Contributions of Red Blood Cell Sedimentation in a Driving Syringe to Blood Flow in Capillary Channels

The erythrocyte sedimentation rate (ESR), which has been commonly used to detect physiological and pathological diseases in clinical settings, has been quantified using an interface in a vertical tube. However, previous methods do not provide biophysical information on blood during the ESR test. Therefore, it is necessary to quantify the individual contributions in terms of viscosity and pressure. In this study, to quantify RBC sedimentation, the image intensity (I(b)) and interface (β) were obtained by analyzing the blood flow in the microfluidic channels. Based on threshold image intensity, the corresponding interfaces of RBCs (I(b) > 0.15) and diluent (I(b) < 0.15) were employed to obtain the viscosities (µ(b), µ(0)) and junction pressures (P(b), P(0)). Two coefficients (CH(1), CH(2)) obtained from the empirical formulas (µ(b) = µ(0) [1 + CH(1)], P(b) = P(0) [1 + CH(2)]) were calculated to quantify RBC sedimentation. The present method was then adopted to detect differences in RBC sedimentation for various suspended blood samples (healthy RBCs suspended in dextran solutions or plasma). Based on the experimental results, four parameters (µ(0), P(0), CH(1), and CH(2)) are considered to be effective for quantifying the contributions of the hematocrit and diluent. Two coefficients exhibited more consistent trends than the conventional ESR method. In conclusion, the proposed method can effectively detect RBC sedimentation.