JP2001327476A - Electric characteristic measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain helpful information for diagnosis of a cardiac disease by correlating an electrocardiograph with bioelectricity impedance. SOLUTION: The output from a differential amplifier 26 is transmitted to an LPF 35, and an electrocardiographic component of a voltage Vp between a surface electrode Hp and a surface electrode Lp is subtracted in the LPF 35. The electrocardiographic component is converted to a digital signal by an A/D converter 36, and is outputted from an electrocardiograph 37. The electrocardiograph 37 outputs an electrocardiographic waveform based on this digital signal. The electrocardiograpchic waveform is displayed on a display part 13 as required, and is stored in an RAM'l4 through a CPU 12. Also, the electrocardiographic waveform is outputted from a waveform synthesizing part 38 in the CPU 12. In the waveform synthesizing part 38, the electrocardiographic waveform is synthesized with the bioelectricity impedance waveform to be two-dimensionally outputted, and a synthesized waveform 50 is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrical characteristic measuring apparatus capable of measuring a movement of a subject's heart and a bioelectrical impedance based on a bioelectrical impedance method.

[0002]

2. Description of the Related Art In recent years, research on the electrical characteristics of living organisms has been conducted for the purpose of evaluating the body composition of humans and animals.
The electrical characteristics of the living body are called bioelectric impedance, and can be measured by applying a minute current between a plurality of electrodes attached to the body surface of the living body. Since such bioelectric impedance has a close relationship with the movement of the heart, it is conventionally known to grasp the movement of the heart from the bioelectric impedance.

[0003]

In diagnosing a heart disease, an electric signal (electrocardiogram) due to contraction of the heart muscle is used. However, in a conventional device for measuring bioelectrical impedance, no association is made with an electrical signal due to contraction of the myocardium. Therefore, at present, bioelectrical impedance is not directly used for diagnosing heart disease.

The present invention has been made in view of the above points, and provides an electrical characteristic measuring apparatus which can obtain effective information for diagnosing a heart disease by associating an electrocardiograph with a bioelectrical impedance. The purpose is to:

[0005]

According to the present invention, there is provided an electric characteristic measuring apparatus comprising: signal generating means for generating a measuring signal; and current measuring means for measuring a current flowing when the generated measuring signal is applied to a subject's body. A voltage measuring means for measuring a potential difference generated between predetermined surface portions of the subject's body, and a bioelectric impedance from a current value measured by the current measuring means and a voltage value measured by the voltage measuring means. A calculating means for calculating; and an electrocardiograph for measuring an electrocardiographic waveform of the subject.

Further, the current measuring means or the voltage measuring means and the electrocardiograph also serve as an electrode which is electrically conductively attached to a surface portion of a subject's body, thereby reducing the number of electrodes.
The configuration can be simplified, and the operability can be improved. Further, the calculation of the bioelectric impedance by the calculating means and the measurement of the electrocardiographic waveform by the electrocardiograph are performed at the same time, so that the mutual relationship can be accurately measured.

Further, by providing a filter for separating an electrocardiographic waveform from a current value measured by the current measuring means or a voltage value measured by the voltage measuring means, the bioelectric impedance and the frequency of the electrocardiographic waveform can be reduced. Focusing on the differences, they can be separated from each other. Further, the arithmetic means and the electrocardiograph can correct the bioelectric impedance and the electrocardiographic waveform to each other, thereby canceling each other's influence and obtaining an accurate bioelectric impedance and an electrocardiographic waveform.

Further, by providing a display means for displaying the two-dimensional display by synthesizing the bioelectric impedance and the electrocardiographic waveform, the mutual relationship can be displayed in an easily understandable manner.
In addition, the signal generation unit generates a measurement signal having a frequency of 1 kHz to 1 MHz, so that an accurate bioelectric impedance can be measured without affecting an electrocardiographic waveform.

