JP3291581B2 - Oxygen saturation measurement device and signal processing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to arterial blood oxygen saturation (S)
The present invention relates to a pulse oximeter that detects an external noise level affecting the measurement of PO2), obtains a measured value from which the external noise has been removed, and displays an alarm when an accurate measured value cannot be obtained.

[0002]

2. Description of the Related Art Conventionally, when performing arterial blood oxygen saturation measurement, a light receiving element of a measurement probe is provided with a light source other than infrared light and red light used for measurement, for example, extraneous light from a fluorescent lamp or the like. It is known to be affected by the influence of the noise and the induction noise from an external device such as an electric blanket. For this reason, various methods have been proposed for minimizing the effects other than the target signal and obtaining only the target signal.

FIG. 8 is a block diagram partially showing the configuration of such a conventional pulse oximeter with a circuit. In FIG. 8, in this example, a light emitting diode 2 a that blinks at a frequency f in the preceding section of the data sampling period T / 2 by turning on and off a switching transistor with a red (R) light drive signal, and an infrared ( (IR) a light emitting diode 2b that turns on and off a switching transistor in response to a light drive signal and blinks infrared (IR) light at a frequency f after the period T / 2 and R light from the light emitting diodes 2a and 2b; I
Control is performed so that the emission of R light is alternately repeated at a frequency f.
The control circuit 3 includes a PU, a ROM storing a control program, a working RAM, and the like.

Further, a light receiving diode 4 which receives transmitted light or reflected light when irradiating arterial blood with R light and IR light from the light emitting diodes 2a and 2b and outputs a photoelectrically converted light receiving signal; A current / voltage conversion amplifier circuit 5 that converts the photoelectric conversion current from the amplifier into a voltage and outputs an amplified light reception signal, and focuses on the low band and the high band of the light reception signal from the current / voltage conversion amplifier circuit 5. A band-pass filter (BPF) 6 cut off at a frequency f, an operational amplifier,
An AM detection circuit 7 including a diode and outputting a detection signal obtained by detecting (double-wave rectifying) the light reception signal from the BPF 6 is provided.

In this example, a control circuit 3 divides one data sampling time (period T) into two and derives a light receiving signal of the reflected light in the order of irradiation of R light and IR light. Switching circuit 8 that switches with the R / IR switching signal of
And the detection signal output from the switching circuit 8 is converted to R / IR
An integrating circuit 9 for alternately outputting an R signal or an IR signal integrated by constants of a capacitor C and a resistor R based on a switching signal, and a wireless transmission unit 10 for transmitting measurement data from the control circuit 3 are provided. ing.

Next, the operation of this conventional example will be described. FIG. 9 is a timing chart showing processing waveforms and timings in the conventional operation. 8 and 9, the control circuit 3 supplies the R / IR light emission drive signals shown in FIGS. 9A and 9B to the light emitting diodes 2a and 2b through the transistors Q1 and Q2 at every cycle T / 2, and outputs R / IR. Light and IR light are emitted alternately. The transmitted light or the reflected light when this light emission is applied to the arterial blood is received by the light receiving diode 4.
And outputs a light-receiving signal photoelectrically converted. This light receiving signal is converted into a voltage by the current / voltage conversion amplifier circuit 5 and amplified, and the amplified light receiving signal shown in FIG.
Output to In the BPF 6, the amplified received light signal is passed only in the band of the center frequency f.

The amplified light receiving signal from the BPF 6 is detected by an AM detection circuit 7 and the detected signal shown in FIG.
The switching contact 8 of the switching circuit 8 is switched at the cycle T / 2 of the R / IR switching signal from the control circuit 3 shown in FIG. Are supplied to the integrating circuit 9 through the fixed contacts a and b, respectively. FIG. 9 (f) integrating from this with a CR constant,
An R signal or an IR signal shown in (g) is output. The level of this R signal or IR signal is the level of the R light, I, applied to the arterial blood.
Equal to the transmitted or reflected light level of the R light. That is, it indicates the measured value of the arterial oxygen saturation.

In this case, the emission frequency f of the light emitting diodes 2a and 2b is made higher than that of a conventional frequency, and the amplified light reception signal is passed only in the band (center frequency f) of the BPF 6, thereby increasing the frequency. The pass band can be narrowed and low and high frequency noise can be cut off. In other words, most of the external noise that is an obstacle to the measurement of arterial oxygen saturation is generally distributed at a relatively low frequency of about several times the commercial AC power supply frequency. Improved discrimination performance of signal components (R light, IR light), and accurate measurement values can be obtained

[0009]

However, in the above-described conventional pulse oximeter, R light and IR light are emitted at a higher light emission frequency f than the conventional frequency, and the BPF 6 (center frequency f) is used. By passing the amplified received light signal only in the band, the ability to discriminate between external noise and a signal component can be enhanced, but it does not operate effectively for various external noise and is close to the emission frequency f in the noise. When a frequency component exists, accurate measurement often cannot be performed due to a so-called disturbance.

