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PubMed2001

Object-oriented modeling of patients in a medical federation.

This research explores the development of an object-oriented model to support inter-operation of simulations within a federation for the purpose of conducting medical analysis and training over a distributed infrastructure. The medical federation is referred to as the combat trauma patient simulation system and is composed using high level architecture. The infrastructure contains components that were separately developed and are heterogeneous in nature. This includes a general anatomical computer database capable of generating human injuries, referred to as operational requirements-based casualty assessment, an animated mannequin called the human patient simulator, and other components. The research develops an object model that enables bodily injury data to be shared across the simulation, conducts analysis on that data, and considers possible applications of the technique in expanded medical infrastructures.

Computer Communication Networks↗

PubMed1998

Neural network modeling of developmental effects in discrimination shifts.

This paper presents neural network simulations of developmental phenomena in discrimination shifts. The discrimination shift literature is reviewed in order to identify the empirical regularities. Leading theoretical accounts of the development of shift learning are reviewed, and the lack of a thorough account is highlighted. Recent unsuccessful neural network simulations of shift learning are also reviewed. New simulations, using the cascade-correlation algorithm, show that networks can capture the regularities of the discrimination shift literature better than existing psychological theories. Manipulation of the amount of training that networks receive, which affects depth of learning, simulates developmental phenomena. It is suggested that human developmental differences in shift learning arise from spontaneous overtraining by older participants, an interpretation consistent with the overtraining literature.

Adult↗

PubMed1981

Effects of training on response latency and accuracy for a difficult visual discrimination.

The learning of a difficult discrimination task was investigated in a laboratory simulation of a quality control task. In an earlier experiment, observers were trained to discriminate between 2 brief, masked stimulus patterns. Then, a trained and an untrained group of observers were tested on the same stimulus-discrimination task. Response latency as well as P(Dis) were measured in a forced-choice reaction time paradigm. Untrained observers responded with a mean probability of correct discrimination, P(Dis), = .65 for stimuli with 30-msec. duration and mean P(Dis) greater than or equal to .90 those stimuli with 100-msec. duration. Trained observers produced discrimination scores of P(Dis) greater than or equal to .90 for all stimulus durations tested. Despite this large, reliable training effect of P(Dis), response latencies did not differ reliably between the two groups but instead were a negative function of stimulus duration for both trained and untrained observers.

Discrimination Learning↗

PubMed1996

Teaching Surgical Hysteroscopy with a Computer

Using a hysteroscope can be simulated on a computer. It will improve physician training by measuring basic knowledge and abilities, allow different interventions and anatomic variations, minimize the trauma of surgical intervention, and reduce operative casualties. An integrated questionnaire covers instrumentation, fluid infusion, power source, indications and preparation for endometrial ablation, surgical techniques, and complications to evaluate the user's knowledge. The operation simulation then proceeds. In the endometrial cavity, by virtual simulation, the operating field should appear in real time to allow physicians to adapt the trajectory of the instruments. The computer is an IBM PC compatible. We use a modified joystick with optical encoders to know the instrument position. The simulation can be repeated as desired. An evaluation system is integrated in the software to keep the user informed on the amount of burn area(s) that have been completed. This prototype model is available.

Journal Article↗

PubMed1993

Identification of reentry circuit sites during catheter mapping and radiofrequency ablation of ventricular tachycardia late after myocardial infarction.

