JP2857895B2 - Blood flow detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blood flow detector for detecting a pulsation of a blood flow of a living body.

[Prior art] Conventionally, this type of device is generally mounted on an earlobe or the like of a living body and detects a change in skin blood flow.For example, a pair of light-emitting and light-receiving elements are provided on the skin of the earlobe. The pulsation of the blood flow is detected by detecting the change in the transmittance of the light emitted from the light emitting element due to the skin blood flow rate by the light receiving element.

In this case, the pulse wave detecting means constituted by a pair of light-emitting and light-receiving elements is brought into contact with the skin (earlobe) and the state is maintained, for example, in Japanese Utility Model Laid-Open No. 57-103705,
As shown in JP-A-84605, light-emitting and light-receiving elements are provided so as to face each other in a pair of clip-shaped detection cases, and the earlobe is attached by a mounting member formed of the clip-shaped detection case by the action of a compression spring. And so on.

[Problem to be Solved by the Invention] However, in the above-described clip structure using the compression spring, the opening amount of the clip piece constituting the detection case changes depending on the thickness of the attached portion such as the earlobe. When the thickness of the attached portion such as the earlobe changes due to the characteristics of the compression spring, the pinching force of the detection case changes, and the contact pressure between the pulse wave detecting means and the skin also changes.

Here, if the contact pressure between the pulse wave detecting means and the skin is large, the contact position of the pulse wave detecting means and the surrounding blood vessels are compressed, and the cross-sectional shape of the blood vessels is changed, which affects the normal pulse flow. And it becomes difficult to detect a correct blood flow signal.

The present inventors have previously proposed in Japanese Patent Application No. 1-108101 a method for detecting the warmth of a living body from the amplitude of a blood flow pulse wave, but the change in the cross-sectional shape of a blood vessel due to the contact pressure described above is detected. The pulse wave amplitude V _PP is affected (see FIG. 5), and it is found that when a sense of warmth is detected from the amplitude of the pulse wave, a large error is included due to a change in the contact pressure.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a blood flow detector that can accurately detect the amplitude of a blood flow pulse wave regardless of the thickness of a worn portion such as an earlobe. Aim.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a pulse wave detecting means which is attached by applying a constant pressure load to the skin of a living body and sandwiches the same to generate a pulse wave signal corresponding to the heartbeat of the living body, Based on the pulse wave signal from the wave detecting means, a tissue volume signal corresponding to the tissue volume in the attached portion of the living body is calculated, and the pulse wave amplitude calculated from the pulse wave signal is corrected by the tissue volume signal. In addition, a technical means including pulse wave amplitude correction means for outputting the corrected pulse wave amplitude as a pulse wave amplitude corresponding to a change in blood flow under the skin in the attached portion is adopted.

[Action]

 The operation of the above configuration will be described.

Pulse wave detecting means attached by applying a constant pressure load to the skin of the living body and holding it, detects a change in blood flow under the skin in the attached portion corresponding to the heartbeat of the living body, and generates a pulse wave signal. I do.

Based on the pulse wave signal from the pulse wave detection means, the pulse wave amplitude correction means includes a tissue weight signal corresponding to a tissue amount in the attached portion of the living body and a pulse wave amplitude corresponding to a change in the blood flow. , And the pulse wave amplitude is corrected by the tissue volume signal to generate the corrected pulse wave amplitude.

That is, the influence on the pulse wave amplitude caused by the difference in the tissue volume of the attached portion of the living body depends on the mounting of the pulse wave detecting means by the constant pressure load on the living body and the correction of the pulse wave amplitude by the tissue volume signal of the pulse wave amplitude correcting means. To be removed.

〔Example〕

 Hereinafter, the present invention will be described based on an embodiment shown in the drawings.

FIG. 2 is a block diagram of an electric circuit of a thermal sensor to which the first embodiment of the blood flow detector according to the present invention is applied, and FIG. 3 shows a structure of a pulse wave detecting means formed on the clip-shaped mounting member. It is sectional drawing.

In FIG. 3, the pulse wave detecting means is provided with a clip 100 made of a black material for holding the earlobe M of a living body, and this clip 100 grasps each base end of both clip pieces 100a and 100b from outside. Then, when pressed against the constant pressure spring 104, the distal ends of the clips 100a and 100b are tilted outward with respect to the shaft 102 to release the pinch M from being pinched. On the other hand, when the clip 100 is released from the gripping pressure on the clip pieces 100a and 100b, the clip 100
Each tip of 100a and 100b is tilted inward to each other,
Is to be clamped.

