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At least 1,009 records · Page 56Linked to original sources
PubMed1991

An interactive computer simulator of the circulation for knowledge acquisition in cardio-anesthesia.

Knowledge-based decision support systems for use in cardio-anesthesia can provide online support to the anesthesiologist by generating intelligent alarms. However, the acquisition and validation of a consistent knowledge base for this application bears problems related to the transfer of clinical experiences into a rule system. An interactive simulator of the human circulation is presented that supports the process of knowledge acquisition and testing. The simulator can be controlled in realtime by an anesthesiologist during the simulation run thus providing a basis for interdisciplinary discussion of routine as well as critical situations. The output data can be transferred to a knowledge-based system for test purposes. The simulator is currently being used for the development of the Anesthesia Expert Assist System AES-2. With regard to the special application a model of the heart-function was integrated which enables the simulation of heart insufficiency. Simulation runs under various conditions are presented and discussed. The simulator was implemented on an ATARI ST personal computer.

Anesthesiology↗
PubMed1982

Factors regulating serial dependencies in the discharge patterns of nerve cells: a computer simulation study in relation to dorsal spinocerebellar tract neurones.

This study was undertaken to investigate the factors which may contribute to the strong negative correlation between successive interspike intervals which characteristically occur in the discharge of dorsal spinocerebellar tract (DSCT) neurones. This correlation is reflected by a first-order serial correlation coefficient (R1) which is often less than --0.6(17). This strongly negative correlation would be expected to increase the rate at which the DSCT neurone transmits information from peripheral receptors. A model of a DSCT neurone has been developed and simulated on a digital computer. It was found that the discharge pattern of the model could be very similar to that of a real DSCT neurone and the value of R1 could be less than --0.6. In order for such values of R1 to be generated, a number of conditions had to occur simultaneously. These were that the discharge of the excitatory presynaptic fibres impinging on the neurone had to be fairly regular, that the overall range of firing frequencies on these fibres had to be rather small and that the mean firing rate of the neurone had to be about double that of each presynaptic fibre. Provided these 3 conditions were met, the precise properties of the model were relatively unimportant. Parameter values derived from biophysical studies of real DSCT neurones fulfilled these conditions.

Action Potentials↗
PubMed1977

Analysis and computer simulation of aerobic oxidation of reduced nicotinamide adenine dinucleotide catalyzed by horseradish peroxidase.

Under suitable experimental conditions the aerobic oxidation of NADH catalyzed by horseradish peroxidase occurred in four characteristic phases: initial burst, induction phase, steady state, and termination. A trace amount of H2O2 present in the NADH solution brought about initial burst in the formation of oxyperoxidase. About 2 mol of oxyperoxidase was formed per mol of H2O2. When a considerable amount of the ferric enzyme still remained, the initial burst was followed by an induction phase. In this phase the rate of oxyperoxidase formation from the ferric enzyme increased with the decrease of the ferric enzyme and an approximately exponential increase of oxyperoxidase was observed. A rapid oxidation of NADH suddenly began at the end of the induction phase and the oxidation continued at a relatively constant rate. In the steady state, oxygen was consumed and H2O2 accumulated. A drastic terminating reaction suddenly set in when the oxygen concentration decreased under a certain level. During the reaction, H2O2 disappeared accompanying an accelerated oxidation of NADH and the enzyme returned to the ferric form after a transient increase of peroxidase compound II. Time courses of NADH oxidation, O2 consumption, H2O2 accumulation, and formation of enzyme intermediates could be simulated with an electronic computer using 11 elementary reactions and 9 rate equations. The results were also discussed in relation to the mechanism for oscillatory responses of the reaction that appeared in an open system with a continuous supply of oxygen.

Computers↗
PubMed2006

Using 3D computer simulations to enhance ophthalmic training.

PURPOSE: To develop more effective methods of demonstrating and teaching complex topics in ophthalmology with the use of computer aided three-dimensional (3D) animation and interactive multimedia technologies. METHODS: We created 3D animations and interactive computer programmes demonstrating the neuroophthalmological nature of the oculomotor system, including the anatomy, physiology and pathophysiology of the extra-ocular eye muscles and the oculomotor cranial nerves, as well as pupillary symptoms of neurological diseases. At the University of Vienna we compared their teaching effectiveness to conventional teaching methods in a comparative study involving 100 medical students, a multiple choice exam and a survey. RESULTS: The comparative study showed that our students achieved significantly better test results (80%) than the control group (63%) (diff. = 17 +/- 5%, p = 0.004). The survey showed a positive reaction to the software and a strong preference to have more subjects and techniques demonstrated in this fashion. CONCLUSION: Three-dimensional computer animation technology can significantly increase the quality and efficiency of the education and demonstration of complex topics in ophthalmology.

Computer Simulation↗
PubMed1994

The composition of bone marrow for a dual-energy quantitative computed tomography technique. A cadaver and computer simulation study.

