Transcranial Doppler evaluation of cerebrovascular reactivity to acetazolamide in normal subjects

Acetazolamide (AZ), the selective inhibitor of carbonic anhydrase, was proved by intravenous Xenon 133 technique to increase cerebral blood flow (CBF). In this study cerebrovascular reactivity to AZ was evaluated in 10 normal subjects by transcranial Doppler (TCD) within the middle cerebral artery (MCA), since several reports have demonstrated that velocity of cerebral blood flow is well correlated to CBF. After 1 gr AZ injection blood flow velocity markedly increased in all subjects, with a peak in both systolic and diastolic velocity 20 min after drug administration. At that time systolic velocity increased by 35% and diastolic velocity by 50% in comparison to basal values. In contrast with Xenon 133 technique which gives one measurement only for each investigation, TCD allows a continuous monitoring of haemodynamic change following AZ infusion. MCA diastolic velocity at rest was inversely related to age (r = -.804, p < 0.01); baseline diastolic velocity was inversely related to the maximum percentage increment (r = -.745 p < .05). No change in blood pressure and heart rate was observed under experimental conditions. These results, confirm the usefulness of the AZ test in the evaluation of cerebrovascular reactivity and strongly support the use of TCD technique applied to AZ in order to investigate cerebrovascular haemodynamics in normal healthy subjects and in patients at risk of cerebrovascular insufficiency.