JPH08191808A - Living body electric impedance-measuring apparatus - Google Patents

Abstract

PURPOSE: To more accurately measure the electric impedance of a living body in consideration of a blood flow rate. CONSTITUTION: A measuring signal generator 72 forms a measuring signal (current) Ia changing in frequency within a range of 1-1MHz at every cycle (t) of a clock CL to send the same to the electrode Hc attached to the hand. When the measuring signal Ia is supplied to a living body, the voltages Vp, Vc detected by a differential amplifier 81 and an I/V converter 91 are stored in sampling memories 84, 94 through the electrodes Hp, Lp, Lc attached to the hand or a leg. Further, a comparator 103 detects the peak value of the pulse waves of a human body detected by a pulse wave sensor P to supply a trigger TR to a CPU 3. Whereupon, the CPU 3 performs the sampling continued from the start of measurement only for a time Ts to stop and reads the voltages Vp, Vc stored in the memories 84,94 during the period going back by a predetermined time Ta from the start of measurement to calculate the electric impedance of a subject to display the calculated result on a display part 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bioelectrical impedance measuring device which is useful for estimating a change with time in water content in a subject based on the electric impedance method.

[0002]

2. Description of the Related Art The amount of water in the body is related to hemodynamics and metabolic ability. If the amount of water in the body can be measured, heart disease,
Understanding of diseases that cause abnormal water distribution such as kidney disease,
It is considered that it can be used for treatment, for example, monitoring during artificial dialysis, adequacy of diuretic medication. As a method of measuring the amount of water in the body, a minute current (for example, 300 μA) is passed between a plurality of electrodes attached to the body surface, and the frequency of the minute current is swept in a frequency range of 3 to 400 kHz. , A bioelectrical impedance method for measuring the electrical impedance of the body is known ("Bioelectrical impedance method as an evaluation method of body composition", B
aumgartner, RN, etc., "Bioelectrical impedance and its clinical application", Medical Electronics and Bioengineering, Kanai Hiroshi, 20 (3)
Jun 1982, "Estimation of water distribution in limbs by impedance method and its application", Medical Electronics and Biotechnology, Makoto Haeno et al., 23 (6) 1985, "Long-term measurement of urinary bladder volume by impedance method" , Ergonomics, Yasuo Kuchinomachi, 28 (3) 1992
Etc.).

In the biological system of the human body, electricity is mainly carried by ions in the electrolyte solution inside and outside the cells. Therefore, in the bioelectrical impedance method, as shown in FIG. 5, the electrical impedance of the human body is parallel to the extracellular fluid impedance consisting of the resistance R0 and the intracellular fluid impedance consisting of the resistance Ri and the capacitance C. Think of it as a synthetic impedance (the capacitance is because the cell membrane etc. act as an insulating film). If the human body can be represented as an equivalent circuit model as shown in the figure, at very low frequencies, the electrical impedance of the cell membrane (capacitance C) is too high to pass electricity. Therefore, electricity flows only through the extracellular fluid and the measured bioelectrical impedance is purely resistance R0. Then, as the frequency increases,
The electric current penetrates the cell membrane, and the bioelectrical impedance measured includes a resistance component and a reactance component. At very high frequencies, the cell membrane loses its capacitive capacity, again resulting in purely synthetic resistance Ri.R0 / (Ri
Only + R0) is measured.

From this, by sweeping the frequency, bioelectrical impedance, resistance, reactance, etc. can be obtained, and changes in the body water content (extracellular fluid) can be estimated by these changes. Therefore, the bioelectrical impedance method can be applied to various medical measurements. For example, during artificial dialysis treatment, physical abnormalities such as edema may occur due to excessive dialysis. Therefore, it is desired to accurately know the end time of dialysis. Therefore, if the bioelectrical impedance of the body can be measured by the above-mentioned electrical impedance method, focusing on the fact that the amount of water in the body changes during the process of artificial dialysis, it is possible to accurately know the end time of dialysis.

In addition, for example, when caring for an elderly person, it may be difficult to inform the user of the desire to urinate or the start of urination. So, in the past, you could wear a diaper,
He had a catheter inserted into his bladder and had micturition periodically.
However, wearing a diaper has drawbacks such as restriction of behavior and rash. An increase in the amount of urine in the bladder is a change in the amount of water in the body. Therefore, if the bioelectrical impedance of the body is measured by the above-mentioned electrical impedance method, the amount of urine in the bladder can be measured. Bioelectrical impedance is also related to fat, and it is known that fat has high resistance and muscle tissue has low resistance. Therefore, it is possible to measure the body fat mass by measuring the bioelectrical impedance.

