JP2000097854A - Respiration gas concentration measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure a respiration gas concentration contained in intake gas. SOLUTION: The atmospheric air is taken into a measuring cell 21 with a distance to find a respiration gas concentration contained in respiration gas using a detected signal in an infrared detector 29 at the time of taking-in of the atmospheric air as the maximum signal. Even when rerespiration is generated because of any failure caused by deterioration of a canister, leakage of an exhalation valve and the like, the rerespiration is surely detected thereby. Safety in artificial respiration in anesthesia and the like is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a respiratory gas concentration measuring device for measuring the concentration of gas contained in respiratory gas.

[0002]

2. Description of the Related Art Conventionally, a respiratory gas is irradiated with infrared rays,
There is known a respiratory gas concentration measuring device which detects a signal corresponding to the amount of infrared rays passed at that time and measures the concentration of carbon dioxide gas or the concentration of anesthetic gas.

[0003] A light detecting portion for detecting infrared rays includes P
Quantum infrared detectors such as bSe and thermal infrared detectors such as thermopiles are used. Although PbSe has a fast response speed, it is susceptible to temperature, so it is necessary to detect it repeatedly and intermittently at intervals shorter than the respiratory cycle, for example, at intervals of 25 ms. Further, a driving unit such as a motor for driving the rotation is disposed to detect the amount of light passing through the respiratory gas. Further, PbSe has an unstable dark resistance, and a great deal of design or production efforts have been made to solve this problem. For this reason, the size of the device is reduced, the power consumption is reduced,
There was a limit to the robustness, and there was the disadvantage of being expensive.

On the other hand, the response speed of the thermopile is as slow as 59 ms to 200 ms, and the light from the light source is 25 ms.
Although the method of chopping at the following intervals cannot be adopted, it has a feature that it has less drift compared to PbSe and is inexpensive, and has been adopted because of demands for downsizing and cost reduction of the device. . In addition, as a carbon dioxide concentration measuring device using a thermopile, for example, the invention (JP-A-8-233808, JP-A-8-233) is used.
No. 810).

FIG. 5 shows an example of a conventional carbon dioxide concentration measuring apparatus using the above carbon dioxide concentration measuring apparatus in an anesthesia respirator. In this figure, while anesthesia is applied, oxygen O _2, nitrous oxide N ₂ O, and volatile anesthetic gas are supplied through a flow meter 1 and a vaporizer 2. Part of the exhaled gas from which carbon dioxide CO ₂ has been removed by 3 is mixed and sent to the patient. When the anesthesia is stopped, a part of the exhaled gas from which the carbon dioxide CO ₂ has been removed is mixed with the mixed gas of oxygen O ₂ and air and sent to the patient. The canister 3 is filled with an absorbent that absorbs carbon dioxide gas. While this operation is being performed, a part of the exhaled gas is reused as described above, but most of the remaining exhaled gas is supplied by the pop-off valve 4 and the air supply unit 5 to perform an anesthesia (not shown). Released into the gas elimination device. The intake path and the exhalation path are provided with an intake valve 6 and an exhalation valve 7 for preventing backflow.

[0006] The breathing gas of the patient is supplied to the airway adapter 8.
The sample is guided to a carbon dioxide concentration measuring device 10 through a sampling tube 9 communicating with the sample, and the carbon dioxide concentration is determined.
In this case, the carbon dioxide concentration measuring device 10 uses the output of the photodetector when the intake gas is introduced as a maximum signal, and uses the difference between this maximum signal and the output of the photodetector when the light source is turned off as a reference signal. The difference between the output of the photodetector when the exhaled gas is introduced and the maximum signal is divided by the reference signal to obtain a carbon dioxide gas concentration signal. Then, a predetermined calculation is performed on the basis of the concentration signal to obtain the carbon dioxide gas concentration, and the result is numerically displayed.

