JPH061126Y2 - Carbon dioxide measuring device during exhalation - Google Patents

Description

TECHNICAL FIELD The present invention relates to a device for measuring carbon dioxide during exhalation, and more particularly to a device for measuring carbon dioxide which automatically corrects a measured value according to atmospheric pressure. .

2. Description of the Related Art Various physiological information such as the ventilation, circulation, and metabolic status of a subject can be obtained from the amount of carbon dioxide contained in exhaled breath. Especially, the amount of carbon dioxide at end-expiration is the amount of carbon dioxide in arterial blood. It is said to be indispensable information in the management of anesthesia and artificial respiration. The amount of carbon dioxide gas in the exhaled air is measured as a concentration or a partial pressure by a carbon dioxide gas sensor or the like that uses the infrared absorption characteristics of carbon dioxide gas, and the measured value changes with the change in atmospheric pressure. . Therefore, it is considered to measure the actual atmospheric pressure using a barometer and automatically correct the measured value of carbon dioxide based on the atmospheric pressure.

However, there is a problem in that it is not always economical to provide a barometer or the like only for such carbon dioxide measurement, and the device becomes expensive.

The present invention has been made in view of the above circumstances, and an object thereof is to automatically correct the measured value of carbon dioxide by measuring atmospheric pressure without using a barometer.

Means for Solving the Problems To achieve the above object, the present invention has a carbon dioxide gas sensor for measuring the amount of carbon dioxide gas contained in the exhaled air of a living body, and the measured value measured by the carbon dioxide gas sensor is atmospheric pressure. A carbon dioxide measuring device of the type that automatically corrects based on (a) based on the output signal output from the pressure sensor used for blood pressure measurement, based on the relationship between the predetermined output signal and atmospheric pressure. It is characterized by comprising atmospheric pressure determining means for determining the actual atmospheric pressure and (b) correcting means for correcting the measured value based on the actual atmospheric pressure determined by the atmospheric pressure determining means.

Action and effect of the invention That is, the amount of carbon dioxide in the exhaled breath is measured,
Usually, when an anesthesia or artificial respiration is applied to a subject, in such a case, blood pressure measurement is usually performed at the same time, and the present invention provides a pressure sensor used for such blood pressure measurement. I used it to measure atmospheric pressure. According to the carbon dioxide measuring device of the present invention, the actual atmospheric pressure is determined by the atmospheric pressure determining means based on the output signal output from the pressure sensor used for blood pressure measurement, and the atmospheric pressure is determined by the correcting means. The carbon dioxide measurement value is automatically corrected according to. Therefore, as compared with the case where a barometer or the like is provided only for measuring carbon dioxide, the device is simplified and the cost is reduced.

Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

In FIG. 1, 10 is a cuff wrapped around the upper arm of a living body, and an electric pump 14,
It is connected to the exhaust device 16 and the pressure sensor 18. The electric pump 14 is for pumping air into the cuff 10. The exhaust device 16 is in a closed state in which the communication between the cuff 10 and the atmosphere is completely cut off, and the cuff 10 and the atmosphere are communicated via a throttle. It can be switched to three states of a slow exhaust state in which the air in the cuff 10 is gradually exhausted, and a rapid exhaust state in which the air in the cuff 10 is rapidly exhausted by completely communicating the cuff 10 and the atmosphere. Further, the pressure sensor 18 includes a preset constant reference pressure chamber such as 1 atmospheric pressure,
The pressure in the cuff 10 (hereinafter, referred to as cuff pressure) of the reference pressure of the reference pressure chamber to P _K detected by the strain gauge or pressure-sensitive diode or the like as a reference, the pressure signal amplifies the electric signal corresponding to the differential pressure Output as SP.

The pressure signal SP is supplied to the sphygmomanometer 20 and the atmospheric pressure determining means 22. The sphygmomanometer 20 measures the blood pressure value by the oscillometric method, and is configured as shown in FIG. 2, for example, and the pressure signal SP is supplied to the low pass filter 24 and the band pass filter 26.
The low-pass filter 24 removes a vibration component such as a pulse wave synchronized with the pulse of the living body from the pressure signal SP to detect the static pressure in the cuff 10, and determines the static pressure signal SS corresponding to the static pressure to determine the blood pressure. Output to the means 28. The bandpass filter 26 extracts only the pulse wave component from the pressure signal SP,
The pulse wave signal SM corresponding to the pulse wave is output to the blood pressure determining means 28.

