Fluid mechanics of vascular systems, diseases, and thrombosis

The cardiovascular system is an internal flow loop with multiple branches c irculating a complex liquid. The hallmarks of blood flow in arteries are pu lsatility and branches, which cause wail stresses to be cyclical and nonuni form. Normal arterial flow is laminar, with secondary flows generated at cu rves and branches. Arteries can adapt to and modify hemodynamic conditions, and unusual hemodynamic conditions may cause an abnormal biological respon se. Velocity profile skewing can create pockets in which the wall shear str ess is low and oscillates in direction. Atherosclerosis tends to localize t o these sites and creates a narrowing of the artery lumen-a stenosis. Plaqu e rupture or endothelial injury can stimulate thrombosis, which can block b lood flow to heart or brain tissues, causing a heart attack or stroke. The small lumen and elevated shear rate in a stenosis create conditions that ac celerate platelet accumulation and occlusion. The relationship between thro mbosis and fluid mechanics is complex, especially in the post-stenotic flow field. New convection models have been developed to predict clinical occlu sion from platelet thrombosis in diseased arteries. Future hemodynamic stud ies should address the complex mechanics of flow-induced, large-scale wall motion and convection of semisolid particles and cells in flowing blood.