Variability in motor learning: relocating, channeling and reducing noise.

Variability in motor performance decreases with practice but is never entirely eliminated, due in part to inherent motor noise. The present study develops a method that quantifies how performers can shape their performance to minimize the effects of motor noise on the result of the movement. Adopting a statistical approach on sets of data, the method quantifies three components of variability (tolerance, noise, and covariation) as costs with respect to optimal performance. T-Cost quantifies how much the result could be improved if the location of the data were optimal, N-Cost compares actual results to results with optimal dispersion at the same location, and C-Cost represents how much improvement stands to be gained if the data covaried optimally. The TNC-Cost analysis is applied to examine the learning of a throwing task that participants practiced for 6 or 15 days. Using a virtual set-up, 15 participants threw a pendular projectile in a simulated concentric force field to hit a target. Two variables, angle and velocity at release, fully determined the projectile's trajectory and thereby the accuracy of the throw. The task is redundant and the successful solutions define a nonlinear manifold. Analysis of experimental results indicated that all three components were present and that all three decreased across practice. Changes in T-Cost were considerable at the beginning of practice; C-Cost and N-Cost diminished more slowly, with N-Cost remaining the highest. These results showed that performance variability can be reduced by three routes: by tuning tolerance, covariation and noise in execution. We speculate that by exploiting T-Cost and C-Cost, participants minimize the effects of inevitable intrinsic noise.

Permanent sacral nerve stimulation for treatment of idiopathic constipation.

BACKGROUND: Constipation can usually be managed using conservative therapies. A proportion of patients require more intensive treatment. Surgery provides variable results. This paper describes an alternative approach, in which the neural control of the bowel and pelvic floor is modified, using permanent sacral nerve stimulation. METHODS: Four women (aged 27-36 years), underwent temporary and then permanent stimulation. All had idiopathic constipation, resistant to maximal therapy, with symptoms for 8-32 years. Clinical evaluation, bowel diary, Wexner constipation score, symptom analogue score, quality of life questionnaire and anorectal physiology were completed. RESULTS: There was a marked improvement in all patients with temporary, and in three with permanent, stimulation. Median follow-up was 8 (range 1-11) months. Bowel frequency increased from 1-6 to 6-28 evacuations per 3 weeks. Improvement occurred, at longest-follow-up, in median (range) evacuation score (4 (0-4) versus 1 (0-4)), time with abdominal pain (98 (95-100) versus 12 (0-100) per cent), time with bloating (100 (95-100) versus 12 (5-100) per cent), Wexner score (21 (20-22) versus 9 (1-20)), analogue score (22 (16-32) versus 80 (20-98)) and quality of life. Maximum anal resting and squeeze pressures increased. Rectal sensation was altered. Transit time normalized in one patient. CONCLUSION: Permanent sacral nerve stimulation can be used to treat patients with resistant idiopathic constipation.

Regional topical hypothermia of the beating heart: preservation of function and tissue.

BACKGROUND: Protection of the myocardium during beating heart operations is paramount. The goal of this study is to determine if regional topical hypothermia (RTH) preserves myocardial viability and function during periods of temporary coronary artery occlusion. METHODS: Sixteen pigs were divided into two groups (RTH and control). Each group received 40 minutes of midleft anterior descending coronary occlusion followed by 3 hours of reperfusion. The RTH group (n = 10) received RTH and the control group (n = 6) received no cooling. Myocardial and core temperatures were measured with thermistors. Sonomicrometers and micromonameters were used to determine load independent indices of myocardial function. These indices were measured at base line, during coronary occlusion, and at 3 hours of reperfusion. The myocardium at risk and the infarct area were determined with monastral blue dye and triphenyl tetrazolium chloride staining. RESULTS: The mean myocardial temperature in the risk zone during coronary occlusion was significantly less in the RTH group (29.4 degrees C +/- 5.6 degrees C versus 35.7 degrees C +/- 1.1 degrees C, p < 0.05). After 40 minutes of coronary occlusion, both the RTH group and control had a significant reduction in regional elastance (9.38 +/- 3.54 and 11.05 +/- 1.67 mm Hg/mm) compared with base line measurements (14.70 +/- 2.42 and 16.80 +/- 4.79 mm Hg/mm), p < 0.05. However, after 3 hours of reperfusion, the elastance returned to base line levels in the RTH group (15.83 +/- 3.06 mm Hg/mm) but remained significantly depressed in the control group (9.97 +/- 3.63 mm Hg/mm, p < 0.04). Myocardial necrosis as a percentage of the risk zone was significantly less in the hypothermia group (25% +/- 2% versus 62% +/- 5%, p < 0.001). CONCLUSIONS: Regional topical hypothermia during isolated temporary coronary occlusion provides regional myocardial protection expressed as a return of function and decreased necrosis. Regional topical hypothermia may be clinically applicable to myocardial preservation during beating heart operations.

