JP2003153882A - Blood component measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a blood component measuring instrument for measuring a blood component with excellent precision. SOLUTION: A pulse oximeter (blood component measuring instrument) measures a transmission light amount obtained by transmission through a living body by periodically irradiating the living body with a red light and an infrared ray and measures a pulse wave component in the transmission light amount time sequentially in this order. The oximeter also measures an oxygen saturation degree in arterial blood based on a differential value between the two pulse wave components measured at time interval Δtm. The time interval Δtm is set to allow its time differential value to correspond to nearly the half HM of amplitude concerning a pulse wave form (at a slow inclination side). Thus, the time differential value has a proper largeness by setting a differential time corresponding to a pulse rate so that the blood component is measured by excellent S/N ratio with high precision.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a blood component measuring device such as a pulse oximeter.

[0002]

2. Description of the Related Art For example, in a blood component measuring device such as a pulse oximeter, a light emitting element is caused to emit light, and light transmitted through a living body is measured by an electric circuit including a photodetecting element to determine the blood oxygen saturation level. Can be measured.

In this blood component measuring device, the pulse wave component of the light transmitted through the living body is measured, and the blood oxygen saturation is measured by using the time difference value of the pulse wave component with respect to the constant time interval Δt.

[0004]

However, in the above-described blood component measuring device, the pulse rate differs depending on the individual difference and the physical condition. Therefore, if the time interval Δt is constant when obtaining the time difference value, A person with a low pulse rate has a small time difference value. As a result, the S / N ratio with respect to the time difference value decreases, and the measurement accuracy of the blood component deteriorates.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a blood component measuring device capable of measuring blood components with high accuracy.

[0006]

In order to solve the above-mentioned problems, the invention of claim 1 is an apparatus for measuring blood components of arterial blood in a living body, which comprises (a) a light emitting means periodically at a first timing. A predetermined amount of light to the living body, and a light amount detecting means for detecting a light amount measurement value of the light transmitted through the living body by the light detecting means; and (b) without causing the light emitting means to emit light, a cycle at the second timing. A dark detection means for detecting a dark measurement value by the light detection means, (c) a pulse rate detection means for detecting a pulse rate relating to the arterial blood, and (d) a time interval corresponding to the pulse rate. And a blood component measuring unit for measuring a blood component of the arterial blood based on the light amount measurement value, the dark measurement value, and the time difference value. Equipped with.

According to a second aspect of the invention, in the blood component measuring apparatus according to the first aspect of the invention, the calculating means is (d
-1) A pulse wave component is extracted from the light quantity measurement value, and a pulse wave detection means for detecting the pulse wave measurement value, and (d-2) a change corresponding to approximately half the amplitude of the pulse wave component is the pulse wave. And a means for calculating a time difference value regarding two pulse wave measurement values detected at time intervals occurring in the wave component.

According to a third aspect of the present invention, a device for measuring the blood component of arterial blood in a living body by inputting the output voltage output from the first measuring section and the second measuring section, which are analog circuits, into a digital circuit. And the first measuring unit is (a
-1) Photodetection means for irradiating the living body with a predetermined intensity at a predetermined intensity, and outputting a detection voltage for the light transmitted through the living body; and (a-2) amplifying the detection voltage with a first amplification factor. First amplification means for outputting a light quantity measurement voltage as the output voltage;
The second measurement unit includes (b-1) a reference voltage generating unit that generates a reference voltage set based on a non-pulse wave component of the light amount measurement voltage; and (b-2) the light amount measurement voltage. The reference voltage is subtracted, the pulse wave measurement voltage amplified by the second amplification factor,
A second amplifying means for outputting the output voltage.

According to a fourth aspect of the invention, in the blood component measuring apparatus according to the third aspect of the invention, the predetermined intensity, the first amplification factor, the second amplification factor, and the reference voltage are set as follows: It is updated at predetermined time intervals.

According to a fifth aspect of the present invention, the device for measuring the blood component of arterial blood in a living body by inputting the output voltage output from the first measuring section and the second measuring section which are analog circuits into a digital circuit. And the first measuring unit is (a
-1) irradiating the living body with a predetermined light periodically, and a light detecting means for outputting a detection voltage relating to the light transmitted through the living body,
(a-2) An amplifying unit that outputs a light quantity measurement voltage obtained by amplifying the detection voltage as the output voltage, and the second measurement unit is (b-1) the light quantity measurement measured at a previous timing. A voltage holding means for holding a voltage, (b-2) a light quantity measurement voltage held by the voltage holding means, and a differential voltage obtained by amplifying a difference between the light quantity measurement voltage measured at this timing and the output voltage. And a second amplifying means for outputting as.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION <First Embodiment><Pulse Oximeter Measurement Principle> In a pulse oximeter 1A (FIG. 1) according to a first embodiment of the present invention, blood components in arterial blood of a living body, specifically Can measure blood oxygen saturation. First, the principle of measuring the oxygen saturation of the pulse oximeter 1A will be described below.

FIG. 2 is a diagram for explaining the absorbance of a living body. In FIG. 2, the horizontal axis represents time and the vertical axis represents absorbance.

When the living body is irradiated with light, part of the light is absorbed. This light absorption is classified into a light absorption component KL by a tissue, a light absorption component SL by a vein, and a light absorption component DL by an artery. In the light absorption component DL by an artery, the absorbance varies with the pulse rate.

FIG. 3 is a diagram showing absorption spectra of oxyhemoglobin and reduced hemoglobin. In FIG. 3, the horizontal axis represents the wavelength of light and the vertical axis represents the absorbance.

Absorption spectrum OX of oxygenated hemoglobin
And the absorption spectrum HI of reduced hemoglobin have different waveforms. At the wavelength of red light (R), the absorbance of reduced hemoglobin is high, whereas at the wavelength of infrared light (IR), the absorbance of oxyhemoglobin is high.

