Placental Oxygen Transfer in Pregnant Ewes During Hyperbaric Oxygenation

Abstract

ExtractExposure of pregnant ewes to oxygen administration under three atmospheres of pressure produced large increases in maternal arterial blood p02, together with acidosis associated with an increase in pCO,. Although maternal arterial blood pressure tended to increase and uterine arterial blood flow rate tended to fall, the changes had no statistical significance. Simultaneously, it was possible to increase umbilical venous blood PO, within the range 90-550 mm Hg, with corresponding changes in pCO, and pH as occurred in maternal blood. There was a significant decrease in umbilical venous flow rate, which failed to return to control levels after air-breathing was resumed at one atmosphere of pressure. Fetal arterial pressure was unchanged. In five animals studied, umbilical oxygen transfer was also unchanged during hyperbaric oxygenation. SpeculationThe lack of comparable increases in umbilical venous and maternal arterial blood p 0 2 during oxygen administration to gravid ewes and the small reduction in umbilical oxygen transfer rates have been interpreted to be primarily the result of the nonlinearity of sheep oxyhemoglobin dissociation functions. Hyperbaric oxygenation allows umbilical oxygen transfer to occur independently of the function of maternal hemoglobin. The results of this study are consistent with, but do not prove, this hypothesis.