AJP - Heart and Circulatory Physiology, Vol 249, Issue 6 1098-H1105, Copyright © 1985 by American Physiological Society
Effect of graded reductions in uteroplacental blood flow on the fetal lamb
C. A. Skillman, M. A. Plessinger, J. R. Woods and K. E. Clark
Graded reductions in uteroplacental blood flow (UBF), produced by an
externally adjustable vascular occluder, were studied in unanesthetized
pregnant sheep. This method was designed to simulate the physiological
occurrence of reduced UBF to study its effects on fetal status. Sheep were
divided into four groups in which average percent changes (+/- SE) in UBF,
as measured by electromagnetic flow probes, were 7 +/- 2, -24 +/- 1, -49
+/- 1, and -63 +/- 2% for 1 h. Maternal and fetal cardiovascular (heart
rate and blood pressure) and blood gas measurements of PO2 and PCO2, pH,
and O2 content were determined before, during, and after recovery from UBF
reduction. UBF reduction had no significant effect on maternal
measurements. Changes in fetal PO2 and O2 content were directly related to
the extent of vascular occlusion (P less than or equal to 0.05). Fetal pH
markedly decreased after 1 h of 49% UBF reduction (P less than or equal to
0.05) and within 10 min after 63% UBF reduction (P less than or equal to
0.05). Fetal bradycardia (P less than or equal to 0.05) resulted from 63%
reduction in UBF. Fetal heart rates at recovery were greater than base-line
heart rate values (P less than or equal to 0.05) in the three groups whose
UBF was restricted. The results of the present study suggest that the
uterus of the pregnant ovine is perfused in sufficient excess to protect
the fetus during short-term reductions of less than 50% UBF.
