Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Computer Simulation”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 343 records · Page 19Linked to original sources
PubMed2006

Statistical methods for analysing Barthel scores in trials of poststroke interventions: a review and computer simulations.

BACKGROUND AND PURPOSE: Arguments persist as to whether parametric or non-parametric methods should be used to analyse ordinal data in trials. This paper aims to assess methods used for presenting and analysing an ordinal scale, the Barthel Index, in trials of poststroke interventions. METHODS: All randomized controlled trials (RCTs) of poststroke interventions published from 1995 to 2004 in two journals (Stroke and Clinical Rehabilitation) were scrutinized for methods used to present and analyse Barthel scores. Computer simulations were used to compare the type I errors and the statistical power of different statistical methods under a range of assumed circumstances. RESULTS: One hundred and fifty-six RCTs were identified within the two journals. The central tendency of Barthel scores was measured by the median in 47 trials and by the mean in 35 trials. Non-parametric analyses of Barthel scores were conducted in 47 trials and parametric methods used in 18 trials. The results of computer simulations demonstrate that the t-test has a similar type I error rate and statistical power when compared with the rank sum test. However, when a zero final Barthel score is assigned to patients who have died, the statistical power of the t-test is much reduced. The possible maximal statistical power of dichotomization and ordinal regression is usually much lower than that of the rank sum test. CONCLUSIONS: To facilitate comparison and meta-analysis, we recommend that mean values (with standard deviations or standard errors) of Barthel scores should be routinely reported in trials of poststroke interventions. The rank sum test appears the most powerful inferential technique for detecting differences in Barthel scores.

Computer Simulation↗
PubMed1987

Computer simulations of the diffusion of a substrate to an active site of an enzyme.

Computer simulations of the diffusion of a substrate to an enzyme active site were performed. They included the detailed shape of the protein and an accurate description of its electrostatic potential. Application of the method to the diffusion of the superoxide anion to the protein superoxide dismutase revealed that the electric field of the enzyme enhances the association rate of the anion by a factor of 30 or more. Calculated changes in the association rate as a function of ionic strength and amino acid modification paralleled the observed behavior. Design principles of superoxide dismutase are considered with respect to insights provided by the simulations. A possible means of enhancing the enzyme turnover rate through site-directed mutagenesis is proposed.

Binding Sites↗
PubMed1991

Computer simulation of surface-induced aggregation of ferritin.

Models are presented describing the transient mass-transport limited adsorption and cluster growth of ferritin at a solid surface. Computer simulations are carried out on a hexagonal lattice using a computer model that can be characterized as a two-dimensional stochastic cellular automaton allowing different rules regarding association, lateral interaction and dissociation to be incorporated in the model. The fractal dimensions of individual clusters were extracted from simulated aggregates and for similar rules found to be consistent with literature values on reversible diffusion-limited aggregation in two dimensions. The distribution of clusters versus free surface were shown to be affected by neighbor-dependent association probability. Low fractal dimension clusters were generated by a combination of strong lateral cohesion and neighbor-dependent dissociation to the bulk. By comparing computer simulated aggregation to experimental electron micrographs of adsorbed ferritin layers it is suggested that neighbor-dependent association, neighbor-dependent dissociation and lateral interactions are important factors in the complex dynamics of adsorbed protein layers.

Computer Simulation↗
PubMed1991

Computer simulations of cell-target encounter including biased cell motion toward targets: single and multiple cell-target simulations in two dimensions.

