Abstract:

Computer models of the electrophysiological processes in the human heart become increasingly precise and detailed. The dream of supporting diagnosis of arrhythmias and planning of therapeutic interventions comes into reach. Recent progress in the field of cellular models (including e.g. pathological cases), in the field of coupled cell patches (including e.g. heterogeneity) and in the field of validation (including e.g. intracardial multi-channel recordings) are reported.

Abstract:

Numerical field calculations and experimental investigations were performed to examine the heating of the surface of human skin during the application of a new electrode design for the patient return electrode. The new electrode is characterised by an equipotential ring around the central electrode pads. A multi-layer thigh model was used, to which the patient return electrode and the active electrode were connected. The simulation geometry and the dielectric tissue parameters were set according to the frequency of the current. The temperature rise at the skin surface due to the flow of current was evaluated using a two-step numerical solving procedure. The results were compared with experimental thermographical measurements that yielded a mean value of maximum temperature increase of 3.4 degrees C and a maximum of 4.5 degrees C in one test case. The calculated heating patterns agreed closely with the experimental results. However, the calculated mean value in ten different numerical models of the maximum temperature increase of 12.5 K (using a thermodynamic solver) exceeded the experimental value owing to neglect of heat transport by blood flow and also because of the injection of a higher test current, as in the clinical tests. The implementation of a simple worst-case formula that could significantly simplify the numerical process led to a substantial overestimation of the mean value of the maximum skin temperature of 22.4 K and showed only restricted applicability. The application of numerical methods confirmed the experimental assertions and led to a general understanding of the observed heating effects and hotspots. Furthermore, it was possible to demonstrate the beneficial effects of the new electrode design with an equipotential ring. These include a balanced heating pattern and the absence of hotspots.

Abstract:

The aim of this work is to enlarge the knowledge about the electrophysiological phenomena that describes the defibrillation procedure. We simulated this using a three-dimensional computer model in which the human cardiac tissue is incorporated in blood bath medium. Two initial situations were imposed: the tissue being in a resting state and the tissue being half resting, half depolarized, before the electrical shock was applied. For obtaining a more detailed look over these situations we varied the fiber orientation and the magnitude of the electrical impulse. The effects of intracellular electrical discontinuities represented an important target in our study. The temporal evolution of the transmembrane voltage was always followed until the tissue went back into the resting phase.

Abstract:

The contact free conductivity measurement is a noninvasive method to find electrical characteristics of tissue that can be used e.g. for monitoring. The system consists of an excitation coil and two sensing coils coupled together as a gradiometer. The excitation coil is driven by an alternating current. Due to this alternating magnetic field eddy currents are generated in the tissue that create a secondary magnetic field. Because of the geometrical arrangement, the induced voltage of the secondary field in the upper and the lower coil is different. The presented sensor can be used e.g. for detection of ischemic areas, monitoring wound healing or detection of hematoma beneath the skull. To demonstrate this sensor, two measurements are carried out to detect post mortem changes in a pig liver. The known characteristics from literature can be reproduced using a noncontact method. For this purpose frequencies between 50 kHz and 400 kHz are used. At a frequency of 350 kHz a phase shift of 0.3 degrees is observed post mortem after 2 to 4 hours corresponding to a conductivity change of approximately 0.4 S/m.

Abstract:

Clinical measurements of atrial excitation propagation were performed to validate the results of noninvasive cardiac source reconstructions. Epicardial potentials and transmembrane voltages were reconstructed using an individual volume conductor model of the patient. Activation times were measured with a basket catheter and compared with the time course of the reconstructed epicardial potentials and transmembrane voltages.

Abstract:

Simulation of the forward problem in Magnetic Induction Tomography (MIT) is one of the key issues in development of the technology of MIT. We simulate the process of measurement in MIT using an edge based finite element technique. We also present the simulation of this forward problem by a program, MAFIA based on finite integration technique. In both methods the same geometrical arrangements are simulated and results are compared.