Blood pressure determining means 28 is constituted by a microcomputer or the like, static pressure in a state where the exhaust system 16 from the value B of the static pressure signal SS is a quick discharge condition cuff pressure P _K is equal to the atmospheric pressure P _A The value B _{A of the} signal SS is subtracted, and from the predetermined relationship shown in FIG.
Static pressure P _S obtained by subtracting atmospheric pressure P _A from the static pressure in the cuff 10.
Ask for. The relationship between the subtracted value (B-B _A ) and the static pressure P _S is that the known atmospheric pressure P ₀ and the value of the static pressure signal SS at that time when the cuff pressure P _K and the atmospheric pressure P _A are equalized. Although it is set based on B ₀ in consideration of the output characteristics of the pressure sensor 18 and the like, this is set by the cuff pressure P _K and the atmospheric pressure P _A.
By storing the value (B ₀ ) of the static pressure signal SS in the state where and are equalized, and measuring and inputting the actual value (P ₀ ) of the atmospheric pressure P _A at that time by a barometer or the like, it is necessary. It can be appropriately set according to the above.
The value B _A of the static pressure signal SS is stored in advance in the temporary storage means such as the RAM by setting the exhaust device 16 to the rapid exhaust state prior to the blood pressure measurement, and is updated every time the blood pressure measurement is performed. To be done.

In the blood pressure determining means 28, air is pumped into the cuff 10 by the electric pump 14, and the static pressure P _S obtained based on the static pressure signal SS is higher than the preset maximum blood pressure value of the subject. After the exhaust pressure is raised to a target pressure, for example, about 180 mmHg, the exhaust device 16 is switched to the gradual exhaust state and the air in the cuff 10 is gradually exhausted. The systolic blood pressure value and the diastolic blood pressure value are determined from the static pressure P _S based on the change in

A display device 30 is connected to the sphygmomanometer 20 configured as described above, and the maximum blood pressure value and the minimum blood pressure value determined by the blood pressure determining means 28 are displayed on the display device 3.
Displayed at 0.

Meanwhile, the atmospheric pressure determining means 22 is constituted by a microcomputer or the like with pressure compensation means 50 to be described later, in a state in which the cuff pressure P _K is the exhaust system 16 and quick exhaust state is equal to the atmospheric pressure P _A Value C _{A of} pressure signal SP
Based on the above, the actual atmospheric pressure P _A is determined from the predetermined relationship shown in FIG. The relationship between the value C _A and the atmospheric pressure P _A is set based on the known atmospheric pressure P ₀ and the value C ₀ of the pressure signal SP at that time in consideration of the output characteristic of the pressure sensor 18 and the like. However, this stores the value (C ₀ ) of the pressure signal SP in the state where the cuff pressure P _K and the atmospheric pressure P _A are equalized, and at the same time, stores the actual value (P ₀ ) of the atmospheric pressure P _A at that time. By measuring and inputting with a barometer or the like, it is possible to appropriately set again as necessary. Then, the value of the atmospheric pressure P _A is stored in a temporary storage unit such as a RAM, and is read from the storage unit to output an atmospheric pressure signal SA representing the atmospheric pressure P _A. The atmospheric pressure P _A stored in the storage means is held at a constant value while the blood pressure is being measured by pumping air into the cuff 10 by the electric pump 14, but when the blood pressure is not being measured. The atmospheric pressure P _A is determined based on the pressure signal SP supplied from the pressure sensor 18 while the exhaust device 16 is in the rapid exhaust state, and is sequentially updated.

Further, a carbon dioxide sensor 32 is attached to the subject whose blood pressure is measured, and the amount of carbon dioxide in the exhaled breath is measured. The carbon dioxide sensor 32 detects the amount of carbon dioxide by utilizing the absorption spectrum of carbon dioxide existing in the infrared region. For example, as shown in FIG. 5, an infrared gas analyzer with a heating tube can be used. Consists of In FIG. 5, the infrared light emitted from the light source device 34 has a convex lens 36, a glass cell 38 through which breath is passed, an infrared filter 40, and a convex lens 4.
2 through photocell 44. Since the infrared light transmitted through the glass cell 38 is changed in inverse proportion to the amount of carbon dioxide gas in the exhaled gas passed through the glass cell 38, the signal output from the photocell 44 is also inversely proportional to the amount of carbon dioxide gas. Change. Then, the signal is amplified by the amplifier 46 and is inverted by the inversion circuit 48 with reference to the reference value when the carbon dioxide amount is 0, which is usually the value near the upper peak of the signal output from the photocell 44, as a reference. It is output as the gas signal SC. The reference value of the inversion circuit 48 is preset in consideration of the intensity of infrared light emitted from the light source device 34, the output characteristics of the photocell 44, and the like.

