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To investigate the effects of lung distension and oxygenation on umbilical blood flow (UBF) and plasma prostaglandin E2 (PGE2) in relation to arousal and stimulation of breathing movements, we studied eight chronically instrumented, unanesthetized fetal sheep between 137 and 143 d of gestation. Electrocorticogram, electro-oculogram, nuchal and diaphragmatic electromyograms, arterial pH and blood gas tensions, Hb oxygen saturation, body temperature, and UBF were recorded in each fetus. Electrocorticogram, electro-oculogram, and nuchal electromyograms were used to define sleep states. No sooner than 4 d after surgery, fetal lungs were distended with 100% O2 or N2 in a randomized order via an in situ Y-endotracheal tube. PGE2 concentrations were analyzed by RIA. A significant increase in fetal arousal and stimulation of breathing during nonrapid eye movement sleep was observed during lung distension with O2 as compared with control periods and lung distension with nitrogen. In all sleep states, UBF significantly decreased during oxygenation as compared with the control values. However, no significant correlation was observed between the time of the onset of arousal and the decrease in UBF. Lung distension with N2 resulted in increased plasma PGE2 concentrations, whereas, no change was observed during oxygenation. Our data suggest that an increase in fetal partial pressure of arterial O2 leads to a decrease in UBF. However, the onset of arousal and stimulation of breathing during lung distension and oxygenation were not dependent on a decrease in plasma PGE2 concentrations.

Umbilical Arterial Blood Flow and Plasma Prostaglandin E2 Concentrations during Arousal and Breathing Movements in Fetal Sheep