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At least 1,189 records · Page 66Linked to original sources
PubMed2006

Computational simulations of the human magneto- and electroenterogram.

Many functional pathologies of the small intestine are difficult to diagnose clinically without an invasive surgical intervention. Often such conditions are associated with a disruption of the normal electrical activity occurring within the musculature of the small intestine. The far field electrical signals on the torso surface arising from the electrical activity within the small intestine cannot be reliably measured. However, it has been shown that abnormal electrical activity in the small intestine can be distinguished by recording the magnetic fields of intestinal origin immediately outside the torso surface. We have developed an anatomically-based computational model to simulate slow wave propagation in the small intestine, the resulting cutaneous electrical field and the magnetic field outside the torso. Using both a one-dimensional and a three-dimensional model of the duodenum we investigate the degree of detail that is required to realistically simulate this far field activity. Our results indicate that some of the qualitative behavior in the far field activity can be replicated using a one-dimensional model, although there are clear situations where the greater level modeling detail is required.

Action Potentials↗
PubMed1988

Modeling and computer simulation of ultrasound imaging systems and human tissues.

A simulator has been developed for an ultrasound linear scan B-mode imaging system. First, a numerical method of calculating field patterns or pulse echo patterns is presented for a full-aperture system with a given transducer geometry in nonattenuating and attenuating media, based on the measured temporal impulse response for a single transducer element immersed in water, and taking into account the variation of attenuation and acoustic velocity in human tissue. The simulator then models and simulates the receiver subsystems in detail using the received pulse echo. In particular, a dynamic inverse filter, to improve the axial resolution, and an unconventional TGC gain function, to reduce the SNR deterioration through logarithmic compression, are proposed. Finally, simulation and experimental results are presented and discussed.

Computer Simulation↗
PubMed1987

A computer simulation program to facilitate budgeting and staffing decisions in an intensive care unit.

ICUs have unique problems in choosing their best staffing levels for direct patient care because each unit's total patient needs per shift, quantitated in acuity points, vary widely. We devised a computer program to simulate our 12-bed medical/cardiac ICU workload and staffing system. Nursing staffing policies, costs, and availabilities, and a table of past patient acuities per shift were input; total overstaffing, understaffing, and cost per year for full-time nursing equivalents (FTEs) for direct patient care were output for different staffing levels. Using the model, we considered financial concerns, quality of care issues, and staff working preferences and determined that our best staffing level would be based on 5.5 direct FTEs per shift. The stimulation analysis is straightforward, flexible, adaptable, and easy to update and use.

Budgets↗
PubMed1983

Analysis of numerical methods for computer simulation of kinetic processes: development of KINSIM--a flexible, portable system.

A flexible and convenient computational method for the simulation of kinetic progress curves has been developed. A mechanism is represented in conventional chemical format with either kinetic or rapid equilibrium steps separating chemical species. A table describing the differential equations of the mechanism is generated and a direct numerical integration is performed. The same program can be used to simulate any number of mechanisms. The user may interactively set kinetic parameters to seek the optimal fit for a set of experiments, as determined by graphical superimposition of simulated curves with experimental data. Standard error analysis and automatic optimization may also be included. The program is computationally efficient and its interactive nature makes it a good teaching tool. The source code is written in FORTRAN IV and adheres closely with the ANSI 1966 standard, so as to make it maximally portable and machine independent.

Chemistry Techniques, Analytical↗
PubMed1991

Pharmacokinetics of the dermal route of exposure to volatile organic chemicals in water: a computer simulation model.

A kinetic model of dermal absorption of nonpolar organic nonelectrolytes in dilute aqueous solutions is described. The model uses systems dynamics STELLA software and is designed for a Macintosh computer. The model assumes the outer stratum corneum layer of skin to be the rate-determining barrier to dermal absorption and assumes that both stratum corneum and viable epidermal layers have storage capacity for lipophilic solutes. The model predicts between 30 and 94% of experimental results with humans under the same conditions. The degree of departure between experimental and theoretical results is inversely related to the solute's octanol/water partition coefficient, which is consistent with the most recently hypothesized mechanisms of transport of molecules across the dermal barrier. The model has potentially useful applications for risk assessment if used within its defined limits.

