0051] In the exemplary embodiment, the fluid conveying unit 24a continuously conveys the gas mixture Gg. A controllable valve 24b, preferably a proportional valve, allows the flow of the gas mixture generated by the fluid conveying unit 24a to pass through or blocks it completely or entirely, depending on its position, thereby contributing to the generation of the individual ventilation strokes and determining the amplitudes and frequencies of these ventilation strokes.

[0052] A PEEP valve 24c (PEEP = "positive end-expiratory pressure") also ensures that a sufficiently high air pressure is maintained in the patient's lungs P even at the end of exhalation or during a brief opening or interruption of the ventilation circuit 40. This reduces the risk of the patient's lungs P collapsing due to insufficient pressure.

[0053] A pressure relief valve 29 is able to reduce overpressure in the ventilation circuit 40 by causing gas to escape from the ventilation circuit 40 when the pressure becomes too high. Preferably, the released gas is discharged into a line for anesthetic gas and enters a purifier (not shown).

[0054] A signal-processing ventilation control unit 35, shown only schematically, receives a signal from an optional pressure sensor 58, which measures the ambient air pressure Pamb around the anesthesia machine 1 and thus the ventilation circuit 40, and a signal from an optional temperature sensor 39, which measures the ambient temperature Tempamb. The ventilation control unit 35 also receives readings from a pressure sensor 36, which measures the current pressure in the ventilation circuit 40, for example, the pressure in the airway (Paw) applied to the patient P, in an embodiment as a differential pressure relative to the ambient pressure Pamb. The measuring position of the pressure sensor 36 can be in the inspiratory line 32 or in, or as shown, on or near the Y-piece 22. Preferably, the measuring position of the pressure sensor 36 is located on the tube closest to the patient.The ventilation control unit 35 controls the fluid delivery unit 24a, the valve 24b, the anesthetic dosing unit 31 and other components of the ventilation circuit 40 in order to achieve the desired artificial ventilation and anesthesia of the patient P.

[0055] It is often desired that the gas mixture Gg administered to the patient P fulfills a specific, predetermined property. In particular, the concentration of a component of the gas mixture Gg should be within a specified target range. Specifically, the proportion of pure oxygen (O₂) is often required to be within a predetermined range, for example, between 40% and 50% by volume or between 25% and 30% by volume. Alternatively, the proportion of anesthetic may need to be within a specific range. In the following, the term "concentration" of a gas component in a gas mixture is used. A synonymous term is "proportion."

[0056] For this purpose, a sample (hereinafter: a gas sample Gp) is taken (dipped) from the gas mixture Gg, At in the ventilation circuit 40 via a gas sample fluid delivery unit in the form of a sampling tube 52, analyzed, and fed back into the ventilation circuit 40 via a drainage tube 56. The sampling tube 52 begins at a branch point 34 between the patient-side coupling unit 21 and the Y-piece 22. Because the branch point 34 is positioned at this location, the gas sample Gp contains either a sample from the breathable gas mixture Gg or from the exhaled gas mixture At, depending on the time of the branching. Specifically, the sampling tube 52 receives, at times, a gas mixture Gg from the inspiratory line 22 and, at other times, a gas mixture At from the expiratory line 33.At branch point 34, there is optionally a valve (not shown) which, in a closed position, isolates the extraction tube 52 from the ventilation circuit 40 and can be controlled by the ventilation control unit 35. With the valve fully open or omitted, the extraction tube 52 is in unrestricted fluid communication with the ventilation circuit 40. The drainage tube 56 leads to an inlet point 37 upstream of the carbon dioxide absorber 25a.

[0057] The sampling tube 52 directs the gas sample Gp to a sensor assembly 50. This sensor assembly 50 is spatially separated from the patient-side coupling unit 21 and from the lines 32 and 33 and preferably also belongs to the ventilator 1 shown schematically. Figure 1 The sensor arrangement 50 is shown outside the ventilator 1 for illustrative purposes.

[0058] In the exemplary embodiment, the sensor assembly 50 comprises a pump 55, which draws the gas sample Gp from the ventilation circuit 40 and draws it through the sampling tube 52. Preferably, the pump 55 continuously generates a negative pressure on the side facing the sampling tube 52 and a continuous positive pressure on the side facing the discharge tube 56. The pump 55 is capable of generating a volume flow rate that is preferably constant over time and is, for example, 200 ml / min. A water trap 51 is arranged at the inlet of the sensor assembly 50, in which moisture condenses and is collected. This reduces the water content in the gas sample Gp.

[0059] A sensor 54 is capable of generating signals, the signals of which correlate with the respective measured concentrations of CO₂ and N₂O in the extracted gas sample Gp. Preferably, this sensor 54 comprises an infrared measuring head that utilizes the dipole moment of molecules in the gas sample Gp and quantitatively evaluates the absorption of infrared-active gases to determine the respective concentration. Preferably, the sensor 54 comprises a radiation source that emits electromagnetic radiation and a detector that measures the intensity of incident electromagnetic radiation and generates a corresponding signal.

[0060] A sensor 53 is capable of generating a signal that correlates, among other things, with the concentration of O₂ or another paramagnetic component of the gas sample Gp. The sensor 53 is described further below with reference to Figures 2 to 5 described in more detail.

[0061] Furthermore, the sensor assembly 50 includes a pressure sensor 57 that measures the pressure Pcell of the gas sample Gp at the inlet of the sensor assembly 50. This pressure Pcell varies over time because the pressure in the ventilation circuit 40 oscillates and because the sampling tube 52 is in fluid communication with the ventilation circuit 40 when no valve is present at the branch point 34 or as long as the optional valve at the branch point 34 is open. In the absence of a valve or when the valve is open, the pressure in the ventilation circuit 40 propagates to the sensor assembly 50 at approximately the speed of sound.

[0062] A density sensor 59, 60 measures the density of the gas sample Gp, which flows through the sensor arrangement 50. This density sensor 59, 60 is described further below with reference to Figure 6 and Figure 7 described. In the example of Figure 1The density sensor 59, 60 is arranged in parallel to the sensors 53, 54, 57. It is also possible that the sensors 53, 54, 57 are arranged in series with the density sensor 59, 60 and the diverted gas sample Gp flows through all four sensors.

