JP2019122552A - Biological signal processing device and control method of the same - Google Patents

Abstract

To provide a biological signal processing device and its control method capable of determining a pulse rate from a pulse wave signal by a method hardly affected by noise while reducing an arithmetic amount.SOLUTION: A pulse rate is obtained on the basis of a frequency spectrum of a pulse wave signal. An arithmetic amount is reduced by calculating the frequency spectrum for a range of a frequency determined on the basis of a reference value when calculating the frequency spectrum. The reference value may be determined, for example, on the basis of the pulse rate obtained in the past.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a biological signal processing apparatus and a control method thereof, and more particularly to a technology for obtaining a pulse rate from a pulse wave signal.

  The pulse wave signal is a biological signal containing various information on the heart and blood vessels, and is widely used because it is easy to measure. The pulse wave signal can be measured by various methods, but the change in the internal pressure of the air bag in the cuff is measured as a pulse wave signal, or the change in the amount of transmitted or reflected human tissue is measured as a pulse wave signal. The method is known.

  Further, as a method of obtaining a pulse rate from a pulse wave signal, a method based on a feature point of the pulse wave signal and a method based on a frequency spectrum of the pulse wave signal are known. The former is a method in which feature points (for example, peak and bottom) of pulse wave signals are detected, time t between adjacent feature points is obtained, and pulse rate = 60 / t (times / minute (bpm). The latter method is a method of selecting a frequency due to pulsation from a frequency spectrum obtained by frequency analysis of a pulse wave signal, and converting it into a pulse rate with 1 Hz as 60 bpm (Patent Document 1).

Patent No. 5655721 gazette

  Although the method based on the feature point is simple, when noise is mixed in the pulse wave signal due to a body movement or the like, the detection accuracy of the feature point tends to decrease. Therefore, there is a problem that the accuracy of the pulse rate is susceptible to noise. On the other hand, although the method based on the frequency spectrum is less susceptible to noise, the amount of operation for obtaining the frequency spectrum is large. Therefore, for example, in applications where it is necessary to update the pulse rate every second, it is necessary to use a processor with a large processing capacity or a memory with a large capacity, which causes factors such as an increase in power consumption and manufacturing cost, and an increase in equipment size. .

  The present invention has been made in view of such problems of the prior art. An object of the present invention is to provide a biological signal processing apparatus capable of obtaining a pulse rate from a pulse wave signal in a method less susceptible to noise while reducing the amount of calculation, and a control method thereof.

  The above object has signal processing means for obtaining a frequency spectrum of a pulse wave signal, and first obtaining means for obtaining a pulse rate based on the frequency spectrum, and the signal processing means has a frequency determined based on a reference value The present invention is achieved by a biological signal processing apparatus characterized by determining a frequency spectrum for the range of.

  With such a configuration, according to the present invention, there is provided a biological signal processing apparatus capable of obtaining a pulse rate from a pulse wave signal by a method less susceptible to noise while reducing the amount of calculation, and a control method thereof. Can.

It is a block diagram showing an example of functional composition of an arterial blood oxygen saturation measuring device as an example of a living body signal processing device concerning an embodiment of the present invention. It is a flowchart for demonstrating the determination operation | movement of the noise mixing presence or absence which concerns on embodiment. It is a figure which shows the example of the pulse wave signal at the time of rest, and a frequency spectrum. It is a figure which shows the example of the pulse-wave signal and the frequency spectrum which the body movement noise mixed.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Here, an arterial blood oxygen saturation (SpO ₂ ) measurement apparatus will be described as an example of the biological signal processing apparatus according to the present invention. However, the present invention is applicable to any electronic device capable of acquiring a pulse wave signal. Such electronic devices include not only medical devices such as a biological information monitor, a sleep evaluation device (polygraph), a sphygmomanometer, and a sphygmograph, but also general computer devices (smartphones and tablets) capable of executing biological signal processing applications Terminals, media players, smart watches, game consoles, etc.), but is not limited thereto.

