[Cardiac output control of total artificial heart during exercise--a predictive control method based on objective functions obtained from changes in cardiac output of the natural heart with respect to time].

Abstract

In order to establish a total artificial heart (TAH) control method during exercise, a predictive control method was developed to increase the cardiac output (CO) during exercise in a profile similar to that of a natural heart; this was achieved by predicting changes in CO as a time function at various treadmill speeds. During exercise, the CO of the TAH was controlled to follow the time function by changing operating parameters such as the positive and negative pressures, S/D ratio, and pulse rate of both artificial heart pumps under a computerized control algorithm. To evaluate this control method, four TAH goats were exercised on a treadmill. The hemodynamics were recorded before, during, and after exercise; the blood lactate, blood catecholamine, A-V oxygen difference, and blood hemoglobin were measured before and immediately after exercise. The predictive control method was then compared with both the natural heart and also the fixed control method, in which the operating parameters remained unchanged during exercise. It was concluded that 1) with the predictive control method, changes in the CO of the TAH were almost the same as in the natural heart. On the other hand, no increase in CO occurred with the fixed control method. 2) with the predictive control method, changes in the blood lactate, blood catecholamine and A-V oxygen difference were significantly lower than with the fixed control method. This study showed that the TAH goat with the predictive control method resulted in being subjected to less stress than with the fixed control method, and that this method can be usefully employed until such time as an ideal feedback control method for the TAH can be developed.