JP2001025462A - Physiological signal detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the detecting probability of a pulse wave by improving the S/N ratio in a physiological signal detecting device equipped with a light emitting element and a photo-detecting element. SOLUTION: A pulse wave of a human body is detected by a photo-detecting element by detecting a reflected light or a scattered light from hemoglobin in the organism from among light emitted to the organism from a light emitting element 11. In this case, the light emitting element 11 is equipped with light emitting wavelength characteristics for a wavelength region wherein light absorption wavelength characteristics of hemoglobin and photo-detection sensitivity wavelength characteristics of a photo-detecting element 12 are combined. The light emitting element 11 is a light emitting diode wherein the light emitting wavelength characteristics can be converted, and its light emitting wavelength characteristics have light emitting wavelength peaks in approximately 440 nm and 550 nm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biological signal detecting apparatus for measuring a pulse wave of a human body by utilizing the absorption characteristics of hemoglobin in blood.

[0002]

2. Description of the Related Art Conventionally, a biological signal detecting device for measuring a pulse wave of a human body includes a light emitting element for irradiating light to a living body such as a finger, and a light receiving element for receiving light emitted from the light emitting element. Things are considered.

In this biological signal detecting device, irradiation light from a light emitting element hits a capillary in a living body, a part of which is absorbed by hemoglobin in blood, and a part is reflected or scattered to be reflected light or scattered light. The reflected light or the scattered light is received by the light receiving element. At this time, if the amount of blood flowing through the blood vessels increases, the proportion of irradiation light absorbed by hemoglobin increases, and the reflected light or scattered light received by the light receiving element becomes weaker. The proportion absorbed by hemoglobin is reduced, and reflected light or scattered light is increased.
Therefore, quantitative numerical data of the pulse wave can be detected by calculating the intensity change of the reflected light or the scattered light detected by the light receiving element.

[0004]

In such a biological signal detecting device, red light (for example, a wavelength of 700 nm) is conventionally used as light emitted from a light emitting element. However, with red light, the absorbance of hemoglobin is small,
In addition, since reflection or scattering at the skin surface is large, there is a problem that the S / N ratio is poor and the detection probability of a pulse wave is small.

[0005] Japanese Patent Application Laid-Open No. 8-80288,
-266493, 300-700n
A biological signal detection device including a light emitting element having a single emission wavelength peak in a wavelength range of m is described. However, this device does not take into account the specific absorption wavelength characteristics of hemoglobin and the sensitivity wavelength characteristics of the light receiving element, and the S / N ratio is low.

In view of the above, it is an object of the present invention to improve the S / N ratio and improve the probability of detecting a pulse wave in a biological signal detecting device provided with a light emitting element and a light receiving element.

[0007]

In order to achieve the above object, according to the first aspect of the present invention, the light emitting element (11) includes a light-absorbing wavelength characteristic of hemoglobin and a light-receiving element (12). It is characterized by having an emission wavelength characteristic having a peak near a peak wavelength region of the absorption sensitivity wavelength characteristic multiplied by the light reception sensitivity wavelength characteristic.

[0008] As the irradiation light of the light emitting element (11) is light in a wavelength region where the absorbance of the hemoglobin (31) is large, the intensity of reflected light or scattered light detected by the light receiving element without being absorbed by the hemoglobin (31). Responds sensitively to changes in the amount of blood flowing through the capillaries. Also, the light emitting element (11)
As the irradiation light from the light source is a light in a wavelength region where the light receiving sensitivity of the light receiving element (12) is high, the reflected light or the scattered light can be detected with higher sensitivity by the light receiving element (12).

Accordingly, the emission wavelength characteristic of the light emitting element (11) is obtained by multiplying the emission wavelength characteristic of hemoglobin by the light absorption wavelength characteristic of the light receiving element (12). By having a peak in the vicinity, the S / N ratio can be improved when detecting a pulse wave, and the detection probability of a pulse wave can be improved.

The term "hemoglobin" as used herein refers to oxygenated hemoglobin combined with oxygen flowing in a capillary artery.

