Influence of adsorbed plasma proteins on erythrocyte rheological properties: in vitro and ex vivo studies

The influence of plasma protein adsorption on the mechanical properties cha racterizing erythrocyte behaviour under flow was studied in human and rats. The deformability index, elastic modulus and surface viscosity were measur ed by laser diffractometry. In in vitro studies, human and rat erythrocytes were washed to remove their original protein coating, and then incubated i n saline-diluted plasma media. For erythrocytes incubated in the most dilut ed solutions (plasma/saline 1:3, v/v), the deformability index increased 30 % for both species (human, P <0.01 and rat, P <0.2); the elastic modulus de creased 20% (human, P <0.05) and 60% (rat, P <0.01); and surface viscosity decreased 20% (human, P <0.05) and 40% (rat, P <0.01), relative to values f or erythrocytes incubated in pure plasma. Ex vivo experiments were performe d using rats. Plasma proteins were diluted replacing 15% volemic plasma by saline in three consecutive plasmapheresis steps. The rheological propertie s of erythrocytes, tested after each step, followed the general trends of t he in vitro pattern. These results suggest that the decrease in plasma prot ein concentration affects blood rheology in two ways. The first is the well known decrease in plasma viscosity, and the second is an improvement of er ythrocyte deformability, as has been shown in this work. Thus, a new argume nt supporting the benefits of normovolemic hemodilution in patients with po or peripheral perfusion is provided.