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PubMed2004

[Simulation--an efficient way of learning in graduate and continuous medical education].

BACKGROUND: Different types of simulators and simulated situations are being used in the training of doctors. Even though simulation as a learning method has been used in various areas such as aviation and oil industry, it has only recently been applied to medical education. Simulation seems to be very well suited in training for and building skills and experience with life threatening situation that are seldom seen. It represents no risk to the patient and it opens up for training in realistic scenarios. METHODS: Simulations are illustrated by using Miller's learning pyramid and Bloom's cognitive levels to show how different types of simulation can be used depending on the skills that are to be acquired. Team simulation is seen as a main factor for quality improvement in medicine. INTERPRETATION: Simulation and team simulation in particular is highly rated by participating professionals. There seems to be a problem in finding objective criteria for assessing the simulated scenarios and then to generalise the findings to real situations.

Clinical Competence↗
PubMed1997

A decision analytic method for scoring performance on computer-based patient simulations.

As computer based clinical case simulations become increasingly popular for training and evaluating clinicians, approaches are needed to evaluate a trainee's or examinee's solution of the simulated cases. We developed a decision analytic approach to scoring performance on computerized patient case simulations. We developed decision models for computerized patient case simulations in four specific domains in the field of infectious disease. The decision models were represented as influence diagrams. A single decision node represents the possible diagnoses the user may make. One chance node represents a probability distribution over the set of competing diagnoses in the simulations. The value node contains the utilities associated with all possible combinations of diagnosis and disease. All relevant data that the user may request from the simulation are represented as chance nodes with arcs to or from the diagnosis node and/or each other. Probabilities in the decision model were derived from the literature, where available, or expert opinion. Utilities were assessed by standard gamble from clinical experts. The process of solving computer based patient simulations involves repeated cycles of requesting data (history, physical examination or laboratory) and receiving these data from the simulations. Each time the user requests clinical data from the simulation, the influence diagram is evaluated with and without an arc from the corresponding chance node to the decision node. The difference in expected utility between the two solutions of the influence diagram represents the expected value of information (VOI) from the requested clinical datum. The ratio of the expected VOI from the data requested and the expected value of perfect information about the diagnosis is a normative measure of the quality of each of the user's data requests. This approach provides a continuous measure of the quality of the user's data requests in a way that is sensitive to the previous data collected. The score distinguishes serious from minor misdiagnoses. And the same influence diagram can be used to evaluate performance on multiple simulations in the same clinical domain.

Computer Simulation↗
PubMed1993

Molecular dynamics simulations of poly(dA).poly(dT): comparisons between implicit and explicit solvent representations.

The program AMBER 3.0 has been used to generate molecular dynamics trajectories of a poly(dA).poly(dT) decamer. The simulations were performed using different methods to treat solvent effects. Results of a simulation including 18 counterions NH4+ and 4109 water molecules under (N, P, T) conditions were compared to simulation runs with implicit solvent representation in which solvent screening effects were represented by the use of a sigmoidal distance-dependent dielectric function. In the latter case, the system was simulated under microcanonical (N, V, E) and canonical (N, V, T) conditions. For the fully hydrated system simulation, a preequilibration protocol was developed since it was observed that long and progressive periods of heating and equilibration on the overall system were necessary in order to avoid energetic collisions between the solute and the solvent molecules, leading to severe irreversible deformation of the solute. A detailed analysis of DNA conformations, sugar puckers, and stability of the hydrogen bonds, Watson-Crick and three-center H bonds, is reported. The results show that DNA remains essentially in the B conformer with a tendency in the hydrated model to adopt a slightly distorted, unwound, and stretched conformation in comparison to standard B-DNA. Concerning sugar puckers, the mean pseudorotation phases of the adenine residues are systematically higher than those of the thymine residues, except in the case of the hydrated model for which a articular behavior is observed for the adenine strand. In this case, the terminal bases oscillate between C2'-endo and O4'-endo and the central ones stay in the C3'-endo domain. The mean lifetimes of the internal Watson-Crick H-bond (A) HN6...O4(T) are also dependent on the base pairs included in the calculation, excepted for the implicit solvent simulation at constant temperature. The three-center H bonds have very small mean lifetimes in all three cases of MD simulation. In the minor groove of the hydrated model, a spine of hydration is found as observed by x-ray crystallography and other theoretical simulations. On the basis of the rms deviations, it appears that the fully hydrated simulation has not reached a plateau at the end of the run, while the implicit simulation at constant energy seems to have converged. At constant temperature, very large oscillations in rms deviations are observed.

