Transient Hemodynamic Perturbations: An Approach to the Study of Ventricular Interaction and Restoring Forces

Summary

In the intact circulation, it is often difficult to delineate the significance and magnitude of complex, interactive phenomena. To overcome this problem, we have developed approaches using transient (single-beat) hemodynamic perturbations that eliminate the confounding effects of series interactions and filling variations. In experimental studies in open-chest dogs, we have employed rapid changes in right heart volume to quantitate direct right-to-left diastolic ventricular interaction gain. Using transient increases in right-ventricular afterload, we have delineated the magnitude of left-to-right systolic interaction and documented an effect of increased right-ventricular afterload that resulted in slowing of left-ventricular relaxation. Using transient perturbations in left heart loading we have correspondingly demonstrated left-to-right systolic interaction and an effect of left-ventricular afterload on venous return to the right heart. Using a servomotor connected to the left atrium that allows abrupt clamping of the left-atrial pressure at a predetermined value, we have produced single-beat, nonfilling, left-ventricular diastolic intervals that allow measurement of the fully relaxed left-ventricular pressure with the ventricle in the end-systolic configuration, thereby providing an estimate of the presence and magnitude of restoring forces. Under physiological conditions in open-chest dogs, we have documented the presence of significant restoring forces at the lower levels of physiological filling. Finally, parallel clinical studies suggest that the ability to generate restoring forces may play a role in determining the level of exercise tolerance in patients with systolic ventricular dysfunction.