A TRANSCRANIAL DOPPLER STUDY OF BASILAR HEMODYNAMICS IN PROGRESSIVE CAROTID-ARTERY DISEASE

In carotid artery disease (CAD) the basilar artery (BAI may act as an important intracranial collateral to supply hypoperfused middle cerebr al artery (MCA) territories. Transcranial Doppler studies were perform ed to study the dependency between BA hemodynamics in relation to the MCA perfusion status. BA and MCA blood flow velocities (BFV), pulsatil ity indices (API) and cerebrovascular reactivity (CVR) were assessed i n 40 patients with a progressive MCA hypoperfusion due to progressive CAD. All patients had patent cervical segments of their vertebral arte ries with an antegrade vertebral flow profile. Duplex studies were per formed to diagnose the severity of CAD. Hypoperfusion of the MCA as di agnosed by the degree of vasoparalysis assessed by a Diamox(R) procedu re. Analysis showed that the basilar BFV significantly increased in ca ses of progressive CAD, the basilar PI decreased but the basilar CVR r emained unchanged. However, in cases of bilateral hemodynamic signific ant CAD and bilateral exhausted CVR in the MCA territory, the basilar artery did not exhibit an increase of BFVs or a decrease of the basila r Pl,but the basilar CVR showed a significant decrease. Basilar artery CVR is not impaired if this artery has a function as intracranial col lateral in CAD. However in cases of bilateral hypoperfused MCA territo ries the basilar artery does not function as a collateral pathway. The basilar CVR declines under these circumstances which merely reflects the exhausted hemodynamics in the anterior/posterior borderzones. This situation might lead to an increased stroke risk in the distal basila r supply zones.