referring to fig1 a body fat measuring apparatus is shown as an embodiment of the present invention . this apparatus comprises an electronic body weighing meter 5 having a base 1 on its upper surface , an electronic height meter 4 , and a display unit 6 . this electronic body weighing meter 5 electronically calculates a patient &# 39 ; s body weight when a patient stands on the base 1 . the electronic height meter 4 detects the height of a patient standing on the base 1 using a detector 4 a and electronically calculates the height value . as shown in fig2 and 3 , the base 1 formed of an insulating material , and a pair of conductive electrodes 3 for a patient &# 39 ; s heels and conductive electrodes 2 for a patient &# 39 ; s toes are mounted symmetrically with respect to the width of the base spaced to allow the patient to stand upright so that the patient &# 39 ; s feet are not touching when the patient stands thereon on both feet . the electrodes 2 and 3 are set to 5 cm or more apart so as to eliminate the influence of a potential distribution . the electrodes 2 are formed in an elliptical shape so as to correspond to various sizes of a patient &# 39 ; s foot . the electrodes 2 are used as current supply electrodes , and the electrodes 3 are used as voltage detecting terminals . heel guides 7 are provided at the rear of the electrodes 3 so that a user can always stand at a predetermined position on the base 1 with his heels in contact with the electrodes . an electronic circuit for carrying out a body impedance measuring method according to the present invention is placed in the housing of the electronic body weighing meter 5 , and an example of the electronic circuit as shown in a block diagram of fig4 . in fig4 electrodes a correspond to the electrodes 2 for the patient &# 39 ; s toes in fig1 to 3 , and electrodes b correspond to the electrodes 3 for the patient &# 39 ; s heels in fig1 to 3 . the body impedance measuring electronic circuit in fig4 measures a patient &# 39 ; s body impedance when a patient stands on the base 1 of the apparatus in fig1 in such a manner that the patient &# 39 ; s toes and heels are contacted correspondingly with the electrodes 2 ( a ) and the electrodes 3 ( b ). an oscillator 11 generates a sine wave of 50 khz as a constant - voltage source , which is converted to a constant current of 800 microamperes by a voltage / current converter 12 , which does not affect influence to linearity of a body impedance . the constant current is supplied from a pair of electrodes a through a plurality of reference resistors 12 , 14 , 15 having known resistances to cover an average measuring range ( a range necessary to measure an impedance between the extremities of a patient &# 39 ; s body as individual differences : 0 to 1 kilo - ohm ). values of voltage drops of the reference resistors 13 , 14 , 15 in a group , and values of voltage drops of the pair of electrodes b mounted inside a living body from the electrodes a are momentarily switched by a switch 16 to be controlled by a microprocessor unit ( mpu ) 21 which includes a calculator , and differences therebetween are output by a differential amplifier 17 . the voltage value output by the differential amplifier 17 is rectified by a rectifier 18 , waveform - shaped by a low pass filter ( lpf ) 19 to be dc - converted , a / d - converted by an analog / digital converter ( ad ) 20 , and input as digital data to be microprocessor unit 21 obtains a correlation formula between the measured value of the reference resistor and the impedance , and determines a living body impedance from the measured value of the patient &# 39 ; s living body and the correlation formula . an electronic circuit for using in a body fat measuring method according to the present invention is also associated in the housing of the electronic body weighing meter 5 . this body fat measuring electronic circuit calculates a patient &# 39 ; s body fat as below from the patient &# 39 ; s weight measured by the electronic body weighing meter 5 , the patient &# 39 ; s height measured by the electronic height meter 4 and the patient &# 39 ; s body impedance calculated by the above - described body impedance measuring electronic circuit . an inference formula of body density ( db ) of segal et al ., using weight ( w ), height ( ht ) and impedance ( z ), is represented by : the value proportional to the weight and the impedance z and inversely proportional to the square of the height is subtracted from the constant a . however , as described above , it is known that the impedance value varies due to various factors such as variation in body water ratio in fat - free tissue due to variation in weight , blood plasma due to variation in motion or attitude and movement of interstitial liquid in a short period . the variation in the impedances greatly influences the body density in the formula ( 1 ), but the variation factor of the impedance does not originally greatly vary the body density . in order to reduce the influence of the variation in the impedances to the body density , a correction term for reversely affecting the influence of the variation in the impedances of the formula ( 1 ) of the body density , i . e ., a correction term for increasing the body density if the impedance is increased is provided as a third term , and a corrected reference formula is represented by : on the other hand , the above - described assumption is based on the premise that the variation in the weight is small with respect to the variation in the impedance , and it can be corrected if the variation in weight is responsive to the variation on the measured impedance . it is replaced by providing the correction term for performing the same operation as the influence of the variation in the weight in the formula ( 1 ) to the body density , i . e ., the correction term for reducing the body density if the weight is increased as a third term , and a correction formula is represented by : in order to reduce measuring conditions of an impedance between a patient &# 39 ; s feet , with the patient in a standing attitude , and to accurately measure the impedance , tests were conducted by a number of subjects under various conditions to obtain correlation between the above - described assumption and an underwater body weighing method , and most desirable coefficients in the formulae ( 2 ) and ( 3 ) have been decided . the coefficients a , k ′ k ″ may be determined experimentally and / or statistically so that the equations provide measures of body density which most closely approximate those measured by means of an underwater body weighing method . the following formula could be obtained as a most suitable inference formula for estimating a patient &# 39 ; s body density by using the impedance value between both of the patient &# 39 ; s feet in a standing position based on the formula ( 2 ): on the other hand , the following formula could be obtained as a most suitable inference formula for estimating a patient &# 39 ; s body density by using the impedance value between both of the patient &# 39 ; s feet in a standing position based on the formula ( 3 ): the correlation to the underwater body weighing method of the result for calculating the body fat by the above - described inference formula is of the same degree as that for fixing the measuring conditions without a correction term , the variation due to the difference of the measuring conditions is reduced to ½ of that without the correction term , thereby obtaining a satisfactory result . according to the present invention , body fat can be concurrently measured in a standing position with extremely small error in the measurements by correcting the inaccuracy of the measured values due to the variation in the impedance value according to the measuring conditions . further , the body fat measuring apparatus according to the present invention can readily be used by a user to measure his body fat by himself merely be standing upright at a designated position , and he can repeatedly measure it under the same conditions and can also take the measurements in the standing position . therefore , restrictions in the mounting position of the measuring instrument are remarkably reduced .
a body fat measuring apparatus for measuring body fat in a patient &# 39 ; s body comprises apparatus for simultaneously measuring an impedance between the patient &# 39 ; s feet , and for measuring the patient &# 39 ; s height and the patient &# 39 ; s weight , and a calculator for calculating body fat from the measured impedance value , height and weight . the calculator estimates body density using a formula having a correction term either for increasing the body density upon increase of the impedance compared to the original impedance or a correction term for decreasing the body density upon increase of the weight with respect to the original weight .