Cortical computations via transient attractors.

The ability of sensory networks to transiently store information on the scale of seconds can confer many advantages in processing time-varying stimuli. How a network could store information on such intermediate time scales, between typical neurophysiological time scales and those of long-term memory, is typically attributed to persistent neural activity. An alternative mechanism which might allow for such information storage is through temporary modifications to the neural connectivity which decay on the same second-long time scale as the underlying memories. Earlier work that has explored this method has done so by emphasizing one attractor from a limited, pre-defined set. Here, we describe an alternative, a Transient Attractor network, which can learn any pattern presented to it, store several simultaneously, and robustly recall them on demand using targeted probes in a manner reminiscent of Hopfield networks. We hypothesize that such functionality could be usefully embedded within sensory cortex, and allow for a flexibly-gated short-term memory, as well as conferring the ability of the network to perform automatic de-noising, and separation of input signals into distinct perceptual objects. We demonstrate that the stored information can be refreshed to extend storage time, is not sensitive to noise in the system, and can be turned on or off by simple neuromodulation. The diverse capabilities of transient attractors, as well as their resemblance to many features observed in sensory cortex, suggest the possibility that their actions might underlie neural processing in many sensory areas.

Screening for asbestos-related pleural disease with digital storage phosphor radiography.

Digital storage phosphor radiography (SR) has a wide dynamic range and unique postprocessing capabilities that may improve the performance of screening studies for asbestos-related pleural disease compared with conventional film radiography (FR). In a group of 32 asbestos-exposed and nine control subjects with established pleural data, we compared the screening performance of FR and SR obtained with a single isoexposure, dual-energy technique (system resolution 0.2 mm, 10 bits). Performance was evaluated for 7320 observations by eight readers using a paired t test (P less than .02 with Bonferroni correction) of averaged receiver operating characteristic curve (ROC) areas (Az +/- standard error). We found that SR alone and SR supplemented by dual-energy soft-tissue and calcium images (SRde) were superior to FR in the overall detection of pleural abnormalities (Az = 0.90 +/- 0.01, 0.90 +/- 0.01, and 0.88 +/- 0.01, respectively). In the specific detection of pleural calcification, SRde was superior to FR (Az = 0.91 +/- 0.01 and 0.87 +/- 0.01, respectively; P less than 0.01). Analysis of variance indicated that SRde most closely reproduced an established pleural score based on the International Labor Organization (ILO) classification of the pneumoconioses (P less than 0.05, Scheffé's multiple comparison test). We conclude that isodose SR performs at least as well as FR in screening for asbestos-related pleural disease. SR supplemented by dual-energy images might improve the specific detection of pleural calcifications compared with FR.

The indoor air we breathe.

Increasingly recognized as a potential public health problem since the outbreak of Legionnaire's disease in Philadelphia in 1976, polluted indoor air has been associated with health problems that include asthma, sick building syndrome, multiple chemical sensitivity, and hypersensitivity pneumonitis. Symptoms are often nonspecific and include headache, eye and throat irritation, chest tightness and shortness of breath, and fatigue. Air-borne contaminants include commonly used chemicals, vehicular exhaust, microbial organisms, fibrous glass particles, and dust. Identified causes include defective building design and construction, aging of buildings and their ventilation systems, poor climate control, inattention to building maintenance. A major contributory factor is the explosion in the use of chemicals in building construction and furnishing materials over the past four decades. Organizational issues and psychological variables often contribute to the problem and hinder its resolution. This article describes the health problems related to poor indoor air quality and offers solutions.

Chest pain in rubber chemical workers exposed to carbon disulphide and methaemoglobin formers.

