AN EXERCISE-RESPONSIVE PACEMAKER CONTROLLED BY RIGHT VENTRICULAR BLOOD TEMPERATURE (CARDIAC)
Abstract
A cardiac pacemaker is an electronic device designed to deliver repetitive, short duration (approx. 2ms), low voltage (approx. 6v), electrical impulses to the heart for the purpose of stimulating contraction. Pacemakers are used when a pathologic condition results in an abnormally slow intrinsic heart rate. Most current commercially available cardiac pacemakers stimulate at a fixed rate regardless of the physiologic needs of the body. Consequently, patients dependent on these pacemakers generally have markedly reduced exercise tolerance because cardiac output during exertion is compromised by the low resting level heart rate. An exercise responsive pacemaker would increase the stimulation rate in accordance with metabolic needs of the body during exercise. Many physiologic parameters have been proposed (pH, SAO2, BP, Resp. Rate, Q-T interval) for control of pacemaker rate. Reliable measurement of these quantities on a long-term basis using implantable sensors has proven to be technically difficult. This thesis describes the research and development of an exercise responsive pacemaker in which stimulation rate is changed based upon intracardial venous blood temperature. This pacemaker should prove more feasible than previously proposed designs since temperature measurement can be performed by a thermistor which is a simple solid-state sensor suitable for long term biological implant. To determine the natural relationship between heart rate and temperature, the electrocardiogram and right ventricular blood temperature of dogs with normal hearts were measured during rest and exercise on a treadmill. To determine if heart rate affected the change in temperature during exercise, the right ventricular blood temperature of dogs with fixed heart rates were measured during rest and treadmill exercise. Several potential pacemaker rate control algorithms were derived from these data. The algorithms were evaluated using computer simulations and with prototype exercise-responsive pacing systems. Finally, a prototype of a fully implantable, temperature controlled exercise-responsive was developed and tested in a dog.
Degree
Ph.D.
Subject Area
Biomedical research
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