Analyzing shear stress-elongation index curves: comparison of two approaches to simplify data presentation

Ektacytometry is frequently used to study red blood cell (RBC) deformability. This method is capable of measuring RBC deformation under a wide range of shear stresses, and the results are usually presented as shear stress-elongation index curves. These curves are very useful for detailed analyses of RBC mechanical behavior under various shearing conditions, yet may not be appropriate for clinical and experimental studies where a global parameter of deformability is satisfactory. That is, presenting data at a selected shear stress may not always be appropriate, since the selected stress level may not accurately reflect variations of the whole curve. We have thus compared two approaches to calculate parameters that represent the entire shear stress-elongation index curve; data were obtained using a commercial laser diffraction ektacytometer (LORCA) and compared in terms of their power to detect a difference between groups. Usage of these parameters (i.e., shear stress at half maximal deformation and maximal deformation) appears to offer a simplified approach to data presentation and interpretation in clinical and experimental hemorheological studies.