Changes in the functional state of the erythrocyte membrane: significance for red cell filterability and blood viscosity.

Blood samples from nine healthy men were studied to determine the effect of ouabain and elevated serum calcium concentration on blood viscosity, measured by a rotational viscometer, and on red cell filterability by the St George's Filtrometer, giving values for clogging particles (CP) and red cell transit time (RCTT). Blood viscosity at a standardized haematocrit of 45% and red cell filterability was investigated in blood samples incubated for 1 h with Ringer's solution only (control), with ouabain (0.70 mmol/l) in plasma, or with serum calcium concentration increased by 3.0 mmol/l by addition of CaCl2. Incubation with ouabain significantly reduced erythrocyte K+ concentration and increased that of Na+. Ouabain caused a decrease in blood viscosity (p less than 0.05-0.005) compared to controls, although there was no decrease in red cell filterability parameters. When incubating with calcium, CP and RCTT increased significantly indicating 'stiffer' red cells, but there was no increase in blood viscosity. It is concluded that blood viscosity may be influenced by red cell factors not detected by CP or RCTT, which in turn appear to reflect red cell deformability with greater sensitivity and specificity than blood viscosity. It is concluded also that the functional state of the cell membrane may be of significance for the rheological properties of erythrocytes.