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 (E-es), preload-recruit able stroke work, dP/dt(max), the dP/dt(max) end-diastolic volume rela tion, cardiac index, heart rate, arterial elastance (E-a), and the rat io E-a/E-es at rest, during isoproterenol infusions (0.05-1.0 mu g/kg/ min), and after propranolol (1 mg/kg i.v.). Resting heart rate and car diac index decreased between 1 and 6 wk. In 1 wk olds, resting E-es wa s at maximum and was unchanged during isoproterenol infusion; isoprote renol increased other contractility indices. Two, 4, and 6 wk olds dem onstrated reserve using all contractility indices. Contractile efficie ncy was not different between ages. In 1 wk olds, E-es decreased durin g isoproterenol infusion; isoproterenol did not change E-a at 6 wk. E- a/E-es was higher at rest at 6 wk than at 1 wk, and fell significantly on isoproterenol; isoproterenol did not change E-a/E-es at 1 wk. With beta-adrenergic stimulation, 1 wk olds increased cardiac index by inc reasing heart rate and decreasing afterload, 6 wk olds increased cardi ac index by increasing heart rate and contractility; no change in cont ractile efficiency was found in either group. In summary, contractile reserve is limited at 1 wk when measured by E-es, but other indices de monstrated reserve. Indexed E-a falls in response to beta-adrenergic s timulation in all ages but 6 wk. Ventricular-vascular coupling is opti mized at 1 wk even under baseline conditions.