[0006]

By the way, the bioelectrical impedance has a close relationship with the blood flow rate. That is, the blood flow in the body is a part of the water content in the body, and changes according to the expansion and contraction of the heart. On the other hand, the bioelectrical impedance changes according to the amount of water in the body, as described above. Therefore, the bioelectrical impedance must be measured in consideration of the blood flow volume that changes according to the expansion and contraction of the heart. However, in the bioelectrical impedance measuring device described above, although the bioelectrical impedance and the blood flow rate are closely related, the measurement is not performed in consideration of the blood flow rate (that is, the measurement is performed asynchronously with the heartbeat). However, there is a problem in that an error may occur and an accurate bioelectrical impedance cannot be measured.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a bioelectrical impedance measuring device capable of measuring bioelectrical impedance with higher accuracy.

[0008]

In order to solve the above-mentioned problems, the bioelectrical impedance measuring device according to claim 1 detects a pulse wave of a living body and a pulse wave detecting means for detecting the pulse wave of the living body. In synchronization with the pulse wave, a measurement signal generating means for generating a measurement signal whose frequency changes over time within a predetermined frequency width and sending it to the living body, and the measurement signal generating means sent to the living body. Electric quantity detecting means for detecting a potential difference and a current generated between any two surface parts of the living body, which are separated from each other, based on the measurement signal, and a frequency difference between the electric potential difference and the electric current detected by the electric quantity detecting means. Storage means for storing each of them, and the electrical impedance between the parts of the living body or the electrical impedance between the parts of the living body based on the potential difference and the current stored for each frequency in the storage means. Calculating means for calculating a physical quantity, it is characterized by comprising an output means for outputting the results calculated by said calculating means.

According to a second aspect of the invention, there is provided the bioelectrical impedance measuring apparatus according to the first aspect, which is for promoting generation of the measurement signal based on the pulse wave detected by the pulse wave detecting means. It is characterized in that it comprises a trigger generating means for generating the trigger and supplying it to the measurement signal generating means.

[0010]

In the structure of the present invention, the pulse wave detecting means detects the pulse wave of the living body. The measurement signal generation means generates a measurement signal whose frequency changes with time within a predetermined frequency width range in synchronization with the pulse wave detected by the pulse wave detection means, and sends the generated measurement signal to the living body. The electrical quantity detecting means detects a potential difference between any two surface portions of the living body which are separated from each other and a current flowing between the two portions based on the measurement signal synchronized with the pulse wave. The detected potential difference and current are once stored in the storage means for each frequency. The calculation means is synchronized with the pulse wave in the storage means, and
Based on the potential difference and the current stored for each frequency, the electrical impedance between the above-mentioned parts of the living body or the physical quantity based on the electrical impedance is calculated. The calculated result is output to a display device or a printer.

According to the configuration of the present invention, the bioelectrical impedance is calculated based on the electrical quantities detected in synchronization with the pulse wave, so that the blood flow rate is measured when measuring the body water content or body fat content. The effect of can be removed. Therefore, the body water content and body fat content of the subject can be more accurately estimated, and can be expected as an effective measuring means for edema and the like. It is also possible to clarify the relationship between blood flow and bioelectrical impedance.

[0012]

Embodiments of the present invention will now be described with reference to the drawings. A. Configuration of Embodiment FIG. 1 is a block diagram showing an electrical configuration of a human body electrical impedance measuring apparatus according to an embodiment of the present invention. The measuring device 100 is a device for measuring the change with time of the body water content in the human body.
A measurement processing unit 2 for sending a measurement signal to a human body and digitally processing the voltage / current information obtained from the human body.
And a CPU (central processing unit) 3 for controlling each part of the device and continuously calculating the electrical impedance of the human body based on the processing result of the measurement processing part 2, and this CP
The display unit 4 is configured to display the electric impedance of the human body calculated by U3, the ROM 5 that stores the processing program of the CPU 3, and the RAM 6 in which the work area of the CPU 3 is set.