Here, the principle of measuring the concentration of carbon dioxide using a thermal infrared detector such as a thermopile will be briefly described. The amount of infrared light received by the intake gas in which no carbon dioxide gas exists can be obtained by the following equation. I _max = I ₀ · EXP (−α × C _min × l) + I _offset (1) where I _offset is the offset signal of the infrared detector. Also, the amount of infrared light received by the carbon dioxide gas obtained during the measurement is Is obtained by the following equation. I = I ₀ · EXP (-α x C x l) + I _offset ... (2)

If the signal output of the amount of infrared light received when the light source is cut off is I _offset , then (I _max -I)
/ (I _max −I _offset ) = I ₀ × (EXP (−α × C _min × l)
-EXP (-α × C × l) ) / EXP (-α × C min × l) = at the k, the concentration of carbon dioxide is obtained by the following equation. _{C = C min - (Ln (} lk)) / (α × l) ... (3)

Where C: carbon dioxide concentration C _min : minimum concentration of carbon dioxide during inspiration Ln: natural logarithm k: (maximum signal due to minimum carbon dioxide concentration during inspiration-signal due to carbon dioxide concentration) / ( (Maximum signal due to minimum carbon dioxide concentration-dark signal) α: Infrared absorption coefficient of carbon dioxide l: Measurement optical path length

[0010]

The respiratory gas concentration measuring device using the conventional carbon dioxide gas concentration measuring device has the following problems. That is, while the intake gas always has the same minimum carbon dioxide concentration, the output of the infrared detector for the intake gas is used as the maximum signal to determine the carbon dioxide concentration. However, the deterioration of the carbon dioxide absorbent in the canister 3 and the expiration valve 7 If carbon dioxide gas is present in the inspired gas due to the backflow of exhalation due to the leak of the gas, the maximum signal cannot be obtained, and the value of C _{min in} the equation (3) changes greatly. Becomes impossible.

For example, as shown in FIG. 6, the expiration gas usually contains about 5% of carbon dioxide gas. However, due to the failure of the canister 3 and the expiration valve 7, etc., for example, 1% If the carbon dioxide gas is contained, the output signal of the infrared detector when the intake gas is introduced becomes the maximum signal, so that the measurement result includes an absolute error of 1%.

Accordingly, an object of the present invention is to provide a respiratory gas concentration measuring device capable of accurately measuring the concentration of respiratory gas contained in exhaled and inspired respiratory gases including gases other than carbon dioxide gas.

[0013]

To achieve the above object, a respiratory gas concentration measuring device according to the present invention irradiates a respiratory gas with infrared rays, detects a signal corresponding to the amount of transmission, and measures the respiratory gas concentration. In a respiratory gas concentration measuring device, the air is taken in at an arbitrary timing, a signal corresponding to the amount of transmission when this atmosphere is irradiated with infrared rays is set as a maximum signal, and the concentration of the respiratory gas is measured based on the maximum signal. Features.

According to this configuration, the atmosphere is taken into the measuring cell at an arbitrary timing, and the signal corresponding to the amount of transmission when the atmosphere is irradiated with infrared rays is set as the maximum signal, and the concentration of the gas contained in the respiratory gas is determined. I asked for it. This allows
For example, even if some trouble occurs due to deterioration of the canister, leak of the exhalation valve, etc., and the intake gas contains carbon dioxide gas, the concentration of carbon dioxide gas in the atmosphere (0.035%) is constant. The gas concentration can be determined correctly. As a result, it is possible to prevent a patient's accident due to a failure of the breathing circuit from occurring, and to enhance safety.

The present invention focuses on using a thermal infrared detector, such as a thermopile, as an infrared detector for detecting the amount of transmitted infrared light, thereby using a quantum infrared detector, such as PbSe. The size and cost of the apparatus can be reduced as compared with the apparatus.

Further, in the present invention, it is required to arbitrarily take in the atmosphere and store the signal of the infrared detector at that time, but during this period, the gas concentration of the respiratory gas cannot be measured. For example, when a thermopile is used as the thermal infrared detector, the period is about 100 to 250 msec.
c. Therefore, when displaying the gas concentration, if the value immediately before taking in the air is continuously displayed during the period when the maximum signal is obtained by taking in the air, the gas concentration measured next by taking in the breathing gas will be displayed unnaturally. It can be performed.

However, for that purpose, it is necessary that the concentration of the respiratory gas during the period of taking in the atmosphere is constant. For example, since the concentration of carbon dioxide is constant during the inhalation period of the breathing gas, if the inhalation can be reliably detected, the gas concentration can be stably displayed by this method.