Further, in FIG. 3, reference numeral 103 denotes a shaft for rotatably fixing the spring bobbin 104a of the constant pressure spring 104 to the clip piece 100b.
By arranging it on the center side of 00, an earlobe holding force is created.

Reference numeral 104 denotes a constant pressure spring configured to obtain a constant earlobe holding force (contact pressure) even when the degree of opening between the clip pieces 100a and 100b, that is, the thickness of the earlobe changes. This constant pressure spring 104 is a spring bobbin 104
A thin spiral plate (for example, using a Coupling made by Osaka Heat Treatment Co.) is wound around a.
The spring bobbin 104a is fixed to 100a, and is rotatable about the shaft 103, thereby holding the earlobe with a constant contact force regardless of the thickness of the earlobe.

Next, in FIG. 3, reference numeral 105 denotes an infrared light emitting diode 105a having a peak wavelength near 900 nm and a phototransistor.
Pulse wave optical detection means constituted by 105b, respectively, by appropriate means in the inner recesses of the clip pieces 100a and 100b, supported parallel to the bottom wall of the recess and arranged facing each other. I have.

106 and 107 are disk-shaped spacers made of black foam material, and the light-emitting diodes 105a and the phototransistors 105b are fitted in the hollow portions thereof, so that the concave portions of the clip pieces 100a and 100b are respectively fitted. Is fixed to the opening end. The spacers 106 and 107 are more convex than the opening surfaces of the light emitting diode 105a and the phototransistor 105b. When the earlobe M is sandwiched by the clip 100, the spacers 106 and 107 are contracted in the thickness direction of the earlobe M, and the light emitting diode 105a and the phototransistor 105b Has a function of uniformly contacting the opening surface of the earlobe M with the surface of the earlobe M.

Reference numerals 108 and 109 denote covers for protecting a connection part that outputs terminal signals of the light emitting diode 105a and the phototransistor 105b to the outside, and 101 denotes a lead wire that outputs signals from the light emitting diode 105a and the phototransistor 105b. is there.

The operation of the pulse wave detecting means configured as described above will be described below.

When the light emitting diode 105a emits light due to its conduction, the light from the light emitting diode 105a enters the earlobe M, is absorbed by the earlobe tissue and blood in the earlobe M, and the rest is received by the phototransistor 105b as the amount of transmitted light. The phototransistor 105b generates a pulse wave signal. In that case, the amplitude V _PP of the pulse wave signal
Is the amount of light received by the phototransistor 105b, ie, the earlobe M
It corresponds to the amount of change in the blood flow inside. FIG. 4 shows an example of the waveform of the pulse wave signal.

Here, the arteriolar blood vessel shape in the earlobe M is represented by the clip 10
0 and the contact pressure of the earlobe by the constant pressure spring 104,
The cross-sectional shape changes. That is, the blood vessel cross-sectional shape when there is no contact pressure is substantially circular, but when the contact pressure is applied, the blood vessel cross-sectional shape changes to an elliptical shape. The change in the blood vessel cross-sectional shape due to the contact pressure is caused by the pulse wave amplitude V _PP output from the phototransistor 105b as shown in FIG.
Affect. By the way, in the structure using a compression spring disclosed in the above-mentioned Japanese Utility Model Application Laid-Open No. 1-84605, for example, the contact pressure of the earlobe changes depending on the opening amount of the holding piece. However, there is a problem that the blood vessel cross-sectional shape changes with the change, and as a result, the pulse wave amplitude changes. On the other hand, in the mounting member structure of the present embodiment, a constant contact pressure is obtained regardless of the opening amount of the clip pieces 100a and 100b, so that even if the thickness of the earlobe changes, a constant blood vessel cross-sectional shape is obtained. Can be maintained.

However, since the pulse wave amplitude in the pulse wave signal from the pulse wave detecting means configured as described above still includes an optical error due to the difference in the thickness of the earlobe, it must be electrically corrected. That is, since the infrared light emitted from the light emitting diode 105a is also absorbed by the tissue of the earlobe M, if the amount of tissue (here, mainly the thickness of the earlobe) is different, the amount of light received by the phototransistor 105b is reduced. The pulse wave amplitude. FIG. 6 shows the optical error characteristics due to the difference in the earlobe reach.

Here, it is a signal calculated from the transmitted light amount detected by the tissue amount signal phototransistor 105b, that is, the pulse wave signal, by electric processing according to the electric circuit block diagram shown in FIG. The calculated tissue volume signal is a signal corresponding to the amount of transmission absorbed by the skin tissue of the earlobe (excluding blood), and is a signal proportional to the thickness of the earlobe. In the present embodiment, the earlobe thickness correction means determines the earlobe thickness by the tissue volume signal, and simultaneously detects the pulse wave amplitude detected by the tissue volume signal, as shown in equation (1). Correction was made so that the pulse wave amplitude when mm was obtained.

