JP2000325330A - Biomedical signal detection device and emitted light level control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain stable results of measurement constantly by a biomedical signal detection device and emitted light level control device for irradiating a subject (subject to be irradiated) and measuring the condition of the subject based on the transmitting light and reflected light without being affected by the light from outside. SOLUTION: In this device, a red LED 11a and an infrared LED 11b in a light emitting device 11 in the probe part 1 are made to emit light alternately to irradiate a subject 10. And the transmitting light is received at a photodiode 12a of a light receiving device 12, and the oxygen saturation ratio is measured based on the ratio between the received light level signals Va (R) and Va (IR) of each emitted light wavelength read into the CPU 25 from a current/voltage conversion circuit 22 by way of an A/D conversion circuit 24 according to the received light current 1F. In this case, the received light level signal Va with the light emitting device 11 emitting no light yet is read, and the standard voltage at the motion point in the current/voltage conversion circuit 22 is corrected by a voltage control circuit 26 so that the read signal Va is equal to a previously set reference voltage VREF of the light receiving motion according to the difference Vb (VREF-VA).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biological signal detecting device for irradiating an object or an illuminated object with light and detecting and measuring the state of the object or the illuminated object based on transmitted light or reflected light, and light emission. It relates to a level control device.

[0002]

2. Description of the Related Art A pulse oximeter is a typical conventional biosignal detection device.

[0003] This pulse oximeter is composed of oxygenated hemoglobin combined with oxygen among hemoglobin in blood,
The ratio of reduced hemoglobin not bound to oxygen is detected and calculated and displayed as oxygen saturation%. There are two types: an infrared-emitting LED having a high absorbance for oxyhemoglobin and a red-emitting LED having a high absorbance for reduced hemoglobin.
And a light-receiving element that receives transmitted light transmitted through the living body by irradiating the living body (finger or earlobe) alternately with the two light-emitting elements having different emission wavelengths and irradiating the living body with the light-emitting element. The ratio of the amount of received light of each living body transmitted light at the time of infrared light emission and the time of red light emission by the element, that is, the ratio of absorbance is calculated and calculated as oxygen saturation%.

[0004]

However, in the conventional pulse oximeter, the light receiving level of the transmitted light received by the light receiving element is affected by the degree to which the external light is received together. The light is received by the light-receiving element because the installation environment of the light-receiving element is different, or the positional relationship between the light-emitting element and the light-receiving element and the finger or the ear lobe sandwiched between them is different, or the shape of the object itself is different. When the amount of extraneous light changes, the reference light reception level before actually receiving the transmitted light of the subject also changes from time to time, and eventually, the received light level of the transmitted light also changes. There is a problem that the measurement cannot always be performed stably.

[0005] For example, even for the same subject, a change in the amount of extraneous light received causes a change in the amount of transmitted light received, resulting in variations in measurement results.

In the conventional pulse oximeter, the light transmittance varies depending on the individual difference of the subject, for example, the thickness of the finger or the difference of the body tissue, and the light receiving level obtained by the light receiving element greatly changes. Therefore, the extremely thick finger and extremely low light transmittance result in extremely low transmitted light reception level, and the extremely thin finger and extremely high light transmittance result in extremely low transmitted light reception level. Or higher,
There is a problem that proper measurement cannot be performed.

[0007] In other words, the measurement accuracy varies due to individual differences between the subjects.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and a first object of the present invention is to provide a biological signal detecting apparatus capable of always obtaining a stable measurement result without being affected by extraneous light. Is to provide.

A second object of the present invention is to provide a biological signal detecting apparatus capable of always obtaining an appropriate transmitted light receiving level and performing measurement without being affected by individual differences between subjects. To provide.

Further, a third object of the present invention is to provide a light emission level control device for correcting the light emission level of light applied to an object to be irradiated (object) to an appropriate level.

[0011]

That is, a biological signal detecting apparatus according to a first aspect of the present invention comprises a light-emitting means and a light-emitting device which emits light emitted from the light-emitting means to the object. A probe having light receiving means for receiving light, and a biological signal detecting device having measuring means for measuring a state of the subject based on a signal level of a light receiving signal output from the light receiving means of the probe, The light emitting device further includes a reference point correction unit that corrects a reference point for signal level measurement based on a signal level of a light receiving signal output from the light receiving unit when the light emitting unit is not emitting light.

In such a biological signal detecting device, the reference point for signal level measurement is corrected based on the signal level of the light receiving signal output from the light receiving means when the light emitting means is not emitting light. Even in an environment where extraneous light that is not light from the subject accompanying light emission from the subject is received, the reference point of the light receiving operation can be corrected to the reference level, and the light emission from the light emitting means is actually performed. When receiving the accompanying light from the subject, an accurate light receiving signal level corresponding to the light from the subject can be obtained without being affected by extraneous light.

A biological signal detecting device according to a second aspect of the present invention is the biological signal detecting device according to the first aspect, wherein the light emitting means is output from the light receiving means in a light emitting state. A light emission control means is provided for controlling the light emission amount of the light emission means to increase or decrease based on the signal level so that the signal level at the time of measurement falls within a preset range.

