Balance Between Right and Left Ventricular Output

Abstract

The right ventricular ejection pattern is characterized by early onset, gradual rise to peak flow velocities in midsystole and gradual return to baseline. Left ventricular ejection begins very shortly after right ventricular systole, abruptly reaches peak flow, and diminishes during the remainder of the systolic interval, terminating with a brief, sharp, retrograde surge as the aortic valves close. The duration of ejection is shorter in the left ventricle than in the right. In healthy dogs, respiratory activity produces very slight fluctuations in right and left ventricular output that are almost in phase. In dogs with hydrothorax and pulmonary atelectasis, the right and left ventricular outputs fluctuate in greatly exaggerated fashion with each forced respiratory effort. Under such conditions, the changes in right and left ventricular stroke volume are nearly 180 Degrees out of phase. Pulmonary outflow resistance is increased and the right ventricular ejection pattern closely resembles those generally characteristic of the left ventricle. Assume that the erect posture causes cardio-acceleration and large changes in right and left ventricular stroke volume. which are essentially synchronous. Treadmill exercise with sudden and unexpected onset produces changes in the outputs of the right and left ventricles without obvious lead or lag of one ventricle over the other. These experiments do not support the concept that changes in "venous return" are dominant mechanisms inducing alterations in cardiac output.