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PubMed2006

Outcomes of autoconjunctival grafting for primary pterygia when performed by consultant compared with trainee ophthalmologists.

PURPOSE: To define rates of recurrence and surgical complications of primary pterygia excision with autoconjunctival grafting when the surgery is performed by consultant ophthalmologists compared with trainee ophthalmologists. METHODS: A total of 174 patients with primary pterygia treated by excision and autoconjunctival grafting were included for analysis. Patients were divided into two groups according to whether their surgery was performed by a consultant ophthalmologist (group A) or a trainee ophthalmologist (group B). Data were collected with respect to demographics, surgical complications and recurrence. Recurrence rates were analysed utilizing Fisher's exact test. Additionally, Kaplan-Meier survival curves for interval censored data were constructed. Surgical complications were analysed utilizing Fisher's exact test. RESULTS: The recurrence rate in group A was 6.8% and in group B was 19.4%. This difference was statistically significant (P = 0.05). The rate of surgical complication occurring in group A was 6.6% and in group B was 23.3% and this was also statistically significant (P = 0.005). No relationship was found between either patient age or the size of pterygium and recurrence or complications in either group A or group B. CONCLUSION: Autoconjunctival grafting is regarded as the gold standard for preventing pterygium recurrence following excision. This study suggests that the experience of the surgeon can influence success rates and complications. There is a significant learning curve indicating the need to supervise trainee surgeons.

Adult↗

PubMed2006

Concomitant deficits in working memory and fear extinction are functionally dissociated from reduced anxiety in metabotropic glutamate receptor 7-deficient mice.

Metabotropic glutamate receptor 7 (mGluR7), a receptor with a distinct brain distribution and a putative role in anxiety, emotional responding, and spatial working memory, could be an interesting therapeutic target for fear and anxiety disorders. mGluR7-deficient (mGluR7-/-) mice showed essentially normal performance in tests for neuromotor and exploratory activity and passive avoidance learning but prominent anxiolytic behavior in two anxiety tests. They showed a delayed learning curve during the acquisition of the hidden-platform water maze, and three interspersed probe trials indicated that mGluR7-/- mice were slower to acquire spatial information. Working memory in the water maze task and the radial arm maze was impaired in mGluR7-/- mice compared with mGluR7+/+. mGluR7-/- mice also displayed a higher resistance to extinction of fear-elicited response suppression in a conditioned emotional response protocol. In a non-fear-based water maze protocol, mGluR7-/- mice displayed similar delayed extinction. These observed behavioral changes are probably not attributable to changes in AMPA or NMDA receptor function because expression levels of AMPA and NMDA receptors were unaltered. Extinction of conditioned fear is an active and context-dependent form of inhibitory learning and an experimental model for therapeutic fear reduction. It appears to depend on glutamatergic and higher-level brain functions similar to those involved in spatial working memory but functionally dissociated from those that mediate constitutional responses in anxiety tests.

Analysis of Variance↗

PubMed2004

Computer-simulated phacoemulsification.

OBJECTIVE: To develop a simulator for training in phacoemulsification to be used as a learning device for both beginners and experienced surgeons to shorten the learning curve. DESIGN: Experimental study. METHODS: The system consists of a personal computer, a 3-dimensional visual interface, a phacoemulsification handpiece, and a nucleus manipulator and foot pedals for control of the phacoemulsification procedure and microscope adjustments. The simulation is based on generalized simulation software that can be also used for the development of other medical simulations. MAIN OUTCOME MEASURES: Qualitative statements given in a questionnaire. Medical students and ophthalmic surgeons with varying experience of phacoemulsification were tested. RESULTS: A simulator for training in phacoemulsification has been developed. The surgical procedures can be practiced any number of times, and there is no risk to patients. The efforts of the surgeon can be evaluated objectively. CONCLUSIONS: Studies have shown that the number of complications for an ophthalmic surgeon learning phacoemulsification decreases exponentially, reaching close to the asymptote only after several hundred procedures. Simulator training might shorten the learning period, reduce expensive supervision by an experienced surgeon, and maintain and improve the skills of experienced surgeons.

Computer Simulation↗

PubMed2000

Analysis of variation in success rates in conjunctival autografting for primary and recurrent pterygium.