Base Sequence↗
PubMed1991

A computer management system for patient simulations.

A series of interactive videodisc patient simulations is being used to teach clinical problem-solving skills, including diagnosis and management, to dental students. This series is called Oral Disease Simulations for Diagnosis and Management (ODSDM). A computer management system has been developed in response to the following needs. First, the sequence in which students perform simulations is critical. Second, maintaining records of completed simulations and student performance on each simulation is a time-consuming task for faculty. Third, the simulations require ongoing evaluation to ensure high quality instruction. The primary objective of the management system is to ensure that each student masters diagnosis. Mastery must be obtained at a specific level before advancing to the next level. The management system does this by individualizing the sequence of the simulations to adapt to the needs of each student. The management system generates reports which provide information about students or the simulations. Student reports contain demographic and performance information. System reports include information about individual patient simulations and act as a quality control mechanism for the simulations.

Computer Simulation↗
PubMed2006

Simulation of mammographic lesions.

RATIONALE AND OBJECTIVES: This study presents a method for generating breast masses and microcalcifications in mammography via simulation. This simulation method allows for the creation of large image datasets with particular lesions, which may serve as a useful tool for perception studies measuring imaging system performance. MATERIALS AND METHODS: The study first characterized the radiographic appearance of both masses and microcalcifications, examining the following five properties: contrast, edge gradient profile of masses, edge characteristics of masses, shapes of individual microcalcifications, and shapes of microcalcification distributions. The characterization results then guided the development of routines that created simulated masses and microcalcifications. The quality of the simulations was verified by experienced breast imaging radiologists who evaluated simulated and real lesions and rated whether a given lesion had a realistic appearance. RESULTS: The radiologists rated real and simulated lesions to have similarly realistic appearances. Using receiver operating characteristic analysis to characterize the degree of similarity, the results showed an A(z) of 0.68 +/- 0.07 for benign masses, 0.65 +/- 0.07 for malignant masses, and 0.62 +/- 0.07 for microcalcifications, thus showing notable overlap in the simulated and real lesion ratings. CONCLUSION: This research introduced a new approach for simulating breast masses and microcalcifications that relied on anatomic characteristics measured from real lesions. Results from an observer performance experiment indicate that our simulation routine produced realistic simulations of masses and microcalcifications as judged by expert radiologists.

Breast Diseases↗
PubMed2006

Learning curves and reliability measures for virtual reality simulation in the performance assessment of carotid angiography.

OBJECTIVES: Improvement in performance as measured by metric-based procedural errors must be demonstrated if virtual reality (VR) simulation is to be used as a valid means of proficiency assessment and improvement in procedural-based medical skills. BACKGROUND: The Food and Drug Administration requires completion of VR simulation training for physicians learning to perform carotid stenting. METHODS: Interventional cardiologists (n = 20) participating in the Emory NeuroAnatomy Carotid Training program underwent an instructional course on carotid angiography and then performed five serial simulated carotid angiograms on the Vascular Interventional System Trainer (VIST) VR simulator (Mentice AB, Gothenburg, Sweden). Of the subjects, 90% completed the full assessment. Procedure time (PT), fluoroscopy time (FT), contrast volume, and composite catheter handling errors (CE) were recorded by the simulator. RESULTS: An improvement was noted in PT, contrast volume, FT, and CE when comparing the subjects' first and last simulations (all p < 0.05). The internal consistency of the VIST VR simulator as assessed with standardized coefficient alpha was high (range 0.81 to 0.93), except for FT (alpha = 0.36). Test-retest reliability was high for CE (r = 0.9, p = 0.0001). CONCLUSIONS: A learning curve with improved performance was demonstrated on the VIST simulator. This study represents the largest collection of such data to date in carotid VR simulation and is the first report to establish the internal consistency of the VIST simulator and its test-retest reliability across several metrics. These metrics are fundamental benchmarks in the validation of any measurement device. Composite catheter handling errors represent measurable dynamic metrics with high test-retest reliability that are required for the high-stakes assessment of procedural skills.

Cardiology↗
PubMed2005

The SIMRI project: a versatile and interactive MRI simulator.

