Impairment of cerebrovascular reactivity to acetazolamide in patients with normal pressure hydrocephalus.

Cerebrovascular reactivity (CVR) to acetazolamide was investigated in 41 patients with normal pressure hydrocephalus (NPH). The aetiology was subarachnoid haemorrhage in 20 patients, trauma in nine, brain tumour in three and idiopathic in nine. Mean cerebral blood flow (CBF) of the whole brain was measured by performing first-pass radionuclide angiography using 99Tcm-hexamethylpropylene++ amine oxime. Cerebrovascular reactivity was measured as the percentage change from the baseline mean CBF value after the administration of 500 mg of acetazolamide. Cerebrovascular reactivity was significantly (P < 0.001) reduced in patients with the complete triad of NPH (1.4 +/- 3.1%), regardless of the aetiology, compared with normal controls (14.7 +/- 3.3%). Patients with the incomplete triad also showed significantly (P < 0.05) reduced CVR (9.6 +/- 5.4%). Patients with the complete triad had significantly (P < 0.001) lower CVR than those with the incomplete triad. Post-operative CVR in both groups (20 patients with the complete triad and 9 patients with the incomplete triad) increased significantly, from 1.5 +/- 3.5% to 10.0 +/- 5.5% (P < 0.001) and from 8.7 +/- 4.9% to 14.9 +/- 5.4% (P < 0.05), respectively. Cerebrovascular reactivity is impaired in patients with NPH regardless of the aetiology and improves after shunting.