Assessment of Cerebrovascular Reactivity by Doppler C0 2 and Diamox Testing: Which Is the Appropriate Method?

Cerebrosvascular reserve capacity can be estimated by Doppler CO2 or acetazolamide (Diamox) stimulation. These two methods were compared in 18 normal subjects. The variability of CO2 reactivity (mean 27.4 ± 3.8%/ vol% CO2) was markedly lower than that of Diamox reactivity (mean 41.2 ± 21.3%), which was partly caused by reactive hyperventilation. Unexpectedly, there was no positive correlation between CO2 and acetazolamide challenge (r = –0.14). A maximum dilation of the cerebral arterioles after acetazolamide administration could not be achieved as demonstrated by a diminished, but still existing CO2 reactivity during Diamox testing. Compared to CO2 stimulation, Diamox testing was more time-consuming and caused numerous, though reversible side effects. Thus, using transcranial Doppler sonography for assessing cerebrovascular reserve capacity, CO2 stimulation seems preferable to acetazolamide administration in most cases.