The keyboard 1 is an input device for the operator to set / change the total measurement time T, time Ts, Te, Ta, etc. described later according to the purpose of measurement, and is supplied from the keyboard 1. The operation data of each key is converted into a key code by a key code generation circuit (not shown) and supplied to the CPU 3.

The measurement processing section 2 has an output processing circuit including a reference clock generator 71, a measurement signal generator 72, an output buffer 73 and an electrode Hc attached to a predetermined part of the body, and a predetermined body part. Electrodes Hp, Lp, Lc attached to the parts, differential amplifier 81, I / V converter 91, LPFs 82, 92, 102, A / D converter 83,
93, sampling memory (ring buffer) 84,9
4, an input processing circuit including an amplifier 101 and a comparator 103. In the measurement processing unit 2, the reference clock generator 71 keeps the cycle t during the entire measurement time T.
A clock CL of (for example, 800 ns) is generated and supplied to the measurement signal generator 72. The measurement signal generator 72 sweeps the frequency for each of the clocks CL, and the frequency is 1 to 1 MHz.
The measurement signal (current) Ia that changes in the range of
In the meantime, it is repeatedly generated and sent to the electrode Hc (see FIG. 4) via the output buffer 73. The frequency sweep time of the measurement signal Ia is sufficiently shorter than the change of the pulse wave described later, and in this example, the clock is generated every 10 ms. The electrode Hc is attached to the hand of the subject by the suction method. Therefore, the measurement signal (current)
Ia enters the human body through the subject's hand.

Next, the differential amplifier 81 detects the voltage (potential difference) between the two electrodes Hp and Lp. In this example, the electrode Hp is attached to the hand of the subject by the suction method, and the electrode Lp is attached to the leg by the suction method (see the same figure). Therefore, when the measurement signal Ia is supplied to the human body, the differential amplifier 81 detects the voltage Vp between the limbs of the subject and supplies it to the low-pass filter 82. This voltage Vp is a voltage drop between the electrodes Hp and Lp due to the electrical impedance of the human body. The low-pass filter 82 removes noise from the voltage Vp and supplies it to the A / D converter 83. Each time the CPU 3 supplies the digital conversion signal Sd, the A / D converter 83 converts the noise-free voltage Vp into a digital signal and supplies the digital signal to the sampling memory 84. In the sampling memory (ring buffer) 84, the digitized voltage Vp is longer than one cycle of the pulse wave,
It is stored for each cycle t defined by the clock CL and for each frequency of the measurement signal Ia.

Next, the I / V converter 91 has two electrodes H
The current flowing between c and Lc is detected and converted into a voltage. In this example, the electrode Hc is attached to the hand of the subject by the suction method, and the electrode Lc is attached to the leg by the suction method (see the same figure). Therefore, the I / V converter 91
When the measurement signal Ia is supplied to the human body, after detecting the current Ib flowing between the limbs of the subject and converting it into the voltage Vc,
It is supplied to the low-pass filter 92. Low-pass filter 9
2 removes noise from the voltage Vc, and the A / D converter 93
Supply to Each time the CPU 3 supplies the digital conversion signal Sd, the A / D converter 93 converts the noise-free voltage Vc into a digital signal and supplies the digital signal to the sampling memory 94. In the sampling memory (ring buffer) 94, the digitized voltage Vc is 1
Longer than the cycle, cycle t defined by the clock CL
For each frequency of the measurement signal Ia.

Next, the amplifier 101 amplifies the voltage Vh corresponding to the change of the pulse wave detected by the pulse wave sensor P to a predetermined level and supplies it to the low pass filter 102. The pulse wave sensor P of this example is an optical type that detects a pulse by a change in the reflection amount (or the transmission amount) when light is applied to the finger, and is attached to the finger of the subject as shown in FIG. Used. The pulse wave sensor P changes the subject's pulse wave,
In other words, the change in blood flow is detected. The low-pass filter 102 removes noise from the voltage Vh, and the comparator 1
Supply to 03. The comparator 103 detects the peak value of the voltage Vh, that is, the peak value of the pulse wave of the subject by comparing the noise-removed voltage Vh with a predetermined threshold value, and triggers a detection signal (synchronization). Signal) C as TR
It is supplied to the PU 3 (the trigger is applied by the peak value of the pulse wave in order to prevent erroneous detection).

