RELATIONSHIPS BETWEEN CEREBRAL REGIONAL BLOOD-FLOW VELOCITIES AND VOLUMETRIC BLOOD FLOWS AND THEIR RESPECTIVE REACTIVITIES TO ACETAZOLAMIDE

Background and Purpose The technique of transcranial Doppler ultrasono graphy (TCD) is widely used for assessment of cerebral blood flow velo city. Whether measurement of changes in TCD velocity can be used for s tudying volumetric cerebral blood flow variations remains a matter of debate. We therefore investigated the relationship between flow veloci ty and volumetric cerebral blood flow before and during acetazolamide- induced vasodilation. Methods The middle cerebral artery mean blood ho w velocity (MV) measured by TCD and the corresponding regional and hem ispheric cerebral blood flows assessed with Xe-133 single-photon emiss ion CT were measured in 52 unselected patients. Absolute values of flo w and velocity before and after stimulation and their reactivity to ac etazolamide were compared. When the correlation was statistically sign ificant, the linearity of the relationship was tested. Results Absolut e values of hemispheric cerebral blood flow were correlated with MV bo th before (r=.315, P=.02) and after acetazolamide (r=.436, P=.001), wh ereas regional cerebral blood flow was correlated with MV only after a cetazolamide (before, r=.262, P=.06; after, r=.446, P=.001). All these relationships fitted a linear model. In contrast, there was no correl ation between acetazolamide-induced relative increments of flow and ve locity. Conclusions Our results support a Linear model describing the relationship between absolute values of flow and velocity when arteria l section is the slope and anastomotic blood flow is the intercept. In contrast, relative increments in volumetric flow and velocity may be proportional only if anastomotic flow is negligible, ie, in subjects w ithout cerebrovascular disease. We conclude that, for patients with ce rebrovascular disease, TCD does not satisfactorily model cerebral vaso reactivity in terms of volumetric cerebral blood how.