Robustness study of the different immittance spectra and frequency ranges in bioimpedance spectroscopy analysis for assessment of total body composition.

The estimation of body fluids is a useful and common practice for assessment of disease status and therapy outcomes. Electrical bioimpedance spectroscopy (EBIS) methods are noninvasive, inexpensive and efficient alternatives for determination of body fluids. One of the main source of errors in EBIS measurements in the estimation of body fluids is capacitive coupling. In this paper an analysis of capacitive coupling in EBIS measurements was performed and the robustness of the different immittance spectra against it tested. On simulations the conductance (G) spectrum presented the smallest overall error, among all immittance spectra, in the estimation of the impedance parameters used to estimate body fluids. Afterwards the frequency range of 10-500\ua0kHz showed to be the most robust band of the G spectrum. The accuracy of body fluid estimations from the resulting parameters that utilized G spectrum and parameters provided by the measuring device were tested on EBIS clinical measurements from growth hormone replacement therapy patients against estimations performed with dilution methods. Regarding extracellular fluid, the correlation between each EBIS method and dilution was 0.93 with limits of agreement of 1.06 \ub1 2.95 l for the device, 1.10 \ub1 2.94 l for G [10-500\ua0kHz] and 1.04 \ub1 2.94 l for G [5-1000\ua0kHz]. Regarding intracellular fluid, the correlation between dilution and the device was 0.91, same as for G [10-500\ua0kHz] and 0.92 for G [5-1000\ua0kHz]. Limits of agreement were 0.12 \ub1 4.46 l for the device, 0.09 \ub1 4.45 for G [10-500\ua0kHz] and 0.04 \ub1 4.58 for G [5-1000\ua0kHz]. Such close results between the EBIS methods validate the proposed approach of using G spectrum for initial Cole characterization and posterior clinical estimation of body fluids status