That is, an external noise component having a frequency close to the emission frequency f is superimposed on the detection signal, and an offset voltage is added to the R signal and the IR signal from the integration circuit 9. Also, a noise signal of a beat sound is generated due to a phase difference between the frequency f and the light emission period T.

At present, the measured value of the arterial blood oxygen saturation when noise is generated is displayed on the screen as it is. In other words, since the measurer cannot identify an incorrect measurement value with superimposed noise, move the measurement location or turn off the noise source to obtain an accurate measurement value. There is a disadvantage that no countermeasures can be taken.

The present invention solves the above-mentioned problems in the prior art, and provides an accurate measurement value from which an extraneous noise level affecting quantitatively detected measurement of arterial oxygen saturation is removed. In addition, the purpose is to provide a pulse oximeter that can display the case where the external noise level cannot be removed and affects the accurate measurement and can warn the measurer, and can perform the accurate measurement based on this warning. I do.

[0013]

In order to achieve the above object, an oxygen saturation measuring apparatus according to the present invention emits a first wavelength light, a second wavelength light, and a non-light emission to a measurement object every data sampling cycle. Light-emitting means for repeating, light-receiving means for receiving light from the object to be measured and outputting a light-receiving signal corresponding to the light, and the light-emitting signals of the first wavelength light emission, the second wavelength light emission, and the non-light emission from the light reception signal And integrate
Emission signal level of each of first wavelength emission and second wavelength emission
And a level detecting means including an integration circuit for obtaining the non-light emission noise level, and the non-light emission noise level subtracted from the light reception signal levels of the first wavelength light emission and the second wavelength light emission. Signal generation means for generating measurement signals for the one-wavelength emission and the second-wavelength emission, and a change in the noise level detected by the level detection means being a predetermined value.
Determining means for determining whether the value is within the level variation allowable value .

In addition , the measurement pair is set every data sampling period.
Emission of the first wavelength, second wavelength and non-emission
Returning light emitting means, and receiving light from the object to be measured.
A light receiving means for outputting a light receiving signal corresponding to the light;
The first wavelength emission and the second wavelength emission are received from the signal.
Levels for detecting the optical signal level and the non-emitting noise level
Detector and the first wavelength emission and the second wavelength emission, respectively.
From the received light signal level,
The first wavelength emission and the second wavelength emission are subtracted.
Signal generation means for generating a measurement signal; storage means for storing the light reception signal level and the non-light emission noise level of each of the first wavelength emission and the second wavelength emission in a plurality of data sampling periods; And determining means for determining whether or not the non-light emission noise levels in a plurality of data sampling periods are similar, wherein the determination means determines that the non-light emission noise levels are close to each other. When it is determined that the first wavelength emission and the second wavelength emission are measured, the signal generation means subtracts the non-light emission noise level from the respective light reception signal levels of the first wavelength emission and the second wavelength emission to measure the first wavelength emission and the second wavelength emission. so as to output a signal
Configured . Further, the level detecting means integrates the light receiving signals of the first wavelength light emission, the second wavelength light emission, and the non-light emission to integrate the light reception signal levels of the first wavelength light emission and the second wavelength light emission and the non-light emission. The configuration is such that an integration circuit for obtaining a noise level is provided. Further, in the data stored in the storage means, when the determination means determines that the non-light emission noise level in a plurality of data sampling periods is not approximate, notification means for notifying that external noise cannot be removed. The configuration was provided with. Furthermore, a configuration is provided in which first control means is provided for controlling the start timing of storage and discharge of the integration circuit in synchronization with the data sampling cycle.

Further, the determination means is configured to make a determination based on a maximum level and a minimum level among the non-light emission noise levels stored in the storage means. Further, a second control means for erasing the light receiving signal level and the noise level stored in the storage means based on predetermined conditions is provided. Further, the determination means determines a difference between a maximum level and a minimum level among the non-light emission noise levels stored in the storage means, and makes a determination based on a comparison between the difference and a predetermined threshold. . Furthermore, the determination hand
The stage is configured such that the fluctuation of the noise level is a predetermined level fluctuation allowable value.
The external noise cannot be removed based on the judgment that
Informing means for informing is further provided .

