Abstract:

BACKGROUND: Previous studies suggest that auditory evoked potentials (AEP) may be used to monitor anaesthetic depth. However, during surgery and anaesthesia, the quality of AEP recordings may be reduced by artefacts. This can affect the interpretation of the data and complicate the use of the method. We assessed differences in expert ratings of the signal quality of perioperatively recorded AEPs. METHODS: Signal quality of 180 randomly selected AEP, recorded perioperatively during a European multicentre study, was rated independently by five experts as 'invalid' (0), 'poor' (1), or 'good' (2). Average (n=5) quality rating was calculated for each signal. Differences between quality ratings of the five experts were calculated for each AEP: inter-rater variability (IRV) was calculated as the difference between the worst and best classification of a signal. RESULTS: Average signal quality of 57% of the AEPs was rated as 'invalid', 39% as 'poor', and only 4% as 'good'. IRV was 0 in only 6%, 1 in 62%, and 2 in 32% of the AEP, that is in 32% one expert said signal quality was good, whereas a different expert thought the identical signal was invalid. CONCLUSIONS: There is poor agreement between experts regarding the signal quality of perioperatively recorded AEPs and, as a consequence, results obtained by one expert may not easily be reproduced by a different expert. This limits the use of visual AEP analysis to indicate anaesthetic depth and may affect the comparability of AEP studies, where waveforms were analysed by different experts. An objective automated method for AEP analysis could solve this problem.

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:

Mathematical models of cardiac anatomy and physics provide information, which help to understand structure and behavior of the heart. Miscellaneous cardiac phenomena can only be adequately described by combination of models representing different aspects or levels of detail. Coupling of these models necessitates the definition of appropriate interfaces. Adequateness and efficiency of interfaces is crucial for efficient application of the combined models.In this work an integrated model is presented consisting of several models interconnected by interfaces. The integrated model allows the reconstruction of macroscopic electro-mechanical processes in the heart. The model comprises a three-dimensional are of left ventricular anatomy represented as truncated ellipsoid. The integrated model includes electrophysiological, tension development and elastomechanical models of myocardium at levels of single cell, proteins, and tissue patches, respectively.The model is exemplified by simulations of extracorporated left ventricle of small mammals. These simulations yield temporal distributions of electrophysiological parameters as well as descriptions of electrical propagation and mechanical deformation. The simulations show characteristic macroscopic ventricular function resulting from the interplay between cellular electrophysiology, electrical excitation propagation, tension development, and mechanical deformation.

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:

Modeling of mechanisms involved in electrophysiology and tension development of cardiac myocytes can enhance the understanding of physiological and pathophysiological cardiac phenomena. Interactions of divers components are necessary for cellular electro-mechanics. Particularly, the interactions between proteins in the cell membrane, sarcoplasmic reticulum and sarcomere are of importance. In this work hybrid electro-mechanical models of cardiac myocytes were derived on basis of recently developed models as well as of measurements ranging from protein to multi-cell level. The models quantify dynamically the electrophysiology and tension development by states, partly associated to configurations of the involved proteins, and the transition between these states. The models allow the reconstruction of electro-mechanical phenomena. Results of simulations with the hybrid models were performed illustrating their properties. The models may help to clarify feedback and cooperativity mechanisms, pathophysiological changes and metabolism of myocytes.

Abstract:

Modeling of cardiac electro-mechanics enables and simplifies understanding of physiology and pathophysiology of the heart. In this work a model is presented, which allows the reconstruction of macroscopic electro-mechanical processes in the left ventricle of small mammals. The model combines a three-dimensional model of left ventricular anatomy represented as truncated ellipsoid with an integrated electromechanical model. The integrated model includes electrophysiological, force development and elastomechanical models of myocardium. The model is illustrated by simulations, which reflect the behavior of an extracorporated heart. These simulations yield temporal distributions of electrophysiological parameters as well as descriptions of electrical propagation and mechanical deformation. The simulations show the connection between cellular electrophysiology, electrical excitation propagation, force development, and mechanical deformation.

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.

Abstract:

Die Erfindung betrifft ein Verfahren zur Personenerkennung bei einer Körperanalysewaage sowie eine Meßvorrichtung zur Durchführung dieses Verfahrens. Bezüglich des Verfahrens wird vorgeschlagen, daß die Messung von zumindest zwei physiologischen und/oder anthropometrischen Parametern erfolgt, wobei wenigstens einer der Meßparameter dem physiologischen Bereich und ein zweiter Meßparameter dem anthropometrischen Bereich der zu erkennenden Person zugeordnet ist. Die Meßvorrichtung zeichnet sich dadurch aus, daß eine Trittplatte 2 zum einen mit Sensoren 3 zur Erfassung zumindest eines physiologischen Parameters und zum anderen mit zumindest einem Kraftaufnehmer 4 zur Erfassung eines anthropometrischen Parameters versehen ist, wobei die Sensoren 3 und der beziehungsweise die Kraftaufnehmer 4 mit einer Auswerteeinheit 10 verbunden sind, die aus dem Parameter die Kenngröße zur Personenerkennung ermittelt.

