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 541 records · Page 30Linked to original sources
PubMed1987

Computer simulation of human mitral valve mechanics and motion.

The human mitral valve is the left atrio-ventricular valve which is composed of several components including leaflets, chordae tendineae, papillary muscles, and the valve annulus. Any or all of these components may fail and contribute to various valvular diseases including mitral regurgitation and mitral valve prolapse. A computer simulation of mitral valve mechanics and motion was written in BASIC for micro-computers. This program allows valvular geometry and biomechanical parameters to be varied and records time varying motion of the valve and all components during systole including a graphic display of the valve leaflets.

Chordae Tendineae↗
PubMed1973

Kinetics of diffusion and convection in 3.2-A pores. Exact solution by computer simulation.

The kinetics of transport in pores the size postulated for cell membranes has been investigated by direct computer simulation (molecular dynamics). The simulated pore is 11 A long and 3.2 A in radius, and the water molecules are modeled by hard, smooth spheres, 1 A in radius. The balls are given an initial set of positions and velocities (with an average temperature of 313 degrees K) and the computer then calculates their exact paths through the pore. Two different conditions were used at the ends of the pore. In one, the ends are closed and the balls are completely isolated. In the other, the ball density in each end region is fixed so that a pressure difference can be established and a net convective flow produced. The following values were directly measured in the simulated experiments: net and diffusive (oneway) flux; pressure, temperature, and diffusion coefficients in the pore; area available for diffusion; probability distribution of ball positions in the pore; and the interaction between diffusion and convection. The density, viscosity, and diffusion coefficients in the bulk fluid were determined from the theory of hard sphere dense gases. From these values, the "equivalent" pore radius (determined by the same procedure that is used for cell membranes) was computed and compared with the physical pore radius of the simulated pore.

Cell Membrane Permeability↗
PubMed1993

Estimation of steady-state flux rates in metabolic systems by computer simulations of radioactive tracer experiments.

The dynamics of radioactive tracers in metabolic systems can be mathematically modelled by coupled systems of differential equations for both the concentrations and the specific radioactivities of the metabolites involved. Computer simulations, i.e. direct fitting of numerical solutions of these equations to observed time-courses of metabolites and specific radioactivities, enables one to estimate unknown kinetic parameters of the system. The theoretical fundamentals of this approach and the main steps towards the quantitative assessment of flux rates in stationary metabolic systems are outlined. An application of the method to the purine nucleotide metabolism of Ehrlich ascites tumor cells is given based on a simplified model of this pathway. The obtained steady-state flux rates indicate a marked increase in the metabolism of the adenine nucleotides during the proliferating phase in comparison to the resting phase of tumor growth.

Adenine Nucleotides↗
PubMed2001

A conformational study of the trisaccharide beta-D-Glcp-(1-->2)[beta-D-Glcp-(1-->3)]alpha-D-Glcp-OMe by NMR NOESY and TROESY experiments, computer simulations, and X-ray crystal structure analysis.

Proton-proton cross-relaxation rates have been measured for the trisaccharide beta-D-Glcp-(l --> 2)[beta-D-Glcp-(1 --> 3)]alpha-D-Glcp-OMe in D2O as well as in D2O/[D6]DMSO 7:3 solution at 30 degrees C by means of one-dimensional NMR pulsed field gradient 1H,1H NOESY and TROESY experiments. Interatomic distances for the trisaccharide in D2O were calculated from the cross-relaxation rates for two intraresidue and three interglycosidic proton pairs, using the isolated spin-pair approximation. In the solvent mixture one intraresidue and three interglycosidic distances were derived without the use of a specific molecular model. In this case the distances were calculated from the cross-relaxation rates in combination with "model-free" motional parameters previously derived from 13C relaxation measurements. The proton-proton distances for interglycosidic pairs were compared with those averaged from Metropolis Monte Carlo and Langevin Dynamics simulations with the HSEA, PARM22, and CHEAT95 force fields. The crystal structure of the trisaccharide was solved by analysis of X-ray data. Interresidue proton pairs from the crystal structure and those observed by NMR experiments were similar. However, the corresponding proton-proton distances generated by computer simulations were longer. For the (1 --> 2) linkage the glycosidic torsion angles of the crystal structure were found in a region of conformational space populated by all three force fields, whereas for the (1 --> 3) linkage they occupied a region of low population density, as seen from the simulations.