Due to the difference between the absorption spectra OX and HI, when the oxygen saturation in blood becomes high, the absorbance of infrared light (IR) becomes large, and when the oxygen saturation becomes low, the red light (R) becomes red.
The absorbance of becomes large. By utilizing this, in the pulse oximeter 1A, the red light (R) that passes through the living body is transmitted.
The oxygen saturation in the blood can be obtained from the ratio of the pulse wave component Ma (see FIG. 6) between the transmitted light of the above and the transmitted light of the infrared light (IR).

Here, in obtaining the ratio of the pulse wave amplitude of the transmitted light of the red light and the infrared light, it is considered that the transmitted light amount is also proportional to the emitted light amount of the light source. Therefore, the amplitude of the pulse wave component is divided by the amount of transmitted light to eliminate the influence of the amount of light emitted from the light source.

Further, when obtaining the ratio of the amplitudes of the pulse wave components of the transmitted light relating to the red light and the infrared light, the difference TP between the peaks and valleys of the pulse wave as shown in FIG. 4 (a) is not used, As shown in FIG. 4B, the pulse wave is divided into minute time intervals, and the difference value in the time interval (hereinafter referred to as “time difference value”) DP is used to increase the number of samples.

The ratio between the time difference value of the pulse wave component and the amount of transmitted light is obtained for red light and infrared light, and the p value is calculated from the ratio as shown in the following equation (1).

[0020]

[Equation 1]

In the above equation (1), R is the amount of transmitted red light, I
R indicates the amount of transmitted infrared light, and Δt indicates the difference time.
In this way, the p value is calculated by the ratio of the time difference value of the pulse wave component divided by the amount of transmitted light for R and IR.

Then, a table showing the relationship between the p-value and the blood oxygen saturation is prepared in advance, and by referring to this table, the p-value calculated based on the transmitted light amounts of red light and infrared light is calculated. Oxygen saturation will be derived.

<Structure and Operation of Pulse Oximeter 1A> FIG. 1 is a diagram showing a main structure of the pulse oximeter 1A. Further, FIG. 5 is a diagram showing the configuration of the measurement circuit of the pulse oximeter 1A. An algorithm for measuring the oxygen saturation in the pulse oximeter 1A will be described with reference to FIGS. 1 and 5.

The pulse oximeter 1A functions as a blood component measuring device and measures oxygen saturation, which is one of blood components. This pulse oximeter 1A includes a main body 2
And a probe 3 electrically connected to the main body 2 via a lead wire 10.

The main body 2 has, on its front surface, a display unit 11 for displaying measurement results of blood components, a menu button 12 for displaying a menu screen on the display unit 11, and various settings on the menu screen. Two selection switches 13 for performing, and a connector unit 1 connected to the end of the lead wire 10.
And 4 are provided.

The probe 3 uses red light (R) and infrared light.
It has light emitting elements 31a and 31b emitting (IR) and a photodetector element 32.

In order to obtain the oxygen saturation with the pulse oximeter 1A, it is necessary to measure the amount of transmitted light between red light and infrared light and the time difference value of its pulse wave component, as shown in the equation (1). is there. Then, the red and infrared light emitting elements 31a and 31b provided in the probe 3 are alternately pulsed to emit light, and the light passing through the finger FG inserted into the probe 3 is measured by the photodetector 32. The probe 3 may be of a transmissive type or a reflective type for measuring the amount of light, but in both cases, since the light transmitted through the arterial blood in the living body is measured, these are referred to as transmitted light without distinction. To

The output of the photo-detecting element 32 is output by the current-voltage converting circuit 21 and the variable amplifying circuit 22 as an output voltage V.
2 is generated. For this output voltage V2,
As in (2) and (3), the output voltage in a non-light-emission state in which the light-emitting element 31 does not emit light (hereinafter, "dark level").
By measuring the difference between V2 and the output voltage (transmitted light amount measured value) V2 in the light emitting state, it is possible to perform dark correction by eliminating the dark level from the transmitted light amount measured values of red light and infrared light. .

[0029]

[Equation 2]

FIG. 6A shows an example of the measurement result of the transmitted light amount V2 for red light and infrared light.

As shown in FIG. 6A, generally, the pulse wave component M with respect to the total amount of transmitted light measured in the transmitted light of the living body.
The amplitude of a is very small. Therefore, in order to obtain the time difference value of the pulse wave component Ma by the difference calculation from the measured value of the transmitted light amount, the A / D conversion circuit 27 for measuring the transmitted light amount needs to have a very high resolution.

Therefore, in addition to the measurement of the transmitted light amount, the measured value of the pulse wave component is measured from the measured value of the transmitted light amount in a predetermined electric circuit.
(Pulse wave measurement value) is extracted and amplified, and then A / D conversion is performed. As a result, compared to the case where the transmitted light amount is input to the A / D conversion circuit 27 and the time difference value is calculated from this, the quantization error can be suppressed and the oxygen saturation can be calculated accurately. Specifically, when measuring the pulse wave component, the subtraction circuit 25 subtracts the reference voltage corresponding to the non-pulse wave component Mb and generated by the reference voltage generator 24 from the transmitted light amount V2. Then, the output from the subtraction circuit 25 is fed to the variable amplification circuit 2
After amplification in 6, the A / D conversion circuit performs A / D conversion processing. FIG. 6B shows an example of the measurement result of the pulse wave component waveform V3 which is the output of the variable amplifier circuit 26. By performing the above processing, the pulse wave component Ma shown in FIG.
It is amplified and expanded.

FIG. 7 is a diagram for explaining the measurement timing of the pulse oximeter 1A. In FIG. 7, the measurement of red light is R, the measurement of infrared light is IR, the amount of transmitted light is DC,
The pulse wave component is represented as AC. For dark measurement, which is the measurement of the non-light emitting state of the light emitting element 31, red light,
The operation is substantially the same with infrared light, but for identification,
Notated as R.Dark and IR.Dark.

As shown in FIG. 7, the pulse oximeter 1
In A, the amount of transmitted light (DC) for red light and infrared light
And the pulse wave component (AC) are alternately measured in time division. That is, for each of the transmitted light amount measurement and the pulse wave component measurement, the measurement of R → R.Dark → IR → IR.Dark is sequentially performed.

