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Campbell, Kenneth S; University of Kentucky WPI Seminar Room 08.135 Mon, 22. Sep 14, 11:30
Myocardial strain rate modulates the speed of relaxation in dynamically loaded twitch contractions
Slow myocardial relaxation is an important clinical problem in about 50% of patients who have heart failure. Prior experiments had suggested that the slow relaxation might be a consequence of high afterload (hypertension) but clinical trials testing this hypothesis have failed; lowering blood pressure in patients with slow relaxation does not help their condition. We performed new experiments using mouse, rat, and human trabeculae and showed that it is not afterload but the strain rate at end systole that determines the subsequent speed of relaxation. To investigate the molecular mechanisms that drive this behavior, we ran simulations of our experiments using the freely available software MyoSim (http://www.myosim.org). This software simulates the mechanical properties of dynamically activated half-sarcomeres by extending A.F.Huxley’s cross-bridge distribution technique with Ca2+ activation and cooperative effects. We discovered that our experimental data could be reproduced using a relatively simple framework consisting of a single half-sarcomere pulling against a series elastic spring. Further analysis of the simulations suggested that quick stretches speed myocardial relaxation by detaching myosin heads and thereby disrupting the cooperative mechanisms that would otherwise prolong thin filament activation. The simulations therefore identify myofilament kinetics and tissue strain rate as potential therapeutic targets for heart failure attributed to slow relaxation.

Evangelos Latos WPI Seminar Room 08.135 Wed, 24. Sep 14, 10:05
Existence and Blow-up of Solutions for Semilinear Filtration Problems
We examine the local existence and uniqueness of solutions to the semi-linear filtration equation, with positive initial data and appropriate boundary conditions. Our main result is the proof of blow-up of solutions. Moreover, we discuss about the existence of solutions for the corresponding steady-state problem. It is found that there exists a critical value, above which the problem has no stationary solution of any kind, while below that critical value there exist classical stationary solutions. Exactly this critical value of the parameter acts as a threshold also for the corresponding parabolic problem between blow-up and global existence
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