CEREBRAL VASOREACTIVITY ASSESSED WITH TRANSCRANIAL DOPPLER AND REGIONAL CEREBRAL BLOOD-FLOW MEASUREMENTS - DOSE, SERUM CONCENTRATION, AND TIME-COURSE OF THE RESPONSE TO ACETAZOLAMIDE

Background and Purpose To improve the assessment of cerebral vasoreact ivity using acetazolamide (ACZ), we studied the time course of the res ponse and the relationship between dose, response, and serum concentra tion. Methods Blood flow velocities were measured with the use of tran scranial Doppler ultrasonography in one of the middle cerebral arterie s of 48 healthy subjects after the intravenous administration of 1 to 1.6 g ACZ. In 34 subjects (group 1), velocities were measured every se cond minute to detect the maximum middle cerebral artery velocity incr ease. We also measured regional cerebral blood Row using single-photon emission computed tomography in 27 of the subjects in group 1 before and approximately 15 to 20 minutes after the ACZ injection. The serum concentration of ACZ was measured in 15 subjects. In the remaining 14 subjects (group 2), middle cerebral artery velocity measurements were made 10, 25, 30, and 45 minutes after ACZ administration to obtain inf ormation regarding the late time course of the response. Results In gr oup 1 the plateau phase of the velocity response was reached 8 to 15 m inutes after ACZ administration. A large range of velocity increase wa s observed, and a significant correlation was found between the maximu m velocity increase and the dose and serum concentration of ACZ. In gr oup 2 subjects, maximum velocities were maintained 30 minutes after th e injection, but after 45 minutes velocities had decreased to 68% of t heir highest level. No significant relationship was found between dose or serum concentration of ACZ and the regional cerebral blood flow in crease. The velocity increase after ACZ was similar in both older and younger subjects. Conclusions This study shows that cerebral vasoreact ivity is best assessed 10 to 30 minutes after ACZ administration and t hat the dose should probably exceed 15 mg/kg if a maximum vasodilatory response in the cerebral circulation is to be obtained.