The calculating means calculates the bioelectrical impedance at 30 points / second or more and 500 points / second or less, so that the pulse wave can be sufficiently separated and the bioelectrical impedance can be measured. The point can be a point equal to or less than the reciprocal of half of the lowest frequency of the frequency. Further, the current measuring means has a capacitor for increasing the low-frequency impedance in series with its input, so that the electrocardiographic waveform which is a low-frequency component can be sufficiently prevented.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. The case where the present invention is used for a bioelectrical impedance measuring device will be described in detail. FIG. 1 is a schematic diagram schematically showing a use state of a bioelectrical impedance measuring device according to an embodiment of the present invention, and FIG. 2 is a diagram illustrating a schematic configuration of the bioelectrical impedance measuring device according to the present embodiment. FIG. 3 is a block diagram showing an electrical configuration of the device.

As shown in FIG. 1, the bioelectrical impedance measuring device 1 is housed in a portable holder, and the holder is attached to a belt 4.
The belt 4 is worn on a human body B. As shown in FIG. 2, the bioelectrical impedance measuring apparatus is capable of inserting and removing a cassette tape which is a data recording unit 5 for recording digital data for several times. Digital data can be recorded on a cassette tape on and off.

A cable 3 extends from the bioelectrical impedance measuring device 1, and surface electrodes Hp, Lp, Hc, Lc are attached to the end of the cable 3. During measurement, the surface electrode Hc (first electrode) is electrically conductively adhered to the side of the subject's right breast by an adhesive method, and the surface electrode Lc (second electrode) is adhered to the left breast across the breast. It is stuck conductively by the method. Therefore, the measurement signal (probe current) Ia enters the body B from the right chest portion of the subject.

The surface electrode Hp (third electrode) is conductively attached to the inside of the first electrode Hc next to the right breast of the subject by an adhesive method, and the surface electrode Lp (fourth electrode) is
It is conductively attached to the inside of the second electrode Lc on the left side of the chest across the chest by an adhesive method. The surface electrodes Hp, L
There is no particular limitation on the form of p, Hc, Lc.

In FIG. 3, a bioelectrical impedance measuring device, which is an electrical characteristic measuring device, includes a keyboard 11,
The probe current Ia is transmitted as a measurement signal to the human body B of the subject, and thereby the measurement processing unit for digitally processing the voltage / current information obtained from the human body B of the subject and the respective units of the apparatus are controlled and the processing of the measurement processing unit is performed. CP for calculating bioelectrical impedance etc. of the human body based on the result
U (central processing unit) 12, a display unit 13 for displaying the bioelectric impedance of the human body B of the subject calculated by the CPU 12, and a ROM 15 for storing a processing program of the CPU 12. . The CPU 12 has a waveform synthesizing unit 38 for synthesizing a bioelectric impedance waveform and an electrocardiogram waveform.

The keyboard 11 includes a measurement start switch for the measurer to instruct the start of measurement, a height of the subject,
It is composed of various keys for inputting human body characteristic items such as weight, gender, age, etc., and for setting / changing the total measurement time T, measurement interval t, and the like according to the measurement purpose. Operation data of various keys is converted into key codes by a key code generation circuit (not shown),
It is supplied to U12.

The measurement processing unit includes a PIO (parallel interface) 21, a measurement signal generator 22, a low-pass filter (hereinafter, referred to as LPF) 23, coupling capacitors 24, 25a, 25b, 30, a surface electrode H
p, Lp, Hc, Lc, differential amplifier 26, I / V converter (current / voltage converter) 31, LPFs 32 and 35 composed of analog anti-aliasing filters, BPF 27,
It is composed of A / D converters 28, 33, 36, sampling memories (ring buffers) 29, 34, and an electrocardiograph 37.

FIGS. 4A and 4B are diagrams for explaining the LPF in the measurement processing section of the electric characteristic measuring device according to the present invention. FIG. 4A shows the LPF 35, and FIG.
(B) shows BPF27. The LPF 35 is a surface electrode H
This is a filter for separating a component output to the electrocardiograph among potential differences between p and the surface electrode Lp. Since the electrocardiographic component measured by the electrocardiograph is due to a biological reaction, it has a low frequency (100H).
(within z) band separation is possible. Therefore, LPF
35 is set so as to separate a frequency band of about 50 Hz to 1 kHz or less. Thus, an electrocardiographic component measured by the electrocardiograph can be extracted.

