Ventilatory responses to hypoxaemia during sleep in the newborn

Ventilatory responses to rapidly developing hypoxaemia during N2-rebreathing were compared for active and quite sleep in three newborn lambs and four puppies. In lambs, active sleep was associated with: (i) development of ribcage deflation during inspiration, which persisted during progressive hypoxaemia; (ii) depressed ventilatory response to hypoxaemia despite increments of respiratory rate; (iii) delayed arousal. In the puppies, inspiratory collapse of the ribcage did not occur in active sleep and the ventilatory responses during hypoxaemia were similar to those in quite sleep. While apparently defective when related to adults, these responses to hypoxaemia in the lamb are normal. This study illustrates the importance of considering behavioural state and species differences when studying the regulation of breathing, particularly during development.