Determination of red cell deformation via measurement of light transmission through RBC suspensions under shear

Abstract

Red blood cell (RBC) deformability remains a central issue in clinical hemorheology and thus we have developed a simple quantitative approach to determine this cellular mechanical property. The method is based upon the analysis of light transmission (LT)-shear rate relations for RBC suspended in various media. LT measurements are performed with a small (0.025 ml) sample of RBC suspension via a computerized Myrenne cone-plate shearing system; LT values are measured at eight shear rates from 5 to 500 s⁻¹ using specially developed software. With appropriate combinations of hematocrit and suspending media viscosity, linear relations (r>0.997) between LT and log (shear rate) are obtained for cells in non-aggregating media. LT-shear rate relations are markedly affected by cell rigidity, such that LT decreases for less deformable RBC (i.e., dense or heat treated cells). Simplification of the procedure is possible by testing RBC in aggregating media (e.g., plasma) and measuring LT at 500 s⁻¹ (LT₅₀₀) to completely disperse aggregates; LT₅₀₀ values in both non-aggregating and aggregating media are lower for less deformable cells. The method is sensitive, reproducible (CV < 2%) and can be performed in less than three minutes; LT₅₀₀ values can be obtained within seconds and for RBC in plasma are available during routine aggregation measurements. The methods thus appears to be relevant to clinical studies of erythrocyte deformability.