Electrochemical impedance spectroscopy of blood. Part 3: a study of the correlation between blood conductivity and sedimentation to shorten the erythrocyte sedimentation rate test†
The study of erythrocyte aggregation and erythrocyte sedimentation rate (ESR) is very important both for basic research and medical applications. The duration of the Westergren ESR test is one hour which seems excessive. The hematocrit and conductivity of blood demonstrate high correlation. This makes it possible to evaluate the erythrocyte aggregation kinetics and ESR by measuring changes in the blood conductivity. We measured the time-dependent changes in conductivity at the bottom of the blood column during sedimentation. A digital camera is used to obtain the blood sedimentation curve and to determine the hematocrit profile. The effective conductivity of blood is calculated based on effective medium theory. Simple analytical expressions are derived to extrapolate changes in blood conductivity over time. We proposed an improved physical model of sedimentation which reveals additional information about the kinetics of blood sedimentation and erythrocyte aggregation. An explicit expression is obtained to characterize the rate of aggregate formation. A numerical model was developed to investigate these mechanisms, and it was tested by comparing simulation results with experimental data. Based on our model, the ESR, blood sedimentation curve and hematocrit profiles can be numerically restored using only the first 400 seconds of the recorded changes in blood conductivity. The proposed technique allows measuring the erythrocyte aggregation as well as the sedimentation kinetics. The changes in blood conductivity at the bottom of the blood column at the initial stage of sedimentation reliably reflect the erythrocyte aggregation kinetics and ESR over time.