Algorithms↗
PubMed1991

Propagation of parallel fiber volleys in the cerebellar cortex: a computer simulation.

We have studied the dynamic changes occurring during the propagation of active volleys through the parallel fiber (PF) tract in a portion of molecular layer of the cerebellar cortex, by means of a realistic computer simulation of the fibers (random distribution of PF origin; correlation between length and conduction velocity throughout depth). Surface electrical stimulations as well as mossy fiber stimulations of the PFs were mimicked. From a quantitative analysis of the propagation of the different types of volleys it appears that the constraints enforced by the morphological and functional characteristics of the PFs lead to an important spatial and temporal dispersion of the action potentials during their displacement along the folium. In particular, the time relationship between activity in the deep and superficial fibers as well as the number and location of active fibers at a given time (i.e. locus) will considerably vary during propagation. Moreover, in the case of a mossy fiber stimulation, there exists a striking asymmetry of the volleys travelling on each side of the site of stimulation. Therefore any information coded by the conjunctive activation of more than a few parallel fibers will be spatially and temporally dispersed in such a manner that successive postsynaptic Purkinje cells will receive very different combinations of inputs. This seems in favor of the hypothesis that these neurons function as coincidence detectors.

Action Potentials↗
PubMedDate not supplied

Computer simulation of spermine-porin channel interactions.

Porin channels play a prominent role during fluoroquinolone uptake and spermine strongly alters the diffusion rate of norfloxacine. Consequently the interactions between spermine and bacterial porin were studied by computer simulation. The results indicate that various residues (E62, D 113, E 117,...) closely located in the internal eyelet region of the OmpF channel are potential binding sites. Among them, the D 113 residue, seems to play an important role in the association channel-spermine. This interaction introduces several changes in the internal morphology of the channel which are responsible for the inhibition of antibiotic uptake using the porin route.

Binding Sites↗
PubMed1998

Identification of functional and unfolding motions of cutinase as obtained from molecular dynamics computer simulations.

The implementation of cutinase from Fusarium solani pisi as a fat-stain removing ingredient in laundry washing is hampered by its unfolding in the presence of anionic surfactants. In this work we present molecular dynamics (MD) computer simulations on cutinase and analysis procedures to distinguish the movements related to its functional behavior (e.g., substrate binding) from those related to the unfolding of the enzyme. Two kinds of MD-simulations were performed: a simulation mimicking the thermal motion at room temperature, and several simulations in which unfolding is induced either by high temperature or by using a modified water-protein interaction potential. Essential dynamics analyses (A. Amadei et al., Proteins 17:412-425, 1993) on the simulations identify distinct regions in the molecular structure of cutinase in which the motions occur for function and initial unfolding. The unfolding in various simulations starts in a similar way, suggesting that mutations in the regions involved might stabilize the enzyme without affecting its functionality.

Carboxylic Ester Hydrolases↗
PubMedDate not supplied

Recognizing through feeling. A physical and computer simulation based on educational theory.

This article focuses on the educational theory underpinning computer-based simulation in professional education. An innovative computer-based physical simulation to facilitate student learning of assessment and palpation skills in midwifery has been developed to prototype stage and preliminary evaluations conducted. The learning experience explicitly builds on the learning and teaching theory--a "conversational framework"--developed by Laurillard. A template incorporating all the dimensions of the Laurillard framework in the learning experience is presented and discussed. It is argued that this template could have wider application especially in clinically based health science courses. The case-based learning environment allows the students to solve problems and make valid clinical judgments. Throughout the learning experiences, students effectively examine a pregnant woman while interrelating their experiences with the academic knowledge of the teacher (a world of "descriptions"). The structure for learning relies on a mechanism for identifying and addressing the misunderstandings students initially hold. The creation of situations of cognitive conflict in the student's world of action (Laurillard's concept of intrinsic feedback) is seen as central to the learning experience. Finally, the article will canvass the issues faced by a project team designing and developing a technology-based educational package around an educational theory.

Computer Simulation↗
PubMed2002

Application of computer simulation analysis to assess the effects of relocating a hospital phlebotomy department.

BACKGROUND: This study describes a systematic approach to assess the effects of relocating a hospital department. METHODS: Using the phlebotomy service as an example, computer simulation was applied to predict changes in performance indicators, such as patient turn-around time (TAT), when planning a procedural and/or architectural redesign. RESULTS: Average patient TAT fell from 12 to 8 min, enabling the department to cope with any increase in numbers of patients. CONCLUSION: This type of study can provide useful information in assessing the consequences of future changes in the location of a hospital department.