This paper gives an overview of SIMRI, a new 3D MRI simulator based on the Bloch equation. This simulator proposes an efficient management of the T2* effect, and in a unique simulator integrates most of the simulation features that are offered in different simulators. It takes into account the main static field value and enables realistic simulations of the chemical shift artifact, including off-resonance phenomena. It also simulates the artifacts linked to the static field inhomogeneity like those induced by susceptibility variation within an object. It is implemented in the C language and the MRI sequence programming is done using high level C functions with a simple programming interface. To manage large simulations, the magnetization kernel is implemented in a parallelized way that enables simulation on PC grid architecture. Furthermore, this simulator includes a 1D interactive interface for pedagogic purpose illustrating the magnetization vector motion as well as the MRI contrasts.

Algorithms↗
PubMed2002

Alumina-alumina artificial hip joints. Part II: characterisation of the wear debris from in vitro hip joint simulations.

Until recently it was not possible to reproduce clinically relevant wear rates and wear patterns in in vitro hip joint simulators for alumina ceramic-on-ceramic hip prostheses. The introduction of microseparation of the prosthesis components into in vitro wear simulations produced clinically relevant wear rates and wear patterns for the first time. The aim of this study was to characterise the wear particles generated from standard simulator testing and microseparation simulator testing of hot isostatically pressed (HIPed) and non-HIPed alumina ceramic-on-ceramic hip prostheses, and compare these particles to those generated in vivo. Standard simulation conditions produced wear rates of approximately 0.1 mm3 per million cycles for both material types. No change in surface roughness was detected and very few wear features were observed. In contrast, when microseparation was introduced into the wear simulation, wear rates of between 1.24 (HIPed) and 1.74 mm3 per million cycles (non-HIPed) were produced. Surface roughness increased and a wear stripe often observed clinically on retrieved femoral heads was also reproduced. Under standard simulation conditions only nanometre-sized wear particles (2-27.5 nm) were observed by TEM, and it was thought likely that these particles resulted from relief polishing of the alumina ceramic. However, when microseparation of the prosthesis components was introduced into the simulation, a bi-modal distribution of particle sizes was observed. The nanometre-sized particles produced by relief polishing were present (1-35nm). however, larger micrometre-sized particles were also observed by both transmission electron microscopy (TEM) (0.021 microm) and scanning electron microscopy (SEM) (0.05-->10 microm). These larger particles were thought to originate from the wear stripe and were produced by trans-granular fracture of the alumina ceramic. In Part I of this study, alumina ceramic wear particles were isolated from the periprosthetic tissues from around Mittelmeier ceramic-on-ceramic hip prostheses. Characterisation of the particles by TEM and SEM revealed a bi-modal size distribution. SEM analysis revealed particles in the 0.05-3.2 microm size range. and TEM revealed particles in the 5-90 nm size range, indicating that microseparation of the prosthesis components may be a common event in vivo. This study (Part II) has revealed that the introduction of microseparation of the prosthesis components during the swing phase of the wear simulation reproduced clinically relevant wear rates, wear patterns and wear particles in in vitro hip joint simulators.

Aluminum Oxide↗
PubMed1999

[Anesthesia simulators: benefits and limits of experience gained at several European university hospitals].

Simulation has become essential in all situations where reality was too risky, too expensive, difficult to manage or inaccessible. In anaesthesia, the low rate of accidents and incidents, as well as the necessity to assure patient's safety, limit education and training in crisis management. The progress in data processing allowed the development of realistic anaesthesia simulators, associating the usual environment of an operating room, and made possible the simulation of a wide range of events. Most clinical incidents, mishaps, or manipulation errors can be simulated. A video recording allows the focus of attention on human factors. We assessed simulators in three European University hospitals. In Brussels as in Leiden, simulation was mainly used for training in crisis management. In Basel, the complete operating room staff participated in sessions, including also surgical simulation and improvement of communication within the team was one of the main goals. Simulation is valuable for residents' training, as well as continuing medical education, in crisis management and a better understanding of human factors. It remains without risk for the patient, with video possibilities improving the repetition of selected cases. However, its use for evaluation seems to be premature, due to the absence of studies demonstrating the validity and reproducibility of the results gained with simulation. Beyond technical limits which are amended continuously, the development of simulation is hindered by the very high cost of equipment and instructors.

Anesthesia↗
PubMed2005

Using simulation-based training to improve patient safety: what does it take?

