A comparison of the cerebrovascular responses to CO₂ and diamox in patients with unilateral occlusive cerebral arteries: A H₂¹⁵O PET study

We studied the relationship between the cerebrovascular responses to CO₂ and Diamox in patients with chronic cerebrovascular diseases. The subjects consisted of 11 patients with unilateral occlusive or highly stenotic carotid artery. The cerebral blood flow was measured at the resting state, during the inhalation of 5% CO₂, at both 5 and 20 min after Diamox i.v. (1 g). The rCBF ratios (occlusive/non-occlusive side) during the inhalation of CO₂ and 20 min after Diamox i.v. closely correlated with each other. However, the ratio at 5 min after Diamox i.v. was slightly lower than that during the inhalation of CO₂. The percent increases of rCBF also showed a significant correlation between 5% CO₂ inhalation and 20 min after Diamox i.v. However, the rCBF decreased inversely at 5 min after Diamox i.v. in some regions on the occlusive side, which indicates the presence of a so-called 'steal phenomenon'. The percent increases in the rCBF after 1 g Diamox i.v. were more or equal to those during the inhalation of 5% CO₂. The CO₂ and Diamox were thus considered to be equally useful in the evaluation of the perfusion reserve capacity. However, these various characteristics as described above should be considered in the clinical practice.