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1 Department of Physiology, University of Arizona, Tucson, Arizona 85724-5051; and 2 Department of Physiology, Freie Universität Berlin, D-14195 Berlin, Germany
The interior surfaces of capillaries are lined with a layer (glycocalyx) of macromolecules bound or adsorbed to the endothelium. Here, a theoretical model is used to analyze the effects of the glycocalyx on hematocrit and resistance to blood flow in capillaries. The glycocalyx is represented as a porous layer that resists penetration by red blood cells. Axisymmetric red blood cell shapes are assumed, and effects of cell membrane shear elasticity are included. Lubrication theory is used to compute the flow of plasma around the cell and within the glycocalyx. The effects of the glycocalyx on tube hematocrit (Fahraeus effect) and on flow resistance are predicted as functions of the width and hydraulic resistivity of the layer. A layer of width 1 µm and resistivity 108 dyn · s/cm4 leads to a relative apparent viscosity of ~10 in a 6-µm capillary at discharge hematocrit 45% and flow velocity of ~1 mm/s. This is consistent with experimental observations of increased flow resistance in microvessels in vivo, relative to glass tubes with the same diameters.
apparent viscosity; blood flow resistance; Fahraeus effect; hematocrit; microvessels
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