JP3492038B2 - Body fat measurement device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a body fat measuring device useful for estimating a body fat percentage, a body fat mass, and the like of a subject based on a bioelectrical impedance method. About. [0002] 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, while 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 bioelectrical impedance, and are measured by passing a small current between a plurality of electrodes mounted on the surface of the human body. The method of estimating the body water content, body fat percentage, body fat mass, etc. of the subject from the bioelectric impedance obtained in this way is called bioelectric impedance method ("Bioelectric impedance method as an evaluation method of 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 living 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). It can be determined geometrically as a phase angle. The geometric relationship among these bioelectrical impedance, resistance, reactance and electrical phase angle is frequency dependent as shown in the impedance diagram of FIG. At very low frequencies fL, the bioelectrical impedance at the cell membrane and tissue interface is too high to conduct electricity. Thus, electricity flows only through body moisture and the measured bioelectrical impedance is purely resistance. The resistance in this case is represented by R0 as the resistance when the frequency is 0 Hz. Next, as the frequency increases, the current penetrates the cell membrane, the reactance increases, and the phase angle φ increases. The magnitude of the bioelectrical impedance is equal to the value of the vector defined by the formula (Z = R ² + X ² ). Reactance X and phase angle φ
The frequency at which both are maximum is called the critical frequency fC,
It is one electrical characteristic value of a living body that is a conductor. Above this critical frequency f C, the cell membrane and tissue interface loses their capacitive capacity and the reactance decreases accordingly. At very high frequencies fH, the bioelectrical impedance again becomes purely equivalent to resistance. The resistance in this case is represented by R∞ as the resistance when the frequency is infinite. FIG. 4 is a circuit-equivalent model of the human body.
This corresponds to the impedance diagram of FIG. In this figure, Rm and Cm represent the resistance and capacitance of the cell membrane, respectively, and Ri and Re represent the intracellular resistance and the extracellular resistance, respectively. At low frequencies fL, the current is mainly flowing in the extracellular space and the impedance is the resistance Re.
Is equal to At high frequencies fH, the current will pass completely through the cell membrane and the resistance Rm and the capacitance Cm are substantially equivalent to being short-circuited. Therefore, the impedance at high frequency fH is equal to the combined resistance Ri.Re/(Ri+Re). By the method described above, resistance, reactance,
Bioelectrical impedance and the like can be obtained, and changes in body water content (extracellular fluid), body fat percentage, and body fat amount can be estimated based on these. In the bioelectrical impedance method described above, 50 kHz, which reflects the water content inside and outside the skeletal muscle tissue and is also the critical frequency fC, is used.
z is used. This is based on the assumption that the total conduction of the human body is equal to the total conduction of body water, most of which is contained in muscle tissue, and the water content of adipose tissue is minimal. However, when measuring bioelectrical impedance at 50 kHz, it is susceptible to respiration. The reason is considered as follows. (1) As described above, the resistivity of fat is known to be extremely high, but the electrical impedance of air is also extremely high. (2) As described above, bioelectric impedance is measured by passing a small current between a plurality of electrodes mounted on the body surface of a human body. And to be attached to the foot respectively,
Electric current flows through the arm, upper body, lower body, and legs, and passes through the upper body (lung), which contains a lot of air. (3) In the case of measurement at 50 kHz, the bioelectrical impedance is affected by the capacitance Cm of the cell membrane (see FIG. 4), and this capacitance Cm changes due to respiration. Therefore, there was a problem that accurate bioelectric impedance, body fat amount, and body water amount could not be measured accurately. The present invention has been made in view of the above circumstances, and has as its object to provide a body fat measuring device capable of measuring bioelectric impedance, body fat mass, and body water mass more accurately. [0009] In order to solve the above-mentioned problems, a body fat measurement device according to the first aspect of the present invention generates a measurement signal whose frequency changes with time in a predetermined range, and outputs the measurement signal to a living body. A measurement signal generating unit to be transmitted, and an electrical quantity for detecting a potential difference and a current generated between any two surface portions of the living body separated from each other based on the measurement signal transmitted to the living body from the measurement signal generating unit. Detection means, storage means for storing the potential difference and current detected by the electrical quantity detection means for each frequency, based on the potential difference and current stored for each frequency in the storage means, for each frequency, Calculating bioelectric impedance between the parts of the living body,
Calculating means for calculating the physical quantity based on bioelectric impedance or bioelectrical impedance to be determined from the obtained bioelectrical impedance for each of the frequency is, ing and an output means for outputting the results calculated by said calculating means a body A fat measuring device , wherein the calculating means is
From the bioelectrical impedance for each frequency,
And second bioelectrical impedance with infinite frequency
The first and second bioelectrical impedances.
