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PubMed2005

Simulated hand-assisted laparoscopic surgery (HALS) in microgravity.

INTRODUCTION: Previous simulation and porcine experiments aboard the reduced gravity program KC-135 turbojet have demonstrated that microgravity surgery is feasible. Ideally, surgical care in spaceflight will incorporate recent advances in care while remaining easy enough for a crew medical officer (CMO) lacking surgical proficiency or extensive surgical experience to perform. As a minimally invasive surgical technique, hand-assisted laparoscopic surgery (HALS) benefits the patient via smaller incisions, less pain, and faster recovery than traditional open surgery. HALS also helps less experienced laparoscopic surgeons perform laparoscopic surgery. METHODS: An inexpensive inanimate surgical simulator was constructed to evaluate the usefulness of HALS in microgravity. This simulator was utilized during brief periods of microgravity provided by parabolic flight on the KC-135. The simulator was successfully used by both a physician-astronaut and an experienced laparoscopic surgeon. Task completion included simulated surgery with exploration of the intestines and ligation of the appendix. RESULTS: Simulated HALS was successfully performed in microgravity. HALS effectively contained operative equipment and small amounts of introduced fluids within the simulated abdominal cavity. Astronaut and surgeon experience suggest that HALS could facilitate minimally invasive surgery (MIS) in microgravity. DISCUSSION: HALS holds promise as a surgical approach in microgravity, particularly as space travel extends beyond low earth orbit. HALS provides the benefits of MIS, facilitates MIS surgery by less surgically proficient or experienced CMOs, and contains equipment and fluid within the operative field. Simulation provides an easy, cost-effective platform to evaluate medical technology for space flight as well as a method to train CMOs on-orbit.

Appendix↗
PubMed2002

An investigation of air inlet velocity in simulating the dispersion of indoor contaminants via computational fluid dynamics.

Computational fluid dynamics (CFD) is potentially a valuable tool for simulating the dispersion of air contaminants in workrooms. However, CFD-estimated airflow and contaminant concentration patterns have not always shown good agreement with experimental results. Thus, understanding the factors affecting the accuracy of such simulations is critical for their successful application in occupational hygiene. The purposes of this study were to validate CFD approaches for simulating the dispersion of gases and vapors in an enclosed space at two air flow rates and to demonstrate the impact of one important determinant of simulation accuracy. The concentration of a tracer gas, isobutylene, was measured at 117 points in a rectangular chamber [1 (L) x 0.3 (H) x 0.7 m (W)] using a photoionization analyzer. Chamber air flow rates were scaled using geometric and kinematic similarity criteria to represent a full-sized room at two Reynolds numbers (Re = 5 x 10(2) and 5 x 10(3)). Also, CFD simulations were conducted to estimate tracer gas concentrations throughout the chamber. The simulation results for two treatments of air inlet velocity (profiled inlet velocity measured in traverses across the air inlet and the assumption that air velocity is uniform across the inlet) were compared with experimental observations. The CFD-simulated 3-dimensional distribution of tracer gas concentration using the profiled inlet velocity showed better agreement qualitatively and quantitatively with measured chamber concentration, while the concentration estimated using the uniform inlet velocity showed poor agreement for both comparisons. For estimating room air contaminant concentrations when inlet velocities can be determined, this study suggests that using the inlet velocity distribution to define inlet boundary conditions for CFD simulations can provide more reliable estimates. When the inlet velocity distribution is not known, for instance for prospective design of dilution ventilation systems, the trials of several velocity profiles with different source, air inlet and air outlet locations may be useful for determining the most efficient workroom layout.

Air Movements↗
PubMed2002

Evaluating functional network inference using simulations of complex biological systems.

