The Contribution of Blood Momentum to Left Ventricular Ejection in the Dog

In five conscious dogs and two anesthetized dogs, the pressure gradient between the left ventricle and the ascending aorta was measured with high fidelity micromanometers. Left ventricular pressure exceeded aortic pressure in the first 30 to 50% of the ejection period. Aortic pressure exceeded left ventricular pressure during the remainder of the ejection period. The magnitude of these differences varied from 5 to 20 mm Hg. This finding in late systole implies that at this time blood is flowing out of the ventricle under its own momentum and that the aorta is a pressure source for the ventricle. The ascending aorta was suddenly occluded in five dogs to verify this hypothesis. When occlusion occurred in the last third of the ejection period, there was an abrupt fall of left ventricular pressure, apparently confirming the momentum hypothesis.