Potentially synergistic factors leading to SCI in SCA. Modified from DeBaun et al⁵⁴  with permission. Equation 1: The CMRO₂ is the cerebral metabolic rate for oxygen. The brain relies on a constant delivery of oxygen to maintain CMRO₂. If the delivery is inadequate, permanent tissue injury can occur, depending on the depth and duration of the ischemia. The equation above relates cerebral blood flow (CBF; the bulk delivery of blood to the brain), oxygen extraction fraction (OEF; the fraction of available oxygen blood that leaves the blood by passive diffusion as it passes through the circulation), and the arterial oxygen content (CaO₂). Equation 2: CaO₂, in turn, is a product of the hemoglobin content of blood and the arterial oxygen saturation. Reduced hemoglobin (Hgb; or oxygen carrying capacity of the existing Hgb) or hypoxia may reduce the arterial oxygen content. One can see the potentially synergystic effects of these relationships in reducing the oxygen delivery to the brain below critical thresholds. CaO₂ can fall because of anemia and hypoxia and CBF can fall because of the large artery vasculopathy. Patients with preexisting arteriopathy may be more likely to suffer an ischemic stroke than other patients with the same degree of anemia or hypoxia.