[0014] In such a biological signal detecting device, the signal level at the time of measurement controls the increase / decrease of the light emission amount of the light emitting means based on the signal level output from the light receiving means when the light emitting means emits light. Since the correction is made so as to fall within the preset range, it is possible to obtain a measurement signal level in a range range necessary for appropriately measuring the state of the subject, and the light passing through the subject is extremely low or high. Therefore, proper state measurement can be performed without being affected by the individual difference.

According to a seventh aspect of the present invention, there is provided a light emission level control device, comprising: a light emitting means for irradiating an object to be illuminated; Light-receiving means for receiving light incident from the light-receiving means, based on the level of a light-receiving signal output from the light-receiving means,
Control means for controlling the light emission level of the light emitting means to increase or decrease so that the level of the light receiving signal falls within a preset range.

In such a light emission level control device, based on the level of the light reception signal output from the light reception means, the light reception signal level is controlled to increase or decrease the light emission level of the light emission means so that it falls within a preset range. Since the correction is performed, for example, it is possible to obtain a signal level in a range range necessary for appropriately performing the state detection of the irradiation target, and to perform the appropriate state detection without being affected by the individual difference of the irradiation target. Become.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of an electronic circuit of a biological signal detecting device according to an embodiment of the present invention.

The biological signal detecting apparatus comprises a probe unit 1 for irradiating a subject (for example, a fingertip) 10 with light of two wavelengths alternately and receiving respective transmitted lights, The system unit 2 controls the light emission operation, and also receives the light reception signal obtained by the probe unit 1 to calculate and calculate the oxygen saturation% of arterial blood and outputs the calculated value.

The probe unit 1 is provided with a light emitting device 11 and a light receiving device 12.

The light emitting device 11 includes a red LED 11a that emits light at an emission wavelength of 660 nm and an infrared LED 11b that emits light at an emission wavelength of 890 nm.
The subject 10 sandwiched between the light-receiving device 12 is irradiated with red light emission and infrared light emission alternately emitted by 1.

The light receiving device 12 is provided with a photodiode 12a for receiving transmitted light transmitted through the subject 10 when the light emitting device 11 irradiates the subject 10 with light. The light receiving current IF output according to the light receiving operation is determined by the system unit 2
The current is amplified via an amplifier circuit (current amplifier) 21 in the internal circuit and supplied to a current / voltage conversion circuit 22 to be converted into a voltage.

On the other hand, the light-receiving signal of the transmitted light of the living body (subject 10), which has been converted in voltage by the current / voltage conversion circuit 22, is multiplied N times (N = 2, 4, 8,...) Via the amplification circuit 23. The amplified light is supplied to the first terminal CH1 of the A / D conversion circuit 24, and is converted into a digitally converted light reception level signal Va1 as C1.
The data is read by the PU 25. On the other hand, it is directly supplied to the second terminal CH2 of the A / D conversion circuit 24 and is read by the CPU 25 as a digitally converted light receiving level signal Va2.

On the other hand, in the current / voltage conversion circuit 22, the operation reference voltage when the light emitting device 11 of the probe unit 1 is in a non-light emitting state, that is, the photodiode 12a of the light receiving device 12 is connected to the subject 10 via the subject 10. The operating point voltage that is the reference for the light receiving operation when the transmitted light is not received is
A signal for adjusting the reference voltage to be supplied to the current / voltage conversion circuit 22 from the voltage control circuit 26 is set by controlling the reference voltage supplied from the voltage control circuit 26. When the LED 11 is not emitting light, it is generated by the CPU 25 based on each of the light receiving level signals Va1 and Va2 read from the A / D conversion circuit 24, and the D / A conversion circuit 2 in the voltage control circuit 26.
6a.

That is, in the current / voltage control circuit 22, when it is desired to set an operating point reference voltage according to the light receiving current IF from the light receiving device 12 where the light emitting device 11 in the probe unit 1 is not emitting light as VREF, Part 1
When the external light in the installation environment is received by the photodiode 12a of the light receiving device 12, the light receiving current IF corresponding to the reception of the external light is received even when the light emitting device 11 is not emitting light.
Is output and the operating point reference voltage VREF in the current / voltage conversion circuit 22 shifts. Therefore, in the biological signal detecting device according to the embodiment of the present invention, the operating point reference voltage VREF due to the influence of the extraneous light reception is provided. A correction process is performed to eliminate the fluctuation (shift) of VREF.

That is, when the light emitting device 11 of the probe unit 1 is not emitting light, the CPU 25 reads the light receiving level signal Va1 via the amplifier circuit 23 which is to be the operating point reference voltage VREF of the current / voltage conversion circuit 22. Circuit 23
(N · VREF) obtained by multiplying the reference voltage VREF by the amplification factor N of
If the light receiving level signal Va1 does not match with the light receiving level signal Va1, the difference (shift amount) Vb (= N.VREF-Va1) is calculated and output to the voltage control circuit 26.
6, the voltage obtained by adding the actual shift value Vb / N in the current / voltage conversion circuit 22 obtained by dividing the Vb by the amplification factor N to VREF is defined as a reference voltage (VREF + Vb / N).
It is given to the voltage conversion circuit 22.

