JP6102055B2 - Pulse wave measuring device and signal processing device - Google Patents

Description

  The present invention relates to a technique for measuring a pulse wave of a living body.

  A technique for measuring the pulse of a living body using light is known. For example, Patent Document 1 describes a signal processing method for separating a pulse wave signal and an artifact signal from two measurement signals extracted from the same medium in a pulse photometer.

JP 2009-261458 A

It is known that when a living body is irradiated with light, the depth at which the light reaches differs depending on the wavelength. For example, when the pulse group is measured using light of two wavelengths, the wavelengths are different, and therefore a difference occurs in the depth reached by the lights. Thus, when there is a difference in the depth of light arrival, in two signals observed by these lights, a signal component not included in the other signal is superimposed on one signal. In this case, the correlation between the two signals becomes low, which may adversely affect signal separation as described in Patent Document 1, for example.
An object of the present invention is to reduce an error caused by irradiating a part having a different depth in a living body when measuring a pulse group using a plurality of lights.

  The pulse wave assumption device according to the present invention includes a first irradiation unit that irradiates a first part in a living body with a first light, and a second part deeper than the first part in the living body. A second irradiating unit that irradiates the second light, and a first light receiving unit that receives the first light reflected by the first part and converts the received first light into a first signal. A second light receiving unit that receives the second light reflected by the second part and converts the received second light into a second signal; and the first signal from the second signal. And a removal unit that removes a signal component having a correlation lower than a threshold value and outputs a second signal from which the signal component has been removed. According to this configuration, in the case of measuring a pulse group using a plurality of lights, it is possible to reduce errors caused by irradiating the parts with different depths in the living body.

  The removing unit may remove the signal component using an adaptive filter. According to this configuration, the error described above can be reduced with a simple configuration.

  The pulse wave measurement device separates a pulsation component and a noise component indicating the pulse of the living body from the first signal converted by the first light receiving unit and the second signal output from the removal unit. A separation unit may be provided. According to this structure, the precision which isolate | separates a pulsation component and a noise component can be improved.

  The second light may have a wavelength larger than that of the first light. According to this configuration, in a configuration in which a pulse wave is measured using two-wavelength light, errors caused by irradiating the portions with different depths in the living body can be reduced.

  The distance between the second irradiating unit and the second light receiving unit may be greater than the distance between the first irradiating unit and the first light receiving unit. According to this configuration, in the configuration in which the pulse group is measured using a plurality of lights having one wavelength, it is possible to reduce errors caused by irradiating portions of the living body with different depths.

  In the signal processing device according to the present invention, the first light is applied to the first part in the living body by the first irradiation unit, and is reflected at the first part by the first light receiving unit. Is converted into a first signal, the second irradiation unit irradiates the second part deeper than the first part in the living body with the second light, and the second light receiving unit applies the second light. When the second light reflected by the part is converted into a second signal, a signal component whose correlation with the first signal is lower than a threshold is removed from the second signal, and the signal component is removed. And a removing unit that outputs the second signal. According to this configuration, in the case of measuring a pulse group using a plurality of lights, it is possible to reduce errors caused by irradiating the parts with different depths in the living body.

Diagram showing the appearance of the pulse wave measurement device Block diagram showing the configuration of the pulse wave measurement device Diagram showing the penetration of light into a living body Diagram showing the path of green light and red light in the living body Block diagram showing functional configuration of CPU Conceptual diagram of adaptive filter The figure which shows the signal observation model of G signal and R signal The figure which shows the path | route of the green light in the biological body which concerns on a modification

  FIG. 1 is a diagram illustrating an appearance of a pulse wave measuring apparatus 1 according to the present embodiment. The pulse wave measuring device 1 is attached to a human hand 2. The pulse wave measuring device 1 includes a device main body 3 (an example of a signal processing device) that is worn on a human wrist and a pulse wave sensor 4. The apparatus main body 3 and the pulse wave sensor 4 are connected via a cable 5. The pulse wave sensor 4 is fixed to the palm side of the base of the index finger by a band 6 as shown in FIG.