[0063] The sensor assembly 50, the water trap 51, the signal processing unit 30, and the tubes 52 and 56 together form a measuring system 100, which aspirates the gas sample Gp from the ventilation circuit 40, analyzes it, and returns it to the ventilation circuit 40. The measuring system 100 belongs to the ventilation assembly 200.

[0064] Figure 2 Figure 53 shows an example of a sensor 53 that is capable of measuring the respective concentrations of oxygen (O₂) and another gas in the gas sample Gp. This sensor 53 utilizes the fact that oxygen is a paramagnetic gas, while any other gas that is present or may be present in the gas sample Gp is ​​not paramagnetic.

[0065] Two pole shoes 6, 7 and two field coils 4, 5 generate a magnetic field. An air gap 3 exists between the two pole shoes 6, 7, which functions as a measuring chamber 2. This measuring chamber 2 is bounded by the two pole shoes 6, 7 and by a wall 9. An inlet 10 and an outlet 11 are provided in the wall 9.

[0066] A thermocouple 8 is attached to two support wires 15, 16 at two junctions 12 and 14, with the two support wires 15, 16 passing through the lower pole piece 7 and being in thermal contact with it. The thermocouple 8 comprises two wires 17, 18, which are connected at a junction 13. A voltage source 20 applies an alternating voltage to the two support wires 15, 16 and thus to the thermocouple 8. This heats the thermocouple 8 to an operating temperature higher than the temperature of the gas sample Gp in the measuring chamber 2. An electrical voltage U across a measuring resistor 19 is measured. This electrical voltage U contains an alternating voltage component and a direct voltage component.

[0067] The current operating temperature of thermocouple 8 is measured at junction 13. This temperature depends on the voltage U applied between support wires 15 and 16, and on the thermal conductivity λ of the gas sample Gp in measuring chamber 2. Closed-loop control is implemented to maintain the operating temperature of thermocouple 8 at a constant value. The manipulated variable is the time-varying voltage U applied to support wires 15 and 16 by the voltage source 20. Because the temperature of thermocouple 8 ideally remains constant, an electrical detection parameter of thermocouple 8 correlates with the thermal conductivity λ of the gas sample Gp in measuring chamber 2.

[0068] One way to measure the detection quantity is as follows: The time-varying electrical power supplied to the thermocouple 8 is measured as the detection quantity. The two support wires 15 and 16 are electrically connected by the measuring resistor 19. The electrical voltage U across this measuring resistor 19 is measured. The magnitude of the electric current flowing through the thermocouple 8 is also measured. As is well known, electrical power depends on voltage and current. It is also possible to use the electrical voltage U as the detection quantity.

[0069] A voltage source 43 is connected to one field coil 5 via a power amplifier 42, and the other field coil 4 is connected to electrical ground. The voltage source 43 outputs a sinusoidal electrical voltage. This voltage generates a sinusoidally varying magnetic field in the measuring chamber 2. The thermocouple 8, which is heated to a constant temperature, transfers a quantity of heat per unit time to the gas sample Gp in the measuring chamber 2. This quantity of heat transferred per unit time correlates with the measured electrical power supplied to the thermocouple 8. Because the field strength of the magnetic field in the measuring chamber 2 oscillates periodically, the quantity of heat transferred per unit time also oscillates—provided that a paramagnetic gas is present in the measuring chamber 2 as part of the gas sample Gp. The detection quantity correlates with the thermal conductivity λ of the gas sample Gp.Using the detection quantity, a signal that oscillates depending on the oscillation of the magnetic field, for example an alternating voltage, and a non-oscillating or less oscillating signal, for example a direct voltage, are generated. The oscillating signal correlates with the thermal conductivity of the paramagnetic part of the gas sample Gp and thus with the O₂ concentration. This thermal conductivity is also referred to as the magnetically modulated thermal conductivity λ²f. The other signal correlates with the (total) thermal conductivity λ of the entire gas sample Gp. Figure 3 , Figure 4 and Figure 5 show a further embodiment of sensor 53. The same reference symbols have the same meaning as in Figure 2 The circuit of Figure 5 This can also be used for the design according to Figure 2 apply.

[0070] An electromagnet 62 with an electric coil 63 generates a time-varying, preferably oscillating, magnetic field in the air gap 3, cf. Figure 3 The gas sample Gp to be examined reaches this air gap 3. The time course of the strength of the generated magnetic field is determined by the control of the coil 63. Preferably, the strength of the magnetic field has a sinusoidal course. A measuring unit 64, implemented as a chip, preferably as a semiconductor chip manufactured, for example, using doped silicon, is arranged in the air gap 3.

[0071] Figure 4Figure 64 shows the measuring unit 64 in detail. The measuring unit 64 comprises an electrically controllable thermal conductivity measuring element 65, an electrically controllable heating unit 66, and a membrane 67 within a frame 69. A gas sample Gp can reach the elements 65 and 66 through holes in or around the membrane 67. The heating unit 66 can be an electrically conductive resistance structure deposited on the membrane 67 or designed as a heating wire. Two heating elements of the heating unit 66 are shown, electrically connected to each other by a connecting element 68. The thermal conductivity measuring element 65 and the heating unit 66 can also be designed as a single, integrated element exhibiting a temperature-dependent electrical resistance.

[0072] The heating unit 66 heats the measuring element 65 to an operating temperature higher than the temperature of a gas sample Gp in the measuring chamber 2. The heated measuring element 65 measures the temperature at the measuring position 77. In the illustrated embodiment, the measuring element 65 measures a thermoelectric voltage and utilizes the Seebeck effect. The thermal conductivity of the gas sample Gp at the measuring position 77 changes synchronously with the time-varying magnetic field generated by the electromagnet 62 – provided that the gas sample Gp at the measuring position 77 contains a sufficiently high concentration of a paramagnetic gas. Higher thermal conductivity leads to better dissipation of heat energy. This, in turn, results in a lower temperature, which in turn leads to a lower thermoelectric voltage.

