Left ventricular wall stress and aortic input impedance.

The systolic load faced by the left ventricle has been approached from several different aspects over the past decade. One major approach relates instantaneous levels of ventricular wall stress to ventricular systolic load. This approach, based on a large body of information on in vitro performance of muscle, has provided substantial insight into factors influencing ventricular performance. Another equally useful approach to describing ventricular load has been to assess the hydraulic load faced by the ventricle as arterial input impedance or by pulse transmission wave theory. The studies reviewed and the data presented in this article clearly show that in the intact, but open-chest anesthetized preparation, alterations in characteristic impedance are indeed reflected by alterations in ventricular performance, but these alterations are also reflected by alterations in ventricular wall stress that more adequately predict alterations in ventricular shortening associated with changes in load. Moreover, changes in input impedance do not, in themselves, appear to influence the force-velocity-length framework for examining ventricular function.