Variation in cardiac chamber volume or pressure as a controlling parameter

Claim 1

A rate adaptive pacer comprising: implantable pulse generator means for normally producing cardiac stimulating pulses at a predetermined lower rate; sensing means for sensing impedance in the blood in a selected cardiac chamber; means for producing a time varying impedance signal proportional to the intracardiac impedance measured in the selected cardiac chamber due to the beating action of the heart; means for extracting from the time varying impedance signal a modulation signal due to volume changes; means for relating the modulation signal to and extracting quantitative information therefrom with respect to the respiratory activity of the patient in whom the pulse generator means is implanted, the respiratory activity information including that relating both to the respiration interval (I RESP ) and the respiration depth (D RESP ); and means for producing a rate control signal from the modulation signal which, when applied to the pulse generator means, changes the rate at which the stimulating pulses are produced from the predetermined lower rate to a higher rate, the interval between the cardiac stimulating pulses is made to vary in accordance with the algorithm: ##EQU4## where a and b are constants, I RESP is the respiratory interval and D RESP is the respiratory depth and ##EQU5## are base values relating to values obtained with the patient at rest.