title: Characterizing sleep structure using the hypnogram.
abstract: OBJECTIVE
  Research on the effects of sleep-disordered breathing (SDB) on sleep structure has traditionally been based on composite sleep-stage summaries. The primary objective of this investigation was to demonstrate the utility of log-linear and multistate analysis of the sleep hypnogram in evaluating differences in nocturnal sleep structure in subjects with and without SDB.
  
  
  METHODS
  A community-based sample of middle-aged and older adults with and without SDB matched on age, sex, race, and body mass index was identified from the Sleep Heart Health Study. Sleep was assessed with home polysomnography and categorized into rapid eye movement (REM) and non-REM (NREM) sleep. Log-linear and multistate survival analysis models were used to quantify the frequency and hazard rates of transitioning, respectively, between wakefulness, NREM sleep, and REM sleep.
  
  
  RESULTS
  Whereas composite sleep-stage summaries were similar between the two groups, subjects with SDB had higher frequencies and hazard rates for transitioning between the three states. Specifically, log-linear models showed that subjects with SDB had more wake-to-NREM sleep and NREM sleep-to-wake transitions, compared with subjects without SDB. Multistate survival models revealed that subjects with SDB transitioned more quickly from wake-to-NREM sleep and NREM sleep-to-wake than did subjects without SDB.
  
  
  CONCLUSIONS
  The description of sleep continuity with log-linear and multistate analysis of the sleep hypnogram suggests that such methods can identify differences in sleep structure that are not evident with conventional sleep-stage summaries. Detailed characterization of nocturnal sleep evolution with event history methods provides additional means for testing hypotheses on how specific conditions impact sleep continuity and whether sleep disruption is associated with adverse health outcomes.
authors.affiliation: Department of Biostatistics, Johns Hopkins University, Baltimore, MD, USA.
authors.forename: Bruce J
authors.initials: BJ
authors.lastname: Swihart
authors.forename: Brian
authors.initials: B
authors.lastname: Caffo
authors.forename: Karen
authors.initials: K
authors.lastname: Bandeen-Roche
authors.forename: Naresh M
authors.initials: NM
authors.lastname: Punjabi