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The human face of simulation: patient-focused simulation training.

Simulation is firmly established within health care training but often focuses on training for technical tasks and can overlook crucial skills such as professionalism and physician-patient communication. The authors locate this paper within current developments in health care and relate it to the literature on simulation. They make the case for placing real human "patients" (played by actors) within simulation environments, thereby ensuring that the training experience remains rooted in actual practice. By practicing repeatedly within a safe environment, technical skills, communication with patients and team members, decision making, and clinical judgment may all be practiced and mastered while preserving patient safety. In elaborating this concept of patient-focused simulation (PFS), the authors draw on work already published by their group and several recent studies that are in review. These explore PFS in low, medium, and high complexity settings. Important or rare situations can be recreated and practiced, as well as key procedures required across a range of experience levels and clinical specialties. Finally, the case is made for curriculum redesign to ensure that simulator-based technical skills training and assessment take place within an authentic context that reflects the wider elements of clinical practice.

Computer Simulation↗

The impact of simulation on people who act as simulated patients: a focus group study.

OBJECTIVE: Previous studies have shown that people who act as simulated patients (SPs) experience negative effects caused by performing patient roles. This study was performed to further explore the impact of simulation and the factors that might affect this impact. The aim was to find ways of preventing negative effects of simulation impacting on our SPs. METHODS: Focus groups interviews were conducted among 35 SPs at Skillslab, University of Maastricht. The discussion was guided by 6 pre-established items. RESULTS: The majority of the SPs appeared to experience negative effects of performing a patient role. The effects were considered as inherent to acting as an SP or due to simulation being a strenuous activity. The impact was short-lived and did not affect SPs' enjoyment of their work. Factors that appeared to affect the impact of performing included: the type of role (whether it is emotionally complex or not); the number of consecutive performances; the length of time between performances; the giving of feedback; the amount of experience, and students. DISCUSSION: Although the SPs were found to experience negative effects caused by playing patient roles, the frequency and intensity of the negative effects were minor. The focus group discussions led to various suggestions for measures to reduce the impact of simulation.

Attitude to Health↗

Simulating dynamic activities using a five-axis knee simulator.

This work describes the design and capabilities of the Purdue Knee Simulator: Mark II and a sagittal-plane model of the machine. This five-axis simulator was designed and constructed to simulate dynamic loading activities on either cadaveric knee specimens or total knee prostheses mounted on fixtures. The purpose of the machine was to provide a consistent, realistic loading of the knee joint, allowing the kinematics and specific loading of the structures of the knee to be determined based on condition, articular geometry, and simulated activity. The sagittal-plane model of the knee simulator was developed both to predict the loading at the knee from arbitrary inputs and to generate the necessary inputs required to duplicate specified joint loading. Measured tibio-femoral compressive force and quadriceps tension were shown to be in good agreement with the predicted loads from the model. A controlled moment about the ankle-flexion axis was also shown to change the loading on the quadriceps.

Arthroplasty, Replacement, Knee↗

An MR compatible flow simulator for intravascular pressure simulation.

An MR compatible flow simulator is described which generates physiologically realistic pressure and flow waveforms. The simulator is based on a servomotor-driven gear pump which produces pulsatile flow by modulation of the servomotor rotation rate. Operation of the simulator is under the control of a personal computer, which executes an iterative feedback loop to minimize errors between measured and desired pressure waveforms. The simulator is totally automatic, requiring only a few minutes of iteration to generate the desired pressure waveform. Accurate sinusoidal waveforms with frequencies up to 10 Hz have been generated using the simulator, with high-frequency contamination of the measured waveform at least 80 dB below the fundamental frequency. Aortic waveforms have been produced with realistic flow rates and pressure variations. The pump assembly is mechanically straightforward and can operate at an 8-m distance from the flow phantom to allow the device to be isolated from the MR magnet room.

Biophysical Phenomena↗

Optimization of a stochastically simulated gene network model via simulated annealing.

By rearranging naturally occurring genetic components, gene networks can be created that display novel functions. When designing these networks, the kinetic parameters describing DNA/protein binding are of great importance, as these parameters strongly influence the behavior of the resulting gene network. This article presents an optimization method based on simulated annealing to locate combinations of kinetic parameters that produce a desired behavior in a genetic network. Since gene expression is an inherently stochastic process, the simulation component of simulated annealing optimization is conducted using an accurate multiscale simulation algorithm to calculate an ensemble of network trajectories at each iteration of the simulated annealing algorithm. Using the three-gene repressilator of Elowitz and Leibler as an example, we show that gene network optimizations can be conducted using a mechanistically realistic model integrated stochastically. The repressilator is optimized to give oscillations of an arbitrary specified period. These optimized designs may then provide a starting-point for the selection of genetic components needed to realize an in vivo system.

