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Impedance plethysmograph

  • US 3,340,867 A
  • Filed: 08/19/1964
  • Issued: 09/12/1967
  • Est. Priority Date: 08/19/1964
  • Status: Expired due to Term
First Claim
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1. A PLETHYSMOGRAPH FOR MEASURING CARDIAC OUTPUT COMPRISING IN COMBINATION EXCITATION ELECTRODE MEANS ADAPTED TO BE CONNECTED TO A MAMMALIAN SUBJECT AT THE SUPERIOR AND INFERIOR ENDS OF THE THORAX, A CURRENT GENERATOR MEANS COMPRISING AN ELECTRONIC OSCILLATOR CONDUCTIVELY CONNECTED TO THE ELECTRODE MEANS FOR SUPPLYING A FLUCTUATING EXCITATION CURRENT THERETO, SENSOR MEANS ADAPTED TO BE CONDUCTIVELY CONNECTED TO SAID THORAX FOR CARRYING A SENSED ELECTRICAL SIGNAL WHICH VARIES AS THE IMPEDANCE CHANGES IN THE THORAX BETWEEN SAID ELECTRODE MEANS, A CONTROL MEANS CONDUCTIVELY CONNECTED TO THE OSCILLATOR FOR BALANCING THE CURRENT FROM THE OSCILLATOR WITH THE SENSED SIGNAL, A FIRST AMPLIFIED CONDUCTIVELY CONNECTED TO THE CONTROL MEANS, A SECOND AMPLIFIER CONNECTED TO SAID SENSOR MEANS WHEREBY SIGNALS OF APPROXIMATELY EQUAL STRENGTH ARE FED TO SAID FIRST AND SECOND AMPLIFIERS FROM SAID CONTROL AND SAID SENSOR MEANS RESPECTIVELY AND A VOLTAGE SUBSTRACTING MEANS CONDUCTIVELY CONNECTED TO EACH OF THE AMPLIFIERS FOR COMPARING THE OUTPUT OF EACH SAID AMPLIFIER.

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