Hypersomnolence, insomnia and the pathophysiology of upper airway resistance syndrome.

OBJECTIVE: In order to test the hypothesis that upper airway resistance syndrome (UARS) is merely an extension of the pathophysiology of obstructive sleep apnea/hypopnea (OSA/H) to less severe pharyngeal collapse during sleep, we compared the severity of hypersomnolence and the prevalence of insomnia in UARS patients to the patterns observed for OSA/H patients. Our goal was to determine whether the severity of hypersomnolence and the prevalence of insomnia observed in UARS patients could have been predicted from the patterns observed among OSA/H patients.

METHODS: We performed a retrospective study of a large consecutive patient series evaluated at an academic sleep disorders center, including 220 OSA/H patients and 137 UARS patients. Patients had no other sleep-related diagnosis and underwent an initial evaluation that included a measure of hypersomnolence [a multiple sleep latency test (MSLT); 95%] or insomnia questionnaire (87%). Patients were characterized by anthropometric data, polysomnographic descriptive measures of sleep, MSLT data and insomnia questionnaire data.

RESULTS: Severity of hypersomnolence decreased over the continuum from severe to mild OSA/H. A model fit to the OSA/H patients to predict severity of hypersomnolence significantly underestimated hypersomnolence in UARS patients, which was comparable in severity to that of patients with mild OSA/H. The frequency of sleep-onset insomnia increased over the continuum from severe to mild OSA/H and increased further in UARS.

CONCLUSIONS: UARS is, in some respects, an extension of OSA/H to less severe pharyngeal collapse, but this does not adequately account for the symptom profile of patients with UARS. A physical model is proposed to account for the excess somnolence in UARS relative to expectations and the increasing frequency of sleep-onset insomnia along the continuum from severe OSA/H to UARS.