FEATURES AND POSSIBILITIES OF BLOOD BIOIMPEDANCEMETRY

Abstract

The bioimpedancemetry has long been used to determine some blood parameters used in laboratory diagnostics. Due to the specificity of blood as a liquid disperse substance, its electrical conductivity is directly related to the relative volume of the non-conductive phase, that is, erythrocytes, and therefore, the bioimpedancemetry method is used to determine hematocrit. The ambiguity of the results in determining the frequencies corresponding to the achievement of the limiting value of the high-frequency electrical conductivity of the blood, as well as the patterns that connect the high-frequency electrical conductivity of the blood with the electrical conductivity of the plasma and erythrocytes, demonstrate the urgent need for additional research. The purpose of the study was to determine the features of the frequency dependence of the blood bioimpedance modulus with the values of hematocrit and blood plasma bioimpedance modulus in order to establish the capabilities of the blood bioimpedancemetry method as a whole. The frequency dependence of its bioimpedance was determined on 16 blood samples from healthy donors. For each blood sample, the frequency dependence of the bioimpedance of whole blood was taken, then the plasma formed after erythrocyte sedimentation in a vertically installed test tube. The impedance modulus was measured in the frequency range from 10 kHz to 10 megahertz. The optimal frequency of 5 megahertz was determined, at which the limiting high-frequency value of blood electrical conductivity is reached, which makes it possible to determine the electrical conductivity of the erythrocyte cytoplasm. An expression is obtained for high-frequency electrical conductivity as a function of the electrical conductivity of plasma, cytoplasm and relative hematocrit. It is shown that the measurement of low-frequency (up to 100 kilohertz) and high-frequency values of blood electrical conductivity, as well as plasma electrical conductivity, also makes it possible to determine the hematocrit and the electrical conductivity of the erythrocyte cytoplasm. An equation was obtained that relates the hematocrit index to the ratio of high-frequency and low-frequency values of blood electrical conductivity, which makes it possible to determine the true hematocrit of human blood in vitro. Thus, the measurement of low-frequency and high-frequency electrical conductivity of blood and the measurement of electrical conductivity of plasma make it possible to determine not only the hematocrit index, but also the electrical conductivity of the cytoplasm of cells in one blood sample. The work proves the practical possibility of determining the complex of electrophysical parameters of a native blood sample while maintaining their real values.