JPH1014898A - Bioelectric impedance measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure bioelectric impedance accurately and safely while the configuration remains simple. SOLUTION: An impedance measuring device 100 is composed of a measurement processing part 2, a CPU 3, and a display part 4, wherein the measurement processing part 2 comprises a measuring signal generator 72 to allow a probe current Ia consisting of M-series symbol signals to flow through the body of a subject, an I/V converter 91 and LPF 92 and also A/D converter 93 for sensing the probe current Ia flowing through the body of the subject, a differential amplifier 81 and LPF 82 and another A/D convert 83 for sensing the voltage Vp between his hands and feet, and sampling memories 84 and 94 which store the voltages digitized by the A/D converters 83 and 93. The CPU 3 converts the digital voltages stored in the sampling memories 84 and 94 into a voltage value for each frequency through Fourier's transform processing and calculates bioelectric impedance or the like between different parts of organism on the basis of the result from conversion. The display part 4 displays the obtained bioelectric impedance or the like.

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 apparatus useful for estimating a body fat state and a body water distribution of a subject 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 properties of living organisms vary significantly depending on the type of tissue or organ. For example, in the case of humans, the electrical resistivity of blood is around 150 Ωcm, whereas the electrical resistivity of bone and fat is 1 to 1. There is also 5 kΩ · cm. The electrical characteristics of the living body are called bioelectric impedance, and are measured by passing a small current between a plurality of electrodes attached to the body surface of the living body. The method of estimating the body water distribution, body fat percentage, body fat mass, etc. of the subject from the bioelectric impedance obtained in this way is called the bioelectric impedance method ("Bioelectric impedance method as a method for evaluating body composition", Baumgartner, RN, etc., "Bioelectric Impedance and Its Clinical Application", Medical Electronics and Biotechnology, Hiroshi Kanai, 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).

[0003] Bioelectric impedance is derived from the resistance of a living body to the current carried by ions in the body (resistance) and the reactance associated with various types of polarization processes created by cell membranes, tissue interfaces, or non-ionized tissue. Be composed. Capacitance, which is the reciprocal of reactance, causes a time delay in current rather than voltage, and creates a phase shift (phase shift). This value is the arctangent of the ratio of reactance to resistance (arctangent). It can be determined geometrically as a phase angle.

The bioelectric impedance Z, the resistance R, the reactance X and the electric phase angle φ depend on the frequency. At very low frequencies fL, the bioelectrical impedance Z at the cell membrane-tissue interface is too high to conduct electricity. Thus, electricity flows only through the extracellular fluid and the measured bioelectrical impedance Z is purely a resistance R.

[0005] Next, as the frequency increases, the current penetrates the cell membrane, the reactance X increases, and the phase angle φ increases. The magnitude of the bioelectrical impedance Z is equal to the value of the vector defined by Z ² = R ² + X ² . The frequency at which both the reactance X and the phase angle φ are maximized is called a critical frequency fc, which is one electrical characteristic value of a living body that is a conductive conductor. Beyond this critical frequency fc, the cell membrane-tissue interface loses its capacitive capacity and the reactance X decreases accordingly. At very high frequencies fH, the bioelectrical impedance Z is again purely equivalent to the resistance R.

FIG. 11 is an electrical equivalent circuit diagram (equivalent circuit model) of the human body. In this figure, Cm represents the cell membrane capacity, and Ri and Re represent the intracellular fluid resistance and the extracellular fluid resistance, respectively. At low frequency fL,
The current mainly flows through the extracellular space, and the impedance Z becomes equal to the extracellular fluid resistance Re. High frequency fH
In, the electric current completely passes through the cell membrane, and the cell membrane capacitance Cm is equivalent to substantially being short-circuited. Therefore, impedance Z at high frequency fH
Is equal to the combined resistance Ri · Re / (Ri + Re). By the method described above, the intracellular fluid resistance Ri and the extracellular fluid resistance Re can be determined, and based on these, the state of body fat such as the body fat percentage, fat weight, lean body mass, and body water of the subject are determined. The distribution (intracellular fluid volume, extracellular fluid volume, and their total body water content) can be estimated, and their resistance R
Changes in body water distribution can be estimated by changes in e and Ri. The measurement / estimation of each such parameter is injected into a living body with a small sine wave current of a plurality of frequencies arbitrarily selected,
As a bioelectrical impedance measuring device that performs digital signal processing on the obtained signal, Japanese Patent Application Laid-Open No. 6-506854 is disclosed.
The one described in Japanese Patent Application Laid-Open Publication No. H10-260, 1993 is known.

[0007]

However, in the conventional device described in the above publication, in addition to the complicated structure of the device, minute sine wave currents of a plurality of arbitrarily selected frequencies are applied to a living body at predetermined intervals. It takes several seconds to complete all measurements because it is turned on and processing the resulting signal. Therefore, there is a drawback that it is easily affected by breathing, pulse, and the like for the following reasons.

First, the effect of respiration will be described. As described above, the resistivity of fat is known to be extremely high, but the electrical impedance of air is also extremely high. Bioelectric impedance is measured by flowing a small current between a plurality of electrodes mounted on the body surface of a human body, as described above.The electrodes are usually attached to the right hand and right foot of the subject, respectively. The electric current flows from the right arm to the upper right body to the lower right body to the right foot, and passes through the upper right body (right lung), which is rich in air. The bioelectric impedance is affected by the cell membrane capacitance Cm (see FIG. 11), and this capacitance Cm changes due to respiration.

[0009] Bioelectric impedance is related to hemodynamics, metabolic capacity, and the like, and is also closely related to blood flow. That is, the blood flow of the body is a part of the amount of water in the body, and changes according to expansion and contraction of the heart. On the other hand, bioelectric impedance changes according to the amount of water in the body. Therefore, the bioelectrical impedance must be measured in consideration of the blood flow that changes according to the expansion and contraction of the heart. However, in the above-described bioelectric impedance measuring apparatus, although there is a close relationship between the bioelectric impedance and the blood flow, the measurement is not performed in consideration of the blood flow, so that the apparatus is affected by the pulse. .