MOTIVATION: Although many network inference algorithms have been presented in the bioinformatics literature, no suitable approach has been formulated for evaluating their effectiveness at recovering models of complex biological systems from limited data. To overcome this limitation, we propose an approach to evaluate network inference algorithms according to their ability to recover a complex functional network from biologically reasonable simulated data. RESULTS: We designed a simulator to generate data representing a complex biological system at multiple levels of organization: behaviour, neural anatomy, brain electrophysiology, and gene expression of songbirds. About 90% of the simulated variables are unregulated by other variables in the system and are included simply as distracters. We sampled the simulated data at intervals as one would sample from a biological system in practice, and then used the sampled data to evaluate the effectiveness of an algorithm we developed for functional network inference. We found that our algorithm is highly effective at recovering the functional network structure of the simulated system-including the irrelevance of unregulated variables-from sampled data alone. To assess the reproducibility of these results, we tested our inference algorithm on 50 separately simulated sets of data and it consistently recovered almost perfectly the complex functional network structure underlying the simulated data. To our knowledge, this is the first approach for evaluating the effectiveness of functional network inference algorithms at recovering models from limited data. Our simulation approach also enables researchers a priori to design experiments and data-collection protocols that are amenable to functional network inference.

Adaptation, Physiological↗
PubMed2001

The investigation of the effects of counterions in protein dynamics simulations.

Molecular simulations able to exactly represent solvated charged proteins are helpful in understanding protein dynamics, structure and function. In the present study we have used two different starting structures of papain (a typical, stable, globular protein of intermediate net charge) and different modeling procedures to evaluate some effects of counterions in simulations. A number of configurations have been generated and relaxed for each system by various combinations of constrained simulated annealing and molecular dynamics procedures, using the AMBER force field. The analysis of trajectories shows that the simulations of solvated proteins are moderately sensitive to the presence of counterions. However, this sensitivity is highly dependent on the starting model and different procedures of equilibration used. The neutralized systems tend to evince smaller root mean square deviations regardless of the system investigated and the simulation procedure used. The results of parameterized fitting of the simulated structures to the crystallographic data, giving quantitative measure of the total charge influence on the stability of various elements of the secondary structure, revealed a clear scatter of different reactions of various systems' secondary structures to counterions addition: some systems apparently were stabilized when neutralized, while the others were not. Thus, one cannot unequivocally state, despite consideration of specific simulation conditions, whether protein secondary structures are more stable when they have neutralized charges. This suggests that caution should be taken when claiming the stabilizing effect of counterions in simulations other than those involving small, unstable polypeptides or highly charged proteins.

Computer Simulation↗
PubMed2005

Evaluating clinical simulations for learning procedural skills: a theory-based approach.

Simulation-based learning is becoming widely established within medical education. It offers obvious benefits to novices learning invasive procedural skills, especially in a climate of decreasing clinical exposure. However, simulations are often accepted uncritically, with undue emphasis being placed on technological sophistication at the expense of theory-based design. The author proposes four key areas that underpin simulation-based learning, and summarizes the theoretical grounding for each. These are (1) gaining technical proficiency (psychomotor skills and learning theory, the importance of repeated practice and regular reinforcement), (2) the place of expert assistance (a Vygotskian interpretation of tutor support, where assistance is tailored to each learner's needs), (3) learning within a professional context (situated learning and contemporary apprenticeship theory), and (4) the affective component of learning (the effect of emotion on learning). The author then offers four criteria for critically evaluating new or existing simulations, based on the theoretical framework outlined above. These are: (1) Simulations should allow for sustained, deliberate practice within a safe environment, ensuring that recently-acquired skills are consolidated within a defined curriculum which assures regular reinforcement; (2) simulations should provide access to expert tutors when appropriate, ensuring that such support fades when no longer needed; (3) simulations should map onto real-life clinical experience, ensuring that learning supports the experience gained within communities of actual practice; and (4) simulation-based learning environments should provide a supportive, motivational, and learner-centered milieu which is conducive to learning.

Computer Simulation↗
PubMed2002

Impact of the endoscopic sinus surgical simulator on operating room performance.