[0073] Figure 5 This shows an example evaluation circuit with the following components: an amplifier 70, which is connected as an impedance converter, a voltage divider 71 with variable tap, a DC voltage source 72, a low-pass filter 73 and a high-pass filter 74, which is connected in parallel to the low-pass filter 73.

[0074] The heating unit 66 is connected to the DC voltage source 72 via the amplifier 70 and the voltage divider 71. The output signal of the thermal conductivity measuring element 65 is routed through the low-pass filter 73 and the high-pass filter 74. A signal 75 is present at the output of the high-pass filter 74, which oscillates depending on the oscillation of the magnetic field. Signal 75 correlates with the magnetically modulated thermal conductivity λ 2f and thus with the concentration of the paramagnetic gas, for example, the concentration of oxygen, in the gas sample Gp. A signal 76 is present at the output of the low-pass filter 73, which does not oscillate at all or at least not synchronously with the magnetic field oscillation. Signal 76 correlates with the thermal conductivity λ of the entire gas sample Gp.

[0075] Because the magnetic field strength oscillates, the amount of heat supplied per unit time comprises a superposition of a constant component and a periodically fluctuating component. The periodically fluctuating component correlates with the thermal conductivity and thus with the concentration of oxygen in measuring chamber 2. The constant component, i.e., the component that does not oscillate depending on the strength of the magnetic field, correlates with the thermal conductivity of the entire gas sample Gp in measuring chamber 2. The thermal conductivity λ of the gas sample Gp is ​​contributed by the thermal conductivity of oxygen and the respective thermal conductivity of each other component of the gas sample Gp. Both components are measured. Sensor 53 therefore provides two signals: a signal oscillating depending on the magnetic field strength, here periodically fluctuating, which is a measure of the concentration of oxygen or another paramagnetic gas in the measuring chamber 2 (periodically fluctuating component, alternating voltage), and a signal for the thermal conductivity λ of the gas sample Gp in the measuring chamber 2, whereby this signal does not oscillate or at least not depending on the magnetic field strength (constant component, direct voltage).

[0076] Optionally, a measured value for the concentration of a component and / or for the thermal conductivity λ is displayed on a display device 44, cf. Figure 2 .

[0077] According to the invention, the density of the gas sample Gp is ​​also measured. Figure 6 Figure 59 schematically shows an embodiment of a density sensor in the form of a mechanical bending oscillator. Figure 7An embodiment of an electronic bending oscillator 60, which is implemented as a quartz crystal oscillator. In one embodiment, the density sensor 59, 60 is connected in parallel to the sensor 53, which measures the thermal conductivity and the magnetically modulated thermal conductivity and is described above with reference to Figures 2 to 5 as described. It is possible that the sensor 53 is implemented as a single chip and that the density sensor 60 is mounted on this chip and supplied with electrical voltage by this chip.

[0078] The principle of density measurement described below has been known for a long time, but not for the application described here. In the exemplary embodiment, the density sensor 59, 60 measures the density ρ of the gas sample Gp flowing through the sensor arrangement 50.

[0079] First, a mechanical bending oscillator 59 is described with reference to Figure 6The gas sample Gp, whose density ρ is to be measured, is passed through a U-shaped tube 80 with two legs 80.1, 80.2. The tube 80 is located in a housing 83 and is made of a material that can chemically withstand the components of the gas sample Gp, for example, glass or steel. The two legs 80.1, 80.2 of the tube 80 form the spring elements of a bending oscillator. This principle is similar to that of a tuning fork. The two legs 80.1, 80.2 are clamped at a mounting point 81. A section B of the tube 80 can be set into vibration. This section B is also U-shaped, encompasses one segment of each leg 80.1, 80.2, and is bounded by the mounting point 81.

[0080] In one implementation, the tube 80 can be temporarily closed for measurement purposes. In another implementation, the gas sample Gp continues to flow through the tube 80 even during the measurement.

[0081] A schematically shown actuator excites this bending oscillator to undamped vibrations. In the illustrated embodiment, the actuator is implemented by two transducers 82.1, 82.2. Each transducer 82.1, 82.2 comprises a coil 83.1, 83.2 and a magnet 84.1, 84.2. In one mode, an alternating electrical voltage is applied to each transducer 82.1, 82.2, the transducer 82.1, 82.2 generates mechanical vibrations, and these mechanical vibrations are transmitted to the tube 80, preferably by a mechanical connection between the magnet 84.1, 84.2 and the tube 80.

[0082] The two arms 80.1, 80.2 define a plane. The two directions of the vibrations generated by the excitation are orthogonal to this plane. A section B of the tube 80 is set into vibration. Subsequently, the actuator 84 is switched off. Afterwards, section B continues to oscillate, following a transient phase, at its natural frequency.

[0083] The oscillation involves section B of tube 80 and the portion of the gas sample Gp located within this section B. This oscillating system has a mass, which is the sum of the mass of section B and the mass of the gas sample portion within section B. The mass of section B is predetermined by the design and remains constant. The volume that section B provides for the gas sample Gp also remains constant. Generally, the mass of the portion of the gas sample Gp located within section B can be considered constant during a measurement. The desired density ρ is then proportional to the mass of the gas sample portion.

[0084] The two converters 82.1 and 82.2 are then switched off. The system just described now oscillates at a natural frequency τ. This natural frequency τ depends on the mass of the system and is measured. In the implementation shown, the two converters 82.1 and 82.2 operate in a different mode after being switched off and convert the mechanical oscillations of region B into an alternating voltage. The frequency of this alternating voltage is equal to the natural frequency τ of region B. An amplifier 85 amplifies this alternating voltage. An evaluation unit 86 receives a signal from the amplifier 85 and provides the desired density ρ.

[0085] The desired density ρ is related to the measured natural frequency τ as follows: ρ = A * ⊤ 2 − B .

