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Relationship Between Vasodilatation and Cerebral Blood Flow Increase in Impaired Hemodynamics: A PET Study with the Acetazolamide Test in Cerebrovascular Disease

¹ PET Unit, Research Institute, Shiga Medical Center, Moriyama, Japan
² Biomedical Imaging Research Center, Fukui Medical University, Fukui, Japan

The changes in cerebral blood flow (CBF) and arterial-to-capillary blood volume (V₀) induced by acetazolamide (ACZ) are expected to be parallel each other in the normal circulation; however, it has not been proven that the same changes in those parameters are observed in patients with cerebrovascular disease. To investigate the relationship between changes in CBF, vasodilatory capacity, and other hemodynamic parameters, the ACZ test was performed after an ¹⁵O-gas PET study. Methods: Twenty-two patients with unilateral major cerebral arterial occlusive disease underwent PET scans using the H₂¹⁵O bolus method with the ACZ test after the ¹⁵O-gas steady-state method. CBF and V₀ for each subject were calculated using the 3-weighted integral method as well as the nonlinear least-squares fitting method. After evaluation of accuracy in V₀ values, a new parameter, the CBF/V₀ ratio, which is expected to disclose arterial perfusion pressure, was also compared between the conditions. Results: The regional CBF (rCBF) and V₀ increased significantly after ACZ administration in the hemisphere contralateral to the ischemic side. However, in a subgroup of patients who showed a significant reduction in the rCBF increase in the ipsilateral hemisphere (group A), the ACZ injection caused no change or a slight decrease in rCBF even though the V₀ showed a significant increase. Thus, the increases in rCBF and V₀ did not necessarily parallel each other in the ipsilateral hemispheres of patients who have impaired cerebral circulation. A parameter defined by the rCBF/V₀ ratio decreased significantly in the ipsilateral hemisphere of group A after ACZ administration, although the ratio showed no change in the contralateral hemisphere or in the other subgroup (group B). Conclusion: The change in the rCBF/V₀ ratio after ACZ challenge may represent an alteration in arterial perfusion pressure that is expected to indicate a critical hemodynamic status in patients with cerebrovascular disease, especially in patients who have a reduced rCBF response.

Key Words: acetazolamide • cerebrovascular disease • cerebral blood volume • vasodilatory capacity • cerebral perfusion pressure

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