Abstract:

Die Erfindung betrifft ein Verfahren zur Darstellung des Meßergebnisses eines Körperanalysegerätes, insbesondere einer Körperanalysewaage. Zur Bewertung des Meßergebnisses wird vorgeschlagen, daß die Kombination aus zumindest einem physiologischen und zumindest einem anthropometrischen Parameter über einen Transponder in einer in zumindest drei Gruppen unterteilten, interpretierenden Grafikanzeige dargestellt ist.

Abstract:

Die Erfindung betrifft eine Personenwaage mit einer Trittplatte aus Glas, zumindestest einem einer Kraftaufnehmer und/oder zumindest einer Elektrode und einer mit diesem beziehungsweise diesen über Leiterbahnen verbundenen Elektronik- und Anzeigeeinheit 2. Für eine kostengünstige Großserienfertigung wird vorgeschlagen, daß die Trittplatte 3 als Träger für die mit dieser kraftschlüssig verbundenen Leiterbahnen 5 und/oder Elektroden aus einem leitenden Dünnschichtmaterial ausgebildet ist.

Abstract:

Die Erfindung betrifft eine Meßvorrichtung für eine Körperanalysewaage mit Meßelektroden auf der Trittplatte 1 und mit personen- und funktionsbezogenen Schaltem. Für eine erleichterte Nutzung, kostengünstigere Fertigung und vereinfachte Bedienung wird vorgeschlagen, daß Elektroden 2a, 2b; 3a, 3b auf der Trittplatte 1 angebracht sind, die sowohl als Meßelektroden als auch als personenund funktionsbezogene Schalter ausgeführt sind.

Abstract:

Die computergestu ̈tzte Simulation des Verhaltens von Herzmuskelzellen und der Ausbreitung der elektrischen Erregung im Herzgewebe hilft Technikern und Medizinern, Vorga ̈nge im Herzen zu analysieren und zu verstehen. Exakte Modelle ko ̈nnen die Realita ̈t sehr gut nachbilden. Daher ist die Entwicklung eines Modelles der menschlichen linksventrikula ̈ren Herzwand unter Beru ̈ck- sichtigung transmural heterogener Ionenstro ̈me und der anisotropen Faserorientierung Gegenstand dieser Diplomarbeit.Kapitel 1 liefert eine Einfu ̈hrung in das Thema und erla ̈utert die Aufgabenstellung. Das zweite Kapitel hat die Elektrophysiologie von einzelnen Zellen zum Inhalt. Im darauf folgenden Kapitel wird eine U ̈bersicht u ̈ber die Anatomie und Elektrophysiologie des menschlichen Herzens sowie u ̈ber das Verhalten kardialer Myozyten im Zellverband gegeben.Kapitel 4 stellt die bisher untersuchten elektrophysiologischen Unterschiede innerhalb der ventriku- la ̈ren Herzwand vor. Hauptaugenmerk liegt auf transmuralen Ionenstromgradienten, die in mensch- lichen Ventrikeln festgestellt werden konnten. Weiterhin wird auf Messungen der Faserorientierung im menschlichen Herzen eingegangen.Das Zellmodell, welches im Laufe der Arbeit an die Anforderungen angepasst wurde, wird im fu ̈nften Kapitel vorgestellt. Es handelt sich um ein Modell, bei dem sich die elektrophysiologischen Eigenschaften der Einzelzelle aus gekoppelten Differentialgleichungen ergeben. Eine Simulation der Erregung im Zellverband wird mit einem der anschließend dargestellten Modelle der elektrischen Erregungsausbreitung ermo ̈glicht.In Kapitel 6 wird auf die Entwicklung des heterogenen Ventrikelwandmodelles eingegangen. Die elektrophysiologischen Modellanpassungen finden zuna ̈chst auf einzelzellula ̈rer Ebene statt. Die Definitionen verschiedener Ionenstro ̈me werden so modifiziert, dass das Verhalten dieser Stro ̈me vom Modell realita ̈tsnah abgebildet wird. Als Qualita ̈tskriterium der Anpassung wird anschließend der Verlauf des Aktionspotentials mit den gefundenen Parametrisierungen herangezogen. Durch Untersuchung des Verhaltens im elektrotonisch gekoppelten Zellverband werden weitere Parameter des Ventrikelwandmodelles bestimmt. Die Einbringung der anisotropen Faserorientierung in das zugrunde liegende anatomische Modell bildet den Abschluss dieses Kapitels.Kapitel 7 gibt einen U ̈berblick, wie sich ein Modell der menschlichen ventrikula ̈ren Wand unter Be- ru ̈cksichtigung transmuraler Inhomogenita ̈ten der Ionenstro ̈me und einer anisotropen Orientierung der Herzmuskelzellen im Computer generieren la ̈sst. Die Ergebnisse, die sich mit dem entwickelten Herzwandmodell erzielen lassen, werden im achten Kapitel beschrieben. Mit dem Modell wird sowohl das Verhalten von Einzelzellen als auch das von Zellen in einem eindimensionalen und einem dreidimensionalen gekoppelten Verband untersucht. Weiterhin wird das Verhalten im physiologischen und in pathologischen Fa ̈llen betrachtet. Dabei zeigt sich, dass die erzielten Simulationsresultate zum gro ̈ßten Teil mit denen von Experimenten vergleichbar sind. Lediglich die Ursachen des LQT1-Syndroms mu ̈ssen neu u ̈berdacht werden, da sich die Messergebnisse mit den bisherigen Annahmen nicht erkla ̈ren lassen.