In order for immune cells to carry out many of their functions, including clearance of infectious agents from tissue, they must first encounter their targets in the tissue. This encounter process is often the rate-limiting step in the overall function. Most immune cells exhibit chemotactic ability, and previous continuum models for encounter rates and dynamics have shown that chemotaxis can be a great advantage to cells by greatly increasing encounter rates relative to those for randomly moving cells. This paper describes computer simulations of discrete cell-target encounter events in two dimensions, for the two cases considered by the continuum models: where only a single cell and a single target are present, and where many cells and targets are present. The results of these simulations verify our previous model predictions that a small amount of chemotactic bias dramatically decreases the encounter time, while further increases in the amount of bias have a much smaller effect. Chemotactic ability is shown to be an important determinant of the kinetics of target clearance, and its effects depend on the initial cell-target ratio and the initial distributions of cells and targets. To the best of our knowledge, this work provides the first computer simulations of particle-target encounter in which there is biased motion of particles toward their targets, and is therefore of general interest beyond specific application to immune cell function.

Animals↗
PubMed1988

A computer simulation of simultaneous heat and oxygen transport during heterogeneous three dimensional tumor hyperthermia.

Hyperthermia is a developing modelity for the treatment of cancer. This therapy is occasionally used by itself, however, usually it is used as an adjuvate with chemo or radiation therapy. The mechanism for this treatment is based on the fact that cancer cells are heated preferentially by heat application due to lower vascularity in the tumor tissue as compared with the surrounding normal tissue and that, when used with radiation therapy or chemo therapy, higher oxygen partial pressure in the tumor results in increased tumor cell damage. Appropriate mathematical models and their real time prediction of oxygen and temperature profiles could be very helpful in achieving optimal results via hyperthermia and to avoid possible danger which might occur during the treatment. Because of the complexity and the heterogeneous nature of physiological system, it is necessary to include heterogeneous properties in the mathematical models for them to be useful for biomedical calculations. Of course, it is much more difficult to solve mathematically the heterogeneous system than the homogeneous one. In this paper, the importance of the implementation of heterogeneities in the heat and mass transport for biological system mathematical modelling is discussed. Results of a three dimensional computer simulation of mass and heat transfer in tumor tissue with different capillary geometries during hyperthermia are demonstrated. The method used for the computer simulation is a deterministic/probabilistic technique, Williford-Bruley calculational strategy.

Animals↗
PubMed1994

Variations in base pair composition and associated long-range correlations in DNA sequences--computer simulation results.

Recently, the possible occurrence of long-range correlations between nucleotides in DNA sequences of living organisms has excited considerable interest. Of particular importance is the claim that only intron-containing sequences exhibit these correlations. Different investigations, however, have disproved the claimed difference between intron-containing and intron-less DNA sequences. Moreover, very recent investigations pointed out that the long-range correlations appear only if relatively large variations in nucleotide composition along the DNA sequence are present. Furthermore, some examples demonstrated that these variations may have clear biological reasons. In this paper we investigate in detail, with the aid of computer simulations, the connection between compositional heterogeneity of a DNA sequence and the appearance of long-range correlations. As an explicit example, the DNA sequence of the lambda-phage is compared with different artificial sequences of similar compositional heterogeneity. The results demonstrate that the variations of the nucleotide composition along the sequence can fully account for all properties of the claimed long-range correlations. New results of extensive computer simulations are presented which clearly demonstrate how the apparent 'fractal' (or 'long-range-correlated') character of a sequence gradually evaporates, as the frequency of the compositional variations of a simulated sequence continuously increases.

Bacteriophage lambda↗
PubMed2003

Effects of positive end-expiratory pressure increments can be predicted by computer simulation based on a physiological profile in acute respiratory failure.

