Schematic representation of brain perfusion, oxygen extraction, and oxygen metabolism in children with SCA. (A) Proposed model of cerebral infarction in SCA with cerebral vasculopathy. CBF declines as vasculopathy progresses. The percentage of oxygen extracted from the blood by the brain (OEF) increases to maintain adequate tissue oxygen utilization (CMRO₂). When CBF continues to fall and OEF cannot increase further, CMRO₂ drops, causing cerebral infarction. (B) Proposed model of cerebral infarction in SCA without cerebral vasculopathy. CBF is elevated to compensate for decreased blood oxygen content and has limited additional capacity to increase. As blood oxygen content falls due to acute illness, OEF increases to maintain adequate CMRO₂. When OEF is maximized, a drop in CBF may cause CMRO₂ to fall, and infarction ensues. The figure has been adapted from Powers⁴ with permission.