Collapsibility of the relaxed pharynx and risk of sleep apnoea.

The present study measured hypotonic pharyngeal collapsibility in subjects not known to have obstructive sleep apnoea (OSA), and assessed the variables that affect collapsibility and the relationship with OSA. The critical value of positive end-expiratory pressure (P(crit)) was measured under the hypotonic condition of anaesthesia in 227 subjects who underwent elective surgery. The risk of OSA in this population was estimated using the Berlin questionnaire. The mean P(crit) for all subjects was positive (above atmospheric), ranging from 0.69 (95% confidence interval (CI) -7.39-8.77) to 4.0 (CI -4.82-12.82) cmH(2)O for subjects with low and high prevalence of OSA, respectively. P(crit) < or = -5 cmH(2)O was only found in 3.1% of the study subjects. In the general population, P(crit) was similar in males and females and correlated positively with increasing age, while a correlation with neck circumference was found only in males. P(crit )accounted for only 12.25% of the variability in OSA risk score. In conclusion, subjects with high critical value of positive end-expiratory pressure are at an increased risk for developing obstructive sleep apnoea. However, the human pharynx is prone to collapse and occludes in most people in the absence of neuromuscular support. Therefore, in most subjects, the level of neuromuscular activity may ultimately determine the occurrence of sleep apnoea.