PHYSIOLOGICAL IMPEDANCE-MEASURING APPARATUS

• US 3,608,543 A
• Filed: 10/03/1968
• Issued: 09/28/1971
• Est. Priority Date: 10/03/1968
• Status: Expired due to Term

• Current Assignee: Richard L. Longini, Wils L. Cooley
• Original Assignee: Richard L. Longini, Wils L. Cooley
• Inventors: Longini, Richard L., Cooley, Wils L.
• Primary Examiner(s): Gaudet, Richard A.
• Assistant Examiner(s): Howell, Kyle L.
• Application Number:
  US04/764,748
• Time in Patent Office: 1,090 Days
• Field of Search: 128/2.1,2.06,DIG.4
• US Class Current: 600/536
• CPC Class Codes: A61B 5/0809 by impedance pneumography

Abstract

In a physiological impedance-measuring apparatus, the combination comprising a pair of electrodes for spaced application to predetermined locations of the anatomy, an additional electrode spacedly juxtaposed to one of said firstmentioned electrodes, circuit means for applying a measuring voltage across said first-mentioned electrodes and a portion of said anatomy therebetween and for applying a potential to said additional electrode similar to that on the associated one of said first-mentioned electrodes, and an impedance-measuring circuit coupled to said electrodes for measuring anatomical impedance only between a predetermined pair of said electrodes. In certain applications wherein said circuit means include a unity-gain amplifier for applying a substantially identical potential at lower impedance to said additional electrode for driving the same.

Claims

1. In a physiological measuring apparatus, the combination comprising a pair of electrodes adapted for spaced application to predetermined locations of the anatomy, an additional electrode spacedly juxtaposed to one of said first-mentioned electrodes, circuit means for applying an impedance-measuring voltage only across said first-mentioned electrodes and a portion of said anatomy when juxtaposed therebetween and for applying a potential to said additional electrode similar to that on the associated one of said first-mentioned electrodes, and an impedance-meauring circuit coupled to said electrodes and to said circuit means for measuring anatomical impedance only between a predetermined pair of said electrodes, said circuit comprising a substantially unity gain amplifier for applying a substantially identical potential at lower impedance to said additional electrode for driving the same.

2. The combination according to claim 1 wherein said additional electrode is a guard ring spacedly surrounding said one electrode.

3. The combination according to claim 1 wherein said additional electrode includes a plurality of electrically interconnected electrode segments.

4. The combination according to claim 1 wherein said impedance-measuring circuit includes a phase-discriminating circuit sensitive only to a predetermined phase of impedance changes measured between said electrodes.

5. The combination according to claim 1 wherein said amplifier is coupled to said additional electrode and to said one electrode.

6. The combination according to claim 1 wherein said impedance-measuring circuit includes a phase-sensitive detector circuit including circuit means for relating the maximum sensitivity of said detector circuit to the phase of a predetermined component of impedance changes between said first-mentioned electrodes.

7. The combination according to claim 6 wherein said impedance-measuring circuit includes an impedance bridge having a fixed resistive and capacitive impedance and a variable voltage-sensitive impedance, said last-mentioned impedance being coupled in feedback relation to the output of said detector circuit.

8. The combination according to claim 7 wherein said detector circuit includes an amplifying and matching circuit for relating said feedback to said impedance change component to maintain said bridge in dynamic balance.

9. The combination according to claim 1 wherein dual impedance-measuring paths are coupled to said circuit means and to said impedance-measuring circuit, known impedance means are in one of said paths, said anatomical impedance is in the other of said paths, and means form part of said impedance-measuring circuit for alternately connecting said paths to provide relative aNatomical impedance measurements and an absolute impedance value for comparison purposes.

10. The combination according to claim 9 wherein said paths include known impedances in series and parallel respectively with said anatomical impedance, and said connecting means include shorting circuit means around each of said impedances for selectively coupling and discoupling said impedances so that series and parallel value bases can be alternatively and selectively indicated at any point along an output curve of said impedance-measuring circuit.

11. The combination according to claim 10 wherein said series impedances are relatively small and said parallel impedance is relatively large so that absolute value bases of impedance and conductances can be indicated.

12. The combination according to claim 1 wherein said amplifier is provided with a power supply which is independent of said impedance-measuring voltage.

13. The combination according to claim 1 wherein said additional electrode is a guard ring spacedly surrounding said one electrode.

14. In a physiological measuring apparatus, the combination comprising a pair of electrodes adapted for spaced application to predetermined locations of the anatomy, an additional electrode spacedly juxtaposed to one of said first-mentioned electrodes, circuit means for applying an impedance-measuring voltage only across said first-mentioned electrodes and a portion of said anatomy when juxtaposed therebetween and for applying a potential to said additional electrode similar to that on the associated one of said first-mentioned electrodes, and an impedance-measuring circuit coupled to said electrodes and to said circuit means for measuring anatomical impedance only between a predetermined pair of said electrodes, said impedance-measuring circuit including an impedance bridge having fixed and variable impedances coupled to said first-mentioned electrodes, said variable impedance being coupled in feedback relation to an output circuit of said bridge for dynamically balancing said bridge.

15. The combination according to claim 14 wherein said additional electrode is a guard ring spacedly surrounding said one electrode and having a width at least equal to about the thickness of the thoracic wall structure being measured.