Living donor lung transplantation.

Since 1993 a total of 101 living-donor bilateral lung transplants have been performed with acceptable results when compared with those utilizing cadaveric lung grafts. Though most recipients were patients with cystic fibrosis who were rapidly deteriorating, the indications for live-donor lung transplantation have been expanded to include some cystic fibrosis patients in a more elective setting, as well as select patients with other end-stage pulmonary diseases. One-year Kaplan-Meler recipient survival is 72%. Seventy-six percent of deaths occur within the first 2 months after transplantation. The most common cause of death is infection, which accounts for 62% of the 1-year mortality rate. The incidence of rejection is 0.8 episodes per patient. Thirty percent of rejection episodes are unilateral, and most tend to be mild. Altogether, 203 patients have undergone donor lobectomy, with a mean age of 37 +/- 12 years (range 18-56 years). Operations included left lower lobectomy (102 patents), right lower lobectomy (97 patients), and right middle and lower lobectomy (4 patients). There has been no donor mortality. Postoperative Rand 36 Question Quality of Life scores, rating physical function, social functioning, and role limitation due to physical and emotional health, are well over 92 (of a possible score of 100). Eighty-five percent of donors said that their health was no different or improved since donation.

Cytogenetic proof that the brine shrimp Artemia franciscana (Crustacea, Branchiopoda) is found in Argentina.

Artemia brine shrimps are commercially important and they have been extensively studied. This branchiopod crustacean is extensively used in aquaculture and other commercial and applied practices. The genus also awakes an increasing interest worldwide as an experimental model in other basic areas of research such as evolution and cytogenetics. In the present work adult male meiosis and nauplii mitotic cells in two Artemia populations from Argentina (Mar Chiquita and Las Tunas, Córdoba Province) are analyzed and compared to the reference strains A. franciscana (Great Salt Lake, Utah, USA) and A. persimilis (Salinas Grandes de Hidalgo, La Pampa Province, Argentina). The Mar Chiquita population shows the diploid and haploid numbers characteristic of A. franciscana, and a regular male meiosis. In the Las Tunas population diverse diploid and haploid numbers are encountered, and an irregular meiosis is observed in some individuals. Fluorescent DAPI and CMA banding shows bright chromocenters of intermediate size and number in both populations. Cytogenetic and phenotypic data show that the population of Mar Chiquita could be assigned to A. franciscana; the variation found in chromocenter size and number reflects an heterochromatin polytypism already observed in this species. The cytogenetic and morphological traits in Las Tunas population suggest an occasional hybridization between A. franciscana and A. persimilis.

Safety and efficacy of bilateral total knee arthroplasty.

Recent studies have reported increased morbidity associated with bilateral simultaneous total knee arthroplasty (TKA). The purpose of this study was to evaluate the morbidity and clinical outcome associated with simultaneous bilateral TKA in contrast to unilateral TKA. All primary TKAs, either unilateral or simultaneous bilateral, performed between May 1988 and July 1993 were retrospectively reviewed. Patients were evaluated using Knee Society scores both before surgery and a minimum of 6 months after surgery. In addition to routine demographics, patients were evaluated for the incidence of both local wound and systemic complications. It is concluded that performing simultaneous bilateral TKA does not result in any significant increase in patient morbidity or compromise in postoperative function when compared with unilateral TKA.