CV _PP = V _PP × (K × Y _dc /0.82) (1) where CV _PP is the corrected pulse wave amplitude, V _dc is the tissue volume signal, and K
Is a matting constant, and 0.82 is a tissue volume signal when the earlobe thickness is 4 mm.

Next, the earlobe thickness correcting means and the thermal sensation detecting means as the pulse wave amplitude correcting means will be described with reference to the electric circuit block diagram of FIG.

The infrared light incident on the earlobe M from the light emitting diode 105a is absorbed by the earlobe tissue and blood, and the remaining transmitted light is photoelectrically converted by the phototransistor 105b, and the blood flow change in the earlobe M is converted into a voltage change signal, that is, a pulse wave. AC as signal
The signal is input to the amplifier 30 and the low-pass filter 31.

The AC amplifier 30 amplifies only the AC component of the pulse wave signal, that is, the blood flow change component, and outputs it to the pulse generator 32 and the peak hold circuit 33. The pulse generator 32 creates a heartbeat pulse signal synchronized with the heartbeat from the AC component of the pulse wave signal, c
Input to pu38. In the peak hold circuit 33, the maximum value and the minimum value are peak-held from the AC component of the input pulse wave signal, that is, the pulse wave amplitude, and the differential amplifier is used.
Enter 34. The differential amplifier 34 subtracts the minimum value from the maximum value of the input pulse wave amplitude, and inputs a DC voltage corresponding to the pulse wave amplitude to the A / D converter 37.

On the other hand, in the low-pass filter circuit 31, a low-pass filter (in the present embodiment, the center frequency 1H
z) is applied to remove the blood flow change component and input to the differential amplifier 35. The differential amplifier 35 differentially amplifies the input signal from the low-pass filter 31 and the input signal from the reference value setting circuit 36, and converts the tissue amount signal applicable to the above equation (1) into the A / D converter 3
Enter 7

The A / D converter 37 A / D converts the DC voltage and the tissue volume signal corresponding to the pulse wave amplitude by the control signal from the CPU 38,
Each digital signal is input to cpu38.

cpu38 is under the control flowchart of FIG. 7 performs an operation of correcting the pulse wave amplitude CV _PP and warming amount.

First, in step 40, it is determined whether or not a heartbeat pulse is generated from the heartbeat pulse generation circuit 32 (determined by the rising edge of the heartbeat pulse signal in the present embodiment). A control signal is sent to the converter 37 to start A / D conversion of the pulse wave amplitude and the tissue volume signal, and the values are respectively taken as digital signals into the CPU 38. Thereafter, in step 43 described later, the number n of captured data is 100
Until, the average value is cumulatively calculated in step 42. The determination of whether the number n of captured data has reached 100 in step 43 is based on the number of data, that is, the heart rate.
This corresponds to whether or not 100 beats have been input. If the number of data n is 100 or less, the processing of steps 40 to 43 is repeated until the number of data n becomes 100. Step 42
In computing the corrected pulse wave amplitude CV _PP than the average value of the calculated pulse wave amplitude and the tissue volume signal. In the next step 45, the eighth
A thermal sensation amount is calculated from the relationship between the pulse wave amplitude and the thermal sensation shown in FIG.
And the same processing is repeated.

That is, as shown in FIG. 2, a change in the blood flow in the earlobe is detected by the transmission type photoelectric pulse wave method, and a signal corresponding to the tissue amount of the earlobe and a change in the blood flow are detected from the detected pulse wave signal. And a signal corresponding to the tissue volume is used to correct the tissue volume error of the other signal corresponding to the change in blood flow by equation (1), and based on the corrected signal corresponding to the change in blood flow. To detect warmth.

FIG. 8 shows the thermal sensation-pulse wave amplitude characteristic, in which the pulse wave amplitude detected by the earlobe of each subject when various environmental temperatures of a large number of subjects are variously changed, and the pulse wave amplitude at that time. It shows the relationship of the warmth report when each subject reports the warmth in seven ranks from "cold" to "hot". According to this, it can be confirmed that the pulse wave amplitude changes according to the warm feeling of many subjects. Here, the _VPP characteristic indicates a correlation before the present embodiment is performed, and the _CVPP characteristic indicates a correlation obtained by performing the present embodiment. The correlation coefficient (calculated by exponential interpolation) between the thermal sensation and the pulse wave amplitude was improved from 0.914 to 0.972 by implementing this embodiment.