  FIG. 2 is a block diagram showing the configuration of the pulse wave measuring device 1. The pulse wave measuring device 1 measures a pulse wave using light of two wavelengths. The apparatus body 3 includes a CPU (Central Processing Unit) 11, a ROM (Read Only Memory) 12, a RAM (Random Access Memory) 13, a display unit 14, an operation unit 15, an oscillation circuit 16, and a clock circuit 17. A first filter unit 21a and a second filter unit 21b, a first amplifier circuit 22a and a second amplifier circuit 22b, a first A / D converter 23a and a second A / D converter 23b. The pulse wave sensor 4 includes a drive circuit 18, a first light emitting unit 19a (an example of a first irradiation unit), a second light emitting unit 19b (an example of a second irradiation unit), and a first light receiving unit 20a. And a second light receiving unit 20b.

  The CPU 11 controls each part of the pulse wave measuring device 1 by executing a control program. The ROM 12 is a read-only nonvolatile memory. For example, a basic system program executed by the CPU 11 is stored in the ROM 12. The RAM 13 is a volatile memory used as a work area for the CPU 11. In the RAM 13, for example, various data generated during execution of the control program by the CPU 11 are temporarily stored. The display unit 14 is a liquid crystal display, for example. The display unit 14 displays various information related to pulse wave measurement results and pulse wave measurement under the control of the CPU 11. The operation unit 15 includes a plurality of operation buttons used for operating the pulse wave measuring device 1, for example. The operation unit 15 supplies an operation signal corresponding to a user operation to the CPU 11. The oscillation circuit 16 supplies a clock signal to the CPU 11. The timer circuit 17 measures time under the control of the CPU 11.

  The drive circuit 18 drives the first light emitting unit 19a and the second light emitting unit 19b. For example, when an operation for instructing start of pulse wave measurement is performed using the operation unit 15, the drive circuit 18 alternately drives the first light emitting unit 19 a and the second light emitting unit 19 b. The first light emitting unit 19a includes a light emitting element that emits green light Lg (an example of first light). The peak wavelength of the green light Lg is 525 nm. The second light emitting unit 19b includes a light emitting element that emits red light Lr (an example of second light). The peak wavelength of the red light Lr is 620 nm. The peak wavelength of the red light Lr is larger than the peak wavelength of the green light Lg. When the first light emitting unit 19 a and the second light emitting unit 19 b are driven by the drive circuit 18, the first light emitting unit 19 a and the second light emitting unit 19 b irradiate the measurement site in the living body with light.

  FIG. 3 is a diagram showing the degree of penetration of light into a living body. The vertical axis | shaft shown in FIG. 3 shows the peak wavelength [nm] of light. The horizontal axis shown in FIG. 3 indicates the degree of light penetration into the living body. This penetrance refers to the depth at which light reaches in vivo. This depth refers to the distance from the surface of the living body. As shown in FIG. 3, the penetration degree of light into the living body varies depending on the wavelength. For example, the peak wavelength of the green light Lg is 525 nm, and the peak wavelength of the red light Lr is 620 nm. In this case, the penetration degree of the red light Lr is larger than the penetration degree of the green light Lg.

  FIG. 4 is a diagram illustrating paths of the green light Lg and the red light Lr in the living body. FIG. 4 shows a cross section of the living body skin. The living body skin has an epidermis 31, a dermis 32 under the epidermis 31, and a subcutaneous tissue 33 under the dermis 32. In the shallow part of the dermis 32, capillaries 34 are present. In the deep part of the dermis 32, there is a fibrillation vein 35 including arterioles and venules. As described above, the penetration degree of the red light Lr is larger than the penetration degree of the green light Lg. Therefore, the red light Lr passes deeper in the living body than the green light Lg.

  Specifically, as shown in FIG. 4A, the green light Lg is irradiated to the measurement site T1 (an example of the first site) through shallow portions of the epidermis 31 and the dermis 32. On the other hand, as shown in FIG. 4B, the red light Lr passes through deep portions of the epidermis 31 and the dermis 32 and is irradiated to a measurement site T2 (an example of a second site) deeper than the measurement site T1. . In this case, the green light Lg is affected by the pulsation of the capillaries 34 existing in the shallow part of the dermis 32, whereas the red light Lr is deep in the dermis 32 in addition to the effects of the pulsations of the capillaries 34. It is also affected by the pulsation of the fibrillation vein 35 existing in the portion.

