Effects of venesection on cerebral function in chronic lung disease.

Regional cerebral blood flow measurements and neuropsychological testing were conducted before and after venesection on 6 patients with polycythemia secondary to chronic obstructive pulmonary disease. Venesection resulted in lowered viscosity and hematocrit, and an accompanying improvement in cerebral perfusion and mental function. Blood flow was significantly increased in the left cerebral hemisphere following phlebotomy, and there was significant improvement in sensory/mental function. Cerebral function would appear to be related to blood flow alterations influenced by the viscosity of the blood.