A cross sectional prevalence study of chest pain in 94 rubber chemical workers exposed to carbon disulphide (CS2) and methaemoglobin forming aromatic amines was carried out. The purpose of the study was to determine whether the prevalence of chest pain or coronary heart disease (CHD), or both, in exposed individuals exceeded that of a group of non-exposed individuals from the same plant. Cardiovascular, smoking, and occupational histories were obtained. Blood pressure, height, weight, serum cholesterol, and fasting blood glucose were measured. Resting electrocardiograms (ECGs) were obtained on all study participants, as were exercise stress tests on selected exposed individuals. Matching eliminated important known risk factors for coronary artery disease. Both chest pain and angina were significantly related to exposure, controlling for age and cigarette smoking. This association was not dependent on duration of exposure as defined by 10 or more years of employment in the department of interest. CHD as defined by angina, a history of myocardial infarction, or a coronary ECG or a combination of these occurred more frequently among exposed workers. The number of abnormal ECGs in the exposed group was twice that in the control group, but the difference was not statistically significant. Age rather than exposure appeared to be the important variable associated with raised blood pressure. Neither biological measures of exposure nor ECGs showed an acute effect of workplace exposures on the myocardium. Possible additive or multiplicative effects of individual chemical agents could not be evaluated. Appropriate modification of medical surveillance of rubber chemical workers with exposure to CS2 and aromatic amines is warranted.

Asbestos-related disease in plumbers and pipefitters employed in building construction.

Asbestos-related disease in a group of 153 plumbers and pipefitters employed in building construction was assessed by means of a cross-sectional prevalence study. Study methods were medical questionnaire, spirometry, measurement of diffusing capacity, physical examination of the chest, and chest roentgenogram. The major finding was bilateral pleural thickening in 28 (18.3%) of the participants. Unilateral pleural thickening was found in 12 subjects (7.8%). Small irregular opacities of profusion 1/0 or greater were found in 12 subjects (7.8%). Bilateral pleural thickening was associated with both age and time since first asbestos exposure, while unilateral pleural thickening was associated only with age. Decreases in forced vital capacity (percent predicted) were associated with duration of exposure. The most prevalent abnormality found was bilateral pleural thickening, which is more specific for asbestos exposure than is unilateral pleural thickening.

Diffuse malignant pleural mesothelioma in an urban hospital: clinical spectrum and trend in incidence over time.

This retrospective analysis reviews the clinical experience of a major urban referral hospital with diffuse malignant pleural mesothelioma during the 14-year period from 1973 through 1986. Seventy-five cases of definite or equivocal mesothelioma were identified. There were four cases of primary malignant peritoneal mesothelioma, seven cases of benign fibrous mesothelioma, and 64 cases of diffuse malignant pleural mesothelioma. In 43 cases (67%) of diffuse malignant pleural mesothelioma, there was historic evidence of asbestos exposure. In 21 cases (33%), there was no known history of asbestos exposure. An increase in annual incidence of diffuse malignant pleural mesothelioma was observed over the study period, from three cases in 1973 to ten cases in 1986. Despite greater awareness of this disease, the diagnosis remains a difficult one to establish given the nonspecific symptoms, signs and radiographic appearance, variable histologic appearance, and poor diagnostic sensitivity and specificity of thoracentesis and closed pleural biopsy. Thoracotomy, thoracoscopy, and CT-guided needle biopsies gave higher yields and are the diagnostic measures of choice when diffuse malignant pleural mesothelioma is suspected.

A comparison of two definitions of abnormality on pulmonary outcome in epidemiologic studies.

Definition of abnormal outcome on lung function testing has not been well standardized. Observed test results have been compared with predicted values based on age, height, and sex in 2 ways: as percent of the predicted (PP) and in relation to limits established by the 95% confidence interval around the predicted (CI). The present study examines these 2 methods of comparison with respect to effect on pulmonary outcome in 377 railroad workers and 193 pipefitters exposed to asbestos. Using accepted PP and CI criteria to define abnormal test results, we classified subjects as restricted or obstructed or normal by each method. The proportion restricted or obstructed was higher (p = 0.0001) if definitions were based on PP rather than on CI: restriction, 12.5% by PP versus 7.2% by CI; obstruction, 18.4% by PP versus 16.0% by CI. Twenty-seven percent (n = 47) of those abnormal by PP were normal by CI. Independent indicators of disease were used to compare this discordant group with groups normal (n = 391) or abnormal (n = 129) by both criteria. The subjects in the discordant group were older, with more years of asbestos exposure, longer latency, and more pleural plaques (p less than 0.05). The occurrence of chronic bronchitis and dyspnea was similar to that in the abnormal group. In our study, the method of comparison had a significant effect on outcome; PP appeared a better measure of disease. Our findings suggest that age and underlying risk of the study population should be considered in selecting a method of comparison in epidemiologic studies of respiratory disease.

