JPH0559734B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention non-invasively measures arterial blood oxygen saturation (hereinafter referred to as
This relates to an oximeter that measures and displays SaO ₂ ).

[Prior Art] A conventional arterial blood oxygen saturation measuring device (oximeter) is known that displays a measured value numerically each time it is obtained. This type of device is very convenient for accurately knowing the measured value at that time, but it also allows you to understand the condition of the person being measured from the past to the present (whether it was in a stable state or unstable state). Can not do it. In measuring arterial blood oxygen saturation, it is important to have an accurate measurement value at the present moment, but it is also very important to know changes in the subject's condition over time.
In other words, by knowing the condition of the subject from the past to the present, the measurer can determine whether further care is required from this point forward, whether there is any measure to be taken to stabilize the condition, or whether no treatment is necessary. This means that decisions such as these can be made quickly.

[Object of the Invention] Accordingly, an object of the present invention is to provide an oximeter that makes it possible to easily grasp the current state of a subject from the past.

[Measurement Principle] First, the SaO ₂ measurement principle of the apparatus of the present invention will be explained. Light incident on a living body is absorbed and scattered by blood, muscles, etc. in the living body, and is attenuated. Arterial blood is pulsating and its volume changes periodically, so
The amount of attenuation of light passing through living organisms also changes periodically. If the intensity of light with wavelength λ passing through a living body is λ, then λ＝oλ・Ftλ・Fvλ・f(μλ)e ^-g( 〓〓 ^)(d+ 〓 ^d
) . Here, oλ is the incident light intensity of light with wavelength λ, Ftλ and Fvλ are the transmittance of blood-free part and venous blood at wavelength λ, μλ
is the absorption coefficient at the wavelength λ of arterial blood, f(μλ),
g(μλ) are each a function of μλ, and d and Δd are the average thickness of the arterial blood through which the light passes and its variation, respectively. Δd changes periodically.

Difference between the logarithm of λ and the DC component of the logarithm of λ
Yλ becomes Yλ=−g(μλ)Δd. Since g(μλ) is approximately proportional to the square root of μλ, it is expressed as Yλ ² =kλμλ(Δd) ² . kλ is a constant determined by wavelength. μλ is μλ=CHbo ₂・EλHbo ₂ +CHb+EλHb=Ct{S(EλHbo ₂
−EHb)+EλHb}. CHbo ₂ and CHb are the concentrations of oxyhemoglobin and deoxyhemoglobin, Ct =
CHbo ₂ +CHb, S=CHbo ₂ /Ct, EλHbo ₂ and
EλHb is the extinction coefficient of oxyhemoglobin and deoxyhemoglobin at wavelength λ, respectively. Therefore, Yλ ² becomes Yλ ² =kλCt{S(EλHbo ₂ −CλHb)+EλHb}(Δd) ² . The above Yλ at two wavelengths λ ₁ and λ ₂
S can be determined by measuring .
Let Yλ at wavelength λ ₁ be Yλ ₁ and Yλ at wavelength λ ₂ be
Expressed in Yλ ₂ , (Yλ ₁ ) ² = kλ ₁ Ct{S(Eλ ₁ Hbo ₂ −Eλ ₁ Hb) + Eλ ₁ Hb
}(Δd) ² (Yλ ₂ ) ² =kλ ₂ Ct{S(Eλ ₂ Hbo ₂ −Eλ ₁ Hb) + Eλ ₂ Hb
}(Δd) ^2This gives S=-Eλ ₂ Hb・Yλ ₁ ² /Kλ ₁ −Eλ ₁ Hb・Yλ ₂ ² /Kλ ₂ /(
Eλ ₂ Hbo ₂ −Eλ ₂ Hb)・Yλ ₁ ² /Kλ ₁ −(Eλ ₁ Hbo ₂ −Eλ ₁ H
b) By using a wavelength λ ₁ satisfying Yλ ₂ ² /Kλ ₂ and Eλ ₁ Hbo ₂ =Eλ ₁ Hb, S=kλ ₁ /kλ ₂ Eλ ₁ Hb/Eλ ₂ Hbo ₂ −Eλ ₂ Hb·(Yλ _twenty ^two
/Yλ ₁ ) ² −Eλ ₂ Hb／Eλ ₂ Hbo ₂ −Eλ ₂ Hb Since SaO ₂ is defined as S×100 (%), it can be calculated as SaO ₂ = A・(Yλ ₂ /Yλ ₁ ) ² +B. I can do it. Here, A and B are constants determined by the optical properties of blood.

[Example] The configuration of an example of the present invention will be described below. 1st
As shown in the figure, an illumination optical system 1 for irradiating light onto a measuring part M such as a finger or the like to be measured, and a measuring part M
For example, the light passing through is 650μm, 710μm, 805μm
A light receiving device including first to third light receiving elements 36, 37, and 38 that split light into first, second, and third different wavelength ranges and convert each light into first to third electrical signals. The reference light section 2 includes a reference light section 3 including a reference light receiving element 34 for monitoring the emission intensity of the light source, and a reference light current/voltage conversion section 4 that converts the output current of the reference light section 3 into a voltage. Further, from the output of the reference photocurrent voltage converter 4 and the output of the first to third light receiving elements of the light receiving unit 3, the logarithms of the outputs of the first to third light receiving elements are calculated.
First to third low-pass filters 8, 9, 1 for removing pulsating components in the outputs of the third logarithmic converter 5, 6, 7 and the first to third logarithmic converters 5, 6, 7
0, the first to third logarithmic converters that output the differences between the outputs 5, 6, and 7 of the first to third logarithmic conversion units and the outputs of the first to third low-pass filters 8, 9, and 10 corresponding thereto. 3 differential amplifier sections 11, 12, 13, first to
First to third double-wave rectifiers 14 and 1 that double-wave rectify the outputs of the third differential amplifiers 11, 12, and 13, respectively.
5, 16, and a light amount measuring section 17 that performs a predetermined calculation on the output of the third logarithmic conversion section 7.

The analog multiplexer 18 selects one of the outputs of the first to third double-wave rectifying sections 14, 15, and 16 and the light amount measuring section 17, and transmits the selected output to the next stage. The analog output is supplied to an AD converter 20 consisting of a double integrator 19a and a comparator 19b and converted into a digital value. The digital output is supplied to a control calculation section 26, which will be described later. The output of the first differential amplifier section 11 is supplied to the control calculation section 26 via the pulse wave shaping section 21 which converts it into a pulse waveform.

Furthermore, a pulse wave signal converter 22 converts the output of the first differential amplifier 11 into a signal suitable for input to the pulse wave display ammeter 29, and Pulse wave output unit 23 that converts into input, multiple switches that set the upper and lower limits of measured values for warning, a switch that controls the generation of alarm sounds, a switch that controls the display unit, etc. - It has a switch input section 24 consisting of a control circuit that reads the off state, and a display section 25 that displays the measured SaO ₂ and pulse rate. The control calculation unit 26
~Third double-wave rectifier 14, 15, 16, analog multiplexer 18, AD converter 20, and display unit 2
5, switch input section 24, etc., and SaO ₂
and calculate the pulse rate. Furthermore, this device includes a screen copy section 27 that hard copies the display contents of the display section 25, a digital output section 28 for connecting to an external printer, an alarm generation section 30 that emits an alarm sound, and a power supply that supplies power to each section. 31
has.

