DE102008047511A1 - Gas i.e. respiratory gas, analyzing device for optimal treatment of patient, has evaluation device to provide data considering current in conducting units and measured values, where carbon dioxide concentration is determined from data - Google Patents

Abstract

The device has a conveyance unit to convey gases i.e. respiratory gas, and electrical conducting units e.g. platinum wires (5-7) consecutively arranged with respect to a gas flow. Measuring units measure an electrical measured value e.g. electrical voltage, current or resistance, of the conducting units, and other measured values such as tensile stress, temperature, and thermal capacity and conductivity. An evaluation device provides data for regulation in consideration of current in the conducting units and the values, where carbon dioxide concentration of the gas is determined from the data. An independent claim is also included for a method for determining carbon-dioxide concentration of a gas in a device for conveyance of the gas.

Description

The The invention relates to a device for gas analysis, consisting in particular from a device for the passage of the gas and a device with at least two in proportion to the gas flow in essentially arranged behind one another electrically conductive means.

The Invention relates to this In addition, a method for determining the CO2 content of a gas in a device for the passage of the gas, by means of data from at least two in proportion to the gas flow in essentially arranged behind one another electrically conductive means.

to optimal treatment of patients to a device for delivery of Respiratory gas are connected, is usually a continuous monitoring the proportion of CO2 in the exhaled air realized. The won Allow data an explanation about the metabolism of the treated patient. This is often done by means of a sidestream procedure a certain part of the breathing air (in / expiratory) sucked off and fed to an evaluation unit.

Of Further, according to the state of the art, the flow and thus also the respiratory minute volume (AMV) determined. This can be done with ultrasonic sensors as well as with sensors that work according to the hot-wire transit time method, happen.

Of Further, breathing gas temperature sensors are used to control the temperature to be able to determine the respiratory gas.

The The device described above requires a flow sensor and a Extra unit for determining the CO2 concentration in the air. For this are an additional Sensor as well as other elements needed to pump out the sample gas, For example, suction, pump, test gas drying, necessary. moreover is needed with the sidestream method an additional hose, which in some situations prone to hooking and for the user an additional Application difficulty means. Also occurs through the derivative of the sample gas, a time shift in the measurement, if, for example the flow is measured close to the patient, with the proportion of CO2 mostly in the device determined itself. this leads to to a shift of the measurement results in the presentation by the device. Furthermore, to determine the breathing gas temperature, a separate temperature sensor needed.

Also There are procedures that involve the determination of flow and breathing gas composition (mainly CO2) allow the assumption of the respiratory quotient. This happens with a sound sensor and the determination of the speed of sound in the breathing gas. This method can be achieved by means of the so-called Realize mainstream process, ie the determination of parameters directly over that total, exhaled and inhaled volumes of respiratory gas. This has the Advantage that only one sensor is needed. Disadvantages of this method, however, are the resulting size and the additionally necessary Temperature sensor. Another disadvantage is a lack of autoclaving of the sensor and its high energy requirement.

task It is the object of the present invention to provide a device mentioned type to improve such that a good measurement accuracy provided in the simplified structure.

These Task is inventively characterized solved, that means are present, which cause by at least one of the electric conductive Means one in strength in controlled form changing current is passed that measuring means are present, with which at least one of the electrically conductive means at least temporarily an electrical measurement (such as electrical Voltage, current or electrical resistance) or other measured value (such as z. Tensile stress, temperature, heat capacity, thermal conductivity) is measured, and that one Evaluation device is present, taking into account in particular of changing in a controlled manner amperage in at least one conductive Medium and under consideration the one of the measuring means measured values (s) Data available represents the basis of the CO2 content of the gas is determined at least temporarily.

Further The object of the present invention is to provide a method of the introductory mentioned type to improve such that the construction of a compact measuring device supports becomes.

This object is achieved in that at least one of the electrically conductive means in the strength in a controlled manner changing current is passed and at least time For example, an electrical measured value (such as electrical voltage, current or electrical resistance) or other measured value (such as tensile stress, temperature, heat capacity, thermal conductivity) of at least one of the electrically conductive means is used, in particular taking into account the current in a controlled manner changing in at least one conductive means from the / measured at the electrically conductive measuring means measured value (s) to determine the CO2 content of the gas at least temporarily.

By which explained below The invention provides an apparatus and a method, with which the flow, the temperature as well as the gas composition of the breathing gas, in particular the proportion of CO2, with only one sensor can be determined.

It deleted thus the whole unit for the determination of the CO2 content including breathing gas extraction, hoses, Drying of the extracted gas and the CO2 sensor.

