title: Are the adverse effects of body position in patients with obstructive sleep apnea dependent on sleep stage?
abstract: OBJECTIVE
  The purpose of the study was to determine if the adverse effect of body position on obstructive sleep apnea (OSA) is worsened during rapid eye movement (REM) sleep and if patients with OSA decrease the time spent supine during REM sleep.
  
  
  METHODS
  Overnight polysomnography from 80 sequential patients referred to Buffalo VA Sleep Lab for suspected OSA were analyzed with 20 patients in each of the following groups: normal with apnea-hypopnea indices (AHI) <5/h, mild (AHI, 5-< 15/h), moderate (AHI, 15-<30/h), and severe (AHI, >30/h). We used extended Cox models with the Anderson-Gill modification for multiple events with two time varying covariates: sleep stage and body position. Generalized estimating equations with logit link were used to take into account correlated data within each patient for the relation between sleep stage and body position.
  
  
  RESULTS
  The hazard ratios for events in REM vs non-REM sleep was significant for the normal, mild, and moderate groups only: 1.71 (95% CI 1.4-2.08), 1.45 (95% CI 1.22-1.73), 1.28 (95% CI 1.1-1.5), respectively. The hazard ratio for events in the supine vs non-supine position was significant for the mild and moderate groups only: 1.25 (95% CI 1.02-1.52) and 1.24 (95% CI 1.04-1.47), respectively. The addition of an interaction effect between sleep stage and body position was not statistically significant for any group. The odds ratios of sleeping in supine position for REM vs non-REM sleep were 0.47 (95% CI 0.27-0.82) for moderate OSA group and 0.54 (95% CI 0.3-0.95) for severe OSA.
  
  
  CONCLUSIONS
  In summary, we found significant effects of both sleep stage and body position in mild and moderate but not severe OSA. Patients with moderate and severe OSA were less likely to spend time in the supine position during REM compared with non-rapid eye movement sleep.
authors.affiliation: Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, University of Buffalo, Buffalo, NY, USA. mador@buffalo.edu
authors.forename: M Jeffery
authors.initials: MJ
authors.lastname: Mador
authors.forename: Youngmi
authors.initials: Y
authors.lastname: Choi
authors.forename: Abid
authors.initials: A
authors.lastname: Bhat
authors.forename: Jacek
authors.initials: J
authors.lastname: Dmochowski
authors.forename: Mark
authors.initials: M
authors.lastname: Braun
authors.forename: V A
authors.initials: VA
authors.lastname: Gottumukkala
authors.forename: Brydon J
authors.initials: BJ
authors.lastname: Grant
mesh_terms: D004569:Electroencephalography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017286:Polysomnography; D011187:Posture; D012307:Risk Factors; D012720:Severity of Illness Index; D020181:Sleep Apnea, Obstructive / Q000175:diagnosis* / Q000503:physiopathology*; D012894:Sleep Stages / Q000502:physiology*