Calculate the bioelectric impedance to be obtained from the
It is characterized by . In the configuration of the present invention, the measurement signal generation means generates a measurement signal whose frequency changes with time in a predetermined range, and sends the generated measurement signal to a living body. The electric quantity detection means detects a potential difference generated between any two surface portions of the living body separated from each other and a current flowing between the two portions based on the measurement signal. The detected potential difference and current are temporarily stored in the storage unit. The calculating means calculates the bioelectric impedance between the parts of the living body for each frequency based on the potential difference and the current stored for each frequency in the storage means, and obtains the bioelectric impedance from the obtained bioelectric impedance for each frequency. A bioelectric impedance to be calculated or a physical quantity based on the bioelectric impedance is calculated. The calculated result is output to a display device or a printer. According to the configuration of the present invention, the bioelectric impedance to be obtained is calculated from the bioelectric impedance at a frequency which is not affected by the capacitance which is considered to be changed by breathing. In, the effect of respiration can be reduced. Therefore, the body fat amount and the body water amount of the subject can be more accurately estimated. Embodiments of the present invention will be described below with reference to the drawings. The description will be made specifically using an embodiment. A. FIG. 1 is a block diagram showing an electrical configuration of a body fat measurement device according to an embodiment of the present invention. Measurement device 10
0 sends the keyboard 1 and the measurement signal Ia to the human body,
Thus, the measurement processing unit 2 for digitally processing the voltage and current information obtained from the human body and the respective units of the apparatus are controlled, and based on the processing results of the measurement processing unit 2, the bioelectric impedance of the human body, the amount of body fat, the body water A CPU (Central Processing Unit) 3 for calculating the amount and the like, a display unit 4 for displaying a bioelectric impedance, a body fat amount, a body water amount, and the like of a human body calculated by the CPU 3;
A ROM 5 for storing a processing program of U3;
And a RAM 6 in which a work area is set. The keyboard 1 is composed of a measurement start switch for the operator to instruct the start of measurement, and various keys for setting / changing the total measurement time, the number of measurements, and the like according to the purpose of measurement. 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 CPU 3. The measurement processing unit 2 includes 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. An input processing circuit including electrodes Hp, Lp, Lc attached to the site, a differential amplifier 81, an I / V converter 91, LPFs 82, 92, A / D converters 83, 93, and sampling memories (ring buffers) 84, 94. It is composed of In the measurement processing section 2, the reference clock generator 71 has a period (for example, 800 ns) during the entire measurement time.
The clock CL of c) is generated and supplied to the measurement signal generator 72. The measurement signal generator 72 outputs a measurement signal (current) Ia whose frequency changes within a predetermined range (for example, a range of 1 kHz to 1 MHz) at predetermined intervals (for example, every 15 kHz) for each clock CL during the entire measurement time. The electrode Hc is repeatedly generated and output via the output buffer 73 (see FIG. 1).
