[Recent physiologic and pathophysiologic studies in heart function in the perinatal period]

Recent investigations of the cardiac output in fetal lambs have shown that left ventricular output reaches nearly exclusively the upper circulation of the body (head, neck, forelegs) via the ascending aorta. Right ventricular output supplies predominantly the descending aorta via the ductus arteriosus. Increasing afterload results in reductions of stroke volumes in the fetus as well as in the neonate. The Frank-Starling-mechanism is only weakly developed in lambs before and after birth. Immediately after birth the rise of myocardial contractility in the newborn is related to his important endogenic sympathoadrenergic stimulation. This large postnatal increase of contractility depends strictly on a normally functioning thyroid gland during the last trimester of gestation. Presumably, T3 influences the prenatal development of the cardiac beta-receptors.