The role of the upper airway in neonatal apnoea.

Up to 50% of apnoeic episodes are obstructive or mixed apnoeas in which, by definition, there is upper airway obstruction. The other 50% of apnoeas are central in origin, but in 40% of these there is evidence of upper airway obstruction, which also occurs in periodic breathing. The obstruction occurs in the upper pharynx. It is due to a failure of activation of the muscles, including the genioglossus, which support the compliant pharynx and normally prevent its collapse. Fibreoptic studies have demonstrated obstruction also at the entrance to the larynx by the arytenoid masses and the aryepiglottic folds. There is some evidence that inspiring against a closed airway can induce central apnoea, possibly via the intercostal-phrenic inhibitory reflex. Upper airway secretions can trigger obstruction. Continuous positive airway pressure distends both the pharynx and laryngeal aperture and so prevents mixed and obstructive apnoeas, but has no effect on central apnoea.