OBJECTIVE: We examined whether computer simulation predicts airway pressures after increments of positive end-expiratory pressure (PEEP) in acute respiratory failure. DESIGN AND SETTING: Prospective, nonrandomized comparative trial in an intensive care unit of a university hospital. PATIENTS: Twelve consecutive acute respiratory failure patients. INTERVENTIONS. PEEP increments from 0 to 2.5, 5, 7.5, 10, and 15 cm H(2)O. MEASUREMENTS AND RESULTS: A physiological profile comprising values for compliance, respiratory resistance and CO(2 )elimination as a function of tidal volume was established from a recording of ordinary breaths prior to increments of PEEP. Airway pressures and CO(2 )elimination were measured 30 s after resetting, pressures also after 10 min. Values from simulation of the resetting, based on the profile, were compared to measured values. The profiles indicated vast differences in physiology between the 12 subjects. Errors of simulation of airway pressures were nonsignificant or trivial up to PEEP levels of 10 cm H(2)O (95% of errors <3 cm H(2)O). After 10 min plateau pressure averaged 1.5 cm H(2)O lower than 30 s after resetting. At increments to PEEP 7.5, 10, and 15, CO(2 )elimination fell by on average 4%, 8%, and 11%, respectively. As tidal volume and respiratory rate was unchanged this was not predicted. CONCLUSIONS: On the basis of a simple lung model, simulation predicted effects of moderate increments of PEEP on airway pressures in patients with complex physiology.

Acute Disease↗
PubMed1997

A multisegment computer simulation of normal human gait.

The goal of this project was to develop a computer simulation of normal human walking that would use as driving moments resultant joint moments from a gait analysis. The system description, initial conditions and driving moments were taken from an inverse dynamics analysis of a normal walking trial. A nine-segment three-dimensional (3-D) model, including a two-part foot, was used. Torsional, linear springs and dampers were used at the hip joints to keep the trunk vertical and at the knee and ankle joints to prevent nonphysiological motion. Dampers at other joints were required to ensure a smooth and realistic motion. The simulated human successfully completed one step (550 ms), including both single and double support phases. The model proved to be sensitive to changes in the spring stiffness values of the trunk controllers. Similar sensitivity was found with the springs used to prevent hyperextension of the knee at heel contact and of the metatarsal-phalangeal joint at push-off. In general, there was much less sensitivity to the damping coefficients. This simulation improves on previous efforts because it incorporates some features necessary in simulations designed to answer clinical science questions. Other control algorithms are required, however, to ensure that the model can be realistically adapted to different subjects.

Ankle Joint↗
PubMed2004

Competitive adsorption of proteins and low-molecular-weight surfactants: computer simulation and microscopic imaging.

Proteins and low-molecular-weight (LMW) surfactants are used in the food industry as emulsifying (and foaming) ingredients and as stabilizers. These attributes are related to their ability to adsorb at fluid-fluid (and gas-fluid) interfaces lowering the interfacial (and surface) tension of liquids. Hence, the study of the properties of adsorbed layers of these molecules can be expected to lead to a better understanding of their effect on food products. Direct proof of the validity of mesoscopic models of systems of proteins and LMW surfactants can only be achieved by quantitative theoretical predictions being tested against both macroscopic and mesoscopic experiments. Computer simulation constitutes one of the few available tools to predict mathematically the behaviour of models of realistic complexity. Furthermore, experimental techniques such as atomic force microscopy (AFM) now allow high resolution imaging of these systems, providing the mesoscopic scale measurements to compare with the simulations. In this review, we bring together a number of related findings that have been generated at this mesoscopic level over the past few years. A useful simple model consisting of spherical particles interacting via bonded and unbonded forces is described, and the derived computer simulation results are compared against those from the imaging experiments. Special attention is paid to the adsorption of binary mixtures of proteins, mixtures of LMW surfactants, and also protein+surfactant mixed systems. We believe that further development of these mathematically well-defined physical models is necessary in order to achieve a proper understanding of the key physico-chemical processes involved.

Adsorption↗
PubMed1997

[Computer simulation of system controlling--application to designing of anti-shock resuscitation therapy for burn injured patient].

The computer simulation of aim-controlling of changes in the circulative plasma volume, plasma protein concentration, hematocrit and electrolytes for five burn injured patients during their shock phase was carried out by using back-propagation algorithm of the simulation system. Based on the aim-controlling, the better resuscitation therapy protocol for the patient was given by computer. The clinical application in five cases of the burns showed that the new method helped us to make individualized clinical anti-shock resuscitation formula for the burn injured patient more reasonable.

