A 3-dimensional FEM model of the human thoracic cavity for simulation of impedance cardiography

The authors developed a three-dimensional quasi-static finite-element model of the human thoracic cavity to emulate the perturbations in conduction-current characteristics associated with physiological dynamics. This model provides a theoretically sound basis for the origin of thoracic impedance waveform components. In the model, the thoracic cavity is represented as an inhomogeneous and anisotropic medium, and constitutive parameters are described as vector quantities. A collection of equations, each describing the shape, position, orientation, and constitutive characteristics of an organ or region of the thoracic cavity, are solved to obtain a mesh for a particular point in time. A solution to Poisson´s equation is found for the mesh using iterative finite-difference or finite-element techniques. The results indicate that the sudden decrease in thoracic impedance that is periodic with the ECG waveform (2dZ/dt complex) is primarily due to a sudden increase in the descending aorta´s diameter during left-ventricular ejection