Journal of Applied Physiology, Vol 61, Issue 6 2018-2022, Copyright © 1986 by American Physiological Society
Fetal and uteroplacental heat production in sheep
R. D. Gilbert and G. G. Power
To separate heat production of the fetus from that of the placenta,
endometrium, and uterine muscle, we measured total uterine heat production
first with the fetus intact and then after the umbilical cord was snared
and the fetus killed. Heat production was measured with the Fick principle
using thermistors chronically implanted in a maternal artery and major
uterine vein and a flowmeter placed on the common internal iliac artery. In
nine ewes, carrying lambs weighing 4.46 +/- 0.42 (SE) kg, total uterine
heat production fell from 10.6 to 2.9 W after fetal death. Uterine blood
flow fell progressively to 90% of control levels during the first hour
after death. The caloric equivalent for O2 averaged 4.1 cal/ml O2 for the
uterus, 2.2 for the uteroplacenta, and 4.6 for the fetus per se. It was not
possible to explain these results using a simple model of maternal-fetal
heat transfer. Rather, it was necessary to assume an additional pathway for
heat transfer between small uterine veins on the surface of the uterus and
cooler structures in the maternal abdomen, presumably the ventral abdominal
wall.
