Relationship between cerebral circulatory reserve and oxygen extraction fraction in patients with major cerebral artery occlusive disease: a positron emission tomography study.

BACKGROUND AND PURPOSE The present study examined the relationship between circulatory and metabolic reserve in patients with hemodynamic impairment. METHODS Positron emission tomography was used to investigate 40 patients with major cerebral artery occlusive disease. The ratio of cerebral blood volume to cerebral blood flow (CBV/CBF) and vasoreactivity in response to hypercapnia (%CBF(hypercapnia)) and acetazolamide (ACZ) stress (%CBF(ACZ)) were measured to evaluate circulatory reserve. Oxygen extraction fraction (OEF) was measured to evaluate metabolic reserve. To detect relationships between circulation reserve and OEF, cerebral hemispheres were grouped into 5 or 6 stepwise groups based on reduction of circulation reserve. RESULTS OEF was significantly elevated in hemispheres with CBV/CBF > or =0.11 minutes and in hemispheres with %CBF(hypercapnia) <0%. OEF was significantly increased according to %CBF(ACZ) in hemispheres with %CBF(ACZ) <15% and plateaued at levels below -15%. CONCLUSIONS Metabolic reserve consumption began at CBV/CBF > or =0.11 minutes, CBF(hypercapnia) <0%, and CBF(ACZ) <15%.