CEREBRAL VASOMOTOR REACTIVITY IS SIGNIFICANTLY REDUCED IN LOW-FLOW ASCOMPARED TO THROMBOEMBOLIC INFARCTIONS - THE KEY ROLE OF THE CIRCLE OF WILLIS

To test the hypothesis that cerebral vasomotor reactivity (CVMR) is si gnificantly more reduced in patients with hemispheric low-flow infarct ions than in brain infarctions due to arterio-arterial embolism, a ser ies of 64 consecutive patients with internal carotid artery occlusions were studied. CVMR was calculated from relative changes of blood flow velocity within the middle cerebral artery (MCA) measured by transcra nial Doppler ultrasonography (TCD) during hypo- and hypercapnia. The c onfiguration of the circle of Willis (COW) was also determined by TCD using common carotid artery compression tests. Anterior,. posterior or ophthalmic artery collateral flow, and absence or combinations of the se, were differentiated. CT scans were categorized as showing either n o infarction (group I; n = 20) or territorial (group II; n = 28), or l ow-flow infarctions (group III; n = 16). As compared to normal, CVMR w as significantly reduced but equal in groups I and II, however, even m ore reduced in group III. CVMR was lowest, and low-flow infarctions we re most frequent in patients whose collateral hemispheric blood supply was from the ophthalmic artery as opposed to patients with a complete or nearly complete COW. Our findings indicate that low-flow infarctio ns in extracranial ICA occlusions represent brain damage due to a crit ical reduction in cerebral perfusion pressure, as opposed to thromboem bolically induced lesions. The configuration of the COW seems to play the key role. Our findings also support the view that the pattern of h emispheric infarction seen on CT indicates the pathogenesis of stroke.