An example in which the present invention is applied to a thermal sensor and an air conditioner for a vehicle is implemented will be described with reference to a block diagram of FIG.

For example, it is mounted on an earlobe of a vehicle occupant and optically detects blood flow pulse waves in arterioles in the earlobe by pulse wave detection means shown in FIG. 3, and outputs a pulse wave signal from this pulse wave detection means to a second pulse wave. The pulse wave amplitude is corrected by the earlobe thickness correcting means described in the figure. That is, the earlobe thickness correction means is a means for correcting an optical detection error of the pulse wave detection means for optically detecting a pulse wave of the earlobe. The detection error due to the difference in thickness is corrected. Then, based on the corrected pulse wave amplitude, as shown in the previous application (Japanese Patent Application No. 1-108101), a corresponding thermal sensation is calculated by the thermal sensation detecting means, and the amount of air conditioning is calculated based on the amount of the thermal sensation. The control means controls the air-conditioning so that the occupant feels no warmth or cold, for example.

According to the air conditioning control having the above-described configuration, even if the driver or the occupant has an individual difference in a portion where the pulse wave detection unit is mounted,
Since the amplitude of the blood flow pulse wave can be detected with high accuracy, even if a sense of warmth is detected from the amplitude of the pulse wave, a large error does not occur, and good air conditioning control can be realized.

It goes without saying that the present invention can be applied not only to the vehicle air conditioner but also to various types of air conditioners.

Further, the above embodiment is applied to a thermal sensor for detecting a thermal sensation from a pulse wave amplitude, but may also be applied to a sensor configured to detect various amounts of exercise of a living body.

Further, as shown in FIG. 3, in the above-described embodiment, a structure in which the contact pressure is constant using a close-contact spiral-shaped thin plate spring is shown. However, the present invention is not limited to this, and a structure in which the contact pressure is constant. If so, for example, an air bag or the like may be used.

Further, in the above embodiment, a light-emitting diode and a photoelectric pulse wave type heart rate sensor comprising a phototransistor are employed.However, the present invention is not limited to this. The present invention can also be used for an impedance prestimo method for detecting a change.

〔The invention's effect〕

As described above, the blood flow detector according to the present invention can measure the influence on the pulse wave amplitude caused by the difference in the amount of Since it is removed by correcting the pulse wave amplitude based on the tissue volume signal of the correction means, for example, when it is attached to an earlobe or the like of a living body, regardless of the thickness of the attached portion such as the earlobe, the blood flow pulse wave is removed. There is an excellent effect that the amplitude can be accurately detected.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of the present invention, FIG. 2 is an electric circuit block diagram of a thermal sensor to which the first embodiment of the present invention is applied, and FIG. 3 shows a structure of a pulse wave detecting means shown in FIG. FIG. 4 is a waveform diagram of a pulse wave signal from the pulse wave detecting means shown in FIG. 2, and FIG. 5 is a characteristic diagram showing an influence of a contact pressure of the pulse wave detecting means on a living body on a pulse wave amplitude. FIG. 6 is a characteristic diagram showing an optical error characteristic to a pulse wave amplitude due to a difference in earlobe thickness.
The figure is a control flowchart of the CPU 38 in FIG. 2, FIG. 8 is a characteristic diagram showing the correlation between the pulse wave amplitude and the feeling of warmth, and FIG. 9 is a diagram in the case where the thing shown in FIG. It is a block block diagram. 31 ... Low-pass filter circuit, 33 ... Peak hold circuit, 34, 35 ... Differential amplifier, 36 ... Reference value setting circuit, 37 ...
A / D converter, 38… cpu, 100… clip, 102 …… axis, 104
…… Constant pressure spring, 105a …… Light emitting diode, 105b ……
Phototransistor.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) A61B 5/02

Claims (1)

(57) [Claims] 1. A pulse wave detecting means which is attached by applying a constant pressure load to the skin of a living body and clamps the same to generate a pulse wave signal corresponding to the heartbeat of the living body, and a pulse wave from the pulse wave detecting means. Based on the signal, a tissue volume signal corresponding to the tissue volume in the attached portion of the living body is calculated, and a pulse wave amplitude calculated from the pulse wave signal is corrected by the tissue volume signal, and the corrected pulse wave A blood flow detector, comprising: a pulse wave amplitude correction unit that outputs the amplitude as a pulse wave amplitude corresponding to a change in blood flow under the skin in the attached portion.