Similarly, the light emitting device 1 of the probe unit 1
1 is a light receiving level signal Va2 that is to be the operating point reference voltage VREF of the current / voltage conversion circuit 22 in the non-light emitting state.
Is read by the CPU 25, and the light receiving level signal V
If a2 does not match the reference voltage VREF, the difference (shift amount) Vb (= VREF-Va2) is calculated and output to the voltage control circuit 26. A voltage obtained by adding the actual shift value Vb in the conversion circuit 22 to VREF is supplied to the current / voltage conversion circuit 22 as a reference voltage (VREF + Vb).

As described above, by performing the correction control of the operating point reference voltage VREF for the two-stage current / voltage conversion circuit 22 based on the received light level signal Va1 passed through the amplifier circuit 23 and the received light level signal Va2 as it is, Even if external light is received by the light receiving device 12, the operating point reference voltage VREF in the current / voltage conversion circuit 22 can be set to be constant.

On the other hand, the CPU 25 further includes an emission current control circuit 25a and a timing generation circuit 25b. The emission current control signal from the emission current control circuit 25a and the emission timing control signal from the timing generation circuit 25b are: It is output to the LED drive device 27.

The LED driving device 17 includes a red emission driving circuit 27a and an infrared emission driving circuit 27b for lighting the red LED 11a and the infrared LED 11b of the light emitting device 11 of the probe unit 1, respectively. A constant current circuit 27c for setting the respective light emission drive currents of the drive circuits 27a and 27b is provided.

The set value of the light emission drive current in the constant current circuit 27c is adjusted by the light emission current control signal from the light emission current control circuit 25a in the CPU 25, and each of the LEDs 11a and 11b is controlled by the light emission drive current. The drive timing (see FIG. 4) is determined by the CPU
25 is controlled by a light emission timing control signal from a timing generation circuit 25b.

Here, the set value of the light emission drive current for the red LED 11a and the set value of the light emission drive current for the infrared LED 11b by the constant current circuit 27c of the LED drive device 27 are determined by the respective light emission. The light receiving level signal Va1 read from the A / D conversion circuit 24 to the CPU 25 while the transmitted light from the light receiving device 10 is received by the light receiving device 12 is adjusted by the light emitting current control circuit 25a so as to be set to a predetermined level. In this case, the subject 1
The timing at which the flow of arterial blood with respect to 0 is the minimum, that is, the fixed absorption by the tissue and the venous blood of the subject 10 is mainly performed, the absorption by the arterial blood is minimized, and the amount of light received by the photodiode 12a is maximized and read into the CPU 25. At the timing when the received light level signal Va1 becomes maximum (see FIGS. 2 and 5), the received light level signal V
a1 is set to a predetermined level.
The light emission amounts of a and 11b are adjusted.

As described above, as the transmitted light from the subject 10 is received by the light receiving device 12 when the light emitting device 11 emits light, the light receiving level signals Va1 for red and infrared light are obtained as predetermined levels. By correcting the LED light emission amount in this way, even if there is an individual difference such as the light transmittance of the subject 10 being very low or high, the stable light reception level signal Va1 is read and the arterial blood oxygen saturation is read. % Can be measured properly.

Further, the CPU 25 has an input device 2
8, an external storage device 29, a display unit 30, a backlight control device 32 for controlling lighting of a backlight 31 of the display unit 30, and an output device 33 are connected.

The input device 28 is provided with a measurement start switch for instructing the start of the biological signal detection processing by the present device and a switch for turning on the backlight 30.

The external storage device 29 stores various data measured in accordance with the biological signal detection processing centered on the CPU 25.

The backlight control device 32 includes a display unit 30
Control of turning on and off the backlight 31 and lighting level control at the time of turning on the backlight 31. The light emitting device 11 does not emit light due to the reference voltage correction processing of the light receiving operation in the current / voltage conversion circuit 22. When the light receiving level signal Va1 corresponding to the amount of external light received by the light receiving device 12 in the state is read into the CPU 25, the brightness of the external environment is determined by the received light level signal Va1, and the backlight 31 Is controlled to an optimal level.

Here, the principle for measuring the arterial oxygen saturation of the subject 10 by the biological signal detecting device will be described.

The present apparatus measures arterial blood oxygen saturation by utilizing the change in arterial blood volume due to the pulse, and eliminates the need for blood collection.
It can be measured simply by illuminating it, so it is used as an equipment for various tests and clinical research equipment, including an anesthesia and intensive care area monitor.

Of the hemoglobin in the blood, hemoglobin bound to oxygen is referred to as oxyhemoglobin (HbO ₂ ), and hemoglobin not bound to oxygen is referred to as reduced hemoglobin (Hb). Degree (SpO ₂ ).

Blood becomes red if it contains oxygen, and black if it loses oxygen. Therefore, the amount of oxygen can be evaluated by looking at the color of the blood. When measuring from outside the body, the arterial flow and the venous flow are obtained in a mixed state. However, since it is actually desired to measure the saturation of the arterial flow alone, the pulsation of the arterial flow is used.

FIG. 2 is a diagram showing the ratio of each light-absorbing component to the total light absorbance when light is transmitted through the human body, and the change in the light absorbance due to the pulsation.

The degree of light absorption when light is transmitted through the subject 10 naturally has a pulsating component. This pulsating component is caused by the pulsation of the artery.

