PubMed · 15258339
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Sandro Forconi. 2004. From hyperviscosity to endothelial dysfunction: a return trip?. https://pubmed.ncbi.nlm.nih.gov/15258339/
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The effects of nonionic polymers on human red blood cell (RBC) aggregation were investigated. The hydrodynamic radius (Rh) of individual samples of dextran, polyvinylpyrrolidone, and polyoxyethylene over a range of molecular weights (1,500-2,000,000) were calculated from their intrinsic viscosities using the Einstein viscosity relation and directly measured by quasi-elastic light scattering, and the effect of each polymer sample on RBC aggregation was studied by nephelometry and low-shear viscometry. For all three polymers, despite their different structures, samples with Rh <4 nm were found to inhibit aggregation, whereas those with Rh >4 nm enhanced aggregation. Inhibition increased with Rh and was maximal at approximately 3 nm; above 4 nm the pro-aggregant effect increased with Rh. For comparison, the Rh of 12 plasma proteins were calculated from literature values of intrinsic viscosity or diffusion coefficient. Each protein known to promote RBC aggregation had Rh >4 nm, whereas those with Rh <4 nm either inhibited or had no effect on aggregation. These results suggest that the influence of a nonionic polymer or plasma protein on RBC aggregation is simply a consequence of its size in an aqueous environment, and that the specific type of macromolecule is of minor importance.
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In clinical practice, neonatal polycythemia has been used as a marker for neonatal hyperviscosity, implicated as a cause of long-term neurologic delay and damage in the growing child. Clinicians have focused on the newborn infant's hematocrit (Hct) level as the criterion for therapeutic intervention. Partial exchange transfusion is traditionally used as the method to lower the Hct and treat hyperviscosity; however, it is unclear whether this is an effective approach in preventing the long-term neurologic consequences. This article re-evaluates this clinical approach to the diagnosis and treatment of neonatal polycythemia and suggests that this controversial therapy needs re-evaluation.