Here, in addition to the optical signal emitted from the light emitting element 31 and transmitted through the living body, induction noise of commercial frequency and light from the fluorescent lamp are mixed in the measurement signal, but the influence of these noises is removed. Therefore, the time interval between the measurement cycle TO, that is, the first timing for measuring R or IR and the second timing for measuring these dark levels is the cycle of the commercial frequency (50Hz or 60Hz) (1 / 50sec or 1 / 60sec). ). As a result, the levels of the periodic noise when measuring R and IR become equal to the levels of the periodic noise when measuring R.Dark and IR.Dark, and the levels of R and IR in the above equations (2) and (3) are During dark correction in which the dark signal is subtracted from the actual measurement signal, the periodic noise of the commercial frequency and the frequency of an integral multiple thereof is canceled, so that the oxygen saturation can be accurately measured. The same applies to the dark correction of the pulse wave component described later.

Further, in the dark correction, a constant offset component such as an offset voltage of the amplifier circuit can be removed.

Returning to FIG. 5, each circuit of the pulse oximeter 1A will be described in detail.

The light emitting element 31 is a red light emitting element 31a.
And an infrared light emitting element 31b. Then, in the light emitting element 31, in order to measure the transmitted light amount of the living body in a time division manner, the pulsed light emission PL (see FIG. 6A) is alternately emitted from the red light and the infrared light.

The light emitted from the light emitting element 31 and transmitted through the living body is detected by the light detecting element 32 and converted into a voltage V1 proportional to the photocurrent by the current / voltage conversion circuit 21. The detection voltage V1 of the current / voltage conversion circuit 21 is amplified by the variable amplification circuit 22 to a voltage level of an appropriate magnitude.

Next, the transmitted light quantity measurement and the pulse wave light quantity measurement will be described below.

In the transmitted light amount measurement, the output voltage of the reference voltage generator 24 is set to a predetermined voltage, and the amplification factor of the variable amplification circuit 26 is set to a predetermined amplification factor. The voltage V2 is measured. It should be noted that these set values are not changed in this transmitted light amount measurement.

Then, the control circuit 28 adjusts the amplification factor G1 of the variable amplification circuit 26 based on the transmitted light amount signal output from the A / D conversion circuit 27 so as to be within the output voltage range. Further, the control circuit 28 adjusts the intensity of each of the light emitting elements 31a and 31b, that is, the emitted light amount, so that the measured values of the transmitted light amount of red light and the transmitted light amount of infrared light are close to each other (substantially equal values). To do.

On the other hand, in the pulse wave component measurement, R, IR, Dark
A DC voltage Vo corresponding to the non-pulse wave component Mb (FIG. 6 (a)) is generated by the reference voltage generator 24, and the subtraction circuit 25 converts the output voltage V2 of the transmitted light amount into this non-pulse wave component. The corresponding voltage Vo is subtracted. The reference voltage generator 24 may be a D / A converter, for example. Then, the pulse wave component waveform as shown in FIG. 6B is output from the variable amplifier circuit 26, and this pulse wave component voltage is A / D.
It is converted into a digital signal by the conversion circuit 27.

In the variable amplifier circuit 26, the pulse wave amplitude waveform obtained by measuring the transmitted light amount (the magnitude of the pulse wave component Ma in FIG. 6A)
Based on the above, the amplification factor G2 is adjusted so that the amplitude of the amplified pulse wave voltage V3 falls within the measurement range of the A / D conversion circuit 27.

Reference voltage generator 24 for pulse wave component measurement
The voltage setting value of is the pulse wave component information obtained by the transmitted light amount measurement.
Based on (magnitude of Ma), non-pulse wave component information (magnitude of non-pulse wave component Mb shown in FIG. 6A), and amplification factor G2 set by the variable amplification circuit 26, subtraction of the reference voltage and The reference voltage value is set so that the amplified pulse wave voltage V3 is within the measurement voltage range of the A / D conversion circuit 27.

The set value of the voltage of the reference voltage generator 24 and the set value of the amplification factor G2 of the variable amplification circuit 26 are determined according to the measurement result of the transmitted light amount, but when these set values are updated, Is determined using the transmitted light amount measurement data of the living body obtained by the transmitted light amount measurement for a predetermined time (for example, the past 3 seconds) immediately before the update time. The predetermined time is preferably a measurement time including at least one cycle of the pulse wave data, that is, a time sufficient to acquire the amplitude information of the pulse wave component.

The reference voltage of the reference voltage generator 24, the amplification factor G1 of the variable amplification circuit 22, the amplification factor G2 of the variable amplification circuit 26, and the intensity of the light emitting element 31, that is, the drive current value, are constant time intervals ( For example, it is updated at 1 second intervals.

Also in the pulse wave component measurement, dark correction for excluding the dark level is performed as in the transmitted light amount measurement. That is, the calculation as shown on the right side of the following equations (4) and (5) is performed.

[0049]

[Equation 3]

The analog switch 23 uses the reference voltage generated by the reference voltage generator 24 to generate an A / D conversion circuit 27.
This is a switch for calibrating. The A / D conversion circuit 27 is adjusted so that the output from the variable amplification circuit 22 is cut off before measurement and the measurement value of the A / D conversion circuit 27 is adapted to the reference voltage value.

The measurement data measured by the above-described measurement circuit is sent to the control circuit 28, and the p value shown in the following equation (6) is calculated.

[0052]

[Equation 4]

The control circuit 28 is provided with a CPU 28a and a memory 28b composed of, for example, a ROM, and functions as a digital circuit for integrally controlling each of the above circuits. Further, the control circuit 28 has a built-in timer counter for measuring the measurement timing and the light emission timing of the light emitting element.

The control circuit 28 can also perform digital filtering such as low-pass filtering or high-pass filtering on the measurement data.

When calculating the time difference value of the pulse wave component, if the reference voltage set value of the reference voltage generator 24 is different between the measurement time t + Δt and the measurement time t, the above-mentioned p The value (in other words, blood oxygen saturation) is not calculated. This is because there is an error between the voltage set value of the reference voltage generator 24 and the actual output voltage even if the output voltage difference of the reference voltage generator 24 is obtained from the difference between the reference voltage set values. This is because sufficient accuracy may not be obtained in some cases.