Algorithms↗

Simulating individual cow milk yield for milking parlor simulation models.

A method of simulating individual cow milk yield per milking as a function of herd milk yield and month was formulated for milking parlor simulation models. Milk yield per milking was modeled for each month in three herd milk yield categories: 8165, 8845, and 9525 kg/yr of milk per cow. Actual individual cow DHIA test day milk weight data for three Florida dairy herds in each herd milk yield category and month were adjusted to the mean of their respective actual milk shipped per cow on test day then pooled and converted to a basis of three times per day milk yield per milking. After minor truncation, Weibull probability distributions fitted to these data sets adequately modeled milk yield per milking per cow. Analysis of simulation results for milk yield per milking per cow indicated no significant differences between actual and simulated means for any herd milk yield category or month. Simulations of monthly and yearly total herd milk yield for each herd indicated that fitted Weibull distributions also adequately modeled monthly and yearly herd milk yield characteristics and reflected seasonal herd milk yield patterns typical of Florida.

Animals↗

Simulator sickness in the U.S. Army UH-60A Blackhawk flight simulator.

Realistic training in aviation now includes the use of sophisticated flight simulators which can provide near total perception of aircraft flight. Reports of simulator sickness seem to be increasing in simulators with multi-directional motion, computer-generated imagery, and infinity optics. A voluntary, subjective, symptom-oriented questionnaire was completed by 141 pilots after training in the UH-60A 2B38 Blackhawk flight simulator. Thirty-six percent reported positive symptoms of motion sickness. Pilots may be at risk if they fly too soon after simulator training and a mandatory grounding time is advised.

Computer Simulation↗

Interactive simulation training: computer simulated standardized patients for medical diagnosis.

SIMmersion LLC is a software development company that creates human interactive training simulations. SIMmersion produces PC-based simulations of people with whom trainees are able to hold conversations. Trainees communicate with simulated characters in face-to-face conversations, using voice recognition technology. Topics that would match well with SIMmersion's simulation capabilities include diagnosis of depression, alcoholism, or drug use, grievance counseling, marriage counseling, suicide intervention, and first responder training for biological terrorism. SIMmersion's technology could be integrated with modeling technology to create a speech-interactive, mannequin-based patient simulation system for healthcare training and assessment. Systems currently being developed involve early detection of smallpox as a result of a biological attack.

Computer Simulation↗

Pharmacokinetic-pharmacodynamic modelling and simulation using the electrical circuit simulation program SPICE2.

The use of the electrical circuit simulation program SPICE2 for performing digital computer simulations of linear and non-linear pharmacokinetic-pharmacodynamic models is described. SPICE2 utilizes the principles of network thermodynamics (thermodynamics of electrical circuits). These principles dictate analogy between the conservation laws of chemical reactions and mass transport and Kirchhoff's laws of current and voltage balance, and also prove that Fick's law of diffusion is isomorphous with the conductance form of Ohm's law. Detailed descriptions of program inputs, formats, and options for simulation of linear and non-linear pharmacokinetic-pharmacodynamic systems are provided, with appropriate examples. Single as well as multiple dose simulations (accumulation kinetics and dynamics) are discussed. The advantages of SPICE2 over other available simulation packages, including user-friendliness, ease of operation, versatility, power, and the economy of time and effort afforded, are emphasized. The educational value of SPICE2 as a highly versatile tool for teaching both fundamental and complex pharmacokinetic-pharmacodynamic concepts, as well as its routine usage in elucidating complex research problems, are also discussed.

Cimetidine↗

Psychophysiological evaluation of simulator sickness evoked by a graphic simulator.