It is the arterial component that changes in accordance with the pulsation of the heart. Therefore, by extracting the color of the blood in the pulsating portion, it is possible to separately measure only the color of the arterial blood.

That is, as shown in FIG. 2, the absorption of light by tissues other than blood vessels and venous blood is constant because it is not affected by the heartbeat, whereas the absorption of light by its components is synchronized with the heartbeat because arterial blood pulsates. And fluctuate.

As described above, since the light absorption due to arterial blood fluctuates with the heartbeat, by subtracting the invariant component of the fluctuation numerically from the total light absorption, the light absorption component due to human body tissue and venous blood is removed. Only the light-absorbing component due to arterial blood remains, which indicates the arterial oxygen saturation.

The principle of measuring oxygen by light is described in Lamb
Based on ert-Beer's law and the principle of measurement by absorption.

(Lambert-Beer's Law) Basic: "The amount of light absorbed is proportional to the product of the incident light and the solute concentration." A solution in which a substance is dissolved in a liquid.
The out ratio attenuates by an amount proportional to the concentration of the substance and the optical path length.

A = log (Iin / Iout) = E · C · D A: Absorbance C: Concentration E: Absorption coefficient D: Thickness The extinction coefficient E is a constant representing the intensity of light absorption specific to a sample. It depends on the wavelength of the incident light.

Here, it is assumed that the thickness increases by ΔD and the transmitted light decreases (Iin−ΔI). This is equivalent to the fact that the incident light Iout is incident on the thickness ΔD and transmitted light (Iout−ΔI) is obtained. Therefore, the following equation is established.

ΔA = log ｛Iout / (Iout−Δ
I)｝ = E · C · ΔD In this apparatus, it is considered that the thickness change ΔD is caused by the pulsation of the arterial blood, and as a result, the absorbance is changed by ΔA.

Here, when ΔA is measured at two wavelengths, ΔA 1 = E 1 · C · ΔD ΔA 2 = E 2 · C · ΔD E 1: Absorption coefficient of arterial blood at wavelength 1 E 2: Absorption coefficient of arterial blood at wavelength 2 Absorbance ratio When ΔA1 / ΔA2 is obtained as φ, the concentration C
And the change ΔD in thickness are constant irrespective of the wavelength, so that φ = ΔA1 / ΔA2 = E1 / E2.

Since the oxygen saturation S and φ have a one-to-one relationship, once φ is determined, S is also determined.

Therefore, it is possible to obtain the arterial oxygen saturation from the ratio of oxyhemoglobin to reduced hemoglobin using light sources of two different wavelengths.

FIG. 3 is a graph showing a change in absorbance for oxyhemoglobin and reduced hemoglobin at a red emission wavelength and an infrared emission wavelength, and a change in oxygen saturation in accordance with the absorbance ratio. FIG. 3A shows oxyhemoglobin. FIG. 4B is a diagram showing the relationship between the light emission wavelength and the absorbance for the reduced hemoglobin, and FIG. 4B is a diagram showing the relationship between the absorbance ratio of the red light and the infrared light and the oxygen saturation.

FIG. 4 shows a red LED of the biological signal detecting device.
It is a timing chart which shows the light emission drive interval in 11a and infrared LED11b.

FIG. 5 shows a red LED of the biological signal detecting device.
It is a figure which shows each light-receiving signal waveform according to the pulsation accompanying the light emission of 11a and infrared LED11b.

That is, the red LED 11a and the infrared LED 11b in the light emitting device 11 of the probe unit 1
As shown in FIG.
b is time-divisionally driven according to a light emission timing control signal output to the LED driving device 27, and as shown in FIG.
The arterial blood oxygen saturation (SpO ₂ ) is determined by the ratio (A / B) of the received light level signal Va for each emission wavelength separated from the combined received light signal corresponding to the pulsation read from the A / D conversion circuit 24 to the CPU 25. It is calculated.

In this case, the timing at which arterial blood flows into the subject 10 is the maximum, that is, the fixed absorption by the tissue and the venous blood of the subject 10 and the absorption by the arterial blood are maximized, and the amount of light received by the photodiode 12a is minimized. At the timing when the light receiving level signal Va read by the CPU 25 becomes minimum (the dark level is maximum in FIG. 5), the light receiving level signal VaR accompanying red light emission and the light receiving level signal VaIR accompanying infrared light emission are changed. Separated,
Arterial blood oxygen saturation (Sp) corresponding to the ratio (A / B)
O ₂ ) is measured.

The oxygen saturation (SpO ₂ ) corresponding to the ratio of the light receiving levels of the red light R and the infrared light IR is determined in advance by RO
The data may be stored as an M table and the corresponding data may be read out at the time of measurement, or may be calculated and calculated based on the absorbance ratio (ΔA1 / ΔA2) accompanying the pulsation each time.

Next, a series of operations of the biological signal detecting device having the above configuration will be described.

FIG. 6 is a flowchart showing a biological signal detection process by the biological signal detection device.

The subject 10 is sandwiched between the light emitting device 11 and the light receiving device 12 in the probe unit 1 and the input device 28
When the measurement start key provided in the CPU 25 is operated, the biological signal detection processing in FIG. 6 is started in accordance with the system program stored in the internal ROM of the CPU 25 or the external storage device 29.

