title: Sex dependency of cerebrovascular CO2 reactivity in normal subjects.
abstract: OBJECTIVE
  Cerebrovascular CO2 reactivity can be assessed easily and reliably by transcranial Doppler sonography. The objectives of the present study were to evaluate sex differences in cerebral CO2 reactivity and to specify the relation between CO2 and cerebral blood flow velocity.
  
  
  METHODS
  CO2 reactivity of the circulation of both middle cerebral arteries was measured by bilateral transcranial Doppler sonography in 60 healthy volunteers (30 men, 30 women) aged 21 to 58 years. End-tidal carbon dioxide tensions (PETCO2) were elevated with the use of carbogene gas (95% O2, 5% CO2). In each subject the mean blood flow velocity (Vmean) was plotted as a function of PETCO2.
  
  
  RESULTS
  The best-fit curves for the relation of Vmean/PETCO2 were exponential functions, with the following basic equation: Vmean (cm/s) = aebx, where a is a theoretical quantity representing Vmean at a PCO2 of 0 mm Hg, b is the relative slope of the curve (slope divided by the value of the function) corresponding to the definition of reactivity, and x is the PETCO2 (mm Hg). The mean value of b was 0.037 +/- 0.008 in women and 0.030 +/- 0.010 in men. ANOVA demonstrated a significant difference between men and women (P < .001).
  
  
  CONCLUSIONS
  This study demonstrates a highly significant sex-related difference in CO2-induced cerebral vasomotor reactivity. The relation between altered carbon dioxide tensions and blood flow velocities of both middle cerebral arteries in 60 healthy volunteers was found to be exponential.
authors.affiliation: Department of Neurology, University of Tübingen, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Kastrup
authors.forename: C
authors.initials: C
authors.lastname: Thomas
authors.forename: C
authors.initials: C
authors.lastname: Hartmann
authors.forename: M
authors.initials: M
authors.lastname: Schabet
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000187:drug effects; D002245:Carbon Dioxide / Q000494:pharmacology*; D002536:Cerebral Arteries / Q000000981:diagnostic imaging / Q000187:drug effects; D002560:Cerebrovascular Circulation / Q000187:drug effects*; D005260:Female; D006801:Humans; D008297:Male; D012016:Reference Values; D012727:Sex Characteristics; D017585:Ultrasonography, Doppler, Transcranial; D014666:Vasomotor System / Q000187:drug effects
chemical_list: D002245:Carbon Dioxide