Surgery – Diagnostic testing – Measuring electrical impedance or conductance of body portion
Reexamination Certificate
2000-01-12
2001-09-18
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Measuring electrical impedance or conductance of body portion
Reexamination Certificate
active
06292690
ABSTRACT:
FIELD OF INVENTION
The present invention relates to measurement devices in general and more particularly to a method and apparatus for measuring impedance of a biological organism.
DESCRIPTION OF PRIOR ART
There exist in the prior art numerous methods and apparatus for measuring or determining body impedance and body composition (i.e. body fat).
For instance, U.S. Pat. No. 4,144,763 discloses a method of measuring body fat using Boyle's law. U.S. Pat. No. 4,831,527 discloses a system where a fat-to-lean ratio is measured by having a subject stand on a platform and raise his or her heels and then allowing the weight to fall near a transducer to produce a force. The subject's stomach and other flesh continue to move in a downward direction after skeletal motion has stopped, resulting in a downward force which is registered as a data peak and measured by a computer. A technique for measuring body fat by immersing the subject in a liquid is disclosed in U.S. Pat. No. 5,052,405. U.S. Pat. No. 5,105,825 teaches a method of measuring body fat by transferring controlled volumes of gas between two chambers and measuring pressure while U.S. Pat. No. 5,335,667 measures body composition using bioelectric impedance measurements.
In U.S. Pat. No. 5,372,141 a body fat calculator is described which basically measures body fat by the impedance of the network and uses various algorithms after measuring the impedance of the body.
A physical fitness evaluation system is disclosed in U.S. Pat. No. 5,435,315 which, besides measuring body fat, can calculate the overall fitness of the individual. This means for measuring body fat uses a large caliper in conjunction with a variable resistor. Pat. No. 5,579,782 shows a high frequency signal generator which is used to measure impedance. The body fat ratio is calculated from those measurements.
U.S. Pat. No. 5,595,189 relies on measuring body fat by determining a subject's weight using two gases at different densities. The weight of the person is measured with a precision balance and the person's body fat is determined by the density of both of the gaseous environments.
U.S. Pat. No. 5,415,176 issued on May 16, 1999 entitled APPARATUS FOR MEASURING BODY FAT, to Sato et al. discloses a method of determining body impedance using two pairs of electrodes placed at the toes and heels of a person, applying a constant current to the toe electrodes, measuring the voltage at the heel electrodes, and calculating the impedance as the ratio of the measured voltage over the constant current. The body fat is then calculated from the body impedance. U.S. Pat. No. 5,611,351 issued on Mar. 18, 1997 entitled METHOD AND APPARATUS FOR MEASURING BODY FAT, to Sato et al. is a continuation of U.S. Pat. No. 5,415,176 and calculates body fat from the impedance value and the person's height and weight.
However, numerous problems and limitations are encountered with the application of each of the above systems and methods for determining body impedance (or body fat). Such limitations include accuracy and reliability, portability and ease of use, size and circuit complexity, and response time. Accordingly, a method and apparatus for determining body impedance which obviates these shortcomings is highly desired.
SUMMARY OF THE INVENTION
A circuit for measuring body impedance comprising a voltage source having a predetermined frequency and a current source; a first pair of electrodes adapted to receive one portion of the body for applying the current source to the body; a second pair of electrodes adapted to receive another portion of the body for sensing a voltage therebetween; a comparator having first and second inputs and an output for producing an output signal based on signals applied to the first and second inputs; a differential amplifier arrangement coupled to one of the comparator inputs and responsive to the voltage across the second pair of electrodes for providing an input signal to the first comparator input; a variable resistor coupled to the second input of the comparator and responsive to the voltage source for developing a first voltage signal applied to the second comparator input; and a processor responsive to the output signal of the comparator for adjusting the resistance of the variable resistor to cause a corresponding change in the first voltage, whereby when the voltage at the first input corresponds to the voltage at said second input of said comparator, the comparator output signal transitions from a first state to a second state to cause the processor to terminate resistor adjustment, whereby the body impedance value corresponds to the adjusted resistance value of the variable resistor.
An apparatus for measuring body composition in a patient's body comprising a measuring station for measuring impedance between the patient's feet and an operating circuit coupled to the measuring station, the measuring station including a base on which a patient can stand, first and second pairs of electrodes mounted on the base, the first pair of electrodes adapted to receive one portion of the body for transmitting a drive current thereto; the second pair of electrodes adapted to receive another portion of the body for sensing a voltage therebetween; a comparator having inputs for receiving first and second input signals and an output terminal for providing an output signal; an amplifier arrangement responsive to the voltage across the second pair of electrodes for providing one input signal to the comparator; a digital potentiometer coupled between the first pair of electrodes and the second input of the comparator for providing a second input signal thereto; and a processor responsive to the output signal of the comparator for producing a control signal to the potentiometer for adjusting the resistance of the potentiometer to cause a corresponding change in voltage of the second input signal; whereby when the voltage of the second input signal corresponds to the voltage output produced by the amplifier arrangement, the comparator output signal transitions from a first state to a second state indicative of a null condition, whereby the body impedance value corresponds to the resistance of the potentiometer; and an operating circuit coupled to the measuring station for determining body composition as a function of body impedance value.
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Orbine Stephen A.
Petrucelli Steven P.
Duane Morris & Heckscher
Lateef Marvin M.
Mantis Mercader Eleni
Measurement Specialities Inc.
Plevy Arthur L.
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