title: Hypercapnia is a key correlate of EEG activation and daytime sleepiness in hypercapnic sleep disordered breathing patients.
abstract: BACKGROUND
  The key determinants of daytime drowsiness in sleep disordered breathing (SDB) are unclear. Hypercapnia has not been examined as a potential contributor due to the lack of reliable measurement during sleep. To overcome this limitation, we studied predominantly hypercapnic SDB patients to investigate the role of hypercapnia on EEG activation and daytime sleepiness.
  
  
  METHODS
  We measured overnight polysomnography (PSG), arterial blood gases, and Epworth Sleepiness Scale in 55 severe SDB patients with obesity hypoventilation syndrome or overlap syndrome (COPD+ obstructive sleep apnea) before and ∼3 months after positive airway pressure (PAP) treatment. Quantitative EEG analyses were performed, and the Delta/ Alpha ratio was used as an indicator of EEG activation.
  
  
  RESULTS
  After the PAP treatment, these patients showed a significant decrease in their waking pCO(2), daytime sleepiness, as well as all key breathing/oxygenation parameters during sleep. Overnight Delta/Alpha ratio of EEG was significantly reduced. There is a significant cross-correlation between a reduced wake pCO(2), a faster (more activated) sleep EEG (reduced Delta/Alpha ratio) and reduced daytime sleepiness (all p < 0.05) with PAP treatment. Multiple regression analyses showed the degree of change in hypercapnia to be the only significant predictor for both ESS and Delta/ Alpha ratio.
  
  
  CONCLUSIONS
  Hypercapnia is a key correlate of EEG activation and daytime sleepiness in hypercapnic SDB patients. The relationship between hypercapnia and sleepiness may be mediated by reduced neuro-electrical brain activity.
authors.affiliation: Department of Respiratory and Sleep Medicine, Royal Prince Alfred Hospital, Sydney, Australia (work performed) ; Woolcock Institute of Medical Research, University of Sydney, Sydney, Australia.
authors.forename: David
authors.initials: D
authors.lastname: Wang
authors.affiliation: Department of Respiratory and Sleep Medicine, Royal Prince Alfred Hospital, Sydney, Australia (work performed) ; Woolcock Institute of Medical Research, University of Sydney, Sydney, Australia.
authors.forename: Amanda J
authors.initials: AJ
authors.lastname: Piper
authors.affiliation: Department of Respiratory and Sleep Medicine, Royal Prince Alfred Hospital, Sydney, Australia (work performed) ; Woolcock Institute of Medical Research, University of Sydney, Sydney, Australia ; Centre for Integrated Research and Understanding of Sleep (CIRUS), University of Sydney, 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 (work performed) ; Woolcock Institute of Medical Research, University of Sydney, Sydney, Australia ; Centre for Integrated Research and Understanding of Sleep (CIRUS), University of Sydney, 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, Sydney, Australia ; School of Physics, University of Sydney, Sydney, Australia.
authors.forename: Jong-Won
authors.initials: JW
authors.lastname: Kim
authors.affiliation: Woolcock Institute of Medical Research, University of Sydney, Sydney, Australia ; Centre for Integrated Research and Understanding of Sleep (CIRUS), University of Sydney, Sydney, Australia.
authors.forename: Angela
authors.initials: A
authors.lastname: D'Rozario
authors.affiliation: Woolcock Institute of Medical Research, University of Sydney, Sydney, Australia.
authors.forename: Luke
authors.initials: L
authors.lastname: Rowsell
authors.affiliation: Surrey Sleep Research Centre, University of Surrey, UK.
authors.forename: Derk-Jan
authors.initials: DJ
authors.lastname: Dijk
authors.affiliation: Department of Respiratory and Sleep Medicine, Royal Prince Alfred Hospital, Sydney, Australia (work performed) ; Woolcock Institute of Medical Research, University of Sydney, Sydney, Australia ; Centre for Integrated Research and Understanding of Sleep (CIRUS), University of Sydney, Sydney, Australia.
authors.forename: Ronald R
authors.initials: RR
authors.lastname: Grunstein
mesh_terms: D001921:Brain / Q000503:physiopathology*; D006970:Disorders of Excessive Somnolence / Q000209:etiology* / Q000503:physiopathology; D004569:Electroencephalography; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000209:etiology* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D017286:Polysomnography; D012891:Sleep Apnea Syndromes / Q000150:complications* / Q000503:physiopathology
keywords: CO2; EEG Spectra; O2; cortical depression.; daytime drowsiness; hypersomnolence; hypoxia