IMPEDANCE MEASURING SYSTEM

• US 3,871,359 A
• Filed: 06/25/1973
• Issued: 03/18/1975
• Est. Priority Date: 06/25/1973
• Status: Expired due to Term

• Current Assignee: Allan F. Pacela
• Original Assignee: Allan F. Pacela
• Inventors: Pacela, Allan F.
• Primary Examiner(s): Gaudet, Richard A.
• Assistant Examiner(s): Cohen, Lee S.
• Application Number:
  US05/373,435
• Time in Patent Office: 631 Days
• Field of Search: 128/2.1Z,2.1R 324/62,63,64,65R
• US Class Current: 600/547
• CPC Class Codes: A61B 5/0295 using plethysmography, i.e. measuring the variations in the volume of a body part as modified by the circulation of blood therethrough, e.g. impedance plethysmography
• CPC Class Codes: A61B 5/0535 Impedance plethysmography for measuring blood flow A61B5/0295
• CPC Class Codes: A61B 5/25 Bioelectric electrodes therefor
• CPC Class Codes: A61B 5/256 Wearable electrodes, e.g. having straps or bands
• CPC Class Codes: G01R 27/02 Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant by measuring phase angle only G01R25/00

Abstract

There is disclosed a constant magnitude alternating current source connected to at least one electrical impedance to be measured. First and second voltage detectors are connected to the electrical impedance to measure voltage across first and second portions of the electrical impedance, respectively, in response to the current conducted from the current source. A computer is attached to the first and second voltage detectors for processing the measured voltage to compute desired characteristics of the electrical impedance.

Claims

1. Impedance measuring apparatus for measuring first and second electrical impedances, comprising:

current source means for producing an alternating current of constant magnitude;

first and second voltage detector means for measuring voltages;

first electrode pair means attached to said current source means and adapted to be connected between the first and second electrical impedances;

second electrode pair means electrically connected together and adapted to be connected between said first and second electrical impedances to complete an electrical circuit comprising said current source means connected to the series combination of said first and second electrical impedances;

third electrode pair means connected to the first voltage detector means and adapted to be connected across the first electrical impedance for measuring the voltage thereacross in response to said alternating current of said current source means;

fourth electrode pair means connected to the second voltage detector means and adapted to be connected across said second electrical impedance for measuring the voltage thereacross in response to said alternating current of said current source;

computer means connected to said first and second voltage detector means for computing the ratios of changes in the electrical impedance of said first and second electrical impedances to the steady-state value thereof, respectively; and

display means for displaying said ratios computed by said computer means.

2. The impedance measuring apparatus described in claim 1 further including a plurality of isolation transformers, one transformer being connected between said current source means and said first electrode pair means, a second transformer being connected between said first voltage detector means and said third electrode pair means and a third transformer being connected between said second voltage detector means and said fourth electrode pair means, said transformers coupling electrical currents and voltages derived from said current source means and substantially isolating all other electrical currents and voltages which are not derived from said current source means.

3. The impedance measuring apparatus described in claim 1 wherein each of the electrode pair means comprises a pair of conductive strips and wherein said current source means is connected between a first conductive strip adapted to be wrapped around one limb of a living subject and a second conductive strip adapted to be wrapped around the same part of the opposite limb of said livIng subject, the first and second conductive strips being said first electrode pair means, and wherein said first voltage detector means is connected between a third conductive strip and a fourth conductive strip, said third conductive strip being adapted to be located adjacent said first conductive strip and said fourth conductive strip being adapted to be located at the other end of a region of said one limb being measured, the third and fourth conductive strips being said third electrode pair means, and wherein a fifth conductive strip is adapted to be located adjacent said fourth conductive strip and wherein said fifth conductive strip is connected to a sixth conductive strip adapted to be wrapped around at the same point on said opposite limb corresponding to said fifth conductive strip on said one limb, the fifth and sixth electrode strips being said second electrode pair means, and wherein said second voltage detector means is connected between a seventh conductive strip being adapted to be located adjacent said sixth conductive strip and said eighth conductive strip being adapted to be located adjacent said second conductive strip, the seventh and eighth conductive strips being said fourth electrode pair means.

4. The impedance measuring apparatus described in claim 3 further including a plurality of flexible base members, each having two adjacently located conductive strips attached thereto whereby four electrode pairs are formed, a first pair comprising the first and third conductive strips, a second pair comprising the fourth and fifth conductive strips, a third pair comprising the sixth and seventh conductive strips, and a fourth pair comprising the eighth and second conductive strips, each of said flexible base members having connecting areas thereon for attaching each of said base members to itself when wrapped around the limb of a living subject.

5. The impedance measuring apparatus described in cllaim 4 wherein said first voltage detector means and said second voltage detector means are synchronous detectors whereby both the magnitude and phase of the voltage measured can be detected.

6. The impedance measuring apparatus described in claim 1 wherein aid computer means is a pair of electronic circuits of which one is connected to said first voltage detector and one is connected to said second voltage detector, each electronic circuit including:

a first and second resistor connected in series between the output of the respective voltage detector and the circuit ground, said second resistor; and

means for varying automatically said second resistor to maintain a constant voltage output thereacross irrespective of the value of the steady-state voltage applied to said first resistor from said respective voltage detector, said second resistor not being adjusted in response to dynamic changes in the voltage from said respective voltage detector whereby the voltage across said second resistor is proportional to the fractional change of the impedance being measured.

7. Bilateral impedance measuring apparatus comprising:

four pairs of electrodes, a first and second pair of said four pairs being adapted to be attached to a first impedance being measured and a third and a fourth pair of said four pairs being adapted to be attached to a second impedance being measured;

an alternating current source of constant magnitude attached between one electrode of the first pair of electrodes and one electrode of the fourth pair of electrodes;

a conductor attached between one electrode of the second pair of electrodes and one electrode of the third pair of electrodes;

a first and a second voltage detector, the first voltage detector being connected between the other electrode of said first pair and the other electrode of said second pair, the second voltage detector being connected between the other electrode of said third pair and the other electrode of said fourth pair;

computer means attached to the first and second voltage detectors For computing impedance ratios and impedance diffeences; and

display means for displaying said impedance ratios and impedance differences.