title: Marked reduction in obstructive sleep apnea severity in slow wave sleep.
abstract: BACKGROUND
  Obstructive sleep apnea (OSA) is widely accepted to improve during slow wave sleep (SWS) compared to lighter stages of NREM sleep. However, supporting data to establish the magnitude and prevalence of this effect is lacking. Consequently, we examined this phenomenon, controlling for posture, in a large group of patients investigated for OSA at an academic clinical sleep service.
  
  
  METHODS
  A detailed retrospective analysis was conducted on data obtained from each 30-sec epoch of sleep in 253 consecutive full-night diagnostic polysomnography studies performed over a 3-month period. Respiratory and arousal event rates were calculated within each stage of sleep, in the supine and lateral postures, and across the whole night, with OSA patients classified on the basis of an overall apnea-hypopnea index (AHI) > or =15 events/h. Central sleep apnea (CSA) patients were defined by a central apnea index > 5/h. Sleep latency and time, and respiratory and arousal event rates in OSA, CSA, and non-OSA patients were compared between sleep stages and postures using linear mixed model analysis. The numbers of patients achieving reduced event rates in SWS and in the lateral posture were also examined.
  
  
  RESULTS
  There were 171 patients with OSA, 14 with CSA, and 68 non-OSA patients. OSA patients took significantly longer to achieve slow wave and REM sleep (p < 0.001) than non-OSA patients and had less stage 4 sleep (p = 0.037). There were striking improvements in AHI and arousal index (Al) from stage 1 to 4 NREM sleep (p <0.001), with intermediate levels in REM sleep. AHI and Al were also markedly reduced in lateral versus supine sleep in all sleep stages (p < 0.001), with an effect size comparable to that of the slow wave sleep effect. The majority of OSA patients achieved low respiratory event rates in SWS. Eighty-two percent of patients achieved an AHI <15 and 57% < 5 events/hour during stage 4 sleep.
  
  
  CONCLUSIONS
  Although OSA patients demonstrate both a delayed and reduced proportion of SWS compared to non-OSA subjects, once they achieved SWS, AHI, and Al markedly improved in most patients.
authors.affiliation: Adelaide Institute for Sleep Health, Repatriation General Hospital, Adelaide, Australia. rajeev.ratnavadivel@health.sa.gov.au
authors.forename: Rajeev
authors.initials: R
authors.lastname: Ratnavadivel
authors.forename: Nuy
authors.initials: N
authors.lastname: Chau
authors.forename: Daniel
authors.initials: D
authors.lastname: Stadler
authors.forename: Aeneas
authors.initials: A
authors.lastname: Yeo
authors.forename: R Doug
authors.initials: RD
authors.lastname: McEvoy
authors.forename: Peter G
authors.initials: PG
authors.lastname: Catcheside
mesh_terms: D001143:Arousal; D001315:Australia / Q000453:epidemiology; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017286:Polysomnography / Q000379:methods / Q000706:statistics & numerical data; D011187:Posture; D012119:Respiration; D012189:Retrospective Studies; D012720:Severity of Illness Index; D020182:Sleep Apnea, Central / Q000453:epidemiology / Q000503:physiopathology; D020181:Sleep Apnea, Obstructive / Q000453:epidemiology* / Q000503:physiopathology*; D012894:Sleep Stages; D012895:Sleep, REM
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