Abstract:
A four electrode bio-electrical impedance analyzer having a 45 KHz constant current pulse waveform and a synchronized detection scheme to measure the human body impedance and therefore calculate total body resistivity. The resistivity is used in conjunction with the pre-input data concerning characteristics of the person under tests to determine the percentage of body fat in a manner which is repeatable and which suppresses electrical interference.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION  
         [0001]    The present invention relates to an improved impedance analyzer or bio-electrical impedance measurement for calculations to related to body fat.  
           [0002]    The impedance to electrical flow of an injected current has been found to be a function of the volume of a conductor and the square of the conductor&#39;s length. For clinical purposes, bio-electrical impedance measurements make use of this fact to determine a person&#39;s impedance to electrical flow based on the volume of the human body and the square of the height of the human. The measurement of volume impedance in a human using a traditional method provides problems with respect to repeatability and electrical noise interference (hum).  
           [0003]    It is an object of the present invention to provide a circuit arrangement for establishing volume impedance measurements having improved interference suppression as well as consistent repeatability.  
           [0004]    The present invention provides a system of outputting an AC constant current pulse wherein body conductivity is measured in response to the applied pulse to provide a measure of the body fat/body mass ratio.  
           [0005]    Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 is a functional block diagram of the body fat analyzer;  
         [0007]    [0007]FIG. 2 is a circuit diagram of the constant current pulse source of FIG. 1;  
         [0008]    [0008]FIG. 3 is a circuit diagram of the measurement and amplification circuit of FIG. 1; and  
         [0009]    [0009]FIG. 4 is a circuit diagram of the central processor and display unit of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0010]    The bio-electrical impedance analyzer (BIA) of FIG. 1 is a four-electrode system which generates 45 KHz constant current pulse waveforms and provides a synchronized detection scheme to measure human body impedance. From this measurement, the total body “resistivity” is computed using pre-input data concerning the body weight, height, age and sex to determine the percentage of body fat to body mass ratio of the person being tested.  
         [0011]    The 45 KHz constant current pulse source circuit  100  provides the output to electrode A and B which may be typically located on the respective left and right hand bars of a handgrip device. Current flows between terminals A and B when a person places their right and left hand of the bar to establish contact through contact electrode plates M and N also respectively positioned on the left and right handgrip bars. The motoring takes place by way of the impedance measurement and amplification circuit  200  which provides a measure of the body resistivity. The output measured signal strength F from the impedance and amplification circuit  200  is processed in the CPU and display circuit  300 . The output signal strength F is synchronized with the constant current pulse source circuit  100  by way of the output S from the circuit  100  which functions to suppress electrical interference and to improved the ability to repeat measurements on an consistent basis. The microprocessor, using the synchronized measured signal strength determines body fat/body mass ratio.  
         [0012]    A constant current pulse source circuit  100 , in the preferred embodiment is formed by a 45 KHz oscillator  110 , the constant current source  120 , the polarity switching circuit  130  and the synchronized conditioning and detection circuit  140 . The oscillator circuit  110  is formed by oscillator elements L 3   a , L 3   b , L 3   c  and L 3   d  as shown in FIG. 2. The constant current source uses the transistor N 1  supported by interconnected resistor circuits R 3 -R 6  in conjunction with capacitor E 1  and Zener diode Z 1 . The modulation of the output of constant current source  120  by the oscillator  110  is provided by polarity switching circuit  130  using analogs switch L 2   a , L 2   b , L 2   c  and L 2   d  to provide an AC current between the contact electrodes A and B as a stimulant signal. Amplifier circuits L 1   b  and LSN form the conditioned output circuit  140  which output the synchronization signal S.  
         [0013]    Induced current flow is measured from the contact electrodes M and N by op-amps L, L 1   a , L 1   c  and L 4   c  in the measuring circuit  210  of FIG. 3. Subsequently the bipolar magnitude signal is modified and combined by rectifier circuit  220  to provide the output signal F as an analog signal to the processor circuit  300  of FIG. 4. Incoming induced current flow signal due to the body resistivity is converted, in processor circuit  300 , by the analog/digital converter L 8  and is output to the micro-controller L 7 . The micro-controller L 7  is an 8-bit micro-controller which is the main processor for all control and the key pressing functions and display. S 1 , S 2 , and S 3  are keyinputs. S 3  is a Set key used to enter the parameter setup mode. S 1  is the UP key to increase a selected parameter and S 2  is the Down key to decrease the selected parameter. The display portion includes the LED&#39;s  301 ,  302 ,  303  and seven-segment drivers  311 , 312 , 313 . L 9  is a  3 - 8  decoder for converting output to drive the LEDs.  
         [0014]    The micro-controller L 7  includes pre-input data concerning body weight, height, age and sex of the person holding the handgrip. This pre-input data is combined with the digital magnitude of the induced current flow due to the body resistivity to provide an index for body fat to body mass ratio on the LED display.  
         [0015]    Although specific circuitry is used for providing the oscillator  110 , the switching circuit  130 , the conditioning circuit  140 , the constant current source  120  and the measurement circuit  210  and rectifier circuit  220  and well as the analog/digital converter L 0 , other circuitry known to those skilled in the art for accomplishing the same purpose may be used for each of the specific elements.  
         [0016]    The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.