Uteroplacental blood flow during hyperthermia with and without respiratory alkalosis

Abstract

The effect of induced maternal hyperthermia (1.5 degrees C rise over 60 min) on the uterine and umbilical circulations was examined in two groups of chronically instrumented pregnant sheep. Hyperventilation occurred in both groups. In the group in which the resultant respiratory alkalosis was untreated (N = 5), uterine blood flow decreased to 53 +/- 3% (mean +/- SE; P less than 0.01) of control at maximal maternal temperature. Umbilical blood flow also decreased 30 +/- 6% (P less than 0.01) below control levels. In the other group, normocapnia was maintained (N = 4). Uterine blood flow decreased in this group to 75% +/- 2% (P less than 0.01) of control levels, but umbilical blood flow did not significantly change. There was no significant change in maternal or fetal mean arterial pressure during hyperthermia in either group. Thus, maternal hyperthermia per se results in a significant decrease in uterine blood flow primarily through an effect on uterine vascular resistance, but without a concomitant change in umbilical blood flow.

Feto‐Maternal Relationships in Goats During Heat and Cold Exposure

“…The feto-maternal temperature difference was similar to that recorded for sheep (Oakes et al 1976;Cefalo & Hellegers, 1978;Laburn, 1996) as well as other small to medium-sized mammals, and humans (Adamsons & Towell, 1965;Morishima et al 1975;Schröder & Power, 1994). Although the feto-maternal body temperature gradients varied somewhat among goats, under the fixed ambient conditions of the laboratory holding pens, the gradient for each individual mother and her fetus remained constant throughout the last trimester of pregnancy.…”

Contribution of the BOHR effect to the fall in fetal Po2caused by maternal alkalosis

“…oxygen binding capacity is in the blood. Assu-The average va me of the oxygen tensions meaming a fetal cardiac output of 30 ml/min [4] sured in situ by the mass spe ctrometer is about and a blood volume of 12 ml [8] the mean 6 Torr lower than the average va i ue obtained circulation time is 25 seconds. An interval of by conven tional analysis of blood samples from two minutes ought therefore to allow complete the fetal heart [5]> whereas the average Pco 2 reestabhshment of the steady state oxygen flux value is almost identical to that of the previous across the placenta after the start of the base study The di ff er ence in Po 2 may be due to the infusion.…”

“…Finally, it has been clai- med that the effect of alkalosis on fetal Ρθ2 is exerted through the fetal placental circulation. A reduction in umbilical blood flow has been demonstrated experimentally in respiratory alkalosis induced by mechanical hyperventilation [24], but in alkalosis due to hyperthermia [25] or to moderate exercise [17] there was no significant change in fetal placental perfusion. The present study is a theoretical and experimental analysis of the contribution of the BOHR effect to the reduction in fetal Ρθ2 caused by maternal alkalosis.…”

“…Secondly, the rise in pH, or the fall in Pco2, could provoke constriction of the vessels supplying the maternal side of the placenta, thereby reducing blood flow and the oxygen supply to the fetus. This has been shown to occur during experiments on the pregnant ewe and her fetus when alkalosis is induced by ingestion of sodium bicarbonate [3] or by hyperventilation due to hyperthermia [25] or exercise [6,16,17]. Finally, it has been clai- med that the effect of alkalosis on fetal Ρθ2 is exerted through the fetal placental circulation.…”

Fetal and maternal fluid balance in sheep during hyperthermia with and without water deprivation

“…It has been postulated that the increased uterine blood flow is diverted through arteriovenous shunts which may be responsible for increasing the transfer of heat from the fetus to the mother (Andrianakis & Walker, 1994). Although Oakes et al (1976) and Dreiling & Carman (1991) do not comment about availablity of drinking water in their studies, water was available ad libitum in the study by Andrianakis & Walker (1994).…”