Asbestos-related radiographic abnormalities in public school custodians.

A cross-sectional prevalence study of 120 public school custodians was carried out to investigate the prevalence of asbestos-related disease and to determine the proportion with disease attributable to asbestos exposures in school buildings. Medical and occupational histories, flow-volume loops, and posterior-anterior, lateral, and anterior oblique (AO) chest radiographs were obtained. Single breath DLCO was measured and chest auscultation performed. The present report describes radiographic abnormalities and associations with exposure. Mean age of subjects was 57 years and mean duration of work as a custodian, 27 years. Fifty-seven (47.5%) had no known or likely exposure to asbestos outside of their work as a school custodian (NOE). Pleural plaques (PP) occurred in 40 (33%) of the total group and 12 (21%) of the group with NOE. Multivariate analysis revealed significant associations (p less than 0.05) between PP and duration of asbestos exposure. The proportion with PP increased PP detection by a factor of 1.9. Our results reveal PP prevalence in excess of background in the study population and indicate that PP are attributable to asbestos exposure in schools in a subset with NOE. Prudent management of asbestos in buildings is indicated for the prevention of related disease.

Asbestos-related disease in public school custodians.

A cross-sectional prevalence study of 120 public school custodians was carried out. The purposes were 1) to investigate the prevalence of asbestos-related disease in a group of custodians at risk for asbestos exposure in public schools and 2) to determine the proportion with disease attributable to exposures in school buildings. Medical and occupational histories, flow-volume loops, and posterior-anterior, lateral, and anterior oblique (AO) chest radiographs were obtained. Single breath DLCO was measured and chest auscultation performed. Mean age of subjects was 57 years and mean duration of work as a custodian, 27 years. Fifty-seven (47.5%) had no known or likely exposure to asbestos outside of their work as a school custodian (NOE). Pleural plaques (PP) occurred in 40 (33%) of the total group and 12 (21%) of the group with NOE. Pulmonary restriction (FVC less than 80% predicted, FEV1/FVC% greater than or equal to 70) occurred in 22 (18%) of the total group and 10 (17%) of those with NOE. DLCO was lower in the group with restriction. Multivariate analysis revealed significant associations (p less than 0.05) between both PP and restriction and duration of asbestos exposure. AO radiographs increased PP detection by a factor of 1.9. Our results reveal PP prevalence in excess of background and pulmonary restriction in the study population, and indicate that PP are attributable to asbestos in schools. Findings with regard to pulmonary restriction need further investigation. Prudent management of asbestos in buildings is indicated for the prevention of related disease.

Asbestos-related pleural plaques and lung function.

The present study examines the association between asbestos-related pleural plaques and lung function in a group of workers with occupational exposure to asbestos. Exposure, smoking, and respiratory histories, chest radiographs, flow-volume loops, and single breath DLCOs were obtained on 383 railroad workers. A score based on the ILO-1980 classification system was used to quantify the extent of plaquelike thickening. In order to eliminate potential confounders, we excluded from final analysis subjects with diffuse pleural thickening (n = 10) or small irregular opacities classified as profusion 0/1 or greater (n = 6) on chest radiograph. Definite pleural plaques were observed in 22.6%. The single breath DLCO was similar in the groups with and without plaques (p = 0.0550). Decrement in FVC and the occurrence of pulmonary restriction were associated with the presence of definite plaques (p = 0.0306 and 0.0431, respectively) and with quantitative pleural score (p = 0.0135 and 0.0126), controlling for duration of asbestos exposure and smoking. A test for trend revealed an association between level of diagnostic certainty (none, suspect, definite) for pleural plaques and these measures of lung function (p less than 0.02). Our findings reveal an association between asbestos-related pleural plaques and decrement in lung function as measured by FVC and criteria for pulmonary restriction.