Burns↗
PubMed1994

Computer simulation of the effect of dDAVP with saline loading on fluid balance after 24-hour head-down tilt.

Fluid loading (FL) before Shuttle reentry is a countermeasure currently in use by NASA to improve the orthostatic tolerance of astronauts during reentry and postflight. The fluid load consists of water and salt tablets equivalent to 32 oz (946 ml) of isotonic saline. However, the effectiveness of this countermeasure has been observed to decrease with the duration of spaceflight. The countermeasure's effectiveness may be improved by enhancing fluid retention using analogs of vasopressin such as lypressin (LVP) and desmopressin (dDAVP). In a computer simulation study reported previously, we attempted to assess the improvement in fluid retention obtained by the use of LVP administered before FL. The present study is concerned with the use of dDAVP. In a recent 24-hour, 6 degree head-down tilt (HDT) study involving seven men, dDAVP was found to improve orthostatic tolerance as assessed by both lower body negative pressure (LBNP) and stand tests. The treatment restored Luft's cumulative stress index (cumulative product of magnitude and duration of LBNP) to nearly pre-bedrest level. The heart rate was lower and stroke volume was marginally higher at the same LBNP levels with administration of dDAVP compared to placebo. Lower heart rates were also observed with dDAVP during stand test, despite the lower level of cardiovascular stress. These improvements were seen with only a small but significant increase in plasma volume of approximately 3 percent. This paper presents a computer simulation analysis of some of the results of this HDT study.

Computer Simulation↗
PubMed1977

Computer-simulated clinical encounters. I. Development, utilization, and evaluation of a program.

Positive findings from the two-year pilot study indicated no significant difference in academic learning and clinical performance when students substituted computer-simulated experiences for hospital-based clinical experiences. There was also strong evidence that the time spent by students in fewer hospital-based clinical experiences was more decisively monitored by faculty. Based on these positive findings, the computer-simulated clinical encounters are being continued as part of the established curriculum in the coordinated undergraduate program in dietetics at The Ohio State University.

Clinical Competence↗
PubMed1972

Computer simulation model of an x-ray department.

A computer simulation model has been designed to predict the effects of changes in the work load and resources of an x-ray department. The model has been used to produce histograms of patient waiting times and to show the effect on these of introducing changes in the speed of processing films and in the numbers of cubicles and radiographers available. The predicted benefit of using a faster film processor has been confirmed in practice.

Appointments and Schedules↗
PubMed2006

Particle method for computer simulation of red blood cell motion in blood flow.

A particle method for the computer simulation of blood flow was proposed to analyze the motion of a deformable red blood cell (RBC) in flowing blood plasma. The RBC and plasma were discretized by particles that have the characteristics of an elastic membrane and a viscous fluid, respectively. The membrane particles were connected to their neighboring membrane particles by springs, and the motion of the particles was determined on the basis of the minimum energy principle. The incompressible flow of plasma that was expressed by the motion of the fluid particles was determined by the moving-particle semi-implicit (MPS) method. The RBC motion and plasma flow were weakly coupled. The two-dimensional simulation of blood flow between parallel plates demonstrated the capability of the proposed method to express the blood flow phenomena observed in experiments, such as the downstream motion of the RBC and the deformation of the RBC into a parachute shape.

Blood Circulation↗
PubMed1992

Molecular details of the activation of soluble phospholipase A2 on lipid bilayers. Comparison of computer simulations with experimental results.