In general, the concentration of inspired carbon dioxide is lower than the concentration of exhaled carbon dioxide, so that the period of inspiration can be detected by monitoring the signal of the infrared detector. However, if the flow of breathing gas is measured, the period of inspiration can be more reliably determined. Can be determined.
In addition, the concentration of anesthetic gas contained in the respiratory gas is such that the concentration of inspiration is higher than the concentration of expiration during anesthesia, and the concentration of expiration is higher than the concentration of inspiration during awakening. It is not possible. Therefore, if the flow of the respiratory gas is measured as in the present invention, it is possible to reliably determine the direction of the flow signal, so that the display of the gas concentration can be expressed in a natural manner.

[0019]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a respiratory gas concentration measuring apparatus according to an embodiment of the present invention. (A) Configuration of Respiratory Gas Concentration Measuring Apparatus FIG. 1 is a block diagram showing the configuration of an embodiment of a respiratory gas concentration measuring apparatus according to the present invention. The respiratory gas concentration measuring device of this embodiment includes a sampling tube 9, electromagnetic valves 20, 25, a measuring cell 21, a pump 23, a pump driving unit 24, an infrared light source 26, a light source driving unit 27, a light source driving switch 28, an infrared detection , Filter F, thermistor 30, amplifier 31, A / D converter 32, control unit 33, R
OM 34, RAM 35, operation unit 36, display unit 37, sampling tubes 40a, 40b, flow measurement device 41
In particular, the apparatus has a function of sampling the atmosphere at an arbitrary timing, obtaining a maximum signal of the infrared detector 29 for the respiratory gas, and measuring the respiratory gas concentration based on the maximum signal.

In FIG. 1, the solenoid valve 20 has two input ports 20a and 20b and one output port 20c.
And In this case, arrow 20d indicates the direction in which the valve is active. Input port 2 of solenoid valve 20
0a is connected to the sampling tube 9, and the input port 20b is open to the atmosphere. The output port 20c is connected to the gas inlet 21 of the measurement cell 21.
a. The solenoid valve 20 includes a control unit 33 described later.
Is switched to the input port 20a side and the input port 20b side (indicated by an arrow 20d), and the input port 20a
Switch to the input port 20a and output port 2
0c is in communication with the input port 20b, and the input port 20b and output port 20c are in communication with each other.

At the mouth of the airway adapter 8, two sampling tubes 40a, 4a for flow measurement are provided.
0b is connected, and the pressure in each is detected by the flow measurement device 41, and the flow measurement of the respiratory gas is performed. In this case, as shown in FIG. 2, a valve 42 for generating a differential pressure due to a flow is provided at the sampling tube connecting portion of the airway adapter 8. The sampling tube 40a is connected to a device (not shown) of the valve 42 such as an anesthesia machine,
0b is connected to the patient side. Note that the above mechanism is one means for flow detection, and is not limited to this mechanism, and flow detection means of another mechanism may be used.

FIG. 3 is a waveform diagram showing an example of a pressure change and a flow at the mouth of a person. As shown in this figure, at the time of intake,
Since the inhalation gas is sent from an anesthesia machine (not shown), the pressure at the mouth rises at once by the resistance, and then
Increase according to compliance. On the other hand, the mouth flow quickly rises to a constant flow set by the ventilator. After sufficient intake is performed, the intake ends after an intake pause period. At the time of exhalation, exhaled gas is exhausted from the patient, so the flow at the mouth falls at a stretch,
Thereafter, it gradually decreases according to the time constant. In FIG. 2, the pressure on the sampling tube 40a side becomes higher than the sampling tube 40b side during inspiration, and the pressure on the sampling tube 40a side becomes lower than the sampling tube 40b side during expiration. Thus, the flow measuring device 41 measures the pressure loss of the valve 42 caused by the patient's respiratory flow, and outputs a flow signal.

Since the polarity is always different between inspiration and expiration, it is possible to stably distinguish between expiration and inspiration by using a flow signal. In addition, since the respiratory mechanics of the patient can be known by measuring the flow and pressure at the mouth caused by the patient's breathing, this is a useful means for managing the breathing of the patient. Returning to FIG. 1, a gas outlet 21b of the measuring cell 21 is connected to a solenoid valve 25 to be described later via a pump 23.
Is connected to the input port 25a. During the measurement, the pump 23 continuously performs a vacuum operation, sucks the gas selected by the electromagnetic valve 20 and introduces the gas into the measurement cell 21. The exhaled gas and the inspired gas introduced into the measurement cell 21 are released from the electromagnetic valve 25 to the atmosphere or to an exhaust device (not shown). The solenoid valve 20 is controlled by the control unit 33 via the solenoid valve driving unit 51.

