Fetal respiratory movements in response to rapid changes of CO₂ in carotid artery

¹ Department of Pediatrics, Johns Hopkins Medical School, Department of Environmental Medicine, Johns Hopkins School of Hygiene, Baltimore, Maryland, and Department of Gynaecology, St. Thomas's Hospital Medical School, London S.E.i, England

Recent studies have suggested that chemoreceptors may respond to the rate of change of carbon dioxide as well as its level in arterial blood. The blood which perfuses the carotid body of the fetus would be expected to have less cyclic changes in blood gases since the placenta is the organ of gas exchange. The absence of oscillations in blood gases may contribute to the lack of sustained respiratory activity in utero. Slow changes in fetal blood gases do not initiate fetal respiratory activity. Rapid infusions of blood equilibrated with high CO₂ mixtures into the carotid artery of exteriorized fetal guinea pigs and a lamb were associated with gasps. It is proposed that the initiation of rhythmic breathing at birth may depend in part on the oscillations in CO₂ which follow use of the lung as the organ of gas exchange.

Submitted on July 20, 1964