Computer Simulation↗
PubMed2005

Computational simulation of a non-newtonian model of the blood separation process.

The aim of this work is to construct a computational fluid dynamics model capable of simulating the transient non-Newtonian process of apheresis. A Lagrangian-Eulerian model has been developed which tracks the blood particles within a two-dimensional flow configuration. Within the Eulerian method, the fluid mass and momentum conservation equations within the separator are solved using the density and the viscosity is calculated from the blood particle concentrations. Subsequently, the displacement of the blood particles is calculated with a Lagrangian method. Hawksley's model for the density of supensions is used in the variable density calculation. The viscosity is calculated with two models based on Vand's rigid particle suspension viscosity concepts, followed by the flow field calculation in the separator. Simulations were performed for various inlet hematocrit values and separator lengths. The simulations are in satisfactory agreement with experimental results reported in literature, indicating a complete separation of plasma and red blood cells (RBCs), as well as nearly complete separation of red blood cells and platelets. No hemolysis was observed in the simulations because the shear rate remained under the critical value of 150 N/m2.

Biophysical Phenomena↗
PubMed2006

Applicability of the single equivalent moving dipole model in an infinite homogeneous medium to identify cardiac electrical sources: a computer simulation study in a realistic anatomic geometry torso model.

We have previously proposed an inverse algorithm for fitting potentials due to an arbitrary bio-electrical source to a single equivalent moving dipole (SEMD) model. The algorithm achieves fast identification of the SEMD parameters by employing a SEMD model embedded in an infinite homogeneous volume conductor. However, this may lead to systematic error in the identification of the SEMD parameters. In this paper, we investigate the accuracy of the algorithm in a realistic anatomic geometry torso model (forward problem). Specifically, we investigate the effect of measurement noise, dipole position and electrode configuration in the accuracy of the algorithm. The boundary element method was used to calculate the forward potential distribution at multiple electrode positions on the body surface due to a point dipole in the heart. We have found that the position and not the number of electrodes as well as the site of the origin of the arrhythmia in the heart have a significant effect on the accuracy of the inverse algorithm, while the measurement noise does not. Finally, we have shown that the inverse algorithm preserves the topology of the source distribution in the heart, thus potentially allowing the cardiac electrophysiologist to efficiently and accurately guide the tip of the catheter to the ablation site.

Action Potentials↗
PubMed2003

Prediction of brachial plexus stretching during shoulder dystocia using a computer simulation model.

OBJECTIVE: The purpose was to study the impact of maternal endogenous and clinician-applied exogenous delivery forces on brachial plexus stretching during a shoulder dystocia event. STUDY DESIGN: A computer software crash dummy model (MADYMO, version 5.4, TNO Automotive, Delft, The Netherlands) was modified on the basis of established maternal pelvis and fetal anatomic specifications. The brachial plexus was modeled as a spring, with mechanical properties that were based on previously reported experimental data. Increasing amounts of endogenous or exogenous loading forces were applied until delivery of the anterior fetal shoulder occurred. Brachial plexus deformation was assessed as percent stretch in the nerve (Change in length/Original length x 100). RESULTS: With lithotomy positioning, both maternal endogenous and clinician-applied exogenous delivery forces were associated with brachial plexus stretching (15.7% vs 14.0%, respectively). McRoberts positioning reduced needed loading forces for delivery and resulted in 53% less brachial plexus stretch (6.6%). Downward lateral displacement of the fetal head was associated with a 30% increase in brachial plexus stretch (18.2%) compared with axial positioning of the head (14.0%). CONCLUSION: Brachial plexus stretch varied as a result of the load required for delivery, the source of the applied force, pelvic orientation, and fetal head positioning. Maternally derived and clinician-applied delivery forces can both lead to brachial plexus deformation when shoulder dystocia is encountered. The McRoberts maneuver can reduce brachial plexus stretching. Management of fetal head position may also be important in reducing unnecessary brachial plexus stretch.

Brachial Plexus↗