Simulation of hemodynamics and regulatory mechanisms in the cardiovascular system based on a nonlinear and time-varying model

Article Abstract:

Software is developed to simulate pressure-flow relationships and regulatory mechanisms in the cardiovascular system. The core of the software is a set of state equations that characterizes the cardiovascular dynamics based on an analog electrical model. The state is propagated forward in time by numerical integration with a time step of 1ms. Nonlinear and time-varying elements are treated in the simulation by updating the state equations every 5 ms. Hemodynamic waveforms from each cardiac cycle are averaged and used as input to several models of circulatory regulation. The regulatory mechanisms under investigation include the systemic autoregulation, the carotid baroreflex, and the effect of intramyocardial accumulation of calcium ions on left ventricular contractility. It is shown that the simulation accurately represents several observations of the cardiovascular dynamics and physiology. The software should be valuable for developing hypotheses and protocols of in vivo studies, for integrating and interpreting experimental results, and as a tool of computer aided instruction. (Reprinted with permission of the publisher.)

Circulatory system, Blood, Technical, Models, Simulation, Medical Diagnosis, Analog Signals, Cardiovascular System

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An efficient method for handling time-dependent boundary conditions with the DSS/2 differential equation solver

Article Abstract:

This paper discusses an efficient method for handling time dependent boundary conditions with the DSS/2 differential equation solver. The method was evaluated by using it in the numerical solution of a diffusion problem. The proposed method is also particularly useful for boundary conditions in which only derivatives of the dependent variables are involved. The method is based on transforming the boundary conditions at the interface to a set of algebraic equations which must be solved simultaneously at each integration step. Both algebraic and numerical solutions of this set of equations are discussed, and the relative merits of each one of these solutions are evaluated. The proposed method provides significant improvements in computation times and is capable of handling more complex boundary conditions as compared to other conventional methods. (Reprinted by permission of the publisher.)

Algorithm Analysis, Methods, Boundary-Value Problems, Theoretical Approach, technical, Difference Equations

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