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Method and apparatus for rate-responsive cardiac pacing

  • US 5,271,395 A
  • Filed: 04/17/1992
  • Issued: 12/21/1993
  • Est. Priority Date: 04/17/1992
  • Status: Expired due to Term
First Claim
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1. A pacemaker, enclosed within a housing, comprising:

  • a rate control circuit;

    a pulse generator adapted to be coupled to a patient'"'"'s heart via a cardiac lead, and coupled to said rate control circuit, said pulse generator responsive to a triggering signal from said rate control circuit to generate a pacing pulse;

    said rate control circuit having means for producing triggering signals at a rate varying between predetermined upper and lower pacing rates;

    an activity sensor adapted to be coupled to said patient, producing an output signal indicative of patient activity;

    a Δ

    Z processor;

    an impedance circuit, adapted to be coupled to said heart via said cardiac lead and coupled to said Δ

    Z processor, said impedance circuit producing an impedance voltage waveform corresponding to changes in impedance in said heart;

    said Δ

    Z processor having sampling means for periodically sampling said impedance voltage waveform and further having means for producing a serial bit stream output signal in response to each said sample, the number of logical `1` bits (hereinafter referred to as `counts`) in said bit stream output signal corresponding to a change in said impedance voltage waveform;

    said rate control circuit receiving said bit stream output signal, and having counting means responsive to said bit stream output signal to count said counts occurring during a plurality of successive two-second intervals and having calculating means to calculate the following values;

    LTA (Long-Term Average);

    an average count, over a predetermined long-term interval, of said counts occurring in each two-second portion of said long-term interval;

    LSTA (Limited Short-Term Average);

    an average count, over a predetermined short-term interval, of said counts occurring in each two-second portion of said short-term interval, where said rate control circuit constrains said LSTA value to a range determined by said predetermined upper and lower pacing rates;

    DZ (Limited Positive Difference);

    a value representing a comparison of LSTA and LTA, defined as ##EQU14## where DZmm is a predefined upper limit on said DZ value and where said rate control circuit producing triggering pulses at a rate determined as a function of said DZ value.

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