title: Effect of simulated altitude during sleep on moderate-severity OSA.
abstract: OBJECTIVE
  These studies were conducted to test the hypothesis that isobaric hypoxia would switch OSA to central sleep apnoea (CSA).
  
  
  METHODS
  Five adult men (mean age 54.2 +/- 5.5 years, mean BMI 29.9 +/- 6.7 kg/m(2)) with moderate OSA underwent overnight polysomnography at three altitudes. The highest altitude was simulated in a normobaric hypoxic chamber.
  
  
  RESULTS
  The obstructive respiratory disturbance index fell from 25.5 +/- 14.4/h at 60 m to 17.3 +/- 9.2/h at 610 m and 0.5 +/- 0.7/h at 2750 m (P = 0.004 compared with 60 m). The central respiratory disturbance index rose from 0.4 +/- 0.5/h at 60 m to 8.1 +/- 5.8/h at 610 m and 78.8 +/- 29.7/h at 2750 m (P < 0.001 compared with 60 m). Mean sleep SaO(2) fell from 94 +/- 1% at 60 m to 93 +/- 1% at 610 m to 85 +/- 4% at 2750 m (P < 0.001 compared with 60 m).
  
  
  CONCLUSIONS
  Moderate severity OSA at sea level (60 m) was completely replaced by severe CSA at a simulated altitude of 2750 m. The authors believe that the OSA resolved because of an increased respiratory drive [corrected] and an increase in upper airway tone, whereas CSA developed because of hypocapnia in non-rapid eye movement sleep.
authors.affiliation: Peninsula Private Sleep Laboratory, Manly, New South Wales, Australia. kburgess@nsccahs.health.nsw.gov.au
authors.forename: Keith R
authors.initials: KR
authors.lastname: Burgess
authors.forename: Jacky
authors.initials: J
authors.lastname: Cooper
authors.forename: Anthony
authors.initials: A
authors.lastname: Rice
authors.forename: Keith
authors.initials: K
authors.lastname: Wong
authors.forename: Tahnee
authors.initials: T
authors.lastname: Kinsman
authors.forename: Allan
authors.initials: A
authors.lastname: Hahn
mesh_terms: D000704:Analysis of Variance; D001273:Atmosphere Exposure Chambers; D001274:Atmospheric Pressure; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D017286:Polysomnography; D020182:Sleep Apnea, Central / Q000503:physiopathology*; D020181:Sleep Apnea, Obstructive / Q000503:physiopathology*; D012894:Sleep Stages