Morphological determinants of red cell deformability

The influence of cellular morphology on the rheological behaviour of human red blood cells (RBC) and RBC suspensions has been examined for both fresh and ATP-depleted erythrocytes. Macrorheological measurements were made using a cone-plate viscometer and microrheological measurements included cell deformation by high-speed centrifugation and direct microscopic observation using a counter-rotating rheoscope. Evaluation of the experimental observations indicates the importance of RBC shape as a determinant of RBC deformability, such that either echinocytic or stomatocytic shape alterations result in increased deformability. Thus, cellular morphology, in addition to S/V ratio, membrane and cytoplasmic material properties must be considered in assessing the response of the cell to deforming forces. It is to be noted, however, that these morphology effects are shear-stress dependent and may escape detection in systems in which high stress levels are employed, e.g. micropore filtration using large pressure gradients.