The BPF 27 is a filter for separating a component output for measuring bioelectrical impedance from the potential difference between the surface electrode Hp and the surface electrode Lp. The component for measuring bioelectrical impedance is in a higher frequency band than the electrocardiographic component. Therefore, the BPF 27
low (lower limit) is about 50 Hz to 1 kHz, and fchigh
(Upper limit) is set to about 100 kHz to 1 MHz, and fclo
A frequency band between w and fchigh is extracted.
Thereby, a component for measuring bioelectrical impedance can be extracted.

It is preferable that the number of measurement points of the bioelectric impedance is not more than the reciprocal of half of the lowest frequency. For example, if the lowest frequency is 1 kHz, 500 points or less are preferable. In order to separate a pulse wave from a component for measuring bioelectric impedance, 30 points / second is required.

By setting the cutoff frequencies of the LPF 35 and the BPF 27 in this manner, it is possible to easily separate the component for the electrocardiograph and the component for the bioelectrical impedance, and the potential difference between a pair of surface electrodes. From this, it is possible to obtain an electrocardiographic waveform and a bioelectric impedance waveform. The operation of the bioelectrical impedance measuring device having the above configuration will be described. FIG. 5 is a diagram showing an impedance locus of a human body, and FIG. 6 is an electrical equivalent circuit diagram of cells in a tissue of the human body that is close to actual.

In the measurement processing section, the measurement signal generator 22
Is 10 kΩ or more over the entire range of the signal frequency at which the output resistance is generated. Each time the signal generation instruction signal is supplied from the CPU 12 via the PIO 21 at the predetermined cycle t during the entire measurement time T, the longest is obtained. Linear code (maximal li
LPF2 that repeatedly generates a probe current Ia of a (near codes) series (M series) a predetermined number of times and uses the generated probe current Ia as a measurement signal to remove high-frequency noise thereof
3 and a coupling capacitor 24 that removes a direct current component from the human body B of the subject so as not to flow to the surface electrode Hc.

The value of the probe current Ia is, for example, 500
８００800 μA. The supply period of the signal generation instruction signal matches the measurement interval t set by the measurer using the keyboard 11. Further, in this example, the number of repetitions of the probe current (measurement signal) Ia is 1 to 256 per signal generation instruction signal. The number of repetitions may be arbitrarily set by the measurer using the keyboard 11. Although the number of repetitions increases as the number of repetitions increases, it is preferable that the number of repetitions be 1 to 256 in spite of a minute current, in consideration of the influence on the human body when the current is continuously applied to the human body for a long time.

When an impulse signal is used, energy concentrates in a short time interval (about 0.1 μsec), whereas a probe current using an M-sequence signal contains many frequency components, Since the energy is dispersed in about 1 msec, the living body is not injured, and the energy is generated at a time interval sufficiently shorter than the pulse or respiratory cycle, so that these are not affected. Furthermore, for example, in the case of a rectangular wave signal with a duty of 50%, the amplitude of the frequency spectrum is large at low frequencies and small at high frequencies, so that the frequency characteristic of the SN ratio deteriorates in the high frequency region, whereas the M-sequence signal is Since the amplitude of the frequency spectrum is substantially flat over the entire frequency range, the frequency characteristic of the SN ratio is also substantially flat. For details of the M-sequence signal,
R. C. Dixon, "Spread Spectrum Communication System"
56-p89).

The differential amplifier 26 detects a potential (potential difference) between the surface electrode Hp and the surface electrode Lp. That is, the differential amplifier 26 detects that the probe current Ia
, The voltage Vp between the surface electrode Hp and the surface electrode Lp is detected and input to the BPF 27. The voltage Vp is a voltage drop between the surface electrode Hp and the surface electrode Lp due to the bioelectric impedance of the human body B of the subject.

The BPF 27 removes high-frequency noise from the voltage Vp, extracts a component for measuring bioelectric impedance, and supplies this component to the A / D converter 28. As described above, the BPF 27 has a fclow (lower limit) of about 50 Hz to 1 kHz and a fchigh (upper limit).
Is set to about 100 kHz to 1 MHz, and the cutoff frequency fchigh is set to be lower than half the sampling frequency of the A / D converter 28. Thus, the aliasing noise generated in the A / D conversion processing by the A / D converter 28 is removed, and the bioelectric impedance component is extracted.

