Age-related changes in pumping mechanical behavior of rat ventricle in terms of systolic elastance and resistance

Abstract

Both the maximal systolic elastance (Emax) and the theoretical maximal flow (Q̇max) can quantify the systolic mechanical behavior of the ventricular pump. Physically, Emax can reflect the intrinsic contractility of the myocardium as an intact heart. The quantity in Q̇max is inversely related to the internal resistance of the left ventricle. How great the effects of age are on these Emax and Q̇max has never been examined, however. This study was to determine the ventricular pumping mechanics in terms of the systolic elastance and resistance in male Fischer rats at 6, 12, 18, and 24 months of age. We measured left ventricular (LV) pressure and ascending aortic flow waves using a high-fidelity pressure sensor and an electromagnetic flow probe, respectively. Those two parameters that characterize the systolic pumping mechanics of the left ventricle are obtained by making use of an elastance-resistance model. The basic hemodynamic condition in those animals with different ages is characterized by (i) no significant change in cardiac output and (ii) a decrease in basal heart rate, LV end-systolic pressure, as well as effective arterial volume elastance. Changes that take place in the left ventricle with age include a decline in Emax and an increase in Q̇max, especially at 24 months. These results demonstrate that the impaired intrinsic contractility of an aging heart may be compensated to some extent by the diminished ventricular internal resistance. Such compensation in aging rats may maintain normal blood flow essential for the metabolic needs of tissues and/or organs before heart dysfunction and failure occur.