title: Comparing the effect of hypercapnia and hypoxia on the electroencephalogram during wakefulness.
abstract: OBJECTIVE
  Hypoxia has been postulated as a key mechanism for neurocognitive impairment in sleep-disordered breathing. However, the effect of hypoxia on the electroencephalogram (EEG) is not clear.
  
  
  METHODS
  We examined quantitative EEG recordings from 20 normal volunteers under three 5-min ventilatory control protocols: progressive hypercapnia with iso-hyperoxia (pO2=150mmHg) (Protocol 1), progressive hypercapnia with iso-hypoxia (pO2=50mmHg) (Protocol 2), and progressive hypoxia with a CO2 scrubber in the circuit (Protocol 3). Each protocol started with a 5-min session of breathing room air as baseline.
  
  
  RESULTS
  In Protocol 1, compared to its baseline, iso-hyperoxia hypercapnia led to a lower Alpha% and higher Delta/Alpha (D/A) ratio. Similarly, in Protocol 2, the iso-hypoxia hypercapnia induced a higher Delta%, a lower Alpha% and higher D/A ratio. No difference was found in any EEG spectral band including the D/A ratio when Protocols 1 & 2 were compared. In Protocol 3, the Delta%, Alpha% and D/A ratio recorded during hypoxia were not significantly different from baseline.
  
  
  CONCLUSIONS
  We found that hypercapnia, but not hypoxia, may play a key role in slowing of the EEG in healthy humans.
  
  
  CONCLUSIONS
  Hypercapnia may be a greater influence than hypoxia on brain neuroelectrical activities.
authors.affiliation: Department of Respiratory and Sleep Medicine, Royal Prince Alfred Hospital, Sydney, Australia; Woolcock Institute of Medical Research, University of Sydney, Australia. Electronic address: david.wang@sydney.edu.au.
authors.forename: David
authors.initials: D
authors.lastname: Wang
authors.affiliation: Department of Respiratory and Sleep Medicine, Royal Prince Alfred Hospital, Sydney, Australia; Woolcock Institute of Medical Research, University of Sydney, Australia; Centre for Integrated Research and Understanding of Sleep (CIRUS), University of Sydney, Australia.
authors.forename: Brendon J
authors.initials: BJ
authors.lastname: Yee
authors.affiliation: Department of Respiratory and Sleep Medicine, Royal Prince Alfred Hospital, Sydney, Australia; Woolcock Institute of Medical Research, University of Sydney, Australia; Centre for Integrated Research and Understanding of Sleep (CIRUS), University of Sydney, Australia.
authors.forename: Keith K
authors.initials: KK
authors.lastname: Wong
authors.affiliation: Centre for Integrated Research and Understanding of Sleep (CIRUS), University of Sydney, Australia; School of Physics, University of Sydney, Australia.
authors.forename: Jong Won
authors.initials: JW
authors.lastname: Kim
authors.affiliation: Surrey Sleep Research Centre, University of Surrey, UK.
authors.forename: Derk-Jan
authors.initials: DJ
authors.lastname: Dijk
authors.affiliation: Department of Anaesthesia, University of Toronto, Canada; Department of Physiology, University of Toronto, Canada.
authors.forename: James
authors.initials: J
authors.lastname: Duffin
authors.affiliation: Department of Respiratory and Sleep Medicine, Royal Prince Alfred Hospital, Sydney, Australia; Woolcock Institute of Medical Research, University of Sydney, Australia; Centre for Integrated Research and Understanding of Sleep (CIRUS), University of Sydney, Australia.
authors.forename: Ronald R
authors.initials: RR
authors.lastname: Grunstein
mesh_terms: D000280:Administration, Inhalation; D000328:Adult; D004569:Electroencephalography / Q000379:methods*; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000175:diagnosis / Q000503:physiopathology*; D000860:Hypoxia / Q000175:diagnosis / Q000503:physiopathology*; D008297:Male; D014851:Wakefulness / Q000502:physiology*; D055815:Young Adult
keywords: Brain waves; CO(2); Cortical depression; Daytime sleepiness; EEG spectra; O(2)