Key points are not available for this paper at this time.
Background and Purpose Cerebrovascular CO 2 reactivity can be assessed easily and reliably by transcranial Doppler sonography. The objectives of the present study were to evaluate sex differences in cerebral CO 2 reactivity and to specify the relation between CO 2 and cerebral blood flow velocity. Methods CO 2 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 (P etco 2 ) were elevated with the use of carbogene gas (95% O 2 , 5% CO 2 ). In each subject the mean blood flow velocity (V mean ) was plotted as a function of P etco 2 . Results The best-fit curves for the relation of V mean /P etco 2 were exponential functions, with the following basic equation: V mean (cm/s)= a e bx , where a is a theoretical quantity representing V mean at a P co 2 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 P etco 2 (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 CO 2 -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.
Kastrup et al. (Mon,) studied this question.