In this embodiment, a microcomputer is used as the control calculation section 26, and a halogen lamp is used as the light source 1 that emits light to the measurement section. A part of the light from the light source is incident on the light receiving element of the reference light section 3, and the rest is guided to the measuring section by an optical fiber or the like (not shown). The light passing through the measuring section is guided to the light receiving section 2 by another optical fiber or the like (not shown), where it is separated into light in the first to third wavelength ranges, and each of the separated lights is First to third light receiving elements 3
6, 37, and 38. The light receiving element in the reference light section 3 and the first to third light receiving elements 3 of the light receiving section 2
6, 37, and 38 each output a current proportional to the intensity of the incident light. The output of the light receiving element of the reference light section 3 is converted into a voltage by the reference light current/voltage conversion section 4. The outputs of the reference photocurrent-voltage converter 4 are the first to third outputs.
is input to logarithmic conversion units 5, 6, and 7.

The first to third logarithmic converters 5, 6, and 7 convert the outputs of the first to third light receiving elements from the outputs of the first to third light receiving elements and the output of the reference photocurrent voltage converter 4, respectively. Each outputs a logarithmically proportional signal. Each of the logarithmic conversion sections 5, 6, and 7 has a light source light amount fluctuation correction circuit, which will be described later, and thereby noise caused by changes in the light amount of the light source is removed from the output of each logarithmic conversion section. The outputs of the first to third logarithmic conversion units 5, 6, and 7 are transmitted to the first to third low-pass filters 8, 9,
10 and first to third differential amplifier sections 11, 12,
13, respectively. Outputs of the first to third low-pass filters 8, 9, and 10 are connected to first to third differential amplifiers 11, 12, and 13, respectively. First to third differential amplifier sections 11, 12, 1
3 are first to third logarithmic conversion units 5, 6, and 7, respectively.
output and the first to third low-pass filters 8,
The difference between the outputs of 9 and 10 is calculated and increased. Therefore, only photoplethysmogram signals in the corresponding wavelength ranges are obtained as outputs from the first to third differential amplifiers 11, 12, and 13. This pulse wave signal is generated by a change in the volume of arterial blood at the measuring section, and contains information regarding the extinction coefficient of the arterial blood. Outputs of the first to third differential amplifiers 11, 12, and 13 are connected to first to third double-wave rectifiers 14, 15, and 16, respectively. The first to third double-wave rectifiers each include a half-wave rectifier circuit and a differential integrator. 1st
~The first to third differential amplifier sections 1 in the third double-wave rectifier section
The outputs of the outputs 1, 12, and 13 are each subjected to double-wave rectification, integrated by the integrator of the double-wave rectifier for a certain period of time under the control of the control calculation section 26, and then held for a predetermined period of time. The first to third double-wave rectifiers 1 held
Outputs of 4, 15, 16 and the light amount measurement section 17, which will be described later.
The output of
is input. Which input the analog multiplexer 18 selects is controlled by the control calculation unit 26.

A double integrator 19a, a comparator 19b, and a counter built into the microcomputer 26 constitute a double integration type A/D converter, and the signal input to the double integrator 19a is A/D converted. Ru. The first A/D conversion is performed every time one A/D conversion is performed.
~The integrators of the third double-wave rectifiers 14, 15, and 16 are discharged. These first to third double-wave rectifiers 14,
The 15th and 16th integrators integrate, hold, and
The discharge is repeated and A/D conversion is performed, and the A/D conversion of the output of the light quantity measuring section 17 is also repeated at a constant cycle. The offset voltages of the first to third double-wave rectifiers that have been A/D-converted and stored in advance are subtracted from the A/D-converted outputs of the first to third double-wave rectifiers 14, 15, and 16, respectively. , first to third pulse wave amplitude values proportional to the amplitude of the pulse wave signal are determined. Then, the first oxygen saturation SaO ₂ is determined by a predetermined calculation from the first and second pulse wave amplitude values.
(1) is calculated. Further, a second oxygen saturation SaO ₂ is determined by a predetermined calculation from the first and third pulsation amplitude values.
(2) is calculated and stored. SaO ₂ (1) is used to detect the presence or absence of noise due to vibration of the measurement unit, which will be described later. SaO ₂ (1) and
SaO ₂ (2) is calculated one after another at regular intervals, but from the latest SaO ₂ (2) and a certain number of previous SaO ₂ (2)
The SaO ₂ average value is calculated according to a predetermined method and the result is displayed on the display section 25. The calculation of the average value of SaO ₂ will be explained in detail later. Further, the output of the first differential amplifier section 11 is also connected to a pulse wave shaping section 21, a pulse wave signal converting section 22, and a pulse wave output section 23.

In the pulse wave shaping section 21, the output signal of the first differential amplification section 11 is binarized depending on whether it is larger or smaller than a certain threshold value, converted into a pulse signal, and input to the control calculation section 26. The control calculation unit 26 detects the rising and falling edges of this input pulse signal, calculates the period, and calculates the number of pulses per minute based on the period. The calculation of pulse rate is also repeated at regular intervals for SaO ₂ (1) and SaO (2) and agitation. Calculation of pulse rate will also be described later. The calculated pulse rate is displayed on the display section 25. The pulse wave signal converter 22 converts the output signal of the first differential amplifier 11 into a pulse wave display ammeter 2.
Convert it to be suitable for the input of 9. It can be confirmed whether the pulse wave signal is being obtained normally using the pulse wave display ammeter. The pulse wave output section 23 is for adapting the output signal of the first differential amplification section 11 to the input of the recorder. When the switch of the switch input section 24 is pressed, the display contents of the display section 25 are hard-copied by the screen copying section 27, and the SaO ₂
The average value, pulse rate, etc. are recorded graphically.

The average value of SaO ₂ and the pulse rate signal are digitally outputted via the digital output section 28.

When the SaO ₂ and pulse rate are outside of a certain range, an alarm must be issued because the patient is in danger and requires some kind of treatment. In the device of the present invention, the upper and lower limits of SaO ₂ and pulse rate at which an alarm should be issued can be set by switches in the switch input section 24, respectively. The set value is displayed on the display section 25.

The alarm is displayed on the display section 25 and is also emitted by sound from the alarm sound generating section 30. Whether or not to emit an alarm sound when an alarm occurs can be selected by a switch provided in the switch input section 24.
Further, if the generation of an alarm is to be prohibited when the measured value exceeds the upper limit and/or when the measured value falls below the lower limit, this can be done by setting a specific value.

The light amount measurement section 17 converts the output of the logarithmic conversion section 7 into an A/D
This is a circuit that converts to match the conversion input. The output of the light amount measuring section 17 is A/D converted at regular intervals and is used to check whether the light amount of the light source 1 is appropriate. If the amount of light is very large, the light receiving element and the logarithmic conversion circuits 5, 6, and 7 will become saturated and the accuracy of pulse wave calculation will deteriorate. Also, when the measuring part is off the specified position, the amount of light becomes very large, making it difficult to accurately measure the
Unable to measure _SaO2 . Similarly, when the amount of light is small, the characteristics of the light receiving element and the logarithmic conversion circuits 5, 6, and 7 deteriorate, making it impossible to perform accurate SaO ₂ measurements. Therefore, in order to constantly monitor whether the light amount is appropriate, the output of the light amount measuring section 17 is A/D converted, and it is checked whether the value is within a certain range.

