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Biochemistry & Molecular Biology.

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Rapid Pacing of Weak Stimuli in the Heart. Deborah Janks and Bradley J. Roth, Oakland University, Department of Physics, Rochester, MI 48309

With the development of pacemakers and defibrillators comes an important question: what are the underlying mechanisms responsible for the induction of reentry within the heart? At least two mechanisms are known to lead to an arrhythmia (or "reentry"): inhomogeneities occurring within the tissue as well as a difference in electrical conductivity parallel and perpendicular to the fibers surrounding an electrode. Each of these mechanisms were modeled with the objective being to determine the dominant mechanism responsible for reentry. Our results are compared to experimental studies leading to the conclusion that the different electrical conductivity parallel and perpendicular to the fibers leads to results that agree more closely to those observed experimentally.

Theoretical Multisite Pacing Methods for Ventricular Fibrillation Utilizing Algorithms Formed by Nonlinear-Dynamics-Feedback. Victor D. Hosfeld and Bradley J. Roth, Oakland University, Department of Physics, Rochester, MI 48309

Ventricular fibrillation is one of the leading causes of death among cardiovascular disease patients worldwide. Gauthier et al. (Chaos, 2002, 952-961) experimentally tested a method to pace the heart utilizing algorithms formed by nonlinear-dynamics-feedback applied through a low-energy, single electrode stimulus. Pacing was applied to cardiac tissue of sheep as the tissue dynamics diverged from the desired periodic rhythm. This theoretical study applies the algorithms developed by Gauthier et al. to pace ventricular cardiac tissue models as the tissue dynamics enter a state of fibrillation. Low-energy stimuli are applied to ventricular tissue employing the use of multiple electrodes to terminate fibrillation. Multisite pacing algorithms have been shown to improve fibrillation termination both experimentally (Pak et al., Am. J. Physiol., 2003, 285:H2704-H2711) and theoretically (Puwal & Roth, Journal Biological Systems, in press). In this study, multisite pacing protocol is established by algorithms developed by nonlinear-dynamics-feedback response to terminate ventricular fibrillation.

Optical Mapping of Voltage in the Heart. Phillip Prior and Bradley J. Roth, Oakland University, Department of Physics, Rochester, MI 48309

An important question in cardiology is how electrical stimulation of the heart affects the transmembrane potential during ventricular defibrillation. One way of experimentally determining the potential is by optical mapping using voltage-sensitive fluorescent dyes. The fluorescent light of these dyes originates from a few millimeters below the tissue surface as well as at the surface, causing the optical signal to be averaged over a depth. In our study, the transmembrane potential is calculated due to a point source that injects current at the surface of the tissue. The average transmembrane potential is numerically integrated over a finite range of values, which is made possible by a change in variables. Numerical integration is performed using the trapezoidal rule, while values of the average transmembrane potential are investigated over a range of optical decay constant and electrode radii.

Using Experiments and Simulations to Understand the Role of Amyloid Fibers in Huntington's Disease. John M. Finke, Oakland University, Department of Chemistry, Rochester, MI 48309-4477

Despite many advances in the area of protein folding, much less is understood about the process of protein misfolding. This is especially notable concerning mechanisms and structures involved in the assembly of large fibers comprised of many miscoded proteins which have...

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