AJP - Regulatory, Integrative and Comparative Physiology, Vol 251, Issue 2 409-R416, Copyright © 1986 by American Physiological Society
Fetal vascular pressure and heart rate responses to nonlabor uterine contractions
R. A. Brace and D. S. Brittingham
The purpose of this study was to determine whether there are changes in
fetal arterial pressure, venous pressure, or heart rate during nonlabor
uterine contractions (i.e., contractures) in late gestation pregnant sheep.
To do this, amniotic fluid pressure was continuously recorded using on-line
computer techniques and subtracted from fetal arterial and venous
pressures. With randomly selected data, there were no statistically
significant changes with time in the fetal variables. However, when
averaged with respect to time of the contractures, fetal arterial and
venous pressures increased significantly during the contractures, and heart
rate decreased. In addition, there were small but statistically significant
decreases in each of the three fetal variables just before the
contractures. Blocking the fetal autonomic nervous system eliminated the
decreases in the variables before the contractures as well as the decrease
in heart rate during the contractures, but arterial and venous pressure
increased normally. Infusion of 1 liter of warmed saline into the amniotic
space did not alter the fetal cardiovascular or amniotic fluid pressure
changes during contractures. In summary, there are significant fetal
cardiovascular changes during nonlabor uterine contractions, and these are
consistent with a translocation of fetal blood from the placenta into the
fetal body. Although the cause of fetal cardiovascular changes just before
the contractures is unknown, they suggest but do not prove that the fetus
may provide the signal for the nonlabor uterine contractions to occur.