When the biological signal detection processing is started, first, when the light emitting device 11 does not emit light, the light receiving level signal Va1 on the side via the amplifier circuit 23, that is, before receiving the transmitted light through the subject 10. However, the light receiving level signal Va1 multiplied by N by the amplifying circuit 23 and output from the A / D converting circuit 24 is read by the CPU 25 in accordance with the external light receiving operation of the light receiving device 12 according to the installation environment of the probe unit 1. (Step S1).

Then, the amplification-side light-receiving level signal V read by the CPU 25 when the light emitting device 11 does not emit light.
Whether or not a1 is equal to the reference voltage (N · VREF) of the light receiving operation multiplied by N, that is, the output voltage according to the light receiving operation in the light receiving device 12 output from the voltage / current conversion circuit 22 is:
It is determined whether or not the reference voltage is a preset reference voltage VREF (step S2).

Here, since extraneous light corresponding to the installation environment of the probe section 1 is received by the photodiode 12a of the light receiving device 12, the light from the current / voltage conversion circuit 22 is increased in accordance with the rise of the received light current IF. The output voltage shifts from the reference voltage VREF, whereby the light receiving level signal Va1 on the amplification side read by the CPU 25 is changed to the reference voltage (N ·
If it is determined that they are not equal to (VREF), the difference (shift amount), Vb (= N.VREF-Va1), is calculated and output to the voltage control circuit 26 (step S2 → S3).

Then, the voltage control circuit 26 outputs the V
The voltage obtained by adding the actual shift value Vb / N in the current / voltage conversion circuit 22 obtained by dividing b by the amplification factor N to VREF is given to the current / voltage conversion circuit 22 as a reference voltage (VREF + Vb / N) (step). S4).

Thus, the first-stage current / voltage conversion circuit 22 based on the light reception level signal Va1 through the amplification circuit 23
Is controlled by the correction of the operating point reference voltage VREF with respect to the light receiving device 12, even if extraneous light is received by the light receiving device 12, the amplification-side light receiving level signal Va1 when the light emitting device 11 does not emit light is N times the reference voltage of the light receiving operation. If it is determined that the setting is equal to (N · VREF), the light receiving device 11 of the probe unit 1 receives light as it is to be the operating point reference voltage VREF of the current / voltage conversion circuit 22 when the light emitting device 11 is not emitting light. The level signal Va2 is read by the CPU 25 (steps S1, S2 → S5).

If it is determined that the received light level signal Va2 read by the CPU 25 does not match the reference voltage VREF, the difference (shift amount) Vb (= shift amount) is obtained.
(VREF-Va2) is calculated and output to the voltage control circuit 26 (step S6 → S7).

Then, the actual shift value Vb in the current / voltage conversion circuit 22 is changed from the voltage control circuit 26 to VREF.
Is supplied to the current / voltage conversion circuit 22 as a reference voltage (VREF + Vb) (step S8).

In this way, by controlling the correction of the operating point reference voltage VREF with respect to the current / voltage conversion circuit 22 in the second stage based on the received light level signal Va2 from the current / voltage conversion circuit 22 as it is, the external light to the light receiving device 12 is controlled. Is received, when it is determined that the light receiving level signal Va2 when the light emitting device 11 does not emit light is set to be equal to the reference voltage (VREF) of the light receiving operation, the process proceeds to the light emitting level control processing in steps S9 to S16. (Step S5,
S6 → S9).

As described above, by performing the correction control of the operating point reference voltage VREF for the two-stage current / voltage conversion circuit 22 based on the received light level signal Va1 via the amplifier circuit 23 and the received light level signal Va2 as it is, Even when external light is received by the light receiving device 12, the operating point reference voltage VREF in the current / voltage conversion circuit 22 can be set at a high accuracy and constant.

When the correction control of the operating point reference voltage VREF in steps S1 to S8 is performed, step S9 is performed.
First, a light emission current control circuit 25a of the CPU 25 outputs a light emission current control signal for driving a red light emission of a predetermined initial level to the constant current circuit 27c of the LED driving device 27, and the process proceeds to S16. The red LED 11a of the light emitting device 11 of the probe unit 1 is turned on by the light emission drive circuit 27a at a predetermined initial level light emission amount (step S9).

Then, the transmitted light of red emission passing through the subject 10 is received by the photodiode 12a of the light receiving device 12, and the current / voltage conversion circuit 22 outputs the light according to the light receiving current IF output from the photodiode 12a. Is a light reception voltage signal shifted from the reference voltage VREF by the light reception amount. In response to this, a light reception level signal Va1 output from the A / D conversion circuit 24 is read into the CPU 25, and the red light emission is output. Light reception level signal V according to transmitted light
It is determined whether or not a1 is equal to a predetermined light receiving level in a range necessary for performing an appropriate measurement process (steps S10 and S11).

