JP2002238866A - Pulse wave measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of complexity in the conventional gain setting of an amplifier. SOLUTION: This pulse wave measuring device is provided with a pulse wave sensor part 1 for detecting the increase/decrease of bloodstream from reflected light or transmitted light from the body surface as a pulse wave signal; an amplifier 2 for amplifying the output of the pulse wave sensor part; a storage part 43 storing the tolerance of output signals that can be taken in the amplifier 2, and an instrument processing part 3 outputting a reset signal for setting the output signal of the amplifier 2 to a reference level when the output signal level of the amplifier 2 is outside the tolerance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse wave measuring device for optically detecting a change in blood flow to measure a pulse rate.

[0002]

2. Description of the Related Art In a measuring device of this type, a pulse wave sensor unit has a built-in photoelectric conversion element including a light emitting unit and a light receiving unit. The light reflected by the hemoglobin flowing through the capillaries is received by the light receiving unit, and the output signal resulting from the light reception is used as a pulse wave signal, and the signal is amplified to a predetermined level by an amplifier circuit. Outputs pulse rate.

Since the level of the pulse wave signal from the pulse wave sensor section is extremely small, the gain of the amplifier circuit is set to a high value. Therefore, if there is disturbance due to body motion or the incidence of external light, a relatively large level signal is supplied to the amplifier circuit, so that the operation of the amplifier circuit is saturated. It cannot be detected.

Therefore, a means for automatically correcting the gain in the amplifier circuit according to the level of the input signal is required.
Generally, this gain is set based on the measurement result for a certain period, but in the "measuring device" of JP-A-10-234684, the gain setting of the detection signal can be quickly performed before the instruction to start the measurement. It is set to 4 seconds to perform, and is set every 20 seconds to reduce the frequency of gain change after the instruction to start timing.

[0005]

However, for that purpose, the gain must be set according to a complicated rule, and there is a problem that the apparatus itself becomes complicated in terms of hardware and software.

[0006] The present invention provides a pulse wave measuring apparatus that can simplify the system.

[0007]

According to the pulse wave measuring device of the present invention, a light emitting section for irradiating light to a body surface such as an earlobe and the light emitted from the light emitting section is reflected or transmitted from the body surface. A pulse wave sensor unit that detects an increase or decrease in blood flow below the body surface as a pulse wave by a photoelectric conversion element having a light receiving unit that receives incoming light, and an amplifier that amplifies the output of the pulse wave sensor unit.
A storage unit for storing an allowable range of the output signal of the amplifier, and an instrument processing unit for outputting a reset signal for setting the output signal of the amplifier to a reference level when the output signal level of the amplifier is out of the allowable range. And an arithmetic processing unit for calculating a pulse wave number from an output signal from the amplifier.

In order to correct a sudden signal change caused by setting the output signal of the amplifier to the reference level,
And a correction means for adding a correction signal of a predetermined level to the output signal.

The correction means may add the difference between the output signal of the amplifier at the immediately preceding sampling time and the output signal of the amplifier at the immediately preceding sampling time to the output signal. Good.

The instrument processing section comprises an analog switch having a low impedance in response to the input of a HIGH level control signal, and is connected between the input section of the amplifier and a reference potential.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 shows an embodiment of a pulse wave measuring apparatus according to the present invention. It comprises a pulse wave sensor section 1 and a main body section 6 including an amplifier 2, an instrument processing section 3, an arithmetic processing unit 4 and a display 5. The pulse wave sensor unit 1 has a built-in photoelectric conversion element including a light emitting unit and a light receiving unit, and among the light emitted from the light emitting unit,
The light reflected by the hemoglobin flowing through the capillaries on the body surface is received by the light receiving unit, and an output signal resulting from the light reception is supplied to the amplifier 2 in the main unit 6 as a pulse wave signal.

The amplifier 2 is constituted by AC coupling, and the amplification factor is fixed to a relatively large value in the range of 40 dB to 60 dB, and the output from the light receiving portion of the photoelectric conversion element which is usually several mV to several tens mV. The signal level is amplified to the order of several volts. The arithmetic processing unit 4 includes an A / D converter 41, a D / A converter 42, a storage unit 43, a central processing unit 44, and a comparison determination unit 45.

