Expiratory flow limitation in awake sleep-disordered breathing subjects

Increased upper airways (UA) collapsibility has been implicated in the pathogeny of sleep-disordered breathing (SDB). An increased UA instability during expiration has recently been shown in healthy subjects. The present study assessed UA collapsibility in SDB patients by applying negative pressure during expiration. Full-night polysomnography was performed in 16 subjects (all snorers) with a wide range of SDB, and in six healthy control subjects. Physical examination, spirometry, and maximal inspiratory and expiratory flow rates were within normal limits for all 22 subjects. Negative expiratory pressure (NEP) (-5 cmH2O) was applied during quiet breathing in seated and supine position. Flow limitation (FL) during NEP was expressed as the percentage of tidal volume during which expiratory flow was less than or equal to the flow recorded during quiet breathing (%FL). The mean desaturation index (DI) of the 16 subjects was 27.3+/-26.4 (+/-sD) and the average FL in supine position was 38.4+/-37.9%. A close correlation between %FL supine during wakefulness and DI during sleep (r=0.84, p<0.001) was found. All obstructive sleep apnoea subjects had >30%FL supine. There was no FL in the six control subjects. In conclusion, negative expiratory pressure application during expiration appears to be a useful, noninvasive method for the evaluation of subjects with sleep-disordered breathing. Present results suggest that upper airway collapsibility can be detected in these subjects during wakefulness.