Left ventricular systolic function, arterial elastance, and ventricular-vascular coupling: a developmental study in piglets.

Circulatory changes occur during perinatal life that increase cardiac output and left ventricular contractile reserve. To examine postnatal changes in left ventricular systolic function and ventricular-vascular coupling, piglets underwent cardiac catheterization at 1, 2, 4, and 6 wk of age. We measured end-systolic elastance (Ees), preload-recruitable stroke work, dP/dt(max), the dP/dt(max) end-diastolic volume relation, cardiac index, heart rate, arterial elastance (Ea), and the ratio Ea/Ees, at rest, during isoproterenol infusions (0.05-1.0 microg/kg/min), and after propranolol (1 mg/kg i.v.). Resting heart rate and cardiac index decreased between 1 and 6 wk. In 1 wk olds, resting Ees was at maximum and was unchanged during isoproterenol infusion; isoproterenol increased other contractility indices. Two, 4, and 6 wk olds demonstrated reserve using all contractility indices. Contractile efficiency was not different between ages. In 1 wk olds, Ea decreased during isoproterenol infusion; isoproterenol did not change Ea at 6 wk. Ea/Ees was higher at rest at 6 wk than at 1 wk, and fell significantly on isoproterenol; isoproterenol did not change Ea/Ees at 1 wk. With beta-adrenergic stimulation, 1 wk olds increased cardiac index by increasing heart rate and decreasing afterload, 6 wk olds increased cardiac index by increasing heart rate and contractility; no change in contractile efficiency was found in either group. In summary, contractile reserve is limited at 1 wk when measured by Ees, but other indices demonstrated reserve. Indexed Ea falls in response to beta-adrenergic stimulation in all ages but 6 wk. Ventricular-vascular coupling is optimized at 1 wk even under baseline conditions.