Therefore, in order to reduce the influence of the pulse and respiration, it is conceivable to measure the bioelectric impedance continuously for a longer period than the pulse or respiration cycle. However, if current is continuously applied to the human body for a long time (for example, 1 second or more),
May cause harm to human body. That is, when a sine wave signal is used, there has been a problem that accurate bioelectric impedance, body fat amount, and body water amount cannot be measured.

In order to solve the above problems, it is necessary to measure the bioelectrical impedance in a very short time so as not to be affected by the pulse or the breathing. Instead, it is conceivable to use an impulse-like minute current containing many frequency components. However, in this method, for an extremely short time (for example, 0.1 μm).
In order to concentrate electric energy for about 2 sec., not only a circuit that generates a high voltage is required, but also a very large amount of energy is injected into the human body even in an extremely short time, so that there is no damage or burns. Depending on the danger of life, it is not practical.

The present invention has been made in view of the above-mentioned circumstances, and can more safely and accurately measure bioelectric impedance with a simple structure, and is suitable for use in measuring body fat and body water distribution. An object of the present invention is to provide an impedance measuring device.

[0013]

According to a first aspect of the present invention, there is provided a bioelectrical impedance measuring apparatus having a length of (2 ⁿ -1) bits (n is a positive integer). A longest linear code signal is generated, and the generated longest linear code signal is used as a measurement signal through first and second electrodes conductively attached to two predetermined surface portions of the body of the subject that are separated from each other. Measurement signal supply means for inputting to the body, current measurement means for measuring the current value of the measurement signal input to the body of the subject, and two predetermined surfaces of the body of the subject separated from each other A voltage measuring means for measuring a voltage value generated between predetermined surface portions of the body of the subject through the third and fourth electrodes conductively attached to the site, and the current measuring device and the voltage measuring device Each measured power A storage unit for temporarily storing a value and a voltage value at least at every one cycle of the measurement signal, and a current value and a voltage value stored at least at every one cycle of the measurement signal in the storage means by a Fourier transform process. Converted into a current value and a voltage value for each frequency, for each frequency, calculate the bioelectric impedance between the parts of the living body, and the bioelectric impedance or bioelectric impedance to be obtained from the obtained bioelectric impedance for each frequency And an output means for outputting a result calculated by the operation means.

According to a second aspect of the present invention, there is provided the bioelectrical impedance measuring apparatus according to the first aspect of the present invention, wherein the measuring signal supply means shifts an input signal according to a clock having a predetermined period. (N is a positive integer) of shift registers and a plurality of logic circuits, each of which includes at least one output signal of the n shift registers or an output signal of another logic circuit. Is input to any of the shift registers to generate a longest linear code signal having a length of (2 ⁿ -1) bits, and using the generated longest linear code signal as a measurement signal, Is inserted into the body of the subject via first and second electrodes conductively attached to two predetermined surface portions of the body that are separated from each other.

According to a third aspect of the present invention, there is provided the bioelectrical impedance measuring apparatus according to the first aspect of the present invention, wherein the measuring signal supply means has a length of (2 ⁿ -1) bits (n is The longest linear code signal of (positive integer) is generated by software.

According to a fourth aspect of the present invention, there is provided the bioelectrical impedance measuring apparatus according to the second aspect of the present invention, wherein the measurement signal supply means includes the n shift registers (n is a positive integer). And the plurality of logic circuits are configured by software.

The invention according to claim 5 is based on claim 1,
5. The bioelectrical impedance measuring apparatus according to the invention described in 2, 3, or 4, wherein the measurement signal supply means has a cycle of 2 ^p times (p is a positive integer) the cycle of the longest linear code signal, A signal obtained by modulating the longest linear code signal with a rectangular wave signal having a duty of 50% is input to the body of the subject as the measurement signal, and the calculation means stores the measurement signal in the storage means. The present invention is characterized in that the current value and the voltage value stored at least for each cycle are converted into the current value and the voltage value for each frequency by a fast Fourier transform process.

The invention according to claim 6 is based on claim 1,
The bioelectrical impedance measuring apparatus according to any one of claims 2, 3, 4, and 5, further comprising human body characteristic data input means for inputting human body characteristic data including at least height data and weight data of the subject, The calculating means obtains an impedance locus based on the bioelectrical impedance for each frequency using a least squares calculating method, and obtains the bioelectricity of the subject at a frequency of 0 and at an infinite frequency from the obtained impedance locus. Calculate impedance, calculate the intracellular fluid resistance and extracellular fluid resistance of the subject based on the calculated bioelectric impedance at the time of frequency 0 and the frequency infinity, and the intracellular fluid resistance and extracellular fluid resistance, Based on the human body characteristic data of the subject input by the human body characteristic data input means, the intracellular fluid volume and extracellular Of the amount and total serving fluid volume thereof it is characterized by estimating an at least.

The invention according to claim 7 is based on claim 1,
The bioelectrical impedance measuring apparatus according to any one of claims 2, 3, 4, and 5, further comprising human body characteristic data input means for inputting human body characteristic data including at least height data and weight data of the subject, The calculating means obtains an impedance locus based on the bioelectrical impedance for each frequency by using a least squares calculating method, and obtains the biological locus of the subject at a frequency of 0 and at an infinite frequency from the obtained impedance locus. Calculate the electrical impedance, calculate the intracellular fluid resistance and the extracellular fluid resistance of the subject based on the calculated bioelectrical impedance at the time of the frequency 0 and the frequency infinity, and calculate the intracellular fluid resistance and the extracellular fluid resistance. And, based on the human body characteristic data of the subject input by the human body characteristic data input means,
It is characterized in that at least one of the body fat percentage, fat weight and lean body mass of the subject is estimated.