The pump 23 is driven by a pump driver 24. The pump drive unit 24 is controlled by the control unit 33. The solenoid valve 25 has one input port 25a and two output ports 25b and 25c. Arrow 25d indicates the direction in which the valve is active. The output port 25b of the solenoid valve 25 is connected to the exhaust device described above, and the output port 25c is open to the atmosphere. The solenoid valve 25 is controlled by the control unit 33 via the solenoid valve driving unit 50.

The measurement cell 21 is a ventilation pipe through which exhaled gas and inspired gas flow, and windows W1 and W2 made of a member such as quartz glass which transmits infrared rays are provided at opposing portions at predetermined positions. I have. These windows W1 and W2 are subjected to antifogging processing for preventing fogging due to water vapor or the like in the exhaled gas.

Above the window W1, an infrared light source 2 such as a lamp is provided.
6, and light is emitted toward the window W1. Also,
An infrared detector 29 made of a thermopile is arranged near the lower portion of the window W2, and detects infrared rays transmitted from the infrared light source 26 through the windows W1 and W2. Infrared detector 2
The light receiving surface 9 is provided with an interference filter F having a wavelength that is absorbed by the gas to be measured in the exhaled gas (for example, approximately 4.3 μm if carbon dioxide is the gas to be measured).
A thermistor 30 is attached to or near the infrared detector 29 and is used for temperature detection near the infrared detector 29. The output of the infrared detector 29 and the output of the thermistor 30 are amplified by the amplifier 31 respectively. Then, the amplified output of the infrared detector 29 and the output of the thermistor 30 are digitally converted by the A / D converter 32 and then taken into the control unit 33.

The infrared light source 26 is driven by a light source driving section 27. The light source driving unit 27 includes, for example, a constant current circuit, and causes the infrared light source 26 to emit light at a constant luminance. Power is supplied to the light source driving unit 27 via the light source driving switch 28, and the control unit 33 controls the light source driving switch 28 to turn on / off the infrared light source 26. The light source drive switch 28 is formed of, for example, an electronic switch such as a semiconductor, and is normally turned on.

The control unit 33 comprises, for example, a CPU.
Each unit of the apparatus is controlled based on a control program for measuring the concentration of respiratory gas stored in the OM 34. RAM35
Is used in the operation of the control unit 33, and temporarily stores, for example, set parameters, measured respiratory gas concentration data, and the like. The operation unit 36 includes, for example, a plurality of push buttons, and performs setting of required data and the like. Display 3
Reference numeral 7 denotes a display element such as an LCD (liquid crystal), for example, and displays the measured respiratory gas concentration in a waveform or numerical value according to the change in concentration.

The sampling tube 9 and the solenoid valve 2
0, 25, the pump 23, and the pump drive unit 24 constitute a means for taking in and exhausting gas. Further, the infrared light source 26 corresponds to an infrared irradiation means. Light source drive switch 2
Reference numeral 8 corresponds to on / off means. In addition, the infrared detector 29
Corresponds to infrared detecting means. The RAM 35 corresponds to first and second signal storage units. The control unit 33
Corresponds to the control means. The control unit 33 and the display unit 3
7 corresponds to a display means. The sampling tubes 40a, 40b, the flow measuring device 41, and the valve 42 constitute a flow measuring unit. The operation unit 36 corresponds to a setting unit.

(B) Operation of Respiratory Gas Concentration Measurement Apparatus At the start of measurement of the apparatus configured as shown in FIG.
The control unit 33 performs an operation of acquiring the maximum signal of the infrared detector 29 for the respiratory gas. First, while controlling the solenoid valve 20 to switch to the input port 20b side, controlling the solenoid valve 25 to switch to the output port 25c side, air is introduced into the measurement cell 21, and gas in the measurement cell 21 is released. Release to atmosphere.

When the measurement cell 21 is sufficiently filled with the atmosphere and the output of the infrared detector 29 is stabilized, the control unit 33
Captures the detection signal of the infrared detector 29 at that time, and stores the signal in the RAM 35 as the maximum signal (maximum value) of the infrared detector 29. Next, the light source drive switch 2
8, the light source 26 is turned off, the detection signal (that is, the dark current component) of the infrared detector 29 at that time is taken in, and it is taken as R
The difference between the maximum value and the maximum value stored in the RAM 35 is obtained while storing the result in the AM 35, and the result is stored in the RAM 35 as a reference value for the maximum signal.

