The Role of Cerebral Hemodynamics in Moyamoya Disease. NIH R01NS051631. The purpose of this study is to determine if people with moyamoya disease who have insufficient blood flow are at a higher risk for stroke. The natural history of this disorder is not defined. It is very likely that hemodynamic factors play an important role in the risk of future stroke. Some patients are treated surgically with a variety of procedures intended to improve collateral blood flow to the brain. The effect of these procedures on cerebral blood flow and on subsequent stroke risk reduction is unknown. This blinded, prospective study investigated the role of cerebral hemodynamic factors in the pathogenesis of stroke in patients with moyamoya disease. We tested the hypothesis that increased oxygen extraction in the cerebral hemisphere distal to the occlusion is a predictor of the subsequent risk of ipsilateral ischemic stroke in medically treated patients.