Computation of the average shear-induced deformation of red blood cells as a function of osmolality

A model was developed for computing the average deformation of red cells as a function of suspending medium osmolality. It assumes a population of red cells characterized by a single value for surface area and for isotonic volume, but having a Gaussian distribution in mean intracellular hemoglobin concentration (MCHC). The ability of cells of a given hemoglobin concentration to deform is assumed to be limited by either the amount of redundant surface area available or the intracellular viscosity, determined by the intracellular hemoglobin concentration. The surface area limitation is calculated by finding the dimensions of a prolate ellipsoid having the volume and surface area of the red cell. The viscosity limitation is incorporated in two ways. First, the ratio of intracellular to extracellular viscosity must lie below a certain threshold to permit deformation, and second, its magnitude determines the extent of cell elongation. This model gave a reasonable fit to experimental data for a threshold viscosity ratio close to 1. Extension to cell populations for which either mean cell hemoglobin concentration or surface area had been modified also provided a close reproduction of the experimental curves.