Next, the CPU 3 starts the measurement by the above-described measurement processing unit 2 according to the processing program stored in the ROM 5, and a predetermined time Ts (for example, 20) from the start of the measurement.
Trigger TR output from the comparator 103 after 0 ms)
Is received and the trigger TR is supplied, control is performed to stop the measurement after sampling a specified number of times for a specified time (time Ts; for example, 800 ms), and trace back a predetermined time Ta (for example, 600 to 1000 ms) from the stop of the measurement. Voltage V stored in the sampling memories 84, 94 during
The electric impedance Z (= Vp / Vc) of the subject is calculated by sequentially reading p and Vc. Thus, the reason why the measurement is not started at the time when the trigger TR is supplied and the trigger TR is accepted after the lapse of a predetermined time Ts from the start of the measurement is to enable the measurement even in the phase where the pulse wave rises. Is. The predetermined time Ta is set longer than at least one cycle of the pulse wave so that all phases of the pulse wave can be measured. Therefore, the electrical impedance Z of the subject is always calculated based on the voltages Vp and Vc sampled in all phases of the pulse wave. Then, for example, the electrical impedance Z calculated based on the voltages Vp and Vc sampled in synchronization with a predetermined phase of the pulse wave is a display controller and a display (for example, LCD).
It is displayed on the display unit 4 including.

B. Operation of the Embodiment Next, the operation of the above configuration will be described. Figure 2
4 is a flowchart for explaining the operation of the human body electrical impedance measuring apparatus, and FIG. 3 is a timing chart for explaining the operation. First, prior to the start of measurement, as shown in FIG. 4, the electrodes Hc, Hp are attached to the subject's hand and the electrodes Lp, Lc are attached to the subject's legs (at this time, the electrodes Hc, Lc are attached to the electrodes Hp, Lp. Installed farther from the center of the human body). The pulse wave sensor P is attached to the finger of the subject. Then, the measurement start switch provided on the keyboard 1 is turned on. As a result, the power is turned on, and the CPU 3 first performs a predetermined initialization, and then in step S1, the measurement signal Ia generated by the measurement signal generator 72 according to the clock CL of the reference clock generator 71 is output from the electrode Hc. The measurement is started by sending it to the body. When the measurement signal Ia is supplied to the human body, the differential amplifier 81 detects the voltage Vp generated between the limbs to which the electrodes Hp and Lp are attached, and the voltage Vp is supplied to the A / D converter 83 via the low-pass filter 82. It On the other hand, in the I / V converter 91, the current Ib flowing between the limbs to which the electrodes Hc and Lc are attached is detected, converted into the voltage Vc, and then supplied to the A / D converter 93 via the low-pass filter 92. It At this time, the CPU 3 supplies the digital conversion signal Sd to the A / D converters 83 and 93 at each sampling cycle. Further, in the amplifier 101, the voltage Vh corresponding to the change of the pulse wave is detected by the pulse wave sensor P.
Is detected and passed through the low pass filter 102 to the comparator 10
3 is supplied.

Each time the A / D converter 83 receives the supply of the digital conversion signal Sd, it converts the voltage Vp into a digital signal and supplies it to the sampling memory 84. The sampling memory 84 sequentially stores the digitized voltage Vp. On the other hand, in the A / D converter 93, each time the digital conversion signal Sd is supplied, the voltage Vc is converted into a digital signal and supplied to the sampling memory 94. The sampling memory 94 sequentially stores the digitized voltage Vc. The CPU 3 proceeds to step S2 and determines whether the time Ts (FIG. 3) has elapsed from the start of measurement. In this determination, if it is determined that the time Ts has not elapsed, the process returns to step S1 and the above-described processing is repeated.

When it is determined that the time Ts has elapsed from the start of measurement, the process proceeds to step S3, and it is determined whether or not the trigger TR is supplied from the comparator 103.
That is, after the time Ts has elapsed, the trigger TR is accepted. If the trigger TR is not supplied in this determination, the process returns to step S1 and the above-described processing is repeated until the trigger TR is supplied. On the other hand, when the peak of the pulse wave of the subject is detected, the comparator 10
3 supplies a trigger TR (shown in the figure) to the CPU 3. When the trigger TR is supplied to the CPU 3, step S
From 3 to step S4, it is determined whether or not the time Te has passed since the trigger TR was supplied. In this determination, when it is determined that the time Te has not elapsed, the process returns to step S1 and until the time Te elapses,
The above process is repeated. When it is determined that the time Te has passed since the trigger TR was supplied, the process proceeds to step S5. In step S5, the measurement signal I
Based on the voltages Vp and Vc detected for each frequency of a,
The electrical impedance of the subject is calculated according to a predetermined algorithm, and the obtained electrical impedance is stored in the RAM 6 and displayed on the display unit 4. Then, the process ends.