FIG. 1 is a block diagram showing an example of a functional configuration of an SpO ₂ measurement apparatus according to an embodiment of the present invention.
The sensor unit 100 includes a first light emitting unit 101 that emits light of a first wavelength, a second light emitting unit 102 that emits light of a second wavelength, and a light receiving unit 103 that outputs an electrical signal according to the amount of light received. Have. The light receiving unit 103 is disposed to receive transmitted light or reflected light of the light emitted from the first light emitting unit 101 and the light emitted from the second light emitting unit 102.

As the first and second light emitting units 101 and 102, an LED emitting red light and infrared light is generally used in the SpO ₂ measuring device. However, the wavelengths and types of light sources are not limited to these, and assuming that the absorbance of oxygenated hemoglobin at wavelengths λ1 and λ2 is a1 _λ1 and a1 _λ2 , and the absorbance of reduced hemoglobin is a2 _λ1 and a2 _λ2 , a1 _λ1 and a1 _λ2 , Any light source can be used that generates light of any wavelength _λ1 and _λ2 where a2 _λ1 and a2 _λ2 are significantly different. In this embodiment, as an example, an LED that generates red light with a wavelength of 660 nm in the first light emitting unit 101 is used, and an LED that generates infrared light with a wavelength of 900 nm in the second light emitting unit 102 is used.

  In the case of the configuration for detecting the amount of transmitted light, the light receiving unit 103 is disposed at a position facing the first and second light emitting units 101 and 102 with the measurement site (such as an earwax or a finger tip) interposed therebetween. Further, in the case of a configuration in which the amount of reflected light is detected, the first light emitting unit 101, the light receiving unit 103, and the second light emitting unit 102 are disposed in proximity to each other. The first and second light emitting units 101 and 102 are disposed close to each other regardless of whether the transmitted light amount is detected or the reflected light amount is detected, and the light receiving unit 103 is similar to that from the first and second light emitting units. It is arranged to receive transmitted light or reflected light under conditions (for example, distance or angle).

  The light receiving unit 103 receives transmitted light or reflected light of the light emitted from the first light emitting unit 101 and the second light emitting unit 102, and outputs an electrical signal according to the amount of light received. The light receiving unit 103 may be a light receiving sensor, for example, a photodiode or a phototransistor, whose sensitivity is the wavelength of transmitted light or reflected light to be detected. The light receiving unit 103 detects the first and second pulse wave signals as a change in the amount of light transmitted or the amount of light reflected by the measurement site for the light of the first and second wavelengths.

Control unit 110, for example a programmable processor, a nonvolatile memory (ROM), and volatile a memory (RAM), a program stored in the ROM and controls each unit by executing read into RAM, SpO ₂ measurement device To realize the function of Note that at least part of the operation of the control unit 110 may be realized by a hardware circuit such as a programmable logic array.

  The driving unit 120 drives the first and second light emitting units 101 and 102 in accordance with the light emission amount and the light emission timing according to an instruction of the control unit 110. The control unit 110 emits light so that the first light emitting unit 101 and the second light emitting unit alternately emit light for a predetermined time, in order to detect the transmitted light amount or the reflected light amount for two wavelengths using one light receiving unit 103. Control the timing.

  The signal processing unit 130 applies signal processing such as amplification and A / D conversion to the signal output from the light receiving unit 103, and outputs the signal as a pulse wave signal to the control unit 110. The signal processing unit 130 outputs an output signal of the light receiving unit 130 according to the light emission timing of the first light emitting unit 101 and the second light emitting unit 102, and a first pulse wave indicating the transmitted or reflected light quantity of the light emitted by the first light emitting unit 101. It outputs as a 2nd pulse-wave signal which shows the permeation | transmission or reflected light quantity of the signal and the light which the 2nd light emission part 101 emitted.