  The first light emitting unit 19a, the second light emitting unit 19b, the first light receiving unit 20a, and the second light receiving unit 20b include a distance D1 between the first light emitting unit 19a and the first light receiving unit 20a, and It arrange | positions so that the distance D2 between the 2nd light emission part 19b and the 2nd light-receiving part 20b may become equal. The green light Lg emitted from the first light emitting unit 19a is reflected by the measurement site T1 and received by the first light receiving unit 20a. When receiving the green light Lg, the first light receiving unit 20a converts the received green light Lg into a first analog signal (an example of a first signal) and outputs the first analog signal. The first analog signal includes a first signal component indicating the pulsation of the capillary vessel 34 existing in the shallow portion of the dermis 32. The red light Lr emitted from the second light emitting unit 19b is reflected by the measurement site T2 and received by the second light receiving unit 20b. When receiving the red light Lr, the second light receiving unit 20b converts the received red light Lr into a second analog signal (an example of a second signal) and outputs the second analog signal. In addition to the first signal component described above, the second analog signal includes a second signal component indicating pulsation of the fibrillation vein 35 existing in a deep portion of the dermis 32.

  The first analog signal output from the first light receiving unit 20a is input to the first filter unit 21a shown in FIG. The first filter unit 21a includes an AC (Alternating Current) filter and a DC (Direct Current) filter (both not shown). When the first analog signal is input, the AC filter removes a pulsation component (AC component) indicating pulsation from the input first analog signal and outputs a DC component of the first analog signal. When the first analog signal is input, the DC filter removes the fluctuation component (DC component) of the baseline of the pulse wave from the input first analog signal and outputs the AC component of the first analog signal. .

  The second analog signal output from the second light receiving unit 20b is input to the second filter unit 21b. Similar to the first filter unit 21a, the second filter unit 21b includes an AC filter and a DC filter (not shown). When the second analog signal is input, the AC filter removes a pulsation component (AC component) indicating pulsation from the input second analog signal and outputs a DC component of the second analog signal. When the second analog signal is input, the DC filter removes the fluctuation component (DC component) of the baseline of the pulse wave from the input second analog signal and outputs the AC component of the second analog signal. .

  The AC component of the first analog signal output from the first filter unit 21a is input to the first amplifier circuit 22a. When the AC component of the first analog signal is input, the first amplifier circuit 22a amplifies and outputs the AC component of the input first analog signal. The AC component of the second analog signal output from the second filter unit 21b is input to the second amplifier circuit 22b. When the AC component of the second analog signal is input, the second amplifier circuit 22b amplifies and outputs the AC component of the input second analog signal. The gains of the first amplifier circuit 22a and the second amplifier circuit 22b are set by the CPU 11.

  The AC component of the first analog signal output from the first amplifier circuit 22a and the DC component of the first analog signal output from the first filter unit 21a are first A / D (analog to digital). Input to the converter. The first A / D conversion unit 23a includes a first A / D conversion circuit and a second A / D conversion circuit (both not shown). When the AC component of the first analog signal is input, the first A / D conversion circuit converts the AC component of the input first analog signal from an analog signal to a digital signal and outputs the converted signal. Specifically, the first A / D conversion circuit samples and quantizes the AC component of the first analog signal at a preset sampling frequency. This sampling frequency is, for example, 100 Hz. Quantization is performed, for example, with 10 bits. When the DC component of the first analog signal is input to the second A / D conversion circuit, the DC component of the input first analog signal is converted into an analog signal in the same manner as the first A / D conversion circuit. To digital signal and output.

  The AC component of the second analog signal output from the second amplifier circuit 22b and the DC component of the second analog signal output from the second filter unit 21b are input to the second A / D conversion unit 23b. Is done. The second A / D converter 23b includes a third A / D converter circuit and a fourth A / D converter circuit (not shown). When the AC component of the second analog signal is input to the third A / D conversion circuit, the AC component of the input second analog signal is converted into an analog signal in the same manner as the first A / D conversion circuit. To digital signal and output. When the DC component of the second analog signal is input to the fourth A / D conversion circuit, the DC component of the input second analog signal is converted into an analog signal in the same manner as the first A / D conversion circuit. To digital signal and output.