As described above, according to the above configuration, based on the voltages Vp and Vc sampled in synchronization with the pulse wave,
Since the electrical impedance Z is calculated, the influence of the blood flow can be removed in the measurement of the water content in the body. Therefore, the water content in the body of the subject can be estimated more accurately, and can be expected as an effective measuring means for edema and the like. In addition, the voltage Vp, which is sampled in all phases of the pulse wave,
Since the bioelectrical impedance Z is calculated based on Vc, the relationship between the blood flow rate and the bioelectrical impedance can be clarified.

The embodiment of the present invention has been described in detail above with reference to the drawings. However, the specific structure is not limited to this embodiment, and there are design changes and the like within the scope not departing from the gist of the present invention. Also included in the present invention. For example, the calculated electrical impedance of the human body may be output to the printer. Further, in the above-described embodiment, the case where the trigger is applied by the peak value of the pulse wave of the subject has been described, but the present invention is not limited to this. Also, the calculated electrical impedance is not limited to the synthetic electrical impedance of the human body, for example,
It may be the extracellular fluid resistance of the human body, the intracellular fluid resistance, and the temporal changes thereof or a part thereof, and in this case, it can be expected to be applied to dialysis condition measurement. Also,
The attachment location of the electrodes is not limited to the hands and legs.

[0024]

As described above, according to the configuration of the present invention, the bioelectrical impedance is calculated based on the electrical quantities detected in synchronization with the pulse wave. In measuring the amount of fat and the like, the influence of blood flow can be removed. Therefore, the body water content and body fat content of the subject can be more accurately estimated, and can be expected as an effective measuring means for edema and the like. It is also possible to clarify the relationship between blood flow and bioelectrical impedance.

[Brief description of drawings]

FIG. 1 is a block diagram showing an electrical configuration of a bioelectrical impedance measuring device according to an embodiment of the present invention.

FIG. 2 is a flowchart for explaining the operation of the measuring apparatus.

FIG. 3 is a timing chart for explaining the operation of the measuring apparatus.

FIG. 4 is a diagram showing a mounting state of various electrodes of the measuring apparatus.

FIG. 5 is a diagram showing an equivalent circuit model of bioelectrical impedance.

[Explanation of symbols]

 2 measurement processing unit 3 CPU (calculation means) 71 reference clock generator 72 measurement signal generator (measurement signal generation means) 73 output buffer 81 differential amplifier (electrical quantity detection means) 82, 92, 102 low-pass filter 83, 93 A / D converter (electrical quantity detecting means) 84,94 Sampling memory 91 I / V converter (electrical quantity detecting means) 101 Amplifier (pulse wave detecting means) 103 Comparator (pulse wave detecting means) P Pulse wave Sensor (pulse wave detection means)

Claims (2)

[Claims] 1. A pulse wave detecting means for detecting a pulse wave of a living body,
A measurement signal generation unit that generates a measurement signal whose frequency changes with time in a predetermined frequency width range in synchronization with the pulse wave detected by the pulse wave detection unit and sends the measurement signal to a living body, and the measurement signal. Based on the measurement signal sent to the living body from the generating means, an electrical quantity detecting means for detecting a potential difference and a current generated between any two surface parts of the living body separated from each other, and the electrical quantity detecting means. Storage means for storing the detected potential difference and current for each frequency, based on the potential difference and current stored for each frequency in the storage means, the electrical impedance between the parts of the living body or a physical quantity based on the electrical impedance Measuring bioelectrical impedance, and an output means for outputting the result calculated by the calculating means. Location. 2. A trigger generation means for generating a trigger for prompting the generation of the measurement signal based on the pulse wave detected by the pulse wave detection means and supplying the trigger to the measurement signal generation means. The bioelectrical impedance measuring device according to claim 1.