Automatic Cardiac Pacing Technique for Electrophysiologic Investigations: Measurement of Myocardial Excitability in the Dog during Exposure to +Gz

摘要

The objective of this effort was to quantify changes in the excitability of the heart muscle during exposure to various G acceleration profiles. Dogs were catheterized with cardiac pacing electrodes which were inserted into the ventricle of the heart. The exteriorized end of the catheter was protected by a cloth and tape collar allowing the animals to reside in ordinary cages with experimentation taking place for at least 3-4 weeks. A microcomputer-controlled pacemaker was designed, built, and programmed to pace the heart with a basic rhythm established with periodic suprathreshold pulses (S1), and a test stimulus (S2) inserted at a frequency (typically every tenth beat) chosen by the investigation. Other parameters which can be varied by the investigator include pulse amplitudes, durations and S1-S2 delay. The automated equipment described, has been used to collect experimental data on dogs undergoing +G(z) forces on the NAVAIRDEVCEN animal centrifuge. The threshold of stimulation levels are plotted as a function of +G(z). A system was demonstrated in which an animal with a chronic pacing catheter and a computer-based instrument have been combined to provide a useful model in which cardiac threshold of excitability changes can be observed in response to stressors such as +G(z). Keywords: Multi-application technology animal subjects, Cardiac excitability, Cardiac arrhythmia, Acceleration physiology, Exposure(Physiology). (SDW)