IMPEDANCE RELATED BLOOD FLOW MEASURING DEVICE

• US 3,730,171 A
• Filed: 09/23/1971
• Issued: 05/01/1973
• Est. Priority Date: 09/23/1971
• Status: Expired due to Term

• Current Assignee: Richard Namon
• Original Assignee: Richard Namon
• Inventors: Namon, Richard
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US05/183,217
• Time in Patent Office: 586 Days
• Field of Search: 128/2.5F,2.5R,2.5U,2.6R,2.08,2.1R,2.1Z
• US Class Current: 600/526
• 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: 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

A cardiac blood flow measuring method and apparatus including two current electrodes and two voltage pick-up electrodes positionable in direct contact with the subject, with a circuit for applying a high frequency, low voltage current to the current electrodes and a circuit for measuring the total impedance across the voltage pick-up electrodes by using a summing circuit for adding selectively either a resistive or a reactive voltage to the subject'"'"''"'"'s total impedance voltage to determine selectively either the subject'"'"''"'"'s resistive impedance or reactive impedance with the reactive impedance being employed to measure cardiac blood volume flow.

Claims

1. A blood measuring device, comprising:

electrode means adapted to be positioned relative to a portion of the subject, and means for measuring the blood flow of the subject including means for measuring the reactive impedance between the electrode means.

2. A blood flow measuring device, comprising:

a first pair of input current electrodes, a second pair of pick-up voltage electrodes, both of said pairs of electrodes being positionable relative to the subject, said current electrodes being positioned with respect to said voltage electrodes to provide a current path between the voltage electrodes, means for applying a current to said first pair of electrodes, and means for indicating the blood flow of the subject including means for measuring the reactive impedance across said second pair of electrodes.

3. A method of measuring body impedance, comprising the step of placing one of a pair of current or voltage electrodes on the subject'"'"''"'"'s sternum approximately bracketing the heart, placing the other pair of electrodes each approximately one heart length away from each of said one pair of electrodes, and measuring the reactive impedance between the voltage electrodes.

4. A method of measuring body impedance as defined in claim 3, wherein said one pair of electrodes are placed midline on the sternum and the other pair of electrodes are positioned to flank and be in line with said one pair.

5. A blood flow measuring device as defined in claim 2, wherein said means for measuring reactive impedance includes means for measuring total subject impedance between the second pair of electrodes, means for adding a reference reactive impedance signal to a total reactive impedance signal and providing a total signal, and means for measuring the peaks of said total signal.

6. A blood flow measuring device as defined in claim 5, wherein said means for applying a current to said first pair of electrodes includes a source of low magnitude current of approximately two ma rms having a frequency of approximately 37k Hertz.

7. A blood flow measuring device as defined in claim 5, wherein said reference reactive impedance signal is at least ten times greater in amplitude than the measured total impedance signal.

8. A monitoring apparatus for measuring body impedance, comprising:

electrode means adapted to be applied to the subject, means for deriving a voltage signal representing a reference impedance in phase with the impedance desired to be measured, means for measuring the total impedance across said electrode means and deriving a subject total impedance voltage, and means for vectorally adding and measuring said reference voltage and said subject voltage.

9. A monitoring apparatus for measuring body impedance as defined in claim 8, including means for measuring the peak values of the voltage resulting from the addition of the reference voltage to the subject voltage.

10. A monitoring apparatus for measuring body impedance as defined in claim 8, wherein said electrode means includes two voltage pick-up electrodes, two current electrodes for providing a current flow between the voltage electrodes, and a current source connected to said current electrodes, said voltage electrodes being positioned with respect to said current electrodes to sense voltage provided thereby.

11. A monitoring apParatus as defined in claim 10, including means for applying a low magnitude current to said current electrodes, a series connected load to said current electrodes providing said reference voltage.

12. A monitoring apparatus as defined in claim 11, including a mode selection circuit converting the device to measure either resistance or reactive impedance, said mode selection circuit including a resistive load and a reactive load and means for selectively connecting said resistive or reactive load to the current electrodes depending on the desired impedance value to be measured.

13. A monitoring apparatus as defined in claim 8, wherein said means for measuring total impedance includes an amplifier coupled to said electrode means, said reference voltage means being coupled to said amplifier, rectifier means coupled to said amplifier, and visual indicating means coupled to said rectifier means.

14. A body impedance measuring apparatus comprising:

electrode means adapted to be applied to the subject, input circuit means for applying a low magnitude alternating current to said electrode means, a mode selection current for measuring either resistive or reactive impedance including a resistive load and a reactive load, selector means for connecting one of said loads in series in said input circuit means, the voltage drop across the desired load representing a reference voltage, subject impedance circuit means for measuring the total impedance across said electrode means and deriving subject impedance voltage, circuit means for vectorally adding said reference voltage and said subject voltage, and means for measuring the voltage produced by the addition of the reference voltage and subject voltage.

15. A body impedance measuring apparatus as defined in claim 14, including means for indicating the peak value of the voltage resulting from the addition of the reference voltage and the subject voltage.

16. A body impedance measuring apparatus as defined in claim 14, wherein said input circuit means has an impedance substantially greater than the subject impedance.

17. A body impedance measuring apparatus as defined in claim 14, including transformer means in said input current means for isolating the current source from ground.

18. A body impedance measuring apparatus as defined in claim 14, including capacitor means in series in said input circuit means to prevent blocking out lower frequency biological signals.

19. A body impedance measuring apparatus as defined in claim 14, including transformer means across said mode selection circuit for isolating the reference voltage.

20. A body impedance measuring apparatus as defined in claim 19, including transformer means across the electrode means employed for subject voltage pick-up for eliminating the necessity of grounding the patient.

21. A body impedance measuring apparatus as defined in claim 14, including an input current compensation circuit including a compensation channel coupled to said reference voltage, and means differentially responsive to said compensation channel output and said adding means.