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PubMed1991

A computer simulation of the natural history of HIV infection: insights and implications.

Computer simulation of the natural history of HIV infection shows that the progression from a silent infection to serious disease need not depend upon any particular biological event but only requires the passage of time. It likewise illustrates why modest efficacy from an antiretroviral agent can go a long way toward treating HIV infection, but a cure will be difficult to develop.

CD4-Positive T-Lymphocytes↗
PubMed1991

Computer simulations as a measure of nursing students' decision-making skills.

Use of computer simulations was studied as a strategy to evaluate clinical decision-making skills of 64 senior baccalaureate nursing students who were randomly assigned to experimental and control groups. All students completed Kolb's Learning Style Inventory, a pre- and posttest that was a computer assisted instruction (CAI) clinical simulation specific to the student's clinical placement, and a 36 item attitudinal and evaluative questionnaire developed for the study. The experimental group complete three additional simulations over a 7 week period. Change scores from pre- and posttests were analyzed to determine: 1) if students completing a CAI series demonstrated higher achievement on information-gathering and decision-making skills than students who did not complete the series; 2) if there was a correlation between achievement and clinical grades; and 3) if there was a relationship between achievement and a particular learning style. Although all students demonstrated that significant learning had occurred during the semester, there was no difference between the students completing the full CAI series and those who did not. Students who made significant improvements in decision-making scores also earned higher clinical grades. Success on the CAI series was found to be independent of learning style. Most students expressed positive attitudes about CAI.

Computer Simulation↗
PubMed1989

Regulation of the cytoplasmic pH by a proton-translocating ATPase in Streptococcus faecalis (faecium). A computer simulation.

Earlier work from this laboratory led to the proposal that the cytoplasmic pH of streptococcal cells is regulated solely by changes in the amount and activity of a proton-translocating ATPase, F1F0 complex [Kobayashi, H., Suzuki, T. & Unemoto, T. (1986) J. Biol. Chem. 261, 627-630]. We have now examined the proposal with the aid of computer simulation. We find that an increase in the amount of the H+-ATPase is necessary for pH regulation and is sufficient to maintain a constant steady-state cytoplasmic pH. An increase in H+-ATPase activity is insufficient by itself to maintain a constant cytoplasmic pH, but suppresses the initial fluctuation of the pH. When both variations were allowed, the simulated cytoplasmic pH remained constant despite large perturbations, suggesting that this regulatory system has ample capacity to compensate for pH changes. The present work shows that a computer simulation is a useful way to examine a model for biological regulatory system; application of the simulation to other regulatory systems is discussed.

Computer Simulation↗
PubMed1990

Computer simulation of the hemodynamic determinants of myocardial oxygen supply and demand.

A computer program was developed that uses a mathematical model of the cardiovascular system to predict myocardial oxygen supply and demand as well as cardiac hemodynamics. This model combines the time-varying elastance model of the left ventricle, the modified Windkessel model of the arterial system, and the left ventricular pressure-volume area prediction of myocardial oxygen demand. The computer simulation permits independent control of variables, thus providing the opportunity to design "experiments" and to observe the results. The model predicts that tachycardia leads to reduced myocardial oxygen supply and increased demand. Hypertension caused by increased systemic vascular resistance increases supply more than it increases demand. On the other hand, increased contractility or left ventricular end-diastolic pressure increases demand more than supply, and may cause ischemia in the presence of coronary artery stenosis. The model is an aid in understanding how hemodynamic variables affect the balance between myocardial oxygen supply and demand. It can be used for education and to analyze study protocols prior to animal experimentation.

Animals↗
PubMed1990

Computer simulation in the design of local exhaust hoods for shielded metal arc welding.

Computer simulations were used to examine competing exhaust hood configurations for shielded metal arc welding. The welder's breathing zone concentration appears to be an inverse linear function of the computer-predicted hood capture efficiency. Hood aspect ratio, hood flow, and the welder's position relative to the hood all have a significant effect on the breathing zone concentration. The height of the hood above the welding surface showed no significant effect in reducing breathing zone concentration. Further examination of breathing zone concentration as a function of capture efficiency is needed before reliable design methods can be developed using this parameter.

Air Movements↗
PubMed1990

Computer simulation for optimization of high-performance liquid chromatography of some phenolic pollutants.

Computer simulation was used to optimize high-performance liquid chromatography of phenol and its chloro and nitro derivatives. On the basis of two linear gradient runs of different steepness (RP-18-water + methanol + 1% acetic acid), several simulated gradient runs allowed the optimum gradient programme and flow-rate to be chosen so that the time of analysis could be considerably shortened. Good agreement between simulated and experimental chromatograms was obtained in spite of changes in experimental conditions.

Air Pollutants↗
PubMedDate not supplied

Using a computer simulation program to assess the decision-making process in child health care.