The A / D converter 28 converts the noise-free voltage Vp into a digital signal at a predetermined sampling cycle every time the digital conversion signal Sd is supplied from the CPU 12, and converts the digitized voltage Vp Is supplied to the sampling memory 29 every sampling period.

The I / V converter 31 detects a current flowing between the surface electrode Hc and the surface electrode Lc and converts it into a voltage. That is, when the probe current Ia is applied to the human body B of the subject, the I / V converter 31 detects the probe current Ia, converts it to a voltage Vc, and supplies the voltage Vc to the LPF 32.

The LPF 32 removes high-frequency noise from the input voltage Vc and supplies it to the A / D converter 33.
Similarly to the BPF 27, the LPF 32 has a cutoff frequency of about 100 kHz to 1 MHz, and is set to be lower than half the sampling frequency of the A / D converter 33. Also in this case, aliasing noise generated in the A / D conversion processing by the A / D converter 33 is removed. The A / D converter 33 converts the noise-removed voltage Vc into a digital signal at a predetermined sampling cycle every time the digital conversion signal Sd is supplied from the CPU 12, and converts the digitized voltage Vc into a sampling cycle. The data is supplied to the sampling memory 34 every time.

On the other hand, the output of the differential amplifier 26 is
5, where the electrocardiographic component of the voltage Vp between the surface electrode Hp and the surface electrode Lp is extracted by filtering. The electrocardiographic component is converted to a digital signal by the A / D converter 36 and then output to the electrocardiograph 37. The electrocardiograph 37 outputs this electrocardiographic waveform as shown in FIG.
This electrocardiographic waveform is displayed on the display unit 13 as necessary, and is stored in the RAM 14 via the CPU 12.
The electrocardiographic waveform is output to the waveform synthesizing unit 38 of the CPU 12.

The CPU 12 starts the measurement by the above-described measurement processing unit according to the processing program stored in the ROM 15, and detects the detection voltage V at a predetermined sampling cycle.
After sampling p and Vc a predetermined number of times, control for stopping measurement and the following processing are performed. That is, CP
U12 first reads out the voltages Vp and Vc, which are functions of time, stored in the sampling memories 29 and 34 sequentially, and performs Fourier transform processing on the voltages Vp (f) and Vc (f) (which are functions of frequency). After converting to f), averaging is performed to calculate bioelectric impedance Z (f) ｛= Vp (f) / Vc (f)｝ for each frequency.

Next, the CPU 12 obtains an impedance locus D as shown in FIG. 5 based on the obtained bioelectric impedance Z (f) for each frequency by making full use of a least squares calculation method. Obtained impedance locus D
The bioelectrical impedance R0 of the body B of the subject at the frequency 0 and the bioelectrical impedance R∞ at the infinite frequency of the subject B are calculated from the calculation results. Is calculated.

In an actual human body tissue, cells of various sizes are arranged irregularly. Therefore, an electrical equivalent circuit close to the actual one has a time constant τ = Cmk · Rik as shown in FIG. It is represented by a distributed constant circuit in which elements connected in series with the capacitance and the resistance are distributed (Re is the extracellular fluid resistance, Rik is the intracellular fluid resistance of each cell, and Cmk is the cell membrane capacitance of each cell). . Therefore, in this embodiment, the intracellular fluid resistance and the extracellular fluid resistance are determined by using an electrical equivalent circuit (see FIG. 6) which is close to the actual one. As shown in the figure, the center is an arc that is higher than the real axis.

Next, based on the calculated intracellular fluid resistance and extracellular fluid resistance, and the human body characteristic data such as the height, weight, sex, and age of the subject input from the keyboard 11, a processing program is prepared in advance. The body fat percentage, fat weight, lean body mass, intracellular fluid volume, extracellular fluid volume, and the sum of these amounts of body water (body fluid volume) ) Is calculated. Then, the calculated data are displayed on a display unit 13 including a display controller and a display (for example, an LCD).

Next, the CPU 12 determines whether or not the total measurement time T has elapsed.
If the subsequent measurement processing is terminated, and if not, the same measurement processing is started again after waiting for a time t corresponding to the measurement interval to elapse. Then, the above process is repeated until the entire measurement time T has elapsed. Thus, the bioelectrical impedance is measured.