The A / D converter 41 converts an analog output signal of the amplifier 2 into a digital signal. The storage unit 43 holds the maximum value (Vmax) and the minimum value (Vmin) of the range that the output signal of the amplifier 2 can take according to the specifications of the amplifier 2 in advance. Each time the output signal of the amplifier 2 is A / D converted, the comparison determination unit 45 compares the digital value after the A / D conversion with the maximum value (Vmax) and the minimum value (Vmin) held in the storage unit 43. By comparing, it is determined whether or not the amplifier 2 is operating in a saturated state.

When the digital value after A / D conversion is larger than the maximum value (Vmax) stored in the storage unit 43, or when the digital value after A / D conversion is the minimum value stored in the storage unit 43 (Vmin), the amplifier 2
Is determined to be saturated. The sampling frequency of the A / D conversion is set to 10
It is appropriate to be about 0 Hz to 1 kHz, and the number of bits for quantization is suitably 8 bits or more because it is necessary to extract the characteristics of the pulse wave signal in the subsequent stage.

When the comparison / determination section 45 determines that the amplifier 2 is saturated, the D / A converter 42 outputs 1
A pulse voltage having the width of the sampling period is generated, and the amplifier 2
Is supplied to the instrument processing unit 3 as a reset signal of
The instrument processing unit 3 is composed of an analog switch circuit.
When a GH level control signal is input, the impedance between the input and output of this switch circuit becomes low impedance (ON state). When a LOW level is input, high impedance (OF
F state).

As shown in FIG. 2, when the amplifier 2 is composed of an operational amplifier 21, a resistor R connected to a reference potential (V _GND ) immediately after the DC component is cut by the capacitor C.
And an analog switch circuit 22 is connected in parallel. With this configuration, the analog switch circuit 22 becomes HIGH
When the analog switch circuit 22 receives the level control signal, the analog switch circuit 22 has a low impedance, so that the electric charge charged in the capacitor C is instantaneously discharged, and the output signal from the amplifier 2 becomes the reference potential (V _GND ).
become. When a first-order or higher-order low-pass filter is added to the feedback circuit portion of the operational amplifier 21, one input / output channel of the analog switch circuit 23 is associated with one capacitor constituting the low-pass filter,
Connect in parallel.

FIG. 2 shows a case where a first-order low-pass filter is formed. Two analog switch circuits are schematically described. If an analog switch circuit having multi-channel input / output is used, one analog switch circuit can be used. it can.

The behavior of the output signal in the amplifier 2 by the above processing will be described with reference to FIG. The solid line (thin line) is the output signal of the amplifier 2, and is from time (t ₂ ) to time (t ₉ )
During the period, the output signal of the amplifier 2 is actually a solid line (thick line) due to the operation of the instrument processing unit 3. From around the time (t ₀ ), a sudden change occurs in the output signal from the light receiving unit due to disturbance such as body movement, and after the time (t ₁ ), the output signal level of the amplifier 2 is stored at the time (t ₂ ). Since the value exceeds the maximum value (Vmax) held at 43, the D / A converter 32 during one sampling period from the time (t ₂ ) to the time (t ₃ ).
A pulse voltage is generated and supplied to the instrument processing unit 3.

In the instrument processing section 3, the impedance between the input and output of the analog switch circuit becomes low impedance (ON state).
The output signal of the amplifier 2 approaches the reference potential (V _GND ). This state is almost the same as the transient response at the time of discharging the electric charge accumulated in the capacitor C in the RC circuit.
The behavior for the output signal of becomes the reference potential (V _GND) becomes exponential decay, during one sampling period up to time (t _3), a reference well in advance potential (V _GND) To reach. After the time (t ₃ ), since the saturated state of the amplifier 2 has been eliminated, stable pulse wave measurement can be continued.

On the other hand, when the instrument processing unit 3 does not function, the output signal level of the amplifier 2 is almost out of the allowable range from the time (t ₂ ) to the time (t ₇ ), and the pulse wave is measured during the time. I cannot do it.

The case where the output signal level of the amplifier 2 exceeds the maximum value (Vmax) stored in the storage unit 43 has been described above. The output signal level of the amplifier 2 is stored in the storage unit 43. The same applies to the case where the voltage falls below the minimum value (Vmin). In this case, the behavior until the output signal of the amplifier 2 reaches the reference potential (V _GND ) increases exponentially.

