Comparison of regional vasomotor responses to acetazolamide and CO2 in rabbit cerebrum and cerebellum, measured by a hydrogen clearance method

Aim:  Many investigators have proved the usefulness of acetazolamide provocation and the carbon dioxide test for assessment of the local cerebrovascular reactivity by measurement of the regional cerebral blood flow in patients with occlusive cerebrovascular disease. Data originating from a comparison of these two different vasomotor stimuli as concerns the differences in sensitivity to them in various parts of the central nervous system are scarce. Our aim was to compare the cerebral blood flow responses to hypercapnic and acetazolamide stimuli in different brain regions. Methods:  The cerebral blood flow was measured in the cerebrum (cortex and caudate nucleus) and cerebellum (cortex), as measured by a hydrogen clearance method in anaesthetized, artificially ventilated rabbits. Results:  In normocapnia, the cerebral blood flow values in the cerebrum and the cerebellum differed significantly. The cerebral blood flow responses to both vasodilatory stimuli were to be significantly higher in the cerebrum than in the cerebellum, but the relative increases, i.e. the mean relative reactivities, were similar in the different regions measured. Conclusion:  The regional dissimilarity might explain to some extent the different sensitivities of the various brain areas to sudden blood pressure changes (infarction or haemorrhage). The results further suggest that heterogeneity in cerebrovascular reactivity should be considered in the assessment of vasoreactivity in patients with occlusive cerebrovascular disease. Since the comparison of the carbon dioxide and acetazolamide – induced cerebrovascular reactivities revealed a strong linear relationship, it was concluded that acetazolamide provocation is equivalent to the carbon dioxide test in the evaluation of cerebrovascular reactivity.