Quantitative analysis of regional wall motion in dogs in situ--characteristics of end-systolic pressure-length relation.

Regional wall motion was analyzed to deduce the muscle property unique to regional contractile states. End-systolic pressure length relations were evaluated under global changes in a contractile state, under selective intracoronary administration of inotropic agents to produce regional hypo- or hyper-kinesis, and before and after extension of size of the ischemia. Linearity of the end-systolic pressure-length relation was confirmed in each perturbation; however, the behavior of this relation with regard to changes in the slope and X-axis intercept differed among the three situations. When the contractile state was altered globally by intravenous administration of inotropic agents such as dobutamine and propranolol, the slope of the end-systolic pressure-length relation changed in a manner similar to that seen with the pressure-volume relation or stress-strain relation, with no significant changes in the X-axis intercept. Namely, the level of global cardiac function determined the slope of the end-systolic pressure length relation. When regional hypokinesis was produced pharmacologically by selective intracoronary infusion of lidocaine, the X-axis intercept moved rightward, depending on the degree of regional hypokinesis. Expansion in the size of the ischemic area also shifted the X-axis intercept rightward. The latter two phenomena suggested that the hypokinetic segments were stretched by the surrounding intact myocardium. Accordingly, end-systolic pressure-length relations provide useful information concerning the functional state of regional myocardium. The systolic properties of the regional myocardium rendered hypokinetic have to be quantified so as to include the total geometry of the heart.