Next, a method for removing noise caused by fluctuations in the amount of light from the light source 1 will be described. In FIG. 2, light from a halogen lamp 32 as a light source 1 is focused on the end face of an optical fiber 33. As shown in FIG. 34 is a light receiving element for receiving light from a halogen lamp as reference light, and is provided in the hood 34a.
The spectral characteristics of the light incident on the end face of the optical fiber 33 and the spectral characteristics of the light incident on the light receiving element 34 are almost the same, and the intensity of each light is directly proportional. In Fig. 2, a light receiving element 3 that receives the reference light is shown.
4 is assumed to be one, but there may be more than one. The light incident on the optical fiber 33 passes through the optical fiber 33 and is irradiated onto the measurement section, and the light transmitted through the measurement section is guided to the light receiving section 2 (FIG. 1). As described above, the light incident on the light receiving section 2 is separated into the first to third wavelength ranges and is incident on the first to third light receiving elements 36, 37, and 38. 1st to 3rd
FIG. 3 shows a circuit that outputs only the attenuation of light due to the measuring section without receiving the light intensity fluctuation of the light source from the output of the light receiving element 34 of the reference light section 3 and the output of the light receiving element 34 of the reference light section 3.
The light receiving element 34 of the reference light section 3 is connected to the input of the /V converter 35. The first to third light receiving elements 36, 37, and 38 of the light receiving section are connected to inputs of a /V converter 39, a /V converter 40, and a /V converter 41, respectively. Each /V converter 35, 3
Reference numerals 9, 40, and 41 each convert the output current of the light receiving element into a voltage. 42, 43, and 44 are logarithmic amplifiers each having two input terminals A and B and outputting the logarithm of the ratio of input A to input B.

To simplify the explanation, only the circuit corresponding to the first light receiving element 36 of the light receiving section 2 will be described.
The light that enters the first light-receiving element 36 is light in the first wavelength range that is separated by the light-receiving section 2, and has different spectral characteristics from the light that enters the light-receiving element 34 of the reference light section 3. Therefore, the ratio of the change in light intensity due to a change in the amount of light from the light source to the intensity of light incident on the light receiving element 36 is the proportion of the change in light intensity due to a change in the amount of light from the light source to the intensity of light incident on the light receiving element 34. Not equal to percentage. Therefore /V converter 39 and /V
Even if the logarithm of the ratio of the outputs of the converter 35 is calculated, noise due to changes in the light amount of the light source cannot be completely removed. /
In order to remove noise due to changes in the light amount of the light source by calculating the logarithm of the ratio of the output of the V converter 39 and the output of the /V converter 35, the spectral distribution of the light incident on the light receiving element 34 of the reference light section 3 and It is necessary to match the spectral distribution of the light incident on the first light receiving element 36, and to do so, a spectral element is required in front of the light receiving element 34 of the reference light section 3. The reference light section 3 requires as many spectroscopic elements as the number of wavelength ranges that are separated by the light receiving section 2, requiring a very complicated configuration. The present invention eliminates the influence of changes in the light amount of the light source without using a spectroscopic element in the reference light unit 3 by processing the output of one or more reference light receiving elements. There is a difference between the ratio of the change in light intensity due to a change in the light amount of the light source to the intensity of light incident on the light receiving element 34 and the ratio of the change in light intensity due to a change in the light amount of the light source to the intensity of light incident on the light receiving element 36. There is a certain relationship. That is, the ratio of the AC component due to the change in the light amount of the light source to the DC component of the output voltage of the /V converter 35 and the ratio of the AC component due to the change in the light amount of the light source to the DC component of the output voltage of the /V converter 39. There is a certain relationship between them. Therefore, it is only necessary to change the ratio of the AC component due to the change in the light amount of the light source to the DC component of the output of the /V converter 35 so that they match. This also applies to light in the second and third wavelength ranges. The circuit is 45, 46, 47 in Figure 3.
This is an AC/DC conversion circuit. AC/DC conversion circuit 4
The ratio of the AC component due to the change in the light amount of the light source to the DC component in the output of 5, 46, and 47 is /
The ratio of the AC component due to the change in the light amount of the light source to the DC component in the output of the V converters 39, 40, 41 corresponds to the ratio of the AC component in the output of the V converters 39, 40, 41.
In the outputs No. 3 and 44, noise due to changes in the amount of light from the light source is removed.

A specific example is shown in FIG. In FIG. 4, a circuit is used that directly logarithmically transforms the output currents of the first to third light receiving elements 36, 37, and 38 of the light receiving section 2. In FIG. In FIG. 4, in order to simplify the explanation, only the circuit corresponding to the first light receiving element 36 of the light receiving section will be described.

The collector current of the transistor 48 of the logarithmic amplifier 42 is the output photocurrent _L of the light receiving element 36 of the light receiving section 2.
be equivalent to. _L is expressed as the light emission intensity oλ of the light source at the first wavelength and the transmittance or reflectance of the measuring section, and oλ consists of the DC component oλ _DC and the AC noise component oλn due to changes in the light amount of the light source = It can be expressed as (oλ _DC +oλn)F=oλ _DC (1+Nλ)F. Here, Nλ=oλn/ _oλDC , and F is a constant determined by the sensitivity of the light receiving element and the transmittance of the measuring section.

The output current r of the light receiving element 34 of the reference light unit 3 is proportional to the emission intensity o of the light source over the entire wavelength range, and o consists of a DC component and an AC noise component due to changes in the light intensity of the light source, so r=K ₁ It can be expressed as (o _DC +on)=K ₁ o _DC (1+N). Here, N=on/o _DC and K ₁ is a constant. Converts the output of the light receiving element 34 of the reference light section 3 into a voltage/Output voltage Vr of the V converter 35
is expressed by the following equation.

Vr=R ₀ K ₁ o _DC (1+N) The current flowing through the resistor R ₁ is Vr/R ₁ = K ₁ R ₀ /R ₁ o _DC (1+N), and the current flowing through the resistor R ₂ has its AC component cut off and Vr R/R+R ₃ +R ₄・1・K ₁ o _DC /R ₂ =K ₁・R・R ₀ /
(R + R ₃ + R ₄ ) R ₂・o _DC . Here, R is a parallel combined resistance of _R2 and _R5 . As a result, the collector current of the transistor 51 is K ₁ [o _DC R ₀ (1/R ₁ +R/R ₂ (R+R ₃ +R ₄ )+1
/R ₁ N] =K ₁ o _DC R ₀ (1/R ₁ +R/R ₂ (R+R ₃ +R ₄ ))
(1+N/(1+R・R ₁ /R ₂ (R+R ₃ +R ₄ ))). Therefore, the output Vout of the logarithmic amplifier 42
is Vout=K ₂ logeF(1+Nλ)/K ₁ R ₀ (1/R ₁ +R/R ₂ (
R+R ₃ +R ₄ )) (1+N/(1+R・R ₁ /R ₂ (R+R ₃ +
R ₄ )) =K ₂ logeF/K ₁ R ₀ (1/R ₁ +R/R ₂ (R+R ₃ +R ₄ ))
+loge1+Nλ/1+N/(1+R・R ₁ /R ₂ (R+R ₃ +R
₄ )).

The first term is a part that includes information about the measuring section, and the second term is a component that includes only noise due to changes in the light amount of the light source.
Here, N/(1+R・R ₁ /R ₂ (R+R ₃ +R ₄ ))=Nλ
By selecting R ₁ , R ₂ , R ₃ , and R ₄ so as to satisfy the following, it is possible to eliminate components in Vout that include noise due to changes in the light amount of the light source.

If the ratio of the AC component due to the change in the light amount of the light source to the DC component in the collector current of the transistor 51 is made larger than the ratio of the DC component in the output current of the light receiving element 34 of the reference light section 3 to the AC component due to the change in the light amount of the light source, , resistor R ₃ , R ₄ , R ₅ capacitor C1
A high-pass filter can be used instead of a low-pass filter. The same applies to the second and third logarithmic amplifiers 43 and 44.

Next, the double wave rectifier will be explained. The double-wave rectifying sections 14, 15, and 16 are sections that convert a pulse wave signal, which is an alternating current signal obtained from light passing through the measuring section, into a direct current signal. Since the frequency of the pulse wave signal is usually low, conventionally a circuit combining a half-wave rectifier circuit and an integrator as shown in FIG. 5 has been used.