In the transmitted light amount measurement and the dark level measurement thereof, the amplification factor G1 of the variable amplification circuit 22 and the amplification factor G2 of the variable amplification circuit 26 are set to be equal, and the pulse wave component measurement and the dark level measurement thereof are performed. Amplification factor G1 of variable amplification circuit 22 and amplification factor G of variable amplification circuit 26
Control is performed to make 2 equal. This is because accurate dark correction cannot be performed unless the amplification factors are equal.

In the transmitted light quantity measurement and the pulse wave component measurement, red light (R) and infrared light (IR) are alternately measured, so that the measurement data of R and IR are different at the measurement time points. Therefore, by interpolating the measurement data before and after each measurement time point, the measured values of R and IR that are assumed to be at the same time point are obtained.

Then, in the control circuit 28, the memory 28b
The blood oxygen saturation level is obtained from the p value calculated by the equation (6) based on the table showing the relationship between the p value and the oxygen saturation level stored in the table. The measured oxygen saturation is displayed on the display unit 1.
It is displayed in 1.

By the above operation of the pulse oximeter 1A, the measurement timing is set to a cycle obtained by multiplying the cycle of the commercial frequency by an integer and the periodic noise relating to the commercial frequency is removed, so that the oxygen saturation can be accurately measured.

<Second Embodiment> The pulse oximeter 1B of the second embodiment of the present invention has a configuration similar to that of the pulse oximeter 1A of the first embodiment, but has two A / D conversion circuits. What they are doing is different.

FIG. 8 is a diagram showing the configuration of the measuring circuit of the pulse oximeter 1B.

Compared to the pulse oximeter 1 (FIG. 5) of the first embodiment, an A / D conversion circuit 272 is provided in addition to the A / D conversion circuit 271.

With the configuration of this pulse oximeter 1B, R, R. Dark and IR are measured at the measurement timing shown in FIG.
And IR.Dark can be measured. 9 (a) and 9
In (b), the horizontal axis indicates time. In addition, FIG.
The measurement timing of the transmitted light amount is shown in FIG.
The measurement timing of the pulse wave component is shown.

In the pulse oximeter 1A of the first embodiment, the measurement of the amount of transmitted light (DC) and the measurement of the pulse wave component (AC) were alternately performed, but in the pulse oximeter 1B,
The transmitted light amount (DC) and the pulse wave component (AC) are simultaneously measured by the two A / D conversion circuits 271 and 272. Also in this case, the measurement intervals of R, R. Dark, IR and IR. Dark are set to the cycle of the commercial frequency. This allows
With the pulse oximeter 1 of the first embodiment, twice as much measurement data can be obtained per unit time.

By the above operation of the pulse oximeter 1B, the periodic noise relating to the commercial frequency can be removed as in the first embodiment, so that the oxygen saturation can be accurately measured. Further, since the amount of transmitted light and the pulse wave component are simultaneously measured, the number of measurement data points can be doubled, and the measurement accuracy of oxygen saturation can be further improved.

<Third Embodiment> The configuration of a pulse oximeter 1C of the third embodiment of the present invention is similar to that of the pulse oximeter 1A of the first embodiment, but the configuration of the control circuit 28 is different. .

In general, in order to obtain the blood oxygen saturation, the more the number of measurement data points is, the more accurate the measurement can be. However, in the pulse oximeter 1C, the measurement data points are compared with the pulse oximeter 1A of the first embodiment. It is configured so that it can be tripled.

Control circuit 28 of pulse oximeter 1C
Stores a program for executing the operation of the pulse oximeter 1C described below in the memory 28b.

As described above, when the oxygen saturation is calculated from the equation (6), the calculation processing for obtaining the measured values of R and IR at the same time point by interpolating based on the measured data before and after is performed. To do. Here, since the interpolation accuracy deteriorates as the measurement interval between the measurement data before and after the interpolation is increased, it becomes difficult to obtain the oxygen saturation with high accuracy. Therefore, in the pulse oximeter 1C, R and IR are retained while maintaining the ability to remove periodic noise that is an integral multiple of the commercial frequency.
In addition to improving the interpolation accuracy with, the measurement accuracy of oxygen saturation is improved by increasing the number of measurement data points.

FIG. 10 is a diagram for explaining the operation of the pulse oximeter 1C. In each of FIGS. 10A to 10C, the horizontal axis represents time, and the transmitted light amount (DC)
The measurement timings of R, R. Dark, IR, and IR. Dark regarding the pulse wave component (AC) are shown.

In the pulse oximeter 1C, as shown in FIG.
As shown in FIG. 10C, three measurement patterns shown in FIG. 7 are combined with a period TO of the commercial frequency at a time interval of TO / 3, that is, a phase shift of 120 degrees. The subscripts 1 to 3 at the measurement timing in the figure indicate the respective phase numbers. That is, the measurement pattern PT1 (FIG. 10A) has the first phase
2 (FIG. 10 (b)) shows the second phase, and the measurement pattern PT3 (FIG. 10 (c)) shows the third phase. However, in each of the measurement patterns PT1 to PT3, the time interval of the measurement timing of R, R. Dark, IR and IR. Dark is the cycle TO of the commercial frequency as in the first embodiment. Here again, the period TO of the commercial frequency is compared with the measured values R and IR.
In dark correction that subtracts distant dark levels, it is possible to remove noise that is an integral multiple of the commercial frequency.

As for the dark correction by the pulse oximeter 1C, a constant offset component can be canceled regardless of time, as in the first embodiment.

These measurement patterns PT1 to PT3 are
FIG. 11 shows a summary on the time axis of 1. Figure 11
As described above, compared with the measurement timing (FIG. 7) of the first embodiment, the data measurement can be performed at a density three times higher per unit time.