  Sampling data obtained by the sampling of the first A / D conversion unit 23a and the second A / D conversion unit 23b is supplied to the CPU 11, and the gains of the first amplification circuit 22a and the second amplification circuit 22b are set. It is used as a judgment material when doing. In the following description, the AC component and the DC component of the first analog signal output from the first A / D conversion unit 23a are collectively referred to as “G signal”. Further, the AC component and the DC component of the second analog signal output from the second A / D conversion unit 23b are collectively referred to as “R signal”.

  FIG. 5 is a block diagram illustrating a functional configuration of the CPU 11. The CPU 11 includes a removal unit 41 and a separation unit 42. The G signal output from the first A / D conversion unit 23 a and the R signal output from the second A / D conversion unit 23 b are input to the removal unit 41. When the G signal and the R signal are input, the removing unit 41 removes a signal component having no correlation with the R signal from the input R signal using an adaptive filter. This “no correlation” means that the correlation with the G signal is strictly lower than the threshold value. “Removal” is a concept that includes not only completely removing uncorrelated signal components but also attenuating uncorrelated signal components.

  FIG. 6 is a conceptual diagram of the adaptive filter. The G signal output from the first A / D conversion unit 23 a is input to the delay unit 51. When the G signal is input, the delay unit 51 delays and outputs the input G signal. The G signal output from the delay unit 51 is input to the adder 52. The R signal output from the second A / D converter 23 b is input to an FIR (finite impulse response) filter 53. When an R signal is input, the FIR filter 53 performs a filtering process on the input R signal using a coefficient and outputs the filtered signal. The R signal output from the FIR filter 53 is input to the adder 52. When the G signal and the R signal are input, the adder 52 outputs a difference between the input G signal and the R signal as an error signal ε. The coefficient of the FIR filter 53 is updated using an algorithm such as an LMS (Least Mean Square) algorithm so that the expected value of the square of the error signal ε output from the adder 52 is minimized.

  As described above, the R signal includes the second signal component that is not included in the G signal. In this case, the FIR filter 53 removes the second signal component that has no correlation with the G signal from the R signal. As a result, the R signal from which the second signal component has been removed is output from the FIR filter 53. Since the R signal includes only the first signal component as in the G signal, it has a high correlation with the G signal.

  The G signal output from the first A / D conversion unit 23 a and the R signal output from the FIR filter 53 are input to the separation unit 42. When the G signal and the R signal are input, the separation unit 42 separates the pulse wave component and the body motion noise component from the input G signal and R signal. This body movement noise refers to an error caused by vibration when the body moves. When the separation unit 42 separates the pulse wave component and the body motion noise component, a pulse wave is obtained based on the pulse component.

  FIG. 7 is a diagram illustrating a signal observation model of the G signal and the R signal. In FIG. 7, p is a pulsation signal indicating pulsation at time tn, and n is a noise signal indicating noise at time tn. G is the first light receiving portion 20a, that is, the terminal for green light Lg, and R is the second light receiving portion 20b, that is, the terminal for red light Lr. The pulsation signal p is transmitted to the G terminal with the transmission coefficient 1, and is transmitted to the R terminal with the transmission coefficient φs. The noise signal n is transmitted to the G terminal with the transmission coefficient 1, and is transmitted to the R terminal with the transmission coefficient φn.

  In the signal observation model shown in FIG. 7, when the pulsation signal p and the noise signal n are mixed by the following equation (1), the G signal observed at the G terminal and the R signal observed at the R terminal are obtained. That is, in order to separate the pulsation signal p and the noise signal n, an inverse matrix operation represented by the following equation (2) may be performed. The inverse matrix in Equation (2) is a separation matrix.

  In order to separate the pulsation signal p and the noise signal n using the separation matrix shown in Expression (2), it is necessary to estimate φs and φn. This φs is the norm ratio of the vector of the R signal to the G signal in a stable period that is hardly affected by body movement. Φn is the norm ratio of the vector of the R signal to the G signal during the noise period affected by body movement.

The separation unit 42 calculates the norm ratio of the stable period by the following equation (3). In the formula (3), ‖R _ACpulse ‖ ₂ is the norm of the AC component of the R signal in the stable period, ‖G _ACpulse ‖ ₂ is the norm of the AC component of the G signal in the stable period, ‖R _DCpulse ‖ ₂ is the norm of the DC component of the R signal during the stable period, and ‖G _DCpulse ‖ ₂ is the norm of the DC component of the G signal during the stable period. Further, the separation unit 42 calculates the norm ratio of the noise period by the following equation (4). In the formula (4), ‖R _ACnoise ‖ ₂ is the norm of the AC component of the R signal in the noise period, ‖G _ACnoise ‖ ₂ is the norm of the AC component of the G signal in the noise period, ‖R _DCnoise ‖ ₂ is the norm of the DC component of the R signal in the noise period, and ‖G _DCnoise ‖ ₂ is the norm of the DC component of the G signal in the noise period.