When a sine wave signal is input to the circuit shown in Figure 5,
The output current ₁ of the half-wave rectifier circuit 100 has a waveform where the negative side is larger than the positive side, and the peak on the positive side from the reference value
p1 and the negative peak p2 satisfy p1≠p2.
This is due to the current flowing through the resistor _R8 due to the difference in offset voltage between the half-wave integer circuit and the integrator, and the bias current of the half-wave rectifier circuit and the integrator flowing through the resistor _R8 .
The integrator in Figure 5 also has two switches S1 and S2.
is provided, and the switch is turned on when switch S1 is ON.
Integrate the input with S2 OFF, then switch
S1 turns OFF, stopping input integration and putting the integrator in a hold state. After holding for a certain period of time, switch S2 is turned on and integrator capacitor C4 is discharged. This operation is repeated for the integrator. Since the input of the integrator is connected to the capacitor C2 and the resistor _R9 connected in series, the current ₂ causes a transient change, which causes an error. Also, when measuring only the offset voltage of the circuit shown in Figure 5, the switch
A method is used in which only the offset voltage is integrated by turning on S3 and shorting the input, turning on switch S1 and turning off switch S2. However, the Switch S3
The offset voltage obtained by turning ON and switch S3 are
It does not match the offset voltage when it is turned off and an AC signal is input.

In the circuit shown in Fig. 5, a sine wave signal V=a・sinωt
When input, the output voltage V ₁ of the half-wave rectifier circuit is R ₆
= R ₇ , then V ₁ = V _OFF1 −a・sinωt (V≦R ₆ V _OFF1 −V _OFF2 /R ₇
+R ₈ ) V _OFF1 R ₈ +V _OFF2 R ₇ /R ₇ +R ₈ (V>R ₆ V _OFF1 −V _OF
When _F2 /R ₇ + R ₈ ). Here, V _p1 and V _p2 are the input offset voltages of the half-wave rectifier circuit and the integrator, respectively.

Therefore, the current ₁ is ₁ = 1/R ₆ (V _OFF1 −a・sinωt−V _OFF2 ) (V≦R
₆ V _OFF1 −V _OFF2 /R ₇ +R ₈ ) V _OFF1 −V _OFF2 /R ₂ +R ₈ (V＞R ₆ V _OFF1 −V _OFF2 /
(When R ₇ + R ₈ ) Furthermore, if enough time has passed since the switch S1 was turned on, ₂ is ₂ = 1/R ₉ a·sinωt. If R ₉ = 2R ₈ , then the integrator capacitor
The current flowing into C2 is ₁ + ₂ , ₁ + ₂ = 1/R ₈ (V _OFF1 −V _OFF2 −1/2a・sinωt)
(When V≦R ₆ V _OFF1 −V _OFF2 /R ₇ +R ₈ ) V _OFF1 −V _OFF2 /R ₇ +R ₈ +1/2R ₈ a・sinωt(V
>R ₆ V _OFF1 −V _OFF2 /R ₇ +R ₈ ). This is shown in FIG. When ₁ + ₂ is integrated by an integrator, there is no direct relationship between the output of the integrator and the amplitude a of the sine wave signal. Therefore, even if only the offset voltage is measured and stored without inputting the sine wave signal and subtracted from the output when the signal is input, a value proportional to the amplitude of the signal cannot be obtained. This is because a current flows through _R7 due to the difference between the input offset voltages of the half-wave rectifier circuit and the integrator. To prevent this, set V _OFF1 = V _OFF2 .
Even if V _OFF1 ≠ V _OFF2 , the configuration should be such that no current flows through resistor _R7 . Also, since the integrator repeats charging, holding, and discharging, switch S1 is activated at predetermined intervals.
Repeat ON and OFF. At this time, the current flowing through C2 and _R9 changes transiently, causing an error in the output of the integrator.

Therefore, in the double-wave rectifying section of the present invention, a buffer circuit 57 and a buffer circuit 58, which are operational amplifiers, are inserted between the half-wave amplifier 100 and the integrator, as shown in FIG. Even if there is a difference in the input offset voltage due to the buffer circuit 58, the resistance R ₇
This prevents current from flowing. In the circuit shown in Fig. 7, the output voltage V ₁ ' of the half-wave rectifier circuit 100 when an AC signal is input with switches S3-S1 and S3-2 turned OFF is V ₁ '= V _OFF1 -V (V≦0 ) V _OFF1 (when V > 0). However, here it is assumed that R ₆ =R ₇ and the bias currents of the buffer circuit 58 and the half-wave rectifier circuit 100 are sufficiently small and can be ignored. and switch
When switch S1 is turned on after a sufficient period of time has passed since S3-1 was turned on, the input current of the integrator
₁ ′+ ₂ ′ is ₁ ′+ ₂ ′= 1/2R ₈ (2V _OFF1 −3V _OFF2 +2V _OFF3 +V
_OFF4 -V/2R ₈ (When V≦0) 1/2R ₈ (2V _OFF1 -3V _OFF2 +2V _OFF3 +V _OF
F4 +V/2R ₈ (when V>0), and the output of the integrator has a linear relationship with the input signal amplitude of the double-wave rectifier. Therefore, measure and store only the offset voltage without inputting the signal.
By subtracting this value from the integrator output when the signal is input, a value proportional to the input signal can be obtained.

When measuring only the offset voltage, it is necessary to prevent any signal from being input. Since offset voltage drift occurs during SaO ₂ measurements, only the offset voltage of the double-wave rectifier must be measured once every few minutes. If a method is used in which the inputs of the double-wave rectifier are short-circuited using switch S3 as shown in the circuit of Figure 5, a transient response will occur immediately after switch S3 is closed, and the correct offset voltage will have to be maintained until a steady state is reached. Cannot be measured. Since it is necessary to wait until the steady state is reached, it takes a long time until the next SaO ₂ measurement is restarted. In this embodiment, as shown in FIG. 7, the switch S3-1 and the switch S3-
2 is inserted to shorten the time from turning on these switches to reaching a steady state.

When measuring only the offset voltage of the double-wave rectifier, switches S3-1 and S3-2 are turned on and the outputs of buffer circuits 57 and 58 are integrated. The time from when the switch S3-1 is turned on until the input of the buffer circuit 57 reaches a steady state is determined by the on-resistance of the capacitor C2 and the switch S3-1. The ON resistance of switch S3-1 is resistance
Since R is very small compared to ₁₀ , the time it takes to reach a steady state is very short. Also, switch S3-
2 is turned on, current flows from voltage source E1 to diode D1 via resistor R ₁₁ and switch S3-2, and the current flowing through resistor R ₁₁ is set to be sufficiently large, so the output of the half-wave rectifier circuit becomes V _OFF1. Become. Therefore, the offset voltage can be measured immediately after the switches S3-1 and S3-2 are turned on, and the time until the SaO ₂ measurement is restarted can be shortened.

SaO ₂ and pulse rate can be measured accurately even at minute signal levels by using the circuit that removes noise caused by changes in the light intensity of the light source and the dual-wave rectifier that can accurately obtain the offset voltage as described above.

Next, a motion artifact detection method according to the present invention will be described. The motion artifact detection method according to the embodiment of the present invention is characterized in that continuous or periodic motion artifacts can be detected, and there is little influence due to differences in subjects. In the present invention, photoplethysmograms for three types of wavelengths are measured and are obtained as the respective outputs of the first to third operational amplifiers 11, 12, and 13 in FIG. SaO ₂ can be calculated from pulse wave signals at two different wavelengths, and since pulse wave signals at three different wavelengths are obtained in the present invention, SaO 2 can be calculated using up to three different calculation formulas.
SaO ₂ can be calculated. Here are the multiple
The values of SaO ₂ match when there is no motion artifact, but when there is a motion artifact, a difference occurs between these multiple SaO ₂ values. In one embodiment of the present invention, two values of SaO _{2 are calculated from pulse wave signals at three different wavelengths using two different calculation formulas, and when the absolute value of the difference between these SaO 2 values} is greater than or equal to a reference value, It is determined that the motion artifact has occurred.

