Apparatus and method for measuring bioelectric impedance

• US 6,292,690 B1
• Filed: 01/12/2000
• Issued: 09/18/2001
• Est. Priority Date: 01/12/2000
• Status: Expired due to Term

• Current Assignee: Measurement Ltd (Measurement Ltd., Inc.)
• Original Assignee: Measurement Specialties Incorporated (TE Connectivity Limited)
• Inventors: Petrucelli, Steven P., Orbine, Stephen A.
• Primary Examiner(s): Lateef, Marvin M.
• Assistant Examiner(s): MANTIS MERCADER, ELENI M
• Application Number:
  US09/481,584
• Time in Patent Office: 615 Days
• Field of Search: 600/547, 600/546, 600/506, 177/4, 177/245, 335/11, 335/12, 335/15, 324/98, 324/99.R, 324/100, 324/99.D, 324/101
• US Class Current: 600/547
• CPC Class Codes: A61B 5/05 Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves impedance plethysmography A61B5/0295; measuring movement of the entire body or parts thereof A61B5/11; detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof A61B5/24
• CPC Class Codes: A61B 5/0537 Measuring body composition by impedance, e.g. tissue hydration or fat content
• CPC Class Codes: A61B 5/4872 Body fat

Abstract

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 said current source to said 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 said first and second inputs; an instrumentation amplifier arrangement coupled to one of said comparator inputs and responsive to the voltage across the second pair of electrodes for providing an input signal to said first comparator input; a variable resistor coupled to the second input of said comparator and responsive to said voltage source for developing a first voltage signal applied to said second comparator input; and a processor responsive to the output signal of the comparator for controlling the resistance of the variable resistor to cause a corresponding change in said first voltage, whereby when said voltage at said first input corresponds to the voltage at said second input of said comparator; said 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 resistance value of the variable resistor.

Claims

1. A method of determining body impedance comprising the steps of:

coupling a first pair of electrodes to one portion of the body and applying a current through said electrodes;

coupling a second pair of electrodes to another portion of the body;

sensing a first voltage signal indicative of the voltage across said second pair of electrodes due to said current applied to said first pair of electrodes;

providing an impedance in electrical communication with said first pair of electrodes so as to produce a second voltage signal; and

comparing said first and second voltage signals to produce a control signal and adjusting said impedance in response to said control signal until said first and second signals are substantially equal, wherein the adjusted impedance corresponds to said body impedance.

2. The method according to claim 1, wherein the step of coupling said first pair of electrodes to one portion of the body comprises connecting one electrode to a toe portion of a patient'"'"'s left foot and the other of said first pair of electrodes to the toe portion of a patient'"'"'s right foot.

3. The method according to claim 1, wherein the step of coupling said first pair of electrodes to one portion of the body comprises connecting one electrode to a heel portion of a patient'"'"'s left foot and the other of said first pair of electrodes to the heel portion of a patient'"'"'s right foot.

4. The method according to claim 1, wherein the step of adjusting said impedance comprises changing the impedance value in a stepped fashion and iteratively comparing said first and second voltage signals until said voltage signals are substantially equal.

5. A circuit for measuring body impedance comprising:

a voltage source having a predetermined frequency;

a first pair of electrodes adapted to receive one portion of the body for applying a current to said body through said electrodes;

a second pair of electrodes adapted to receive another portion of the body for sensing a voltage therebetween in accordance with the current through said first electrodes;

a comparator having first and second inputs and an output for producing an output signal based on signals applied to said first and second inputs;

first means coupled to one of said comparator inputs and responsive to the voltage across the second pair of electrodes for providing an input signal to said first comparator input;

an adjustable impedance device coupled to the second input of said comparator for developing a first voltage signal applied to said second comparator input; and

means responsive to the output signal of the comparator for varying the impedance of said impedance device to cause a corresponding change in said first voltage, wherein when said voltage at said first input corresponds to the voltage at said second input of said comparator, said comparator output signal transitions from a first state to a second state indicative of a null condition, wherein the body impedance value corresponds to said impedance value of said impedance device.

6. The circuit according to claim 5, wherein said first means includes:

a differential amplifier arrangement having an input coupled to said second pair of electrodes and an output for providing said input signal.

