Mechanics of shear stress transmission to endothelial cells in blood vessels lined with an endothelial surface layer

摘要

Interior surfaces of blood vessels are lined with a layer of bound or adsorbed macromolecules, known as the endothelial surface layer (ESL). In vivo investigations of blood flow in capillaries have shown that this layer is of order 1 μm thick. The presence of the ESL is believed to be a major factor causing low tube hematocrit in capillaries [1], and higher flow resistance in microvessels than in glass tubes with corresponding diameters [2]. Disruption of the ESL by a light-dye treatment [3] increases the widths of columns of red blood cells and labeled dectran-70 in capillaries, without observable changes in capillaries' anatomical diameters, implying that the ESL restricts the space available for red blood cell motion and plasma flow in capillaries. The ability of the ESL to impede plasma flow is accounted for by assuming that it is a porous medium with a hydraulic resistivity of at least 10{sup}8 dyn≌s/cm{sup}4 [4]. To describe the ability of the layer to exclude flowing red cells, Damiano et al. [5] modeled the layer as an elastic solid, while Pries et al. [2] hypothesized that the layer resists flattening because of colloid osmotic pressures generated by plasma proteins adsorbed to the ESL. According to the latter hypothesis, the colloid osmotic pressure within the ESL is increased by an amount )B{sub}p above that of free plasma, and this additional pressure is balanced by tension in membrane-bound glycoprotein chains or strands [6]. An applied force sufficient to compress the ESL must exceed )B{sub}p in order to relieve the tension in the strands.