Rhelogical measurements on a dilute suspension of red blood cells (RBCs) are interpreted by means of a microheological model that relates the shear evolution of the apparent viscosity to the intrinsic properties of the suspended particles. It is then possible to quantify the average deformability of a RBC population in terms of a mean value of the membrane shear elastic modulus, Es. Dilute suspensions of erthrocytes exhibit a shear-thinning behavior with a constant high shear viscosity. This behavior is identical to the one predicted for a suspension of spherical capsules where the same phenomena of deformation and orientation prevail. A comparison between theoretical and experimental curves yields a mean value of Es, assuming all other cell properties—internal viscosity, geometry—to be otherwise equal. In Dextran, the values of Es for normal RBCs are found to be of order 3.10−6 N/m. For erythrocytes hardened by heat exposure for 15 minutes at 48°C, the increase in Es reaches 45 percent. This procedure of shear elastic modulus determination is easy to perform and seems to give a good discrimination between normal and altered erythrocytes.

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