Impedance plethysmography method and apparatus

Claim 3

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.

Claim 4

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.

Claim 5

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.

Claim 6

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.

Claim 7

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.

Claim 8

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

Claim 9

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.

Claim 10

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.

Claim 11

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.

Claim 12

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.

Claim 13

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.