Expiratory flow limitation in awake sleep-disordered breathing subjects

Increased upper airways (UA) collapsibility has been implicated in the path ogeny of sleep-disordered breathing (SDB). An increased UA instability duri ng expiration has recently been shown in healthy subjects. The present stud y 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 examinat ion, spirometry, and maximal inspiratory and expiratory flow rates were wit hin normal limits for all 22 subjects. Negative expiratory pressure (NEP) ( -5 cmH(2)O) was applied during quiet breathing in seated and supine positio n. 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 rec orded during quiet breathing (%FL). The mean desaturation index (DI) of the 16 subjects was 27.3+/-126.4 (+/-sD ) and the average FL in supine position was 38.4+/-37.9%. A close correlati on between %FL supine during wakefulness and DI during sleep (r=0.84, p<0.0 01) was found. All obstructive sleep apnoea subjects had >30%FL supine. The re was no FL in the six control subjects. In conclusion, negative expiratory pressure application during expiration a ppears to be a useful, noninvasive method for the evaluation of subjects wi th sleep-disordered breathing. Present results suggest that upper airway co llapsibility can be detected in these subjects during wakefulness.