AIMS: To evaluate the success rates of conjunctival autografting for primary and recurrent pterygium performed in a tertiary ophthalmic centre. METHODS: The outcome of 139 cases with primary pterygia and 64 cases with recurrent pterygia who underwent excision with conjunctival autografting was retrospectively reviewed. Outcome was evaluated in terms of recurrence of pterygia onto the cornea. The recurrence rates were determined using Weibull survival functions, in a mixture model that included a component allowing for cure. The suitability of this model was verified using Turnbull's non-parametric method for interval censored data (1974). Estimated recurrence free probabilities were based on the fitted Weibull survival curves. RESULTS: Mean follow up was 8.4 months in the primary group, and 9.5 months for the recurrent group. 29 out of 139 cases of primary pterygia recurred (20.8%) while 20 out of 64 cases in the recurrent group (31.2%) recurred. Recurrence rates varied widely among surgeons, ranging from 5% to 82%. Recurrence rates were inversely related to previous experience in performing conjunctival grafting. The recurrence free probability was 84% at 3 months, 73% at 1 year for primary pterygia, and 80% at 3 months, 67% at 1 year for recurrent pterygia. There was no statistical difference in recurrence rates between primary and recurrent groups (p= 0.80). CONCLUSION: The success of conjunctival autografting for pterygium in this series varies widely, and may be related to a significant learning curve or differing surgical techniques for this procedure. This may account for the wide variation in reported success of this procedure in the ophthalmic literature.

Adult↗

PubMedDate not supplied

Is impaired recall in dementia of the Alzheimer type a consequence of a contextual retrieval deficit?

Eighty-eight patients with mild to moderate dementia of the Alzheimer type were tested in a word list and a spatial pattern recall task. With increasing degree of dementia severity we found a decline in the initial recall scores while learning curves over five consecutive trials remained normal in the mildly demented patients. Furthermore, there was a loss of the primacy effect in the word list task in our moderately demented patients. These findings are consistent with the pattern that have been reported after medial temporal lobe dysfunction. The data are discussed in the framework of cognitive dual process theories of memory as indicators of a contextual retrieval deficit.

Aged↗

PubMed2003

Learning-related changes in response patterns of prefrontal neurons during instrumental conditioning.

A crucial aspect of organizing goal-directed behavior is the ability to form neural representations of relationships between environmental stimuli, actions and reinforcement. Very little is known yet about the neural encoding of response-reward relationships, a process which is deemed essential for purposeful behavior. To investigate this, tetrode recordings were made in the medial prefrontal cortex (PFC) of rats performing a Go-NoGo task. After task acquisition, a subset of neurons showed a sustained change in firing during the rewarded action sequence that was triggered by a specific visual cue. When these changes were monitored in the course of learning, they were seen to develop in parallel with the behavioral learning curve and were highly sensitive to a switch in reward contingencies. These sustained changes correlated with the reward-associated action sequence, not with sensory or reward-predicting properties of the cue or individual motor acts per se. This novel type of neural plasticity may contribute to the formation of response-reinforcer associations and of behavioral strategies for guiding goal-directed action.

Action Potentials↗

PubMed2004

Surgery for left ventricular aneurysm: early and late survival after simple linear repair and endoventricular patch plasty.

OBJECTIVE: Simple linear resection and endoventricular patch plasty are alternative techniques to repair postinfarction left ventricular aneurysm. The aim of the study was to compare these 2 methods with regard to early mortality and long-term survival. METHODS: We retrospectively reviewed 159 patients undergoing operations between 1989 and 2003. The epidemiologic design was of an exposed (simple linear repair, n = 74) versus nonexposed (endoventricular patch plasty, n = 85) cohort with 2 endpoints: early mortality and long-term survival. The crude effect of aneurysm repair technique versus endpoint was estimated by odds ratio, rate ratio, or relative risk and their 95% confidence intervals. Stratification analysis by using the Mantel-Haenszel method was done to quantify confounders and pinpoint effect modifiers. Adjustment for multiconfounders was performed by using logistic regression and Cox regression analysis. Survival curves were analyzed with the Breslow test and the log-rank test. RESULTS: Early mortality was 8.2% for all patients, 13.5% after linear repair and 3.5% after endoventricular patch plasty. When adjusted for multiconfounders, the risk of early mortality was significantly higher after simple linear repair than after endoventricular patch plasty (odds ratio, 4.4; 95% confidence interval, 1.1-17.8). Mean follow-up was 5.8 +/- 3.8 years (range, 0-14.0 years). Overall 5-year cumulative survival was 78%, 70.1% after linear repair and 91.4% after endoventricular patch plasty. The risk of total mortality was significantly higher after linear repair than after endoventricular patch plasty when controlled for multiconfounders (relative risk, 4.5; 95% confidence interval, 2.0-9.7). Linear repair dominated early in the series and patch plasty dominated later, giving a possible learning-curve bias in favor of patch plasty that could not be adjusted for in the regression analysis. CONCLUSIONS: Postinfarction left ventricular aneurysm can be repaired with satisfactory early and late results. Surgical risk was lower and long-term survival was higher after endoventricular patch plasty than simple linear repair. Differences in outcome should be interpreted with care because of the retrospective study design and the chronology of the 2 repair methods.