According to the signal processing method for measuring arterial blood oxygen saturation of the present invention, the first wavelength light emission, the second wavelength light emission, and the non-light emission are repeatedly performed on the measurement object at each data sampling period, and the light from the measurement object is emitted. obtain a light reception signal corresponding to the light receiving, the first wavelength emitted from the light receiving signal, and detecting the received light signal level and noise level of the non-emission of the respective second wavelength emission, fluctuations of the noise level
Is determined to be within a predetermined level fluctuation tolerance.
Sign . In addition, the first wavelength emission, the second wavelength emission, and the non-emission are repeatedly performed on the measurement target for each data sampling period, and the light from the measurement target is received to obtain a light reception signal corresponding to the light. Detecting the light-receiving signal level of each of the first-wavelength light emission and the second-wavelength light emission and the noise level of the non-light emission, and calculating the noise level in the non-light emission from the light-receiving signal levels of the first-wavelength light emission and the second-wavelength light emission. , The first wavelength emission, the second
Generating a measurement signal for each of the wavelength emission, and generating the measurement signal includes, in the plurality of data sampling periods, the light reception signal levels of the first wavelength emission and the second wavelength emission and the non-emission noise, respectively. The level is stored, and in the stored data, it is determined whether or not the non-emitting noise level in a plurality of data sampling periods is approximated, and when it is determined that the non-emitting noise level is approximated. Then, the measurement signal of the first-wavelength emission and the second-wavelength emission is output by subtracting the noise level of the non-light emission from the light reception signal level of each of the first-wavelength emission and the second-wavelength emission. Further, in the step of detecting the light reception signal level and the noise level, the light reception signals of the first wavelength emission, the second wavelength emission, and the non-emission are integrated to integrate the first wavelength emission and the second wavelength emission, respectively. The light reception signal level and the non-light emission noise level are determined. Further, when it is determined that the non-light emission noise levels in the plurality of data sampling periods in the stored data are not approximate, it is notified that external noise cannot be removed. Further, the timing of starting the integration and clearing the integration value is controlled in synchronization with the data sampling period.

Further, the determination is made based on the maximum level and the minimum level of the stored non-light emission noise levels. Further, the erasure of the stored light receiving signal level and the noise level is erased based on a predetermined condition. Further, in the determination, a difference between a maximum level and a minimum level among the stored non-emission noise levels is obtained, and the determination is made based on a comparison between the difference and a predetermined threshold. Further, in the determination, the noise level
Level fluctuation is not within the specified level fluctuation tolerance.
When it does, it is made to notify that the external noise cannot be removed .

[0018]

According to the oxygen saturation measuring apparatus having the above-mentioned configuration, the measurement of the transmitted light or the reflected light when the section of the first wavelength emission, the second wavelength emission and the non-emission is repeated for each data sampling period is performed on the measurement object. A non-emitting noise level is detected. Then, the non-light emission noise level is set to the first wavelength light emission,
The signal level obtained by subtracting from the level of the light receiving signal of the wavelength emission is obtained. Therefore, an accurate measurement value excluding an external noise level that affects the measurement of the quantitatively detected arterial oxygen saturation can be obtained. Further, the storage means stores the received light signal levels of the first wavelength light emission and the second wavelength light emission in a plurality of data sampling periods, and
The noise level of light emission is stored, and the determining means determines whether or not the noise level of non-light emission in a plurality of data sampling periods in the stored data is similar to each other . The non-light emission noise level is
When it is assumed that they are close to each other , the signal generation means subtracts the non-light emission noise level from the respective light reception signal levels of the first wavelength light emission and the second wavelength light emission, and outputs the first wavelength light emission and the second wavelength light emission. Output the measurement signal. Further, the level detecting means obtains the light receiving signal level and the noise level by integrating the light receiving signals of the first wavelength emission, the second wavelength emission, and the non-light emission. Further, the determination means may determine the non-light emission noise level in a plurality of data sampling periods in the data stored in the storage means.
When it is determined that is not approximate , the notifying unit notifies that the external noise cannot be removed. Further, the first control means controls the storage of the integration circuit in synchronization with the data sampling cycle,
Controls the start of discharge.

Further, the determination means makes a determination based on a maximum level and a minimum level among the non-light emission noise levels stored in the storage means. Further, the second control means controls the light receiving signal level and the noise stored in the storage means.
The sound level is deleted based on a predetermined condition. Further, the determining means obtains a difference between a maximum level and a minimum level among the non-light emission noise levels stored in the storage means, and based on a comparison between the difference and a predetermined threshold value. to decide. Further, the light emitting means emits red light as the first wavelength light and emits infrared light as the second wavelength light.

[0020]

Next, an embodiment of the pulse oximeter of the present invention will be described in detail with reference to the drawings. FIG. 1 shows the first embodiment of the present invention.
FIG. 3 is a block diagram showing a configuration of the embodiment by a partial circuit. FIG.
In this example, one data sampling time (period T) is divided into three parts.
The switching transistor Q1 is generated by the light emission drive signal Sa.
Is turned on and off to emit red (R) light, and a switching transistor is provided by an IR emission drive signal Sb having a frequency f in a second section obtained by dividing one data sampling time (period T) into three. A light emitting diode 12b that emits infrared (IR) light when Q2 is turned on and off is provided.

Further, as will be described in detail below, the emission of the R light in the first section, the emission of the IR light in the second section, and the emission of the IR light in the second section obtained by dividing one data sampling time (period T) into three. And a control circuit 13 for controlling the third section, which is not dark, to obtain a measured value of the arterial oxygen saturation (SPO2). This control circuit 13
PU 13a and an R storing a control program of this device.
It has an OM 13b, a working RAM 13c, and an external input / output (I / O) control unit 13d.

In this example, a light receiving signal which is connected to the control circuit 13 and receives the transmitted light or reflected light when the R light and IR light from the light emitting diodes 12a and 12b are irradiated on the arterial blood and photoelectrically converts the received light or the reflected light. A light receiving diode 14 that outputs
A current / voltage conversion amplifier circuit 15 using an operational amplifier is provided, which converts the photoelectric conversion current from the light receiving diode 14 into a voltage and outputs an amplified light receiving signal Sd.