BACKGROUND: Ventricular tachycardia reentry circuits in chronic infarct scars can contain slow conduction zones, which are difficult to distinguish from bystander areas adjacent to the circuit during catheter mapping. This study developed criteria for identifying reentry circuit sites using computer simulations. These criteria then were tested during catheter mapping in humans to predict sites at which radiofrequency current application terminated ventricular tachycardia. METHODS AND RESULTS: In computer simulations, effects of single stimuli and stimulus trains at sites in and adjacent to reentry circuits were analyzed. Entrainment with concealed fusion, defined as ventricular tachycardia entrainment with no change in QRS morphology, could occur during stimulation in reentry circuit common pathways and adjacent bystander sites. Pacing at reentry circuit common pathway sites, the stimulus to QRS (S-QRS) interval equals the electrogram to QRS interval (EG-QRS) during tachycardia. The postpacing interval from the last stimulus to the following electrogram equals the tachycardia cycle length. Pacing at bystander sites the S-QRS exceeds the EG-QRS interval when the conduction time from the bystander site to the circuit is short but may be less than or equal to the EG-QRS interval when the conduction time to the circuit is long. The postpacing interval, however, always exceeds the tachycardia cycle length. When conduction in the circuit slows during pacing, the S-QRS and postpacing intervals increase and the slowest stimulus train most closely reflects conduction times during tachycardia. Endocardial catheter mapping and radiofrequency ablation were performed during 31 monomorphic ventricular tachycardias in 15 patients with drug refractory ventricular tachycardia late after myocardial infarction. During ventricular tachycardia, trains of electrical stimuli or scanning single stimuli were evaluated before application of radiofrequency current at the same site. Radiofrequency current terminated ventricular tachycardia at 24 of 241 sites (10%) in 12 of 15 patients (80%). Ventricular tachycardia termination occurred more frequently at sites with entrainment with concealed fusion (odds ratio, 3.4; 95% confidence interval [CI], 1.4 to 8.3), a postpacing interval approximating the ventricular tachycardia cycle length (odds ratio, 4.6; 95% CI, 1.6 to 12.9) and an S-QRS interval during entrainment of more than 60 milliseconds and less than 70% of the ventricular tachycardia cycle length (odds ratio, 4.9; 95% CI, 1.4 to 17.1). Ventricular tachycardia termination was also predicted by the presence of isolated diastolic potentials or continuous electrical activity (odds ratio, 5.2; 95% CI, 1.8 to 15.5), but these electrograms were infrequent (8% of all sites). Combinations of entrainment with concealed fusion, postpacing interval, S-QRS intervals, and isolated diastolic potentials or continuous electrical activity predicted a more than 35% incidence of ventricular tachycardia termination during radiofrequency current application versus a 4% incidence when none suggested that the site was in the reentry circuit. Analysis of the postpacing interval and S-QRS interval suggested that 25% of the sites with entrainment with concealed fusion were in bystander areas not within the reentry circuit. At restudy 5 to 7 days later, 6 patients had no monomorphic ventricular tachycardia inducible, and inducible ventricular tachycardias were modified in 4 patients. None of these 10 patients have suffered arrhythmia recurrences during a follow-up of 316 +/- 199 days, although 4 continue to receive previously ineffective medications. CONCLUSIONS: Regions giving rise to reentry after myocardial infarction are complex and can include bystander areas, slow conduction zones, and isthmuses for impulse propagation at which radiofrequency current lesions can interrupt reentry.

Aged↗

PubMed1993

Acoustic image representation of a point target in the bat Eptesicus fuscus: evidence for sensitivity to echo phase in bat sonar.

Echolocating bats, Eptesicus fuscus, were trained in two distinct behavioral tasks to investigate the images they perceive of a sonar point target. In the first task, bats were trained in a two-alternative forced-choice procedure to detect electronically simulated target echoes at a range of approximately 57 cm. Half of the trials in the detection task contained echoes from a stationary target (simulated by a fixed echo delay) and half contained echoes from a jittering target (simulated by an echo delay alternating between two time values over successive sonar emissions). In the second task, bats were trained in a two-alternative forced-choice procedure to discriminate between electronically simulated stationary and jittering targets, centered about a range of 57 cm. Both target detection and target jitter discrimination performance were assessed as a function of jitter magnitude, with jitter values ranging from 0-60 microseconds (corresponding to a change in distance of 0 to 10.3 mm). In both detection and discrimination tasks, the bat's performance changed cyclically with the magnitude of echo jitter. Specifically, when the phase of the playback echoes was unchanged, performance levels were poorest at 0 and 30 microseconds, and when the phase of the echoes alternated by 180 deg from one to the next, performance levels were poorest at 15 and 40-50 microseconds. The results suggest that Eptesicus is sensitive to the phase reversal of echoes and thus have implications for assessing receiver models of echolocation.