Retinal safety of oral and topical ofloxacin in rabbits.

Ofloxacin is a broad spectrum fluoroquinolone antibiotic with good ocular penetration. We investigated the potential for retinal toxicity associated with increased intraocular penetration following intensive topical, oral, and combined topical and oral administration. We confirmed ofloxacin concentrations in aqueous and vitreous following these forms of administration. Rabbits received either topical, oral, or a combination of oral and topical ofloxacin. Topical administration consisted of one drop of ofloxacin 0.3% drops given every thirty minutes for a total of eight doses. Oral ofloxacin was administered at a dose of 10 mg (4 mg/kg for average weight 2.5 kg rabbit) every 12 hours for a total of three doses. Six rabbits were followed longitudinally for 4 weeks for evidence of retinal toxicity by indirect ophthalmoscopy and serial ERGs. Electron and light microscopic histopathologic examination of the retina were performed 4 weeks following drug administration. To verify intraocular penetration, ten rabbits received identical dosing schedules followed by HPLC measurement of aqueous and vitreous drug concentrations at 1, 4, 8, 12, and 24 hours following dose completion. No evidence of retinal toxicity was detected by indirect ophthalmoscopy, electroretinography, or histopathological examination. Vitreous ofloxacin levels were highest after combined oral and topical administration, peaking at 0.892 microgram/ml 8 hours following dosage completion. The peak vitreous level following oral administration was 0.230 microgram/ml and 0.026 microgram/ml following topical administration. Peak aqueous humor levels were achieved one hour following drug administration and were 11.400 micrograms/ml after topical, 0.206 microgram/ml after oral, and 8.180 micrograms/ml after combined administration. Our study suggests that intensive topical and oral ofloxacin administration does not cause retinal toxicity in rabbits, despite achieving effective aqueous and vitreous humor antimicrobial concentrations.

Experience with living-donor lobar transplantation for indications other than cystic fibrosis.

OBJECTIVE: Since development of a living donor bilateral lobar transplantation protocol for patients with cystic fibrosis, our indications have expanded to include recipients with other diagnoses. METHODS: We report on our experience in eight patients with primary pulmonary hypertension, postchemotherapy pulmonary fibrosis, bronchopulmonary dysplasia, idiopathic pulmonary fibrosis, and obliterative bronchiolitis. The average age of the eight patients was 19.1 years (range 9 to 40). The mean preoperative carbon dioxide tension for the four patients who did not have primary pulmonary hypertension was 92 mm Hg (range 64 to 120 mm Hg), and the two patients with pulmonary fibrosis were intubated (one on high-frequency jet ventilation). Each recipient received a right lower lobe (n = 7) or middle lobe (n = 1) and a left lower lobe (n = 8) from a total of 16 donors representing various combinations of the recipient's family (n = 15) and an unrelated friend (n = 1). RESULTS: With an average follow-up of 1 year the overall survival is 75%. For the five patients followed up for at least 1 year, mean forced vital capacity was 80.6%, forced expiratory volume in 1 second was 75.6%, mid-forced expiratory flow was 64%, and diffusing lung capacity corrected for alveolar volume was 73% of predicted. For those patients with primary pulmonary hypertension, preoperative hemodynamics revealed mean pressures as follows: blood pressure 84.8 mm Hg, right atrial pressure 7.8 mm Hg, pulmonary artery pressure 71.3 mm Hg, pulmonary capillary wedge pressure 9.5 mm Hg, cardiac index 2.9 L/min per square meter, and pulmonary vascular resistance index 22.8 Wood units. Postoperative hemodynamics revealed a mean blood pressure of 84.3 mm Hg, right atrial pressure of 2.7 mm Hg, pulmonary artery pressure of 16 mm Hg, pulmonary capillary wedge pressure of 7.3 mm Hg, cardiac index of 4.2 L/min per square meter, and pulmonary vascular resistance index of 1.9 Wood units. CONCLUSIONS: Early results of living-donor bilateral lobar transplantation for diseases other than cystic fibrosis have resulted in satisfactory survival and pulmonary function. Additionally, patients with severe primary pulmonary hypertension have had dramatic normalization of their hemodynamics despite the limited amount of lung tissue transplanted. We believe that the data from this small cohort experience compares favorably with our larger series with cystic fibrosis and supports an expanded role for living-donor lobar transplantation in patients with alternate indications.