Here, for example, since the finger as the subject 10 sandwiched between the probe portions 1 is very thick, its light transmittance is extremely low, and the light from the reference voltage VREF obtained by the light receiving operation of the red transmitted light is obtained. When the shift amount is very small and the light receiving level signal Va1 corresponding thereto is determined to be significantly smaller than the predetermined light receiving level, the light emitting current control circuit 25a of the CPU 25 sends the signal to the constant current circuit 27c of the LED driving device 27. The emission drive current for the red LED 11a from the red emission drive circuit 27a is controlled to increase by the output emission current control signal for red emission drive (steps S11 → S12).

As described above, as the amount of light emitted by the red LED 11a is increased, the amount of red light transmitted through the subject 10 and received by the light receiving device 12 is also increased.
When it is determined that the light receiving level signal Va1 read from the D conversion circuit 24 to the CPU 25 has become equal to a predetermined light receiving level in a range necessary for performing an appropriate measurement process, the light emitting current control of the CPU 25 is similarly performed. Circuit 25
a, an emission current control signal for infrared emission drive of a predetermined initial level is output to the constant current circuit 27c of the LED drive device 27, and the infrared emission drive circuit 27b sets the infrared LED 11b in the light emission device 11 of the probe unit 1 to a predetermined value. The light is emitted at the initial light emission amount (steps S10, S11 → S1).
3).

Then, the transmitted light of the infrared emission passing through the subject 10 is received by the photodiode 12a of the light receiving device 12, and the current / voltage conversion circuit 22 is output in accordance with the received light current IF output from the photodiode 12a. Outputs a received light voltage signal shifted from the reference voltage VREF by the amount of received light. In response to this, a received light level signal Va1 output from the A / D conversion circuit 24 is read into the CPU 25, and Light receiving level signal V according to transmitted light of light emission
It is determined whether or not a1 is equal to a predetermined light receiving level in a range necessary for performing an appropriate measurement process (steps S14 and S15).

Here, for example, the finger which is the subject 10 sandwiched between the probe portions 1 is very thick as described above, so that the transmittance of the light is extremely low, and the reference voltage obtained by the operation of receiving infrared transmitted light is obtained. Since the shift amount from VREF is also very small, the corresponding light receiving level signal Va1 is determined to be significantly smaller than the predetermined light receiving level.
25 light emitting current control circuit 25a to LED driving device 27
The emission drive current for the infrared LED 11b from the infrared emission drive circuit 27b is controlled to increase in response to the infrared emission drive emission control signal output to the constant current circuit 27c (steps S15 → S16).

As described above, as the amount of light emitted by the infrared LED 11a is increased, the amount of infrared transmitted light passing through the subject 10 and received by the light receiving device 12 is also increased.
When it is determined that the light reception level signal Va1 read from the D conversion circuit 24 to the CPU 25 has become equal to a predetermined light reception level in a range necessary for performing an appropriate measurement process, the arterial blood oxygen saturation (SpO ₂ ) is determined. (Steps S14, S15)
→ S17).

In this case, the timing at which the arterial blood flows into the subject 10 is the minimum, that is, the fixed absorption by the tissue and the venous blood of the subject 10 is the main, the absorption by the arterial blood is the minimum, and the light receiving amount in the photodiode 12a is minimized. At which the light receiving level signals Va1 (R) and Va1 (IR) read by the CPU 25 become the maximum (FIG. 5).
In this case, the received light level signal Va1 (R)
, Va1 (IR) are set to predetermined light receiving levels, and the light emission amounts of the LEDs 11a and 11b are controlled.

As described above, by correcting the LED light emission amount so that the respective light receiving level signals Va1 (R) and Va1 (IR) at the time of red and infrared light emission are obtained as predetermined levels, the subject 10 Even if there is an individual difference such as a very low or high light transmittance, it is possible to read the stable received light level signal Va1 and appropriately measure the arterial blood oxygen saturation.

That is, the red light from the red LED 11a and the infrared LED 11
The received light level signals Va1 (R) and Va1 (IR) of the respective transmitted lights corresponding to the infrared light from b are sequentially read, and the timing at which the inflow of the arterial blood into the subject 10 becomes maximum, that is, the absorption by the arterial blood At the timing when the amount of light received by the photodiode 12a becomes the minimum and the light receiving level signal Va read into the CPU 25 becomes the minimum (the maximum dark level in FIG. 5), the light receiving level signal Va1 based on the red light and the infrared light. The arterial oxygen saturation (SpO ₂ ) is calculated based on the ratio (A / B) of the absorbance in the subject 10 obtained as the ratio of (R), Va1 (IR), stored in the external storage device 29, and displayed on the display unit. 30 is displayed (step S17).

On the other hand, L in steps S1 to S8
The brightness of the external environment is determined according to the light receiving level signal Va read from the A / D converting circuit 24 to the CPU 25 in accordance with the reference voltage correcting process of the light receiving operation in the current / voltage converting circuit 22 when the ED is not emitting light, In response, the backlight control device 32 controls the lighting level for the backlight 31 to an optimal level.

That is, for example, the light receiving level signal Va1 corresponding to the amount of extraneous light received by the light receiving device 12 when the LED is not emitting light drops below the first level set in advance, and the surrounding brightness becomes slightly dark. If it is determined that the backlight 31 has become light, the backlight controller 32 drives the backlight 31 of the display unit 30 to emit light at the first level of light emission.