The reference value varies depending on the SaO ₂ value obtained by calculation. This means that even if the size of the motion artifact is the same, _multiple motion artifacts can be
This is because the difference between the _two SaO values is different. This point will be explained in more detail.

Photoplethysmograms in three different wavelength ranges are obtained in the light receiving section 2 as outputs of the first to third differential amplifying sections 11, 12, and 13, respectively. This pulse wave signal is transmitted to the first to third double-wave rectifiers 14 and 1, respectively.
5 and 16, the signal is double-wave rectified, integrated for a certain period of time, and then held. The voltages held in the first to third double-wave rectifiers 14, 15, and 16 are sequentially A/D converted and stored. The stored first to third double-wave rectifiers 14, 15,
After the offset voltage values of the first to third double-wave rectifiers 14, 15, and 16, which have been measured and stored in advance, are subtracted from the hold values of 16, they are stored as _Y1 , _Y2 , and _Y3, respectively. Ru.
Y ₁ , Y ₂ , and Y ₃ are proportional to the amplitude of the pulse wave signals output from the first to third differential amplifiers 11, 12, and 13, respectively.

And Y ₁ , Y ₂ , and Y ₃ have wavelengths of 805 mm and 710 mm, respectively.
mm, if obtained for light around 650 mm, Y ₁ and
From Y ₂ , SaO ₂ (1) = A ₁ (Y ₂ / Y ₁ ) ² + B ₁ , from Y ₁ and Y ₃ , SaO ₂ (2) = A ₂ (Y ₃ / Y ₁ ) ² + B ₂ is calculated and stored. be done.

SaO ₂ (1) and (Y ₂ /Y ₁ ) ² and SaO ₂ (2) and (Y ₃ /
The relationship between Y ₁ ) ² is shown in Figure 11. If there is no motion artifact, the values of SaO ₂ (1) and SaO ₂ (2) match. When there is a motion artifact, the noise caused by it is almost unrelated to the wavelength, so (Y ₂ /Y ₁ ) ² and (Y ₃ /Y ₁ ) ² have values close to 1, and SaO ₂ (1) and SaO ₂ (2) does not match. For example, true
When SaO ₂ is 95% and there is no motion artifact, (Y ₂ /Y ₁ ) ² = 0.437, (Y ₃ /Y ₁ ) ² =
0.671, but if there is a motion artifact, almost the same noise will be superimposed on Y ₁ , Y _{2 ,} and Y _3, resulting in (Y ₂ /Y ₁ ) ² = 1, (Y ₃ /Y ₁ ) ² = 1, SaO ₂
(1) and SaO ₂ (2) approach 64.5% and 89.7%, respectively, so the difference between SaO ₂ (1) and SaO (2) becomes large. Therefore, |SaO ₂ (1)−SaO(2)| is compared with the reference value, and when it is larger than the reference value, it can be determined that there is a motion artifact. |SaO ₂ (1)−SaO ₂ (2)| differs depending on the true SaO ₂ even if the noise due to motion artifacts is the same, so the reference value is
Should be configured differently depending on SaO ₂ .
true when there is a motion artifact.
Since it is not possible to know SaO _2, SaO ₂ (1) and SaO ₂ (2)
The reference value is set differently depending on the _Y1 ,
If Y ₂ and Y ₃ are pulse waves for light with wavelengths around 805 mm, 710 mm, and 650 mm, respectively, then when there is no motion artifact, the true SaO ₂ is 95%, 80%, and 70%.
%, SaO ₂ (1) is represented by points A ₁ , B ₁ , C ₁ and SaO ₂ (2) is represented by points A ₂ , B ₂ , C ₂ in FIG. 11, respectively. 3 types of SaO ₃
, if there are identical motion artifacts, A ₁ , B ₁ , and C ₁ move to D ₁ , E ₁ , and F _{1 ,} respectively. Then A ₂ , B ₂ , and C ₂ move to D ₂ , E ₂ , and F ₂ . In this case, for each true value of SaO ₂ there is a motion artifact |SaO ₂ (1)
−SaO ₂ (2)| is indicated by Δ ₁ , Δ _{2 , Δ 3} in FIG _.
(2)) This situation is shown in FIG.

To detect motion artifacts above a certain level, |SaO ₂ (1)−SaO ₂ (2)| and the reference value (f
(SaO ₂ (1), SaO ₂ (2))), the reference value f (SaO ₂ (1), SaO ₂ (2)) is almost the same as that shown in Figure 8. Just use it.

As described above, since the motion artifact detection method of the present invention does not detect changes in the waveform or amplitude of the pulse wave signal, there is little difference in detection sensitivity between subjects, and periodic motion artifacts can also be detected. .

If pulse waves are obtained for light of three or more wavelengths and then three or more types of SaO ₂ are calculated, each other's SaO ₂
Two or more differences can be obtained. those two or more
As an example of detecting motion artifacts from the difference in SaO ₂ , set reference values for each absolute value of the difference in SaO ₂ and correspond to those reference values.
A method of comparing the absolute value of the difference in SaO ₂ and determining that a motion artifact exists when at least one absolute value of the difference in SaO ₂ exceeds the corresponding reference value, or a method in which motion artifacts are determined to exist when at least one absolute value of the difference in SaO ₂ exceeds the corresponding reference value. There is a method of determining that a motion artifact exists when all the absolute values of the differences exceed their corresponding reference values.

Next, a method for calculating the SaO ₂ average value will be explained.

In the apparatus of the present invention, SaO ₂ (1) and SaO ₂ (2) are calculated at regular intervals. calculated SaO ₂ (1) or
It is possible to display one of SaO ₂ (2) sequentially each time it is calculated. however
If the measurement accuracy of SaO ₂ (1) or SaO ₂ (2) cannot be guaranteed, for example when the intensity of the light reaching the light receiving part is not appropriate, or when the amplitude of the pulse wave signal is too large or small, the calculated SaO ₂ (1) and SaO ₂ (2) contain many errors, so it is not recommended to display them. When such measurement accuracy cannot be guaranteed in relatively many cases, the conventional method frequently fails to display SaO ₂ and is extremely difficult to use. For example, if SaO ₂ (1) and SaO ₂ (2) are calculated every second, if the measurement accuracy is not guaranteed every few seconds, SaO ₂ will not be displayed every few seconds. , the display becomes very difficult to see.

Conventionally, the following method has been used to solve this problem.

Normally, it is extremely rare for SaO ₂ to change suddenly in one second. Therefore, if a situation occurs where the measurement accuracy of SaO ₂ is not guaranteed at time i, then at time i
If the value calculated and displayed at time i-1 is continuously displayed, the problem _that there is a period when nothing is displayed will be solved.

However, with this method, if the condition in which the measurement accuracy of SaO ₂ is not guaranteed continues for several seconds, the same value will be displayed for the duration of the condition in which the measurement accuracy of SaO ₂ is not guaranteed, and the true value will not be displayed during that time.
If SaO ₂ changes, the difference between the displayed SaO ₂ and the true SaO ₂ will increase, increasing the possibility of making an incorrect diagnosis.