To send to. The electrode Hc is attached to a subject's hand by a suction method, as shown in FIG. therefore,
The measurement signal (current) Ia enters the human body from the hand of the subject. Next, the differential amplifier 81 detects a potential (potential difference) between the two electrodes Hp and Lp. Electrode Hp
As shown in FIG. 2, the electrode Lp is attached to the subject's hand by the suction method, and the electrode Lp is attached near the ankle of the foot by the suction method. 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 electrode Hp and the electrode Lp due to the bioelectric impedance of the human body. The low-pass filter 82 removes high-frequency noise from the voltage Vp and supplies it to the A / D converter 83. The A / D converter 83 converts the noise-removed voltage Vp into a digital signal every time the digital conversion signal Sd is supplied from the CPU 3,
Supply to Sampling memory (ring buffer) 8
4, the digitized voltage Vp is the clock CL
Is stored for each cycle defined by the following equation 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. As shown in FIG. 2, the electrode Hc is attached to the subject's hand by the suction method, and the electrode Lc is attached to the vicinity of the ankle of the foot by the suction method. Therefore, I / V converter 9
When the measurement signal Ia is supplied to the human body, 1 detects the current Ib flowing between the limbs of the subject, converts it into a voltage Vc, and supplies it to the low-pass filter 92. The low-pass filter 92 removes high-frequency noise from the voltage Vc and supplies it to the A / D converter 93.
The A / D converter 93 outputs a digital conversion signal S from the CPU 3.
Each time d is supplied, the voltage Vc from which the noise is removed
Is converted into a digital signal and supplied to the sampling memory 94. The sampling memory (ring buffer) 94 stores the digitized voltage Vc for each cycle defined by the clock CL and for each frequency of the measurement signal Ia. Next, according to the processing program stored in the ROM 5, the CPU 3 starts measurement by the above-described measurement processing unit 2, performs sampling for a specified number of times (eg, 100 times), and then performs control to stop the measurement. The following processing is performed. That is, the CPU 3 first reads out the voltages Vp and Vc stored in the sampling memories 84 and 94 sequentially for each frequency of the measurement signal Ia, averages them, and then sets the bioelectric impedance Z (= Vp / Vc) for each frequency. Calculate resistance and reactance. Next, CPU3
Creates an impedance diagram shown in FIG. 3 based on the obtained bioelectric impedance Z, resistance and reactance for each frequency, and obtains the resistances R0 and R∞ from the impedance diagram. And CPU3
Is the frequency 5 from the determined resistances R0 and R∞.
A resistance R50k of 0 kHz is calculated based on the following equation. R50k = (R0 + R∞) / 2 (1) Then, the CPU 3 sets the resistance R50k obtained by the equation (1) as the bioelectric impedance of the subject, and calculates the body fat amount and the body water amount based on this. calculate. Then, the calculated bioelectric impedance, the amount of body fat, the amount of water in the body, and the like are displayed on the display unit 4 including a display controller and a display (for example, an LCD). B. Next, the operation of the above configuration will be described. First, prior to the measurement, as shown in FIG. 2, the electrodes Hc and Hp are attached to the subject's hand, and the electrodes Lp and Lc are attached to the vicinity of the ankle of the subject's foot by suction.
c, Lc are mounted farther from the center of the human body than the electrodes Hp, Lp). Next, the measurer sets the body fat measurement device 100
, The total measurement time from the start of measurement to the end of measurement, the number of measurements, and the like are set. The entire measurement period is at least 2 seconds or more (ie,
(Respiratory cycle or more). The number of measurements is set to 100 times. The number of measurements
For example, about 1 to 300 times is preferable. Next, when the measurer turns on the measurement start switch, the CPU 3 first performs predetermined initial settings, and then instructs the measurement processing unit 2 to transmit a measurement signal. Thus, the measurement signal generator 72 generates the measurement signal Ia in accordance with the clock CL of the reference clock generator 71, and the measurement signal Ia is transmitted to the human body via the output buffer 73 and the electrode Hc (see FIG. 2). The measurement starts. When the measurement signal Ia is supplied to the human body, the voltage Vp generated between the limbs to which the electrodes Hp and Lp are attached is detected in the differential amplifier 81 of the measurement processing unit 2, and the low-pass filter 8
The signal is supplied to the A / D converter 83 via the line 2. On the other hand, I / V
In the converter 91, the current Ib flowing between the limbs to which the electrodes Hc and Lc are attached is detected, converted into a voltage Vc, and then supplied to an A / D converter 93 via a low-pass filter 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 repeats the above-described processing for the designated number of measurements (in this case, 100 times). When the number of measurements reaches 100,
After performing the control to stop the measurement, the CPU 3 firstly sets the voltages Vp, Vp stored in the sampling memories 84, 94.
c is sequentially read and averaged for each frequency of the measurement signal Ia, and the bioelectrical impedance Z (= Vp / V
c) Calculate resistance and reactance. Next, the CPU 3 determines, based on the obtained bioelectric impedance Z, resistance, and reactance for each frequency,
The impedance diagram shown in FIG. 3 is created, and the resistances R0 and R∞ are obtained from the impedance diagram. Then, the CPU 3 determines the obtained resistances R0 and R∞.