Further, a light receiving signal in which the low band of the amplified light receiving signal Sd from the current / voltage conversion amplifier circuit 15 is cut off is output, the pass band is the center frequency f, and a resistor, a capacitor, and an operational amplifier (buffer) are provided. An AM detection circuit 17 that includes a band-pass filter (BPF) 16 composed of a BPF, an operational amplifier, and a diode, and outputs a detection signal Se that detects (double-wave rectified) a light-receiving signal from the BPF 16, and a control signal Ssa, The detected signal S based on Ssb
and an integrator 22 that outputs an integration signal Sr obtained by integrating e. The integrator 22 includes a switch SW1 for interrupting the detection signal Se, a switch SW2 for opening and closing both ends of the capacitor C for charging and discharging, a resistor R for obtaining an integrated value, a capacitor C, and an operational amplifier. And

In this example, the A / D converter 23 converts the integrated signal Sr from the integrator 22 into a digital signal and outputs the digital signal to the control circuit 13, and affects the accurate measurement of arterial oxygen saturation. When detecting an external noise level,
A display unit 24 for displaying the detection, a threshold value for detecting an external noise level affecting accurate measurement of arterial blood oxygen saturation, and a warning display when the external noise level is detected An operation switch unit 25 for selecting and setting a type, a speaker 26 for issuing a warning sound when an external noise level affecting accurate measurement of arterial blood oxygen saturation is detected, and a warning using synthesized voice There are provided a synthesized voice circuit 27 for outputting, and a light emitting diode 28 for blinking and displaying a warning.

Next, the operation of the first embodiment will be described. FIG. 2 is a diagram showing the processing signal waveforms of the respective units in the basic operation of the first embodiment. In FIG.
In this operation, one data sampling time (period T) is divided into three, and the control is such that the first section, R light emission, the second section, IR light emission, and the third section, dark section with no light emission, are repeated. It is carried out.

The control circuit 13 reads out the control program of this device from the ROM 13b and starts the control. First, the R light emission drive signals Sa and I shown in FIGS.
The R light emission drive signal Sb is supplied to the light emitting diodes 12a and 12b through the transistors in the first section of the cycle T / 3 and the second section following this, and the R light emission drive signal Sb
a, The dark section where emission of the IR emission drive signal Sb is stopped and there is no emission is repeated. Then, the transmitted light or the reflected light when the artery blood of the subject is irradiated with the R light and the IR light is received by the light receiving diode 14, and the photoelectric conversion current is voltage-converted by the current / voltage conversion amplifier circuit 15 and amplified. Fig. 2
The amplified light receiving signal Sd shown in (c) is output to the BPF 16. In the BPF 16, the amplified light receiving signal Sd whose center is limited to only the pass band of the frequency f is passed. That is, noise signals in the low band and the high band of the frequency f are removed.

The amplified received light signal Sd from the BPF 16 is
The detection signal Se detected by the detection circuit 17 and shown in FIG.
Is output to the integrator 22. In this integrator 22, FIG.
With the control signal Ssa shown in (e), the switch SW1 is turned on at the rise of each of the first to third sections of the data sampling time (cycle T), and is turned off before the rise of the next section. After this off and before the rise of the next section, the switch SW2 is turned on. That is, the capacitor C is short-circuited and discharged to start the integration operation in the next section. Accordingly, the R signal S corresponding to the darkness without the R light emission in the first section, the IR light emission in the second section, and the light emission in the third section obtained by dividing the cycle T into three.
An integrated signal Sr shown in FIG. 2 (g) in which ra, IR signal Srb and dark signal Src are continuous is obtained.

The voltage values of the R signal Sra and IR signal Srb are converted into digital values by the A / D converter 23. This digital integration signal St is output to the control circuit 13, and under the control of the control circuit 13, through the external input / output control unit 13d, noise is removed as will be described in detail below, and an R signal of only a reception signal corresponding to light emission is provided. The Sra and IR signals Srb are generated. If the noise cannot be removed, the measurer is notified to that effect. The processing data is displayed on the display unit 24, and is transmitted to the data collection device, such as a host computer, which is installed at a remote place via the wireless transmission unit 20 and the antenna.

Next, the operation when noise occurs near the frequency f will be described. FIG. 3 is a timing chart showing the processing signal waveforms of the respective units when the noise exists near the frequency f and the timing thereof. FIG. 4 shows the processing procedure when the noise exists near the frequency f. It is a flowchart shown. 1 to 4, first, in step 10 in FIG. 4, the same operation as in FIGS. 2A to 2G is performed, and the R signal Sra, the IR signal Srb, and the dark signal Src are output from the integrator 22. Is output to the control circuit 13 through the A / D converter 23.

