Fetal responses to maternal exercise in the sheep

Abstract

Fetal responses to maternal exercise were studied in twelve long-term sheep preparations. After hysterotomy, a polyvinyl catheter was inserted into the fetal aorta via the femoral artery (11 fetuses) or via a ligated umbilical artery (4 fetuses) and exteriorized. Seven to ten days later, the ewes were exercised on a treadmill (2.0 to 2.5 miles per hour) for 30 to 60 min. Maternal and fetal arterial pressures, heart rates, and blood pH, Po2, and Pco2 were monitored before exercise, at the end of exercise, and after a 30 min. recovery period. The results indicate that fetal responses to maternal exercise generally follow those of the mother. A significant increase in fetal pH and decrease in fetal Pco2 were observed at the end of exercise, and these were associated with maternal hyperventilation and respiratory alkalosis. Moreover, a significant reduction in fetal Po2 was noted with maternal exercise. A moderate increase in fetal heart rate was also observed with insignificant change in mean arterial blood pressure. The responses were similar in both fetuses with intact umbilical circulation and those with a ligated umbilical artery. However, the latter fetuses had a lower pre-exercise Po2 level and had greater decreases of oxygen tension with maternal exercise. The observed changes were reversible after 30 min. of recovery. These observations suggest that moderately severe maternal exercise may be detrimental to fetuses with some compromise of the umbilical circulation but that the normal fetus tolerates maternal exercise well. It is suggested that the decrease in fetal Po2 is due primarily to reduction in uterine flow during exercise and partially to changes of the oxygen affinities of maternal and fetal hemoglobins consequent to respiratory alkalosis.