Effects of ischemia on pressure-velocity and pressure-volume relationships in the isolated rabbit left ventricle.

Abstract

The pressure-velocity and pressure-volume relationships were determined in the isolated rabbit left ventricle in order to evaluate ventricular function during global ischemia (low pressure perfusion) and under reperfusion after a 10 min complete coronary occlusion (reperfusion after coronary occlusion). Reducing coronary perfusion pressure, the maximum isovolumic pressure (P0) decreased, but the maximum ejection velocity (Vmax) did not. The slope of the end-systolic pressure-volume relationship (Emax) decreased without any significant change in the volume-axis intercept. On the other hand, under reperfusion after coronary occlusion, both P0 and Vmax were depressed considerably, but Emax quickly recovered to the control level. Thus, Vmax and Emax show different behavior depending on the ischemic conditions. To analyze the relaxation process under low pressure perfusion and reperfusion after coronary occlusion, the pressure-velocity relations during the relaxation phase were determined by the isovelocity method. Similar to the relation for contraction phase, the relation obtained here could be adequately approximated by a hyperbolic equation. Under the control condition, the relaxation velocity was always lower than the contraction velocity at the corresponding pressure level, and the ratio of the maximum filling velocity (Rmax) to Vmax was relatively constant. Although both Rmax and Rmax/Vmax were little affected by the low pressure perfusion, Vmax and Rmax, especially Vmax, decreased when the ventricle was reperfused after coronary occlusion, resulting in an increased Rmax/Vmax.