Quantitative measurement of regional cerebral perfusion pressure and evaluation of autoregulatory function for cerebral blood flow

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Autoregulatory mechanism to keep cerebral blood flow (CBF) and perfusion pressure may be impaired in patients with cerebrovascular disease. To investigate the critical hemodynamic status in the impaired cerebral circulation, changes in regional CBF and arterial-to-capillary blood volume (Vo) induced by acetazolamide (ACZ) were measured in patients with cerebrovascular disease, as well as changes in hemodynamic parameter defined by CBF/Vo ratio, which is expected to be proportional to the regional perfusion pressure. Patients with unilateral major cerebral arterial occlusive disease underwent H^2 15O-PET at baseline and 10 min after ACZ administration to calculate CBF, Vo and CBF/Vo ratio. The hemodynamic parameters in the territories of bilateral middle cerebral arteries were obtained and compared between the two hemispheres and two conditions. Following ACZ administration, the group of patients who had a reduced CBF response in the ipsilateral hemisphere (= reduced vasodilatory capacity group) showed a significant Vo increase in the same region. Thus, the CBF/Vo ratio decreased significantly after ACZ administration in the ipsilateral hemisphere of patients with reduced vasodilatory capacity. This ratio did not change in the contralateral hemisphere of this group nor in the other group with normal vasodilatory capacity, suggesting that its reduction represented severe hemodynamic impairment and dysfunction of autoregulation for regional perfusion pressure. The significant decrease in CBF/Vo ratio was associated with strokes in patients of reduced vasodilatory capacity. The decrease in the CBF/Vo ratio after ACZ challenge is presumed to represent altered regional cerebral perfusion pressure reflecting a critical hemodynamic status in patients with cerebrovascular disease.