The light-emitting element (11) can be, specifically, a light-emitting diode whose emission wavelength characteristic can be converted, as described in the second aspect of the present invention. The emission wavelength characteristic of 11) can have an emission wavelength peak around 440 nm or around 550 nm as in the invention described in claim 3.

Incidentally, the reference numerals in parentheses of the above means are examples showing the correspondence with specific means described in the embodiments described later.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A biological signal detecting apparatus to which the present invention is applied will be described below with reference to the drawings.

The biological signal detecting apparatus 100 detects a pulse wave as a biological signal and continuously monitors the pulse wave,
For example, it is used for medical diagnosis, health management, personal recognition and the like, such as detection of the condition of a cared person in a hospital.

Hereinafter, the configuration of the biological signal detecting device 100 will be described with reference to FIGS. FIG. 1 shows a ring-type biological signal detecting device 100 to which the present invention is applied, and FIG. 2 shows an enlarged cross section of a pulse wave detecting section 1 provided in the biological signal detecting device 100.

As shown in FIG. 1, the biological signal detecting device 10
0 is a pulse wave detecting unit 1 for detecting a pulse wave,
And a signal processing unit (not shown) for processing a signal detected by the pulse wave detecting unit 1 and the like.

The pulse wave detector 1 includes a light emitting element 11 composed of a light emitting diode (LED) and a light receiving element 12 composed of a photodiode (PD) inside a case 10. 12 is case 10
Are located adjacent to each other. Finger (living body) from light emitting element 11
The light is irradiated toward the light 30, and the light not absorbed by the hemoglobin 31 in the blood is received by the light receiving element 12 as reflected light or scattered light, whereby a pulse wave can be detected.

A window 13 made of an acrylic plate or the like through which light is transmitted is provided in an upper portion of the case 10 (a portion in contact with a finger) in the drawing.

The biological signal detecting apparatus 100 shown in FIG. 1 is arranged such that the upper side of the page is located on the back side of the finger 30 and the lower side of the page is located on the ventral side of the finger 30, that is, the pulse wave detecting section 1 It is arranged so as to be located on the ventral side. In this way, by arranging the light emitting element 11 and the light receiving element 12 on the abdominal side having more blood vessels than the back side of the finger 30, pulse wave can be effectively detected.

In this embodiment, the light emitting element 11 is In
GaN-based (indium-gallium-nitrogen-based) blue LE
D is a wavelength conversion LED that can convert the wavelength of light by passing emitted light through a fluorescent paint applied to an acrylic plate or the like. Further, a GaAsP (gallium-arsenic-phosphorus) PD is used as the light receiving element 12.

By the way, when detecting a pulse wave of a human body by the biological signal detecting device 100, light reflected or scattered in the living body among the light irradiated from the light emitting element 11 toward the living body is a signal to be detected. On the other hand, of the irradiation light of the light emitting element 11, light reflected or scattered on the skin surface, tissue in the living body, the window 13, or the like becomes noise.

The intensity of the reflected or scattered light not absorbed by the hemoglobin 31 changes with the change in the amount of blood flowing through the capillary artery as the irradiation light of the light emitting element 11 is in a wavelength region where the absorbance of the hemoglobin 31 is large. Reacts with high sensitivity. For this reason, the S / N ratio (pulse wave detection rate) improves when the wavelength characteristic of the irradiation light from the light emitting element 11 matches the absorption wavelength characteristic of hemoglobin 31 as much as possible.

Further, as the irradiation light from the light emitting element 11 is in the wavelength region where the light receiving sensitivity of the light receiving element 12 is high, the light receiving element 12 can detect reflected light or scattered light with higher sensitivity. Therefore, the S / N ratio is improved when the wavelength characteristic of the irradiation light from the light emitting element 11 matches the light receiving sensitivity wavelength characteristic of the light receiving element 12 as much as possible.

Therefore, it is desirable that the absorption wavelength characteristic of the hemoglobin 31 and the light reception sensitivity wavelength characteristic of the light receiving element 12 be as close as possible.

However, these wavelength characteristics do not match. Specifically, as shown in FIG. 3, hemoglobin has an absorption wavelength characteristic having a large peak near 420 nm, and the light-receiving element 12 As shown in FIG.
It has a light receiving sensitivity wavelength characteristic having a peak near 0 nm.