BACKGROUND: Through simulations health care workers can learn by practicing skills taught and experiencing mistakes before interacting with an actual patient. A number of areas within the health care industry are currently using simulation-based training to help individuals and teams improve patient safety. WHAT IS SIMULATION-BASED TRAINING? The key components of simulation-based training are as follows: performance history/skill inventory, tasks/competencies, training objectives, events/exercises, measures/metrics, performance diagnosis, and feedback and debrief. WHAT DOES IT TAKE FOR SIMULATION-BASED TRAINING TO BE EFFECTIVE? To be effective, simulation-based training must be implemented appropriately. The guidelines are as follows: understand the training needs and requirements; instructional features, such as performance measurement and feedback, must be embedded within the simulation; craft scenarios based on guidance from the learning outcomes; create opportunities for assessing and diagnosing individual and/or team performance within the simulation; guide the learning; focus on cognitive/psychological simulation fidelity; form a mutual partnership between subject matter experts and learning experts; and ensure that the training program worked. CONCLUSION: The health care community can gain significantly from using simulation-based training to reduce errors and improve patient safety when it is designed and delivered appropriately.

Guidelines as Topic↗
PubMed2006

Investigation of finite system-size effects in molecular dynamics simulations of lipid bilayers.

In the absence of external stress, the surface tension of a lipid membrane vanishes at equilibrium, and the membrane exhibits long wavelength undulations that can be described as elastic (as opposed to tension-dominated) deformations. These long wavelength fluctuations are generally suppressed in molecular dynamics simulations of membranes, which have typically been carried out on membrane patches with areas <100 nm2 that are replicated by periodic boundary conditions. As a result, finite system-size effects in molecular dynamics simulations of lipid bilayers have been subject to much discussion in the membrane simulation community for several years, and it has been argued that it is necessary to simulate small membrane patches under tension to properly model the tension-free state of macroscopic membranes. Recent hardware and software advances have made it possible to simulate larger, all-atom systems allowing us to directly address the question of whether the relatively small size of current membrane simulations affects their physical characteristics compared to real macroscopic bilayer systems. In this work, system-size effects on the structure of a DOPC bilayer at 5.4 H2O/lipid are investigated by performing molecular dynamics simulations at constant temperature and isotropic pressure (i.e., vanishing surface tension) of small and large single bilayer patches (72 and 288 lipids, respectively), as well as an explicitly multilamellar system consisting of a stack of five 72-lipid bilayers, all replicated in three dimensions by using periodic boundary conditions. The simulation results are compared to X-ray and neutron diffraction data by using a model-free, reciprocal space approach developed recently in our laboratories. Our analysis demonstrates that finite-size effects are negligible in simulations of DOPC bilayers at low hydration, and suggests that refinements are needed in the simulation force fields.

Computer Simulation↗
PubMed2005

Use of a virtual reality, real-time, simulation model for the training of urologists in transurethral resection of the prostate.

OBJECTIVE: There is a growing need to develop surgical skills outside the operating theatre. In this study we describe the development of a virtual reality training system for practising transurethral resection of the prostate (TURP). MATERIAL AND METHODS: A face validity study was performed using a questionnaire sent to 28 experienced urologists to find out the ideal characteristics of a simulated TURP. Based on the comments a simulator was constructed and a content validity study was then performed in which nine experienced urologists tested the simulator and answered a second questionnaire. After corrections to the simulator, a basic construct validity test was performed. RESULTS: We have developed a computer-based simulator based on the requirements listed by 17 urologists. It consists of a modified resectoscope connected to a haptic device and supported by a frame. The software provides a virtual view of the prostatic lumen and resectoscope tip, a haptic rendering that generates force feedback and a simulation module that computes the information from the haptic device, resectoscope fluid tap and handle and the foot pedals. The software also simulates bleeding, absorption of irrigation fluid and pressure gradients. Variables are measured and presented in a result file after each "operation". Nine experienced urologists performed a content validity study and changes were made accordingly. A basic construct validity test performed by seven inexperienced students showed a significant improvement in performance after they each performed six simulated procedures. CONCLUSION: We have developed a simulator that may be used to practise TURP and which meets most of the demands raised in a face validity study. A basic construct validity test showed improved performance after repeated practice in the simulated environment.

Computer Simulation↗
PubMed2001

A method of simulating dynamic multileaf collimators using Monte Carlo techniques for intensity-modulated radiation therapy.

