The pre-ejection period of the fetal heart: Response to stress in the term fetal lamb

Abstract

The pre-ejection period (PEP) of the cardiac cycle was studied in the mature lamb fetus exteriorized by cesarean section with the umbilical circulation intact. It was shown to be a reliable index of myocardial contractility. Changes in PEP and therefore in contractility during stress were studied. Fetal hypoxemia induced by a period of maternal anoxia consistently produced shortening of the PEP, whereas changes in the fetal heart rate over the same period were variable. The decrease in PEP was unexpected and was felt to result from catecholamines released by hypoxic stimulation of the adrenal medulla. Umbilical cord occlusion produced lengthening of PEP during occlusion and shortening on release, effects most likely related to great changes in aortic diastolic pressure.