The resistance R50k of frequency 50kHz from
It is calculated based on equation (1) . Then, the CPU 3
The resistance R50k obtained by the equation (1) is used as the bioelectric impedance of the subject, and the body fat amount and the body water amount are calculated according to a predetermined algorithm using the bioelectric impedance. Then, the CPU 3 stores the calculated bioelectric impedance, the body fat amount, the body water amount, and the like in the RAM.
6 and displayed on the display unit 4. And
The process ends. As described above, according to the above configuration, the frequency 50 kHz is obtained from the resistances R0 and R # which are not affected by the capacitance Cm which is considered to be changed by breathing.
Is determined as the bioelectrical impedance, so that the influence of respiration can be removed in the measurement of body fat mass and body water mass. Therefore, the body fat amount and the body water amount of the subject can be more accurately estimated. Although the embodiment of the present invention has been described in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and a design change or the like may be made without departing from the gist of the present invention. The present invention is included in the present invention. For example, the calculated bioelectric impedance of the human body may be output to a printer. Further, the calculated bioelectrical impedance of the human body is not limited to the synthetic electrical impedance of the human body, and may be, for example, the extracellular fluid resistance of the human body, the intracellular fluid resistance and their temporal changes and a part thereof. In this way, not only measurement of body fat percentage, etc.,
It can be expected to be applied to various medical measurements (for example, dialysis state measurement). In addition, the location where the electrode is attached is not limited to the hand or foot. Furthermore, a pulse wave sensor or a sensor capable of detecting the cycle of breathing may be attached to the human body, and the measurement timing may be set based on the output signal of each sensor. As described above, according to the body fat measuring device of the present invention, the bioelectric impedance to be obtained is calculated from the bioelectric impedance which is not affected by respiration. In the measurement of the water content in the body, the influence of respiration can be reduced. Therefore, the body fat amount and the body water amount of the subject can be more accurately estimated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an electrical configuration of a body fat measurement device according to one embodiment of the present invention. FIG. 2 is a diagram showing a mounting state of various electrodes of the device. FIG. 3 is a diagram illustrating an example of an impedance diagram. FIG. 4 is a diagram showing a circuit-equivalent model of bioelectric impedance. [Description of Signs] 2 Measurement processing unit 3 CPU (arithmetic means) 72 Measurement signal generator (measurement signal generation means) 73 Output buffer 81 Differential amplifier (electric quantity detection means) 82,92 Low-pass filter (electric quantity detection) Means) 83,93 A / D converter (electric quantity detection means) 84,94 Sampling memory (storage means) 91 I / V converter (electric quantity detection means)

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) A61B 5/05

Claims (1)

(57) [Claim 1] A measurement signal generating means for generating a measurement signal whose frequency changes with time in a predetermined range and transmitting the measurement signal to a living body, and transmitting the measurement signal from the measurement signal generating means to the living body. Based on the measured measurement signal, an electric quantity detecting means for detecting a potential difference and a current generated between any two surface portions of the living body separated from each other; and a potential difference and a current detected by the electric quantity detecting means. Storage means for storing for each frequency, based on the potential difference and the current stored for each frequency in the storage means, for each frequency, the bioelectrical impedance between the parts of the living body was calculated and obtained Calculating means for calculating a bioelectric impedance to be determined from the bioelectric impedance for each frequency or a physical quantity based on the bioelectric impedance; A Ru body fat measurement device name and an output means for outputting the the result, the arithmetic means, bioelectrical impedance for each of the frequency
The first and second frequencies of 0 Hz and infinity
Calculating bioelectrical impedance, the first and second
Bioelectric impedance to be found from bioelectric impedance
A body fat measuring device for calculating a dance .