Next, a routine shown in FIGS. 3C, 3D and 3G for examining the level fluctuation of the dark signal Src in one pulse of the subject is executed. Here, FIG.
As shown in (d), the amplified light receiving signal Sd and the detection signal Se
Is superimposed on the noise signal. In the integrated signal Sr obtained by integrating the detection signal Se on which the noise is superimposed by the integrator 22, R
The signal Sra, the IR signal Srb, and the dark signal Src are each at a level on which noise is superimposed as shown in FIG. In step 11, the CPU in the control circuit 13
13a, the control circuit 13 takes in the integrated signal Sr.

Next, at step 12, the current dark signal S
The level m of rc and the maximum level max of the dark signal Src stored in the RAM 13c up to the previous time are read and compared, and the level m of the dark signal Src of this time is smaller than the maximum level max of the dark signal Src up to the previous time. In the case (Yes), the process proceeds to the next step 13. Step 13
Now, the level m of the dark signal Src this time and the RAM1
3c is read out and compared with the minimum level min of the dark signal Src up to the previous time, and when the level m of the current dark signal Src is larger than the minimum level min of the dark signal Src up to the previous time (Yes), Step 14
Proceed to.

In step 12, the current dark signal S
If the level m of rc is larger than the maximum level max of the dark signal Src up to the previous time (No), the next step 1
In step 5, the current level is regarded as the maximum level max, and the process proceeds to step 14. Further, if the level m of the current dark signal Src is smaller than the minimum level min of the previous dark signal Src in step 13 (No), the process proceeds to step 16 to execute processing for regarding the minimum level min as the current level. To step 14.

In step 14, steps 12, 13,
The level fluctuation value Δm of the dark signal Src in one pulse of the subject is calculated by subtracting the minimum level min from the maximum level max determined in 15 and 16, and the maximum and minimum levels of the dark signal Src are determined. . Next, at step 17, the level fluctuation allowable value Δpm stored in the RAM 13c or the like in advance is read. In step 18, it is determined whether or not the level variation value Δm calculated in step 14 is within the level variation allowable value Δpm read in step 17.
Thus, it is determined whether or not the level m of the dark signal Src is similar. In this case, the R signal Sra in FIG. 3G is obtained by adding the noise N to the R signal component indicated by the dashed line.
The level of 1 is shown by the added solid line. The IR signal Srb is obtained by adding a noise N2 to an IR signal component indicated by a dashed line.
Are added to the level indicated by the solid line. Also,
The dark signal Src has a level of only the noise component N.

If the level m of the noise N, which is the integral value of the dark section, from the integrator 22 is approximated in step 18 (Yes), the CPU 13a in the control circuit 13 takes in in step 19 The level of the noise N, in other words, the level of the noise N1 is subtracted from the R signal Sra obtained by adding the level of the noise N1 to the R signal component in the integrated signal Sr in FIG. In addition, noise N
By subtracting the level of the noise N, in other words, the level of the noise N2, from the IR signal Srb to which the level of the R signal S2 has been added, the R signal S having only the R signal component level is obtained.
ra and the IR signal Srb having only the IR signal component level can be extracted.

If the level variation value Δm is equal to or greater than the level variation allowable value Δpm in step 18 (No), the noise N in the dark section is discrete as described with reference to FIG.
Since the level fluctuation value Δm is not approximate and cannot be removed, the subroutine of step 20 is displayed, which indicates that the accurate measurement is affected, and warns the measurer. move on.

Next, when the measurement in one pulse period is completed by the routine up to now, step 21 is executed.
Thereby, the measurement data is stored and held in the RAM 13c in the control circuit 13 shown in FIG. Next, in order to determine the end of this one pulse period, the next pulse is detected in step 23, this detection is determined in step 24, and if this determination is not possible (No), Return to 10 and continue this measurement. Step 23
If the next pulse is detected (Yes), the data of the maximum level max and the minimum level min determined in the previous measurement and stored in the predetermined working address (area) of the RAM 13c are deleted.

Thereafter, the arterial blood oxygen saturation is calculated and transmitted from the wireless transmission unit 20, and the process returns to step S10 to restart the measurement in the next pulse period.

As described above, in the first embodiment, the data sampling time (period T) is divided into three, and the dark section where there is no light emission in the third section together with the R light emission in the first section and the IR light emission in the second section. The noise N level at the time of darkness for a plurality of data sampling times (cycle T) is determined by the CPU.
13a, and the level of the noise N is subtracted from the R signal Sra level and the IR signal Srb level,
Only the R signal component level and the IR signal component level corresponding to only the transmitted light or reflected light level, respectively, are obtained. Therefore, the arterial blood oxygen saturation can be accurately measured by the R signal component level and the IR signal component level.

FIG. 5 is a timing chart showing the processing signal waveforms and their timings in the operation of the second embodiment. FIG. 6 is a flowchart showing the subroutine processing procedure of step 20. 1, 2, 5, and 6, this processing is performed when the level variation value Δm is equal to or more than the level variation allowable value Δpm in step 18 in FIG. 4 (No).
In addition, it is assumed that the noise N in the dark section is discrete, the level fluctuation value Δm is not approximated, and it is impossible to remove the noise, and a process for displaying the accurate measurement impossible and alerting the operator is performed.

