IMPEDANCE PLETHYSMOGRAPHY METHOD AND APPARATUS

• US 3,835,840 A
• Filed: 09/27/1973
• Issued: 09/17/1974
• Est. Priority Date: 09/27/1973
• Status: Expired due to Term

• Current Assignee: Bruce E. Mount
• Original Assignee: Bruce E. Mount
• Inventors: Mount, Bruce E.
• Primary Examiner(s): Gaudet, Richard A.
• Assistant Examiner(s): Cohen, Lee S.
• Application Number:
  US05/401,407
• Time in Patent Office: 355 Days
• Field of Search: 128/2.5V,2.5F,2.5R,2.1Z,2.1R 324/65R
• US Class Current: 600/506
• CPC Class Codes: A61B 5/0535 Impedance plethysmography for measuring blood flow A61B5/0295
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: G06G 7/60 for living beings, e.g. their nervous systems ; for problems in the medical field

Abstract

Apparatus and method for noninvasive measurement of volume rate of flow of blood in an artery. A system using an impedance plethysmograph to measure the impedance of a body section, and circuitry having the impedance signal as an input for developing an output signal proportional to the volume rate of blood flow.

Claims

1. A method of noninvasively measuring volume rate of flow of blood in an artery, including the steps of:

measuring the impedance of a section of the body containing the artery;

computing the rate of change of volume of the artery with time to obtain a time derivative of arterial volume;

providing a zero reference value for the time derivative; and

integrating the time derivative over a period of time producing as an integrated output a number substantially proportional to the volume rate of flow of blood in the artery.

2. A method as defined in claim 1 including providing the zero reference value for the time derivative by bringing the negative peaks of the wave to zero.

3. A method as defined in claim 1 including measuring the flow velocity in the artery and setting the zero reference value as a function of the flow velocity.

4. In an apparatus for noninvasive measurement of volume rate of flow of blood in an artery for use with an impedance plethysmograph providing an output signal varying as a function of the impedance of a section of a body having an artery therein, the improvement comprising in combination:

first means having as an input the plethysmograph output signal Zo and providing as an output a signal DVa/dt proportional to the time rate of change of volume of the artery by calculating dVa/dt -( Rho a 12/Zo2)dZo/dt where Rho a is the resistivity of blood and 1 is the length of the section;

second means for providing a dc level to a time varying signal and having said first means output signal as an input; and

integrator means for integrating the input thereto over a predetermined time period and having the output of said second means as an input, with the integrated output of said integrator means being a value substantially proportional to the volume rate of flow of blood in the artery section.

5. Apparatus as defined in claim 4 wherein said second means includes means for setting the negative peaks of the time varying signal substantially to a zero dc level.

6. Apparatus as defined in claim 5 wherein said second means includes a diode and resistor connected in parallel across the first means output.

7. Apparatus as defined in claim 5 wherein said second means includes a transistor and resistor connected in parallel across the first means output, and an operational amplifier having the first means output signal and a reference signal as inputs and having an output connected to the gate of said transistor.

8. Apparatus as defined in claim 4 wherein said second means includes means for varying the dc level as a function of the flow velocity of blood in the artery.

9. Apparatus as defined in claim 4 wherein said second means includes a transistor and resistor connected in parallel across the first means output, and an operational amplifier having the first means output signal and a reference signal as inputs and having an output connected to the gate of said transistor.

10. An apparatus as defined in claim 4 including:

means for sampling the integrator means output at the end of predetermined time period to obtain a sampled value;

means for storing the sampled values; and

means for resetting said integrator means initiating another integrating cycle.

11. Apparatus as defined in claim 4 wherein said first means includes:

means for developing an 1 signal variable as a function of the length of said section;

means for multiplying the 1 signal by itself to obtain an 12 signal;

means for dividing the 12 signal by the plethysmograph output signal Zo two times to obtain a 12/Zo2 signal;

means for obtaining an ac signal -Zo(t) which is the negative of the plethysmograph output signal Zo;

means for multiplying the 12/Zo2 and -Zo(t) signals providing a first product signal;

means for selecting a portion of the first product signal proportional to the blood resistivity Rho a to obtain a second product signal Va(t); and

means for differentiating said second product signal as a function of time to provide an output signal dVa/dt.