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%.
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%.