title: Odds ratio product of sleep EEG as a continuous measure of sleep state.
abstract: OBJECTIVE
  To develop and validate an algorithm that provides a continuous estimate of sleep depth from the electroencephalogram (EEG).
  
  
  METHODS
  Retrospective analysis of polysomnograms.
  
  
  METHODS
  Research laboratory.
  
  
  METHODS
  114 patients who underwent clinical polysomnography in sleep centers at the University of Manitoba (n = 58) and the University of Calgary (n = 56).
  
  
  METHODS
  None.
  
  
  RESULTS
  Power spectrum of EEG was determined in 3-second epochs and divided into delta, theta, alpha-sigma, and beta frequency bands. The range of powers in each band was divided into 10 aliquots. EEG patterns were assigned a 4-digit number that reflects the relative power in the 4 frequency ranges (10,000 possible patterns). Probability of each pattern occurring in 30-s epochs staged awake was determined, resulting in a continuous probability value from 0% to 100%. This was divided by 40 (% of epochs staged awake) producing the odds ratio product (ORP), with a range of 0-2.5. In validation testing, average ORP decreased progressively as EEG progressed from wakefulness (2.19 ± 0.29) to stage N3 (0.13 ± 0.05). ORP < 1.0 predicted sleep and ORP > 2.0 predicted wakefulness in > 95% of 30-s epochs. Epochs with intermediate ORP occurred in unstable sleep with a high arousal index (> 70/h) and were subject to much interrater scoring variability. There was an excellent correlation (r(2) = 0.98) between ORP in current 30-s epochs and the likelihood of arousal or awakening occurring in the next 30-s epoch.
  
  
  CONCLUSIONS
  Our results support the use of the odds ratio product (ORP) as a continuous measure of sleep depth.
authors.affiliation: YRT Ltd, Winnipeg, MB, Canada.|Sleep Centre, Foothills Medical Centre, Calgary, Alberta, Canada.|Sleep Disorders Centre, Winnipeg, Manitoba, Canada.
authors.forename: Magdy
authors.initials: M
authors.lastname: Younes
authors.affiliation: YRT Ltd, Winnipeg, MB, Canada.
authors.forename: Michele
authors.initials: M
authors.lastname: Ostrowski
authors.affiliation: YRT Ltd, Winnipeg, MB, Canada.
authors.forename: Marc
authors.initials: M
authors.lastname: Soiferman
authors.affiliation: YRT Ltd, Winnipeg, MB, Canada.
authors.forename: Henry
authors.initials: H
authors.lastname: Younes
authors.affiliation: YRT Ltd, Winnipeg, MB, Canada.
authors.forename: Mark
authors.initials: M
authors.lastname: Younes
authors.affiliation: Sleep Centre, Foothills Medical Centre, Calgary, Alberta, Canada.
authors.forename: Jill
authors.initials: J
authors.lastname: Raneri
authors.affiliation: Sleep Centre, Foothills Medical Centre, Calgary, Alberta, Canada.
authors.forename: Patrick
authors.initials: P
authors.lastname: Hanly
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000416:Alberta; D000465:Algorithms; D001143:Arousal / Q000502:physiology; D058256:Brain Waves / Q000502:physiology; D004569:Electroencephalography; D005260:Female; D006801:Humans; D008297:Male; D008350:Manitoba; D008875:Middle Aged; D016017:Odds Ratio; D017286:Polysomnography; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012890:Sleep / Q000502:physiology*; D012894:Sleep Stages / Q000502:physiology; D014851:Wakefulness / Q000502:physiology; D055815:Young Adult
keywords: ORP; Sleep quality; odds ratio product; sleep depth; sleep staging