  In addition, since the first light emitting unit 101 and the second light emitting unit 102 do not simultaneously emit light, strictly, the acquisition timings of the first pulse wave signal and the second pulse wave signal are different. However, by making the light emission frequency of the light emitting unit 101 and the second light emitting unit 102 sufficiently higher than the frequency component of the pulse wave, the first pulse wave signal and the second pulse wave signal are sampled as measurement value groups sampled at the same timing. It can be handled. Therefore, in the following description, it is assumed that the first pulse wave signal and the second pulse wave signal are acquired at the same timing.

The control unit 110 records the first and second pulse wave signals in the recording unit 140. The recording unit 140 is, for example, a non-volatile memory, and may be a removable recording medium such as a memory card.
The display unit 150 is, for example, a liquid crystal display, and displays the SpO ₂ measurement value, the operating state of the SpO ₂ measurement apparatus, the setting menu screen, and the like under the control of the control unit 110.

The operation unit 160 includes a button, a switch, a key, and the like for the user to input an instruction to the SpO ₂ measurement apparatus. When the display unit 150 is a touch display, the touch panel portion is included in the operation unit 160.
An external interface (I / F) 170 is a communication interface for communicating with an external device in a wired or wireless manner.

SpO ₂ measurement device using, for example, law Lambert-Beer, a molar extinction coefficient of hemoglobin in blood (reduced and oxidized hemoglobin hemoglobin), the SpO ₂ from the amount of transmitted light of two wavelengths having different absorption by hemoglobin It can be measured. In addition, since the measuring method of SpO ₂ based on these parameters is known, the description about the detail is abbreviate | omitted.

  Next, the method of measuring the pulse rate according to the present invention will be described with reference to the flowchart of FIG. The present invention can be implemented for at least one of the first pulse wave signal and the second pulse wave signal.

  At S101, the control unit 110 acquires pulse wave signal data. The control unit 110 may acquire pulse wave signal data recorded in the recording unit 140, or may acquire pulse wave signal data from an external device through the external I / F 170. Alternatively, pulse wave signal data supplied from the signal processing unit 130 may be used. There is no particular limitation on the acquisition source of pulse wave signal data. The control unit 110 can use a part of the internal RAM as a buffer for accumulating pulse wave signal data for the latest predetermined time, and apply the pulse rate measurement process to pulse wave signal data in the buffer. .

  In the present embodiment, measurement of the pulse rate based on the distance of the feature point of the pulse wave is also performed, so that pulse wave signal data for at least two beats is included in the buffer. In addition, frequency analysis requires pulse wave signal data for a time that is twice the reciprocal of the frequency. In this embodiment, as an example, pulse wave signal data for the last 10 seconds is stored in the RAM. The resolution can be increased as the pulse wave data stored in the buffer becomes longer, but the appropriate time is determined according to the device specifications (range of measurable pulse rate) and the memory capacity of the device. be able to.

  The sampling frequency of pulse wave signal data to which frequency analysis is applied may be lower than the sampling frequency for generating pulse wave signal data for recording. For example, when the upper limit of the pulse wave is up to 300 bpm, the upper limit of the frequency band of the pulse wave is 5 Hz. Therefore, a sampling frequency of about 20 to 30 Hz is sufficient. On the other hand, since pulse wave signal data for recording is often set to a sampling frequency of about 100 to 300 Hz, the control unit 110 downsamples pulse wave signal data as needed and accumulates it in the RAM.

  At S103, the control unit 110 starts the process of measuring the pulse rate based on the feature points of the pulse wave signal. The control unit 110 detects a predetermined feature point (for example, peak or bottom) from the pulse wave signal, and obtains the cycle of one beat based on the distance (the number of samples) between adjacent feature points and the sampling cycle. . Then, the control unit 110 obtains a pulse rate (times / minute or bpm) by dividing 60 seconds by a cycle of one beat. The control unit 110 obtains the pulse rate for each beat based on the two most recent feature points.