In the configuration shown in FIG. 1, the R and IR light emission drive signals Sa and Sb shown in FIGS. 5A and 5B have R light emission in a first section of a cycle T / 3 and a second section following the same. , And emits IR light. When the light receiving signal from the light receiving diode 14 for this light emission is converted into a voltage by the current / voltage conversion amplifier circuit 15 and amplified, the amplified light receiving signal S shown in FIG.
In d, noise having a frequency F different from the light emission frequency f may be repeated.

In this case, R light emission in the first section obtained by dividing the data sampling time (period T) into three, and IR emission in the second section
Period T / 3 of dark section without light emission and no light emission in third section
And the frequency F, the amplified light receiving signal S
5D, a beat noise signal (see FIG. 5) indicated by a solid line and a dotted line (next repetition) in the amplified received light signal Sd in FIG.
(C) triangular waveform).

Therefore, due to the generation of the beat noise signal, the R signal Sra in the integrated signal Sr shown in FIG. 5 (g) for each data sampling time (period T) becomes
As shown by a dotted line or a solid line obtained by adding a beat noise signal indicated by a solid line and a dotted line (next repetition) to an R signal component of only the R emission indicated by a dashed line, the level of the signal is determined for each period of the beat noise signal. Fluctuates. The IR signal Srb is
As shown by a solid line or a dotted line obtained by adding a beat noise signal indicated by a solid line and a dotted line (next repetition) to an IR signal component of only the emission of the IR signal indicated by a dashed line, the level thereof is changed for each period of the beat noise signal. fluctuate. Similarly, the level of the dark signal Src varies in each cycle of the beat noise signal as indicated by the solid line or the dotted line.

As described above, the levels of the R signal Sra, IR signal Srb, and dark signal Src in the integrated signal Sr fluctuate with time due to the beat noise signal. When beat noise also occurs in the integrated value of the dark signal Src,
The level will fluctuate with each sampling. Therefore, even by subtracting the level of the noise N1, the R signal component level of only the R emission and the IR signal component level of the IR emission only, from which the influence of noise has been removed, cannot be obtained. In this case, if the level of the beat noise signal greatly fluctuates on the time axis, an accurate measurement value of arterial blood oxygen saturation cannot be obtained.

At this time, the CPU 13a executes step 18
When the level variation value Δm is equal to or greater than the level variation allowable value Δpm (No), that is, the noise component N of the dark signal Src
As a result of observing the temporal fluctuation of only the level, when the fluctuation of the noise component N caused by this beat noise signal becomes a degree that affects the measured value of the arterial oxygen saturation within the allowable range, the control of the CPU 13a, In addition, the image is displayed on the display unit 24 through the processing of the external input / output control unit 13d. First, in step 20a in FIG. 6, the external input / output control unit 13d, the CPU 1
A warning is issued from the speaker 26 through the RAM 13 through the RAM 13a.
It is determined whether or not c is set. When the alarm is set in step 20a (Yes)
Is executed by the CPU 13a to issue an alarm from the speaker 26 in step 20b.

If the alarm is not set in step 20a (No), the flow advances to the next step 20c. In this step 20c, a process of displaying a screen with characters or symbols on the display unit 24 in FIG. Also,
The speaker 26 issues an alarm, displays a screen using characters or symbols on the display unit 24, and controls the synthesized voice circuit 27 in FIG.
Output from In addition, the light emitting diode 28 is turned on and off to emit light for easy visual confirmation.

As described above, in the second embodiment, the RAM 13
When it is determined that the noise signal levels in a plurality of data sampling periods in the data stored in c are not approximated, the inability to remove the extraneous noise level is displayed by screen display, sound output, synthesized voice output, and flashing light emission. are doing. Therefore, when there is an influence on the accurate measurement, the measurer can easily know the influence. This allows the measurer to:
By moving the measurement location or turning off the fluorescent lamp or the like, disturbance due to this noise is prevented, and accurate measurement can be performed thereafter.

FIG. 7 is a block diagram showing a part of the configuration of the third embodiment. In the third embodiment, a sample and hold circuit 30 having a high frequency cutoff characteristic is used instead of the integrator 22 shown in FIG. The sample-and-hold circuit 30 performs R light emission in the first section obtained by dividing the cycle T into three,
Switches SW11, SW12, and SW13 that are sequentially turned on and off by control signals Sse, Ssf, and Ssg corresponding to a dark section where there is no IR emission in the section and no light emission in the third section.
A resistor R and a capacitor C for performing integration are provided on the output side of the switches SW11 to SW13. Other configurations are the same as those of the first embodiment shown in FIG.

In this configuration, the sample and hold circuit 30
Switches SW11 to SW13 are turned on at the rising edge of each of the R light emission of the first section, the IR light emission of the second section, and the dark section where no light emission of the third section is obtained by dividing the cycle T into three, and off at the falling edge. And the integral signal Sr
(R signal Sra, IR signal Srb, dark signal Src)
Is output. Other operations are the same as those of the first embodiment shown in FIGS. 1 to 5, and the advantages thereof are also the same.