RATIONALE AND OBJECTIVES: The authors have been developing a dual-energy quantitative computed tomography (DE-QCT) technique that requires calibration standards that mimic the x-ray attenuation properties of bone, red marrow, and yellow marrow. To resolve questions regarding the compositions of red and yellow marrow that appear in the literature, the authors performed chemical analyses of bone marrow samples. The newly derived compositions were used in a simulation study to test the accuracy of the DEQCT technique. METHODS: Red marrow samples were extruded from the vertebrae of cadavers of young boys. Yellow marrow samples were removed directly from the femurs of cadavers of elderly women. The fat, protein, water, and mineral contents of these samples were determined. The compositions of 12 mixed marrow samples extruded from cadaver vertebrae also were measured. A computer simulation study was performed in which calibration standards with the new compositions were employed to estimate the fat and bone contents of spongiosas containing the 12 mixed marrows. RESULTS AND CONCLUSIONS: The red marrow samples contained 3% to 6% fat, 6% to 8% protein, 82% to 86% water, and 0.5% to 1% mineral. The yellow marrow samples contained 71% to 92% fat, 1% to 2% protein, 7% to 26% water, and 0.2% to 0.4% mineral. The simulation study yielded good results in three cases and mediocre to poor results in nine cases. An alternative approach was tried in which an average fat-free marrow was derived from the compositions of the 12 mixed marrows, and this substance, fat, and bone were used as the calibration standards. The DEQCT technique with these standards was applied to simulated spongiosas containing the 12 original mixed marrows plus nine additional mixed marrows. All of the estimates were in good agreement with the true compositions. The rms error of the mass fractions of fat was 0.03, and the rms error of the bone concentrations was 3.7 mg/mL.

Aged↗
PubMed2006

Octree indexing of DICOM images for voxel number reduction and improvement of Monte Carlo simulation computing efficiency.

The purpose of the present study is to introduce a compression algorithm for the CT (computed tomography) data used in Monte Carlo simulations. Performing simulations on the CT data implies large computational costs as well as large memory requirements since the number of voxels in such data reaches typically into hundreds of millions voxels. CT data, however, contain homogeneous regions which could be regrouped to form larger voxels without affecting the simulation's accuracy. Based on this property we propose a compression algorithm based on octrees: in homogeneous regions the algorithm replaces groups of voxels with a smaller number of larger voxels. This reduces the number of voxels while keeping the critical high-density gradient area. Results obtained using the present algorithm on both phantom and clinical data show that compression rates up to 75% are possible without losing the dosimetric accuracy of the simulation.

Algorithms↗
PubMed1999

A computer simulation of free-range exercise in the laboratory.

We present a technique for simulating dynamic field (free-range) exercise, using a novel computer-controlled cycle ergometer. This modified cycle ergometer takes into account the effect of friction and aerodynamic drag forces on a 70-kg cyclist in a racing position. It also affords the ability to select different gear ratios. We have used this technique to simulate a known competition cycle route in Cape Town, South Africa. In an attempt to analyze the input stimulus, in this case the generated power output of each cyclist, eight subjects cycled for 40 min at a self-selected, comfortable pace on the first part of the simulated route. Our results indicate that this exercise input excites the musculocardiorespiratory system over a wide range of power outputs, both in terms of amplitude and frequency. This stimulus profile thereby complies with the fundamental requirement for nonlinear (physiological) systems analysis and identification. Through a computer simulation, we have devised a laboratory exercise protocol that not only is physiologically real but also overcomes the artificiality of most traditional laboratory exercise protocols.

Computer Simulation↗
PubMed1995

Errors in transrectal ultrasonic planimetry of the prostate: computer simulation of volumetric errors applied to a screening population.

Three systemic errors in routine ultrasonic planimetric volume measurements of the prostate were assessed. A computer model using ellipsoids was used to simulate the step section technique and different forms of rotational movements of the prostate during planimetry. The planimetric volume was up to 12% smaller than the exact volume, depending on the degree of rotational movement, the shape, and the length of the ellipsoid. In vivo study of a screening population showed that it is worthwhile to compare caliper length with the number of planimetric steps, as the difference might be an indication of the difference between planimetric and caliper measured volume. In shorter prostates the planimetric volume was smaller than the prolate spheroid volume when compared to longer prostates, as was seen in the computer simulation.

Computer Simulation↗
PubMed2004

Predicting the impact of a new information system on workflow using a discrete event simulation.

Computer simulation of an information system prior to its implementation can predict time and workflow changes in a hospital department, while offering a common ground of communication across various levels in the organization. Often, the simulation can predict unexpected effects of changes to the work environment and allow experimentation with alternative scenarios at minimal cost to the department or the organization. In this paper we describe a discrete-event simulation experiment that predicted an unexpected increase in routine specimen processing time with the introduction of an information system in the HLA tissue typing lab at a major transplant center. The computer simulation enabled the reallocation of existing staff prior to the system implementation.

Clinical Laboratory Information Systems↗
PubMed2004

Exploring alternative models of rostral-caudal patterning in the zebrafish neurectoderm with computer simulations.

The StarLogo and NetLogo programming environments allow developmental biologists to build computer models of cell-cell interactions in an epithelium and visualize emergent properties of hypothetical genetic regulatory networks operating in the cells. These environments were used to explore alternative models that show how a posteriorizing morphogen gradient might define gene-expression domains along the rostral-caudal axis in the zebrafish neurectoderm. The models illustrate how a hypothetical genetic network based on auto-activation and cross-repression could lead to establishment of discrete non-overlapping gene-expression domains.