Adult↗

PubMed1998

Bimodal (auditory and visual) left frontoparietal circuitry for sensorimotor integration and sensorimotor learning.

We used PET to test whether human premotor and posterior parietal areas can subserve basic sensorimotor integration and sensorimotor learning equivalently in response to auditory and visual stimuli, as has been shown in frontoparietal neurons in non-human primates. Normal subjects were studied while they performed a spatial compatibility task. They were instructed to respond to lateralized auditory and visual stimuli with the ipsilateral hand (compatible condition) or with the contralateral hand (incompatible condition). Reaction times were faster in the compatible than in the incompatible condition, for both auditory and visual stimuli. Left rostral dorsal premotor and posterior parietal blood-flow increases were observed in the incompatible condition, compared with the compatible condition, for both auditory and visual modalities. Blood-flow increases, which were correlated with the reaction-time learning curves, were observed in both auditory and visual modalities in the left caudal dorsal premotor cortex. These data suggest that, as in non-human primates, human frontoparietal areas can subserve basic sensorimotor transformations equivalently in the auditory and visual modality. Further, they reveal a functional rostrocaudal fractionation of human dorsal premotor cortex that resembles the rostrocaudal anatomical and physiological fractionation observed in non-human primates.

Acoustic Stimulation↗

PubMed1995

[In vitro study of the properties of bioresorbable lactic acid polymer materials].

PURPOSE OF THE STUDY: The potential applications of biodegradable osteosynthesis implants present many advantages over conventional metallic devices. Polyesters of the poly and hydroxy-acid type were recognized early as serious candidates. These polymers have demonstrated a very good biocompatibility and are biodegradable in vivo. After biological and chemical testing poly L. lactic acid 98 (PLA 98) was selected as a candidate. We used a static and dynamic investigation in vitro to assess firstly the material properties of PLA 98 and secondly how its characteristics could be modified within a physiological environment. MATERIAL: Michel Vert and colleagues have shown that polymers of lactic acid have a similar time to resorption providing they contain 98 per cent of the "L" form of the polymer. In vitro studies were assessed on bars made in PLA 98. METHODS: In a first time in vitro studies in traction and flexion on bars allowed an assessment of mechanical properties of PLA 98. In a second time stresses were applied on bars using a physiological environment (Haemacel - 37 degrees C). In a third time we assessed the mechanical properties at the temperature of 37 degrees C with dynamic tests on bars in traction and flexion. RESULTS: The stress-strain curves on bars showed that the material is fragile. Sterilisation with ethylene-oxide did not affect the mechanical properties. When bars were placed in a thermostatically controlled (37 degrees C) physiological environment, the stress-strain curve showed that the material became ductile. With a temperature of 37 degrees C and with a frequency better than one hertz, the dynamic tests on bars showed that the material endurance is good up to 20,000 cycles. At 37 degrees C and at the end of one month, the Young modulus and the maximal strain before breaking lose 50 per cent of their initial value. DISCUSSION: All things considered and as the digital value showed, the PLA 98 appear to be ten times less strong than steel. In a physiological environment the mechanical properties improved due to hydratation of the polymer. The material become quickly ductile or malleable. This allowed transient loading without causing breakage. CONCLUSION: The mechanical properties of bioresorbable materials are very different from those of stainless steel and there is a learning curve in their utilisation. The PLA 98 polymer has demonstrated a very good biocompatibility and is totally biodegradable in vivo. With these results we think that PLA 98 can be used in clinical practice. Indications and clinical use should remain limited to bones regions with low applied stresses.

Biocompatible Materials↗

PubMed1997

Experiences with computed radiography: can we afford the cost?