Living-donor lobar lung transplantation experience: intermediate results.

OBJECTIVE: Living-donor lobar lung transplantation offers an alternative for patients with a life expectancy of less than a few months. We report on our intermediate results with respect to recipient survival, complications, pulmonary function, and hemodynamic reserve. METHODS: Thirty-eight living-donor lobar lung transplants were performed in 27 adult and 10 pediatric patients for cystic fibrosis (32), pulmonary hypertension (two), pulmonary fibrosis (one), viral bronchiolitis (one), bronchopulmonary dysplasia (one), and posttransplantation obliterative bronchiolitis (one). Seventy-six donors underwent donor lobectomies. RESULTS: There were 14 deaths among the 37 patients, with an average follow-up of 14 months. Predominant cause of death was infection, consistent with the large percentage of patients with cystic fibrosis in our population. The overall incidence of rejection was 0.07 episodes/patient-month, representing 0.8 episodes/patient. Postoperative pulmonary function testing generally showed a steady improvement that plateaued by postoperative months 9 to 12. Fourteen patients who were followed up for at least 1 year underwent right heart catheterization; pressures and pulmonary vascular resistances were within normal ranges. Bronchiolitis obliterans was definitively diagnosed in three patients. Among the 76 donors, complications in the postoperative period included postpericardiotomy syndrome (three), atrial fibrillation (one), and surgical reexploration (three). CONCLUSIONS: We believe that these data support an expanded role for living-donor lobar lung transplantation. Our intermediate data are encouraging with respect to the functional outcome and survival of these critically ill patients, who would have died without this option.

Talc pleurodesis: talc slurry versus thoracoscopic talc insufflation in a porcine model.

BACKGROUND: Pleurodesis using both talc slurry and thoracoscopic talc insufflation has been shown to be clinically effective. This study compares these two modalities of pleural talc instillation in an animal model. METHODS: Eleven immature pigs underwent general endotracheal anesthesia. On one side, a slurry of 5 g sterile United States Pharmacopeia talc in 50 mL of saline solution was instilled through a thoracostomy tube. On the other side, the lung was deflated and 5 g of dry talc was insufflated under thoracoscopic visualization. The animals were sacrificed 30 days later, and the quality of pleural adhesions was graded from 0 to 2 (0 = absent; 1 = light; 2 = dense) in each of six regions of each hemithorax. The distribution of adhesions on each side was graded from 0 to 6, according to the number of areas that contained adhesions. RESULTS: One animal died of anesthetic complications. Among the survivors, adhesions produced by both methods were dense and diffuse in 8 of 10 animals, and light and diffuse in 1 animal. One animal had light or absent adhesions on the talc slurry side, and dense and diffuse adhesions on the thoracoscopic talc insufflation side. There was no difference between the techniques for density of adhesion scores (talc slurry, 9.9 +/- 2.2; thoracoscopic talc insufflation, 10.0 +/- 2.5) or distribution of adhesion scores (talc slurry, 5.5 +/- 1.0; thoracoscopic talc insufflation, 5.8 +/- 0.4) (p > 0.1). CONCLUSIONS: Effective pleurodesis in a porcine model can be obtained with either talc slurry or thoracoscopic talc insufflation.

Bilateral lobar transplantation utilizing living related donors.

