title: Arterial oxygen content and age are determinants of middle cerebral artery blood flow velocity.
abstract: OBJECTIVE
  Transcranial Doppler blood flow velocities are inversely related to age and hematocrit, but the relative importance of age, oxygenation, and hemorheological factors has not previously been examined. We evaluated the relative contributions of these factors to middle cerebral artery blood flow velocity in adults with chronic renal failure, a population subject to significant fluctuations in hematologic profile.
  
  
  METHODS
  Twenty-six subjects were studied, with arterial shunt blood sampled at the time of transcranial Doppler before dialysis. Twenty subjects from the original cohort were studied twice to examine the effects of intraindividual changes in blood oxygenation and rheology on Doppler velocities.
  
  
  RESULTS
  Age (r = -.61, P < .001), high-shear viscosity (r = -.46, P < .02), and arterial oxygen content (r = -.44, P < .05) were all inversely related to middle cerebral artery blood flow velocity. Age was the strongest velocity predictor, accounting for 37% of variance by simple regression analysis. Intraindividual change in arterial oxygen content explained most (54%) of the middle cerebral artery blood flow velocity variation between studies (r = -.74, P < .001). Multiple regression analysis showed that inclusion of additional variables could not account for more velocity variation than change in arterial oxygen content alone.
  
  
  CONCLUSIONS
  In this population, age and arterial oxygen content were the most important determinants of interindividual middle cerebral artery blood flow velocity variance and intraindividual middle cerebral artery blood flow velocity variation, respectively.
authors.affiliation: Department of Neurology, University of Southern California School of Medicine, Los Angeles.
authors.forename: R F
authors.initials: RF
authors.lastname: Macko
authors.forename: S F
authors.initials: SF
authors.lastname: Ameriso
authors.forename: M
authors.initials: M
authors.lastname: Akmal
authors.forename: A
authors.initials: A
authors.lastname: Paganini-Hill
authors.forename: J G
authors.initials: JG
authors.lastname: Mohler
authors.forename: S G
authors.initials: SG
authors.lastname: Massry
authors.forename: H J
authors.initials: HJ
authors.lastname: Meiselman
authors.forename: M
authors.initials: M
authors.lastname: Fisher
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D001783:Blood Flow Velocity; D002339:Carotid Arteries / Q000502:physiology; D002536:Cerebral Arteries / Q000502:physiology*; D002561:Cerebrovascular Disorders / Q000503:physiopathology*; D005260:Female; D006801:Humans; D007676:Kidney Failure, Chronic / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood*
chemical_list: D010100:Oxygen