Asbestos-related disease in railroad workers. A cross-sectional study.

A cross-sectional prevalence study of 377 railroad workers was carried out. The purpose was to investigate the prevalence of asbestos-related disease. We compared conventional with more recently adopted criteria for defining abnormal lung function. We compared the test results of those who performed reproducibly on spirometry with those who did not. Medical and occupational histories, flow-volume loops, and posteroanterior and lateral chest radiographs were obtained. Single-breath carbon monoxide diffusing capacity (DLCO) was measured, and chest auscultation was performed. Related to time since onset of exposure, pleural plaques occurred in 22.9%. There was radiographic evidence of interstitial disease in 1.6%. Reduced single-breath DLCO (12.4%), crackles (18.4%), and dyspnea (49.6%) were significantly associated with asbestos exposure. The prevalence of restriction and obstruction was 5.1 and 12.4%, respectively, but differed (p = 0.0001) with the definition criteria selected. The proportion with each of these abnormalities was higher in the nonreproducible group. That group was older, with more pleural plaques and chronic bronchitis. Railroad workers are a group at risk for asbestos-related disease. Extent of disease and assumptions about causality are likely to vary with definitions of normalcy and the use of reproducibility criteria.

T-cell alveolitis in lung lavage of asbestos-exposed subjects.

In sarcoidosis and idiopathic pulmonary fibrosis, it has been reported that lymphocyte proportions in lung lavage predict the subsequent clinical course. Recent evidence has suggested that lymphocytes are important in the alveolitis of asbestosis. We hypothesized that a greater relative proportion of T-lymphocytes in lung lavage of asbestos-exposed subjects is associated with immune activation and may predict the subsequent clinical course. We assessed lymphocyte subsets in lung lavage and peripheral blood (PB) of 97 asbestos-exposed subjects and 10 unexposed normal, using flow cytometry analysis of monoclonal antibody-treated cells. T-cell alveolitis was defined as follows: [%lymphocytes in lavage x %CD3 in lavage] greater than 2 SD above that product in normals. Eighteen subjects had T-cell alveolitis (group 1) and 79 did not (group 2). There were no significant differences between the groups in age, smoking status, duration of exposure, lung function results, or frequency of plaques or profusion greater than or equal to 1/0. Percent CD2 was higher in lavage of group 1 compared with group 2. There was a trend for higher %Ia in lavage of group 1 compared with group 2. These results identify a subgroup of asbestos-exposed subjects with T-cell alveolitis but no present excess of asbestos-related disease who may be at risk for future asbestos-related disease.

Cobalt exposure and lung disease in tungsten carbide production. A cross-sectional study of current workers.

A cross-sectional study of 1,039 tungsten carbide (TC) production workers was carried out. The purposes were (1) to evaluate the prevalence of interstitial lung disease (ILD) and work-related wheezing, (2) to assess correlations between cobalt exposure and pulmonary disease, (3) to compare lung disease in grinders of hard carbide versus nongrinders, and (4) to evaluate the effects of new and previous threshold limit values for cobalt of 50 and 100 micrograms/m3. We obtained medical and occupational histories, flow-volume loops, single breath carbon monoxide diffusing capacity (DLCO), and chest radiographs. Time-weighted average cobalt levels were determined at every step in the production process. Work-related wheeze occurred in 113 participants (10.9%). Profusion greater than or equal to 1/0 occurred in 26 (2.6%) and interstitial lung disease (defined as profusion greater than or equal to 1M, FVC or DLCO less than or equal to 70%, and FEV1/FVC% greater than or equal to 75) in 7 (0.7%). The relative odds of work-related wheeze was 2.1 times for present cobalt exposures exceeding 50 micrograms/m3 compared with exposures less than or equal to 50 micrograms/m3. The relative odds of profusion greater than or equal to 1/0 was 5.1 times for average lifetime cobalt exposures exceeding 100 micrograms/m3 compared with exposures less than or equal to 100 micrograms/m3 in those with latency exceeding 10 yr. ILD was found in three workers with very low average lifetime exposures (less than 8 micrograms/m3) and shorter latencies. Grinders of hard carbide had lower mean DLCO than nongrinders, even though their cobalt exposures were lower.(ABSTRACT TRUNCATED AT 250 WORDS)

