[Fetal respiratory movements and their regulation]

In 1972, fetal breathing movements were clinically rediscovered. Details of their episodic occurrence, frequency, inspired volume, pleural pressure, and the nearly absolute independence of fetal blood gases were investigated in animal experiments. In the human being, there is also an association between fetal breathing and sleep state: fetal breathing movements were confined almost exclusively to periods of REM sleep. The pattern of respiratory frequency changes as gestation progresses; the rates decrease as term approaches. Hardly any breathing movement can be detected during labor. The fetal respiratory centre is capable of rhythmic movements, but there is a lack of response to basic chemical stimuli from the periphery of the body. The association between fetal breathing and REM sleep implies that the connection between breathing and behaviour is already established before birth; but in the fetus, the link between breathing and metabolism is not yet forged. Throughout postnatal life this linkage predominantly regulates breathing. The difference between fetus and newborn in the reaction to chemical stimuli implies a change at birth related to the glomera cells of the carotid bodies. Under the influence of the marked increase in the sympathetic tone there is a major increase in the sensitivity of the receptor cells to oxygen deficiency immediately after birth.