Haemorheological disturbances and possibility of their correction in cerebrovascular diseases.

The presence of a hemorheological disturbance must be considered in the pathophysiological and therapeutical approach to vascular diseases, including cerebral diseases. A reduction of blood fluidity, due either to increase of hematocrit (polycythemic hyperviscosity) or of fibrinogen concentration (plasmatic hyperviscosity) or of red cell rigidity (sclerocythemic hyperviscosity) is commonly considered a condition of high risk for acute or chronic brain ischemia. So many attempts have been made for improving blood fluidity with the purpose to prevent stroke and to delay cerebral deterioration in chronic condition. This paper will present a review of the literature on this subject and the personal experience of our research group with the use of hemodilution, plasmapheresis and pharmacological agents. In our opinion the possible correction of hyperviscosity is very helpful in the prevention of acute ischemic attacks and in the reduction of their incidence in chronic cerebral ischemia. During the acute phase of stroke, hemorheological disturbance is only a part of the complex hemodynamic situation: a primary blood hyperviscosity can favor the onset of the disease but, because of its secondary increase after stroke, a vicious circle might be set in motion resulting in a further reduction of blood supply to the brain. Considering this, attempts in improving blood fluidity during stroke could be made, but with the caution that is required in this complicated "circulatory storm".