A method of modelling the dynamic motion of multileaf collimators (MLCs) for intensity-modulated radiation therapy (IMRT) was developed and implemented into the Monte Carlo simulation. The simulation of the dynamic MLCs (DMLCs) was based on randomizing leaf positions during a simulation so that the number of particle histories being simulated for each possible leaf position was proportional to the monitor units delivered to that position. This approach was incorporated into an EGS4 Monte Carlo program, and was evaluated in simulating the DMLCs for Varian accelerators (Varian Medical Systems, Palo Alto. CA, USA). The MU index of each segment, which was specified in the DMLC-control data, was used to compute the cumulative probability distribution function (CPDF) for the leaf positions. This CPDF was then used to sample the leaf positions during a real-time simulation, which allowed for either the step-shoot or sweeping-leaf motion in the beam delivery. Dose intensity maps for IMRT fields were computed using the above Monte Carlo method, with its accuracy verified by film measurements. The DMLC simulation improved the operational efficiency by eliminating the need to simulate multiple segments individually. More importantly, the dynamic motion of the leaves could be simulated more faithfully by using the above leaf-position sampling technique in the Monte Carlo simulation.

Biophysical Phenomena↗
PubMed2004

Hybrid simulation of cellular behavior.

MOTIVATION: To be valuable to biological or biomedical research, in silico methods must be scaled to complex pathways and large numbers of interacting molecular species. The correct method for performing such simulations, discrete event simulation by Monte Carlo generation, is computationally costly for large complex systems. Approximation of molecular behavior by continuous models fails to capture stochastic behavior that is essential to many biological phenomena. RESULTS: We present a novel approach to building hybrid simulations in which some processes are simulated discretely, while other processes are handled in a continuous simulation by differential equations. This approach preserves the stochastic behavior of cellular pathways, yet enables scaling to large populations of molecules. We present an algorithm for synchronizing data in a hybrid simulation and discuss the trade-offs in such simulation. We have implemented the hybrid simulation algorithm and have validated it by simulating the statistical behavior of the well-known lambda phage switch. Hybrid simulation provides a new method for exploring the sources and nature of stochastic behavior in cells.

Algorithms↗
PubMed1994

The Leiden anaesthesia simulator.

We describe an anaesthesia simulator capable of simulating all possible situations during anaesthesia. The Leiden anaesthesia simulator (LAS) may be used with most commercially available anaesthesia equipment and monitors, which are connected to the simulated patient as they are to a patient. A commercially available intubation manikin attached to an electromechanical lung model represents the patient. The lung allows both spontaneous and mechanical ventilation. Compliance, resistance, tidal volume and ventilatory frequency may be altered by a controlling computer. Carbon dioxide production and oxygen uptake are simulated. Physiological signals (ECG, arterial, pulmonary arterial and central venous pressure waveforms) generated by a signal generator under software control provide input to the monitors. All types of ECG disturbances may be simulated. There are facilities for simulating non-invasive arterial pressure measurement and pulse oximetry. A series of physiological models is being developed to control interactions between the cardiovascular and respiratory variables. During a simulation session, a pre-defined scenario is presented to the trainee. The task of the trainee is to diagnose and treat the problem as if in real life. The simulator experiences on the LAS were judged as highly realistic by 28 subjects. This simulator is currently being used for teaching and training of anaesthetists, trainees and anaesthesia personnel and for research.

Anesthesiology↗
PubMed2002

An evaluation of a virtual reality airway simulator.