The purpose of this paper was to describe the development and testing of a computer simulation program designed to assess the decision-making process in the public health nurses' work in child health care. The work was based primarily on theories of problem-solving and decision making; on knowledge of child development, health care, and education; and on the soft systems methodology. An authoring program and two simulations were designed and produced at the University of Turku by a team of two nurse researchers, a computer specialist, and three public health nurses. The simulations presented two typical situations encountered by the public health nurses' work in child health care. A total of 61 public health nurses from 11 health centers in the southwestern part of Finland completed the simulations. The public health nurses responded positively to the simulations and the program worked very well. The results revealed some inconsistencies in the decision-making process of the public health nurses with respect to the needs of the child and the family. The public health nurses' decisions were more closely related to the developmental stage of the child than to the unique needs of each family. The simulation is acting to test the public health nurses' ability to make decisions "here and now" but not about caring it forward. These shortcomings can be corrected by asking them to explain their decisions and thoughts after each stage and by tape recording their answers. The findings gave many answers to the question of how the computer simulation program can be developed.

Computer Simulation↗
PubMed1990

The development of computer simulations of the geometries and thermodynamics of biological molecules.

The historical development of computer simulations of molecular geometry and thermodynamics (molecular mechanics, force field method) is outlined. The advantages and disadvantages of techniques such as energy minimization, molecular dynamics and free energy perturbation are discussed. An example is included that shows how energy minimization studies of dopamine D-2 antagonists have been used to develop an understanding of the three-dimensional pharmacophore necessary for this pharmacological activity.

Computer Simulation↗
PubMed1992

Synthesis and conformational properties of the lanthionine-bridged opioid peptide [D-AlaL2,AlaL5]enkephalin as determined by NMR and computer simulations.

We report the synthesis and conformational analysis by means of NMR and computer simulations of a novel opioid peptide with the sequence [formula: see text], which we write as [formula: see text], abbreviated [D-AlaL2,L-AlaL5]EA, where AlaL denotes each of the lanthionine amino acid ends linked by a monosulfide bridge and EA indicates enkephalinamide. Data from 2D NMR (HOHAHA and ROESY) provide short-range NOEs that are used as constraints in molecular modeling; measurement of coupling constants shows that chi 1 (D-AlaL2) is predominantly in either the t or g- conformation, and temperature coefficient data suggest the participation of the AlaL5 amide proton in an intramolecular hydrogen bond. The use of NOE and hydrogen-bond constraints in a distance-geometry program yields a large number of initial conformations compatible with the data. Energy minimization of these structures using CHARMM results in three families of backbone ring conformations, labled A1, A2, and B. The torsion chi 1 in D-AlaL2 remains close to trans for all three conformations. Molecular dynamics in vacuo at 300 K show that these three families of conformers interconvert, with concerted shifts in two of the three torsions psi(Phe), phi(AlaL5), and chi(AlaL5). The [D-AlaL2,L-AlaL5]EA is superactive in the guinea pig ileum (GPI) and mouse vas deferens (MVD) in vitro tests and also in the rat hot plate test in vivo. At the same time, this analog with a constrained 13-membered ring shows virtually no selectivity with a ratio IC50 (MVD)/IC50 (GPI) of 0.882.

Amino Acid Sequence↗
PubMed1989

Positron emission tomographic measurement of blood-to-brain and blood-to-tumour transport of 82Rb. I: Error analysis and computer simulations.

Unidirectional blood-to-brain and blood-to-tumour transport rate constants (K1) for 82Rb (half-life 76 s) and plasma water volume per unit mass of brain/tumour tissue (Vp) can be estimated in vivo using dynamic positron emission tomography (PET). The accuracy of these estimates depends upon the accuracy of PET measurements of regional brain/tumour radioactivity and scintillation well detector measurements of whole-blood radioactivity, which, in turn, depend upon the time course of arterial blood radioactivity. A two-compartmental model has been employed to derive estimates for K1, k2 (efflux rate constant) and Vp from 82Rb/PET data. Errors in these parameter estimates have been studied (1) qualitatively using sensitivity function analysis and (2) quantitatively using computer simulations. The effect of adding a third irreversible compartment and its unidirectional rate constant, k3, has also been investigated. The advantages and disadvantages of bolus injection vs continuous infusion protocols are discussed. Precision in estimated parameters from actual patient data is compared to that obtained from computer simulations in part II of this paper.

Blood↗
PubMed1975

Analysis of expert diagnosis of a computer simulation of congenital heart disease.

Analysis of data from five expert cardiologists indicates substantial agreement on the first step to be taken in response to an emergency case of computer-simulated congenital heart disease. There was little or no agreement among these same subjects on the specific steps undertaken following their initial response. The problem was solved in 11, 10, 8, and 6 steps by four of the cardiologists. The problem-solving sequence employed by one expert resulted in the patient's death. It is concluded that while the behavior of experts in the hospital and clinic is the primary means of evaluating successful student performance, computer simulations of patient cases offer the opportunity to use expert data in the calibration of student error.

Computers↗
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↗
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↗
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↗