After the reference value is stored in the RAM 35, the solenoid valve 20 is switched to the input port 20a side, and the solenoid valve 25 is switched to the output port 25b to change the measurement cell 2
1 introduces the patient's breathing gas. When the measurement cell 21 is sufficiently filled with the respiratory gas and the output of the infrared detector 29 is stabilized, the detection signal of the infrared detector 29 at that time is taken in, and the difference between this signal and the maximum value stored in the RAM 35 is calculated. Ask. In this case, the difference between the maximum value and the maximum value can eliminate the dark current components included in each other.
After finding the difference between the maximum value and the detection signal, the result is stored in RAM
Divide by the reference value stored in 35 to obtain the calculation parameter of the respiratory gas. Further, the calibration coefficient of the measurement system is stored in the RAM 34 in advance by a calibration gas using a known carbon dioxide concentration in the manufacturing process of the apparatus. Then, a calculation is performed using the calculation parameters and the calibration coefficient to obtain and display the respiratory gas concentration. Once the maximum value and the dark current value are obtained, the respiratory gas concentration at that time can be calculated and measured at an early cycle, for example, 20 msec, until the next maximum value and the dark current value are obtained.

The control unit 33 determines the acquisition timing of the maximum value and the dark current value based on, for example, the output change gradient of the thermistor 30. That is, when the temperature in the respiratory gas concentration measuring device is not stable, the radiation intensity of the infrared light source 26 and the sensitivity of the infrared detector 29 change, so the control unit 33 monitors the output change gradient of the thermistor 30. The maximum value and the dark current value are frequently measured, and the solenoid valves 20, 25 and the light source drive switch 28 are controlled so as to perform calculations.

When the temperature in the apparatus becomes stable, the infrared light source 2
Since the radiation intensity of No. 6 and the sensitivity of the infrared detector 29 are stable, the control unit 33 monitoring the output change of the thermistor 30 performs control to reduce the measurement frequency of the maximum value and the dark current value. The control of capturing the maximum value and the dark current value can be performed in any period by judging expiration or inspiration by monitoring the concentration pattern of the carbon dioxide concentration, if only measuring the carbon dioxide concentration, By using the flow signal of the flow measurement device 41, it is possible to reliably determine inhalation or expiration based on the polarity of the flow signal, regardless of which gas concentration in the respiratory gas is measured.

In the period during which the maximum signal is acquired (about 200 msec or more in the case of the present invention), the respiratory gas concentration cannot be measured because the respiratory gas of the patient cannot be obtained. Therefore, the control unit 33 extends the period of the density signal immediately before the operation of acquiring the maximum signal and outputs the signal, and connects it to the density signal obtained immediately after the operation of acquiring the maximum signal is completed. That is, the respiratory gas concentration stored in the RAM 35 immediately before the operation of acquiring the maximum signal is continuously output until the end of the acquisition of the maximum signal until the process of acquiring the maximum signal ends. With this processing, it is possible to make the signal appear as if there is no break in the signal.

The reason why the detection signal of the infrared detector 29 when the atmosphere is taken in is set to the maximum signal (maximum value) is as follows.
This is because even the concentration of carbon dioxide in the atmosphere is 0.035%, which is negligible compared to approximately 5% of the concentration of carbon dioxide contained in the exhaled gas. Furthermore, other gases contained in the breathing gas, such as nitrous oxide gas and volatile anesthetic gas, do not exist in the atmosphere. This makes it possible to reliably detect even a slight rebreathing of carbon dioxide gas of the inspired gas due to deterioration of the canister or leak of the exhalation valve, thereby ensuring patient safety.

Next, FIG. 4 is a flow chart showing the flow of the operation starting from the start of the maximum signal acquisition when the maximum signal acquisition is set during inspiration. First, in step S10, it is determined whether or not the patient is exhaling based on the output of the flow measurement device 41. If it is determined that the patient is not inhaling, the current gas concentration is output in step S12 and the process exits.
On the other hand, if it is determined that the patient is inhaling, it is determined in step S14 whether or not the calibration flag is “1”. In this determination, if it is determined that the in-calibration flag is not “1”, the process proceeds to step S16, and the current gas concentration is stored. Then, in step S18, the stored gas concentration is output. After outputting the gas concentration, step S
Proceeding to 20, the calibration flag is set to "1". Next, in step S22, the solenoid valve 20 is switched to guide the atmosphere to the measurement cell 21 and the solenoid valve 25 is switched to change the measurement cell 2
The gas in 1 is released into the atmosphere. Next, step S2
In step 4, the number of the operating solenoid valve is set to "1", and the process exits.

