THE DISTRIBUTION OF CARDIAC OUTPUT IN PREGNANT SHEEP

Abstract

Cardiac output has been estimated in pregnant and non-pregnant ewes by the thermal dilution and radioactive microsphere techniques. In some ewes microspheres were injected into the foetus to assess placental blood flow. Cardiac output in the ewe rose from 4131 ± 135 ml/min (121.5 ± 3.9 ml/kg/min) in non-pregnant animals to 6025 ± 403 ml/min (156.7 ± 7.9 ml/kg/min)near term. The major increase in output occurred after about 90 days. Insufficient data are available at 30 days gestation but at 60 days the cardiac output was significantly higher than in nonpregnant ewes. Amongst individual organ blood flows only mammary gland and uterine blood flow in the maternal circulation showed a statistically significant gestational trend. The main increase in uterine flow occurred after about 90 days and in mammary flow after about 120 days gestation. Uterine and umbilical flow in the control animals was within the range reported previously. In contrast, in ewes carrying post-mature adrenalectomised foetuses while uterine blood flow/(kg uterus and contents) was in the low normal range, umbilical blood flow/(kg foetus) was about half that found in normal foetuses or in adrenalectomised foetuses examined just before normal term. In hypophysectomised fetuses the umbilical flow/(kg weight of foetus) was low while in their mothers the uterine flow per unit weight was half that found in the other groups. In normal animals uterine blood flow before 120 days appeared to keep pace with the growth of the uterus and its contents but after 120 days both uterine and umbilical flows per unit weight were lower.