Acoustic Stimulation↗

PubMed1991

Visual tasks in helicopter shipboard landing.

The purpose of this research was to identify visual scene content important in helicopter shipboard landings, particularly in the hover phase, for further study in a research simulator. A second purpose was to illustrate the use of a methodology (Protocol Analysis) which may hold promise for many areas of human factors research. Discussions with pilots, reviews of relevant Naval Aviation Training and Operational Procedures (NATOPS) manuals and observation of simulated helicopter shipboard landings suggested that the visual elements required in helicopter shipboard landings may depend upon whether experienced or inexperienced pilots are flying, a simulator or an aircraft is flown, the environment is day or night, or the pilot seeks to acquire or maintain a skill level. A scenario involving an experienced pilot flying dusk/night approaches in a simulator was intensively studied. As he flew each approach, the pilot dictated real-time verbal protocols of his visual and control activities. These protocols were subsequently partitioned by the authors into nine phases defined in terms of range or altitude from the ship, and the visual tasks required in each segment were described. An outcome of this analysis was a list of visual cue augmentations that may be useful for providing augmented feedback in training.

Aircraft↗

PubMed2002

Cryotherapy simulator for localized prostate cancer.

Cryotherapy is a treatment modality that uses a technique to selectively freeze tissue and thereby cause controlled tissue destruction. The procedure involves placement of multiple small diameter probes through the perineum into the prostate tissue at selected spatial intervals. Transrectal ultrasound is used to properly position the cylindrical probes before activation of the liquid Argon cooling element, which lowers the tissue temperature below -40 degrees Centigrade. Tissue effect is monitored by transrectal ultrasound changes as well as thermocouples placed in the tissue. The computer-based cryotherapy simulation system mimics the major surgical steps involved in the procedure. The simulated real-time ultrasound display is generated from 3-D ultrasound datasets where the interaction of the ultrasound with the instruments as well as the frozen tissue is simulated by image processing. The thermal and mechanical simulations of the tissue are done using a modified finite-difference/finite-element method optimized for real-time performance. The simulator developed is a part of a comprehensive training program, including a computer-based learning system and hands-on training program with a proctor, designed to familiarize the physician with the technique and equipment involved.

Computer Simulation↗

PubMed1998

Virtual reality applied to hepatic surgery simulation: the next revolution.

OBJECTIVE: This article describes a preliminary work on virtual reality applied to liver surgery and discusses the repercussions of assisted surgical strategy and surgical simulation on tomorrow's surgery. SUMMARY BACKGROUND DATA: Liver surgery is considered difficult because of the complexity and variability of the organ. Common generic tools for presurgical medical image visualization do not fulfill the requirements for the liver, restricting comprehension of a patient's specific liver anatomy. METHODS: Using data from the National Library of Medicine, a realistic three-dimensional image was created, including the envelope and the four internal arborescences. A computer interface was developed to manipulate the organ and to define surgical resection planes according to internal anatomy. The first step of surgical simulation was implemented, providing the organ with real-time deformation computation. RESULTS: The three-dimensional anatomy of the liver could be clearly visualized. The virtual organ could be manipulated and a resection defined depending on the anatomic relations between the arborescences, the tumor, and the external envelope. The resulting parts could also be visualized and manipulated. The simulation allowed the deformation of a liver model in real time by means of a realistic laparoscopic tool. CONCLUSIONS: Three-dimensional visualization of the organ in relation to the pathology is of great help to appreciate the complex anatomy of the liver. Using virtual reality concepts (navigation, interaction, and immersion), surgical planning, training, and teaching for this complex surgical procedure may be possible. The ability to practice a given gesture repeatedly will revolutionize surgical training, and the combination of surgical planning and simulation will improve the efficiency of intervention, leading to optimal care delivery.

Computer Simulation↗

PubMed2005

Post-training quality of syndromic management of sexually transmitted infections by chemists and druggists in Pokhara, Nepal: is it satisfactory?