[0086] A and B are two constants of the density sensor (flexural transducer) 59. In a prior calibration, these two constants A and B are determined empirically, for example by means of a regression analysis. For this purpose, at least two different gases with known and differing densities are passed through the density sensor 59, and the respective resulting natural frequency is measured.

[0087] Figure 7 Figure 60 schematically shows a bending oscillator 60 in the form of a quartz crystal. This quartz crystal has the shape of a tuning fork with two arms 61.1 and 61.2. Figure 7A The diagram schematically shows this quartz oscillator. Electrodes are connected to this bending oscillator 60 in such a way that two opposing fields occur in the x-direction. This forces a bending motion in the z-direction. Figure 7BFigure 61.1 and 61.2 illustrate the oscillations of these two arms, where the x-direction and the z-direction lie in the plane of the drawing. Feedback ensures that the forced frequency is equal to the natural frequency τ.

[0088] Such a bending oscillator 60 is described, for example, in Th. Voglhuber-Brunnmeier et al.: Fluid Sensing Using Quartz Tuning Forks - Measurement Technology and Applications, Sensors, Vol. 19 (2019) No. 10.

[0089] In one version, the following relationship is used: ρ = − B 2 A + B 2 A 2 + τ − C A 2 2

[0090] Again, A, B, and C are device-specific constants that are determined beforehand through calibration. Because three constants need to be determined, at least three different gases with known and differing densities are used for calibration.

[0091] As previously explained, the sensor assembly 50 is intended to measure the respective concentration (proportion) in vol% of oxygen and anesthetic (anesthetic gas) in the diverted gas sample Gp. This gas sample Gp may contain other components which, without appropriate countermeasures, could distort the measurement. In particular, the noble gas argon (Ar) in the gas sample Gp can distort the measurement. It is known that the proportion of argon in ambient air is approximately 0.93 vol%. However, the concentration of argon in the gas sample Gp can be significantly higher than that of argon in the ambient air.This situation occurs particularly when the concentration of oxygen in the ventilation circuit 40 and therefore in the gas sample Gp is ​​greater than the concentration of oxygen in the ambient air, especially when the gas mixture Gg is produced from ambient air and the oxygen concentration has been increased with the help of a so-called oxygen concentrator.

[0092] In some situations, information about the measured argon concentration is additionally used from another sensor or other component of the anesthesia machine 1. For example, the measured argon concentration is compared with an upper limit. As soon as this upper limit for the argon concentration is reached, the ventilation circuit 40 is purged.

[0093] In the exemplary embodiment, the gas sample Gp n contains various components, including nitrogen (N 2 ), pure oxygen (O 2 ), carbon dioxide (CO 2 ), an anesthetic gas (A-gas), nitrous oxide (N 2 O), water (H 2 O), and argon (Ar). The respective density ρ(xi ) (i=1, ..., n) and the respective thermal conductivity λ(xi ) of these n components are known and specified. Preferably, the sensor arrangement 50 has at least temporary read access to a data storage device in which the densities and thermal conductivities are stored. The following table shows, by way of example, the respective density and thermal conductivity of components that occur or can occur in the ventilation circuit 40 and thus in the gas sample Gp, where the densities and thermal conductivities refer to a reference ambient temperature of 15 °C and a reference ambient pressure of 1 bar. Table 1 Thermal conductivity and density of various gas components Gas xi Density ρ(xi ) [gdm 3< ] Thermal conductivity λ(xi ) [WmK] Oxygen (O2) 1,336 0,02615 Nitrogen (N2) 1,169 0,02566 Carbon dioxide (CO2) 1,8474 0,01643 dry ambient air 1,209 0,02603 water vapor 1 0,0199 Isofluran 7,701 0,00942 Nitrous oxide (N₂O) 1,848 0,0173 Argon (Ar) 1,669 0,01782

[0094] The gas components have different densities. It can be seen that the anesthetic isoflurane, mentioned as an example, has a density many times greater than the other gas components.

[0095] As previously explained, an optional pressure sensor 36 measures the pressure in the ventilation circuit 40 and preferably provides the airway pressure PAW. The optional pressure sensor 58 measures the ambient pressure Pamb, the optional temperature sensor 39 the ambient temperature Tempamb, and an optional pressure sensor 57 the pressure Pcell of the gas sample Gp at the inlet of the sensor array 50. The values ​​listed in Table 1 are referenced to a specific reference ambient temperature and pressure. Optionally, the signal processing unit 30 uses signals from sensors 36, 58, and / or 39 to derive the actual thermal conductivity and density of the possible gas constituents at the actual ambient temperature Tempamb and pressure Pamb.

[0096] The goal is to find the respective concentration ξ(xi ), i.e. the proportion in vol.-%, of each component xi (i=1, ..., n).

[0097] In many cases, it can be said with sufficient accuracy that the density ρ of the gas sample Gp is ​​a weighted average of the respective densities ρ(xi ) of the n components, i.e., that: ρ = ξ x 1 * ρ x 1 + … + ξ x n * ρ x n .

[0098] The desired concentrations ξ(x 1 ), ..., ξ(xn ) of the gas components x 1 , ..., xn function as the weighting factors.

[0099] The above discussion referred to Figures 2 to 5 A sensor 53 measures a detection parameter that correlates with the thermal conductivity λ of the gas sample Gp. In the example of Figure 2 This is a detection parameter of thermocouple 8, in the example of Figure 5 Signal 76. In many cases, it can be said with sufficient accuracy that the thermal conductivity λ of the gas sample Gp is ​​a weighted average of the respective thermal conductivities λ(xi ) of the components: λ = ξ x 1 * λ x 1 + … + ξ x n * λ x n .

[0100] The desired concentrations ξ(x 1 ), ..., ξ(xn ) of the gas components x 1 , ..., xn function as the weighting factors.

[0101] It is also possible to use the following functional dependency: λ = ∑ i = 1 n λ x i 1 + ∑ k = 1 k # i n G i k ξ x k ξ x i

[0102] The factors G(i,k) (i=1, ..., n; k=1, ..., n) can be determined empirically beforehand.