[0020] Further, the invention according to claim 8 is based on claim 1,
7. The bioelectrical impedance measuring apparatus according to claim 2, 3, 4, 5, or 6, wherein the first to fourth electrodes are connected to corresponding circuits by coaxial cables,
At least a shield portion of the coaxial cable connected to the third and fourth electrodes is maintained at a potential intermediate between the potential of the third electrode and the potential of the fourth electrode.

[0021]

According to the structure of the present invention, despite the fact that the measurement signal contains many frequency components, the energy is dispersed to the extent that it is instantaneous but not dangerous to the subject, and the amplitude of the frequency spectrum is equal to the entire frequency. Since the longest linear code signal, which is substantially flat over the region, is used, the measurement of the state of body fat and the distribution of water in the body can be performed without damaging the living body, and can eliminate the effects of respiration and pulse. Good S / N measurement over the frequency domain is possible. Further, the measurement signal can be generated only from the shift register and the plurality of logic circuits, so that the configuration becomes very simple.

In another configuration of the present invention, a signal obtained by modulating a longest linear code signal with a rectangular wave signal is used as a measurement signal, and a current value and a voltage value, which are measurement results, are subjected to fast Fourier transform processing. Thus, since the current value and the voltage value are converted into the values for each frequency, the calculation time can be greatly reduced.

Further, in another configuration of the present invention, the bioelectrical impedance at the infinite frequency can be obtained by making full use of the calculation method of the least squares method, so that the influence of stray capacitance and external noise can be avoided, and the cell membrane Pure extracellular fluid resistance and pure intracellular fluid resistance can be obtained without containing a capacity component.
Therefore, much better measurement reproducibility and measurement accuracy than before can be realized.

Further, in another configuration of the present invention, the first to fourth electrodes are connected to the corresponding circuits by coaxial cables, and the shield portion of the coaxial cable connected to at least the third and fourth electrodes. Is maintained at an intermediate potential between the potential of the third electrode and the potential of the fourth electrode, so that the voltage drop of the AC component of the measurement signal due to the capacitance appearing between the shield part of the coaxial cable and the ground is reduced. This also achieves good S / N measurement accuracy.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. The description will be specifically made using an embodiment. FIG. 1 is a block diagram showing an electrical configuration of a bioelectrical impedance measuring apparatus according to a first embodiment of the present invention.
FIG. 2 is a schematic diagram schematically showing a use state of the device. Bioelectrical impedance measuring apparatus 100 of this example
Sends the probe current Ia as a measurement signal to the keyboard 1 and the body B of the subject, as shown in FIGS.
Thereby, the measurement processing unit 2 for digitally processing the voltage / current information obtained from the body B of the subject and the respective units of the apparatus are controlled, and the bioelectric impedance and the body fat of the human body are determined based on the processing results of the measurement processing unit 2. A CPU (Central Processing Unit) 3 for calculating various quantities related to the distribution of water in the body, and a display for displaying the bioelectric impedance, the body fat amount, the body water amount, and the like of the body B of the subject calculated by the CPU 3 A ROM 5, which stores a processing program of the CPU 3, a data area for temporarily storing various data (for example, height, weight, sex of the subject, amounts of extracellular fluid and intracellular fluid, etc.) and a work area of the CPU 3; And a RAM 6 to be set.

The keyboard 1 is used by a measurer to input a measurement start switch for instructing the start of measurement, a human body characteristic item such as height, weight, sex, and age of the subject, and to measure the total measurement time T and measurement interval t. The operation data of each key supplied from the keyboard 1 is converted into a key code by a key code generation circuit (not shown), and Supplied to

The measurement processing unit 2 is attached to a PIO (Parallel interface) 71, a measurement signal generator 72, a low-pass filter (hereinafter, referred to as LPF) 73, a coupling capacitor 74, and a predetermined part of the body. An output processing circuit composed of an electrode Hc, electrodes Hp, Lp, Lc, a coupling capacitor 80a, 80b, 90, a differential amplifier 81, and an I / V converter (current / voltage conversion) which are also adhered to a predetermined part of the body. Device) 91, LPF 82 comprising an analog anti-aliasing filter,
92, an A / D converter 83, 93 and an input processing circuit comprising sampling memories (ring buffers) 84, 94.

In the measurement processing section 2, the measurement signal generator 7
1 is equal to or greater than 10 kΩ over the entire signal frequency range in which the output resistance is generated. Each time a signal generation instruction signal is supplied from the CPU 3 via the PIO 71 at a predetermined cycle t during the entire measurement time T, The longest linear code (maximal li
LPF7 that repeatedly generates the probe current Ia of the (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.
3 and a coupling capacitor 74 that removes the DC component from flowing to the subject's body B so as not to flow to the surface electrode Hc. The value of the probe current Ia is, for example, 500 to
800 μA. The supply period of the signal generation instruction signal is set to a measurement interval t set by the measurer using the keyboard 1.
Matches. 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 set arbitrarily by the measurer using the keyboard 1.
The number of repetitions increases as the number of repetitions increases, but although it is a minute current, it may adversely affect the human body when continuously applied to the human body for a long time. Therefore, the number of repetitions is preferably 1 to 256.

As shown in FIG. 2, the surface electrode Hc is conductively attached to the right back part H of the subject during measurement by an adsorption method. Therefore, the measurement signal (probe current)
Ia enters body B from the right hand part of the subject. The coupling capacitor 74 and the surface electrode Hc are connected by a coaxial cable (not shown), and the shield of the coaxial cable is grounded.

Here, the M-sequence signal will be described. M
The sequence signal is a code signal generally used in a spread spectrum communication system or a spread spectrum ranging system, and is the longest code sequence generated by a shift register or a delay element having a certain length. A binary M-sequence signal generator that generates an M-sequence signal having a length of (2 ⁿ -1) bits (n is a positive integer) is a logical combination of an n-stage shift register and the n-stage state And a logic circuit (exclusive OR circuit) that feeds back to the input of the shift register. The output of the M-sequence signal generator and the state of each stage at a certain sample time (clock time) are functions of the output of the feedback stage at the immediately preceding sample time. In this embodiment, as the measurement signal generator 71, an M-sequence signal generator having eight stages (n = 8) of shift registers is used. Further, the frequency of the shift clock of the shift register is set to 2 MHz.

