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Applicability of an effective conductivity approach in modeling thoracic impedance changes This publication appears in: Journal of Physics: Conference Series Authors: M. Lewandowska, B. Truyen, C. Boca and J. Wtorek Volume: 434 Number of Pages: 4 Publication Date: Apr. 2013
Abstract: Background. Impedance measurement of heart activity have a great value when trying to evaluate its mechanical function. However, since the mechanism of bioimpedance signal formation is very complex the problem of signal sources identification and separation is still present. The application of an anatomically detailed finite element chest model allows for spatial sensitivity analysis. Having the spatial sensitivity distribution one can assess the impact of components from spatially separable sources. When trying to analyze impedance changes during cardiac cycle the dynamic model has to be generated. The first method to obtain a dynamic model is to generate several static geometric models with finite element mesh, each of them corresponding to the different cardiac cycle phase. Because of the complexity of the human chest it is time consuming and complicated method. The purpose of the article is to examine whether changes in the geometry of individual organs may be replaced by effective conductivity changes inside organs volume. Methods. The simplified finite element model of a human chest was built. It consisted of a cylinder of a 0.4 m height and 0.12 m radius with two concentric spheres inside (left ventricle). The volume of the inner sphere changed linear from 4.46*10LJ m3 to 1.13*10dž m3 that corresponds to changes of a ventricle volume during heart cycle. The radius of the second sphere changes so as to ensure constant volume of the difference between outer and inner sphere. That "shell" corresponds to heart muscle with constant volume and variable wall thickness. Changes of impedance value between two electrodes on the cylinder surface were calculated for each "cardiac cycle phase" assuming constant conductivity within each subdomain. Next, the effective conductivity of the modeled left ventricle was calculated based on Maxwell-Wagner equation, separately for each cardiac cycle phase. Impedance changes were calculated for every effective conductivity value.Results. In the considered range of geometry changes dependence between impedance changes calculated for two models - with changing geometry (deltaZgeom) and that with changing effective conductivity (deltaZeff) - was linear, deltaZeff = 0.98 deltaZgeom .Conclusions. Performed simulations indicate that effective conductivity approach can be utilized in cases of relatively big models when studying dynamic processes involved by volume changes of internal organs. External Link.
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