FIG. 7 shows an electrocardiogram waveform, a bioelectric impedance waveform,
FIG. 3 is a diagram showing a two-dimensional graph in which the two are associated with each other. The waveform of the bioelectric impedance is displayed on the display unit 13 as necessary, as shown in FIG.
It is stored in the RAM 14 via U12. The bioelectric impedance waveform is output to the waveform synthesizing unit 38 of the CPU 12.

The waveform synthesizing unit 38 synthesizes the electrocardiographic waveform shown in FIG. 7A and the bioelectric impedance waveform shown in FIG. 7B and displays it two-dimensionally, and displays the synthesized waveform shown in FIG. Generate 50. The synthesized waveform 50 is displayed on the display unit 13 as necessary, and
It is stored in M14 and further recorded by a data recording unit such as the cassette 5.

As described above, the bioelectrical impedance measuring device, which is the electrical characteristic measuring device according to the present embodiment, outputs an amount in which the electrocardiographic waveform and the bioelectrical impedance waveform are associated with each other. Can be associated with heart movement. Therefore, it is possible to display an amount relating the electrocardiographic waveform and the bioelectric impedance waveform on a two-dimensional graph in real time,
Bioelectrical impedance can be used directly in diagnosing heart disease.

FIG. 8 is a block diagram showing an electrical configuration of a bioelectrical impedance measuring device according to another embodiment. In FIG. 8, a current terminal for measuring bioelectrical impedance and a terminal for an electrocardiograph have the same configuration.

In this case, a BPF 45 is provided downstream of the I / V converter 31 for measuring bioelectrical impedance. The filter shown in FIG. 4B is used for the BPF 45.
That is, the BPF 45 is a filter that separates components output for measuring bioelectric impedance. The component for measuring bioelectrical impedance is in a higher frequency band than the electrocardiographic component. Therefore, the BPF 27
(Lower limit) is about 50 Hz to 1 kHz, fchigh is set to about 100 kHz to 1 MHz, and fclow and fchigh are set.
The frequency band between (upper limit) is extracted. Thereby, a component for measuring bioelectrical impedance can be extracted.

The extracted bioelectric impedance component is output to the A / D converter 33, and thereafter, a bioelectric impedance waveform is obtained by the same processing as described above.
The obtained bioelectric impedance waveform is output to the waveform synthesizer 38 of the CPU 12. In this case, the capacitor 30 has the function of increasing the low-frequency impedance and blocking low-frequency components.

Further, an LPF 42 is provided after the operational amplifier 41 of the electrocardiogram waveform measuring system branched before the capacitor 30. The filter shown in FIG. 4A is used for the LPF 42. That is, the LPF 42 is a filter for separating components for measuring an electrocardiographic waveform. Since the electrocardiographic component measured by the electrocardiograph is due to a biological reaction, it has a low frequency (100 Hz).
Band) is possible. Therefore, LPF4
2 is set so as to separate a frequency band of about 50 Hz to 1 kHz or less. Thus, an electrocardiographic component measured by the electrocardiograph can be extracted.

The extracted electrocardiographic component is supplied to the A / D converter 43
And then converted to an analog signal, and then output to the electrocardiograph 44. In the electrocardiograph 44, an electrocardiographic waveform is obtained using an analog signal. This electrocardiographic waveform is CP
It is output to the waveform synthesizing unit 38 of U12.

The waveform synthesizing unit 38 synthesizes the bioelectric impedance waveform and the electrocardiographic waveform in the same manner as described above, and
The composite waveform 50 as shown in FIG.
Output to Therefore, even in the configuration shown in FIG.
As described above, it is possible to display the quantity relating the electrocardiogram waveform and the bioelectric impedance waveform on a two-dimensional graph in real time, and to directly use the bioelectric impedance in diagnosing a heart disease. it can.

Further, since the bioelectrical impedance measuring device according to the present embodiment can be of a holder type, it can be easily mounted on a human body as shown in FIG. As a result, since the device itself can be carried, it is possible to continuously monitor the amount of association between the electrocardiographic waveform and the bioelectric impedance waveform over a long period of time, regardless of the location. In this case, by providing a data recording unit such as a cassette, it is possible to store the monitoring result for a long time.