As described in the section of “Problems to be Solved by the Invention”, when an impulse signal is used, energy is concentrated at a small time interval (about 0.1 μsec), while an M-sequence signal is used. The probe current using, although containing many frequency components, disperses the energy in about 1 msec, without damaging the living body,
In addition, since they occur at time intervals sufficiently shorter than the pulse or respiratory cycle, they are not affected by these. 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 S / N frequency characteristic 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 S / N frequency characteristic is also substantially flat. For details of the M-sequence signal, see “Spread Spectrum Communication System” by RC Dixon (P56 to P89).

Next, the input processing circuit will be described. As shown in FIG. 2, the surface electrode Hp is conductively attached to the right back part H of the subject by suction, while the surface electrode Lp is conductive to the right instep L by suction. Pasted. As shown in FIG. 3, the coupling capacitors 80a and 80b and the surface electrodes Hp and Lp are connected by coaxial cables C1 and C2, respectively, and the shield portions of the coaxial cables C1 and C2 are, as shown in FIG.
The shield drive circuit 85 holds the potential at an intermediate potential between the potential of the surface electrode Hp and the potential of the surface electrode Lp.
The shield drive circuit 85 includes a voltage follower 86 and reference resistors R0 and R0. Reference resistance R
0 and R0 are connected in cascade, one end is connected to a connection point between one end of the coupling capacitor 80a and the coaxial cable C1, and the other end is connected to a connection point between one end of the coupling capacitor 80b and the coaxial cable C2. The connection point between R0 and R0 is connected to the input terminal of the voltage follower 86. The output terminal of the voltage follower 86 is connected to two coaxial cables C1,
It is connected to the shield part of C2.

Here, the reason for using the shield drive circuit 85 will be described with reference to FIG. Surface electrode H
p and Lp are very high impedance when connected to the coupling capacitors 80a and 80b via ordinary cables without using the shield drive circuit 85 or the coaxial cables C1 and C2, but the coaxial cable C
When the shield part is grounded using C1 and C2, FIG.
As shown in FIG. 7, a capacitance CH appears between the cable and the ground. The potential of the surface electrode Lp is set to approximately 0 by grounding the shield using the coaxial cable C2.
V, but since the potential of the surface electrode Hp is high, the capacitance CH is substantially interposed between the surface electrodes Hp and Lp as shown in FIG. The AC component of the measurement current flows to the ground via
A voltage drop occurs between p and Lp. Therefore, as shown in FIG. 3 and FIG.
As a result, the potential V of the shield portion of the coaxial cables C1 and C2 is
When HP is held at the potential {(VHP-VLP) / 2} between the potential VLP of the surface electrode Hp and the potential of the surface electrode Lp, the capacitor CH is connected in series between the surface electrodes Hp and Lp. Next, as shown in FIG.
Since it is the same as the connection of the capacitor CH / 2 between p and Lp, the voltage drop between the surface electrodes Hp and Lp is also halved as compared with the case of FIG.

With this configuration, the voltage between the surface electrodes Hp and Lp can be measured without loss, and a good S / N can be measured. In addition, when the shield part is grounded using the coaxial cables C1 and C2, the capacitance appearing on the surface electrode Hp and the ground is slightly different from the capacitance appearing on the surface electrode Lp and the ground. The same value is used for the sake of simplicity. The above-described phenomenon can also occur in the surface electrodes Hc and Lc. However, since the surface electrodes Hc and Lc have low impedance, the influence is small, and the shield portion of the coaxial cable may be grounded or shielded. The drive may be performed by the drive circuit 85.

Next, the differential amplifier 81 shown in FIG. 1 detects a potential (potential difference) between the two surface electrodes Hp and Lp.
That is, when the probe current Ia is applied to the body B of the subject, the differential amplifier 81 detects the voltage Vp between the right limbs of the subject and inputs the same to the LPF. This voltage Vp is a voltage drop between the surface electrode Hp and the surface electrode Lp due to the bioelectric impedance of the body B of the subject. The LPF 82 removes high-frequency noise from the voltage Vp and supplies it to the A / D converter 83. LPF8
The cutoff frequency of 2 is lower than half the sampling frequency of the A / D converter 83. Thereby, aliasing noise generated in the A / D conversion processing by the A / D converter 83 is removed. The A / D converter 83 converts the noise-removed voltage Vp into a digital signal at a predetermined sampling cycle every time the digital conversion signal Sd is supplied from the CPU 3, and converts the digitized voltage Vp to the sampling cycle. The data is supplied to the sampling memory 84 every time.

Next, as shown in FIG. 2, the surface electrode Lc is attached to the right instep L of the subject by the suction method. The surface electrode Hc and the coupling capacitor 90 (see FIG. 1) are connected by a coaxial cable (not shown), and the shield of the coaxial cable is grounded. I
The / V converter 91 detects a current flowing between the two surface electrodes Hc and Lc and converts it into a voltage. That is, when the probe current Ia is applied to the subject's body B, the I / V converter 91 detects the probe current Ia flowing between the right limb of the subject, converts the probe current Ia to a voltage Vc, and supplies the voltage Vc to the LPF 92.

The LPF 92 removes high-frequency noise from the input voltage Vc and supplies it to the A / D converter 93.
The cutoff frequency of the LPF 92 is lower than half the sampling frequency of the A / D converter 93. In this case, A /
The aliasing noise generated in the A / D conversion processing by the D converter 93 is removed. The A / D converter 93 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 3, and converts the digitized voltage Vc into a sampling cycle. The data is supplied to the sampling memory 94 every time.

