• Matthew P Butler, Carolina Smales, Huijuan Wu, Mohammad V Hussain, Yusef A Mohamed, Miki Morimoto, and Steven A Shea.
• Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, OR.
• Sleep. 2015 Nov 1; 38 (11): 1793-801.

Study ObjectiveTo test the hypothesis that respiratory event duration exhibits an endogenous circadian rhythm.DesignWithin-subject and between-subjects.SettingsInpatient intensive physiologic monitoring unit at the Brigham and Women's Hospital.ParticipantsSeven subjects with moderate/severe sleep apnea and four controls, age 48 (SD = 12) years, 7 males.InterventionsSubjects completed a 5-day inpatient protocol in dim light. Polysomnography was recorded during an initial control 8-h night scheduled at the usual sleep time, then through 10 recurrent cycles of 2 h 40 min sleep and 2 h 40 min wake evenly distributed across all circadian phases, and finally during another 8-h control sleep period.Measurements And ResultsEvent durations, desaturations, and apnea-hypopnea index for each sleep opportunity were assessed according to circadian phase (derived from salivary melatonin), time into sleep, and sleep stage. Average respiratory event durations in NREM sleep significantly lengthened across both control nights (21.9 to 28.2 sec and 23.7 to 30.2 sec, respectively). During the circadian protocol, event duration in NREM increased across the circadian phases that corresponded to the usual sleep period, accounting for > 50% of the increase across normal 8-h control nights. AHI and desaturations were also rhythmic: AHI was highest in the biological day while desaturations were greatest in the biological night.ConclusionsThe endogenous circadian system plays an important role in the prolongation of respiratory events across the night, and might provide a novel therapeutic target for modulating sleep apnea.© 2015 Associated Professional Sleep Societies, LLC.

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