EFFECT OF MATERNAL HYPOXEMIA ON BEHAVIOR IN UNANESTHETIZED NORMOXIC OR MILDLY HYPEROXIC FETAL LAMBS

To determine whether hypoxemia inhibits fetal activity by substances f rom the mother or placenta, six fetal lambs were chronically instrumen ted at 128-132 days gestation for extracorporeal membrane oxygenation (ECMO). Severe maternal hypoxemia (arterial PO2 decreased to 6.00 +/- 0.60 kPa) was produced while fetal arterial PO2 was maintained normoxi c or mildly hyperoxic using ECMO. The incidences of fetal breathing mo vements were 34.8 +/- 3.1% (SE) during baseline before ECMO, 36.8 +/- 3.4% during baseline with ECMO, and 21.4 +/- 3.5% (P < 0.05 compared w ith baseline with ECMO) during maternal hypoxemia. The durations of pe riods of breathing were 9.8 +/- 1.2 min before ECMO, 9.3 +/- 1.1 min w ith ECMO, and 10.5 +/- 1.7 min (P = NS) during maternal hypoxemia. In 7 of 14 maternal hypoxemia experiments, breathing activity stopped too late (7-23 min) to be attributed to maternal hypoxemia. Fetal electro corticographic activity (P = NS), nuchal electromyographic activity (P = NS), and eye movements were normal before ECMO, with ECMO, and duri ng maternal hyperemia. Fetal blood pressure and heart rate did not cha nge. We conclude that the inhibition of fetal activity during maternal hypoxemia does not seem to be mediated by release of factors from the maternal side of the placenta or the ewe.