The CPU 3 starts the measurement by the measurement processing unit 2 according to the processing program stored in the ROM 5, and detects the detection voltages Vp, Vp at a predetermined sampling cycle.
After sampling c for a predetermined number of times, the following processing is performed in addition to the control for stopping the measurement. That is, the CPU 3
First, the voltages Vp and Vc, which are functions of time, stored in the sampling memories 84 and 94 are sequentially read out, and the voltages Vp (f) and Vc (f) (f Is converted to a frequency), and averaging is performed to calculate bioelectric impedance Z (f) {= Vp (f) / Vc (f)} for each frequency. Next, based on the obtained bioelectric impedance Z (f) for each frequency, the CPU 3 obtained an impedance locus D as shown in FIG. From the impedance trajectory D, the bioelectric impedance R0 of the subject's body B at the frequency of 0 and the bioelectric impedance R∞ at the frequency of infinity are calculated,
From the calculation result, the intracellular fluid resistance and the extracellular fluid resistance of the body B of the subject are calculated.

In the column of “Prior Art”, cells in human cells are represented by a simple electric equivalent circuit (see FIG. 11).
In an actual human body tissue, cells of various sizes are irregularly arranged. Therefore, an electrical equivalent circuit close to the actual one has a capacitance having 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 resistors are distributed (Re is extracellular fluid resistance, Rik is intracellular fluid resistance of each cell, and Cmk is cell membrane capacity of each cell). Therefore, in this embodiment, an electric equivalent circuit (FIG.
) To determine the intracellular fluid resistance and the extracellular fluid resistance, so that the impedance locus D of the human body is
As shown in FIG. 5, the center is an arc that is higher than the real axis.

Next, the calculated intracellular fluid resistance and extracellular fluid resistance, and the height of the subject input from the keyboard 1,
Based on human body characteristic data such as weight, gender and age,
Making full use of the body composition estimation formula incorporated in the processing program in advance, the intracellular fluid, extracellular fluid,
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) are calculated. Then, the calculated data are displayed on the display unit 4 including a display controller and a display (for example, an LCD).

When the bioelectrical impedance measuring apparatus 100 having the above configuration is used, first, as shown in FIG. 2, two surface electrodes Hc and Hp are placed on the right back part H of the subject before measurement. The surface electrodes Lp and Lc are attached to the right instep L of the subject by suction, respectively (at this time, the surface electrodes Hc and Lc are attached to a portion farther from the center of the human body than the surface electrodes Hp and Lp). ). Next, the measurer (or the subject himself) uses the keyboard 1 of the bioelectrical impedance measurement device 100 to
The human body characteristic items such as weight, sex, and age are input, and the total measurement time T from the start of measurement to the end of measurement, the measurement interval t, and the like are set. Data and setting values input from the keyboard 1 are stored in the RAM 5.

Next, when the measurer (or the subject) turns on the measurement start switch of the keyboard 1, the CPU 3
Sends a signal generation instruction signal to the measurement signal generator 72 of the measurement processing unit 2 after performing a predetermined initial setting. As a result, the measurement signal generator 72 repeatedly generates the M-sequence probe current Ia a predetermined number of times, and outputs LP as the measurement signal.
The signal is transmitted to the surface electrode Hc (see FIG. 2) attached to the back H of the subject via the F73, the coupling capacitor 74, and the coaxial cable (not shown).
The measurement signal Ia of 0 μA flows from the surface electrode Hc through the body B of the subject, and the first measurement is started.

When the measurement signal Ia is applied to the body B of the subject, the differential amplifier 81 of the measurement processing unit 2 outputs the electrode H
The voltage Vp generated between the right limb with p and Lp affixed thereto is detected and supplied to the A / D converter 83 via the LPF 82. On the other hand, in the I / V converter 91, the electrodes Hc, Lc
The probe current Ia flowing between the right hand and the foot on which is attached is detected and converted to a voltage Vc, and then supplied to the A / D converter 93 via the LPF 92. At this time, a digital conversion signal Sd is supplied from the CPU 3 to the A / D converters 83 and 93 in each sampling cycle. The A / D converter 83 converts the voltage Vp into a digital signal each time the digital conversion signal Sd is supplied, and supplies the digital signal to the sampling memory 84. The sampling memory 84 sequentially stores the digitized voltage Vp. On the other hand, the A / D converter 93 converts the voltage Vc into a digital signal each time the digital converted signal Sd is supplied, and supplies the digital signal to the sampling memory 94. The sampling memory 94 sequentially stores the digitized voltage Vc.

The CPU 3 calculates the probe current (measurement signal) I
When the number of repetitions of “a” reaches a preset number, after performing control to stop the measurement, first, the voltages Vp, which are stored in the sampling memories 84 and 94 and are a function of time, as a function of time.
The voltages Vp (f) and Vc (f), which are functions of frequency, are sequentially read out and subjected to Fourier transform processing.
(F is a frequency), and after averaging, the bioelectrical impedance Z (f) ｛= Vp (f) /
Vc (f)} is calculated. Next, based on the calculated bioelectrical impedance Z (f) for each of the calculated frequencies, the CPU 3 performs curve fitting by a calculation method of the least squares method, and obtains an impedance locus D as shown in FIG. From the obtained impedance locus D, the bioelectrical impedance R0 of the subject B at the frequency of 0
And the bioelectrical impedance R∞ at the infinite frequency (corresponding to the X coordinate value of the point where the arc of the impedance locus D intersects the X axis). From the calculation result, the intracellular fluid resistance of the subject's body B and Calculate extracellular fluid resistance.

The CPU 3 executes a processing program in advance based on the calculated intracellular fluid resistance and extracellular fluid resistance, and human body characteristic data such as the height, weight, sex, and age of the subject input from the keyboard 1. Making full use of the body composition estimation formula incorporated in, the intracellular fluid, extracellular fluid, body fat percentage, fat weight, lean body mass, intracellular fluid volume, extracellular fluid volume of the subject's body B Each of these total body water amounts (body fluid amounts) is calculated. Then, the calculated data are stored in the RAM 6 and displayed on the display unit 4. Next, the CPU 3 determines whether or not the total measurement time T has elapsed. If it is concluded that the measurement time T has elapsed, the CPU 3 terminates the subsequent measurement processing. If not, the CPU 3 determines the time corresponding to the measurement interval. After waiting for t to elapse, the same measurement processing is started again. Then, the above process is repeated until the entire measurement time T has elapsed.

