Compensatory mechanisms for chronic cerebral hypoperfusion in patients with carotid occlusion

Background and Purpose-The purpose of this experiment was to assess long-te rm cerebral hemodynamic and metabolic changes in patients with increased ox ygen extraction fraction (OEF) in the hemisphere distal to an occluded caro tid artery who remain free of stroke. Methods-Ten patients with increased OEF and no interval stroke underwent re peated positron emission tomography examinations 12 to 59 months after the initial examination. Quantitative regional measurements of cerebral blood f low, cerebral blood volume, cerebral rate of oxygen metabolism (CMRO2), and OEF were obtained. Regional measurements of the cerebral rate of glucose m etabolism (CMRGlc) were made on follow-up in 5 patients. Statistical signif icance (P<0.05) was measured with t tests and linear regression analysis. Results-The ipsilateral/contralateral OEF ratio declined from a mean of 1.1 6 to 1.08 (P=0.022). Greater reductions were seen with longer duration of f ollow-up (P=0.023, r=0.707). The cerebral blood flow ratio improved from 0. 81 to 0.85 (P=0.021). No change in cerebral blood volume or CMRO2 was obser ved. CMRGlc was reduced in the ipsilateral hemisphere (P=0.001 compared wit h normal), but the CMRO2/CMRGlc ratio was normal. Conclusions-Increased OEF improves in patients with carotid occlusion and n o interval stroke. This improvement in OEF is due to an improvement in coll ateral blood flow.