As the recipient list for patients requiring lung transplantation continues to increase, cadaveric donor lung availability has remained static. Our experience with utilizing lobes from living related donors for bilateral pulmonary transplantation in 20 patients has yielded a 75% survival at 1 year follow-up. Morbidity and mortality have been predominately due to infection. Rejection episodes have been mild and unilateral and have responded to augmented corticosteroids. Pulmonary function tests in the recipients tend to improve steadily during the first year postoperatively, and the patients have excellent functional capacity. There have been no significant complications in the donors. On the basis of our clinical experience, we have found that bilateral lobar transplantation utilizing living related donors has resulted in organ availability that can be lifesaving in critically ill patients and can provide a good alternative in certain noncritical, deteriorating patients.

Glaucoma with inflammatory precipitates on the trabecular meshwork: a report of Grant's syndrome with ultrasound biomicroscopy of precipitates.

BACKGROUND: The syndrome of inflammatory precipitates on the trabecular meshwork is a rare form of inflammatory glaucoma that was described by Chandler and Grant in 1968 and subsequently given the eponym Grant's syndrome. METHODS: We present two cases of elevated intraocular pressure associated with inflammatory precipitates on the trabecular meshwork in otherwise relatively quiet eyes, consistent with Grant's syndrome. We review the epidemiology, clinical features, and mechanism of this syndrome. In addition, we demonstrate the use of ultrasound biomicroscopy for imaging angle inflammatory precipitates. RESULTS: Our patients demonstrate the cardinal features of Grant's syndrome, including acute onset, significant elevation of tension, trabecular meshwork precipitates in an otherwise quiet eye, limited response to typical pressure lowering agents, excellent response to topical steroids, evidence of recurrence with bilaterality, and systemic association with sarcoidosis. Ultrasound biomicroscopy proves to be a useful adjunct for pathologic imaging. CONCLUSIONS: The syndrome of glaucoma with inflammatory precipitates on the trabecular meshwork is a rare entity that should be considered as a possible diagnosis of elevated intraocular pressures in otherwise apparently quiet eyes.

Ocular toxicity following topical application of anesthetic cream to the eyelid skin.

BACKGROUND AND OBJECTIVE: The use of topical anesthetic cream in the periorbital region may be of clinical value. The potential for toxic effects from such use has not been studied in a controlled manner. This study was performed to evaluate the potential ocular toxicity of anesthetic cream topically applied to the eyelid in an animal model. MATERIALS AND METHODS: Ten rabbits underwent periorbital eutectic mixture of local anesthetics (EMLA) (2.5 percent lidocaine and 2.5 percent prilocaine) application and were observed for evidence of gross or microscopic ocular toxicity. Baseline external and anterior segment examinations were performed, including biomicroscopy and fluorescein staining, after which a standard quantity of EMLA cream (0.75 g) was applied along the upper eyelid and covered with an occlusive dressing. After 1 hour of treatment, the eyelid and anterior segment were examined for evidence of adverse reaction. The eyelids were excised and examined histopathologically. RESULTS: No significant adverse effects were noted on external lid and anterior segment examination. The histopathologic findings were within normal limits. CONCLUSIONS: This study suggests that external application of EMLA cream to the eyelid does not induce local toxicity in the rabbit model. The external application of EMLA cream may be safe in the periorbital region.

Central retinal artery occlusion in a child with T-cell lymphoma.

PURPOSE/METHODS: Central retinal artery occlusion occurs infrequently in children. We treated a child with central retinal artery occlusion before a systemic disease was discovered. RESULTS/CONCLUSION: Vision improved after paracentesis and anticoagulation. Systemic T-cell lymphoma was subsequently diagnosed. In contrast to older patients in whom atheromatous disease is a common etiologic factor, children frequently have more obscure systemic or ocular associations. Lymphoma should be considered as a possible systemic association in cases of central retinal artery occlusion, especially in younger patients who are less at risk for the more common causes.