Therefore, the light emitting element 11 in the present embodiment
Is the emission wavelength characteristic having a peak near the peak wavelength region of the absorption sensitivity wavelength characteristic obtained by multiplying (synthesizing) the absorption wavelength characteristic of hemoglobin shown in FIG. 3 and the sensitivity wavelength characteristic of the light receiving element 11 shown in FIG. Use what you have.
Specifically, as shown in FIG. 5, the light emitting element 12 of the present embodiment has two emission wavelength peaks, namely, a first peak around 440 nm and a second peak larger than the first peak around 550 nm. It has emission wavelength characteristics.

In this embodiment, a wavelength conversion LED is used for the light emitting element 11 as described above in order to obtain the emission wavelength characteristic shown in FIG. Specifically, the wavelength characteristic of the light emitted from the InGaN-based blue LED has a single peak around 440 nm. By passing this light through the fluorescent paint, a new peak is formed around 550 nm. The light having the emission wavelength characteristics shown in FIG. 5 can be generated by generating the light having the light and combining them.

FIG. 6 shows the scattering or reflection characteristics of light on the surface of the living body (skin). If the emission wavelength characteristics of the light emitting element 11 shown in FIG. 5 are used, the light reflected or scattered on the skin surface is small. And an even better S / N ratio can be obtained.

It should be noted that the light emitting element 1
1 and the light receiving element 12 and an electric wiring (not shown) for electrically connecting the signal processing unit (not shown) to the light emitting element 11 and the light receiving element 12 with this electric wiring. Electricity can be supplied.

Next, the biological signal detecting device 100 shown in FIG.
The operation of will be described.

When the energization is performed, the light emitting element 11 emits light toward the living body (finger). Some of this illuminating light is reflected or scattered on the skin surface. Then, part of the irradiation light in the living body is absorbed by hemoglobin 31 in the blood flowing through the capillary artery, and part is reflected or scattered in the living body. The reflected light or the scattered light is received by the light receiving element 12, and a detection signal corresponding to the intensity of the reflected light or the scattered light is sent from the light receiving element 12 to a signal processing unit (not shown) as a biological signal.

The change in the amount of light received by the light receiving element 12 corresponds to the change in the amount of hemoglobin 31 in the capillary arteries. That is, if the hemoglobin 31 increases, the proportion of the irradiation light absorbed by the hemoglobin 31 increases, and the reflected light or the scattered light weakens. Conversely, if the hemoglobin 31 decreases, the absorption light is absorbed by the hemoglobin 31 of the irradiation light. The proportion decreases and the reflected or scattered light becomes stronger.

The amount of hemoglobin 31 in the capillary arteries changes in a wave-like manner due to the pulsation of blood.
The light absorbed by 1 also changes in a wavelike manner, and the intensity of light reflected or scattered in the living body without being absorbed by the hemoglobin 31 also changes in conjunction with this. Therefore, by continuously measuring the intensity change of the reflected light or the scattered light by the light receiving element 12, the change in the amount of blood flowing in the capillary artery, that is, the pulse wave can be measured.

The biological signal detection device 100 executes the following processing based on the detection signal of the light receiving element 12. FIG. 7 shows a block diagram of this processing, and the processing executed by the biological signal detection device will be described based on this drawing.

As described above, when the light emitting element 11 and the light receiving element 12 are energized, a pulse wave detection signal is sent to the signal processing unit. This detection signal is amplified by an amplifier circuit 20, then noise is removed by a band-pass filter circuit 21, and is converted into a digital signal by an A / D conversion circuit 22.

The digital signal is subjected to data processing by a CPU 23 incorporated in a signal processing unit (not shown). In this data processing, for example, after a digital signal is serialized, a process of adding an additional signal (a header signal, an ID signal, a parity signal, or the like) to the serialized digital signal is performed. Then, the data processed by the transmission device 24 is transmitted.

The transmitted data is received by a separate receiving device (not shown), and the condition of the care receiver is determined based on the received pulse wave data.

Next, the results of measurement of a pulse wave by the present inventors using the biological signal detection device 100 of the present embodiment will be described with reference to FIG.