7. The circuit according to claim 5, wherein said adjusting means comprises a microcontroller.

8. The circuit according to claim 5, wherein said variable impedance device comprises a digital potentiometer.

9. The circuit according to claim 5, wherein said variable impedance device is responsive to said voltage source.

10. The circuit according to claim 5, wherein said voltage source is sinusoidal.

11. The circuit according to claim 10, wherein said sinusoidal voltage source has a frequency of approximately 50 kHz.

12. The circuit according to claim 5, wherein said first pair of electrodes are formed of a conductive resin.

13. The circuit according to claim 5, wherein said second pair of electrodes are formed of a conductive resin.

14. The circuit according to claim 5, wherein said one body portion comprises a patient'"'"'s toes.

15. The circuit according to claim 5, wherein said another portion comprises a patient'"'"'s heels.

16. A circuit for determining impedance of a body comprising:

a first pair of electrodes coupled to a first body portion for providing a constant current thereto;

a second pair of electrodes coupled to a second body portion for sensing a voltage signal therebetween;

variable resistor means for generating a first voltage signal;

a comparator having inputs for receiving first and second input signals and an output terminal for providing an output signal;

means responsive to said output signal for controlling said first voltage signal to produce a null output signal, wherein the value of said body impedance corresponds to the resistive value associated with said resistor means when said output signal is nulled.

17. The circuit of claim 16, wherein said first and second pairs of electrodes are mounted on a platform scale and positioned to receive the toe and heel portions, respectively, of a patient'"'"'s feet.

18. The circuit of claim 16, wherein said electrodes are formed of a conductive paint.

19. The circuit of claim 16, wherein said metal coating is disposed on a plastic.

20. 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 said measuring station, said measuring station including;

a base on which a patient can stand,

first and second pairs of electrodes mounted on said base, said 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;

first means responsive to the voltage across the second pair of electrodes for providing one input signal to the comparator,

second means coupled to the second input of the comparator for providing a second input signal thereto; and

means responsive to the output signal of the comparator for producing a control signal to said second means for adjusting the voltage of said second input signal;

wherein when said voltage of said second means corresponds to said voltage output produced by said first means, said comparator output signal is indicative of a null condition, wherein the body impedance value corresponds to the ratio of the voltage at said second means to said drive current; and

means for determining body composition as a function of said body impedance value.

21. In a circuit for determining impedance of a body comprising a first pair of electrodes coupled to a first body portion for providing a current thereto;

a second pair of electrodes coupled to a second body portion for sensing a voltage signal therebetween;

the improvement therewith comprising;

servo means for producing an output signal indicative of a difference in voltage between the second pair of electrodes and a variable signal from a generator, said variable signal varying in response to said output signal such that when said output signal corresponds to a null output, the value of said variable signal is indicative of said body impedance.

23. The circuit according to claim 21, wherein said generator comprises a digital potentiometer.

22. An apparatus for determining impedance of a body comprising:

first and second electrodes defining a first pair positioned on a platform and spaced apart for engaging respective first and second body parts;

third and fourth electrodes defining a second pair positioned on a platform and spaced apart for engaging respective third and fourth body parts;

means for providing a current to said first and second electrodes to cause a voltage to be produced at said third and fourth electrodes;

a servo system coupled between said first and second pairs electrodes for producing an output signal indicative of a difference in voltage between the second pair of electrodes and a variable signal from a generator, said variable signal varying in response to said output signal such that when said output signal corresponds to a null output, the value of said variable signal is indicative of said body impedance.

24. The apparatus according to claim 22, wherein said servo system includes a comparator for producing said output signal, and a microcontroller responsive to said output signal for producing a signal to said generator to cause adjustment of said variable signal.

25. A method of determining body impedance comprising the steps of:

coupling a first pair of electrodes to one portion of the body and applying a current through said electrodes;

coupling a second pair of electrodes to another portion of the body;

sensing a first voltage signal indicative of the voltage across said second pair of electrodes due to said current applied to said first pair of electrodes;

providing an impedance in electrical communication with said first pair of electrodes so as to produce a second voltage signal;

comparing said first and second voltage signals and generating a control signal associated with a first state in response to said comparison;

adjusting said impedance in response to said control signal; and

repeating said steps of comparing said first and second voltage signals and adjusting said impedance until said control signal transitions from said first state to a second state based on said comparison, wherein the adjusted impedance corresponds to said body impedance.