OBJECTIVES/HYPOTHESIS: The aim of this study is to evaluate an endoscopic sinus surgical simulator (ESS) as a training device and to introduce a methodology to assess its impact on actual operating room performance. STUDY DESIGN: Prospective evaluation of the endoscopic sinus surgical simulator as a trainer. METHODS: Ten junior and senior ear, nose and throat residents served as subjects, some of whom had prior training with the simulator. The evaluation team collected several measures, which were analyzed for a statistical correlation, including simulator scores, operating room performance rating, ratings of videotaped operating room procedures, and surgical competency rating. RESULTS: These findings suggest the ESS simulator positively affects initial operating room performance across all measures as judged by senior surgeons rating anonymous videotapes of those procedures. The two simulation-trained residents were rated consistently better than the other two residents across all measures. These differences approached statistical significance for two items: anterior ethmoidectomy (P =.06; P <.05) and surgical confidence (P =.09; P <.05). In addition, the 3 subjects with the highest overall scores on the competency evaluation also had 3 of the 4 highest cumulative simulation times. CONCLUSIONS: The endoscopic sinus surgical simulator is a valid training device and appears to positively impact operating room performance among junior otolaryngology residents.

Clinical Competence↗
PubMed2006

Simulation improves resident performance in catheter-based intervention: results of a randomized, controlled study.

OBJECTIVES: Surgical simulation has been shown to enhance the training of general surgery residents. Since catheter-based techniques have become an important part of the vascular surgeon's armamentarium, we explored whether simulation might impact the acquisition of catheter skills by surgical residents. METHODS: Twenty general surgery residents received didactic training in the techniques of catheter intervention. Residents were then randomized with 10 receiving additional training with the Procedicus, computer-based, haptic simulator. All 20 residents then participated in 2 consecutive mentored catheter-based interventions for lower extremity occlusive disease in an OR/angiography suite. Resident performance was graded by attending surgeons blinded to the resident's training status, using 18 procedural steps as well as a global rating scale. RESULTS: There were no differences between the 2 resident groups with regard to demographics or scores on a visuospatial test administered at study outset. Overall, residents exposed to simulation scored higher than controls during the first angio/OR intervention: procedural steps (simulation/control) (50 +/- 6 vs. 33 +/- 9, P = 0.0015); global rating scale (30 +/- 7 vs. 19 +/- 5, P = 0.0052). The advantage provided by simulator training persisted with the second intervention (53 +/- 6 vs. 36 +/- 7, P = 0.0006); global rating scale (33 +/- 6 vs. 21 +/- 6, P = 0.0015). Moreover, simulation training, particularly for the second intervention, led to enhancement in almost all of the individual measures of performance. CONCLUSION: Simulation is a valid tool for instructing surgical residents and fellows in basic endovascular techniques and should be incorporated into surgical training programs. Moreover, simulators may also benefit the large number of vascular surgeons who seek retraining in catheter-based intervention.

Angiography↗
PubMed2004

A generalized framework for interactive dynamic simulation for MultiRigid bodies.

This paper presents a generalized framework for dynamic simulation realized in a prototype simulator called the Interactive Generalized Motion Simulator (I-GMS), which can simulate motions of multirigid-body systems with contact interaction in virtual environments. I-GMS is designed to meet two important goals: generality and interactivity. By generality, we mean a dynamic simulator which can easily support various systems of rigid bodies, ranging from a single free-flying rigid object to complex linkages such as those needed for robotic systems or human body simulation. To provide this generality, we have developed I-GMS in an object-oriented framework. The user interactivity is supported through a haptic interface for articulated bodies, introducing interactive dynamic simulation schemes. This user-interaction is achieved by performing push and pull operations via the PHANToM haptic device, which runs as an integrated part of I-GMS. Also, a hybrid scheme was used for simulating internal contacts (between bodies in the multirigid-body system) in the presence of friction, which could avoid the nonexistent solution problem often faced when solving contact problems with Coulomb friction. In our hybrid scheme, two impulse-based methods are exploited so that different methods are applied adaptively, depending on whether the current contact situation is characterized as "bouncing" or "steady." We demonstrate the user-interaction capability of I-GMS through on-line editing of trajectories of a 6-degree of freedom (dof) articulated structure.

Algorithms↗
PubMed1994

Simulated patients in assessing consultation skills of trainees in general practice vocational training: a validity study.

