A transcranial Doppler study of basilar hemodynamics in progressive carotid artery disease.

In carotid artery disease (CAD) the basilar artery (BA) may act as an important intracranial collateral to supply hypoperfused middle cerebral artery (MCA) territories. Transcranial Doppler studies were performed to study the dependency between BA hemodynamics in relation to the MCA perfusion status. BA and MCA blood flow velocities (BFV), pulsatility indices (API) and cerebrovascular reactivity (CVR) were assessed in 40 patients with a progressive MCA hypoperfusion due to progressive CAD. All patients had patent cervical segments of their vertebral arteries with an antegrade vertebral flow profile. Duplex studies were performed to diagnose the severity of CAD. Hypoperfusion of the MCA was diagnosed by the degree of vasoparalysis assessed by a Diamox procedure. Analysis showed that the basilar BFV significantly increased in cases of progressive CAD, the basilar PI decreased but the basilar CVR remained unchanged. However, in cases of bilateral hemodynamic significant CAD and bilateral exhausted CVR in the MCA territory, the basilar artery did not exhibit an increase of BFVs or a decrease of the basilar PI, but the basilar CVR showed a significant decrease. Basilar artery CVR is not impaired if this artery has a function as intracranial collateral in CAD. However in cases of bilateral hypoperfused MCA territories 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 basilar supply zones.