As described above, according to the configuration of this example, the probe current Ia disperses in energy of about 1 msec despite including many frequency components.
Since the amplitude of the frequency spectrum uses an M-sequence signal that is almost flat over the entire frequency range, it does not damage the living body and removes the effects of respiration and pulse in the measurement of body fat status and body water distribution. It is possible,
Good S / N measurement over the entire frequency range is possible. Further, the measurement signal can be generated only from the shift register and the plurality of logic circuits, so that the configuration becomes very simple.
In addition, the bioelectrical impedance at infinite frequency can be obtained by using the curve-squaring method using the least squares method, so that the effects of stray capacitance and external noise can be avoided. External fluid resistance and intracellular fluid resistance can be determined.

Further, the surface electrodes Hc, Hp, Lp, Lc
Since the coupling capacitors 74, 80a, 80b, 90 are interposed between the circuit elements 73, 81, 91,
It can flow into the living body or cut the direct current component of the current flowing in the living body, which is safe for both the living body and the device. In addition, a coaxial cable is inserted between the surface electrodes Hc, Hp, Lp, Lc and the circuit elements 73, 81, 91, and at least a shield portion of the coaxial cable C connected to the surface electrodes Hp, Lp is shielded. Drive circuit 85
(See FIG. 3), the potential between the potential VHP of the surface electrode Hp and the potential VLP of the surface electrode Lp is maintained at an intermediate potential, so that the voltage of the AC component of the measurement signal due to the capacitance appearing between the shield part of the coaxial cable and the ground. The drop can be reduced, and the probe current Ia having a good S / N can be detected.

Further, the output resistance of the measurement signal generator 71 is 10 kΩ over the entire range of the signal frequency for generating the resistance.
At the same time, since the coupling capacitor 74 is interposed between the LPF 73 and the surface electrode Hc, the surface electrode Hc can be substantially regarded as a constant current source, and the probe current is determined by the bioelectric impedance (about 1 kΩ). I
The current value of a does not change, the maximum value of the current flowing through the living body is determined, and the living body is safe. Therefore, it is possible to more accurately and safely estimate the state of the body fat and the distribution of the body water of the subject.

Second Embodiment Next, a second embodiment will be described. This second embodiment
Represents the measurement shown in FIG. 1 in the configuration of the first embodiment.
Only the configuration of the signal generator 72 is different. That is, the first actual
In the example, the measurement signal generator 72ⁿ-1) bit
, And generates it with the probe current I
a, but in the second embodiment, the M sequence
The signal is modulated by a square wave signal, and the modulated signal is
Output as probe current Ia. FIG. 7 shows an exclusive logic.
A modulator 72a composed of a sum circuit, which converts an M-sequence signal SM1
Modulation is performed with the modulation signal SM2. The length of the M-sequence signal SM1 is
As in the first embodiment, (2ⁿ-1) bits, while
The modulation signal SM2 is a square wave signal having a duty of 50%.
Therefore, the cycle is the cycle of the M-sequence signal SM1 (2ⁿ-1)
2^p(P is a positive integer). Modulation with M-sequence signal SM1
FIG. 8 shows an example of a timing chart of the signal SM2. This
In the example of the figure, n = 8 and p = 2. That is, M system
The cycle of the column signal SM1 is determined by the shift of the M-sequence signal generator.
The shift clock frequency of the register is the same as that of the first embodiment.
Like 2MHz, ｛(2 ⁸-1) / (2 × 1
0⁶)｝ = 255 / (2 × 10⁶) = 127.5 μse
c, the period of the modulation signal SM2 is 127.5 μsec^Two
It becomes 510 μsec by double.

When the M-sequence signal SM1 and the modulation signal SM2 are represented on the frequency axis, they are as shown in FIGS. 9A and 9B, respectively. In these figures, f is the modulation signal SM2
1 / (510 × 10 ⁻⁶ ) = 1.9
6 kHz. Therefore, the frequency 0, 2 ^p f of the spectrum shown in FIG. 9 (a), 2 × 2 p f, 3 × 2 p f, ·
.. are 0kHz, about 7.84kHz, about 1 respectively
5.7 kHz, about 23.5 kHz, ... Also, in FIG. 9B, f is the frequency interval of the spectrum (generally equal to the fundamental frequency), (m ₁ ×
m ₂ × ...... × m _k), the period of the M-sequence signal SM1 (2 ⁿ -
1) as a product of divisors, and in this example, n =
8, k = 3, m ₁ = 3, m ₂ = 5, m ₃ = 17, that is, (2 ⁸ −1) = 3 × 5 × 17 = 255. Therefore, the frequency interval f of the spectrum is 1.96 × 10 ³
/255=7.69 Hz. The frequency interval of this spectrum is represented by W. When such an M-sequence signal SM1 and modulated signal SM2 are input to the modulator 72a shown in FIG. 7, convolution integration is performed on the frequency axis, and the spectrum of the modulated signal is as shown in FIG. 9C. . In this figure, the frequency of the spectrum indicated by the arrow is a value higher by W than the center frequency of each spectrum, and it can be seen that energy is concentrated in this portion. In other words, each spectrum of the center frequency 0 × 2 ^p f,
^{1 × 2 p f, 2 ×} 2 p f, relative · · ·, W, ^{i.e., 0 × 2 p f + f} , 1 × 2 p f + f, 2 × 2 p f + f,
..., if ^{generalized, q × 2 p f + f} (q = 0,1,
The energy is concentrated at the frequency (q × 2 ^p +1) f corresponding to (2,...).

Therefore, the modulated signal having the above-mentioned frequency characteristic is applied to the subject's body B as a measurement signal,
By selecting only the frequency (q × 2 ^p +1) f where the energy is concentrated from the obtained signals and performing the fast Fourier transform processing, the number of calculations is reduced by the fast Fourier transform processing for all the spectra. Number of calculations 2 ^P (2 ⁿ −1) (2 × P + m ₁ + m ₂ +... + M _k )
A 1/2 ^P of ^{(2 n -1) (2 ×} P + m 1 + m 2 + ......
+ M _k ) times, and the calculation time can be greatly reduced.