Therefore, with the device of the present invention, even if a situation in which the measurement accuracy of SaO ₂ is not guaranteed occurs sporadically, the display does not disappear frequently, and if the situation in which the accuracy cannot be guaranteed continues, a display is displayed to prevent incorrect diagnosis. is designed to be erased. The method will be explained in detail. In the device of the present invention, SaO ₂ (1) and SaO ₂ (2) are calculated and stored one after another at regular intervals.When SaO (2) (i) is calculated and stored at a certain time i, including time i It is checked whether there are at least a certain number l of SaO ₂ (2) whose accuracy is guaranteed among the certain number k+1 SaO ₂ (2)s calculated and stored previously (k+1≧l). Specifically, SaO ₂ (2) is investigated going back to time i-k, and SaO ₂ (2) whose measurement accuracy is guaranteed is
If there are l or more SaO(2)(i) including SaO(2)(i), l SaO ₂ (2) for which accuracy measurement can be guaranteed is taken from the one closest to time i, the average value of these l is calculated, and the display screen The value will be displayed. If the number of k+1 SaO ₂ (2) from time i to previous time i-k whose accuracy is guaranteed is less than l, then
The SaO ₂ display will disappear and a warning will be issued. At the next time i+1, from time i+1 to previous time i+
Up to k SaO ₂ (2) are checked, and it is checked whether there are l or more SaO ₂ (2) whose accuracy is guaranteed.
, SaO ₂ (2) is taken out and the average value is calculated and displayed.
If the number is less than l, the display will be blank and a warning will be issued. The above-mentioned similar operations are repeated. According to this method, the SaO 2 display will not be blank unless SaO ₂ (2), in which the measurement accuracy is not guaranteed for k-l+2 or more, continues, so even if a situation where the measurement accuracy cannot be guaranteed sporadically occurs, the SaO ₂ display will not be blank _. The display is never blank.

In addition, if the condition where accuracy is not guaranteed continues for k-l+2 or more, the SaO ₂ display will disappear, so an inaccurate SaO ₂ display will not be held for a long time, so there is no possibility of making an incorrect diagnosis. few. As an example, k is chosen to be 7 and l to be 5 if SaO ₂ (2) is calculated every second. in this case,
The display will not be erased unless there are 4 or more SaO ₂ (2)s for which accuracy cannot be guaranteed, and even if SaO ₂ (2)s for which accuracy is not guaranteed are continuously obtained, 4
The SaO ₂ display will not be held for longer than seconds. Also, the accuracy is not guaranteed for only 3 seconds SaO ₂ (2)
When continues, the same value is displayed on SaO ₂ , but 4
Since the SaO ₂ per second does not change suddenly enough to cause a problem, there is no risk of making a wrong diagnosis.

Next, the display function and the like of the device of this embodiment will be explained. In conventional SaO ₂ measuring devices, the measured value is displayed digitally or by the swing of an ammeter. Although a device that can continuously measure SaO ₂ has the great advantage of being able to see the changes in the measured value from moment to moment, the digital display of the measured value or the display based on the swing of the ammeter does not allow for the temporal change in the measured value. difficult to understand. To compensate for this drawback, conventional SaO ₂ measuring devices are equipped with a terminal that outputs the measured values as voltage, etc., or have a built-in pen recorder so that the measured values can be recorded with a pen recorder. However, when measuring continuously over a long period of time, recording measured values on a pen recorder requires a large amount of recording paper, of which only a small amount is important, and most of the recording paper is wasted. Further, even if it is not necessary to record the changes, but it is desired to check the changes between the short axes, the data must be recorded using a pen recorder, which wastes recording paper.

In order to solve the above problems, the device of the present invention uses a _two -dimensional display element 80 in the display section as shown in FIG. It is displayed as a graph.

In FIG. 9, for example, a color CRT (cathode ray tube) is used as the two-dimensional display element 80, and the SaO ₂ display section 81 digitally displays the average value of SaO ₂ calculated by the control calculation section 26, and the pulse rate display section Reference numeral 82 digitally displays the measured pulse rate, a graph section 83 displays _SaO2 , and a graph section 84 displays the pulse rate over time.

59 is an increase key for setting the upper limit value for SaO ₂ alarm, 60 is a decrease key, 61 is an increase key for setting the lower limit value for SaO ₂ , 62 is a decrease key, 63 and 64 are upper limits for pulse rate alarm Increment and decrease keys 65 and 66 are used to set the lower limit of the pulse rate, and these keys are used together with the normal display mode selection key 74 and other keys as shown in FIG. 1, which will be described later. It is included in the input section 24.

70 is SaO ₂ setting upper limit value display element, 71 is
72 is a setting upper limit display element for SaO ₂ , 73 is a pulse rate lower limit display element, and each display element is a two-dimensional display element 80.
1 and included in the display section 25 in FIG.

During normal measurement, the key 74 is pressed and the latest SaO ₂ and pulse rate are displayed numerically on the display sections 81 and 8.
2 and the graph section 8 of the CRT screen.
Dots are displayed at the left end of 3 and 84 at positions corresponding to the respective values. As the measurement time elapses, the dots corresponding to the previously measured SaO ₂ and pulse rate will be replaced with the dots corresponding to the latest SaO ₂ and pulse rate each time a new SaO ₂ and pulse rate are displayed. 10 in the opposite direction, for example, to the right in FIG. In addition, on the screen, upper and lower limit values set for warning of SaO ₂ and pulse rate values at the time of measurement are displayed numerically on display elements 70, 71, 72, 73, and near graphs 83, 84. is displayed as a broken line, etc. The time axis of the graph display can be set by switch 75. A switch 76 can be used to select whether or not to display the upper limit value and lower limit value in a graph for warning. If the measured value of SaO ₂ or pulse rate is outside the set upper and lower limit values, the dot corresponding to the SaO ₂ or pulse rate at that time will be the same as when the measured value is within the upper and lower limit range. Displayed in a format that is distinguishable from dots. Specifically, the color or brightness is changed and displayed. For example, if the measured SaO ₂ or pulse rate is within the upper and lower limits, it will be displayed as a green dot, and if the measured SaO ₂ or pulse rate is above the upper limit, it will be displayed as a red dot. If the SaO ₂ or pulse rate measurement is below the lower limit, it will be displayed as a blue dot. Furthermore, the display at any previous time can be viewed using the switch 77 and lever 78. In addition, by pressing the switch 79, the display can be hard-copied. No numbers are printed on hard copies.
In addition, the digital output section outputs the SaO ₂ value and pulse rate at predetermined intervals.

Next, the operation of the apparatus of the present invention will be explained using the flowchart shown in FIG. In one embodiment of the present invention, calculations of SaO ₂ (1), SaO(2), pulse rate, etc. are performed every second. When the power switch 90 is turned on, "CAL", for example, is displayed on the CRT 80 of the display section 25 to notify that the system is in a warming-up state. In addition, by operating the keys 59 to 66, commonly used values are set as the upper and lower limits of SaO ₂ and pulse rate, and are displayed on the display sections 70, 71, 72, and 73. . For example, if the key 59 is kept pressed, the count value of the counter in the control calculation section 26 increases at regular intervals, the display on the display section 70 increases, and the upper limit value of SaO ₂ increases by one. If you press key 60
The upper limit of SaO ₂ decreases by 1. other keys 60
The operations from 66 to 66 are performed in the same manner. Next, the first to third double-wave rectifiers 14, 16 in FIG.
A group of 5,16 switches are controlled. In this state, the integral switch S1 of the first to third double-wave rectifiers,
S3-1 and S3-2 are turned on and the discharge switch S2 is turned off, and each double-wave rectifier is integrated and held. The held offset voltages of the first to third double-wave rectifiers are sequentially converted to A/D by the A/D converter 20.
The data is converted into D and stored in the memory of the control calculation unit 26. A/D conversion is performed by a double integrator, a comparator, and a counter built into the microcomputer, and input switching is performed by a multiplexer 18. Then, the discharge switches of the first to third double-wave rectifiers are connected to the control calculation unit 2 via the switch control line.
6, each integrating capacitor is discharged. The above-mentioned integral hold of the offset voltage, A/D conversion of the held voltage, storage, and discharge of the integral capacitor of the double-wave rectifier are repeated in sequence as shown in FIG. It is determined whether the circuit is stabilized based on the outputs of the double-wave rectifiers 14, 15, and 16 that have been sequentially A/D converted and stored. in particular,
The A/D converted and stored output offset voltage values of the first to third double wave rectifiers and the previously A/D converted and stored output offsets of the first to third double wave rectifiers. If the differences between each voltage value are all below a predetermined value, it is determined that the circuit is stable. Integration of the first to third double-wave rectifier offset voltages, holding, A/D conversion of the held voltage, storage, and discharge of the integration capacitor are repeated until it is determined that the circuit is stable. The output offset voltage values of the first to third double-wave rectifiers stored immediately before it is determined that the circuit is stable are used as the first to third offset values, and thereafter, the offset value is calculated from the A/D conversion value of the signal. It is used to subtract. When the circuit is determined to be stable, the "CAL" display disappears and the following steps are executed.

