A design of an artificial control system of the cardiac output.

Abstract

An automatic control system of the cardiac output of a dog was designed by a method where a cardiac vagus and the heart were involved in the feedback system. The cardiac output was measured at the ascending aorta by a sine wave electromagnetic flowmeter. The output voltage of the flowmeter was compared with a controllable reference voltage. The error voltage was amplified or integrated, and converted to pulses of the frequencies which was proportional to the input of the AD convertor. A peripheral cut end of a vagus was stimulated by an electric stimulator triggered by those pulses. Vagal stimuli decrease the cardiac output by their negative chronotropic and inotropic action. The error approximated zero when the feedback loop gain was more than about 10 or an integral control was used. Complete stability could not be achieved with a zero error and an unstable oscillation of the smoothed cardiac output signal with a period of several seconds was observed. However, the instability was slight and did not disturb its application. Effects of disturbances such as change of venous return and peripheral resistance were sufficiently reduced.