Influence of Arterial Blood Flow on Impedance Plethysmography

Impedance plethysmography is a simple and low-cost non-invasive method to study the extremity hemodynamics and can be used to measure blood flow in a limb. However, there is no enough information about the physiological sources of the acquired bio-impedance signal exept the fact that it is corresponds to the blood volume change in a segment which is originate from the difference between arterial inflow and venous outflow. Thus, the aim of this study is to estimate the effect of arterial blood flow throw the major arteries in the reign of interest to the electrical impedance change obtained from attached electodes. The contribution of two physiological effects: artery pulsation, and erythrocyte orientation using simplified mathematical model of human lower limb was considered in this study. The model consists of soft tissues assumed to be semi-infinite homogeneous medium and artery suggested to be infinite cylinder. The pulse and base impedance acquired within modeling agrees with the measured signals. According to our estimates, obtained by modeling, the contribution of the artery to the pulse impedance is 0.75 … 9%. And this contribution depends on the value of the resistivity of the soft tissues, the magnitude of the pulsation of its diameter, the depth of the artery, distance between measuring electrodes. In practice, an increase in this contribution can be achieved by a closer location of the measuring electrodes on the limb surface directly above the artery.