By the operation of the pulse oximeter 1C described above, the periodic noise relating to the commercial frequency can be removed as in the first embodiment, so that the oxygen saturation can be accurately measured. Moreover, since the phase of each measurement pattern is shifted and a plurality of combinations are combined to increase the number of measurement data points, the measurement accuracy of oxygen saturation can be further improved.

In this embodiment, the example in which the number of measurement data points is tripled has been shown, but it may be doubled or quadrupled. In this case, to combine n measurement patterns, the time difference TO / n obtained by dividing the phase difference of each measurement pattern by the period n of the commercial frequency is divided by the number n of measurement patterns.
You can set it to.

Fourth Embodiment The configuration of the pulse oximeter 1D of the fourth embodiment of the present invention is similar to the pulse oximeter 1A of the first embodiment, but the configuration of the control circuit 28 is different. .

Control circuit 28 of pulse oximeter 1D
Stores a program for executing the operation of the pulse oximeter 1D described below in the memory 28b.

In the pulse oximeter 1D, the information on the pulse rate is used to measure the blood oxygen saturation level, specifically, to improve the S / N ratio for the calculation of the time difference value.

The blood oxygen saturation is measured by calculating the time difference value for R and IR at time Δt, as in the calculation of the p value in equation (6). Regarding this time difference value,
As shown in FIG. 12A, the difference between the measured values at adjacent, that is, the latest measurement timing may be used, but the pulse oximeter 1D calculates the time difference value as follows.

That is, as shown in FIG. 12 (b), for example, the difference between the measurement values measured at timings six apart is calculated, and the p value is calculated by this time difference value. In this way, not the measured values at adjacent measurement timings,
The time difference value can be increased by obtaining the difference value at the constant time interval Δtm. Thereby, the S / N ratio can be improved in the calculation of the p-value, that is, the oxygen saturation. Here, it is preferable that the difference time Δtm shown in FIG. 12 (b) is a time whose time difference value corresponds to approximately half the amplitude HM of the amplitude of the pulse wave waveform (slow slope side). This is for setting the time difference value to an appropriate size above a certain level.

When the measurement is carried out in a living body, the pulse rate varies depending on individual differences or the physical condition of the same person at the time of measurement. That is, when the oxygen saturation is calculated, the appropriate difference time Δtm varies depending on the pulse rate of the subject.

Therefore, the difference time Δtm is adjusted so as to be the optimum difference time based on the information on the pulse rate of the subject obtained from the measurement data of the pulse wave component. That is, when the pulse rate is high, as shown in FIG.
Is shorter than the difference time Δtm shown in FIG. Even in this case, as described above, it is preferable to set the time at which the change corresponding to almost half of the amplitude of the pulse wave component occurs in the pulse wave component as the difference time Δtm. Note that if the difference time Δtm is set too long, the reference voltage set value may differ between measurement data, so it is preferable to set a certain upper limit.

By the above operation of the pulse oximeter 1D, an appropriate difference time Δtm is set according to the pulse rate, so that the S / N ratio relating to the time difference value can be improved and the oxygen saturation can be measured accurately.

If this difference time Δt is set according to the pulse rate and is set to a time obtained by multiplying the cycle of the commercial frequency by an integer, periodic noise related to the commercial frequency can be removed.

<Fifth Embodiment> The pulse oximeter 1E of the fifth embodiment of the present invention has a configuration similar to that of the pulse oximeter 1 of the first embodiment, but a control circuit 28 has a different configuration. .

The pulse oximeter 1E is constructed so that the dark level can be accurately measured even when the dark level fluctuates with time. Here, the case where the dark level fluctuates corresponds to, for example, the case where the light that has passed through the living body from the sun is detected as a dark level by the photodetector and the magnitude thereof changes momentarily.

Control circuit 28 of pulse oximeter 1E
Stores a program for executing the operation of the pulse oximeter 1E described below in the memory 28b.

FIG. 13 is a diagram for explaining the operation of the pulse oximeter 1E.

The pulse oximeter 1E is the third embodiment.
Similar to (see FIG. 10), the amount of transmitted light (DC) and the pulse wave component
Regarding (AC), three measurement patterns PN1 to PN3 of R, R. Dark, IR and IR. Dark are combined. Here, the measurement cycle TQ is 1/8 (1/1) of the cycle of the commercial frequency.
An embodiment in which it is set to 400 sec or 1/480 sec) is shown. FIG. 14 shows a summary of these measurement patterns PN1 to PN3.

The dark levels of R and IR are similar to those of R.D.
The measured values of ark and IR.Dark are interpolated. Specifically, the interpolation formula for IR measurement is shown in the following formula (7), and the interpolation formula for R measurement is shown in the following formula (8).

[0091]

[Equation 5]

For example, when the dark level (dark measured value) at the timing of IR0 in FIG.
IR1 and IR2 which are shifted by 1/3 TQ back and forth as in (7)
It will be interpolated by the dark level measured at the timing of.

Further, when the dark level at the timing of R0 in FIG. 14 is obtained, the timing of R1 shifted 5/3 TQ before and the timing of R2 shifted 1/3 TQ later are calculated as shown in equation (8). It will be interpolated at the dark level measured in. Here, the formula (8) is different from the formula (7) because the dark level at the time of measuring the transmitted light is used for the dark level interpolation of the transmitted light amount (DC), and the pulse wave component (AC) is used.
This is because it is necessary to use the dark level when measuring the pulse wave component for the dark level interpolation of.

As described above, in the paroximeter 1E,
Compared to each of the above-described embodiments, two dark levels detected at the second timing near the actual measurement (first timing) are used to interpolate the dark level corresponding to the actual measurement, and the dark level is actually measured. Since the dark correction is subtracted from the value, even when the dark level fluctuates, the effect is reduced and the oxygen saturation can be measured accurately.

On the other hand, the periodic noise of the commercial frequency is removed by calculating the following equation (9). Here, N represents an integer.

[0096]

[Equation 6]

As shown in the above equation (9), in the calculation of the time difference value regarding the pulse wave component, the time 8 · N · TQ is set to the difference time and the p value is calculated. That is, for each of the measurement patterns PN1 to PN3, the time difference value relating to the measurement value (pulse wave measurement value) of the two pulse wave components separated by the time interval obtained by multiplying the cycle of the commercial frequency by an integer N is obtained. It becomes possible to remove periodic noise.