First, it is determined whether only the offset voltages of the first to third double-wave rectifiers are to be measured. This is so that when the offset voltages of the first to third double-wave rectifiers drift during measurement, the offset voltages are newly measured and stored. The offset voltage measurement here is performed once every few minutes. When remeasuring the offset voltage, the first to third double-wave rectifiers 14, 15, and 16 are set to the offset input state, and the first to third double-wave rectifiers 14, 1
Only the offset voltages 5 and 16 are integrated and held, and these voltages are sequentially transferred to the A/D converter 20.
The signal is A/D converted and stored in the memory of the control calculation section 26. Then jump to ′. If you do not want to remeasure the offset voltage, directly execute the steps below.

The following operations are repeated at regular intervals.

In ', first, in order to check whether the intensity of the light passing through the measurement section does not affect the measurement accuracy, the output of the light intensity measurement circuit 17 is selected by the multiplexer 18, A/D converted, and stored in the memory.

The output of the light amount measuring circuit is related to the intensity of light incident on the third light receiving element 38 of the light receiving section 2. A/
It is determined whether the output value of the D-converted light amount measurement circuit 17 is greater than or equal to a preset first setting value and less than or equal to a preset second light amount measurement value. If the output value of the light amount measurement circuit 17 is outside the range between the two light amount setting values, the following operation is performed; otherwise, the output value of the light amount measurement circuit 1
The time elapsed since the output value of No. 7 changed from a value equal to or higher than the second light amount measurement value to a value between the two light amount measurement values is checked. If the elapsed time is less than a predetermined time, the pulse wave signal is not yet stable, and the pulse wave signal jumps in this case as well. The following operations will be described later. Since the pulse wave signal is stable for a predetermined time or more, the outputs of the first to third double wave rectifiers 2 are sequentially A/D converted and stored.
The stored first to third double-wave rectifiers 14, 15,
From the 16 output values, the corresponding offset voltages calculated and previously stored are subtracted and stored as pulse wave amplitude values in each of the first to third wavelength ranges. The pulse wave amplitude values in each of the first to third wavelength ranges will be expressed as Y ₁ , Y ₂ , and Y ₃ , respectively. Next, it is determined whether the values of Y ₁ , Y ₂ , and Y ₃ are all greater than or equal to a preset third set value and less than or equal to a preset fourth measurement value.
When Y ₁ , Y ₂ , and Y ₃ are all greater than or equal to the third set value and less than or equal to the fourth set value, the pulse wave amplitude is within a range that can guarantee measurement accuracy. At this time, the following operations are performed.

The first and second pulse wave amplitude values Y ₁ i at time i and
SaO ₂ (1)i from Y ₂ i to time i is SaO ₂ (1)i = A ₁ (Y ₂ i / Y ₁ i) ² + B ₁ , and the first and third pulse wave amplitude values at time i Y ₁ i and
It is calculated and stored as SaO ₂ (2)i=A ₂ (Y ₃ i/Y ₁ i) ² +B ₂ from Y ₃ i to time i. Also, when at least one of Y ₁ i, Y ₂ i, and Y ₃ i is below the third setting value or above the fourth setting value, the measurement circuit may be saturated and the S/N ratio may be Since the measurement accuracy of pulse wave amplitude cannot be guaranteed due to problems etc., the above SaO ₂ (1)i and SaO ₂ (2)
No calculation or storage of i is performed, and SaO ₂ (2)i is stored as invalid and jumps. Y ₁ i,
The values of Y ₂ i and Y ₃ i are all correct and SaO ₂ (1)i, SaO ₂ (2)
Once i has been calculated and stored, a determination is then made as to the presence or absence of a motion artifact. i.e.
Absolute value reference value f of the difference between SaO ₂ (1)i and SaO ₂ i (SaO ₂ (1)
i, SaO ₂ (2)i).

As an example, f(SaO ₂ (1)i, SaO ₂ (2)i) = 6 (%); SaO ₂ (2)i
The case where ≧90% or =18.8(%)−SaO ₂ (2)i/7(%); SaO ₂ (2)i<90% will be explained. When SaO ₂ (2)i is 90% or more, it is determined that there is a motion artifact if |SaO ₂ (1)i−SaO ₂ (2)i| is 6% or more. Also, when SaO ₂ (2)i<90%, |SaO ₂ (1)i−SaO ₂ (2)
If i|>18.8−SaO ₂ (2)i/7, it is determined that there is a motion artifact.

If there is a motion artifact, SaO ₂ (2) at this time i is remembered as invalid because the measurement accuracy is not guaranteed, and jumps.
Also, if there is no motion artifact, the following operation will be performed as is.

Then the average value of SaO ₂ (2) is calculated. SaO ₂ (2)
Eight pieces of data from i to SaO ₂ (2)i-7 are sequentially checked to see if they are valid or invalid, and if valid, they are added to SS. k is incremented by 1 each time it is added. 5 or more non-invalid SaO ₂ (2),
That is, if k becomes 5, SS/5 is calculated as the average value of SaO ₂ (2) and stored in the SaO ₂ display memory.
If there are no 5 or more non-invalid SaO ₂ (2), time i
SaO ₂ (2)i to i+7th value SaO ₂ (2)i
After examining all −7, the value of k becomes less than 5, and in this case it jumps to '. k becomes 5
Once the average value of SaO ₂ is calculated and stored, the pulse rate is then calculated.

The pulse rate is calculated from the time interval between the rise or fall of the output pulse of the pulse wave shaping section 21. The rise and fall of the output pulse of the pulse wave shaping section 21 are as follows:
It is constantly checked by the control calculation unit 26, and the rise time and fall time are sequentially stored. When the pulse rate is calculated, the time of the rise or fall 8 pulses before the most recent rise or fall is examined. Then, the pulse rate per minute is calculated from the difference between the latest rise or fall time and the rise or fall time 8 pulses ago. Once the pulse rate is calculated, it is stored in the pulse rate display memory. Next, the calculated average value of SaO ₂ (2),
It is compared with the SaO ₂ upper limit value and the SaO ₂ lower limit value set for warning and displayed on the display units 70 and 71, respectively.

If the average value of SaO ₂ (2) is greater than or equal to its upper limit or less than its lower limit, 1 is stored in the SaO ₂ high alarm memory or SaO ₂ low alarm memory;
Jump to V. When the average value of SaO ₂ (2) is between its upper and lower limits, zero is stored in the SaO ₂ high alarm memory and the SaO ₂ roller alarm memory and jumps to V. At V, it is determined whether the pulse rate is greater than or equal to the pulse rate upper limit or less than the pulse rate lower limit set for the warning. The pulse rate is
When the pulse rate is above the set upper limit, 1 is stored in the pulse rate high alarm memory, and when the pulse rate is below the lower limit value, 1 is stored in the pulse rate roller alarm memory and jumps. When the pulse rate is within the upper and lower limits, zero is stored in the pulse rate high alarm memory and pulse rate low alarm memory and the pulse rate jumps to zero.