Next, the timing of signal processing in this embodiment will be described. As described above, in order to increase the measurement accuracy by minimizing the effects of breathing and pulse as well as to minimize the effects on the human body, the measurement current was passed through the subject's body for a very short time, and the data was collected multiple times. Capture and average them. In this embodiment, 256 data acquisitions and averaging are performed, and one data acquisition time is one cycle of the modulation signal S _M2 , and the data acquisition interval is 3 times the modulation signal S _M2 . It is assumed to be for a cycle That is, since one cycle of the modulation signal S _M2 is 510 μsec, one data acquisition time is also 510 μsec, and the data acquisition interval is 510 μsec × 3 = 15.
30 μsec, total measurement time is (510 + 1530) μ
sec × 256 ≒ 0.522 sec. Therefore, the time during which the measurement current is continuously applied to the subject's body is about 0.5 sec, and the measurement accuracy can be improved by minimizing the influence of respiration and pulse, and the influence on the human body is minimized. Can be

According to the configurations of the first and second embodiments described above, the measurement accuracy can be increased as compared with the conventional one. However, in order to maintain the measurement accuracy, calibration is periodically performed by the following method. I do. That is, as shown in FIG. 10, the bioelectric impedance measuring device 10 is connected to two reference impedance elements Z ₁ and Z ₂ whose impedance values are known.
After the 0 surface electrodes Hc, Hp, Lc, Lp are connected alternately, the impedance is measured in the same measurement procedure as in the first and second embodiments, and the known impedance values Z ₁ ,
Z ₂ and the impedance value Z ′ ₁ obtained by the measurement,
Calibrated based on the Z _'2 and. Impedance element 20
Ideally, it is necessary to use a temperature characteristic that is flat and has an impedance value and a frequency characteristic equal to the bioelectric impedance of a human body. Is used (resistance value: 200Ω, 500Ω).

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 within the scope of the present invention. The present invention is included in the present invention. For example,
Bioelectric parameters to be calculated are not limited to bioelectric impedance, impedance trajectory, extracellular fluid resistance and intracellular fluid resistance, bioelectric admittance, admittance trajectory, bioelectric impedance or bioelectric admittance, extracellular fluid resistance and intracellular The amount of change over time in liquid resistance and the like and a part thereof may be used. In this way, not only measurement of body fat percentage and the like but also application to various medical measurements (for example, dialysis state measurement) can be performed. Can be expected. Also,
The location where the electrode is attached is not limited to the hand or foot.

The shift register and the logic circuit constituting the M-sequence signal generator may be of a hardware configuration or of a software configuration.

In the above embodiment, the LPF 82 and the A / D converter 83, and the LPF 92 and the A / D converter 93
However, instead of these, a pair of cascade-connected LPFs and A / D converters or one A / D converter and an input terminal and an output terminal thereof are attached. May be provided. Thereby, at least A /
The number of D converters can be reduced to one, and the configuration can be further simplified. Further, in the above-described embodiment, the case where the height, weight, gender, age, and the like of the subject are input as the human body characteristic items has been described. However, gender, age, and the like may be omitted as necessary. Items such as species may be added. The calculated bioelectric parameters of the human body may be output to a printer. Further, a pulse wave sensor or a sensor capable of detecting a respiratory cycle may be attached to a human body, and the measurement timing may be set based on an output signal of each sensor.

[0057]

As described above, according to the bioelectrical impedance measuring apparatus of the present invention, the measurement signal
Despite including many frequency components, energy is dispersed to the extent that it is instantaneous but not dangerous to the subject, and the amplitude of the frequency spectrum is substantially flat over the entire frequency range. Therefore, in the measurement of the amount of body fat and the amount of water in the body, it is possible to remove the influence of respiration and pulse without damaging the living body, and it is possible to perform a good measurement of the S / N over the entire frequency range. Further, the measurement signal can be generated only from the shift register and the plurality of logic circuits, so that the configuration becomes very simple. That is, the bioelectrical impedance, the state of body fat, and the distribution of body water can be measured more accurately and safely with a simple configuration.

Further, since the bioelectrical impedance at the infinite frequency can be obtained by using the curve fitting method by the least square method, the influence of stray capacitance and external noise can be avoided, and the capacitance component of the cell membrane is not included. Pure extracellular fluid resistance and intracellular fluid resistance can be determined.

In another configuration of the present invention, a signal obtained by modulating a longest linear code signal with a rectangular wave signal is used as a measurement signal, and a current value and a voltage value as measurement results are subjected to fast Fourier transform processing. Thus, since the current value and the voltage value are converted into the values for each frequency, the calculation time can be greatly reduced.

Further, in another configuration of the present invention, the bioelectrical impedance at the infinite frequency can be obtained by making full use of the calculation method of the least squares method, so that the influence of stray capacitance and external noise can be avoided, and the cell membrane Pure extracellular fluid resistance and pure intracellular fluid resistance can be obtained without containing a capacity component. Therefore, much better measurement reproducibility and measurement accuracy than before can be realized.

In another configuration of the present invention, the first to fourth electrodes are connected to the corresponding circuits by coaxial cables, and the shield portion of the coaxial cable connected to at least the third and fourth electrodes. Is maintained at an intermediate potential between the potential of the third electrode and the potential of the fourth electrode, so that the voltage drop of the AC component of the measurement signal due to the capacitance appearing between the shield part of the coaxial cable and the ground is reduced. This also achieves good S / N measurement accuracy.

[Brief description of the drawings]

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

FIG. 2 is a diagram schematically showing a state of use of the bioelectrical impedance measuring device.

FIG. 3 is a block diagram illustrating an example of an electrical configuration of a shield drive circuit.