OBJECTIVE: Using simulated client and provider interview methods, this study assessed chemists and druggists' post-training management quality of syndromic sexually transmitted infections focusing on the areas of privacy maintaining, encouraging, history taking, counseling, referral practice, partner notification, and drug prescribing and then compared the findings of two methods. DESIGN: Forty-five pharmacies from a list of 75 in Pokhara, who collected sexually transmitted infections data during 1999, were selected randomly. First simulated client successfully presented either urethral or vaginal discharge syndrome at 37 pharmacies and recorded the events of whole encounter into an observation form within 20 minutes. Later 39 chemists and druggists were interviewed by a pre-tested semi-structured questionnaire. MAIN MEASURE: Results were reported mainly by numbers and corresponding percentages. For comparative purpose, P values were also shown. RESULTS: Overall, interview method revealed satisfactory knowledge of chemists and druggists for management of sexually transmitted infections except drug prescribing but their actual behaviors, revealed by simulated client method, indicated lower quality and differed significantly in the areas of encouraging, history taking, counseling, referral practice, and partner notification. Both methods indicated very poor qualities of drug prescribing. CONCLUSION: Retained knowledge of chemists and druggists for syndromic management of sexually transmitted infections were not applied to simulated client in actual practice. They should not prescribe drugs for patients of sexually transmitted infections, except referring to the doctors/hospitals. Continuous monitoring and further motivations for them may improve syndromic management quality of sexually transmitted infections. Moreover, depending on the purpose of study, various methods should be applied simultaneously to reach a better conclusion.

Adult↗

PubMed2006

Survey of current practices in fellowship orientation.

BACKGROUND: The transition from medical resident to subspecialty fellow is a critical time period in fellowship training that has not been well described. The current practices of fellow orientation in pulmonary and critical care training programs are not known. OBJECTIVES: The aim of this study was to describe orientation practices for training programs in the United States. METHODS: A 10-question survey was sent via e-mail to program directors of pulmonary/critical care fellowship programs identified on the American Thoracic Society (ATS) web-page of current programs. RESULTS: Eighty-seven programs responded (61.7%), of which 86% had a formal orientation program. The mean time spent in fellow orientation was 5-10 h in didactic sessions and 0-5 h in wet labs. The most frequent didactic sessions were bronchoscopy in 69 programs (80.2%), pulmonary function testing in 63 programs (73.3%) and orientation to hospital services in 63 programs (73.3%). The most frequent use of wet labs was in bronchoscopy training in 60 programs (81.1%) and ventilators in 45 programs (60.8%). Simulators were used in 37 programs (43%). The majority reported that these areas were covered with on the job training, without a formal designated orientation. CONCLUSION: This survey demonstrated that early fellow training differs across programs in both time spent and clinical and procedural topics covered. An early, standardized approach to clinical and procedural training can assure appropriate exposure that cannot be guaranteed by on the job training. To provide justification for such an approach, clinical outcomes need to be correlated with training methods.

Bronchoscopy↗

PubMed1980

Theoretical studies of image artifacts and counting losses for different photon fluence rates and pulse-height distributions in single-crystal NaI(T1) scintillation cameras.

Using computer simulations, we have developed a theoretical model to explain the correlation between counting losses and image artifacts in single-crystal NaI(T1) scintillation cameras. The theory, valid for scintillation cameras of the Anger type, is based on the physical properties of the NaI(T1) crystal. Based on a statistical model using random numbers, pulse trains of the light pulses from scintillations were simulated. Pulse-height distributions for different event rates were calculated, with various Compton distributions. Images of point sources and line sources were generated. Counting losses and image artifacts were dependent on the shape of the pulse-height distribution. The calculated counting losses decreased with larger Compton distributions, due to increasing numbers of pileup events in the energy window; this also caused severe image distortion. The improvement of the spatial resolution with pileup rejection was demonstrated. The theoretical results are in good agreement with experimental results obtained previously. It is concluded that, in modern cameras, the decay time of the scintillation determines the amount of pileup, and the resolving time of the electronics governs the count rates. The results indicate that in some modern cameras the limits of the count-rate capacity in Anger cameras may be reached.