On the other hand, if it is determined in step S14 that the calibration-in-progress flag is "1", the process proceeds to step S26.
To output the stored gas concentration. After outputting the gas concentration, the process proceeds to step S28, where the infrared detector 29
It is determined whether or not the output of the infrared detector 29 is stable. If it is determined that the output is not stable, the process directly exits. If it is determined that the output of the infrared detector 29 is stable, step S3 is performed.
Go to 0. When it is determined that the output of the infrared detector 29 is stable and the process proceeds to step S30, it is determined whether or not the operating solenoid valve number is “1”, and if the operating solenoid valve number is not “1”. If it is determined, the process proceeds to step S32, and the calibration flag is set to "0", and the process exits. On the contrary,
If it is determined that the operating solenoid valve number is “1”, the process proceeds to step S34, and it is determined whether the light source drive switch 28 is on. If it is determined in this determination that the light source drive switch 28 is not on, the process proceeds to step S36, and the output of the infrared detector 29 is stored in the RAM 35 as a dark current. Next, in step S38, the solenoid valve 20 is switched to guide the breathing gas to the measurement cell 21, and the solenoid valve 25 is switched to discharge the gas in the measurement cell 21 to the exhaust device. After this process is completed, the process proceeds to step S40, in which the solenoid valve number during operation is set to "0", and in step S42, the light source drive switch 28 is turned on to exit the process. On the other hand, if it is determined in step S34 that the light source drive switch 28 is ON, the process proceeds to step S44, where the output of the infrared detector 29 is stored in the RAM 35 as a maximum signal, and then the light source drive switch 28 is set in step S46. Turn off and exit.

As described above, in this embodiment, the air is taken into the measuring cell 21 during the inhalation, and the detection signal of the infrared detector 29 when the air is taken in is taken as the maximum signal, and the carbon dioxide contained in the respiratory gas is taken as the maximum signal. The gas concentration was determined. As a result, accurate measurement is possible even if the inhalation gas contains carbon dioxide gas due to deterioration of the canister or leakage of the exhalation valve, etc., and safety during artificial respiration such as anesthesia is improved. Can be.

Since a thermopile is used as the infrared detecting means for detecting the amount of transmitted infrared light, the size and cost of the apparatus can be reduced. In addition, by combining with a flow measurement device that measures the flow at the mouth of the patient,
Inspiration and expiration can be reliably distinguished, and the timing for acquiring the maximum signal can be reliably taken during inspiration.

Since the timing for obtaining the maximum value is controlled by monitoring the output change gradient of the thermistor 30, the respiratory gas concentration of the respiratory gas can always be accurately grasped. In addition, while the maximum signal is being obtained, the respiratory gas concentration measured immediately before the maximum signal is obtained is continuously output, so that the signal can be seen as if it were continuous.

[0042]

According to the respiratory gas concentration measuring device of the present invention, the air is taken into the measuring cell at an arbitrary timing, and the detection signal of the infrared detector when the air is taken in is set to the maximum signal. Since the concentration of the respiratory gas contained in the respiratory gas is calculated using the maximum signal, even if re-breathing occurs in the inspired gas due to some troubles such as deterioration of the canister or leak of the exhalation valve, etc. Since the gas concentration of the inspired gas can be measured, patient safety can be improved.

Since a thermal infrared detector such as a thermopile is used as an infrared detector for detecting the amount of transmitted infrared light, the apparatus can be made smaller and less costly than a device using a quantum infrared detector such as PbSe. Can be achieved.

Further, by combining with a flow measuring device for measuring the flow at the mouth of the patient, it is possible to reliably distinguish between inhalation and expiration, and it is possible to reliably obtain the maximum signal at the time of inspiration.

Since the timing for obtaining the maximum value is controlled by the output change gradient of the thermistor, the respiratory gas concentration of the respiratory gas can always be accurately grasped.

Further, while the maximum signal is being obtained, the respiratory gas concentration measured immediately before obtaining the maximum signal is continuously output until the maximum signal is obtained.
You can make it appear as if there is no break in the signal.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a respiratory gas concentration measuring device according to the present invention.