In the following, SaO ₂ , pulse rate, etc. are displayed and screen copied on the two-dimensional display element depending on the states of the switches 74 to 79. First, it is checked whether the display mode is normal mode or preview mode. If the switch 74 is ON, the mode is normal, and if the switch 77 is ON, the mode is preview mode. In the normal mode, the latest SaO ₂ and pulse rate among the contents stored in the SaO ₂ display memory and the pulse rate display memory are displayed in numbers on the display sections 81 and 82. and on the left side of the screen
SaO ₂ , dots are displayed at positions according to the pulse rate,
The older the contents of the SaO ₂ display memory and pulse rate display memory, the older the values, the more dots are displayed on the right side of the screen. The time scale for graph display is set by switch 75. Also, switch 76
When ON, the SaO 2 high alarm memory display memory, SaO ₂ low alarm memory display memory, which stores the contents of the upper and lower limits when each _{SaO 2} and pulse rate were measured,
The contents of the pulse rate high alarm display memory and pulse rate low alarm display memory are displayed on the two-dimensional display element 80.
is displayed with a dashed line. When the switch 76 is pressed, the contents of each alarm memory corresponding to the SaO ₂ and pulse rate displayed in the graph are checked, and the contents of the SaO ₂ high alarm memory are set to 1.
, the corresponding SaO ₂ is displayed as a red dot, when the content of the SaO ₂ low alarm memory is 1, the corresponding SaO ₂ is displayed in blue, and when the content of both alarm memories is 0, the corresponding SaO 2 is displayed as a red dot. The corresponding SaO ₂ will be displayed in green.
The same applies to pulse rate. switch 76
When OFF, the contents of each high alarm display memory mentioned above are not displayed graphically, and the color of the pulse rate dots does not change until SaO ₂ depending on the contents of each alarm memory, and all dots are green. is displayed. Also, if the latest SaO ₂ or pulse rate is not within the respective upper and lower limits, the alarm LED will flash and switch 68 will be activated.
If is ON, an alarm will sound. Also the latest
NOP for display during operation when SaO ₂ cannot be calculated
The LED lights up, the SaO ₂ and pulse rate numeric displays and their corresponding dots are blanked, and if switch 68 is ON, an alarm sounds. And then jump.

The display when the mode is the preview mode, that is, when the switch 77 is turned on, will be explained. In this mode, the left edge of the screen displays the latest SaO ₂
and pulse rate, but not previously obtained.
A dot is displayed at the height representing SaO ₂ and pulse rate, and a number is also displayed. switch 7
5 and switch 76 are the same as in normal mode. The lever 78 is used to set which point in time SaO ₂ and pulse rate are displayed on the left edge of the screen. While the lever 78 is moved to the left, the earlier values are displayed on the left edge of the screen, and the graph is Move to the left. While the lever 78 is moved to the right, newer values are displayed on the right edge of the screen and the graph moves to the right. When the lever 78 is centered, the graph stops moving. The functions of switch 75 and switch 76 are the same as in normal mode. In preview mode, with lever 78 set to the center, press switch 79.
When turned on, the displayed screen is copied onto an appropriate sheet of paper by a printing device (not shown). And then jump. The preview mode is processed by interrupting the integration of the first to third double-wave rectifiers in , or while the time is being adjusted in , so in this mode, new SaO ₂ and pulse rate are calculated and stored.

The A/D conversion value of the output of the light amount measurement circuit 17 is the first
When the light intensity setting value or the second light intensity setting value is lower than or the A/D conversion value of the output of the light intensity measuring circuit is equal to or larger than the second light intensity setting value, the first light intensity setting value and the second light intensity setting value are changed. If a predetermined time has not elapsed since the value is between the set values, and four or more SaO ₂ (2) are invalid in succession, the value jumps to ''.
The following operations are performed below.

First, in order to keep the cycle of calculation of SaO ₂ and pulse rate constant, a standby period approximately equal to the integration time of the first to third double-wave rectifying sections is performed, and then the following operations are performed. ', the operating status is stored in the SaO ₂ display memory and pulse rate display memory. And then jump.

[Effects] As detailed above, the arterial oxygen saturation measuring device of the present invention "displays a plurality of arterial oxygen saturations along the time axis", so it is possible to monitor changes in the condition of the subject over time. It is possible to understand easily. Furthermore, the present invention includes a "setting means for setting a limit value of arterial blood oxygen saturation," and a display means "distinguishably displays arterial blood oxygen saturations that exceed the limit value and those that do not exceed the limit value."
Therefore, even when the measurement person (doctor or nurse) is extremely busy in an operating room or the like, it becomes possible to confirm changes in the condition of the subject at a glance.

Furthermore, as claimed in claim 2, by providing a "changing means for changing the time axis scale of the display means", changes in the condition of the subject can be known at any time axis scale. Become. In other words, when you need to know changes in the condition of the subject over a long period of time, you can increase the display unit of the time axis and check the large flow, and when you need to know the most recent changes in the condition in detail, you can check the large flow. All you have to do is make the axis display unit smaller.

Furthermore, as claimed in claim 3, "storage means for storing a plurality of arterial blood oxygen saturation levels";
"Control means for displaying arterial blood oxygen saturation in an arbitrary time range on the display means based on the stored value in the storage means", thereby grasping changes in the condition of the subject over a predetermined time range in the past. It will also be possible to do so.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the invention, FIG. 2 is a sectional view showing details of the light source used in the embodiment of FIG. 1, and FIGS. 3 and 4 are examples of the embodiment of FIG. 1. 5 is a circuit diagram showing an example of a conventional double-wave rectifier circuit, FIG. 6 is a waveform diagram showing defects occurring in the circuit of FIG. 5, and FIG.
The figure is a circuit diagram showing an example of a double-wave rectifier circuit used in an embodiment of the present invention, FIG. 8 is a graph showing the relationship between the difference between two SaO ₂ measurement values and the true SaO ₂ , and FIG.
The figure is a flowchart showing the operation, FIG. 10 is a front view showing the display section of the device of this invention, and FIG. 11 is a diagram showing (Y ₂ /Y ₁ ) ² , (Y ₃ /
It is a graph showing the relationship between Y ₁ ) ² and SaO ₂ . 1... Light source, 2... Light receiving section, 14, 15, 16
...Double wave rectifier section, 26... Control calculation section, 25...
Display section.

Claims (1)

[Scope of Claims] 1. A light-emitting device that emits measurement light toward a living body containing pulsating blood; and a light-receiving device that receives the light that has passed through the living body after being emitted by the light-emitting device and outputs a pulse wave signal. a calculation means for calculating arterial oxygen saturation based on the pulse wave signal; a control means for repeatedly operating the light receiving means and the calculation means to obtain a plurality of arterial oxygen saturations; and arterial oxygen saturation. a setting means for setting a limit value of the arterial blood oxygen saturation, and a setting means for displaying a plurality of arterial oxygen saturations obtained by the operation of the control means in a graph along a time axis, and a limit value set by the setting means among the arterial blood oxygen saturations; 1. An arterial blood oxygen saturation measuring device comprising: a display means for distinguishing and displaying those exceeding and not exceeding the above while maintaining the form of a graph display. 2. Claim 1, wherein the display means graphically displays arterial blood oxygen saturation using different colors depending on whether the arterial blood oxygen saturation exceeds the limit value set by the setting means or not. The arterial oxygen saturation measurement device described.