Here, the amount of carbon dioxide gas detected by the carbon dioxide gas sensor 32 corresponds to the partial pressure of carbon dioxide gas, and is influenced by the atmospheric pressure at the time of measurement. When the atmospheric pressure is high, the amount of carbon dioxide gas measured is also high. When the atmospheric pressure is low, the amount of carbon dioxide gas measured also becomes low. Therefore, the carbon dioxide signal SC output from the carbon dioxide sensor 32 is supplied to the atmospheric pressure compensating means 50 together with the atmospheric pressure signal SA output from the atmospheric pressure determining means 22, and the influence of atmospheric pressure is eliminated.

This atmospheric pressure compensating means 50 constitutes a correcting means, and determines a correction coefficient K from a predetermined relationship shown in FIG. 6 based on the actual atmospheric pressure P _A represented by the atmospheric pressure signal SA to determine the carbon dioxide signal. This correction coefficient K is multiplied by SC. As a result, regardless of the atmospheric pressure P _A , the pressure is always 1 atm (760 mm
A signal corresponding to the% concentration of carbon dioxide in the Hg) state is obtained, and the signal is output to the display unit 52, so that the display unit 52 displays the signal as shown in FIG. A graph of the carbon dioxide concentration (%) that changes periodically in synchronism with breathing is displayed. In addition to or instead of this carbon dioxide concentration (%), 1 atm (760 mmH
It is also possible to display the carbon dioxide partial pressure based on g).

In the present embodiment, the atmospheric pressure determining means 22, the carbon dioxide gas sensor 32, the atmospheric pressure compensating means 50, and the display 52 constitute a carbon dioxide measuring device. Then, in the state in which the blood pressure measurement is not performed, the carbon dioxide measuring device exhales in a state where the exhaust device 16 of the blood pressure measuring device is in the rapid evacuation state and the cuff pressure P _K is equal to the atmospheric pressure P _A. Carbon dioxide measurement inside is performed. That is, the pressure signal SP output from the pressure sensor 18 of the blood pressure measurement device.
Based on the value C _A determined actual atmospheric pressure P _A by atmospheric pressure determining means 22 sequentially, based on the actual atmospheric pressure P _A carbon dioxide signal SC output from the carbon dioxide sensor 32 by pressure compensation means 50 The carbon dioxide concentration (%) in the state of 1 atm is always displayed on the display 52 regardless of the magnitude of the atmospheric pressure P _A by being corrected.

The exhaust device 16 is closed and the electric pump 1
While air is being pumped into the cuff 10 by 4 and the blood pressure measurement is being performed, the exhaust device 16 is set to the rapid exhaust state before the blood pressure measurement, and the cuff pressure P _K is made equal to the atmospheric pressure P _A. In the state, the carbon dioxide signal SC is corrected using the latest atmospheric pressure P _A determined and stored by the atmospheric pressure determination means 22 based on the pressure signal SP output from the pressure sensor 18. Since the blood pressure measurement by the blood pressure measurement device is generally repeated at regular time intervals, the atmospheric pressure P used to correct the carbon dioxide signal SC is obtained.
_{While A is} also updated each time, since one time of blood pressure measurement is usually several minutes, there is almost no change in the actual atmospheric pressure P _A during that time, and the constant atmospheric pressure stored in the atmospheric pressure determining means 22 is constant. There is no problem even if the carbon dioxide signal SC is corrected using P _A.

Here, in such a carbon dioxide measuring device of the present embodiment, the atmospheric pressure P for correcting the carbon dioxide signal SC is used.
_{Since A} is calculated based on the pressure signal SP output from the pressure sensor 18 used for blood pressure measurement, the device can be compared with a case where a barometer or the like is provided only for measuring carbon dioxide gas. It is simple and cheap.

Although one embodiment of the present invention has been described in detail with reference to the drawings, the present invention can be implemented in other modes.

For example, in the above embodiment, the atmospheric pressure is obtained by using the pressure sensor 18 of the blood pressure measuring device that measures blood pressure by the oscillometric method, but the pressure sensor used in the blood pressure measuring device of another method is used. It is also possible to do so.