The present study investigated the effects of simulator sickness, as an important bias factor on evaluation of emotional changes under the controlled condition of driving a car for 60 min at a constant speed (60 km/h) in a graphic simulator. Simulator sickness was measured and analyzed every 5 min using both subjective evaluation and physiological signals. Results of the subjective evaluation showed there was a significant difference between the rest and the driving conditions 10 min after the main experiment started and that the level of difference increased linearly with time. Analysis of the central and the autonomic nervous systems showed the significant differences in delta, theta, alpha and beta bands of an electroencephalogram (EEG), skin temperature, and the R-R interval between the rest and the driving conditions after about 5 min from the start of driving. In particular, there was the highest correlation between parameter of theta and subjective evaluation, and thus theta was considered an effective physiological parameter for numerically evaluating simulator sickness. The results indicate that physiological changes due to simulator sickness can be a bias factor in evaluation of human sensibility.

Adult↗

Migration from plasticized poly(vinyl chloride) into fatty media: importance of simulant selectivity for the choice of volatile fatty simulants.

An investigation was carried out to determine whether isooctane and ethanol behave like sunflower oil as fatty simulants for overall and for specific migration from PVC containing aromatic plasticizers (bis-2-ethylhexyl phthalate and tris-2-ethylhexyl trimellitate). In these films, the partition coefficients of migrants between simulant and polymer play a major role. The affinities of isooctane and of sunflower oil to all migrants were similar and isooctane can be considered as an alternative fatty simulant for plastized PVC. In contrast ethanol displays a different selectivity, and is not an adequate fatty simulant. Guidelines for the selection of solvents to be used as fatty simulants for migration testing are discussed. The scope of spectroscopic methods (FTIR and 1H-NMR) to monitor migration of aromatic plasticizers is presented.

Diethylhexyl Phthalate↗

Simulated annealing with restrained molecular dynamics using a flexible restraint potential: theory and evaluation with simulated NMR constraints.

A new functional representation of NMR-derived distance constraints, the flexible restraint potential, has been implemented in the program CONGEN (Bruccoleri RE, Karplus M, 1987, Biopolymers 26:137-168) for molecular structure generation. In addition, flat-bottomed restraint potentials for representing dihedral angle and vicinal scalar coupling constraints have been introduced into CONGEN. An effective simulated annealing (SA) protocol that combines both weight annealing and temperature annealing is described. Calculations have been performed using ideal simulated NMR constraints, in order to evaluate the use of restrained molecular dynamics (MD) with these target functions as implemented in CONGEN. In this benchmark study, internuclear distance, dihedral angle, and vicinal coupling constant constraints were calculated from the energy-minimized X-ray crystal structure of the 46-amino acid polypeptide crambin (ICRN). Three-dimensional structures of crambin that satisfy these simulated NMR constraints were generated using restrained MD and SA. Polypeptide structures with extended backbone and side-chain conformations were used as starting conformations. Dynamical annealing calculations using extended starting conformations and assignments of initial velocities taken randomly from a Maxwellian distribution were found to adequately sample the conformational space consistent with the constraints. These calculations also show that loosened internuclear constraints can allow molecules to overcome local minima in the search for a global minimum with respect to both the NMR-derived constraints and conformational energy. This protocol and the modified version of the CONGEN program described here are shown to be reliable and robust, and are applicable generally for protein structure determination by dynamical simulated annealing using NMR data.

Computer Simulation↗

Simulation of micropopulations in epidemiology: tutorial 1. Simulation: an introduction. A series of tutorials illustrated by coronary heart disease models.

This is the first in a series of tutorials concerning the simulation of micropopulation models for use in epidemiological research. The series emphasizes the techniques that are in use at the National Micropopulation Simulation Resource at the University of Minnesota. This initial series of tutorials uses chronic disease models, specifically coronary heart disease models, to illustrate the principles and methodologies employed. The series is intended for persons having some familiarity with electronic, digital computation and desiring to know more about a specific class of simulations, namely those that apply Monte Carlo techniques in the simulation of micropopulation models as a part of biomedical research. It is the author's hope that these tutorials will be particularly useful for students in medical informatics; they could also be of interest to professionals in both the computational and the biomedical sciences.

Chronic Disease↗

Application of the primary hydration shell approach to locally enhanced sampling simulated annealing: computer simulation of thyrotropin-releasing hormone in water.

A unified model of simulated annealing with locally enhanced sampling (LES) in a primary hydration shell (PHS) aqueous environment is developed and tested by predicting the structure of the tripeptide thyrotropin-releasing hormone (TRH) in solution. The model extends the formulation of the restraining force in the PHS method as a function of temperature, number of copies in the LES method, and shell thickness. The dependence of the restraining force on temperature can be shown to follow the relationship c(1)T - c(2), which can be derived from the expression for kinetic energy in molecular dynamics simulations. The calibration of the restraining force for different simulation conditions reveals the dependence of c(1) and c(2) on the number of copies in the LES method and the thickness of the PHS. The predicted structure of TRH is in very good agreement with results from NMR experiments and from a 10-ns PHS simulation at 300 K. The method promises to be useful in predicting structure of peptides and proteins in an aqueous environment.

