[Hemorrheological changes in cerebrovascular disease].

Over the past ten years, several studies have outlined the importance of high blood viscosity as a pathogenetic factor in ischemic cerebrovascular diseases. Clinical studies have demonstrated that a high blood viscosity due to an elevated hematocrit (greater than 46%) increases the risk of cerebral infarction. Furthermore, in patients with high hematocrit, the cerebral blood flow seems to be lower than in controls and, by removing 200-250 ml of blood by venesection, the cerebral blood flow can be normalized. Several authors have therefore proposed that venesection may be used as a preventive measure in patients at risk for cerebral ischemia with high hematocrit. In addition, studies on experimental brain ischemia have shown that hemodilution reduces the size of the infarction. Therefore, hemodilution has been proposed as an effective measure in the treatment of acute cerebral ischemia. In conclusion, it seems that high blood viscosity is a risk factor in cerebral ischemia although its pathogenetic mechanisms and clinical importance are not yet completely clarified.