Although the mixing of the commercial frequency periodic noise in the transmitted light amount measurement is smaller than that in the pulse wave component measurement, it is preferable that the control unit 28 smooths it by a digital low-pass filter if necessary.

By the above operation of the pulse oximeter 1E, even if the dark level fluctuates, the interpolation calculation is performed at the dark level at the measurement timing close to the actual measurement time, so that the blood component can be accurately measured.

In the fifth embodiment, the measurement cycle TQ is 1/8 of the cycle of the commercial frequency, but it is 1/4, 1/2, 1, 2, ... Of the cycle of the commercial frequency. Even in the case of, it is clear that the same effect can be obtained because the difference time of the pulse wave component is an integral multiple of the cycle of the commercial frequency.

The dark level can also be interpolated to suppress its variation by the following method.

In the pulse oximeter 1B of the second embodiment, it is preferable to perform interpolation for averaging the dark levels before and after the actual measurement times of R and IR in FIG. Also in this case,
Divided into transmitted light quantity (DC) measurement and pulse wave component (AC) measurement,
The dark level will be calculated. This calculation formula is shown in the following formula (10).

[0103]

[Equation 7]

With the above operation, the blood component can be measured while suppressing the fluctuation of the dark level even in the second embodiment.

Further, in the pulse oximeter 1C of the third embodiment, the same phase, that is, each of the measurement patterns PT1 to PT1.
The dark level measured at each PT3 may be extrapolated and obtained, but if the change amount of the dark level is obtained from another measurement pattern, the dark level calculation accuracy can be improved.

That is, when calculating the dark level corresponding to the IR (3, AC) measurement in the measurement pattern PT3 shown in FIG. 10 (c), the same measurement pattern PT3 can be obtained by the following equation (11). 2 may be extrapolated to obtain, or another phase, for example, a dark level measured by the measurement pattern PT1 may be used as in the following Expression (12). In either case, the blood component can be measured while suppressing the fluctuation in the dark level calculation.

[0107]

[Equation 8]

<Sixth Embodiment> The configuration of the pulse oximeter 1F according to the sixth embodiment of the present invention is similar to that of the pulse oximeter 1B according to the second embodiment, but the reference voltage generator is omitted and the description will be made later. The difference is mainly in that a holding circuit group 29 is added.

FIG. 15 is a diagram showing the configuration of the measuring circuit of the pulse oximeter 1F.

The pulse oximeter 1F has a voltage holding unit 29 and analog switches 232 and 233 added to the pulse oximeter 1B of the second embodiment.

The voltage holding unit 29 has eight sample & hold circuits 291-298, and each of the sample & hold circuits 291-298 can hold the input voltage.

Also, the analog switches 232, 233
Is a switch for determining the timing of sending the measured values held by the sample & hold circuits 291-294 and the sample & hold circuits 295-298 to the control circuit 28.

FIG. 16 is a diagram for explaining the operation of the pulse oximeter 1F.

In the pulse oximeter 1F, the light emitting elements 31 of red color and infrared color are alternately pulsed to measure the transmitted light amount of the living body in a time division manner.

Here, in the transmitted light amount (DC) measurement,
The signal detected by the photodetector 32 passes through the current-voltage conversion circuit 21 and the variable amplification circuit 22 and then the A / D conversion circuit 27.
The signal is converted into a digital signal in 2 and input to the control circuit 28. The measurement timing of this transmitted light amount is shown in FIG. Here again, the measurement of R, R. Dark, IR, and IR. Dark is performed in order. Regarding this measurement interval, in order to remove the periodic noise of the commercial frequency, it is preferable to set the measurement interval to an integral multiple of the cycle of the commercial frequency.

On the other hand, for the pulse wave component (AC) measurement, the control circuit 28 calculates the time difference value in each of the above-described embodiments, but in the pulse oximeter 1F of the present embodiment, the voltage holding unit 29 is used. Is calculated by analog calculation.

That is, R, R.Dark, IR, IR.Dark
Each measured value of is held by two sets of sample & hold circuit,
The voltage value V2 at each measurement time point separated by the difference time Δt is alternately switched by the analog switches 232 and 233, and the subtraction circuit 25 generates the time difference value of the pulse wave component.

For example, in the measurement of R, the value of the voltage V2 is alternately held in the sample & hold circuit 291 and the sample & hold circuit 295. As a result, the voltage value at the time of this R measurement and the voltage value at the time of the last R measurement are held. Also other measurements
The same applies to (IR, R. Dark, IR. Dark).

Then, the voltage value held at the time of this measurement
The voltage value (for example, R) and the voltage value (for example, R ′) held in the previous measurement are input to the subtraction circuit 25 by timing with the analog switches 232 and 233. The output from the subtraction circuit 25 is amplified to an appropriate voltage level by the variable amplification circuit 26 and then converted into a digital signal by the A / D conversion circuit 271 to obtain a signal of a time difference value regarding the pulse wave component.
(Eg, ΔR) is input to the control circuit 28 (FIG. 16 (b)
reference). That is, the time difference value (ΔR, ΔR.Dark, ΔI
R, ΔIR.Dark) are analog-calculated as in the following equations (13) to (16).

[0120]

[Equation 9]

FIG. 17B shows the measurement timing relating to this time difference value, and FIG. 17 shows the measurement timing of the transmitted light amount.
Shown in (a).

Since the two sets of sample & hold circuits are switched alternately, the sign of the difference voltage output from the subtraction circuit 25 is switched in order, but when the sign is reversed, the control circuit It will be adjusted by performing a sign re-inversion operation at 28.

In the pulse oximeter 1F, similar to the fourth embodiment, the information on the pulse rate can be used to improve the S / N ratio in the measurement of blood oxygen saturation.
This operation will be described below.