Of the inventive sensor works on the hot wire runtime method, which counts among the thermal processes. Located in the gas flow channel transverse to the flow direction three very fine, consecutively arranged current-carrying (platinum) wires as electrically-conductive tel. The middle wire, the transmitting wire, becomes sinusoidal Electricity heated. The inspiratory and expiratory gas flowing by is heated and the heat is transmitted by the air flow to one of the outer wires, the receiver wire.

There the heated gas can noticeably change the resistance of the receiver wires with a constant flow Electricity is also sinusoidal varying voltage can be measured. From the measured phase shift between the current fed into the transmit wire and the receive wire measured voltage can be the running time and therefore the flow of the flowing through Medium can be calculated.

By The symmetrical arrangement of the wires can be bidirectional Flow measurement can be performed. The advantages of this measurement method for determining the volume flow lie in the good dynamics, the small resulting from the wires Pressure drop and independence of temperature, moisture content and composition of the respiratory gas.

As external Environmental conditions that affect the flow measurement an insignificant Exert influence, are the ones already mentioned above Gas temperature and gas composition, as far as usual in respiratory technology gas mixtures from air, oxygen, CO2 and water vapor are used.

In an embodiment The invention can be a prior calibration of the presented here Sensors for further determination of the gas composition by the in the ventilator existing sensors take place. It can be moisture, O2 content as well the temperature of the inspiratory Gasvo lumens measured become; this is how the inspiratory parameters are known.

The Respiratory gas temperature and flow affect the wire impedance the three wires. When the temperature rises and the flow goes down, the resistance decreases to.

Certainly Now let's look at the resistance levels of the three wires, one can get the temperature Determine the breathing gas, since the flow already by the transit time method is determined.

With Help of the determined temperature and of the (barometric) air pressure, which over a hose to the device guided and measured, or by device-internal sensors (pressure, Flow) is estimated, can the absolute proportion of water vapor or moisture calculated (Magnus formula). furthermore, can be expiratory of Completely wasserdampfgesättigtem Gas can be assumed because the respiratory gas during passage through the Respiratory system is moistened. This assumption can also be made in the case of Use of so-called HME filters (Heat Moisture Exchange filters) kept upright. In this application, part of the Moisture and heat the expiratory breathing gas stored in a fleece. The passing Gas is opposite the entering gas cooler, but still fully saturated with water vapor.

The temperature of the gas can in particular be determined from the first wire lying in the direction of flow. Since the measuring current through the wire heats this only slightly, a change in resistance due to different flows and in particular by different gas mixtures is low. Depending on the im The influence of the flow on the measuring accuracy should not be neglected. Here, the independently determined flow (runtime method with 2 , and 3 , Wire) are used to correct the flow influences.

The middle wire generates a flow-, gas- and temperature-dependent temperature oscillation. The energy is passed on to the medium through the gas properties thermal conductivity and heat capacity as well as through the flow-immanent forced convection and from the receiver wire, wire 3 , partially recorded. The resistance level or the temperature of each wire results from the current flowing through this wire, from the temperature of the gas, from the flow flowing past it, and from the gas property (thermal conductivity and heat capacity).

The Gas mixture has a strong influence on the middle level and the amplitude of the resistance changes on the transmitting wire, since here much higher currents are used than at the receiving wires. Based on the amplitude and level of the measured transmission wire voltage Now the gas composition can be determined; so in how far the oxygen content decreases and the carbon dioxide content elevated Has. As a result, an average heat capacity and / or thermal conductivity of the gas mixture are determined.

In a preferred embodiment The invention is for the calculation of the proportion of expiratory CO2 the assumption of a certain respiratory quotient r, ie The relationship of released carbon dioxide volume to absorbed oxygen volume, necessary. additionally is an assumption about the relative humidity of the expiration gas meet to determine the proportion of water vapor in the gas mixture to be able to.

The method can be further improved in terms of greater sensitivity when, in addition to the analysis of the transmission wire voltages nor the average voltage and the amplitude of the signal on 3 , Wire is taken into account. Depending on the gas composition and the average values for heat capacity and thermal conductivity, with constant flow times more, sometimes less heat is given off to the downstream measuring wire in the direction of flow. air O2 N2 Ar CO2 H2 H2O Special heat cap. (20 ° C) 1,010 0.917 1,038 0.523 0.837 14.320 2.08 thermal conductivity 0.024 0.023 0.02 0.016 0,015 0.18 0.0248

The thermal conductivity of O2 and CO2 differ by about 40-60%.

Therefore, according to the invention the determination of respiratory gas parameters, such. As CO2, by an assignment the amplitudes of the gas composition possible.

Also can a relationship between the amplitude eg. The voltage and / or the mean voltage level of the measured voltages or the wirewound resistors and the thermal conductivity and / or the heat capacity produced become.