UNLABELLED: In this research, we sought to test the hypothesis that the AccuTouch Flexible Bronchoscopy Simulator (Simulator) is an effective way to teach clinicians the psychomotor skills necessary to use the fiberoptic bronchoscope as an instrument for intubating the trachea of a pediatric patient. Pediatric residents with no prior experience in fiberoptic bronchoscopy were studied. Residents performed fiberoptic intubation on children undergoing general anesthesia. Tapes of these intubations were analyzed for: time to visualization of the carina, and number and time that the bronchoscope tip hit the mucosa. Residents were then trained on the Simulator. Performance of fiberoptic intubation on a subsequent child was compared. Training on the Simulator was the only instruction that the residents received between the two cases. A control group of residents performed two consecutive intubations without training on the Simulator between cases. Residents studied an average of 17 cases, and spent 39 min on the Simulator. Performance was markedly improved after the Simulator. Time to completion of successful intubation with a bronchoscope was reduced from 5.15 to 0.88 min (P < 0.001). The number of times that the tip of the bronchoscope hit the mucosa was reduced from 21.4 to 3.0 (P < 0.001). The amount of time that the resident spent viewing the mucosa decreased from 2.24 to 0.19 min (P < 0.001). The percent of time viewing the channel of the airway increased from 58.5% to 80.4% (P = 0.004). This bronchoscopy simulator was very effective in teaching residents the psychomotor skills necessary for fiberoptic intubation. Significant improvement was seen in time to completion of endotracheal intubation, as well as other performance indicators. IMPLICATIONS: This research showed that the AccuTouch Bronchoscopy Simulator is an effective way to teach the psychomotor skills necessary to intubate the trachea of patients using a fiberoptic bronchoscope. The residents that practiced on the Simulator dramatically improved their skills compared with a control group of residents.

Anesthesia↗
PubMed2007

Computer modeling of patient flow in a pediatric emergency department using discrete event simulation.

UNLABELLED: Increasing patient census and department overcrowding are universal concerns in pediatric emergency medicine. Accurate predictions of patient flow and resource utilization in the pediatric emergency department (PED) are important in determining what aspects of PED activity could be modified to improve patient flow, reduce patient waiting times, and increase staff efficiency and morale, and thus direct change more effectively. BACKGROUND: We report (1) the construction of a Patient Flow Model (PFM) using discrete event simulation to test simulated PED staffing scenarios that were designed to alleviate the pressures that result from increased census and overcrowding, and (2) a Physician Scheduling Analysis Tool to assist in physician scheduling. METHODS: Arena discrete event simulation modeling software was used to develop a model of PED patient flow after extensive interviews with PED staff and direct observation of patient flow in July 2005. A total of 517 patients were directly observed, and all modeled aspects of their interaction with PED staff and resources were recorded. Historical demographic patient arrival information was combined with observed patient flow data to provide simulated patient arrival rates for the PFM and was also used to construct the Physician Scheduling Analysis Tool. Validation of the PFM was performed by comparing annual simulated patient flow data with actual patient flow data. Previously determined staffing scenarios were applied to the simulation and the resulting performance indicator outputs examined. RESULTS: The PFM was validated on model-wide and process-specific levels, with excellent validation observed on high acuity-patient length of stay and for highly detailed processes such as triage and registration. Simulation of the addition of a hospital volunteer and a second triage nurse demonstrated reductions in pretriage waiting time and the proportion of patients waiting longer than 30 or 60 minutes for pretriage. Simulation of an extra physician shift to the staff schedule demonstrated reductions in length of stay for patients of all triage categories. CONCLUSIONS: The PFM accurately represents patient flow through the department and can provide simulated patient flow information on a variety of scenarios. It can effectively simulate changes to the model and its effects on patient flow.

Appointments and Schedules↗
PubMed2001

Numerical simulation of mechanical mitral heart valve closure.

A computational fluid dynamic simulation of a mechanical heart valve closing dynamics in the mitral position was performed in order to delineate the fluid induced stresses in the closing phase. The pressure and shear stress fields in the clearance region and near the inflow (atrial) side of the valve were computed during the mitral heart valve closure. Three separate numerical simulations were performed. The atrial chamber pressure was assumed to be zero in all the simulations. The first simulation was steady flow through a closed mitral valve with a ventricular pressure of 100 mm Hg (1.3 kPa). In the second simulation, the leaflet remained in the closed position while the ventricular pressure increased from 0 to 100 mm Hg at a rate of 2000 mm Hg/s (simulating leaflet closure by gravity before the ventricular pressure rise - gravity closure). In the third case, the leaflet motion from the fully open position to the fully closed position was simulated for the same ventricular pressure rise (simulating the normal closure of the mechanical valve). Normal closure (including leaflet motion towards closure, and sudden stop in the closed position) resulted in a relatively large negative pressure transient which was not present in the gravity closure simulation. The wall shear stresses near the housing and the leaflet edge close to the inflow side were around 4000 Pa with normal closure compared to about 725 Pa with gravity closure. The large negative pressure transients and significant increase in wall shear stresses due to the simulation of normal closure of the mechanical valve is consistent with the previously reported increased blood damage during the closing phase.

Biomedical Engineering↗