As shown in FIG. 18 (a), if the p-value is calculated as it is by using the time difference value of the pulse wave component regarding a minute time interval, the S / N becomes worse as described above. Therefore, the time difference value of the measured pulse wave component is added for a predetermined time Δta corresponding to time 7Δt, as shown in FIG. 18B. Therefore, the calculation of the p-value can be expressed by the following equation (17). The control circuit 28 performs this calculation.

[0125]

[Equation 10]

However, Σ means that each time difference value measured at the time Δt shown in FIG. 18A is added.

The time Δta shown in FIG. 18B is set to an appropriate difference time based on the information on the pulse rate of the subject, as in the fourth embodiment. Specifically, it is preferable to set the time at which a change corresponding to almost half the amplitude of the pulse wave waveform occurs in the pulse wave component as the difference time Δt.

Note that the time difference values of the amount of transmitted light and the pulse wave component measure R and IR alternately, so the measurement time points are deviated in the measurement data of R and IR. Therefore, the measurement values regarded as the same time point are obtained by interpolating the measurement values before and after the time point by the control circuit 28.

By the above operation of the pulse oximeter 1F, as in the fourth embodiment, an appropriate difference time is set according to the pulse rate, so that the S / N ratio in the time difference value is improved and the oxygen saturation level is increased. Can be measured accurately. Further, since the analog circuit (the voltage holding unit 29 and the like) calculates the time difference value, the quantization error can be suppressed and the oxygen saturation can be measured more accurately than the calculation by the digital circuit (control circuit 28). It will be possible.

As for the pulse oximeter 1F, if each measured value is sampled at the cycle of the commercial frequency,
It is possible to remove the influence of periodic noise and the like on the commercial frequency.

Further, as in the third embodiment, in order to triple the number of measurement data points, the number of sample and hold circuits must be three.
You will need twice. In this case, although the circuit becomes complicated, the number of data points increases, so that the measurement accuracy of oxygen saturation is improved.

<Modification> In the above third embodiment, as shown in FIG. 19, the dark level measurement timing may be set on both sides (in the vicinity) of the R and IR measurement signal measurements. 20 is shown in FIG.
9 (a), 9 (b), and 9 (c) are summarized on one time axis.

The measured signal (R,
For (IR) dark correction, the average value of 2 dark levels measured at the Dark and Dark 'timings on both sides is used.

The cycle T of each measurement pattern may be set to the cycle of the commercial frequency as in the third embodiment, or 1 cycle of the commercial frequency as in the fifth embodiment.
It may be set to / 8, 1/4, or 1/2.

Even in the above-described measurement pattern, if the difference time of the pulse wave component is set to an integral multiple of the cycle of the commercial frequency, the commercial frequency and the noise of the fluorescent lamp can be canceled.

The measuring methods described in the third to fifth embodiments can be applied to the circuit of the second embodiment (FIG. 8) described above.

The intervals TO and TQ of the respective measurement timings in the above-described first to sixth embodiments are not necessarily the intervals of time obtained by multiplying the cycle of the commercial frequency by one. The time interval may be an integral multiple of the above. Also in this case, it is possible to remove the periodic noise and the like related to the commercial frequency.

The specific embodiments described above include inventions having the following configurations.

(1) A blood component measuring device characterized in that the light amount detecting means has means for alternately irradiating the living body with light of two different wavelengths. This can improve the measurement accuracy.

(2) The light amount detecting means has means for alternately irradiating the living body with light of two different wavelengths and detecting the light amount measurement value amplified by the first amplification factor, and the dark detecting means is the light emitting means. And a means for detecting the dark measurement value amplified by the second amplification factor without emitting light, and the first amplification factor and the second amplification factor are equal to each other. Thereby, accurate dark correction can be performed on the transmitted light amount measurement value.

(3) The pulse wave detecting means has means for alternately irradiating the living body with light of two different wavelengths to detect the pulse wave measurement value amplified by the first amplification factor, and the dark detecting means: A blood component measuring device having means for detecting a dark measurement value amplified by a second amplification rate without causing the light emitting means to emit light, and the first amplification rate and the second amplification rate are equal to each other. . As a result, accurate dark correction can be performed on the pulse wave measurement value.

(4) A blood component measuring device characterized by comprising processing means for performing digital filter processing on the time difference value between the light quantity measurement value after dark correction and the pulse wave measurement value after dark correction. This makes it easy to remove noise.

(5) The light detecting means irradiates the light of the first wavelength with the first intensity and outputs the first detection voltage, and the light of the second wavelength with the second intensity. A second light detection means for outputting a second detection voltage, and means for adjusting the first intensity and / or the second intensity so that the first detection voltage and the second detection voltage are substantially equal to each other. A blood component measuring device characterized by: As a result, the detection voltage can be output by emphasizing light having different wavelengths.

(6) The blood component measuring apparatus characterized in that the first amplifying means has means for changing the first amplification factor when the light amount measurement voltage is out of the predetermined voltage range. Thereby, an appropriate light amount measurement voltage can be output.

(7) The blood component measuring apparatus characterized in that the second amplifying means has means for changing the reference voltage when the pulse wave measurement voltage is out of the predetermined voltage range. Thereby, an appropriate pulse wave measurement voltage can be output.

(8) The blood component measuring apparatus characterized in that the second amplifying means has means for changing the second amplification factor when the amplitude of the pulse wave measurement voltage is out of the predetermined voltage range. Thereby, an appropriate pulse wave measurement voltage can be output.

[0147]

As described above, according to the first and second aspects of the present invention, since the time difference value regarding the two light intensity measurement values detected at the time intervals corresponding to the pulse rate is calculated, it is appropriate. The difference time can be set accurately and the oxygen saturation can be measured accurately.

In particular, according to the second aspect of the invention, since the time difference value regarding the two pulse wave measurement values detected at the time intervals corresponding to approximately half the amplitude of the pulse wave component is calculated,
A time difference value having a good S / N ratio can be acquired.

According to the third aspect of the present invention, the reference voltage is subtracted from the light amount measurement voltage and the pulse wave measurement voltage amplified by the second amplification factor is output as the output voltage.
The / D conversion circuit is not necessary, and the oxygen saturation can be accurately measured by suppressing the quantization error.