  The separation unit 42 substitutes the norm ratio obtained by the equation (3) as φs and the norm ratio obtained by the equation (4) as φn into the separation matrix of the equation (2), and the G signal measured in the noise period. By substituting the value of the AC component of the R signal into G and R in equation (2), the pulsation component and the noise component in the noise period are separated.

  As described above, since the red light Lr is irradiated to a deeper part in the living body than the green light Lg, a signal component uncorrelated with the G signal is superimposed on the R signal. However, in the above-described embodiment, since the signal component having a low correlation with the G signal is removed from the R signal in the removing unit 41, the red light Lr and the green light Lg are irradiated to different parts in the living body. The error caused by this can be reduced. In addition, when the correlation between the R signal and the G signal is high, the pulsating component and the noise component are separated from the G signal and the R signal in the separation unit 42 as compared with the case where the correlation between the G signal and the R signal is low. Accuracy can be improved.

  The present invention is not limited to the above-described embodiment, and may be modified as follows. Further, the following modifications may be combined with each other.

(1) Modification 1
In the above-described embodiment, the wavelength of the light emitted from the first light emitting unit 19a is different from the wavelength of the light emitted from the second light emitting unit 19b, so that these lights have different in-vivo depths. The site was irradiated. However, even if the wavelength of the light emitted from the first light emitting unit 19a is the same as the wavelength of the light emitted from the second light emitting unit 19b, the first light emitting unit 19a and the first light receiving unit 20a are used. And the distance between the second light-emitting unit 19b and the second light-receiving unit 20b are different from each other, these light beams are irradiated to different depths in the living body. Become.

  In this modification, the pulse wave measuring device 1 measures pulse waves using light of one wavelength. In this case, the 1st light emission part 19a and the 2nd light emission part 19b irradiate the light of the same wavelength. For example, both the first light emitting unit 19a and the second light emitting unit 19b emit green light. In addition, the first light emitting unit 19a, the second light emitting unit 19b, the first light receiving unit 20a, and the second light receiving unit 20b are distances D4 between the second light emitting unit 19b and the second light receiving unit 20b. Is arranged to be larger than the distance D3 between the first light emitting unit 19a and the first light receiving unit 20a.

  FIG. 8 is a diagram showing a path of green light in the living body according to this modification. As described above, the distance D4 between the second light emitting unit 19b and the second light receiving unit 20b is larger than the distance D3 between the first light emitting unit 19a and the first light receiving unit 20a. In this case, the second green light Lg2 (an example of the second light) emitted from the second light emitting unit 19b has a large proportion of scattered light in a deep part in the living body, and thus the average penetration degree in the living body. Becomes larger. That is, the second green light Lg2 emitted from the second light emitting unit 19b is more in vivo than the first green light Lg1 (an example of the first light) emitted from the first light emitting unit 19a. It will pass through the deep part. Specifically, as shown in FIG. 8A, the first green light Lg1 passes through the shallow portions of the epidermis 31 and dermis 32 and is irradiated to the measurement site T3 (an example of the first site). On the other hand, as shown in FIG. 8B, the second green light Lg2 passes through deep portions of the epidermis 31 and the dermis 32 and enters a measurement site T4 (an example of the second site) deeper than the measurement site T3. Irradiated.

  Even in such a configuration, by performing the same processing as in the above-described embodiment, the first green light Lg1 and the second green light Lg2 are irradiated to the parts having different depths in the living body. The error that occurs can be reduced.

(2) Modification 2
The method of signal separation performed in the separation unit 42 is not limited to the method described in the embodiment. For example, a pulsating component and a noise component may be separated from two signals by applying a method described in Japanese Patent Application Laid-Open No. 2009-261458.

(3) Modification 3
In the adaptive filter described above, the FIR filter 53 is used as the coefficient variable filter. However, the coefficient variable filter used in the adaptive filter is not limited to the FIR filter 53. For example, instead of the FIR filter 53, an IIR (Infinite impulse response) filter may be used.

