Inhibition of breathing movements in fetal life: relevance to the sudden infant death syndrome.

Fetal breathing movements are discontinuous and are inhibited by neural mechanisms associated with the development of non-rapid eye movement sleep. Sudden reduction of arterial PO2 also reduces the incidence of breathing movements in the fetus. Recent work which is directed towards identifying the control pathways and neurotransmitters involved in these effects is discussed. The possibility that breathing may also be inhibited in certain situations after birth is addressed, particularly in relation to the ability of hypoxaemia to produce behavioural arousal in the normal newborn infant, but not in fetal life.