[0103] The sensor 53 is also able to measure the magnetically modulated thermal conductivity λ 2f of the gas sample Gp, for example using the periodic component of the detection parameter of the configuration according to Figure 2 or using the oscillating signal 75 of the circuit from Figure 5 Because O₂ is a paramagnetic gas, λ 2f depends significantly on the O₂ concentration ξ(O₂). In general, the following functional dependence f can be applied: λ 2 f = f ξ O 2 , ξ N 2 O , ξ CO 2 , ξ H 2 O , ξ Ar , Temp amb , P cell

[0104] The functional relationship f is predefined. Temp amb denotes the ambient temperature, which is measured, for example, by temperature sensor 39. The temperature of the gas sample Gp typically does not differ significantly from the ambient temperature Temp amb. The O₂ concentration has an approximately linear relationship. The pressure P cell is measured, for example, by pressure sensor 57.

[0105] Figure 8 This figure shows, as an example, the magnetically modulated thermal conductivity λ²f of a gas mixture as a function of the O₂ concentration ξ(O₂). In this case, the gas mixture consists only of oxygen and N₂O. The x-axis represents the concentration ξ(O₂) of oxygen in the gas mixture in vol.%, and the y-axis represents the magnetically modulated thermal conductivity λ²f. It can be seen that the relationship λ²f = λ²f [ξ(O₂)] is approximately linear, but not perfectly linear.

[0106] Sensor 54 measures the CO₂ concentration ξ(CO₂) and the N₂O concentration ξ(N₂O). Pressure sensor 57 measures the pressure Pcell. A capacitive sensor (not shown) measures the H₂O concentration ξ(H₂O), i.e., the concentration of water vapor in the gas sample Gp. Density sensor 59, 60, which was mentioned above with reference to Figure 6 and Figure 7 As described, the density ρ of the gas sample Gp is ​​measured.

[0107] The CO₂ concentration ξ(CO₂), the N₂O concentration ξ(N₂O), and the water vapor concentration ξ(H₂O) are measured directly. This leaves three unknowns: the O₂ concentration ξ(O₂), the anesthetic concentration ξ(A-Gas), and the argon concentration ξ(Ar). To determine these three unknowns, equations (3), (4), and (6) are used. Taken together, this results in a system of three unknowns, namely ξ(O₂), ξ(A-Gas), and ξ(Ar), and three equations, namely (3), (4), and (6).

[0108] In one implementation form, three values ​​ξ(x 1 ), ξ(x 2 ) and ξ(x 3 ) are calculated for the three unknowns ξ(O 2 ), ξ(A-Gas) and ξ(Ar) such that an objective function Z with Z ξ x 1 , ξ x 2 , ξ x 3 = α 1 * ρ meas − ρ ξ x 1 , ξ x 2 , ξ x 3 2 + α 2 * λ meas − λ ξ x 1 , ξ x 2 , ξ x 3 2 + α 3 * λ 2 f , meas − λ 2 f ξ x 1 , ξ x 2 , ξ x 3 2 + minimized. Here, ρ meas denotes the measured density, λ meas the measured thermal conductivity, and λ 2f,meas the measured magnetically modulated thermal conductivity. ρ[ξ(x 1 ),ξ(x 2 ),ξ(x3)] denotes the density that occurs according to equation (3), λ[ξ(x 1 ),ξ(x 2 ),ξ(x 3 )] the thermal conductivity according to equation (4) or (5), and λ 2f [ξ(x 1 ),ξ(x 2 ),ξ(x 3 )] the magnetically modulated thermal conductivity according to equation (6). The three factors α₁, α₂, α₃ are chosen such that all three summands of the objective function Z have the same order of magnitude and / or different accuracy requirements for the measurement of the three concentrations ξ(x₁), ξ(x₂), ξ(x₃) are met. The sum of the three factors α₁, α₂, α₃ is 1.

[0109] Obviously, the sum of the gas component proportions equals 1, therefore the following applies: ξ x 1 + … + ξ x n = 1 .

[0110] The N 2 concentration ξ(N 2 ) can be derived using equation (8). Reference symbol list

