title: Quantitative changes in the sleep EEG at moderate altitude (1630 m and 2590 m).
abstract: BACKGROUND
  Previous studies have observed an altitude-dependent increase in central apneas and a shift towards lighter sleep at altitudes >4000 m. Whether altitude-dependent changes in the sleep EEG are also prevalent at moderate altitudes of 1600 m and 2600 m remains largely unknown. Furthermore, the relationship between sleep EEG variables and central apneas and oxygen saturation are of great interest to understand the impact of hypoxia at moderate altitude on sleep.
  
  
  METHODS
  Fourty-four healthy men (mean age 25.0 ± 5.5 years) underwent polysomnographic recordings during a baseline night at 490 m and four consecutive nights at 1630 m and 2590 m (two nights each) in a randomized cross-over design.
  
  
  RESULTS
  Comparison of sleep EEG power density spectra of frontal (F3A2) and central (C3A2) derivations at altitudes compared to baseline revealed that slow-wave activity (SWA, 0.8-4.6 Hz) in non-REM sleep was reduced in an altitude-dependent manner (~4% at 1630 m and 15% at 2590 m), while theta activity (4.6-8 Hz) was reduced only at the highest altitude (10% at 2590 m). In addition, spindle peak height and frequency showed a modest increase in the second night at 2590 m. SWA and theta activity were also reduced in REM sleep. Correlations between spectral power and central apnea/hypopnea index (AHI), oxygen desaturation index (ODI), and oxygen saturation revealed that distinct frequency bands were correlated with oxygen saturation (6.4-8 Hz and 13-14.4 Hz) and breathing variables (AHI, ODI; 0.8-4.6 Hz).
  
  
  CONCLUSIONS
  The correlation between SWA and AHI/ODI suggests that respiratory disturbances contribute to the reduction in SWA at altitude. Since SWA is a marker of sleep homeostasis, this might be indicative of an inability to efficiently dissipate sleep pressure.
authors.affiliation: Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland ; Zurich Center for Integrative Human Physiology (ZIHP), University of Zurich, Zurich, Switzerland.
authors.forename: Katrin
authors.initials: K
authors.lastname: Stadelmann
authors.forename: Tsogyal D
authors.initials: TD
authors.lastname: Latshang
authors.forename: Christian M
authors.initials: CM
authors.lastname: Lo Cascio
authors.forename: Noemi
authors.initials: N
authors.lastname: Tesler
authors.forename: Anne-Christin
authors.initials: AC
authors.lastname: Stoewhas
authors.forename: Malcolm
authors.initials: M
authors.lastname: Kohler
authors.forename: Konrad E
authors.initials: KE
authors.lastname: Bloch
authors.forename: Reto
authors.initials: R
authors.lastname: Huber
authors.forename: Peter
authors.initials: P
authors.lastname: Achermann
mesh_terms: D000328:Adult; D000531:Altitude; D003430:Cross-Sectional Studies; D004569:Electroencephalography; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D020182:Sleep Apnea, Central / Q000503:physiopathology*; D012895:Sleep, REM