CENTRAL CHEMORECEPTORS AND THE REGULATION OF FETAL BREATHING MOVEMENTS

Abstract

Publisher Summary This chapter explores central chemoreceptors and the regulation of fetal breathing movements. In the study described in the chapter, the ewe was anesthetized with halothane in oxygen and nitrous oxide. The fetal head and one forelimb were brought out through a hysterotomy incision. Polyvinyl catheters are placed in the fetal axillary artery, brachial vein and trachea, and in the amniotic fluid. The ewe was allowed to recover, and the earliest experiments were performed 48 h after surgery. During the experiment, the ewe was in a small cart and allowed free access to food and water. Pressure was continuously recorded from the fetal trachea and the amniotic fluid. Blood was withdrawn periodically from the fetal axillary artery for measurement of PO2, pCO2, and pK. The chapter describes the effect of hypercarbia, including data from 16 experiments in 10 fetuses. It is found that fetal breathing movements present from 25–34% of the time during the four control hours were significantly increased to 67% and then returned to 20% during the hour after the hypercarbia.