Abstract
Excessive aggregation of red cells is a feature of many cardiovascular disorders. Erythrocyte sedimentation rates (corrected for plasma viscosity and haematocrit) show values from 100 to 1,000 mm/hr, but do not distinguish between different morphologies of red cell aggregation. It is unlikely that rouleaux-based aggregation presents a risk factor unless an excessive aggregation leads to a large increase of the low-shear-rate blood viscosity and/or to a high yield point. (Assuming that electrical currents through the blood circulation route are important, an excessive rouleaux network formation will greatly increase resistance in such electrical conduits).
A risk factor is presented by very large and compact aggregates of red cells; in vitro studies using slit-capillary photoviscometer such clumps contained up to 50,000 red cells in a single clump; could occupy a volume of up to 5 million cubic microns (um), and could occlude a circular vessel of up to 100 micron (um) diameter. The mechanism based on the “inversion phenomenon” explains the role of single rigid red cells or smaller rigid aggregates of red cells or platelets, in the sudden increase of resistance to flow. All parts of the cardiovascular system are susceptible to microocclusions, micro-infarctions and micro-gangrene. Specifically this is of importance in the ischaemic heart disease and in diabetes; in prethrombotic states; in many forms of cancer and peripheral vascular disease; in retinopathy and cerebrovascular insufficiency, etc.
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