Rate responsive cardiac pacemaker with biphasic impedance sensing and method
First Claim
1. A cardiac stimulation apparatus comprisingmeans for stimulating a patient'"'"'s heart;
- means for measuring impedance within the patient'"'"'s body, said impedance measuring means includingmeans for producing a constant current biphasic pulse pair, said pulse pair having a first pulse having current flowing in a first direction and a second pulse having current flowing in a second direction, means for electrically transmitting said pulse pair through at least a portion of said patient'"'"'s body,means for detecting a first voltage associated with said first pulse across at least a part of said patient'"'"'s body,means for producing a first signal proportional to said first voltage,means for detecting a second voltage associated with said second pulse across at least a part of said patient'"'"'s body,means for producing a second signal proportional to said second voltage, andmeans for producing a combined signal from said first and second signals,means for deriving a metabolic demand parameter from said combined signal; and
means for adjusting said means for stimulating said patient'"'"'s heart in relation to said metabolic demand parameter.
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Accused Products
Abstract
An implantable, rate responsive pacemaker, sensitive to impedance changes in the heart as an indicator of cardiac stroke volume or minute volume, wherein common interfering signals such as the intracardiac electrogram, myoelectric signals, pacing artifacts and other pacing after potentials are reduced or eliminated from the measurement of the impedance by the use of a biphasic test signal. The cardiac pacemaker has a signal injector which produces biphasic test pulses of similar duration and magnitude and of constant current, though of opposite polarity. The pacemaker also has a detector which senses voltage resulting from the applied biphasic current pulses in each phase. Since the injector and detector are separate circuits, they can be used with a variety of electrode configurations.
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Citations
20 Claims
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1. A cardiac stimulation apparatus comprising
means for stimulating a patient'"'"'s heart; -
means for measuring impedance within the patient'"'"'s body, said impedance measuring means including means for producing a constant current biphasic pulse pair, said pulse pair having a first pulse having current flowing in a first direction and a second pulse having current flowing in a second direction, means for electrically transmitting said pulse pair through at least a portion of said patient'"'"'s body, means for detecting a first voltage associated with said first pulse across at least a part of said patient'"'"'s body, means for producing a first signal proportional to said first voltage, means for detecting a second voltage associated with said second pulse across at least a part of said patient'"'"'s body, means for producing a second signal proportional to said second voltage, and means for producing a combined signal from said first and second signals, means for deriving a metabolic demand parameter from said combined signal; and means for adjusting said means for stimulating said patient'"'"'s heart in relation to said metabolic demand parameter. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A method of detecting a changing impedance within a patient'"'"'s body comprising the steps of
producing a constant current biphasic pulse pair, said pulse pair having a first pulse having current flowing in a first direction and a second pulse having current flowing in a second direction, transmitting said pulse pair through at least a portion of said patient'"'"'s body, detecting a first voltage associated with said first pulse across at least a part of said patient'"'"'s body, producing a first signal proportional to said first voltage, detecting a second voltage associated with said second pulse across at least a part of said patient'"'"'s body, producing a second signal proportional to said second voltage, producing a combined signal from said first and second signals, and deriving an impedance from said combined signal.
Specification