The initial rate of hydrolysis of large unilamellar vesicles of dipalmitoylphosphatidylcholine by phospholipase A2 from the venom of Agkistrodon piscivorus piscivorus is small and elevates gradually until it suddenly increases by a factor of 10 to 1000 depending on the experimental conditions. This abrupt onset of high enzyme activity appears to be correlated to a specific mole fraction of reaction product at which point a cooperative compositional phase transition in the bilayer occurs. Five models that describe the activation process in terms of its being coupled to the putative product-induced lipid transition are presented. These models include one in which the lipid structure enhances the affinity of enzyme binding to the bilayer surface, two in which the equilibrium position between an active and an inactive form of the enzyme-substrate complex is altered, and two in which the rate of a quasi-irreversible spontaneous activation process is increased. Whether the active form of the enzyme is a monomer or dimer is also considered in the last two pairs of models. Computer simulations of time courses for the different models show how a set of four experimental observables distinguishes qualitatively among them. Comparison of the experimental behavior with the computer-simulated behavior of the observables for each model indicates that activation of phospholipase A2 on the lipid surface involves formation of an enzyme dimer which spontaneously converts to an active form. The active enzyme persists in the active state as it exchanges between vesicles. This model of activation is similar to that proposed previously for activation of porcine pancreatic phospholipase A2.

Computer Simulation↗
PubMedDate not supplied

Computer simulation of optimum personnel assignment in hospital pharmacy using a work-sampling method.

A computer simulation of the dispensing work performed in a hospital pharmacy was undertaken, based on analysis data from a work-sampling method and utilizing a personal computer. As a result it was found to be possible to estimate the complete work volume of a day based on the number of prescriptions in the day, and hence to predict fairly precisely the number of pharmacists required to complete that work. The method also enables the users to assign the optimum number of staff for dispensing duties according to the estimated number of prescriptions and the optimum waiting time of patients. A correlation has been noted between the total residence time of prescriptions and the mean waiting time of patients. Using this simple and effective technique to efficiently assign personnel makes it possible to cope with an increasing workload and limited number of staff.

Computer Simulation↗
PubMed1975

Programmatic computer simulation model for medical school planning.

A comprehensive programmatic computer simulation planning model for a school of medicine was generated by integrating several separate simulation models with on-site cost study information. An elementary validation of the model was achieved. The model generated program costs in terms of both faculty hours and dollars. Results indicated that the size of the medical class could be increased from 75 to 100 students within the present resource limitations by transferring faculty time to education from other programs. The maximum class size was limited by the availability of clinical material. The basic science departments could handle this class size easily without significant reduction in other programs, but the clinical departments could not do so unless inpatient levels increased significantly.

Computers↗
PubMed1996

Inhibitory gating of an evoked response to repeated auditory stimuli in schizophrenic and normal subjects. Human recordings, computer simulation, and an animal model.

BACKGROUND: Altered sensory response is a prominent feature of schizophrenia. Inhibitory gatting mechanisms, shown by diminished P50 evoked responses to repeated auditory stimuli, seem to be deficient in schizophrenic persons. These inhibitory mechanisms usually are studied by averaging the electroencephalographic responses to many presentations of pairs of stimuli. Although averaging increases signal-to-noise ratio, it may obscure trial-to-trial differences. We compared differences between schizophrenic and normal persons in single trials and averages of P50 response. METHODS: Recordings from 10 schizophrenic patients and 10 normal subjects were analyzed using conventional averaging and single-trial measurements. A computer simulation of both methods examined their ability to extract evoked responses from background activity. Related single-neuron activity in the hippocampus in an animal model also was studied, because neuronal action potentials can be reliably identified in single trials. RESULTS: Averaged evoked potentials showed significant suppression of the P50 response to the second stimulus of the pair in normal patients, but not in schizophrenic patients. Single-trial analysis did not detect a response above background activity. Computer simulations gave similar results, suggesting that failure to detect suppression in single trials comes from inadequate differentiation of signal from noise. Recordings in animals confirmed almost complete suppression of the response of hippocampal pyramidal neurons to the second stimulus. CONCLUSIONS: The normal inhibition of response to repeated auditory stimuli seems to be compromised in schizophrenia. This loss of inhibitory gating could reflect a physiological deficit of hippocampal interneurons that is consonant with other evidence for interneuron pathologic defects in schizophrenia.

Acoustic Stimulation↗