Arousal related selfresuscitating reflexes, sighs and startles during airway occlusion in infants

During obstructive sleep apnea (OSA) upper airway reopening has been attributed to a sudden burst of pharyngeal muscle dilating activity. This has been attributed to arousal from sleep as indicated by cortical EEG activity. In order to explain recovery from OSA episodes in infants that occur in the absence of cortical arousal, we performed experimental airway occlusion in sleeping infants. Our hypothesis was that a sleep startle combined with an augmented breath would occur during the occlusion and that such brainstem-mediated reflex might provide an explanation for recovery from OSA in the absence of cortical arousal.

We studied 16 healthy infants (age 4–19 weeks) during sleep by recording EEG, ECG, O2-saturation, submental, diaphragmatic, nuchal and limb electromyogram, face mask pressure, airflow and infrared video. A startle, accompanied by neck extension, limb, nuchal and submental EMG activation, occurred during airway occlusions. The startle occurred simultaneously with the transition from phase I to phase II of a large biphasic inspiratory effort, which had characteristics of a typical augmented breath except that inspiratory flow was absent.

The magnitude of startles correlated positively with peak airway negative pressure and heart-rate increase indicating that arousal processes are graded in intensity. Full cortical arousal was missing with one exception, however, during NREM-sleep a suppression of sleep-spindles indicated arousal activation without progression to full arousal.

We conclude that the neck extension and pharyngeal dilating muscle activity associated with the startle and augmented breath potentially accounts for recovery of airway patency during OSA episodes in infants. This brainstem related reflex together with a drastic increase of heart rate characterises a universal self resuscitating mechanisms during sleep in absence of full cortical arousal.