Effects of reduced uterine blood flow on electrocortical activity, breathing, and skeletal muscle activity in fetal sheep.

Experiments were conducted in 11 unanesthetized fetal sheep during the last third of gestation to examine the effects of prolonged, reversible reduction in uterine blood flow on fetal electrocortical activity, breathing movements, and skeletal muscle activity. With an adjustable clamp placed around the maternal common internal iliac artery, uterine blood flow was restricted for 2 hours to produce a reduction in fetal arterial oxygen saturation from 56.1% +/- 1.9% to 28.8% +/- 0.7%. When blood flow was reduced, there was a decrease in the percentage of time that fetuses spent in low-voltage electrocortical activity, from 57.5% +/- 3.0% to 37.8% +/- 3.5%, and a decrease in the incidence of both breathing movements and integrated skeletal muscle activity. Younger fetuses (110 to 121 days' gestation) demonstrated a lesser degree of reduction in breathing movements when compared with older fetuses (125 to 140 days) whereas the effects of hypoxemia on electrocortical activity became less apparent with advancing gestational age.