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 (EI<inf>max</inf>), 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 H<inf>2</inf>O), which is slightly lower than the normal range of osmolality in plasma (290-310 mOsm/kg H<inf>2</inf>O). The phenomenon that O<inf>max</inf> (the osmolality at EI<inf>max</inf>) is dependent on applied shear stress could play an important role in microcirculation in which osmolality varies widely.