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

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 (P(crit)), 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 (R(phar)) 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(-1) on two nights breathing normally and on nasal continuous positive airway pressure (nCPAP). The P(crit )was 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. R(phar) was measured using airway pressures and flow. Wakeful GG-EMG, early sleep TP-EMG and the sleep decrement in TP-EMG were directly related to P(crit). Muscle activation was negatively correlated with R(phar) for 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.