The role of chronic hyperviscosity in vascular disease.

The pathogenesis of several major cardiovascular diseases, including atherosclerosis, hypertension, and the metabolic syndrome, is not widely understood because the role of blood viscosity is overlooked. Low-density lipoprotein accelerates atherosclerosis by increasing blood viscosity in areas of low flow or shear, predisposing to thrombosis. Atherosclerotic plaques are organized mural thrombi, as proposed by Duguid in the mid-twentieth century. High-density lipoprotein protects against atherosclerosis by decreasing blood viscosity in those areas. Blood viscosity, at the least, contributes to hypertension by increasing systemic vascular resistance. Because flow is inversely proportional to viscosity, hyperviscosity decreases perfusion and glucose utilization by skeletal muscle, contributing to hyperglycemia in the metabolic syndrome. Therapeutic phlebotomy reduces blood pressure and serum glucose levels in the metabolic syndrome by improving blood viscosity.