An analysis of mechanical cardiac assistance

Abstract

The effect of three methods of cardiac assistance on mean systolic pressure, mean diastolic pressure, and aortic end-diastolic pressure were analyzed theoretically in a mathematical model of the arterial system. The results indicate that: (i) The intra-aortic balloon performs better when it is large and when deflation begins before the onset of systole; the rates of inflation and deflation and the balloon shape and location are of lesser importance; the balloon is more effective when the aorta is stiffer, indicating balloon assist might be more useful in older people. (ii) Left heart bypass has little effect on mean diastolic pressure and produces only small reductions in mean systolic pressure; pressure-volume work is reduced in proportion to the bypass flow; the time-tension index is not materially reduced and aortic end-diastolic pressure is increased. (iii) Counterpulsation through the femoral arteries is very sensitive to timing; femoral counterpulsation is less effective than the intra-aortic balloon because the balloon can be inflated and deflated more rapidly than blood can be removed in and out of the circulation system.