FIG. 4 is a diagram for explaining the operation principle of the shield drive circuit.

FIG. 5 is a diagram showing 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 block diagram illustrating an example of an electrical configuration of a modulation circuit.

FIG. 8 is a timing chart for explaining the operation of the modulation circuit.

FIG. 9 is a spectrum diagram for explaining the operation of the modulation circuit.

FIG. 10 is a diagram for explaining calibration of the bioelectrical impedance measuring device.

FIG. 11 is a diagram for explaining the prior art, and is a simplified electrical equivalent circuit diagram of cells in a tissue.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Keyboard (human body characteristic data input means) 3 CPU (calculation means) 4 Display part (output means) 72 Measurement signal generator (part of measurement signal supply means) 72a Modulator (part of measurement signal supply means) 73 LPF (Part of measurement signal supply unit) 81 Differential amplifier (part of voltage measurement unit) 82 LPF (part of voltage measurement unit) 83 A / D converter (part of voltage measurement unit) 84, 94 Sampling memory (Storage means) 85 Shield drive circuit 91 I / V converter (part of current measuring means) 92 LPF (part of current measuring means) 100 Bioelectric impedance measuring device Hc, Hp, Lc, Lp Surface electrode (first) ~ 4th electrode)

Claims (8)

[Claims] 1. A method for generating a longest linear code signal having a length of (2 ⁿ -1) bits (n is a positive integer), and using the generated longest linear code signal as a measurement signal, a predetermined distance apart from the body of the subject. Measuring signal supply means for inputting to the body of the subject through first and second electrodes conductively attached to two surface portions; and a current value of the measurement signal applied to the body of the subject. A current measuring means for measuring, between a predetermined surface portion of the subject's body via third and fourth electrodes conductively attached to two predetermined surface portions of the subject's body separated from each other; Voltage measuring means for measuring a resulting voltage value, and storage means for temporarily storing a current value and a voltage value respectively measured by the current measuring means and the voltage measuring means at least at every one cycle of the measurement signal, The storage means The current value and the voltage value stored at least for each cycle of the signal are converted into the current value and the voltage value for each frequency by Fourier transform processing, and the bioelectric impedance between the parts of the living body is calculated for each frequency. ,
Computing means for calculating a bioelectric impedance to be obtained from the obtained bioelectric impedance for each frequency or a physical quantity based on the bioelectric impedance, and output means for outputting a result calculated by the calculating means. Characteristic bioelectrical impedance measuring device. 2. The measurement signal supply means comprises: n (n is a positive integer) shift registers for shifting an input signal according to a clock having a predetermined period; and a plurality of logic circuits. The circuit inputs the result of the logical sum of at least one of the output signals of the n shift registers or the output signal of another logic circuit to any one of the shift registers, so that the length is (2). ^n- 1) generate a longest linear code signal of bits, and use the generated longest linear code signal as a measurement signal to determine a predetermined 2
The bioelectrical impedance measuring device according to claim 1, wherein the bioelectrical impedance measuring device is put into a subject's body via first and second electrodes that are conductively attached to surface portions of the portion. 3. The measuring signal supply means, wherein the length is (2
The bioelectrical impedance measuring apparatus according to claim 1, wherein the longest linear code signal of ( ^n- 1) bits (n is a positive integer) is generated by software. 4. The measurement signal supply means, wherein the n shift registers (n is a positive integer) and the plurality of logic circuits are configured by software. The bioelectrical impedance measuring device according to claim 1. 5. The longest linear signal is a rectangular wave signal whose period is 2 ^p times (p is a positive integer) the period of the longest linear code signal and whose duty is 50%. A signal obtained by modulating a code signal is input to the body of the subject as the measurement signal, and the arithmetic unit calculates a current value and a voltage value stored in the storage unit at least at least one cycle of the measurement signal. 5. The bioelectrical impedance measuring device according to claim 1, wherein the value is converted into a current value and a voltage value for each frequency by a fast Fourier transform process. 6. A human body characteristic data input means for inputting human body characteristic data including at least height data and weight data of the test subject, wherein the calculating means is configured to calculate a minimum value based on the bioelectrical impedance for each frequency. The impedance trajectory is determined by using the square method, and the bioelectrical impedance of the subject at the time of the frequency 0 and the frequency infinity is calculated from the obtained impedance trajectory. The calculated frequency 0 and the frequency infinity are calculated. Based on the bioelectrical impedance at the time, the intracellular fluid resistance and the extracellular fluid resistance of the subject are calculated, and the intracellular fluid resistance and the extracellular fluid resistance, and the human body characteristics of the subject input by the human body characteristic data input means. Based on the data, at least one of the intracellular fluid volume, the extracellular fluid volume, and the total Bioelectrical impedance measuring apparatus according to claim 1, 2, 3, 4 or 5, wherein the estimating. 7. A human body characteristic data input means for inputting human body characteristic data including at least height data and weight data of the test subject, wherein the calculating means is configured to calculate a minimum value based on bioelectric impedance for each frequency. The impedance trajectory is determined by using the square method, and the bioelectrical impedance of the subject at the time of the frequency 0 and the frequency infinity is calculated from the obtained impedance trajectory. The calculated frequency 0 and the frequency infinity are calculated. Based on the bioelectrical impedance at the time, the intracellular fluid resistance and the extracellular fluid resistance of the subject are calculated, and the intracellular fluid resistance and the extracellular fluid resistance, and the human body characteristics of the subject input by the human body characteristic data input means. Based on the data, it is necessary to estimate at least one of the body fat percentage, fat weight and lean body mass of the subject. Bioelectrical impedance measuring apparatus according to claim 1, 2, 3, 4 or 5, wherein the symptoms. 8. The first to fourth electrodes are connected to a corresponding circuit by a coaxial cable, and at least a shield portion of the coaxial cable connected to the third and fourth electrodes is connected to the third electrode. And a potential between the potential of the fourth electrode and the potential of the fourth electrode.
7. The bioelectrical impedance measuring device according to 2, 3, 4, 5, or 6.