The threshold of acetazolamide vasoreactivity as an indicator of maximum cerebral blood volume

Using xenon-enhanced computed tomographic (Xe-CT) cerebral blood flow (CBF) measurement, we attempted to determine the extent of vasoreactivity indicating reserve autoregulatory potential by comparing maximal cerebral blood volume (CBV) induced by acetazolamide activation (activated CBV) and the resting CBV. We measured the activated and resting CBVs in two different groups by the subtraction technique using contrast-enhanced CT, and measured the resting and activated CBF in both groups to calculate the percentage increase (%deltaCBF). We extracted CBF and CBV in the territory of the middle cerebral artery on both sides separately for each patient, and treated them independently. We then divided the resting CBV values in group B (25 patients, n=50) into 6 subgroups according to their %deltaCBF (below 10%, n=13; 20%, n=7; 30%, n=8; 40%, n=6; 50%, n=6; and over 50%, n=10) and examined the differences from the activated CBVs in group A (12 patients, n=24) by Dunnett's multiple comparison test. Significant differences were seen in subgroups with %deltaCBF exceeding 20% but less than 30%, and in the subgroups with higher %deltaCBF. We consider that %deltaCBF of at least 20% induced by acetazolamide indicates nonmaximal vasodilation, i.e., reserve autoregulatory potential.