  In step S105, the control unit 110 determines the range of frequencies for which a frequency spectrum is to be obtained by frequency analysis. In the present embodiment, the operation load of frequency analysis is reduced by limiting the range of the frequency for which the frequency spectrum is to be obtained to a specific range based on the pulse rate reference value. In the present embodiment, the initial value of the reference value is set to the pulse rate measured based on the feature point started in S103. In addition, when using the pulse rate measured based on the feature point of the pulse wave signal as a reference value at the time of determining the range of the frequency which calculates | requires a frequency spectrum, it has not received the influence of the noise generate | occur | produced by body movement etc. Use a pulse rate that is considered to be highly sexual.

  For example, the control unit 110 calculates the variation of the pulse rate measured on the basis of the feature points in a predetermined number of the most recent times, and uses the average value as a reference value when the variation is less than a predetermined threshold. Can. In addition, this is only an example of the method for evaluating the reliability of the pulse rate measured based on the feature point, You may evaluate reliability by another method. If the reliability of the pulse rate measured based on the feature points is low and the initial value can not be determined, a predetermined pulse rate may be used as the initial value of the reference value. Also, the resolution of the frequency analysis and the number of significant digits of the reference value are determined to meet the accuracy required for the pulse rate. For example, if it is necessary to determine the pulse rate with an accuracy of 1 bpm, the resolution of frequency analysis is made finer than the frequency equivalent to 1 bpm. Also, the number of significant digits of the reference value should be smaller than 1 bpm.

  There is no particular limitation on the method of determining the frequency range based on the pulse rate reference value as long as the frequency range for which the frequency spectrum is to be obtained can be limited. Here, as an example, a range of frequencies corresponding to a pulse rate in a predetermined range centering on a reference value of pulse rates is determined as a range of frequencies for which a frequency spectrum is to be obtained. For example, the range of frequencies corresponding to the reference value ± 8 bpm can be determined as the range of frequencies for which the frequency spectrum is to be determined.

  At S107, the control unit 110 performs frequency analysis on the pulse wave signal data stored in the RAM in the frequency range determined at S105. As long as it is possible to define the range of the frequency of interest, frequency analysis can be performed by any method. Here, wavelet transformation is used as an example, but other methods such as Fourier transformation may be used.

  In step S109, the control unit 110 determines whether a peak exists in the frequency spectrum obtained by the frequency analysis. If it is determined that the peak exists, the process proceeds to step S111. If not determined, the process proceeds to step S117. The determination of the presence or absence of the peak can be performed by any known method.

  When the power of the frequency spectrum is maximized at the upper limit or the lower limit of the frequency range subjected to the frequency analysis, the range of the frequency analysis may be expanded to determine whether it is a peak. For example, when the power of the frequency spectrum is maximized at the upper end of the frequency range, the frequency analysis may be performed to the range of the pulse rate one pulse more than the present. In practice, when the power of the frequency spectrum is maximized at the upper limit or the lower limit of the frequency-analyzed frequency range, the control unit 110 returns the process to S107 and adds a frequency analysis for higher (or lower) frequencies And run. Then, the control unit 110 again determines the presence or absence of a peak in S109.

  At S111, the control unit 110 determines the pulse rate based on the peak of the frequency spectrum. Specifically, control unit 110 determines the pulse rate corresponding to the peak of the frequency spectrum as the current pulse rate measurement value.

  At S113, the control unit 110 updates the reference value with the pulse rate determined at S111. Thus, with the latest pulse rate as a reference value, the frequency range to which the frequency analysis is applied next is updated.

  In S115, the control unit 110 determines whether the measurement termination condition is satisfied, and if it is determined that the measurement completion condition is satisfied, the measurement processing is ended, and if it is not determined that the measurement completion condition is satisfied, the process returns to S105. The measurement end condition may be, for example, detection of an end instruction input from the operation unit 160, completion of measurement up to the end of pulse wave signal data, and the like, but is not limited thereto.

