METHOD AND APPARATUS FOR DETERMINING INTERNAL IMPEDANCE OF ANIMAL BODY PART

• US 3,851,641 A
• Filed: 11/29/1973
• Issued: 12/03/1974
• Est. Priority Date: 11/29/1973
• Status: Expired due to Term

• Current Assignee: Joseph G. Toole, Wade H. Foy
• Original Assignee: Joseph G. Toole, Wade H. Foy
• Inventors: Toole, Joseph G., Foy, Wade H.
• Primary Examiner(s): Gaudet, Richard A.
• Assistant Examiner(s): Cohen, Lee S.
• Application Number:
  US05/420,186
• Time in Patent Office: 369 Days
• Field of Search: 128/2.1Z,2.1R,2.5V 324/57R,71R
• US Class Current: 600/529
• CPC Class Codes: A61B 5/0537 Measuring body composition by impedance, e.g. tissue hydration or fat content
• CPC Class Codes: A61B 5/0809 by impedance pneumography
• CPC Class Codes: A61B 5/4869 Determining body composition

Abstract

Apparatus and a method for determining the internal impedance of a portion of an animal body. Two electrical currents of different frequencies are passed through the body portion and the voltage across the body portion corresponding to each current flow is sensed. In-phase coherent detection is performed to remove the out-of-phase signal components and the resulting in-phase voltage signals are subtracted from each other to yield a measure of only the internal impedance of the body portion. The invention is especially suitable for use in measuring the changes in the amount of fluid in the human lung.

Claims

1. Apparatus for sensing a physiological and pathological change of a body part of an animal comprising:

means for generating two electrical currents with each current being at a respective frequency;

means coupled with said generating means for connecting the same to an animal body part to permit said currents to be directed therethrough, whereby a voltage corresponding to each current, respectively, will be developed across said body part;

a device for detecting the in-phase components of a voltage signal;

means coupled with said connecting means for applying each voltage across the body part to said detection device, whereby the output of the detection device is a signal representing the in-phase component of the voltage corresponding to a respective current;

means coupled with said detection means for subtracting the magnitude of the inphase signal corresponding to the current at a first frequency from the in-phase signal corresponding to the current at a second frequency to provide a difference signal; and

means coupled with said subtracting means for indicating the difference signal.

2. Apparatus as set forth in claim 1, wherein said detection device comprises a mixer having means for developing a reference signal for each voltage, respectively.

3. Apparatus as set forth in claim 2, wherein said developing means comprises a pair of narrow band filters responsive to said current generating means.

4. Apparatus as set forth in claim 1, wherein said current generating means includes a pair of oscillators having output signals at said respective frequencies, a summing amplifier, and switch means for successively applying the output signals of the oscillators to said summing amplifier to obtain a frequency shift signal therefrom, and a current source responsive to said frequency shift signal, said current source being coupled with said connecting means.

5. Apparatus as set forth in claim 1, wherein said current generating means includes a voltage controlled oscillator operable to successively develop a pair of signals at said respective frequencies, means for selectively adjusting the amplitudes of the signals, and a current source responsive to said adjusting means, said current source being coupled with said connecting means.

6. Apparatus as set forth in claim 1, wherein said current generating means includes a pair of oscillators whose output signals are at said respective frequencies, a summing amplifier coupled to the oscillators to receive the output signals therefrom, and a current source responsive to the output of said summing amplifier, said current source being coupled with said connecting means.

7. Apparatus as set forth in claim 1, wherein said detection device includes a mixer having means for developing a reference signal responsive to said current generating means, there being a wideband amplifier between said mixer and said connecting means.

8. Apparatus as set forth in claim 7, wherein said current generating means includes a pair of oscillators having output signals at said respective frequencies, a summing amplifier responsive to said oscillators to provide a frequency shift signal, said developing means including a pair of narrow-band filters responsive to the frequency shift signal of said summing amplifier.

9. Apparatus as set forth in claim 7, wherein said current generating means includes a voltage controlled oscillator operable to successively develop a pair of signals at said respective frequencies, and means for selectively adjUsting the amplitudes of said signals, said developing means including a pair of narrow-band filters responsive to said adjusting means.

10. Apparatus as set forth in claim 7, wherein said current generating means includes a pair of oscillators, means for adjusting the output signals of the oscillators, there being a pair of mixers connected directly to said adjusting means to receive reference signals therefrom, there being a wideband amplifier coupled to said connecting means and responsive to the voltage across the body part corresponding to each current, respectively, and a narrow-band filter for each mixer, respectively, the narrow-band filters connecting said wideband amplifier to each mixer, respectively.

11. Apparatus as set forth in claim 10, wherein said subtracting means includes a difference amplifier having a pair of inputs, there being a low-pass filter coupling each mixer, respectively, with an input of said difference amplifier.

12. Apparatus as set forth in claim 7, wherein said subtracting means includes a track and hold circuit, means responsive to said generating means for providing a gate signal for said track and hold circuit, a clamp for shifting one of the outputs of the track and hold circuit to a predetermined value, and a peak reader for taking the difference of the amplitudes of the outputs of said track and hold circuit.

13. A method for sensing a physiological and pathological change of a body part of an animal comprising:

directing two electrical currents at respective frequencies through the body part during a first time interval to develop a voltage signal across the body part corresponding to each current, respectively;

detecting the in-phase component of each of the voltage signals;

subtracting the in-phase components of the voltage signals from each other to provide a difference signal, and repeating the directing, detecting and subtracting steps at a second time interval spaced from the first time interval to provide a trend which establishes said functional change.

14. A method as set forth in claim 13, wherein the currents are applied successively to the body part.

15. A method as set forth in claim 13, wherein said detecting step includes generating a reference signal corresponding to each current, respectively, and mixing each reference signal with the corresponding voltage signal to provide an inphase component signal.

16. A method as set forth in claim 13, wherein each voltage signal is amplified before said detecting step.

17. A method as set forth in claim 13, wherein said directing step includes adjusting the amplitudes of each current to a predetermined value.

18. Apparatus for sensing fluid content changes in the human being comprising:

means for generating two electrical currents with each current being at a respective frequency;

means coupled with said generating means for connecting the same to the human body at locations to permit said currents to be directed through the lung, whereby a voltage corresponding to each current, respectively, will be developed across the body portion containing the lung;

a device for detecting the in-phase components of a voltage signal;

means coupled with said connecting means for applying each voltage across said body portion to said detection device, whereby the output of the detection device is a signal representing the in-phase component of the voltage corresponding to the respective current;

means coupled with said detection means for subtracting the magnitude of the in-phase signal corresponding to the current at a first frequency from the in-phase signal corresponding to the current at a second frequency to provide a difference signal; and

means coupled with said subtracting means for indicating the difference signal.

19. Apparatus as set forth in claim 18, wherein the frequencies of said currents are in the range of 20 kHz and 100 kHz.

20. Apparatus as set forth in claim 18 wherein the frequencies of said currents is in the range of 20 kHz and 34 kHz.

21. A method for sensing a fluid content change in the human lung comprising:

directing two electrical currents at respective frequencies through the body portion containing the lung during a first time interval to develop a voltage signal across the body portion corresponding to each current, respectively;

detecting the in-phase component of each of the voltage signals;

subtracting the in-phase components of the voltage signals from each other to provide a difference signal; and

repeating the directing, detecting and subtracting steps at a second time interval spaced from the first time interval to provide a trend which establishes said change.