Although simulated patients are increasingly used in medical education, little research has been carried out on their validity. Validity in this case defines the relationship between performance with a simulated patient and performance with a real patient. One of the objectives of this study was to determine the validity of the use of simulated patients in assessing the consultation skills of trainees in vocational training at the Department of General Practice, University of Utrecht, The Netherlands. A check-list with a rating scale was used to assess the consultation skills of trainees at the department with simulated patients as well as in their training practices with real patients. The simulated and the selected practice cases were patients with complex multi-conditional problems like low back pain, headache and chest pain. The consultation skills were subdivided into four groups: the patient-centered approach, the non-somatic approach, communication skills and interpersonal skills. The measurement of skills, in particular of consultation skills, is very difficult. A description is given of the way the research group solved this problem. The analysis was performed by determining the sensitivity and predictive value of the assessment of a simulated encounter with a routine practice encounter. A difference existed in the assessed level of consultation skills in the simulated encounter compared to the level in the training practice. In simulation the level of consultation skills was higher than in day-to-day practice. This difference can reflect the difference between competence and performance. Competence is defined as what a doctor is capable of doing and performance as what a doctor actually does in day-to-day practice.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical Competence↗
PubMed2006

The history of simulation in medical education and possible future directions.

INTRODUCTION: Clinical simulation is on the point of having a significant impact on health care education across professional boundaries and in both the undergraduate and postgraduate arenas. SCOPE OF SIMULATION: The use of simulation spans a spectrum of sophistication, from the simple reproduction of isolated body parts through to complex human interactions portrayed by simulated patients or high-fidelity human patient simulators replicating whole body appearance and variable physiological parameters. GROWTH OF SIMULATION: After a prolonged gestation, recent advances have made available affordable technologies that permit the reproduction of clinical events with sufficient fidelity to permit the engagement of learners in a realistic and meaningful way. At the same time, reforms in undergraduate and postgraduate education, combined with political and societal pressures, have promoted a safety-conscious culture where simulation provides a means of risk-free learning in complex, critical or rare situations. Furthermore, the importance of team-based and interprofessional approaches to learning and health care can be promoted. CONCLUSION: However, at the present time the quantity and quality of research in this area of medical education is limited. Such research is needed to enable educators to justify the cost and effort involved in simulation and to confirm the benefit of this mode of learning in terms of the outcomes achieved through this process.

Education, Medical↗
PubMed1992

On the interpretation of biochemical data by molecular dynamics computer simulation.

The application of computer simulation to molecular systems of biochemical interest is reviewed. It is shown that computer simulation is a tool complementary to experimental methods, which can be used to access atomic details inaccessible to experimental probes. Examples are given in which computer simulation augments the experimental information by providing an atomic picture of high resolution with respect to space, energy or time. The usefulness of a computer simulation largely depends on its quality. The most important factors that limit the accuracy of simulated results are discussed. The accuracy of different simulation studies can differ by orders of magnitude. The accuracy will depend on the type of biomolecular system and process studied. It will also depend on the choice of force field, the simulation set-up and the protocol that is used. A list of quality-determining factors is given, which may be useful when interpreting simulation studies appearing in the literature.

Biochemical Phenomena↗
PubMed2001

A microstructural finite element simulation of mechanically induced bone formation.

A finite element method to simulate the formation of an interconnected trabectular bone microstructure oriented with respect to applied in vivo mechanical forces is introduced and quantitatively compared to experimental data from a hydraulic bone chamber implant model. Randomly located 45 microm mineralized nodules were used as the initial condition for the model simulations to represent an early stage of intramembranous bone formation. Boundary conditions were applied consistent with the mechanical environment provided by the in vivo bone chamber model. A two-dimensional repair simulation algorithim that incorporated strain energy density (SED), SED gradient, principal strain, or principal strain gradient as the local objective criterion was utilized to simulate the formation of an oriented trabecular bone microstructure. The simulation solutions were convergent, unique, and relatively insensitive to the assumed initial distribution of mineralized nodules. Model predictions of trabecular bone morphology and anisotropy were quantitatively compared to experimental results. All simulations produced structures that qualitatively resembled oriented trabecular bone. However only simulations utilizing a gradient objective criterion yielded results quantitatively similar to in vivo observations. This simulation approach coupled with an experimental model that delivers controlled in vivo mechanical stimuli can be utilized to study the relationship between physical factors and microstructural adaptation during bone repair.