FIG. 2 is a diagram for explaining measurement of a flow at a person's mouth;

FIG. 3 is a waveform diagram showing a pressure change and a flow at a mouth of a person.

FIG. 4 is a flowchart showing the operation of the respiratory gas concentration measuring device according to the embodiment.

FIG. 5 shows an example in which a conventional carbon dioxide concentration measuring device is used for anesthesia.

FIG. 6 is a waveform diagram showing a carbon dioxide gas concentration and an output of an infrared detector.

[Explanation of symbols]

 20, 25 Solenoid valve 21 Measurement cell 23 Pump 24 Pump driving unit 26 Infrared light source 27 Light source driving unit 28 Light source driving switch 29 Infrared detector 30 Thermistor 31 Amplifier 32 A / D converter 33 Control unit 34 ROM 35 RAM 36 Operating unit 37 Display unit 40a, 40b Sampling tube 41 Flow measuring device 42 Valve 50, 51 Solenoid valve drive unit

Claims (7)

[Claims] 1. A gas intake means for selectively taking in a respiratory gas or the atmosphere and introducing it into a measurement cell; an infrared irradiation means for irradiating infrared rays to the gas introduced into the measurement cell; and a heat type such as a thermopile. An infrared detector, which includes an infrared detector that detects an amount of transmitted infrared light, an on-off unit that turns on and off the infrared irradiating unit, and first and second signal storage units. The air or breathing gas is taken in, and when the air is taken in, the signal corresponding to the transmission amount when the atmosphere is irradiated with infrared rays is stored as a maximum signal in the first signal storage means, and the infrared irradiation means is stored in the first signal storage means. The signal when turned off is stored in the second signal storage means as a minimum signal, and the signal is captured based on the maximum signal and the minimum signal stored in the first and second signal storage means. And control means for determining the concentration of the respiratory gas, and a display means for displaying a waveform of the respiratory gas concentration determined and / or numerical, the respiratory gas concentration measuring apparatus comprising the. 2. A flow measuring means for measuring a flow at a mouth generated by a subject's breathing; a gas taking means for selectively taking in breathing gas or air and introducing it into a measuring cell; and a gas introduced into the measuring cell. Infrared irradiating means for irradiating infrared rays to the infrared ray; infrared detecting means for detecting a transmission amount of infrared rays which is a thermal infrared detector such as a thermopile; on / off means for turning on and off the infrared irradiating means; Signal storage means, and identifies the inspiration based on the measurement result by the flow measurement means, and when the air or breathing gas is taken in by the gas taking means during inspiration, A signal corresponding to the transmission amount when the atmosphere is irradiated with infrared light is stored as a maximum signal in the first signal storage means, and when the infrared irradiation means is turned off. The signal is stored in the second signal storage means as a minimum signal, and based on the maximum signal and the minimum signal stored in the first and second signal storage means,
A respiratory gas concentration measuring device comprising: a control unit for obtaining a concentration of a respired gas taken in; and a display unit for displaying a waveform and / or a numerical value of the obtained respiratory gas concentration. 3. The method according to claim 3, wherein the gas intake means takes in the atmosphere and stores the maximum signal, frequently at a time when the infrared detecting means and the infrared irradiating means are not stable. The respiratory gas concentration measuring device according to claim 1, wherein the number is reduced. 4. The operation of storing the minimum signal by turning off the infrared light irradiating means in the on / off means, frequently, when the infrared detecting means and the infrared irradiating means are not stable, in accordance with the stabilization. The respiratory gas concentration measuring device according to claim 1, wherein the number of times is reduced. 5. A setting means for setting a timing for obtaining the maximum value, wherein the control means obtains the maximum value at the timing set by the setting means, and updates the previous maximum value. The respiratory gas concentration measuring device according to claim 1, wherein: 6. A setting means for setting a timing for acquiring the minimum value, wherein the control means obtains the minimum value at the timing set by the setting means, and updates the previous minimum value. The respiratory gas concentration measuring device according to claim 1, wherein: 7. When the processing for acquiring the maximum or minimum signal is started, the display means continuously displays the respiratory gas concentration measured immediately before the start until the acquisition of the maximum or minimum signal ends. 7. The method according to claim 1, wherein
A respiratory gas concentration measurement device according to item 1.