The light receiving level signal V corresponding to the amount of external light received by the light receiving device 12 when the LED is not emitting light.
If it is determined that the surrounding brightness has become extremely dark, the backlight controller 32 switches the backlight 31 of the display unit 30 to the second level. Lighting drive is performed based on the light emission amount.

As a result, it is possible to provide a display screen with a brightness that is easy to see at any time, regardless of the change in the brightness of the external environment.
The measured arterial blood oxygen saturation (SpO ₂ ) data can always be clearly displayed.

Therefore, according to the biological signal detecting device having the above structure, the red light L in the light emitting device 11 of the probe unit 1 is
The ED 11a and the infrared LED 11b emit light alternately to irradiate the subject 10, and the transmitted light is received by the photodiode 12a of the light receiving device 12, and the current / voltage conversion circuit 22 outputs an A / A signal in accordance with the received light current IF. D conversion circuit 24
The oxygen saturation (SpO ₂ ) is measured based on the ratio of the received light level signals Va (R) and Va (IR) at each emission wavelength read into the CPU 25 via the light emitting device 1.
1 reads the light receiving level signal Va in a non-light emitting state, and controls the voltage control circuit 26 in accordance with the difference Vb (= VREF−Va) so that this signal becomes equal to a preset reference voltage VREF of the light receiving operation. Since the operating point reference voltage in the current / voltage conversion circuit 22 is corrected, an extra shift of the received light current IF occurs due to the reception of the environment extraneous light by the photodiode 12a separately from the transmitted light transmitted through the subject 10. However, the reference voltage for the light receiving operation can always be set to the preset reference voltage VREF, and the oxygen based on the ratio of the light receiving level signals Va (R) and Va (IR) by the light emission of the LEDs 11a and 11b. Saturation (Sp
Measurement of O ₂ ) can always be performed accurately and stably.

Further, according to the biological signal detecting device having the above configuration, the red LED 11 a and the infrared LED 11
The light receiving level signals Va (R) and Va (IR) at each light emitting wavelength read by the CPU 25 are converted into an appropriate measurement process in response to the light received by the light receiving device 12 in the subject transmitted light accompanying the alternate light emission of b. From the light-emitting current control circuit 25a so as to be equal to a predetermined light receiving level in a range required for performing
The light emission amount control signal output to the constant current circuit 27c of the driving device 27 increases or decreases the light emission amount of each of the LEDs 11a and 11b and corrects the light emission amount.
Even if the finger is thick and the light transmittance is very low, or if the finger is thin and the transmittance is very high, the measurement accuracy is not affected by such individual differences of the subject 10. The measurement of the appropriate oxygen saturation (SpO ₂ ) which does not cause the generation can be performed. Not only that, each LED1
It is also possible to solve the problem of the transmitted light reception level fluctuation accompanying the fluctuation of the light emission amount due to the individual difference between 1a and 11b itself.

Further, according to the biological signal detecting device having the above configuration, the reference voltage for the light receiving operation of the current / voltage conversion circuit 22 when the light emitting device 11 is not emitting light can be obtained via the A / D conversion circuit 24. The process of correcting the reference voltage VREF to a preset reference voltage VREF based on the received light level signal Va is performed by first converting the received light level signal Va1 from the current / voltage conversion circuit 22 through the N-fold amplification circuit to an N-fold reference voltage (N · VREF). ) And a correction process for making the received light level signal Va2 from the current / voltage conversion circuit 22 equal to the reference voltage VREF. However, even if extraneous light is received, the operating point reference voltage VREF in the current / voltage conversion circuit 22 can be set with high accuracy and constant, and each LED thereafter can be set.
Light receiving level signals Va (R) and V due to light emission of 11a and 11b
Measurement processing of oxygen saturation (SpO ₂ ) based on the ratio of a (IR) can be performed more accurately.

In the biological signal detecting device according to the above-described embodiment, the probe unit 1 is configured to transmit the light emitted by the light emitting device 11 to the subject 10 and receive the transmitted light by the light receiving device 12. But the light emitting device 11
May be configured to reflect the light emitted by the light source to the subject 10 and receive the reflected light by the light receiving device 12. Even in such a biological signal detecting device as a probe of the subject reflected light receiving type, the light receiving operation is performed by correcting the light receiving operation reference voltage when light is not emitted and controlling the light emitting current when emitting light, just like the above embodiment. By performing the predetermined value correction processing of the level signal Va, it is possible to perform a stable measurement processing that is not affected by extraneous light, individual differences of the subject 10, and the like.

[0091]

As described above, according to the biological signal detecting device of the first aspect of the present invention, when the light emitting means is not emitting light, the signal is obtained based on the signal level of the light receiving signal output from the light receiving means. Since the reference point of the level measurement is corrected, even in an environment where extraneous light that is not light from the subject accompanying light emission from the light emitting unit is received, the reference point of the light receiving operation is set to the reference level. It is possible to obtain an accurate light receiving signal level according to the light from the subject without being affected by extraneous light when receiving the light from the subject accompanying the light emission from the light emitting means. Can be.

Therefore, without being affected by extraneous light,
It is possible to always obtain stable measurement results.