In summary, we believe that the CR system adds significantly to our department. The film quality is superb, and the learning curve for radiologists to adapt to the added noise from anatomic structures on chest radiographs is short. The inherent film latitude and flexibility add a new dimension to interpretation and film management. System costs are significantly greater than for traditional film-screen systems. Recurring operational costs are yet to be determined but certainly will be greater with the shorter expected life span of the imaging plates. Film cost savings cannot be a justifiable reason for using a CR system. Film cost savings must await the ultimate conversion to soft imaging through networks and workstations. Technical issues are significant and require structured and specific courses of study and workshops for users before implementation of the CR system. As CR owners, we were frustrated by the lack of published protocols and guides for the CR user. Most of our experiences were learned in practice, and we believed published guides would be useful for both existing users and future buyers. Careful attention to accuracy, histogram selection, positioning, collimation, and patient data input is critical to the success of CR. The persistent lack of a CR information system interface has led to occasional labeling errors and requires added vigilance on the part of both the technologist and the radiologist. Other important user problems we experienced with CR included the RVS. When images are reprinted from the RVS, they can be printed on 10 x 14 inch (26 x 36 cm) film only. Images that were acquired on the larger cassettes are printed on this smaller film, minified by one third from the original size. Minified images are unacceptable to our orthopedic colleagues. Networking problems have still not been resolved, and this resolution remains an important goal. The manipulation and transfer of images without loss of data were major reasons for our switch to electronic imaging and have still not been achieved. Unique image artifacts were encountered, as were new parameters to judge the quality of an image. The final issue is radiation dose. To assign dose reduction as an attribute of CR would be misleading. We have found that in many instances the reverse is true. Many examinations have required more radiation exposure than traditional film-screen techniques. At the least, to harvest the benefits of CR one must significantly alter technical exposure factors and understand how the system operates. The problems we encountered were not minor. Our technologists and radiologists and the Fuji personnel have put in many hours to implement and optimize our system. The image quality is superb, and we continue to work on the important networking and archival goals.

Aged↗

PubMed2003

Repeated spatial acquisition: effects of NMDA antagonists and morphine.

Effects of morphine and 2 N-methyl-D-aspartate (NMDA) receptor antagonists, phencyclidine and LY235959, were studied using a within-subject, repeated-acquisition/performance procedure adapted to the Morris Swim Task. In the performance component, subjects swam to a hidden platform that was always in the same location in the pool. In the acquisition component, the platform was moved to a different place for each session. Baseline training produced rapid and direct swims to the platform in the performance component and steep within-session learning curves in the acquisition component. All 3 compounds increased swim distances, escape latencies, and slowed swim speed in a dose-dependent manner, but only morphine consistently produced selective impairments on acquisition. NMDA antagonists generally affected acquisition only at doses that also disrupted performance, although phencyclidine produced selective effects in some animals. These outcomes were different than those from studies of response chains in primates, suggesting that task and species variables may be important determinants of drug effects on acquisition.

Analgesics, Opioid↗

PubMed1995

Sampling strategies in a statistical approach to clinical classification.

This paper studies the sampling strategies for the Expert Network (EexNet), a statistical learning system used for patient record classification at the Mayo Clinic. The goal is to achieve high accuracy classification at an affordable computational cost in very large applications. The learning curves of ExpNet were observed with respect to the choice of training resources, the size, vocabulary coverage and category coverage of a training set, and the category distribution over training instances. A method combining advantages of different sampling strategies is proposed and evaluated using a large training corpus. As a result, Expert Network has achieved its nearly-optimal classification accuracy (measured by average precision) using a relatively small training set, with a fast real-time response which satisfies the needs of human-machine interaction.

Expert Systems↗

PubMedDate not supplied

Bile duct injuries in the era of laparoscopic cholecystectomy.

By the introduction of laparoscopic cholecystectomy a new field of surgical development has been opened, resulting in the reduction of conventional surgical trauma, and giving the chance to the patient seeking for less postoperative pain, short hospital stay and quick return to activity and work. In spite of these advantages, many laparoscopic cholecystectomy related complications occurred, especially in the period of the learning curve. Due to the special technical requirements, problems of the two dimensional vision, depth perception and hand-eye coordination guided to injuries of the bile ducts, which reached a high rate of 3%. This rate is ten times more when compared with conventional cholecystectomy. The authors present a detailed account of the causes of the injuries, their typical localisation and the best way to avoid and treat them.

Activities of Daily Living↗

PubMed1997

Laparoscopic colorectal surgery. Do we get faster?