Elementary Particles↗

PubMed1994

Listeners' expectations about echoes can raise or lower echo threshold.

Echo threshold increases with exposure to redundant trains of stimuli. Three experiments were conducted to test the hypothesis that a change in the ongoing train would affect listeners' perception of the echo, but only if it signified an unusual change in room acoustics. The stimulus train was composed of 4-ms narrow-band noise bursts, with the leading sound from a loudspeaker placed 45 degrees left of midline and the lagging sound or simulated echo from 45 degrees right, delivered in an anechoic chamber. The lagging sound in the test noise, which followed the train after a 750-ms pause, came randomly from loudspeakers at 35 degrees or 55 degrees right, and the listener's task was to choose which position the echo came from on each trial. In experiment 1 the delay between onsets of the leading and lagging bursts was varied between train and test bursts, which simulated a sudden movement of the reflecting surface either toward the listener (if the delay of the test burst was shorter than the train) or away (if the delay was longer). In both cases listeners detected the echo's direction more easily, compared to trials when there was no change between train and test burst delays. In order to check whether any change between train and test bursts would increase echo discriminability, experiment 2 varied frequency and experiment 3 varied intensity. These variations were not expected to affect the echo's detectability because such changes signify that the original sound changed in these characteristics and the echo reflected these changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗

PubMed1998

A PRC based model of a pacemaker cell: effect of vagal activity and investigation of the respiratory sinus arrhythmia.

In this study we present a computer model of a pacemaker cell subjected to vagal stimulation. This model allows us to investigate the entrainment phenomena of the pacemaker cell resulting from its dynamic interaction with a periodic train of vagal bursts. The possibility of entrainment depends mainly on the fact that a vagal stimulation discharge can "correct" the pacemaker rhythm by an amount that depends on its instantaneous relationship to the pacemaker cycle length. This very simple model, is based on the two most important functional properties of the cardiac pacemaker cells. The first property is the intrinsic pacemaker cycle length, which is an "internal" parameter of the cell, describing the most basic feature of a pacemaker cell. The second one is the phase response curve (PRC), which is an "overall collective" function, containing all the "information" about the possible interactions between the pacemaker cell and the outside world (i.e. its interaction with surrounding cells, external stimulus, etc.). A "collective" PRC was reconstructed from the resulting effects of all the pulses composing a burst. It appears that the PRC parameters as well as the vagal burst parameters are important factors in predicting the entrainment phenomena. Specifically, we found that the tendency of the pacemaker cell to become synchronized with bursts of vagal activity is greater, the larger the number of pulses per burst. However, increasing the number of pulses may also increase the tendency of the pacemaker towards instability, which was unveiled as changes in the configuration of the "collective" PRC. We applied the periodic train of vagal bursts so as to simulate the respiratory sinus arrhythmia (RSA) modulation on the pacemaker cell. We included also a modulation of sympathetic origin, represented as periodic changes in the intrinsic pacemaker cycle length. The frequency response of the pacemaker to "autonomic" modulations allowed us to demonstrate that the RSA dynamics can be interpreted in terms of the entrainment of the pacemaker cell by the respiratory modulation of vagal activity.

Autonomic Nervous System↗

PubMed1986

The detection of phantom targets in noise by serotine bats; negative evidence for the coherent receiver.