(4) Modification 4
In the embodiment described above, the removal unit 41 is realized by a digital filter. However, the removal unit 41 may be realized by an analog filter. In this case, the removal unit 41 removes the second signal component that has no correlation with the G signal from the input R signal using an analog filter.

(5) Modification 5
The light emitted by the first light emitting unit 19a and the second light emitting unit 19b is not limited to green light and red light. For example, light of other wavelengths such as blue light and infrared light may be used.

(6) Modification 6
In the embodiment which moved up, the 1st light-receiving part 20a which receives green light, and the 2nd light-receiving part 20b which receives red light were provided separately. However, a two-divided photodiode may be used instead of the first light receiving unit 20a and the second light receiving unit 20b.

(7) Modification 7
The apparatus main body 3 and the pulse wave sensor 4 may be connected by wireless communication. Further, the apparatus main body 3 and the pulse wave sensor 4 may be configured integrally. Further, the part to which the pulse wave sensor 4 is attached is not limited to the finger. For example, other parts of the living body such as the back of the hand, wrist, upper arm, back of the foot, earlobe, etc. may be used.

(8) Modification 8
The program executed in the CPU 11 may be provided in a state of being recorded on a recording medium such as a magnetic tape, a magnetic disk, a flexible disk, an optical disk, a magneto-optical disk, or a memory, and may be installed in the pulse wave measuring device 1. Further, this program may be downloaded to the pulse wave measuring device 1 via a communication line such as the Internet.

DESCRIPTION OF SYMBOLS 1 ... Pulse wave measuring device, 11 ... CPU, 12 ... ROM, 13 ... RAM, 14 ... Display part, 15 ... Operation part, 16 ... Oscillation circuit, 17 ... Time measuring circuit, 18 ... Drive circuit, 19a ... 1st light emission Part, 19b ... second light emitting part, 20a ... first light receiving part, 20b ... second light receiving part, 21a ... first filter part, 21b ... second filter part, 22a ... first amplifier circuit, 22b ... second amplifier circuit, 23a ... first A / D converter, 23b ... second A / D converter, 41 ... removal unit, 42 ... separation unit

Claims (5)

A first irradiating unit that irradiates a first part of the living body with a first light;
A second irradiation unit that irradiates a second part deeper than the first part in the living body with a second light;
A first light receiving unit that receives the first light reflected by the first part and converts the received first light into a first signal;
A second light receiving unit that receives the second light reflected by the second part and converts the received second light into a second signal;
A removal unit that removes a signal component having a correlation with the first signal lower than a predetermined threshold from the second signal and outputs the second signal from which the signal component has been removed , and
The removing unit is
A delay unit for delaying the first signal;
An FIR filter that performs filtering on the second signal using a coefficient;
An adder for outputting an error signal indicating a difference between the delay unit and the output signal of the FIR filter;
Have
The pulse wave measuring device , wherein the coefficient in the FIR filter is updated according to the error signal . A separation unit configured to separate a pulsation component indicating a pulse wave of the living body and a noise component from the first signal converted by the first light receiving unit and the second signal output from the removal unit; pulse wave measuring apparatus of the mounting serial to claim 1, characterized in that. The pulse wave measuring device according to claim 1 or 2 , wherein the second light has a wavelength longer than that of the first light. The distance between the second irradiation unit and the second light receiving unit is longer than the distance between the first irradiation unit and the first light receiving unit. The pulse wave measuring device according to any one of the above. The first light is irradiated to the first part in the living body by the first irradiation unit, the first light reflected by the first part by the first light receiving unit is converted into a first signal, The second light is irradiated to the second part deeper than the first part in the living body by the second irradiation unit, and the second light reflected by the second part by the second light receiving unit. Is converted into a second signal, a signal component whose correlation with the first signal is lower than a predetermined threshold is removed from the second signal, and the second signal from which the signal component has been removed is removed. It has a removal unit that outputs ,
The removing unit is
A delay unit for delaying the first signal;
An FIR filter that performs filtering on the second signal using a coefficient;
An adder for outputting an error signal indicating a difference between the delay unit and the output signal of the FIR filter;
Have
The signal processing apparatus , wherein the coefficient in the FIR filter is updated according to the error signal .