[0111] 1 Anesthesia machine, part of the ventilation setup 200 2 Measuring chamber of sensor 53, formed in air gap 3 3 Air gap, provided by measuring chamber 2 4, 5 Field coils, together with the pole shoes 6, 7, generate a magnetic field in the measuring chamber 2. 6, 7 The pole shoes, together with the field coils 4 and 5, generate a magnetic field in the measuring chamber 2. 8 Thermocouple, comprising wires 17, 18 and support wires 15, 16 9 Wall of measuring chamber 2 10 Entrance to measuring chamber 2 11 Outlet from measuring chamber 2 12 Connection point between the support wire 15 and the wire 17 13 Connection point between wires 17 and 18 14 Connection point between the support wire 16 and the wire 18 15, 16 Support wires for the thermocouple 8 17, 18 The wires of the thermocouple 8 are connected to each other at the junction 13. 19 Measuring resistance of the thermocouple 8 20 voltage source 21 Patient-side coupling unit in the form of a mouthpiece or breathing mask, connected to the Y-piece 22 22 Y-piece, which connects the patient-side coupling unit 21 with the inspiratory line 32 for the supply (inhalation, inspiration) of the breathable gas mixture Gg and the expiratory line 33 for the removal (exhalation, expiration) of the exhaled gas mixture At. 23a Non-return valve that allows gas flow in the direction of patient P in the inspiratory line 32 and blocks it in the opposite direction. 23b Non-return valve that allows gas flow away from patient P in the expiratory line 33 and blocks flow towards patient P. 24a Fluid delivery unit in the form of a blower, which generates a volume flow of the breathable gas mixture Gg in the direction of the patient P. 24b Controllable valve that generates the ventilation strokes 24c PEEP valve, which maintains an end-expiratory pressure in the patient's lungs P. 25a Carbon dioxide absorber, absorbs 40% carbon dioxide from the respiratory circuit 26 Breathing bag, through which the ventilation circuit 40 can be driven 27 Fluid flow of fresh air or other fresh gas to the ventilation circuit 40 28 Fluid flow of vaporous anesthetic to the ventilation circuit 40, generated by the anesthetic metering unit 31 29 adjustable overpressure valve capable of releasing gas from the 40° ventilation circuit 30 Signal processing unit for sensor arrangement 50, evaluates signals from sensors 53, 54, 57 and 58. 31 Anesthetic metering device, generates the anesthetic flow 28 32 The inspiratory line for inhalation, connected to the Y-piece 22, has the non-return valve 23a. 33 The expiratory line for exhalation, connected to the Y-piece 22, has the non-return valve 23b. 34 Branch point of the extraction hose 52, located near the Y-piece 22 35 The ventilation control unit controls the fluid delivery unit 24a, the valve 24b and the anesthetic dosing unit 31, and receives signals about the respective gas concentration and messages from the signal processing unit 30. 36 Pressure sensor in the ventilation circuit 40, preferentially measures the pressure P applied to the patient P aw 37 The inlet point, where the drainage tube 56 enters the ventilation circuit 40, is located upstream of the carbon dioxide absorber 25a. 39 Temperature sensor, measures the temperature Temp amb in the vicinity of the ventilator 1 40 The ventilation circuit, through which patient P is artificially ventilated, comprises the patient-side coupling unit 21, the Y-piece 22, the inspiratory line 32 and the expiratory line 33. 42 Power amplifier between the voltage source 43 and the field coil 5 43 Voltage source, outputs a sinusoidal electrical voltage 44 optional display device of sensor 53 50 Sensor arrangement includes sensors 53, 54, 57, the density sensor 59, 60 and the pump 55 51 Waterfall upstream of sensor array 50 52 The sampling tube, through which the gas sample Gp is ​​taken from the ventilation circuit 40, begins at a branch point 34 between the patient-side coupling unit 21 and the Y-piece 22 and leads to the water trap 51. 53 Oxygen concentration sensor 54 Sensor for the concentration of CO2, N2O and anesthetic in the gas sample Gp 55 Pump which draws a gas sample GP into the sampling hose 52 56 Drainage tube, connects the sensor assembly 50 to the ventilation circuit 40 57 Pressure sensor of sensor assembly 50, measures the pressure of the gas sample Gp 58 Ambient pressure sensor P amb 59 The mechanical bending oscillator, which measures the density of the gas sample Gp, comprises the housing 83, the tube 80 with the legs 80.1, 80.2, the mounting point 81, the electromagnetic transducer 82.1, 82.2, the actuator 84, the amplifier 85 and the evaluation unit 86. 60 electronic bending oscillator in the form of a quartz crystal, comprising legs 61.1, 61.2 62 Electromagnet, generates a time-varying magnetic field in the air gap 3, comprises the coil 63 63 electric coil of the electromagnet 62 64 The measuring unit, implemented as a chip, comprises the heat conduction measuring element 65, the heating unit 66 and the membrane 67. 65 electrically controllable heat conduction measuring element of the measuring unit 64 66 electrically controlled heating unit of the measuring unit 64 67 Membrane of measuring unit 64 68 electrically conductive connecting element between the two heating elements of the heating unit 66 69 Frame of measuring unit 64 70 amplifier 71 Voltage divider 72 DC voltage source 73 Low-pass filter, delivers the signal 76 at its output. 74 High-pass filter, delivers the signal 75 at its output. 75 Signal at the output of the high-pass filter 74, correlated with the concentration ξ(O 2 ) of oxygen 76 Signal at the output of the low-pass filter 73, correlated with the thermal conductivity λ of the gas sample Gp 77 Measuring position of measuring unit 64 80 U-shaped tube, with legs 80.1, 80.2, receives the gas sample Gp, is excited to vibrate. 80.1, 80.2 Leg of the U-shaped tube 80 81 Fixing point where the two legs 80.1, 80.2 are clamped 82.1, 82.2 Electromagnetic converters, which in one mode convert alternating electrical voltage into mechanical vibrations and in another mode convert mechanical vibrations into alternating electrical voltage, comprise the coils 83.1, 83.2 and the magnets 84.1, 84.2 83 The housing of the density sensor 59 accommodates the tube 80. 83.1, 83.2 Coil of converter 82.1, 82.2 84.1, 84.2 Magnet of converter 82.1, 82.2 85 Density sensor amplifier 59 86 Evaluation unit of the density sensor 59 100 The measuring system comprises the sensor assembly 50, the water trap 51, the signal processing unit 30, and the hoses 52 and 56. 200 The ventilation setup includes the anesthesia machine 1, the measuring system 100, the patient-side coupling unit 21, and the lines 32 and 33. At Gas mixture exhaled by patient P, containing carbon dioxide and an anesthetic G(i,k) empirically determined weighting factors Gg The breathable gas mixture, which the ventilator 1 delivers to the patient-side coupling unit 21, contains oxygen, an anesthetic and argon. GP The gas sample is taken from the ventilation circuit 40, routed through the sampling tube 52 to the sensor assembly 50 and fed back into the ventilation circuit 40 through the discharge tube 56. λ Thermal conductivity of the gas sample Gp λ(xi ) Thermal conductivity of the gas component xi (i=1, ... ,n) of the gas sample Gp λ 2f Magnetically modulated thermal conductivity is a measure of the oxygen concentration in the gas sample Gp. λ 2f (xi ) magnetically modulated thermal conductivity of the gas component xi (i=1, ..., n) of the gas sample Gp n Number of gas components in the gas sample Gp P Patient who is artificially ventilated and connected to the patient-side coupling unit 21 P amb Pressure in the vicinity of the ventilation setup 200, measured by pressure sensor 58 P aw Airway pressure in the patient-side coupling unit 21 is measured by the pressure sensor 36 in the inspiratory line 32. P cell Pressure of the gas sample Gp at the inlet of the sensor arrangement 50, measured by the pressure sensor 57 ρ Density of the gas sample Gp ρ(xi ) Density of the gas component xi (i=1, ..., n) of the gas sample Gp Temp amb Ambient temperature, measured by temperature sensor 39 ξ(xi ) Concentration in vol.% of the gas component xi (i=1, ..., n) of the gas sample Gp x 1 , ..., xn Gas components of the gas sample Gp