Using a target simulator three serotine bats, Eptesicus serotinus, were trained to judge whether a phantom target was present or absent. The echolocation sounds emitted by the bats during the detection were intercepted by a microphone, amplified and returned by a loudspeaker as an artificial echo, with a delay of 3.2 ms and a sound level determined by the overall gain and cry amplitude. The cry level of each pulse was measured and the echo level received by the bat was calculated. The target was presented in 50% of the trials and the gain adjusted using conventional up/down procedures. Under these conditions between 40 and 48 dB peSPL were required for 50% detection (Figs. 2, 3). In a subsequent experiment the phantom target was masked with white noise (No) with a spectrum level of -113 dB re. 1 Pa X Hz-1/2. The thresholds were increased by 7-14 dB. Energy density (S) of a single pulse was measured and used to estimate S/No, which ranged from 36-49 dB at threshold. Theoretically the coherent receiver model predicts the ratio between hits and false alarms observed for the bats at a S/No of ca. 1-2 dB. Since the bats require 40-50 dB higher S/No (Fig. 3), this is taken as negative evidence for coherent reception (cross correlation). Furthermore, a strong sensitivity to clutter was found since there seemed to exist a fixed relationship between thresholds and clutter level.

Animals↗

PubMed1997

The oculomotor integrator: testing of a neural network model.

An important part of the vestibulo-ocular reflex is a group of cells in the caudal pons, known as the neural integrator, that converts eye-velocity commands, from the semicircular canals for example, to eye-position commands for the motoneurons of the extraocular muscles. Previously, a recurrently connected neural network model was developed by us that learns to simulate the signal processing done by the neural integrator, but it uses an unphysiological learning algorithm. We describe here a new network model that can learn the same task by using a local, Hebbian-like learning algorithm that is physiologically plausible. Through the minimization of a retinal slip error signal the model learns, given randomly selected initial synaptic weights, to both integrate simulated push-pull semicircular canal afferent signals and compensate for orbital mechanics as well. Approximately half of the model's 14 neurons are inhibitory, half excitatory. After learning, inhibitory cells tend to project contralaterally, thus forming an inhibitory commissure. The network can, of course, recover from lesions. The mature network is also able to change its gain by simulating abnormal visual-vestibular interactions. When trained with a sine wave at a single frequency, the network changed its gain at and near the training frequency but not at significantly higher or lower frequencies, in agreement with previous experimental observations. Commissural connections are essential to the functioning of this model, as was the case with our previous model. In order to determine whether a commissure plays a similar role in the real neural integrator, a series of electrical perturbations were performed on the midlines of awake, behaving juvenile rhesus monkeys and the effects on the monkeys' eye movements were examined. Eye movements were recorded using the coil system before, during, and after electrical stimulation in the midline of the pons just caudal to the abducens nuclei, which reversibly made the integrator leaky. Eye movements were also recorded from two of the monkeys before and after a midline electrolytic lesion was made at the location where stimulation produced a leaky integrator. This lesion disabled the integrator irreversibly. The eye movements that were produced by the monkeys as a result of these perturbations were then compared with eye movements produced by the model after analogous perturbations. The results are compatible with the hypothesis that integration comes about by positive feedback through lateral inhibition effected by an inhibitory commissure.

Algorithms↗

PubMed1987

Treatment of the spastic pelvic floor syndrome with biofeedback.

The spastic pelvic floor syndrome is a functional disorder based on contraction instead of relaxation of the pelvic floor muscle during straining, which inhibits defecation and gives rise to constipation. Until now no adequate treatment has been found for this condition. The treatment described here is aimed at teaching patients to relax their pelvic floor muscle during straining. Treatment consists of a training program with EMG feedback, followed by simulation of the defecation process, using oatmeal porridge. Patients are then given instructions to generalize the relaxation response in their daily lives. Treatment was completely successful in seven of ten patients. The three remaining patients learned to strain in the correct manner, but could not achieve generalization. Two of them underwent subtotal colectomy because of delayed colonic transit times, which subsequently resulted in normal evacuation. In the third patient, the generalization was most likely hampered by psychologic problems, for which she now receives psychotherapy.

Adult↗

PubMed1980

Computer applications in audiology and rehabilitation of the hearing impaired.

Computers are playing an ever-increasing role in audiology. The potential applications of computers in audiology, speech pathology, and aural rehabilitation are described. These include the use of computers in adaptive testing, speech analysis and synthesis, automatic extraction of speech features, supplemental speechreading aids, analysis and synthesis of speechreading cues, language analysis, and computer simulation of the effect of specific speech training strategies.

Audiology↗