Appointments and Schedules↗
PubMed1992

Computer simulation of metoclopramide block of cardiac sodium channels.

Based on the gate-related receptor hypothesis, a quantitative study on kinetics and state-dependency of metoclopramide (Met) blockade of cardiac sodium channels was performed by computer simulation. The characteristics of Met, a sodium channel blocker modulated simultaneously by both activation and inactivation gates were described and analyzed for the first time. The time constant of recovery from blocking for Met at resting potential -85 mV was 2.82 s, which was increased during depolarization or hyperpolarization. Its apparent rate of onset of blocking was 0.49 AP-1 at a stimulation frequency of 2.0 Hz. A concentration-dependent shift of h infinity curve was found at doses higher than 100 mumol/L Met. This study provides a new test and verification for our gate-related receptor hypothesis.

Anti-Arrhythmia Agents↗
PubMed1979

Computer simulation of flow-dependent absorption in microperfused short Henle's loop of rats.

With computer simulation we examined the extent to which current theories and experimental data explain function of single microperfused superficial Henle's loops in rats. In the model standard phenomenological equations describe transport; two sets of transport parameters labeled rat and rabbit were taken from published experiments; Michaelis-Menten kinetics in the ascending thick limb were adjusted arbitrarily; tubular radius is either constant or depends on luminal pressure with compliance based on experimental observations; the interstitium is an infinite sink with salt and urea concentrations constant in the cortex and exponentially increasing in the outer medulla; concentrations resemble those found in hydropenic or saline diuretic rats. The following predictions were obtained. The model with rabbit parameters does not recirculate urea and will not operate with high medullary urea concentrations; with rat parameters too much urea recirculates an the results of perfusion with equilibrium solution are not reproduced. Using a compromise between rat and rabbit parameters, the model reproduces water absorption, salt reabsorption, and urea recirculation as observed in vivo in rat loops perfused at 5-40 nl/min. It also simulates perfusion with saline, equilibrium solution, saline plus furosemide, and 300 mM mannitol. When the model includes a short early distal segment, effluent salt concentration reaches a minimum at a 15 nl/min perfusion rate as observed in vivo; however, concentration at the macula densa is a monotonically increasing function of flow. When permeation rate is a function of wall surface area and thickness a better fit to experimental results is produced. However, the effect is small: water absorption alters by 4% or less and effluent salt concentration is reduced by up to 10% at low perfusion rates. Comparison of rigid and compliant loops shows no relationship between transit time per se and reabsorption.

Animals↗
PubMed2006

Modeling the sexual transmissibility of human papillomavirus infection using stochastic computer simulation and empirical data from a cohort study of young women in Montreal, Canada.

The authors estimated plausible ranges of the probability of human papillomavirus (HPV) transmission per coital act among newly forming couples by using stochastic computer simulation. Comparative empirical data were obtained in 1996-2001 from a cohort study of female university students in Montreal, Canada. Female prevalence and frequency of sexual intercourse and condom use were set equal to those in the cohort. Simulations included 240 combinations of male prevalence, the relative risk for protected versus unprotected sex, and per-act transmission probabilities. Those that produced expected HPV incidence within the 95% confidence interval observed in the cohort were selected. The observed 6-month cumulative incidence following acquisition of a new partner was 17.0% (95% confidence interval: 11.4, 23.0). Expected incidences consistent with those from cohort findings occurred in 54/240 simulations. The range of per-act transmission probabilities was 5-100% (median, 40%). Male HPV prevalence was the same as or greater than that for women in all consistent simulations. Varying condom effectiveness did not produce better-fitting data. This simulation suggests that HPV transmissibility is several-fold higher than that for other viral sexually transmitted infections such as human immunodeficiency virus or herpes simplex virus 2. With high transmissibility, any potential protective effect of condoms would disappear over multiple intercourse acts, underlining the need for an effective HPV vaccine.

Adult↗
PubMed1998

Pulsatile flow computational simulations of mitral regurgitation.

