JPH06277191A - Method for measuring bio-impedance - Google Patents

Abstract

PURPOSE:To determine impedance of a living body based on a measured value of the living body and a correlation equation without being influenced by the environment by obtaining a correlation equation between the measured value based on a standard resistance and the impedance. CONSTITUTION:50kHz sine wave from an oscillator 1 is made as a const. voltage source and it is taken out as a const. electric current with 800 microampere which does not influence on linear characteristics of impedance of a living body by means of an electric voltage-electric current transducer. A const. electric current is energized into a living body 3 from a pair of electrodes A through a plurality of known standard resistances 9, 10 and 11 covering a measuring range on the average. The value of voltage which is the amt. of decrease in electric voltage caused by a group of the standard resistances and the value of voltage which is the amt. of decrease in electric voltage of a pair of electrodes B fixed on the inside of the living body from the electrodes A are instantaneously switched by means of a switch 12 controlled by an MPU 8 and are taken out into a differential amplifier 4. Treatments such as wave shaping and rectification are performed and it is converted into direct current and then, AD conversion 7 is performed and it is taken into an operating part 8 as a digital data and a correlation equation between the measured value of the standard resistance and the impedance are obtd. and the impedance of the living body is obtd. from the measured value of the living body and the correlation equation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring bioimpedance, and more specifically, an internal fat mass meter for calculating the amount of fat in the body based on physical conditions such as impedance between terminal ends of the body and height and weight. The present invention relates to improvement of a method for accurately measuring the absolute value of bioimpedance over a wide measurement range.

[0002]

2. Description of the Related Art As a method of measuring the amount of fat in the body, the impedance between the ends of the body is measured with a 4-terminal Kelvin Bridge bioimpedance meter, and the value and the numerical values relating to the body such as height, weight and sex of the body The method of calculating the fat mass is USP 4,008,712 or USP 4,
It has been proposed as 895, 163 (Japanese Patent Laid-Open No. 2-60626).

For measuring the bioimpedance of the conventional body fat meter, a 50 KHz sine wave is taken out as a constant voltage source from an oscillator, and this is measured by a voltage-current converter.
A constant current of 00 microamperes is applied, the current flows through a pair of electrodes A attached to the human body, and a voltage value corresponding to a voltage drop is taken out by a differential amplifier from a pair of electrodes B attached inside the electrodes A, and waveform shaping, rectification, etc. The above processing is performed, the DC conversion is performed, the AD conversion is performed, and the digital data is taken into the arithmetic unit.

The bioelectrical impedance Z is determined by the bioelectrical current I and the terminal voltage V, and Z = V / I is established, and the bioelectrical impedance Z can be determined by measuring the voltage V when the current I is constant.

However, the output of the constant current source changes due to external influences such as environmental temperature, and is also affected by the degree of change in the electrode impedance, making it difficult to obtain the bioelectric current I as an accurate constant current. This is a cause of the measurement error of the bioelectrical impedance.

On the other hand, the bioimpedance measured as an internal fat mass meter needs to be accurate within the range of 0 ohm to about 1 k ohm, and it is extremely difficult to obtain an ideal proportional relationship within this range, and the measured value It requires a great deal of work such as correction.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to eliminate the above-mentioned drawbacks of the prior art and to accurately measure the absolute value of the bioimpedance in a wide measurement range without being affected by the environment.

[0008]

[Means for Solving the Problems] A plurality of reference resistors are inserted in a current path flowing through a living body, the reference resistance group and the living body are instantaneously switched, each voltage drop is measured, and measurement is performed according to the reference resistance. The correlation equation between the value and the impedance is obtained, and the impedance of the living body is determined by the measured value of the living body and the correlation equation.

[0009]

EXAMPLES The details of the present invention will be described below with reference to examples.
1 is a block diagram of a conventional method, and FIG. 2 is a block diagram of a bioimpedance measuring unit according to an embodiment of the present invention.

From the oscillator (1), a sine wave of 50 KHz is used as a constant voltage source, and a voltage-current converter (2) extracts a constant current of 800 microampere that does not affect the linearity of bioimpedance.

A plurality of known reference resistance groups (9) (10) (11) that cover the measurement range (the range that needs to be measured as the individual difference in the impedance between the distal ends of the body: 0 to 1 kilohm) on average. ), The constant current flows into the living body (3) from the pair of electrodes A.

The voltage value of each voltage drop due to the reference resistance group and the voltage value of the voltage drop of a pair of electrodes B mounted inside the living body from the electrode A are controlled by the switch (12) controlled by the MPU (8). Momentarily switch to differential amplifier (4)
Then, it is subjected to processing such as waveform shaping and rectification, converted into direct current, then AD converted (7), and taken into the arithmetic unit (8) as digital data.

The calculation unit (8) obtains a correlation equation between the measured value of the reference resistance and the impedance, and determines the impedance of the living body from the measured value of the living body and the correlation equation.

[0014]

According to the present invention, the same amount of current that does not affect the linearity of the bioimpedance flows through the reference resistance and the living body without being affected by the fluctuation due to the environmental change of the constant current source,
Accurate biological impedance can be measured compared to the known impedance, and in order to compare with the correlation between the measured value and the impedance obtained by a plurality of reference resistors covering the measurement range for the time being, the straight line of the detector, The proportionality between the measured value and the impedance is corrected, and the impedance of a living body in a wide range can be accurately measured without being influenced by external factors such as the electrode impedance and the environment.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a conventional method.

FIG. 2 is a block diagram of an embodiment of the present invention.

Claims (1)

[Claims] Insert a plurality of reference resistance in the current path to flow to the living body, switch the reference resistance group and the living body instantaneously, measure the voltage drop of each, to obtain the correlation equation between the measured value depending on the reference resistance and the impedance, A bioimpedance measuring method characterized in that the impedance of the living body is determined by the measured value of the living body and the correlation equation.