  On the other hand, if no peak is detected in the frequency spectrum at S109, the pulse rate can not be determined based on the frequency spectrum. In this case, in step S117, the control unit 110 determines whether a highly reliable measurement value is obtained in the process of measuring the pulse rate based on the feature points, which is being executed in parallel. For example, the control unit 110 can determine that the reliability of the pulse rate measured based on the feature point is high if the variation of the latest plurality of measurement values is less than a predetermined threshold. However, the reliability may be evaluated by other methods.

  If it is determined that the reliability of the pulse rate measured based on the feature point is high, the control unit 110 updates the reference value with the pulse rate measured based on the feature point in S119, and advances the process to S115. On the other hand, when it is not determined that the reliability of the pulse rate measured based on the feature point is high, the control unit 110 advances the process to S115 without updating the reference value.

  A peak can not be detected in the frequency spectrum not only when the actual pulse rate deviates from the pulse rate range corresponding to the frequency analysis range. In frequency analysis, since the frequency spectrum of discrete frequencies corresponding to the resolution is obtained, it may happen that the peak is not found if the resolution is coarse. Also, due to the influence of noise, a clear peak may not be found even when the difference between the noise peak and the pulse rate peak becomes smaller.

  If no peak is found due to the influence of noise, the variation in the pulse rate measured based on the feature points also increases, and the reliability decreases. Therefore, when it is not determined in S117 that the reliability of the pulse rate measured based on the feature point is high, the reference value is not updated even if no peak is found in the frequency spectrum.

  On the other hand, when it is determined in S117 that the reliability of the pulse rate measured based on the feature points is high, there may be a case where the actual pulse rate deviates from the range of pulse rates corresponding to the frequency analysis range. Therefore, in step S119, the control unit 110 resets the reference value based on the pulse rate measured based on the feature point (re-evaluates the reference value).

  Although the peak found in S109 may be a noise peak, since the frequency analysis range is limited to the range based on the reference value, the actual pulse rate peak is also included in the frequency analysis range. It is likely to have been. Even if the pulse rate is determined based on the noise peak, the difference with the actual pulse rate is likely to be small, so in this embodiment, the pulse rate is determined based on the peak found in S109.

  FIG. 3A shows an example of a pulse wave signal at rest. Moreover, FIG.3 (b) and (c) have shown the frequency spectrum of the pulse wave signal shown to FIG. 3 (a). For the sake of convenience, FIG. 3B shows a frequency spectrum of a range of frequencies corresponding to the entire range of pulse rates (20 to 300 bpm) which can be measured by the biological signal processing apparatus. Further, FIG. 3C shows a frequency spectrum obtained by limiting the frequency range corresponding to the reference value (here, 65 bpm) ± 9 bpm by the method of the present embodiment.

  In the examples shown in FIGS. 3 (b) and 3 (c), 66 bpm (a frequency corresponding to that) is detected as the peak of the frequency spectrum. For example, in the case of obtaining a frequency spectrum by wavelet transform, it is necessary to calculate the frequency range, the resolution, and an amount proportional to the reciprocal of the frequency. Therefore, the calculation amount can be reduced to about 1/10 by targeting the range of 65 ± 9 bpm, compared with the case of targeting the range of 20-300 bpm.

  FIG. 4A shows an example of a pulse wave signal on which noise due to body movement is superimposed. About this pulse wave signal, the frequency spectrum calculated | required similarly to FIG. 3 is shown in FIG.4 (b) and (c). In the case of a pulse wave signal as shown in FIG. 4 (a), the pulse rate measured based on the feature points largely varies in value due to the influence of noise, and the reliability becomes low. On the other hand, a peak appears at 63 bpm in the frequency spectrum, and the pulse rate can be measured correctly.

