Ventricular contracture and compliance changes with global ischemia and reperfusion, and their effect on coronary resistance in the rat.

We measured ventricular contracture and compliance (passive distensibility) of the isolated rat heart during and after 30 minutes of complete global ischemia. The passive filling or distensibility curves of intra-left ventricular pressure vs. volume were linear between 0 and 30 mm Hg during the control, ischemic, and reperfusion periods. During ischemia the effective stiffness (distensibility slope) of the ventricle increased from the preischemic control of 0.229 0.027 to 0.514 0.083 mm Hg/pl (P < 0.005); with reperfusion, stiffness markedly increased to 1.743 0.442 mm Hg//tl (P < 0.001 vs. control). The changes in passive distensibility were parallel to changes in contracture which occurred when the ventricle was held in the isovolumic condition; during ischemia, contracture increased the preischemic diastolic pressure of -2 1 to 17 3 mm Hg (P < 0.001); in the early reperfusion period intense ventricular contracture occurred to a pressure of 75 6 mm Hg (P < 0.001 vs. preischemic control). After 30 minutes of reperfusion contracture pressure decreased to 34 7 mm Hg, (P < 0.001 vs. control). Contracture during reperfusion was associated with a parallel increase in the coronary vascular resistance; postischemic contracture may thus contribute to the no reflow phenomenon observed with attempted reperfusion of ischemic myocardium. The severity of contracture which occurred during ischemia and reperfusion was inversely related to the amount of ischemic tissue lactate accumulation and did not correlate with changes in tissue water content. Thus, global ischemia and reperfusion markedly decreased passive ventricular compliance; in the intact animal ventricular filling could be impaired by this process and diastolic pressure measurements would reflect the change in compliance as well as in ventricular contractile function.