Osmotic deformability of erythrocytes at various shear stresses

Red blood cell (RBC) deformability is greatly affected by the osmolality, and maximum deformability, which is determined as maximal elongation index (EImax), is usually observed in isotonic conditions at high shear stresses (>20 Pa). Therefore, we examined osmotic RBC deformability over a range of shear stresses (0.5-20 Pa). We found that the RBC deformability at low shear stresses (1-3 Pa) was maximum in hypotonic conditions (225-250 mOsm/kg H2O), which is slightly lower than the normal range of osmolality in plasma (290-310 mOsm/kg H2O). The phenomenon that O-max (the osmolality at EImax) is dependent on applied shear stress could play an important role in microcirculation in which osmolality varies widely.