In the central processing unit 44 in the arithmetic processing unit 4,
The digital value of the output signal of the amplifier 2 is received from the A / D converter 41 and written in the storage unit 43, and the digital value and the digital value of the output signal of the amplifier 2 of the past several samples read from the storage unit 43 are sequentially converted. After processing, the pulse rate and the like are calculated.

By the way, when the output signal of the amplifier 2 is set to the reference potential (V _GND ) by the instrument processing function at the time when the output signal level of the amplifier 2 is out of the allowable range as described above, the vicinity of the time becomes the center. As a result, a steep peak or valley is formed in the output signal of the amplifier 2, and there is a high possibility that this will lead to erroneous detection of the pulse rate and the like. In the present invention, this problem is avoided in the second embodiment described below.

Embodiment 2 FIG. 4 shows a second embodiment of the present invention. 4 is different from FIG. 1 in that the comparison / determination unit 45a
Is determined to be saturated, the output signal is output to the D / A converter 42 and also to the central processing unit 44. In the central processing unit 44 that has received the output signal from the comparison determination unit 45a, as shown in FIG.
Immediately after (t _post ), the difference between the maximum value (Vmax) held in the storage unit 43 and the reference potential (V _GND ) is added to the digital value of the output signal of the amplifier 2 received from the A / D converter 41. Vmax-V _GND )
The digital value is used for sequential processing for calculating a pulse rate and the like, and is written in the storage unit 43.

The same applies to the case where the output signal level of the amplifier 2 falls below the minimum value (Vmin) held in the storage unit 43. In this case, the minimum value (Vmin) held in the storage unit 43 is used. Difference (Vmin) from reference potential (V _GND )
−V _GND ) is corrected.

In order to realize such addition, a variable (δ) for storing the correction amount is prepared in the storage section 43, and the central processing unit 44 sends the A / D converter 41
Each time the digital value of the output signal is received, the correction amount (α) may always be added. The initial value of the correction amount (α) is 0 (δ = 0), and when the output signal level of the amplifier 2 exceeds the maximum value (Vmax) held in the storage unit 43, the correction amount (δ) is set to (Vmax −V _GND ), and when the output signal level of the amplifier 2 falls below the minimum value (V _min ) held in the storage unit 43, the correction amount (δ) is increased by (V _min −V _GND ). What should I do?

As described above, after t _post , the A / D converter 4
4, it is possible to continue to add the correction value (δ) corresponding to the number of times the instrument processing has been performed to the digital value of the output signal of the amplifier 2 received from 1 and, as shown in FIG. When the pulse wave signal (thick line) is reconstructed in a pseudo manner, the rate at which the reconstructed pulse wave signal includes a steep peak or valley caused by disturbance such as body motion is reduced. By extracting the characteristics of the pulse wave signal after the reconstruction, it is possible to reduce the rate of erroneous detection in calculating the pulse rate and the like.

When the output signal of the amplifier 2 is corrected and the pulse wave signal is reconstructed, the output signal of the amplifier 2 at the _immediately preceding sampling time (t _pre0 ) and the _immediately preceding sampling time (t _pre0 ) _pre1 )
The output signal of the amplifier 2 may be corrected by adding the difference (ΔV) from the output signal of the amplifier 2 at step (2), that is, the difference immediately before the output signal of the amplifier 2 to the correction amount (δ). Good.

The maximum value (Vma
the difference between x) and the reference potential _{(V GND) (Vmax-V} GND), or the minimum value held in the storage unit 43 (Vmin) the difference between the reference potential _{(V GND) (Vmin-V} GND) By simply adding and correcting, the pulse wave signal after reconstruction at the previous sampling time (t _pre0 ) and the pulse wave signal after reconstruction at the sampling time (t _post ) are not corrected. As a result, almost the same value is obtained, and the pulse wave signal after the reconstruction is not smooth, ie, there is almost no change in one sampling section. However, in the above-described configuration, the output signal of the amplifier 2 becomes the reference potential (V _Since the displacement amount of the sampling section being converted to _GND ) is estimated to be equal to the displacement amount of the immediately preceding sampling section, the state lacking in smoothness is eliminated.

Although the case where only the immediately preceding difference (ΔV) is used has been described, the estimated displacement amount of the sampling section estimated from the difference a plurality of times ago in the past may be added and corrected.