Animals↗
PubMed2006

Assessment of a new multileaf collimator concept using GEANT4 Monte Carlo simulations.

The aim of the work was to investigate in advance the dosimetric properties of a new multileaf collimator (MLC) concept with the help of Monte Carlo (MC) simulations prior to the production of a prototype. The geometrical design of the MLC was implemented in the MC code GEANT4. For the simulation of a 6 MV treatment beam, an experimentally validated phase space and a virtual spatial Gaussian-shaped model placed in the origin were used. For the simulation of the geometry in GEANT4, the jaws and the two leaf packages were implemented with the help of computer-aided design data. First, transmission values for different tungsten alloys were extracted using the simulation codes GEANT4 and BEAMnrc and compared to experimental measurements. In a second step, high-resolution simulations were performed to detect the leakage at depth of maximum dose. The 20%-80% penumbra along the travel direction of the leaves was determined using 10 x 10 cm2 fields shifted along the x- and y-axis. The simulated results were compared with measured data. The simulation of the transmission values for different tungsten alloys showed a good agreement with the experimental measurements (within 2.0%). This enabled an accurate estimation of the attenuation coefficient for the various leaf materials. Simulations with varying width of the spatial Gaussian distribution showed that the leakage and the penumbra depend very much on this parameter: for instance, for widths of 2 and 4 mm, the interleaf leakage is below 0.3% and 0.75%, respectively. The results for the leakage and the penumbra (4.7+/-0.5 mm) are in good agreement with the measurements. This study showed that GEANT4 is appropriate for the investigation of the dosimetric properties of a multileaf collimator. In particular, a quantification of the leakage, the penumbra, and the tongue-and-groove effect and an evaluation of the influence of the beam parameters such as the width of the Gaussian distribution was possible.

Body Burden↗
PubMedDate not supplied

The cost-effectiveness of screening programs using single and multiple birth cohort simulations: a comparison using a model of cervical cancer.

Despite early recognition of the theoretical advantages of simulations that include different population subgroups/ strata and different birth cohorts, many modeling-based economic evaluations of cervical screening have been based on unrealistic single birth cohort simulations. The authors examined the effect of a multiple birth cohort simulation on the incremental cost-effectiveness estimates of cervical screening programs, compared to a conventional single cohort simulation. The choice of hypothetical cohort that starts the simulation had a major impact on the cost-effectiveness estimates: Compared with a single birth cohort simulation, the incremental cost-effectiveness of a shift from biennial to triennial screening was 30% higher when using the multiple cohort simulation. Multiple cohort simulations using the different age structures of 4 countries had little impact on the cost effectiveness ratios (variation <5%). Future modeling-based evaluations of screening policies should better reflect the age range of the population that is targeted by carefully specifying the nature of the starting cohort(s).

Adult↗
PubMed2005

Simulation-based education for cardiac, thoracic, and vascular anesthesiology.

Simulation has been used for medical teaching and testing for at least four decades in some form, such as that used for cardiopulmonary resuscitation training; however, new technology applied to medical and procedural training has recently led to a marked increase in the use of simulation-based instruction. Educational theory has further supported simulation for medical education and procedural training. Simulation-based testing to demonstrate competence with new procedures is already required by the US Food and Drug Administration for one angiographically-placed device, and it is likely that simulation-based credentialing for procedures will be increasingly prevalent. Anesthesiologists, like other physicians, may be credentialed or certified based on their performance in a simulated environment in the future. This review describes some of the current simulation-based education techniques related to cardiovascular and thoracic anesthesiology. Additional discussion covers some of the applicable educational theory and the expected future uses of simulation modalities in healthcare education, testing, and practice.

Anesthesia↗
PubMed2005

Hybrid dynamic/static method for large-scale simulation of metabolism.

