Time course of the acetazolamide effect in patients with extracranial carotid artery disease.

The acetazolamide test of cerebrovascular reserve is performed as a two-point transcranial Doppler (TCD) measurement of the flow velocity in the middle cerebral artery (MCA) before and 15 to 20 minutes after injection of the carbonic anhydrase inhibitor. The time course was evaluated by bilateral TCD monitoring over 45 minutes in 51 patients with extracranial carotid artery disease. Twenty-nine patients in Group 1 showed a unilateral and 22 patients in Group 2, a bilateral stenosis of the internal carotid artery (ICA). Thirty-one normal hemispheres in 18 normal subjects provided baseline control values. The most useful parameter for the description of the time course was the integral of the mean flow velocity. In both groups integral of the mean flow velocity was significantly reduced compared to that in normal persons (Group 1: 587.2 +/- 538.3 cm, p < 0.01; Group 2: 728.9 +/- 397.1 cm, p < 0.01; normal persons: 967.8 +/- 350.0 cm). The maximal increase of mean flow velocity in a two-point measurement also was significantly lower in the patient groups, but did not reach the same level of significance in Group 2 (Group 1: 19.6 +/- 12.3 cm/sec, p < 0.01; Group 2: 24.2 +/- 10.4 cm/sec, p < 0.05). Thirty-four of 73 hemispheres had reduced integral of the mean flow velocity, but only 29 had a reduced maximal increase. These data indicate that continuous monitoring and evaluation of the time course of the acetazolamide effect provide additional information on cerebrovascular reserve and help to detect an increased number of patients with impaired cerebrovascular reserve.