Although the embodiments of the present invention have been described in detail with reference to the drawings, the specific configuration is not limited to these embodiments, and the design can be changed without departing from the scope of the present invention. Even if there is, it is included in the present invention. For example, the filter may be a digital filter or an analog filter.

[0046]

As described above, the electrical characteristic measuring apparatus of the present invention can obtain effective information for diagnosing a heart disease by associating an electrocardiographic waveform with a bioelectrical impedance.

[Brief description of the drawings]

FIG. 1 is a schematic diagram schematically showing a use state of a bioelectrical impedance measuring device according to an embodiment of the present invention.

FIG. 2 is a perspective view illustrating a schematic configuration of a bioelectrical impedance measuring device according to the present embodiment.

FIG. 3 is a block diagram showing an electrical configuration of the bioelectrical impedance measuring device according to the present embodiment.

FIG. 4 is a diagram illustrating a filter used in the present embodiment.

FIG. 5 is a diagram illustrating an impedance locus of a human body.

FIG. 6 is a close-to-actual electrical equivalent circuit diagram of cells in a tissue of a human body.

FIG. 7 is a diagram showing an electrocardiographic waveform and a bioelectrical impedance waveform measured by the bioelectrical impedance measuring device according to the present embodiment, and a two-dimensional graph in which both are correlated.

FIG. 8 is a block diagram showing an electrical configuration of a bioelectrical impedance measuring device according to another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Bioelectric impedance measuring device 3 Cable 4 Belt 5 Cassette (data recording part) 11 Keyboard 12 CPU (Calculation means) 13 Display part 14 RAM 22 Measurement signal generator (part of signal generation means) 23, 32, 35 LPF ( Part of signal generating means) 26 Differential amplifier (part of voltage measuring means) 27 BPF (part of voltage measuring means) 28, 33, 36 A / D converters 29, 34 Sampling memory 31 I / V converter (Part of current measuring means) 32 LPF (part of current measuring means) 37 electrocardiograph 38 waveform synthesizing unit Hp, Lp, Hc, Lc Surface electrode

Claims (9)

[Claims] 1. A signal generation means for generating a measurement signal; a current measurement means for measuring a current flowing when the generated measurement signal is applied to a body of a subject; Voltage measuring means for measuring a potential difference to be performed; calculating means for calculating bioelectric impedance from a current value measured by the current measuring means and a voltage value measured by the voltage measuring means; and an electrocardiographic waveform of the subject. An electrical characteristic measuring device, comprising: an electrocardiograph for measuring. 2. The current measuring means or the voltage measuring means,
2. The electrical characteristic measuring apparatus according to claim 1, wherein the electrocardiograph also serves as an electrode which is electrically conductively attached to a surface portion of the body of the subject. 3. The electrical characteristic measuring apparatus according to claim 2, wherein the calculating means calculates the bioelectrical impedance and the electrocardiograph measures the electrocardiographic waveform at the same time. 4. An electric device according to claim 2, further comprising a filter for separating an electrocardiographic waveform from a current value measured by said current measuring means or a voltage value measured by said voltage measuring means. Characteristic measuring device. 5. The electrical characteristic measuring apparatus according to claim 2, wherein the calculating means and the electrocardiograph correct the bioelectric impedance and the electrocardiographic waveform mutually. 6. The electrical characteristic measuring apparatus according to claim 2, further comprising a display unit that combines the bioelectric impedance and the electrocardiographic waveform and displays the two-dimensional display. 7. The signal generating means according to claim 1, wherein said signal generating means is 1 kHz to 1 M
2. The electrical characteristic measuring apparatus according to claim 1, wherein a measurement signal having a frequency of Hz is generated. 8. The electrical characteristic measuring apparatus according to claim 1, wherein said calculating means calculates the bioelectrical impedance at 30 points / second or more and 500 points / second or less. 9. An electric characteristic measuring apparatus according to claim 1, wherein said current measuring means has a capacitor for increasing a low-frequency impedance in series with an input of said current measuring means.