Upper airway collapsibility, dilator muscle activation and resistance in sleep apnoea

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Abstract
The calibre of the upper airway is thought to be dependant upon its passive anatomy/collapsibility and the activation of pharyngeal dilator muscles. During awake periods, the more collapsible upper airway in obstructive sleep apnoea (OSA) increases the dilator muscle activity through a negative-pressure reflex.A direct correlation between the critical closing pressure (Pcrit), as a measure of anatomy/collapsability and electromyogram (EMG) activity of genioglossus EMG (GG-EMG) and tensor palatini EMG (TP-EMG), was hypothesised. The relationship between these indices and pharyngeal resistance (Rphar) was also examined.The study involved eight males with a mean age of 48 (interquartile range 46–52) yrs with OSA, and an apnoea/hypopnoea index of 75 (65–101)·hr−1on two nights breathing normally and on nasal continuous positive airway pressure (nCPAP). ThePcritwas measured during nonrapid eye movement sleep on nCPAP using brief, incremental reductions in mask pressure. GG-EMG and TP-EMG were measured breath-by-breath, awake, during sleep onset and on nCPAP.Rpharwas measured using airway pressures and flow.Wakeful GG-EMG, early sleep TP-EMG and the sleep decrement in TP-EMG were directly related toPcrit. Muscle activation was negatively correlated withRpharfor TP-EMG awake and GG-EMG early in sleep.In conclusion these results confirm that dilator muscle activation is directly related to airway narrowing and reduces resistance across patients with obstructive sleep apnoea.