Using localized impedance measurements to study muscle changes in injury and disease

Abstract

We measured localized impedance on the surface of the thigh to determine the properties of underlying muscle; these include rho 1, the resistivity for current flowing parallel to the fibers, and theta avg, the average phase along the thigh (normalized to a standard length). The results for a modest sampling of nominally healthy subjects show that the theta avg values are substantially higher than the whole body phases encountered in standard bioimpedance analysis. When the sample is augmented to include subjects undergoing hemodialysis and/or recovering from serious illness or leg injury, the behavior of the position dependence of the phase theta (z) and the rho 1 vs. theta avg average distribution both strongly indicate a correlation between very low phase angles and injury or disease. Furthermore, measurements on a subject in a weight training program after injury provide evidence of a monotone increase in rho 1 with increasing strength. Measurements on dialysis patients during treatment show a nonlinear response of thigh muscle to the degree of fluid removal and wide disparities between individuals.