According to the invention, the calculation of the composition of the respiratory gas and / or, for example, of the CO2 content is also possible:
In a particularly preferred embodiment of the invention, an advantageous current intensity pattern may be a sinusoid or other modulations in magnitude and magnitude, which may include any interrupts, induction, amplitude, absolute limits.

In a further embodiment of the invention Values other than a specific measurement on the respiratory gas derived elsewhere or, for example, the breathing gas temperature is equal to the average body temperature.

In Another particularly preferred embodiment of the invention can by the evaluation of three wires, which is in the flow channel be implemented with the aid of a in the evaluation device Characteristic field, the measured values are compared with the characteristic field and the CO2 content of the gas can be determined.

The Device for gas analysis, consists in particular of a device for the passage of the gas, a device with at least two in relation to to the gas flow in essentially arranged behind one another electrically conductive means. There are means available which cause at least one of electrically conductive Means one in strength in controlled form changing Electricity is passed. There are measuring means available with which at least one of the electrically conductive means at least temporarily an electrical measurement (such as electrical voltage, current or electrical resistance) or another measured value (such as tensile stress, temperature, heat capacity, thermal conductivity) is measured. It is an evaluation device available, in particular under consideration which change in a controlled manner amperage in at least one conductive Medium and taking into account the / from the measuring means measured values (s) Provides data, from which determines the CO2 content of the gas, at least temporarily can be.

In a further embodiment The invention may include at least one electrically conductive agent one of the following group: bonded between two pins Wire, between two pins attached wire, tracks on a board.

In a further embodiment the invention is the number of electrically conductive agent preferably 3.

In a further embodiment According to the invention, the advantageous pattern of amperage can be a sinusoid be.

In a further embodiment the invention, the CO2 content via a comparison of the data with a characteristic field are determined.

In a further embodiment According to the invention, the gas may be a breathing gas.

In a further embodiment The invention may be the expiratory and / or inspiratory CO2 content a breathing gas are determined.

In a further embodiment The invention may also include at least one internal or external device for determining ambient pressure and / or respiratory gas pressure and / or Respiratory gas humidity and / or respiratory gas temperature and / or inspiratory CO2 content of the respiratory gas be present.

In a further embodiment The invention can over the determination of heat capacity and / or the Wärmeleitfä ability of the gas by means of matching the data with the characteristic field the CO2 content of the gas can be determined.

In a further embodiment The invention can measure the body temperature as a measured value for the temperature T. of the patient is accepted.

moreover can further measured values are accepted.

Brief Description:

1 : Representation of a cross section through a sensor

2 : Illustration of the voltage curve of three different wires

3 : Illustration of the voltage curve of three different wires when the temperature or flow of the gas changes

4 : Characteristic field

1 shows an embodiment of a sensor ( 4 ) according to the above method. This sensor ( 4 ) can with its two ends ( 11 + 12 ), for example, between a patient valve on the one and a respiratory filter are arranged or plugged directly onto a mask / Endotrachealtubus. If the patient is breathing in and out, or if the patient is being ventilated, air volumes will shift across the constriction ( 13 ). The grids ( 9 ) are used to laminarize the flow and to protect the (platinum) wires ( 5 . 6 . 7 ) appropriate. The wires ( 5 . 6 . 7 ) are affected by electrical contacts ( 1 . 2 . 3 ) in the middle of the narrowing ( 13 ) held. There are this wires in the flow direction, which can show depending on the breathing in one direction or another, spanned one after the other. The contacts ( 1 . 2 . 3 ) are led to the outside and can be connected with a plug.

The outlet opening ( 10 ) can be optionally connected to a respiratory gas analyzer or to a pressure evaluator.

2 shows a detail of the sensor ( 18 ). This one has on his pens ( 21 ) electrically conductive means in the form of wires spanned.

3 Figure 3 shows three measured voltage signals emanating from the three wires in the flow channel. signal 1 is attributable to the wire in the flow direction. This signal adjusts depending on the temperature of the gas that has flown past and the type of gas. signal 2 starts from the middle wire, the heating wire. This signal is preferably sinusoidal. signal 3 results from the heating of the wire, which results from heating the air through the wire 2 and the further transport of this energy via the flow also heats this wire sinusoidally. From the phase shift and the known wire distance, the gas velocity and thus flow and respiratory minute volume can be calculated.

4 shows a similar representation as 3 , Here, however, a sudden increase in the gas temperature occurs at time t_1, so that all signals shift upwards by about the same value.

5 shows a graph with different characteristics, which shows the course of, for example, the voltage when changing, for example, the temperature of different Gaszu compositions (moisture, Co2 content, etc.) ( 14 . 16 . 17 ) illustrate.