In the first and second embodiments, the BPF 16
The effect of the dark section due to the offset of the amplifier used in the AM detection circuit 17 and the integrator 22 at the subsequent stage can be eliminated at the same time. Therefore, there is an advantage that the offset adjustment or the like becomes unnecessary.

[0050]

As is apparent from the above description, according to the measuring apparatus and the signal processing method of the present invention, the section of the first wavelength emission, the second wavelength emission and the non-emission are set for the measurement object every data sampling cycle. The noise level at the time of non-light emission is detected from the light reception signal at the time of repetition, and a measurement signal obtained by subtracting this noise level from the light reception signal level of the first wavelength light emission and the second wavelength light emission is obtained. Removes extraneous noise levels that affect the measurement of absorbed blood
This has the effect that an accurate measurement value can be obtained.

Further, in the above-described apparatus and method according to the present invention, in the above-mentioned first and second data sampling cycles, the first and second data sampling periods may be selected.
The received light signal level and the non-emission noise level of each of the wavelength emission and the second wavelength emission are stored, and in the stored data, the non-emission noise levels in a plurality of data sampling periods are approximated. It is determined whether or not the noise level of the non-emission is approximated ,
If the non-light emission noise level is subtracted from the respective light reception signal levels of the first wavelength light emission and the second wavelength light emission to output the first wavelength light emission and the second wavelength light emission measurement signals, the signal can be removed. Since the noise is removed only when the noise is excessive, there is an effect that a more accurate measurement value can be obtained.

Further, in the above apparatus and method, when it is determined that the noise level of the non-light emission in a plurality of data sampling periods in the stored data is not approximate, it is notified that the external noise cannot be removed. The operator can know that extraneous noise cannot be removed, stop measuring at that location, move to another location,
This makes it possible to effectively deal with noise such as turning off the power of the noise generating device at that location, and has the effect that accurate measurement can be performed thereafter.

[Brief description of the drawings]

1 is a block diagram showing a part circuit configuration of a first embodiment of a pulse oximeter of the present invention.

FIG. 2 is a timing chart showing a processing signal waveform of each unit in the operation of the first embodiment and a timing.

FIG. 3 is a timing chart showing a processing signal waveform of each unit and a timing of the processing when noise is present in the operation of the first embodiment.

FIG. 4 is a flowchart illustrating a processing procedure when noise is present in the first embodiment.

FIG. 5 shows a processed signal waveform in the operation of the second embodiment,
It is a timing chart showing the timing.

FIG. 6 is a flowchart showing a processing procedure in the operation of the second embodiment.

FIG. 7 is a block diagram partially showing a configuration of a third embodiment;

FIG. 8 is a block diagram partially showing a configuration of a conventional pulse oximeter by a circuit.

FIG. 9 is a processing waveform of an operation of a conventional example and a timing chart thereof.

[Explanation of symbols]

 12a, 12b Light-emitting diode 13 Control circuit 13a CPU 13b RAM 13d External input control unit 14 Light-receiving diode 15 Current / voltage conversion amplifier circuit 16 BPF 17 AM detection circuit 22 Integrator 24 Display unit 25 Operation switch unit 26 Speaker 27 Synthesized voice circuit 28 Light emitting diode

Claims (18)