Animals↗
PubMedDate not supplied

pH gradients generated by polyprotic buffers. I. Theory and computer simulation.

This paper presents the general equations for computing pH, dissociation coefficients, buffering power and ionic strength of pure polyelectrolyte solutions (polyacids, polybases and zwitterionic species with any number of dissociable groups) and mixtures of any number of these species. A program has been written for simulating the behaviour of mixtures containing up to 50 species (including buffers and titrants), each of them with up to 10 dissociable groups. This allowed one to check the equations with the available data on a few oligoprotic species.

Buffers↗
PubMed1994

A computer simulation for learning about the physiological response to exercise.

An interactive computer program written for IBM-compatible microcomputers, which simulates the physiological response to graded exercise in healthy individuals, is described. The program presents high-resolution graphic data (heart rate, pulmonary ventilation, oxygen consumption, and blood lactate concentration) in a form comparable to that of a chart recorder display. Data are derived from an empirical model that allows users to select certain parameters of the subject they wish to investigate, including sex, age, height, weight, and level of training. Measurements may be taken directly from the monitor screen by use of the cross-hair cursor facility provided. The program has been positively evaluated in use by undergraduate students and shown to be an effective teaching aid. The potential use of the software in light of these findings is discussed.

Adolescent↗
PubMed2004

Computer simulations improve university instructional laboratories.

Laboratory classes are commonplace and essential in biology departments but can sometimes be cumbersome, unreliable, and a drain on time and resources. As university intakes increase, pressure on budgets and staff time can often lead to reduction in practical class provision. Frequently, the ability to use laboratory equipment, mix solutions, and manipulate test animals are essential learning outcomes, and "wet" laboratory classes are thus appropriate. In others, however, interpretation and manipulation of the data are the primary learning outcomes, and here, computer-based simulations can provide a cheaper, easier, and less time- and labor-intensive alternative. We report the evaluation of two computer-based simulations of practical exercises: the first in chromosome analysis, the second in bioinformatics. Simulations can provide significant time savings to students (by a factor of four in our first case study) without affecting learning, as measured by performance in assessment. Moreover, under certain circumstances, performance can be improved by the use of simulations (by 7% in our second case study). We concluded that the introduction of these simulations can significantly enhance student learning where consideration of the learning outcomes indicates that it might be appropriate. In addition, they can offer significant benefits to teaching staff.

Biology↗
PubMed1990

Three-dimensional computer simulation of stereotactic surgery.

Software which can be used to simulate stereotactic surgery on a personal computer was developed. Using the modified Todd-Wells frame coordinates, it can reconstruct a three-dimensional image of the brain structure and simulate the target trajectories before the operation. Also, it can calculate the volume of the target region and the distance between the target and certain points in arbitrary trajectory angles. Its optional mode can be used for simulation of conventional brain surgery for previewing deep-seated brain lesions in the operating position.

Brain Mapping↗
PubMed1993

Computer simulation of the phosphorylation cascade controlling bacterial chemotaxis.

We have developed a computer program that simulates the intracellular reactions mediating the rapid (nonadaptive) chemotactic response of Escherichia coli bacteria to the attractant aspartate and the repellent Ni2+ ions. The model is built from modular units representing the molecular components involved, which are each assigned a known value of intracellular concentration and enzymatic rate constant wherever possible. The components are linked into a network of coupled biochemical reactions based on a compilation of widely accepted mechanisms but incorporating several novel features. The computer motor shows the same pattern of runs, tumbles and pauses seen in actual bacteria and responds in the same way as living bacteria to sudden changes in concentration of aspartate or Ni2+. The simulated network accurately reproduces the phenotype of more than 30 mutants in which components of the chemotactic pathway are deleted and/or expressed in excess amounts and shows a rapidity of response to a step change in aspartate concentration similar to living bacteria. Discrepancies between the simulation and real bacteria in the phenotype of certain mutants and in the gain of the chemotactic response to aspartate suggest the existence of additional as yet unidentified interactions in the in vivo signal processing pathway.

Aspartic Acid↗
PubMed1993

Determining heart-rate variability: comparing methodologies using computer simulations.

Heart rate variation due to respiration is a window onto autonomic nervous system function and many measures exist that quantify this variability. Computer-based simulations of 1-minute deep-breathing tests, along with common artifacts, were used to compare the most frequently used measures. We found distinct differences in the performance of the measures. Some measures (e.g., SDRR and MSSD) are strongly influenced by the underlying mean heart rate while others (e.g., Max-Min and SDHR) are not. All of the measures tested, except R, were influenced by both shifting mean heart rate and single-beat anomalies. R, on the other hand, is strongly influenced by test duration and breathing asynchronies. Sensitivity to phenomena unrelated to ANS function can reduce the diagnostic discrimination of these measures. We suggest simple improvements to the measures and discuss how some measures may be theoretically superior to others.

Computer Simulation↗