Furthermore, a further course is shown, which is generated from the data of the measuring means ( 15 ). By determining the gas temperature, it is then possible to determine, for example, the determination of the gas composition, the heat capacity, the thermal conductivity or the CO 2 concentration of the gas.

In a further embodiment According to the invention, the sensor can be designed as a chip sensor. in this connection the chip sensor consists of at least one semiconductor device and a housing part, which forms a channel. The channel is measured by the liquid or flows through the gas. Arranged in the channel are at least two sensors. continues an evaluation component of the semiconductor device. The Transmitter is set up to detect heat differences at the Sensors occur to identify and evaluate.

Claims (19)

Device for gas analysis, consisting in particular of a device for passing the gas and a device having at least two in relation to the gas flow substantially successively arranged electrically conductive means, characterized in that means are provided which cause, by at least one of the electrically conductive means a current varying in intensity in a controlled manner is conducted, that measuring means are present with which at least one of the electrically conductive means at least temporarily an electrical measurement (such as electrical voltage, current or electrical resistance) or other measured value (Such as, for example, tensile stress, temperature, heat capacity, thermal conductivity) is measured, and that an evaluation device is provided which, in particular taking into account the changing in itself controlled current in at least one conductive means and Berü consideration of the measured value (s) measured by the measuring means provides data from which the CO2 content of the gas is determined at least temporarily. Device according to claim 1, characterized in that that at least one electrically conductive means of the following group is: between two pins bonded wire, between two pins attached wire, tracks on a circuit board. Device according to one of the preceding claims 1 to 2, characterized in that the number of electrically conductive means preferably 3. Device according to one of the preceding claims 1 to 3, characterized in that a vorteilhaf tes pattern of amperage is a sine wave. Device according to one of the preceding claims 1 to 4, characterized in that the CO2 content via an adjustment of the data is determined with a characteristic field. Device according to one of the preceding claims 1 to 5, characterized in that the gas is a breathing gas. Device according to one of the preceding claims 1 to 6, characterized in that the expiratory and / or inspiratory CO2 content of a breathing gas is determined. Device according to one of the preceding claims 1 to 7, characterized in that in addition at least one internal or external device for determining ambient pressure and / or respiratory gas pressure and / or Respiratory gas humidity and / or respiratory gas temperature and / or inspiratory CO2 content of the respiratory gas is present. Method for determining the CO2 content of a gas in a device for the passage of the gas, using data from at least two in proportion to the gas flow in essentially electrically conductive means arranged one behind the other, characterized in that at least one of the electrically conductive means one in strength in controlled form changing Current is passed and at least temporarily an electrical measurement (such z. As electrical voltage, current or electrical resistance) or another measured value (such as tensile stress, temperature, heat capacity, thermal conductivity) of at least one the electrically conductive Means is used, in particular taking into account the self-controlled Shape changing amperage in at least one conductive Means from the measured value (s) measured at the electrically conductive measuring means determine the CO2 content of the gas at least temporarily. Method according to claim 9, characterized that at least one electrically conductive means of the following group is: between two pins bonded wire, between two pins attached wire, tracks on a circuit board. Method according to one of the preceding claims 9 to 10, characterized in that the number of electrically conductive means preferably 3. Method according to one of the preceding claims 9 to 11, characterized in that the advantageous pattern of the current strength Sinusoid is. Method according to one of the preceding claims 9 to 12, characterized in that the CO2 content via a comparison of the data is determined with a characteristic field. Method according to one of the preceding claims 9 to 13, characterized in that the gas is a breathing gas. Method according to one of the preceding claims 9 to 14, characterized in that the expiratory and / or inspiratory CO2 content of a breathing gas is determined. Method according to one of the preceding claims 9 to 15, characterized in that by at least one internal or external device ambient pressure and / or respiratory gas pressure and / or Respiratory gas humidity and / or respiratory gas temperature and / or inspiratory CO2 content of the gas is determined. Method according to one of the preceding claims 9 to 16, characterized in that on the determination of the heat capacity and / or thermal conductivity of the gas by means of matching the data with the characteristic field the CO2 content of the gas is determined. Method according to one of the preceding claims 9 to 17, characterized in that as a measured value for determining the CO2 content is assumed z. B. the body temperature of the patient is equal to the gas temperature T. Method according to one of the preceding claims 9 to 18, characterized in that for determining the CO2 content at least two values from the following group of data from the measurements used to determine the CO2 content of the gas: voltage equal component of a gas flow to the first electrically conductive means, voltage equal to a gas flow second electrically conductive means, voltage equal to a gas flow third electrically conductive means, amplitude of the gas flow to the first electrically conductive agent, Amplitude of a gas flow to the second electrically conductive means, amplitude of a gas flow to the third electrically conductive means.