FIG. 8 shows detected pulse wave intensities in A, B, C, and D when light emitting elements having various emission wavelength characteristics are used. Specifically, A is a light emitting element having the emission wavelength characteristic of the present embodiment, B is a light emitting element having an emission wavelength characteristic having a single peak at 520 nm, and C is 46.
D indicates the case where a light emitting element having an emission wavelength characteristic having a single peak at 5 nm, and D indicates the case of using a light emitting element having an emission wavelength characteristic having a single peak at 655 nm.

As can be understood from FIG. 8, as in the present embodiment, the emission wavelength characteristic having a peak in the vicinity of the peak wavelength region of the absorption sensitivity wavelength characteristic obtained by multiplying the absorption characteristic of hemoglobin and the sensitivity characteristic of the light receiving element 12 is shown. By using the light emitting element 11 having the configuration shown in FIG. 5), it is possible to provide a biological signal detecting device having a good S / N ratio and high pulse wave detection sensitivity.

In the embodiment described above, 440 nm
A light emitting element having a light emission wavelength characteristic having a first peak near 550 nm and a second peak larger than the first peak near 550 nm has been described, but a light emitting element having a peak in either one of the wavelength regions is used. Is also good. However, since the sensitivity of the light receiving element is considerably reduced around 420 nm, which is the peak of the absorption wavelength characteristic of hemoglobin, it is desirable that the light emitting element has a peak wavelength around 550 nm. Specifically, the light emitting element has a size of 520 nm to 580 nm.
, The S / N ratio can be kept at a favorable level in practical use.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a state in which a biological signal detection device according to an embodiment is mounted on a finger.

FIG. 2 is an enlarged cross-sectional view of a pulse wave detection unit of the biological signal detection device of FIG.

FIG. 3 is a characteristic diagram showing absorption wavelength characteristics of hemoglobin.

FIG. 4 is a characteristic diagram illustrating light-receiving sensitivity wavelength characteristics of a light-receiving element.

FIG. 5 is a characteristic diagram showing an absorption wavelength characteristic obtained by multiplying an absorption wavelength characteristic of hemoglobin and a light reception wavelength characteristic of a light receiving element.

FIG. 6 is a characteristic diagram showing reflection scattering characteristics on the surface of a living body (skin).

FIG. 7 is a block diagram of a process executed by the biological signal detection device.

FIG. 8 is a characteristic diagram showing pulse wave intensity when light emitting elements having various wavelength characteristics are used.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Pulse wave detection part, 2 ... Ring part, 10 ... Case, 11 ...
Light emitting element, 12 light receiving element, 30 living body (finger), 31
Hemoglobin, 100: biological signal detection device.

Continuing from the front page (72) Inventor Teisuke Kimura 1-1-1, Showa-cho, Kariya-shi, Aichi Pref. 72) Inventor Satoru Kodama 1-1-1 Showa-cho, Kariya-shi, Aichi F-term in DENSO Corporation 4C017 AA09 AB03 AC28 FF15 4C038 KL07 KM01 VB13 VC01

Claims (3)

[Claims] 1. A light-emitting element (11) for irradiating light to a part of a living body, and a light-receiving element (12) for receiving light emitted from the light-emitting element (11), A biological signal for detecting a pulse wave of a human body by detecting, with a light receiving element, a part of the light irradiated from step 11) as reflected light or scattered light while absorbing part of the light absorbed by hemoglobin in the living body. The detection device, wherein the light emitting element (11) has a peak near a peak wavelength region of an absorption sensitivity wavelength characteristic obtained by multiplying an absorption wavelength characteristic of the hemoglobin and a reception sensitivity wavelength characteristic of the light receiving element (12). A biological signal detection device having emission wavelength characteristics. 2. The biological signal detecting device according to claim 1, wherein the light emitting element is a light emitting diode capable of converting an emission wavelength characteristic. 3. The light-emitting element (11) is provided with a phosphor on a light-emitting body and wavelength-converted to at least four light-emitting elements.
The biological signal detection device according to claim 1, further comprising an emission wavelength characteristic having an emission wavelength peak around 40 nm or around 550 nm.