Dynamics of Ventricular Ejection

Left ventricular ejection in open-chest, anesthetized dogs begins with an abrupt acceleration of blood into the ascending aorta, reaching an average maximum of 4,650 cm./sec./sec. Velocity reaches a sharp peak of 88 cm./sec. (average) within the first one-third to one-half of the ejection period. Deceleration is more gradual and continues to the closure of the aortic valve. The general pattern of the time-course recording is that of a triangle with its peak skewed into early systole and separated from a flat diastolic period of zero flow by a deep notch of backflow attending closure of the aortic valve. Ventricular pressure exceeds aortic pressure only during the brief period between the opening of the valve and peak systolic velocity, a period of approximately 45 per cent of the ejection period. This "positive" (headward) gradient represents the acceleration transient and explains the sharp rise in flow to a maximum in early systole. During the deceleration (terminal) phase of ventricular ejection, the pressure gradient is against the direction of flow. This reversal in pressure gradient brings about a gradual deceleration of flow to zero. These findings are considered experimental proof that the major phenomenon relating pressure and flow in the ascending aorta is that governing mass acceleration.