Deformability of human red blood cells exposed to a uniform shear stress as measured by a cyclically reversing shear flow generator

Red blood cells (RBCs) suspended in a dextran solution were at first loaded with a uniform shear stress of 21, 43 and 64 Pa for the duration of 0, 10, 20, 30, 45 and 60 min, respectively, followed with measurement of the dynamic deformation in terms of stretching and recovery, using a cyclically reversing sinusoidal shear flow with the peak stress of 128 Pa at 2 Hz. The L/W value, where L and W were the major and minor axis length of the RBC images, was derived to compare the effects of the uniform shear stress level and the exposure time. The exposure to the uniform shear stress of 21 Pa for the duration of as long as 60 min caused statistically insignificant L/W change in comparison to the control RBCs with L/W of 4.6 +/- 0.1. The exposure to 43 and 64 Pa for longer than 45 and 20 min, respectively, induced statistically significant change in the maximal L/W when compared to that of 21 Pa (p < 0.05). The composition of the maximal L/W values varied depending on the stress level and exposure time; with 21 Pa, the majority of cells exhibited the maximal L/W larger than 4.0 and few cells less than 2.0, whereas with the increase in the stress level to 43 and 64 Pa, cells having less than 2.0 exceeded 50%. Cyclic reversing shear flow is a useful means to measure dynamic deformation capability of RBCs which may be sub-hemolytically sheared without lysis.