Claims

1. Sensor arrangement (50) for measuring the particular concentration of three gas components of a gas sample (Gp), wherein the particular density and the particular thermal conductivity of each of the three gas components are specified, wherein one gas component (O2) of the three gas components is a paramagnetic gas, wherein the sensor arrangement (50) comprises - a measuring chamber (2) for receiving a gas sample (Gp), - a thermal conductivity sensor (53) and - a density sensor (59, 60), wherein the thermal conductivity sensor (53) is configured to measure the thermal conductivity (A) of the gas sample (Gp), wherein the sensor arrangement (50) is configured to - guide the gas sample (Gp) into the measuring chamber (2), - apply a magnetic field having an oscillating magnetic field strength to the measuring chamber (2) and - measure a magnetically modulated thermal conductivity (λ2f) of the gas sample (Gp) in the measuring chamber (2), wherein the magnetically modulated thermal conductivity (λ2f) is the portion of the thermal conductivity of the gas sample (Gp) that oscillates depending on the magnetic field strength, wherein the density sensor (59, 60) is configured to measure the density (ρ) of the gas sample (Gp), and wherein the sensor arrangement (50) is configured to determine the three gas component concentrations using - the specified densities of the gas components, - the specified thermal conductivities of the gas components, - the measured thermal conductivity (λ) of the gas sample (Gp), - the measured magnetically modulated thermal conductivity (λ2f) of the gas sample (Gp) and - the measured density (ρ) of the gas sample (Gp).

2. Sensor arrangement (50) according to claim 1, characterized in that the sensor arrangement (50) comprises a heating unit (8, 66), the heating unit (8, 66) being configured to supply thermal energy to a gas sample (Gp) in the measuring chamber (2), the sensor arrangement (50) being configured to - measure an electrical detection quantity (U) which correlates with the thermal conductivity (λ) of the gas sample (Gp), and - derive an oscillating signal (75), which oscillates depending on the magnetic field strength, and a further signal (76), of which the time course does not depend on the oscillating magnetic field strength, by filtering the electrical detection quantity (U), and the sensor arrangement (50) being further configured to - measure the magnetically modulated thermal conductivity (λ2f) of the gas sample (Gp) depending on the oscillating signal (75), in particular to use the oscillating signal (75) as the magnetically modulated thermal conductivity (λ2f) of the gas sample (Gp), and - measure the thermal conductivity (λ) of the gas sample (Gp) depending on the further signal (76), in particular to use the further signal (76) as the thermal conductivity (A).

3. Sensor arrangement (50) according to either of the preceding claims, characterized in that the density sensor comprises a flexural resonator (59, 60) having a vibrating body (80, 61.1,61.2), the sensor arrangement (50) being configured to guide the gas sample (Gp) through or along the vibrating body (80, 61.1, 61.2), the flexural resonator (59, 60) being configured to - set the vibrating body (80, 61.1,61.2) into vibrations and - measure the natural frequency of the vibrating body (80, 61.1,61.2), and the sensor arrangement (50) being configured to determine the density (ρ) of the gas sample (Gp) depending on the measured natural frequency of the vibrating body (80, 61.1,61.2).

4. Ventilation arrangement (200) for artificial ventilation of a patient (P), wherein the ventilation arrangement (200) comprises - a medical device (1), in particular a ventilator, - a patient-side coupling unit (21), - a ventilation control device (35) and - a sensor arrangement (50) according to any of the preceding claims, wherein the patient-side coupling unit (21) is connected or at least temporarily connectable to the patient (P), wherein the ventilation arrangement (200) is configured to convey a breathable gas mixture (Gg) from the medical device (1) to the patient-side coupling unit (21), wherein a target range for the concentration [ξ(O2)] of a gas component (O2) in the gas mixture (Gg) is specified, wherein preferably this gas component is the paramagnetic gas, wherein the ventilation arrangement (200) is configured to - divert a gas sample (Gp) from the gas mixture (Gg) that is conveyed to the patient-side coupling unit (21) and - guide the diverted gas sample (Gp) to the sensor arrangement (50), and wherein the sensor arrangement (50) is configured to measure the actual concentration [ξ(O2)] of the gas component (O2) for which the target range is specified in the diverted gas sample (Gp).

5. Ventilation arrangement (200) according to claim 4, characterized in that the ventilation control device (35) is configured to - regulate the concentration [ξ(O2)] of the gas component (O2) for which the target range is specified in the gas mixture (Gg) that is conveyed to the patient-side coupling unit (21) and - use the measured gas component concentration [ξ(O2)] for the regulation, and one regulation objective in the course of the regulation being that the actual gas component concentration [ξ(O2)] in the gas mixture (Gg) remains in the specified target range.

6. Measuring method for measuring the particular concentration of three gas components of a gas sample (Gp), wherein the particular density and the particular thermal conductivity of each of the three gas components are specified, wherein one gas component (O2) of the three gas components is a paramagnetic gas and wherein the measuring method comprises the steps in which - the thermal conductivity of the gas sample (Gp) is measured and - the density of the gas sample (Gp) is measured, wherein the measuring method comprises the further steps in which - the gas sample (Gp) is guided into a measuring chamber (2), - a magnetic field having an oscillating magnetic field strength is applied to the measuring chamber (2) and - a magnetically modulated thermal conductivity (λ2f) of the gas sample (Gp) is measured in the measuring chamber (2), wherein the magnetically modulated thermal conductivity (λ2f) is the portion of the thermal conductivity of the gas sample (Gp) that oscillates depending on the magnetic field strength, and wherein the further step is performed in which the three gas component concentrations are determined using - the specified densities of the gas components, - the specified thermal conductivities of the gas components, - the measured thermal conductivity (A) of the gas sample (Gp), - the measured magnetically modulated thermal conductivity (λ2f) of the gas sample (Gp) and - the measured density (p) of the gas sample (Gp).

