The importance of baro- and chemoreflexes in the control of the fetal cardiovascular system.

The information gained about the afferent traffic from carotid arterial baro- and chemoreceptors by direct recordings made in the sheep fetus is reviewed. Less is known about aortic baro- and chemoreceptor discharge during this period, and virtually nothing is known about the discharge of other vagal mechano- or chemoreceptor afferents. Knowledge about the functional integrity of sympathetic and parasympathetic efferent pathways is reviewed. Then the various methods which have been used for assessing fetal baro- and chemoreflexes are discussed: the crucial problem here is that there are no techniques available for either increasing or decreasing the discharge of these receptors specifically. Because they have been widely used, however, and are of clinical importance, the effects upon the fetal circulation of hypoxia and asphyxia are reviewed specifically. The relative contributions of baro- and chemoreflexes in producing these effects are considered against the background of the plethora of other processes which operate under these conditions.