ORIGIN OF REGIONAL PRESSURE-GRADIENTS IN THE LEFT-VENTRICLE DURING EARLY DIASTOLE

Left ventricular (LV) pressure (P)-diameter, LVP-area, or LVP-volume r elationships used to evaluate LV diastolic function assume uniform LV wall motion and constant LVP. Contrary to these assumptions, there are significant differences in ventricular dynamic geometry and in LV pre ssures measured simultaneously in different parts of the LV, particula rly during early diastole. We instrumented six anesthetized open-chest dogs with three pairs of orthogonal ultrasonic crystals (anterior-pos terior and septal-free wall minor axes, and base-apex major axis) and two micromanometers (in the apex and in the LV base). The mitral valve occluder was implanted during standard cardiopulmonary bypass in the mitral annulus. Data were recorded during 11 transient vena caval occl usions. The mitral valve was occluded for 1 beat every 6-8 beats durin g each vena caval occlusion to produce nonfilling diastole. With the d ecrease of the LV end-systolic volume (V-es) below the equilibrium vol ume V-eq (volume of the completely relaxed LV at LVP = 0), the minimum negative LVP in nonfilling beats increases, the shape of the ventricl e is more ellipsoidal in both filling and nonfilling beats, and the ba se-to-apex pressure gradient at the time of LVP minimum increases rega rdless of the presence or absence of filling. Thus heterogeneous myoca rdial stresses during isovolumic relaxation and early diastole result in ventricular shape changes, intraventricular redistribution of chamb er volume, local accelerations of blood, and associated intraventricul ar LVP gradients. The role of elastic recoil assumes greater importanc e at V-es smaller than V-eq, when the left ventricle becomes more elli psoidal in shape during isovolumic relaxation, leading, in turn, to gr eater shape changes and greater LVP gradient.