Interaction of aortic pressure and left ventricular end-diastolic pressure in the dog.

Fiber length (preload) is an important determinant of left ventricular performance. Mean aortic blood pressure also influences ventricular performance. The present study was undertaken to examine the influence of mean aortic pressure on the fiber length-ventricular performance relationship. Fifteen anesthetized, adrenergically blocked dogs were studied on right-heart bypass at constant heart rate and coronary blood flow. An increase in mean aortic pressure permitted a greater improvement in performance as evaluated by stroke work for a given increase in left ventricular end-diastolic pressure. A given increase in mean aortic pressure at a constant stroke volume produced a greater rise in stroke work over intermediate ranges of left ventricular end-diastolic pressure than occurred with higher or lower left ventricular end-diastolic pressure. Thus, the degree of afterload-induced performance improvement depended on the magnitude of the preload. External circumference-left ventricular end-diastolic pressure data suggested a possible relationship between isovolumic systolic circumferential expansion and the improvement of ventricular performance at higher mean aortic pressures.