In the above embodiment, the static pressure P _S , the atmospheric pressure P _A , and the correction coefficient K are calculated according to the relationships shown in FIGS. 3, 4, and 6. The above relationship is merely an example, and is appropriately set in consideration of the output characteristics of the sensor. It should be noted that it is also possible to obtain them by an arithmetic expression or the like.

Further, the sphygmomanometer 20 of the above-mentioned embodiment is adapted to obtain the static pressure P _S according to the relationship shown in FIG.
It is also possible to determine a static pressure P _S and adopted an atmospheric pressure signal SA outputted from the atmospheric pressure determining means 22.

Further, the blood pressure monitor 20 may be configured by the common microcomputer together with the atmospheric pressure determining means 22 and the atmospheric pressure compensating means 50.

Further, in the above embodiment, the atmospheric pressure determining means 22 and the atmospheric pressure compensating means 50 are composed of a microcomputer, but they may be composed of a hard logic circuit having the same function.

Further, the atmospheric pressure determining means 22 of the above-mentioned embodiment is the exhaust device 16
Is set to the rapid exhaust state, and the pressure signal S is output from the pressure sensor 18.
By supplying P, the atmospheric pressure P _A is sequentially obtained, but during a series of carbon dioxide measurement, the carbon dioxide is determined based on the same atmospheric pressure P _A determined prior to the carbon dioxide measurement. It does not matter if the gas signal SC is corrected.

Further, although the carbon dioxide sensor 32 of the above-mentioned embodiment measures the amount of carbon dioxide by utilizing the infrared absorption characteristic of carbon dioxide, it is also possible to use other types of carbon dioxide sensors.

Further, the carbon dioxide sensor 32 is provided with an inverting circuit 48 so as to output a carbon dioxide signal SC corresponding to the amount of carbon dioxide, but it changes in inverse proportion to the amount of carbon dioxide output from the amplifier 46. It does not matter if the signal is output as it is.

Further, the atmospheric pressure compensating means 50 of the embodiment described above is adapted to obtain the correction coefficient K and correct the carbon dioxide signal SC.
It is also possible to correct the carbon dioxide signal SC according to the magnitude of the atmospheric pressure P _A without obtaining the correction coefficient K.

Further, the display 52 of the above-mentioned embodiment is designed to display the time change of the carbon dioxide concentration, but it is also possible to display only the maximum peak value at the end of expiration, or to display those values on a chart paper or the like. It does not matter if you record it. It is not always necessary to display or record the carbon dioxide concentration, and the corrected carbon dioxide signal SC
Can be used as it is for automatic control of anesthesia or artificial respirator.

Although not illustrated one by one, the present invention can be implemented in various modified and improved modes based on the knowledge of those skilled in the art.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configurations of a carbon dioxide measuring device and a blood pressure measuring device according to an embodiment of the present invention. FIG. 2 is a block diagram showing the configuration of the blood pressure monitor in FIG. FIG. 3 is a diagram showing a relationship between a subtraction value and static pressure preset in the blood pressure determining means in FIG. FIG. 4 is a diagram showing the relationship between the atmospheric pressure and the value of the pressure signal preset in the atmospheric pressure determining means in FIG. FIG. 5 is a diagram showing the configuration of the carbon dioxide gas sensor in FIG. FIG. 6 is a diagram showing the relationship between the atmospheric pressure preset in the atmospheric pressure compensating means in FIG. 1 and the correction coefficient. FIG. 7 is a diagram showing an example of changes in carbon dioxide concentration displayed on the display of the carbon dioxide measuring device in FIG. 18: Pressure sensor 22: Atmospheric pressure determination means 32: Carbon dioxide sensor 50: Atmospheric pressure compensation means (correction means) SP: Pressure signal (output signal)

Claims (1)

[Scope of utility model registration request] 1. A carbon dioxide measuring device of the type having a carbon dioxide sensor for measuring the amount of carbon dioxide contained in the exhaled air of a living body and automatically correcting the measured value measured by the carbon dioxide sensor based on the atmospheric pressure. And an atmospheric pressure determining means for determining an actual atmospheric pressure from a predetermined relationship between the output signal and the atmospheric pressure based on an output signal output from a pressure sensor used for blood pressure measurement, and the atmospheric pressure determining means. And a correction means for correcting the measured value based on the actual atmospheric pressure determined by the means.