Calibration↗

Coarse-grain parallel computing for very large scale neural simulations in the NEXUS simulation environment.

We describe a neural simulator designed for simulating very large scale models of cortical architectures. This simulator, NEXUS, uses coarse-grain parallel computing by distributing computation and data onto multiple conventional workstations connected via a local area network. Coarse-grain parallel computing offers natural advantages in simulating functionally segregated neural processes. We partition a complete model into modules with locally dense connections--a module may represent a cortical area, column, layer, or functional entity. Asynchronous data communications among workstations are established through the Network File System, which, together with the implicit modularity, decreases communications overhead, and increases overall performance. Coarse-grain parallelism also benefits from the standardization of conventional workstations and LAN, including portability between generations and vendors.

Computer Communication Networks↗

Molecular dynamics simulations of phospholipid bilayers: Influence of artificial periodicity, system size, and simulation time.

This article investigates the convergence of structural and dynamical properties with system size and with time in molecular dynamics simulations of solvated phospholipid bilayers performed at constant volume under periodic boundary conditions using lattice-sum electrostatics. The electron density profile across the bilayer, the carbon-deuterium order parameters, and the surface tension are shown to be converged for a bilayer containing 36 lipids per leaflet and simulated over a period of 3-4 ns. Reasonable estimates for these properties can already be obtained from a system containing 16 lipids per leaflet. The convergence limit of 36 lipids per leaflet and the investigation of the correlation between lipid headgroup dipoles suggest a correlation length of about 3-5 nm in the lateral directions for a hydrated DPPC bilayer in the liquid-crystalline phase. Although these (relatively small) system sizes and (relatively short) time scales appear sufficient to obtain converged collective structural properties at constant volume, two restrictions should be kept in mind: (i) the relaxation times associated with the motion of individual lipids may be much longer and (ii) simulated properties converge significantly faster under constant volume conditions as compared to constant pressure conditions. Therefore, an accurate assessment of the dynamical properties of the system or of the relaxation of the bilayer under constant pressure conditions may require longer simulation time scales.

Computer Simulation↗

Unobtrusive vehicle motion prediction cues reduced simulator sickness during passive travel in a driving simulator.

This study investigated cues that permit prediction of turns during passive movement through a virtual environment. Effects on simulator sickness (SS), presence and enjoyment were examined. Subjects were exposed to complex visual motion through a cartoon-like simulated environment in a driving simulator. Forward velocity remained constant and the motion path was the same across all experimental conditions. Using a within-subject design, we examined visual paths that provided different levels of cue salience - detailed, simplified and no cues - for the upcoming simulated vehicle motion. Following each trial, participants completed questionnaires on SS, presence and enjoyment. After all of the trials were completed, a debriefing determined participants' perceptions of vehicle motion attributes and their awareness of the prediction cues. The results showed that SS in the no-cue condition was significantly greater than that in the conditions that provided vehicle motion cues. Presence and enjoyment responses were not different across the conditions. No participants reported differences between prediction cue conditions or recognized that the vehicle motion followed the same path across trials. However, participants tended to report that the motion was smoother for the detailed-cue than the no-cue condition. Participants ranked turn predictability as higher in conditions with prediction cues. The results support the hypothesis that unobtrusive and unreported motion cues may alleviate SS in a virtual environment.

Adolescent↗

Monte Carlo simulation of light-tissue interaction: three-dimensional simulation for trans-illumination-based imaging of skin lesions.

Three-dimensional, voxel-based, and wavelength-dependent skin lesion models are developed and simulated using Monte Carlo techniques. The optical geometry of the Nevoscope with trans-illumination is used in the simulations for characterizing the lesion thickness. Based on the correlation analysis between the lesion thickness and the diffuse reflectance, optical wavelengths are selected for multispectral imaging of skin lesions using the Nevoscope. Tissue optical properties reported by various researchers are compiled together to form a voxel library. Tissue models used in the simulations are developed using the voxel library which offers flexibility in updating the optical properties and adding new media types into the models independent of the Monte Carlo simulation code.

Algorithms↗