BACKGROUND: A variety of parameters can affect the outcome of laparoscopic colorectal surgery. All consecutive laparoscopic colorectal procedures (LCP) were analyzed in an attempt to define an operative time curve for different categories of procedures. Additionally, impacts of case number and procedure type on length of procedure were assessed. METHODS: Our computerized data system was reviewed for all patients who underwent LCP in a 4-year period. Parameters reviewed included age, sex, surgical indications, procedures performed, length of procedure, intraoperative and postoperative complications, incidence and causes for conversion, duration of postoperative ileus, and hospital stay. RESULTS: Between August 1991 and December 1995, 175 patients with a mean age of 48.4 (range 15-88) years underwent LCP. Patients were divided chronologically into five consecutive groups. Procedures were classified as either basic or complex. Complex procedures were those in which there was either a fixed tumor, an abscess or fistula, or extensive intraabdominal adhesions from prior surgery. Complex procedures performed each year ranged from 37% to 66%. As well, the percentage of patients with adhesions increased from 17% in 1991 to 29% in 1995. Despite increased difficulty, the intraoperative complication rate fell significantly from 29% in 1991 to 8% in 1995 (p < 0.005). Additionally, the operative length decreased from a mean of 201 min in 1991 to a mean of 141 min in 1995 (p < 0.05). CONCLUSION: The rapid improvement in these parameters may reflect both ascents in the learning curve and change in type of procedure. Adhesions, due to prior surgery or inflammation making dissection tedious, is the most important technical factor which effects operation time (p < 0.001). However, despite increased complexity, operating time decreased, reflecting improved skills. Thus, the experienced laparoscopic surgeon can increase the spectrum of applications with expectations of shorter operations and lower complication rates.

Colon↗

PubMed1999

State-of-the-art phacoemulsification performed by residents in Buenos Aires, Argentina.

PURPOSE: To analyze the learning curve for state-of-the-art phacoemulsification performed by residents. SETTING: Department of Ophthalmology, Hospital de Clinicas José de San Martin, University of Buenos Aires, Buenos Aires, Argentina. METHODS: The records of patients having phacoemulsification performed by residents from June 1996 to January 1998 were reviewed for preoperative and postoperative best corrected visual acuities and the occurrence of complications. The phacoemulsification technique used for the first 35 surgeries of each resident was compared with that of their last 35 surgeries. RESULTS: The records showed 249 cases of phacoemulsification by residents. Mean preoperative best corrected visual acuity was 0.19 +/- 0.19 (SD). One month postoperatively, it was 0.86 +/- 0.2. Nuclear fracture was performed in a mean of 28.33 +/- 5.0 of the first 35 surgeries by each resident, whereas chopping techniques were used in a mean of 23.33 +/- 1.5 of the last 35 cases. Vitreous loss occurred in 2.8% of cases. CONCLUSION: Residents learned cracking and chopping phacoemulsification techniques safely with satisfactory outcomes.

Adolescent↗

PubMed1992

Associative regulation of Pavlovian fear conditioning: unconditional stimulus intensity, incentive shifts, and latent inhibition.

Conditional stimuli (CS) associated with painful unconditional stimuli (US) produce a naloxone-reversible analgesia. The analgesia serves as a negative-feedback regulation of fear conditioning that can account for the impact of US intensity and CS predictiveness on Pavlovian fear conditioning. In Experiment 1 training under naloxone produced learning curves that approached the same high asymptote despite US intensity. Shifting drug treatment during acquisition had effects that paralleled US intensity shifts. In Experiment 3 naloxone reversed Hall-Pearce (1979) negative transfer using a contextual CS, indicating that conditional analgesia acquired during the CS-weak-footshock phase retards acquisition in the CS-strong-footshock phase. Experiment 5 used a tone CS in both a latent-inhibition and a negative-transfer procedure. Only negative transfer was blocked by naloxone. Therefore, negative transfer but not latent inhibition is mediated by a reduction of US processing.

Animals↗

PubMedDate not supplied

[The acquisition of a cyclic maze habit in rats (as a model of cognitive activity) with removal of the amygdaloid body].

Learning cyclic habit in a multialternative maze (with a possibility of many rewarded choices) was shown to be possible for amygdalectomized rats. All three normal types of the "learning curves" (a number of cycles as a function of the number of sessions) were observed in rats after surgery, i.e., exponent, logistic function, and "no-trend" function. This is in agreement with Simonov's concept. However, the general style of behavior was changed. The behavior became "excessive": there was an increase in the number of errors and in the locomotion rate, which suggests a disbalance of emotional-cognitive interrelations. The extent of deviation from norm is different for each type. The findings suggest the different functional weight of amygdala in the normal activity.

Amygdala↗

PubMed2002

Shape predominant effect in pattern recognition of geometric figures of rhesus monkey.

Three monkeys were trained successively with discrimination, concurrent matching to sample, and sameness-difference judgment tasks in which learning curves were compared. Then, the display duration for the stimuli was shortened to 100, 50, and 30 ms respectively to test the changes in accuracy and reaction time. All results in three experimental paradigms suggested consistently that the geometric shape (triangle, circle, and square) plays a more predominant role than topological features (the hole inside of a figure and the hole numbers) in monkey figure recognition. The results are different from the experiment by human subjects who presented hole predominant in figure recognition. Therefore, the precedence in perception depends on subject species, stimulus set, and ecological significance of the perceiving process.

Animals↗