BACKGROUND: Many computer studies have employed either dynamic simulation or metabolic flux analysis (MFA) to predict the behaviour of biochemical pathways. Dynamic simulation determines the time evolution of pathway properties in response to environmental changes, whereas MFA provides only a snapshot of pathway properties within a particular set of environmental conditions. However, owing to the large amount of kinetic data required for dynamic simulation, MFA, which requires less information, has been used to manipulate large-scale pathways to determine metabolic outcomes. RESULTS: Here we describe a simulation method based on cooperation between kinetics-based dynamic models and MFA-based static models. This hybrid method enables quasi-dynamic simulations of large-scale metabolic pathways, while drastically reducing the number of kinetics assays needed for dynamic simulations. The dynamic behaviour of metabolic pathways predicted by our method is almost identical to that determined by dynamic kinetic simulation. CONCLUSION: The discrepancies between the dynamic and the hybrid models were sufficiently small to prove that an MFA-based static module is capable of performing dynamic simulations as accurately as kinetic models. Our hybrid method reduces the number of biochemical experiments required for dynamic models of large-scale metabolic pathways by replacing suitable enzyme reactions with a static module.

Animals↗
PubMedDate not supplied

Development and validation of assessment measures for a newly developed physical examination simulator.

OBJECTIVE: Define, extract and evaluate potential performance indicators from computer-generated data collected during simulated clinical female pelvic examinations. DESIGN: Qualitative and quantitative study analyzing computer generated simulator data and written clinical assessments collected from medical students who performed physical examinations on three clinically different pelvic simulators. SETTING: Introduction to patient care course at a major United States medical school. PARTICIPANTS: Seventy-three pre-clinical medical students performed 219 simulated pelvic examinations and generated 219 written clinical assessments. MEASUREMENTS: Cronbach's alpha for the newly defined performance indicators, Pearson's correlation of performance indicators with scored written clinical assessments of simulator findings. RESULTS: Four novel performance indicators were defined: time to perform a complete examination, number of critical areas touched during the exam, the maximum pressure used, and the frequency at which these areas were touched. The reliability coefficients (alpha) were time = 0.7240, critical areas = 0.6329, maximum pressure = 0.7701, and frequency = 0.5011. Of the four indicators, three correlated positively and significantly with the written clinical assessment scores: critical areas, p < 0.01; frequency, p < 0.05; and maximum pressure, p < 0.05. CONCLUSION: This study demonstrates a novel method of analyzing raw numerical data generated from a newly developed patient simulator; deriving performance indicators from computer generated simulator data; and assessing validity of those indicators by comparing them with written assessment scores. Results show the new assessment measures provide an objective, reliable, and valid method of assessing students' physical examination techniques on the pelvic exam simulator.

Clinical Competence↗
PubMed2003

The use of advanced simulation in the training of anesthesiologists to treat chemical warfare casualties.

UNLABELLED: Training anesthesiologists to treat nerve gas intoxication in a mass casualty scenario is a complicated task. The scenario is an unfamiliar medical situation involving the need to decontaminate patients before providing definitive medical treatment, and the need for physical protection to the medical team before decontamination. We describe the development of a simulation-based training program. In one site of a virtual hospital, anesthesiologists were trained in initial airway and breathing resuscitation before decontamination while wearing full protective gear. In another site, they were trained in the treatment of critically-ill patients with combined conventional and chemical injuries or severe intoxication. Intubation simulators of newborn, pediatric, and adult patients, advanced full-scale simulators, and actors simulating patients were used. Initial airway, breathing, and antidotal treatment were performed successfully, with or without full protective gear. The gas mask did not interfere with orotracheal intubation, but limited effective communication within the medical team. Chemical protective gloves were the limiting factor in the performance of medical tasks such as fixing the orotracheal tube. Twenty-two participants (88%) pointed out that the simulated cases represented realistic problems in this scenario, and all 25 participants found the simulated-based training superior to previous traditional training they had in this field. Using advanced simulation, we were able to train anesthesiologists to treat nerve gas intoxication casualties and to learn about the limitations of providing medical care in this setting. IMPLICATIONS: Advanced medical simulation can be used to train anesthesiologists to treat nonconventional warfare casualties. The limitations of medical performance in full protective gear can be learned from this training.

Anesthesiology↗