  When noise is superimposed, as shown in FIG. 4B, a noise peak also appears in the frequency spectrum (a peak near 100 bpm). Therefore, when the noise peak is large, it may happen that the measurement value of the pulse rate largely fluctuates due to the false detection of the peak. On the other hand, in the present embodiment, since the range for obtaining the frequency spectrum is limited, as shown in FIG. 4C, the frequency spectrum does not include the noise peak. In other words, by limiting the range for obtaining the frequency spectrum, not only the amount of computation can be reduced, but also the effect of noise at frequencies outside the range of frequency analysis can be eliminated.

  As described above, according to the present embodiment, in the biological information processing apparatus for obtaining the pulse rate based on the frequency spectrum of the pulse wave signal, the frequency range for obtaining the frequency spectrum is limited to the range based on the reference value. I made it. Therefore, the calculation load can be significantly reduced compared to the case of obtaining the frequency spectrum for a wide range of frequencies.

(Other embodiments)
In the above embodiment, the configuration has been described in which the initial value of the reference value (including the initial value after the review process) is determined using the pulse rate measured based on the feature points of the pulse wave signal. However, the pulse rate or heart rate determined by other methods may be used.

  The biological signal processing apparatus according to the present invention can also be realized as a program (application software) that causes a general-purpose information processing apparatus, such as a personal computer, which is generally available, to execute the above-described operation. Therefore, such a program and a recording medium storing the program (an optical recording medium such as a CD-ROM or a DVD-ROM, a magnetic recording medium such as a magnetic disk, a semiconductor memory card, etc.) also constitute the present invention. .

100 ... sensor, 101 ... first light emitting unit, 102 ... second light emitting unit, 103 ... first light receiving unit, 110 ... control unit, 120 ... driving unit, 130 ... signal processing unit

Claims (12)

Signal processing means for determining the frequency spectrum of the pulse wave signal;
And d) first acquisition means for determining a pulse rate based on the frequency spectrum.
The biological signal processing apparatus, wherein the signal processing means determines a frequency spectrum for a range of frequencies determined based on a reference value.   The biological signal processing apparatus according to claim 1, wherein the range of the frequency is a range having a specific magnitude centered on the reference value.   The biological signal processing apparatus according to claim 1, wherein the reference value is based on a pulse rate obtained in the past.   The biological signal processing apparatus according to claim 3, wherein the reference value is based on a pulse rate obtained by means different from the first acquisition means.   The biological signal processing apparatus according to any one of claims 1 to 4, further comprising update means for updating the reference value.   The biological signal processing apparatus according to claim 5, wherein the updating unit updates the reference value by the pulse rate obtained by the first acquisition unit. The image processing apparatus further includes a second acquisition unit that obtains a pulse rate based on a distance between feature points of the pulse wave signal.
The updating means updates the reference value based on the pulse rate obtained by the second obtaining means when the pulse rate is not obtained by the first obtaining means.
The biological signal processing apparatus according to claim 5 or 6, characterized in that   When it is determined that the reliability of the pulse rate obtained by the second acquisition unit is low, the update unit may perform the reference value even if the pulse rate is not calculated by the first acquisition unit. The biological signal processing apparatus according to claim 7, wherein:   The biological signal processing apparatus according to any one of claims 1 to 8, wherein the pulse rate is sequentially obtained in parallel with the measurement of the pulse wave signal.   The biological signal processing apparatus according to any one of claims 1 to 9, wherein the pulse wave signal is a pulse wave signal measured to measure blood oxygen saturation. A biological signal processing method performed by a biological signal processing apparatus, comprising:
A signal processing step of obtaining a frequency spectrum of the pulse wave signal;
And d) obtaining a pulse rate based on the frequency spectrum.
In the signal processing step, a frequency spectrum for a specific frequency range determined based on a reference value is determined.   A program for causing a computer to function as each means of the biological signal processing apparatus according to any one of claims 1 to 10.

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