A Comparative Study Using Transcranial Dopplerometry and CO2 According to some trials, the posterior circulation in subjects with the normal brain has the decreased vasoreactivity if compared with the anterior circulation, according to others, it is similar. To clear up this problem, the authors have quantified and compared the vasodilatation capacity of the middle cerebral and basilar arteries in response to changes of PaCO2 using the index of cerebrovascular reserve. If the index of cerebrovascular reserve in the posterior circulation is physiologically lower, it could mean a higher risk of ictus due to low flow distally from the site of the basilar artery obstruction, and could be the reason for earlier and more aggressive treatment of such a lesion with intervention techniques. The study involved 20 volunteers in whom the flow-limiting obstructive changes had been eliminated. Transcranial dopplerometry was used for monitoring changed velocities of the blood flow simultaneously in the middle cerebral artery on the right and in the basilar artery in response to the CO2 inhalation. A cerebrovascular reserve was measured as percentage of increasing the velocity from the resting basal values at the increase of CO2 concentration in exhaled air by 1 kPa. No significant changes in the cerebrovascular reserve were found out between the drainage area of the middle cerebral artery and that of the basilar artery. Our study has confirmed the fact that the anterior and posterior circulations have similar reserve capacity in subjects without a flow-limiting cerebrovascular obstructive lesion. Thus, there is no base for the hypothesis that in the vascular system of the basilar artery if compared with that of the middle cerebral artery there exists the increased risk for the ictus development on the strength of a limited reserve potential at the presence of an obstructive lesion.

        Key words: basilar artery, cerebrovascular circulation, middle cerebral artery, ischemic ictus, ultrasonography, Doppler, transcranial