According to the biological signal detecting device of the second aspect of the present invention, there is provided the biological signal detecting device of the first aspect, wherein the light emitting means further outputs the light from the light receiving means in a light emitting state. Based on the signal level, the signal level at the time of measurement is corrected so that the light emission amount of the light emitting means is increased or decreased so as to be within a preset range, so that it is necessary to appropriately measure the state of the subject. It is possible to obtain a measurement signal level in a range range, and it is possible to perform appropriate state measurement without being affected by individual differences such as extremely low or high light passing through the subject.

Accordingly, it is possible to always obtain an appropriate level of transmitted light and perform measurement without being affected by individual differences between subjects.

Further, according to the light emission level control device according to the seventh aspect of the present invention, based on the level of the light reception signal output from the light receiving means, this light reception signal level controls the increase or decrease of the light emission level of the light emission means. Since the correction is made so as to fall within the preset range, it is possible to obtain a signal level in a range range necessary for appropriately detecting the state of the irradiation target, for example, without being affected by individual differences of the irradiation target. Appropriate state detection can be performed.

Accordingly, it is possible to correct the light emission level of the light irradiated to the irradiation object (test object) to an appropriate level.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an electronic circuit of a biological signal detection device according to an embodiment of the present invention.

FIG. 2 is a diagram showing the ratio of each light-absorbing component to the total light absorbance when light is transmitted through a human body, and the change in the light absorbance due to the pulsation thereof.

FIG. 3 is a diagram showing a change in absorbance with respect to oxyhemoglobin and reduced hemoglobin at a red emission wavelength and an infrared emission wavelength, and a change in oxygen saturation in accordance with the absorbance ratio. FIG. Diagram showing the relationship between emission wavelength and absorbance for hemoglobin, FIG.
FIG. 3 is a diagram showing the relationship between the absorbance ratio between red light and infrared light and oxygen saturation.

FIG. 4 shows a red LED and an infrared LE of the biological signal detection device.
9 is a timing chart showing light emission drive intervals in D.

FIG. 5 shows a red LED and an infrared LE of the biological signal detection device.
FIG. 9 is a diagram showing each light reception signal waveform corresponding to a pulsation accompanying light emission of D.

FIG. 6 is a flowchart showing a biological signal detection process by the biological signal detection device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Probe part, 10 ... Subject, 11 ... Light emitting device, 11a ... Red LED, 11b ... Infrared LED, 12 ... Light receiving device, 12a ... Photodiode, 2 ... System part, 21 ... Amplifier circuit (current amplifier), Reference numeral 22: current / voltage conversion circuit, 23: amplification circuit (voltage amplifier), 24: A / D conversion circuit, 25: CPU, 25a: emission current control circuit, 25b: timing generation circuit, 26: voltage control circuit, 26a: D / A conversion circuit, 27: LED drive device, 27a: Red LED drive circuit, 27b: Infrared LED drive circuit, 28: Input device, 29: External storage device, 30: Display unit 31: Backlight, 32: Back light Light control device, 33: output device (connector), Va (R): red transmitted light received signal, Va (IR): infrared transmitted light received signal.

Claims (7)

[Claims] 1. A probe having light emitting means, light receiving means for receiving light from a subject obtained by irradiating the object with light emitted by the light emitting means, and output from the light receiving means of the probe. A measuring means for measuring a state of the subject based on a signal level of the light receiving signal, wherein the signal level of the light receiving signal output from the light receiving means when the light emitting means is not emitting light A biological signal detection device, further comprising a reference point correcting means for correcting a reference point for signal level measurement based on the above. 2. The method according to claim 1, further comprising: increasing and decreasing a light emission amount of the light emitting means based on a signal level output from the light receiving means in a state where the light emitting means emits light so that a signal level at the time of measurement falls within a preset range. The biological signal detection device according to claim 1, further comprising a light emission control unit that controls the light emission. 3. The amplifying means for amplifying a light receiving signal output from the light receiving means, and a first input means for inputting a signal level of the light receiving signal amplified by the amplifying means. And a second input means for inputting a signal level of a light receiving signal output from the light receiving means, a signal level output from the first input means, and an output from the second input means. Based on the signal level
The biological signal detection device according to claim 1 or 2, wherein a reference point for signal level measurement is corrected. 4. A display means for displaying a state of the subject measured by the measuring means; an illuminating means for illuminating a display screen of the display means; The living body according to any one of claims 1 to 3, further comprising: an illumination control unit configured to control brightness of illumination by the illumination unit in accordance with a signal level of the output light reception signal. Signal detection device. 5. The apparatus according to claim 1, wherein the light receiving unit transmits light emitted by the light emitting unit to a subject, and receives the transmitted light as light from the subject. The biological signal detection device according to claim 1. 6. The apparatus according to claim 1, wherein the light receiving unit reflects light emitted by the light emitting unit to a subject, and receives the reflected light as light from the subject. The biological signal detection device according to claim 1. 7. A light emitting means for irradiating light to an object to be illuminated, a light receiving means for receiving light incident from the object to be illuminated in response to irradiation of light to the object to be illuminated by the light emitting means; Control means for increasing or decreasing the light emitting level of the light emitting means based on the level of the light receiving signal output from the controller so that the level of the light receiving signal falls within a preset range. Control device.