THE ROLE OF THE CENTRAL NERVOUS SYSTEM IN PERINATAL RESPIRATION: STUDIES OF CHEMOREGULATORY MECHANISMS IN THE TERM LAMB

Abstract

Studies were performed to define the CNS acid-base status in the fetal lamb, as well as the contribution of CNS mechanisms in the initiation and control of breathing in the newly born lamb. The average CSF pH in term fetal lambs was found to be similar to that in young lambs as well as man. When fetal CSF hydrogen ion concentration was noted to be increased, or when perfusion of the ventral lateral medulla with mock CSF high in hydrogen ion concentration was carried out, no respiratory activity was noted. This suggests that the central response to hydrogen ion concentration, which is responsible for control of respiration in the breathing animal, may not be operative in the fetal state. However, in the physiologic setting of these experiments, the onset of breathing was primarily a central function which was little affected by peripheral chemoreceptor or baroreceptor discharge, as animals with their carotid sinus and vagal nerves divided initiated respiration as consistently as controls. Once breathing has been initiated, the central response to hypercarbic breathing could be demonstrated in the absence of any possible peripheral chemoreceptor influence.