Simulation of lung edema in impedance cardiography

Impedance cardiography (ICG) is a simple and non-invasive method to assess hemodynamic parameters. Unfortunately, this technology does not work for all patient groups. This work aimed to identify the reasons for the inaccuracy of ICG to assess the stroke volume (SV) for heart failure patients. Therefore, the effect of lung edema on the impedance cardiogram was analyzed by simulations using the finite element method (FEM). The simulation model, based on human MRI data, includes volumetric changes of heart beat and aortic expansion as well as changes during lung perfusion and erythrocyte orientation. In addition, important static tissues have been implemented. Lung tissue has been substituted stepwise by body fluid. The model had excellent correlation (r = 0.94) with measured signals and a decrease of Z₀ by 6.8% and a decrease of the peak-to-peak impedance by 54% could be observed. Hence, a decrease of the computed SV according to the standard algorithms and models is the consequence.