title: Exploratory analysis of cerebral oxygen reserves during sleep onset in older and younger adults.
abstract: OBJECTIVE
  To explore differences in cerebral oxygen reserves during sleep in old and young adults.
  
  
  METHODS
  Descriptive cross-sectional study.
  
  
  METHODS
  General clinical research center.
  
  
  METHODS
  Nine old (aged 65-84) and 10 young (aged 21-39) adults.
  
  
  METHODS
  Subjects were monitored during the first nightly sleep cycle using standard polysomnography, including measures of arterial oxyhemoglobin saturation (SaO(2)). Changes in regional cerebral oxyhemoglobin saturation (rcSO(2)) were used to estimate cerebral oxygen reserves. General linear models were used to test group differences in the change in SaO(2) and rcSO(2) during sleep.
  
  
  RESULTS
  Older subjects had lower SaO(2) than young subjects before sleep (baseline) (F((1,18))=5.1, P=.04) and during sleep (F((1,18))=10.7, P=.01). During sleep, half of the older subjects and none of the younger ones had SaO(2) values below 95%. In addition, the older subjects had more periods of oxygen desaturation (drops in SaO(2) > or = 4%) (chi-square=24.3, P=.01) and lower SaO(2) levels during desaturation (F((1,18))=11.1, P<.01). Although baseline values were similar, rcSO(2) decreased during sleep 2.1% in older subjects (F((1,8))=3.8, P=.05) but increased 2.1% during sleep in younger subjects (F((1,9))=4.6, P=.04). When the older subjects awakened from sleep, rcSO(2), but not SaO(2), returned to baseline; both returned to baseline in younger subjects.
  
  
  CONCLUSIONS
  This exploratory analysis generated the hypothesis that lower SaO(2), combined with declines in regional blood flow, contributes to decline in cerebral oxygen reserves during sleep in older subjects. Further study will assess the effects of factors (e.g., medical conditions, subclinical disorders, and sleep architecture) that might account for these differences.
authors.affiliation: School of Nursing, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA. bcarlson@email.unc.edu
authors.forename: Barbara W
authors.initials: BW
authors.lastname: Carlson
authors.forename: Virginia J
authors.initials: VJ
authors.lastname: Neelon
authors.forename: John R
authors.initials: JR
authors.lastname: Carlson
authors.forename: Marilyn
authors.initials: M
authors.lastname: Hartman
authors.forename: Sunil
authors.initials: S
authors.lastname: Dogra
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D001921:Brain / Q000098:blood supply / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption / Q000502:physiology*; D010108:Oxyhemoglobins / Q000378:metabolism*; D017286:Polysomnography; D012016:Reference Values; D012039:Regional Blood Flow / Q000502:physiology; D012894:Sleep Stages / Q000502:physiology*; D019265:Spectroscopy, Near-Infrared; D014851:Wakefulness / Q000502:physiology
chemical_list: D010108:Oxyhemoglobins