7. Measuring method according to claim 6, characterized in that the thermal conductivity of the gas sample (Gp) in the measuring chamber (2) is measured as the thermal conductivity (A) and the measuring method comprises the further steps in which - a heating unit (8, 66) is heated, - the heated heating unit (8, 66) supplies thermal energy to the gas sample (Gp) in the measuring chamber (2), - an electrical detection quantity (U) of the heated heating unit (8, 66) is measured, the detection quantity (U) correlating with the thermal conductivity (λ) of the gas sample (Gp), and - an oscillating signal (75), which oscillates depending on the magnetic field strength, and a further signal (76), of which the time course does not depend on the oscillating magnetic field strength, are derived by filtering the electrical detection quantity (U), - the magnetically modulated thermal conductivity (λ2f) of the gas sample (Gp) being measured depending on the oscillating signal (75), in particular the oscillating signal (75) being used as the magnetically modulated thermal conductivity (λ2f) of the gas sample (Gp), and - the thermal conductivity (λ) of the gas sample (Gp) being measured depending on the further signal (76), in particular the further signal (76) being used as the thermal conductivity (λ).

8. Measuring method according to claim 6 or claim 7, characterized in that the measuring method comprises the further steps in which - the gas sample (Gp) is guided through or along a vibrating body (80, 61.1, 61.2) of a flexural resonator (59, 60), - the vibrating body (80, 61.1,61.2) is set into vibrations and - the natural frequency of the vibrating body (80, 61.1,61.2) is measured, the density of the gas sample (Gp) being determined depending on the measured natural frequency of the vibrating body (80, 61.1,61.2).

9. Measuring method according to any of claims 6 to 8, characterized in that the thermal conductivity, the magnetically modulated thermal conductivity and / or the density of the gas sample (Gp) additionally depends on the concentration of a fourth gas component, the density of the fourth gas component being specified and the measuring method comprising the further steps in which - the concentration of the fourth gas component is measured or is determined in some other way and - in the step of determining the particular concentration of the three gas components, the measured concentration of the fourth gas component is additionally used.

10. Measuring method according to claim 9, characterized in that the step of measuring the concentration of the fourth gas component comprises the steps in which - a radiation source emits electromagnetic radiation or sound, - the emitted electromagnetic radiation or the emitted sound penetrates the gas sample (Gp) and strikes a detector, - the detector measures the intensity of the incident electromagnetic radiation or the incident sound and - the detector generates a signal depending on the measured intensity, the concentration of the fourth gas component being measured depending on the signal generated by the detector, in particular the signal generated by the detector being used as the concentration of the fourth gas component.

11. Measuring method according to any of claims 6 to 10, characterized in that three functional relationships, three distance indicators, and one objective function are specified, the first functional relationship describing the thermal conductivity (λ) of the gas sample (Gp) as a function of the three gas component concentrations, the second functional relationship describing the magnetically modulated thermal conductivity (λ2f) of the gas sample (Gp) as a function of the three gas component concentrations, the third functional relationship describing the density (p) of the gas sample (Gp) as a function of the three gas component concentrations, the first distance indicator describing an indicator for the distance between the measured thermal conductivity (λ) of the gas sample (Gp) and the thermal conductivity derived using the first functional relationship, the second distance indicator describing an indicator for the distance between the measured magnetically modulated thermal conductivity (λ2f) of the gas sample (Gp) and the magnetically modulated thermal conductivity derived using the second functional relationship, the third distance indicator describing an indicator for the distance between the measured density (p) of the gas sample (Gp) and the density derived using the third functional relationship, the objective function being an aggregation, in particular a weighted average, of the three distance indicators and the measuring method comprising the further steps in which - the three measured values for the thermal conductivity (λ), the magnetically modulated thermal conductivity (λ2f) and the gas sample density (p) are inserted into the objective function and - a triple of values for the three gas component concentrations is calculated in such a way that the objective function is minimized.

12. Measuring method according to any of claims 6 to 11, characterized in that the three gas components of which the concentrations are measured in the diverted gas sample (Gp) are oxygen (O2), an anesthetic and argon.

13. Ventilation method for artificial ventilation of a patient (P), wherein the patient (P) is connected to a patient-side coupling unit (21) and wherein the ventilation method comprises the automatically performed steps in which - a breathable gas mixture (Gg) is conveyed from a medical device (1), in particular from a ventilator, to the patient-side coupling unit (21), a target range for the concentration [ξ(O2)] of a gas component (O2) in the gas mixture (Gg) is specified, - a gas sample (Gp) is diverted from the gas mixture (Gg) that is conveyed to the patient-side coupling unit (21), - the actual concentration [ξ(O2)] of the gas component (O2) for which the target range is specified is measured, wherein, for the measurement of the actual gas component concentration [ξ(O2)], a measuring method according to any of claims 6 to 12 is applied and wherein the gas component for which the target range is specified is one of the three gas components of which the concentration is measured, preferably the paramagnetic gas, - wherein the actual concentration [ξ(O2)] of the gas component (O2) in the gas mixture (Gg) is preferably regulated using the regulation objective that the actual oxygen concentration is within the specified target range, wherein, for the regulation, the measured gas component concentration [ξ(O2)] in the diverted gas sample (Gp) is used.

14. Ventilation method according to claim 13, characterized in that the gas mixture (Gg) is produced using ambient air, the oxygen concentration being increased during the production of the gas mixture (Gg) and the three gas components of which the concentrations are measured in the diverted gas sample (Gp) being oxygen (O2), an anesthetic and argon.

15. Ventilation method according to claim 13 or claim 14, characterized in that the gas mixture (Gg) is conveyed through a fluid guidance unit (32) from the medical device (1) to the patient-side coupling unit (21) and the detection of the event that at least one gas component in the conveyed gas mixture (Gg) lies outside the target range specified for that gas component triggers the step of flushing the fluid guidance unit (32).