A CAUSE OF EXCESSIVE DAYTIME SLEEPINESS - THE UPPER AIRWAY-RESISTANCESYNDROME

Subjects with isolated complaints of chronic daytime sleepiness are us ually classified as ''idiopathic hypersomniacs'' and treated symptomat ically. A group of these subjects was investigated during nocturnal sl eep and daytime naps. In a subgroup of them, sleep was fragmented by v ery short alpha EEG arousals throughout the sleeping period. These sho rt arousals are usually ignored in sleep analyses, but their impact is significant (in the 15 subjects identified with the syndrome, the mea n sleep latency in multiple sleep latency tests was 5.1 +/- 1 min). Th ese arousals are directly related to an abnormal increase in respirato ry efforts during sleep (the mean peak inspiratory esophageal pressure measured in our subjects in the respiratory cycle just preceding a tr ansient arousal was - 33 +/- 7 cm H2O). Typically, an arousal occurs w ithin one to three breaths of flow limitation associated with abrupt b ut limited reduction in tidal volume (ie, abnormal increase in upper a irway resistance during sleep). The arousal restores normal breathing. Snoring was noted in association with these transient arousals in 10 of the 15 subjects; however, snoring was neither sufficient nor necess ary for the identification of the clinical syndrome. Both sexes were e qually represented in the affected group. All studied subjects had upp er airway anatomy that was mildly abnormal. Nasal continuous positive airway pressure, used as an experimental tool, eliminated the daytime sleepiness (multiple sleep latency mean score = 13.5 min), the transie nt arousals (mean alpha EEG arousal index decreased from 31.3 +/- 12.4 to 8 +/- 2 per hour of sleep), and the abnormal upper airway resistan ce. Chronic daytime sleepiness is a major cause of social, economic, a nd medical impairment. Recognition of this syndrome and its cause is i mportant, as specific treatments can be developed to eliminate the pro blem.