title: Influence of physiological sources on the impedance cardiogram analyzed using 4D FEM simulations.
abstract: Impedance cardiography is a simple and inexpensive method to acquire data on hemodynamic parameters. This study analyzes the influence of four dynamic physiological sources (aortic expansion, heart contraction, lung perfusion and erythrocyte orientation) on the impedance signal using a model of the human thorax with a high temporal resolution (125 Hz) based on human MRI data. Simulations of electromagnetic fields were conducted using the finite element method. The ICG signal caused by these sources shows very good agreement with the measured signals (r = 0.89). Standard algorithms can be used to extract characteristic points to calculate left ventricular ejection time and stroke volume (SV). In the presented model, the calculated SV equals the implemented left ventricular volume change of the heart. It is shown that impedance changes due to lung perfusion and heart contraction compensate themselves, and that erythrocyte orientation together with the aortic impedance basically form the ICG signal while taking its characteristic morphology from the aortic signal. The model is robust to conductivity changes of tissues and organ displacements. In addition, it reflects the multi-frequency behavior of the thoracic impedance.
authors.affiliation: RWTH Aachen University, Philips Chair for Medical Information Technology, Pauwelsstrasse 20, D-52074 Aachen, Germany.
authors.forename: Mark
authors.initials: M
authors.lastname: Ulbrich
authors.forename: Jens
authors.initials: J
authors.lastname: Mühlsteff
authors.forename: Steffen
authors.initials: S
authors.lastname: Leonhardt
authors.forename: Marian
authors.initials: M
authors.lastname: Walter
mesh_terms: D000465:Algorithms; D001011:Aorta / Q000502:physiology; D002307:Cardiography, Impedance; D002320:Cardiovascular Physiological Phenomena; D003198:Computer Simulation; D004553:Electric Conductivity; D017097:Electric Impedance; D004574:Electromagnetic Fields; D004912:Erythrocytes / Q000502:physiology; D020342:Finite Element Analysis; D006321:Heart / Q000502:physiology; D006801:Humans; D008168:Lung / Q000502:physiology; D008954:Models, Biological; D008955:Models, Cardiovascular; D009929:Organ Size; D013318:Stroke Volume; D013909:Thorax; D013997:Time Factors