Particularly, in the invention of claim 4, the settings of the predetermined intensity, the first amplification factor, the second amplification factor, and the reference voltage are updated at predetermined time intervals, so that when each measured voltage changes. However, it is possible to generate an appropriate output voltage.

According to the invention of claim 5, the difference obtained by amplifying the difference between the light quantity measurement voltage measured at the previous timing and held by the voltage holding means and the light quantity measurement voltage measured at this timing. Since the voltage is output as the output voltage, the quantization error can be suppressed and the oxygen saturation can be accurately measured.

[Brief description of drawings]

FIG. 1 is a diagram showing a main configuration of a pulse oximeter 1A according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining the absorbance of a living body.

FIG. 3 is a diagram showing absorption spectra of oxyhemoglobin and reduced hemoglobin.

FIG. 4 is a diagram for explaining a time difference value of a pulse wave component.

FIG. 5 is a diagram showing a configuration of a measurement circuit of a pulse oximeter 1A.

FIG. 6 is a diagram showing an example of measurement results regarding red light and infrared light.

FIG. 7 is a diagram for explaining measurement timings in the pulse oximeter 1A.

FIG. 8 is a diagram showing a configuration of a measurement circuit of a pulse oximeter 1B according to a second embodiment of the present invention.

FIG. 9 is a diagram for explaining measurement timings in the pulse oximeter 1B.

FIG. 10 is a diagram for explaining the operation of the pulse oximeter 1C according to the third embodiment of the present invention.

FIG. 11 is a diagram for explaining measurement timings in the pulse oximeter 1C.

FIG. 12 is a diagram for explaining the operation of the pulse oximeter 1D according to the fourth embodiment of the present invention.

FIG. 13 is a diagram for explaining the operation of the pulse oximeter 1E according to the fifth embodiment of the present invention.

FIG. 14 is a diagram for explaining measurement timings in the pulse oximeter 1E.

FIG. 15 is a diagram showing a configuration of a measurement circuit of a pulse oximeter 1F according to a sixth embodiment of the present invention.

FIG. 16 is a diagram for explaining the operation of the pulse oximeter 1F.

FIG. 17 is a diagram for explaining measurement timings in the pulse oximeter 1F.

FIG. 18 is a diagram for explaining a time difference of pulse wave components in the pulse oximeter 1F.

FIG. 19 is a diagram for explaining measurement timing according to a modified example of the present invention.

FIG. 20 is a diagram for explaining measurement timing according to a modified example of the present invention.

[Explanation of symbols]

1A, 1B, 1C, 1D, 1E, 1F Pulse oximeter 3 Probe 31 Light emitting element 32 Photodetection element 22, 26 Variable amplification circuit 24 Reference voltage generator 27, 271, 272 A / D conversion circuit 28 Control circuits 291-298 Sample and hold circuits PT1 to PT3, PN1 to PN3 measurement patterns

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Akihiro Ukai             2-3-3 Azuchi-cho, Chuo-ku, Osaka-shi, Osaka Prefecture               Osaka International Building Minolta Co., Ltd. F-term (reference) 4C038 KK01 KL05 KL07 KM01 KX02

Claims (5)

[Claims] 1. A device for measuring blood components of arterial blood in a living body, comprising: (a) irradiating the living body with predetermined light from a light emitting means at a first timing, and transmitting the living body by a light detecting means. (B) dark detection means for periodically detecting a dark measurement value by the light detection means at a second timing without causing the light emitting means to emit light; c) pulse rate detecting means for detecting a pulse rate related to the arterial blood; (d) computing means for computing a time difference value regarding two light intensity measurement values detected at time intervals corresponding to the pulse rate; and (e) A blood component measuring device comprising: a blood component measuring unit that measures a blood component of the arterial blood based on the light amount measurement value, the dark measurement value, and the time difference value. 2. The blood component measuring device according to claim 1, wherein the calculating means extracts (d-1) a pulse wave component from the light intensity measurement value and detects the pulse wave measurement value. And (d-2) means for calculating a time difference value regarding two pulse wave measurement values detected at time intervals at which a change corresponding to approximately half the amplitude of the pulse wave component occurs in the pulse wave component. A blood component measuring device comprising: 3. A device for measuring blood components of arterial blood in a living body by inputting output voltages output from a first measuring unit and a second measuring unit composed of analog circuits into a digital circuit, The measuring unit (a-1) irradiates the living body with a predetermined intensity at a predetermined intensity and outputs a detection voltage for the light transmitted through the living body, and (a-2) the detection voltage A second amplifying unit configured to output a light amount measurement voltage amplified by one amplification factor as the output voltage, wherein the second measuring unit is set based on (b-1) a non-pulse wave component of the light amount measurement voltage. A second reference voltage generating means for generating a second reference voltage, and (b-2) a pulse wave measurement voltage obtained by subtracting the reference voltage from the light quantity measurement voltage and amplifying the pulse wave measurement voltage by a second amplification factor as the output voltage. A blood component measuring device comprising: an amplifying unit. 4. The blood component measuring device according to claim 3, wherein the settings of the predetermined intensity, the first amplification factor, the second amplification factor, and the reference voltage are updated at predetermined time intervals. A blood component measuring device characterized by the above. 5. A device for measuring blood components of arterial blood in a living body by inputting output voltages output from a first measuring unit and a second measuring unit, which are analog circuits, into a digital circuit. The measuring unit (a-1) irradiates the living body with predetermined light periodically, and a photodetector that outputs a detection voltage relating to the light transmitted through the living body, and (a-2) amplifies the detection voltage. Amplifying means for outputting a light quantity measurement voltage as the output voltage; and the second measuring section, (b-1) voltage holding means for holding the light quantity measurement voltage measured at a previous timing, -2) A light amount measurement voltage held by the voltage holding means,
A second voltage that outputs a difference voltage obtained by amplifying a difference from the light amount measurement voltage measured at this timing as the output voltage.
A blood component measuring device comprising: an amplifying unit.