When the instrument function frequently operates and the correction amount (δ) increases, the upper limit of the number that the digital value of the reconstructed pulse wave signal can be represented by the number of quantization bits of the A / D converter 41 May be exceeded.

Therefore, the forgetting constant (α) is stored in the storage unit 43, and the correction amount (δ) is multiplied by the forgetting constant (α) every time sampling is performed to obtain the correction amount (δ) as α × δ.
Can be updated at any time. By multiplying the correction amount (δ) by the forgetting constant (α) having a value less than 1 in this way, the digital value of the reconstructed pulse wave signal becomes the number of quantization bits of the A / D converter 41. Exceeding the upper limit of the number that can be expressed by can be prevented.

[0033]

According to the present invention, by adding the instrument processing unit in this way, even if a sudden change occurs in the output signal from the light receiving unit due to disturbance or body movement, the output of the amplifier can be controlled to a predetermined value. And the amplifier operates normally, so that even if there is a large signal change due to disturbance or body movement, pulse wave measurement can be continued stably, and the pulse rate etc. There is an effect that extraction and display can be performed without any trouble.

When the output signal of the amplifier is set to the reference level, a correction means for adding a correction signal of a predetermined level to the output signal is provided, so that a sudden change caused by setting the output signal of the amplifier to the reference level is provided. Signal changes can be corrected.

In addition to the above correction, the difference between the output signal of the amplifier at the immediately preceding sampling time and the output signal of the amplifier at the immediately preceding sampling time is added to the output signal. You may.

The instrument processing section can be constituted by an analog switch having a simple mechanism such that a low impedance is obtained by inputting a HIGH level control signal in order to set the output level of the amplifier to the reference level.

[Brief description of the drawings]

FIG. 1 is a control block diagram of a pulse wave measuring device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of an amplifier and an instrument processing unit in FIG.

FIG. 3 is a diagram showing an output signal of an amplifier when an instrument processing unit functions.

FIG. 4 is a control block diagram of a pulse wave measuring device according to a second embodiment of the present invention.

FIG. 5 is a diagram showing an output signal of an amplifier when a correction function is added according to the second embodiment;

[Explanation of symbols]

1 pulse wave sensor section, 2 amplifier, 3 instrument processing section,
4 arithmetic processing unit, 5 display unit, 6 main unit, 21 operational amplifier, 22, 23 analog switch, 41 A / D converter, 42 D / A converter, 43 storage unit, 44 central processing unit, 45 comparison / determination unit, 45 a Comparison judgment section

Continued on the front page (72) Inventor Takashi Sakaguchi 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Corporation (72) Inventor Kazuo Hashima 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Co., Ltd. In-company F term (reference) 4C017 AA09 AA10 AB08 AC26 BC11

Claims (4)

[Claims] 1. A photoelectric conversion element having a light-emitting portion for irradiating light toward a body surface such as an earlobe and a light-receiving portion for receiving light reflected or transmitted from the body surface out of the light emitted from the light-emitting portion. A pulse wave sensor unit that detects an increase or decrease in blood flow below the body surface as a pulse wave, an amplifier that amplifies the output of the pulse wave sensor unit, and a storage unit that stores an allowable range of an output signal of the amplifier. And when the output signal level of the amplifier is outside the allowable range,
A pulse wave measuring apparatus comprising: an instrument processing unit that outputs a reset signal for setting an output signal of an amplifier to a reference level; and an arithmetic processing unit that calculates a pulse wave number from an output signal from the amplifier. 2. A correction means for adding a correction signal of a predetermined level to said output signal in order to correct a sudden signal change caused by setting an output signal of an amplifier to a reference level. Pulse wave measuring device. 3. An amplifier output signal at the immediately preceding sampling time and a further previous sampling time to correct a sudden signal change caused by setting the output signal of the amplifier to the reference level. 3. The pulse wave measuring apparatus according to claim 2, further comprising a correction unit for adding a difference between the output signal of the amplifier and the output signal of the amplifier to the output signal. 4. The instrument processing unit according to claim 1, wherein said instrument processing unit comprises an analog switch having a low impedance in response to input of a high-level control signal, and is connected between an input unit of said amplifier and a reference potential. A pulse wave measuring device according to any of the above.