Significance of macrorheology and microrheology in atherogenesis.

Atheromatous lesions represent a disturbance of homeostasis in the arterial wall, where the rates of uptake and production of atherogenic materials exceed the rates of egress and metabolic removal. The pressure and flow in the arterial system generate circumferential stress in the wall and shear stress on the wall. The magnitude and distribution of these stresses are affected by local vascular geometry and microrheologic behavior of blood. Circumferential stress is borne primarily by the media and adventitia, and shear stress has a greater influence on the endothelial cells, which form the principal barrier to transport of macromolecules into the arterial wall. Shear stress, turbulence, and longitudinal stretch cause an increase of macromolecular uptake by arterial wall, especially when the mechanical disturbances are periodic. These effects may be explained by an enhanced diffusion of plasmalemmal vesicles in the endothelial cells. Such short-term effects of rheologic factors should be considered together with their long-term influences on the structure and function of the arterial wall in order to elucidate the role of rheology in atherogenesis.