The noninvasive quantification of mitral regurgitation remains an important clinical goal. Recently, the flow convergence method was developed to estimate the regurgitant flow rate. This study used three-dimensional pulsatile flow computational simulations to evaluate the accuracy of the flow convergence method in the presence of complicating factors such as ventricular confinement, noncircular orifice shape, and the presence of aortic outflow. Results showed that in the absence of aortic outflow and ventricular confinement, there was a plateau zone where the calculated flow rate by the hemispheric formula approximated the true flow rate, independent of the orifice shape. In the presence of aortic outflow and in chambers of physiologic dimensions, there was no longer a clear zone where the hemispheric formula was valid. The hemi-elliptic modification of the flow convergence method worked in all cases, independent of the degree of ventricular confinement or the presence of aortic outflow. Therefore, application of the hemi-elliptic formula should be considered in future clinical studies.

Aorta↗
PubMed1976

Implications of fertility patterns in the Republic of Korea: a study by computer simulation.

Implications of various fertility patterns in the Republic of Korea (ROK) are studied by computer simulation. These patterns include the factors: age of marriage, sex preference, abortion (induced), contraception and sterilisation. As a result of studying a large number of combinations of these factors, the following tentative conclusions, among others, are reached. If future cohorts of women in the ROK become limiters after two live births and marry according to an observed high level marriage distribution, at least two of the methods of birth control--abortion, contraception, and sterilisation--will have to be used extensively to yield a mean number of live births (MNLB) in these cohorts of the order 2-2. However, if these women marry later than the observed high level marriage distribution and, in addition, accept effective methods of contraception more widely and use them more effectively, then the MNLB experienced by these cohorts could move below 2-5 wihtout the extensive utilisation of abortion and sterilisation.

Abortion, Induced↗
PubMed1991

Diagnosis of a computer-simulated podiatric patient.

The authors discuss the use of computers in medicine. A patient presenting with a condition requiring surgery is represented by a data file in a computer program. The user obtains data from the file by selecting items from a menu. Data are presented on the screen in pop-up windows. By examining the data and making judgments, the user may determine the pathology and make first a provisional and then a definitive diagnosis.

Computer Simulation↗
PubMed1984

Optimal pacemaker sensing with respect to amplitude and slew rate of intracardiac electrograms: theoretical analysis by computer simulation.

The optimal amplitude and slew rate of intracardiac electrograms for pacemaker sensing were examined on a theoretical basis by computer simulation. The simulation was based on the concept that it is the voltage at the position of the pacing electrode in an electrical field of a moving electrical dipole. By changing the distance between the electrode and the myocardium and the moving velocity of the electrical dipole, simulated ECGs with arbitrary amplitudes and slew rates were generated by the computer and fed to a bandpass filter. This filter was equivalent to those assembled in some models of permanent pacemakers and had a center pass-band frequency of 50 Hz and a Q of 1.0. The outputs of the filter were measured. The results showed that, for pacemakers sensing, simulated intracardiac electrograms with high amplitude should have high slew rates and those with low amplitudes should have low slew rates, although the absolute values depend on the characteristics of the bandpass filter and the sensing threshold of the pacemaker.

Computers↗
PubMed2001

Lutropin receptor function: insights from natural, engineered, and computer-simulated mutations.

The lutropin receptor is a member of the superfamily of G protein-coupled receptors and, in humans, binds two closely related ligands, members of the heterodimer glycoprotein hormone family. As reviewed herein, comparative analyses of natural, engineered, and computer-simulated mutations of the lutropin receptor have provided considerable insight into the molecular basis of receptor function.

Amino Acid Sequence↗
PubMed1982

Histamine as a ligand in blood plasma. Part 5. Computer simulated distribution of metal histamine complexes in normal blood plasma and discussion of the implications of a possible role of zinc and copper in histamine catabolism.

Previously physiological experiments carried out on mice have proved that copper and zinc can interfere with the pharmacological effects of histamine that lead to anaphylactic shock. A quantitative study of the interactions between essential metal ions and histamine in plasma was thus undertaken. The progressive approach towards a reliable computer-simulated distribution of the histamine-containing plasma species necessitated a large series of physicochemical determinations of the formation constants of the binary and ternary metal complexes involved. The present paper deals with the determination of the formation constants in the zinc-serine, zinc-histamine-serine, zinc-histamine-lysine, copper-serine, copper-histamine-serine, and copper-histamine-valine systems, which were still necessary to reach the reliable simulation required. The subsequent final distribution of histamine in plasma has thus been computed, and interpreted in terms of a possible role for zinc in assisting the histamine catabolism process. Further computer calculations simulating the increase of the zinc concentration in human blood plasma support this interpretation. The antagonizing role of copper against that of zinc has also been examined.

Animals↗