(57) [Claims] 1. An oxygen saturation measuring apparatus for measuring arterial blood oxygen saturation, comprising: a light emitting unit that repeats first-wavelength emission, second-wavelength emission, and non-emission for a measurement target every data sampling cycle; light receiving means for outputting a light reception signal corresponding to the light receiving light from the object, the first wavelength emitted from the light-receiving signal, the second wavelength emission and
Integrating the light emission signals of each of the non-light-emitting portions to obtain the first wavelength
The emission signal levels of the emission and the second wavelength emission, and
A level detecting means including an integrating circuit for obtaining a non-light emission noise level; and a first wavelength emission and a second wavelength emission by subtracting the non-light emission noise level from the light reception signal levels of the first wavelength emission and the second wavelength emission, respectively. Signal generation means for generating a measurement signal for each wavelength emission, and the noise level detected by the level detection means
Judgment to judge whether the fluctuation is within the specified level fluctuation tolerance
Means for measuring oxygen saturation. 2. An oxygen saturation measuring apparatus for measuring arterial blood oxygen saturation, comprising: a light emitting unit that repeats first-wavelength emission, second-wavelength emission, and non-emission for a measurement target every data sampling cycle; Light receiving means for receiving light from a target and outputting a light reception signal corresponding to the light; detecting a light reception signal level of each of the first wavelength light emission and the second wavelength light emission and the non-light emission noise level from the light reception signal; Level detection means, and signal generation for generating a measurement signal for each of the first wavelength emission and the second wavelength emission by subtracting the non-emission noise level from the light reception signal level of each of the first wavelength emission and the second wavelength emission. Means for storing the light receiving signal level and the non-light emitting noise level of each of the first wavelength emission and the second wavelength emission in a plurality of data sampling periods. Storage means; and determination means for determining whether or not the non-light emission noise levels in a plurality of data sampling periods in the data stored in the storage means are similar, wherein the determination means When it is determined that the light emission noise level is similar, the signal generation means subtracts the non-light emission noise level from the light reception signal level of each of the first wavelength light emission and the second wavelength light emission to generate the first wavelength light emission. An oxygen saturation measuring device configured to output a measurement signal of the second wavelength emission. 3. The level detection means integrates the light receiving signals of the first wavelength emission, the second wavelength emission, and the non-light emission, and calculates the level of the light reception signals of the first wavelength emission and the second wavelength emission, respectively. 3. The oxygen saturation measuring apparatus according to claim 2, further comprising an integrating circuit for calculating a non-light emission noise level. 4. When the determining means determines that the noise level of the non-light emission in a plurality of data sampling periods in the data stored in the storing means is not approximate, it is notified that external noise cannot be removed. The oxygen saturation measuring device according to claim 2 or 3, further comprising an informing means for performing the measurement. 5. The oxygen saturation according to claim 1, further comprising first control means for controlling a start time of charging and discharging of the integration circuit in synchronization with the data sampling cycle. measuring device. Wherein said determining means, according to any one of claims 2 to 5, characterized in that determining, based on the maximum and minimum levels of the noise level stored in said storage means and said non-emission Oxygen saturation measurement device. 7. The method of claim 2, characterized in that it comprises a second control means for performing on the basis of erasing of the light receiving signal level storage means for storing and the noise level to a predetermined condition
7. The oxygen saturation measuring device according to any one of claims 6 to 6. 8. The determination means obtains a difference between a maximum level and a minimum level among the non-light emission noise levels stored in the storage means, and makes a determination based on a comparison between the difference and a predetermined threshold. The oxygen saturation measuring device according to claim 6, wherein: 9. The method according to claim 8, wherein the determining unit is configured to change the noise level.
Is not within the specified level fluctuation tolerance
Notification means for notifying that external noise cannot be removed,
The oxygen saturation measuring apparatus according to claim 1, further comprising: 10. A signal processing method for measuring arterial blood oxygen saturation, wherein a first wavelength light emission, a second wavelength light emission and a non-light emission are repeatedly performed on a measurement target every data sampling cycle, and light from the measurement target is emitted. receiving and obtaining a light receiving signal corresponding to the light, the first wavelength emitted from the light receiving signal, and detecting the received light signal level and noise level of the non-emission of the respective second wavelength emission, variations in the noise level is predetermined Is within the level fluctuation tolerance
A signal processing method characterized by determining 11. A signal processing method for measuring arterial blood oxygen saturation, wherein a first wavelength emission, a second wavelength emission, and a non-emission are repeatedly performed on a measurement target every data sampling cycle, and light from the measurement target is emitted. Receiving the received light signal corresponding to the received light; detecting the received light signal level of the first wavelength emission and the second wavelength emission and the noise level of the non-emission from the received light signal; Generating a measurement signal for each of the first wavelength emission and the second wavelength emission by subtracting the noise level in the non-light emission from the light reception signal level for each wavelength emission; Storing the light reception signal level and the non-light emission noise level of each of the first wavelength emission and the second wavelength emission in a data sampling cycle; In the data obtained, it is determined whether or not the noise level of the non-light emission in a plurality of data sampling periods is similar. When it is determined that the noise level of the non-light emission is similar, the first wavelength A signal processing method comprising: subtracting the non-light emission noise level from each of the light reception signal levels of light emission and second wavelength light emission to output measurement signals of first wavelength light emission and second wavelength light emission. 12. In the step of detecting the light receiving signal level and the noise level, the light receiving signals of the first wavelength emission, the second wavelength emission, and the non-light emission are integrated to integrate the first wavelength emission and the second wavelength emission. 12. The signal processing method according to claim 11, wherein each of the light receiving signal level and the non-light emitting noise level is obtained. 13. When the non-light emission noise level in a plurality of data sampling periods in the stored data is determined not to be approximated, notification of the inability to remove extraneous noise is provided. Item 11. The signal processing method according to Item 11 or 12 . 14. The method according to claim 1 , further comprising a first control step of controlling a timing of starting integration and clearing an integration value in synchronization with the data sampling cycle.
14. The signal processing method according to 0, 12, or 13. 15. The judgment is stored signal processing method according to any one of claims 11 to 13, characterized in that based on the maximum and minimum levels of the noise level of the non-emission. 16. The method according to claim 10 , further comprising the step of erasing the stored light receiving signal level and the noise level based on predetermined conditions.
6. The signal processing method according to any one of 5. 17. The method according to claim 1, wherein the determination is made based on a difference between a maximum level and a minimum level of the stored non-light emission noise levels, and comparing the difference with a predetermined threshold. The signal processing method according to claim 15, wherein 18. The method as claimed in claim 18 , wherein in said determining,
If it is determined that the fluctuation is not within the specified level fluctuation tolerance
Feature to notify that external noise cannot be removed
The signal processing method according to claim 10 .