Determination of the red blood cell apparent membrane elastic modulus from viscometric measurements

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 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 degrees 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.