Natural killer cell activity in cigarette smokers and asbestos workers.

In order to evaluate the effects of cigarette smoking and asbestos exposure on cellular immunity, we tested a group of cigarette smokers and asbestos workers for natural killer (NK) activity in the peripheral blood. The mean NK activity in cigarette smokers was lower than in normal subjects (13.7 +/- 1.6 versus 29.0 +/- 3%; p less than 0.05). As a group, the mean NK activity for the asbestos-exposed group was also reduced compared with that of the nonsmoking control group (22.6 +/- 3.2%; p less than 0.05). When divided according to the smoking status, the asbestos workers who were nonsmokers or ex-smokers showed similar decreases in NK activity compared with normal subjects (19.5 +/- 6.2 and 21.2 +/- 4.5%, respectively; p less than 0.05). A subgroup of asbestos-exposed subjects who currently smoked showed no decrease in NK activity. The data show that NK activity is reduced in the peripheral blood of cigarette smokers and asbestos workers. The relatively normal NK activity found in asbestos workers who also smoked is unexplained. Impairment of NK activity is a potential mechanism for the increased incidence of infection and cancer in smokers and neoplasia in asbestos workers.

Effects of spirometry standards in two occupational cohorts.

Characteristics of subjects with nonreproducible lung function tests (test failures) are described in two studies of occupational respiratory disease. According to current guidelines for spirometry, subjects with test failure are excluded from analyses of epidemiologic pulmonary function data. Among 415 Chinese cotton textile workers, the prevalence of byssinosis was 5.8% for subjects with repeatable tests and 13.3% for subjects with test failure. In regression analysis, the estimate of the association between cotton dust exposure and FEV1 decreased when subjects with test failure were excluded. In a second cohort of 378 asbestos-exposed machinists, the prevalence of chronic bronchitis was significantly greater among those with test failure. Considering only subjects with repeatable measurements, FEV1 was lower among textile workers with byssinosis and machinists with chronic bronchitis than among their asymptomatic coworkers. This suggests that, on average, subjects with poor test performance had lower (unobserved) FEV1 values, and therefore that the exclusion of subjects with test failure may cause selection bias.

Respiratory symptoms and lung function in workers in heavy and highway construction: a cross-sectional study.

BACKGROUND: Occupational exposures for workers in heavy and highway (HH) construction include cement-containing dusts and diesel exhaust (DE). To investigate possible health effects, respiratory symptoms and lung function were examined in laborers, tunnel workers (TW), and operating engineers (OE) in HH and tunnel construction. The principal outcome of interest was airways disease. METHODS: Subjects were recruited through their unions. Medical and occupational histories and flow-volume loops were obtained. Based on self-report, asthma and chronic bronchitis were categorized as (1) physician-diagnosed or (2) for asthma, undiagnosed likely, and (3) for chronic bronchitis, symptomatic. Trade and time in the union were used as surrogates of exposure. Prevalence of asthma and chronic bronchitis, lung function outcome, and relationships with exposure variables were examined. RESULTS: Data were obtained on 389 workers: 186 laborers, 45 TWs, and 158 OEs. Prevalence of asthma was 13 and 11.4% for laborers (including TW) and OEs, respectively, and of symptomatic chronic bronchitis, 6.5 and 1.9%, respectively. Odds ratios (OR) for undiagnosed asthma likely were significantly elevated in TWs compared to OEs, and marginally elevated for chronic bronchitis. Inverse relationships were observed between time in the union, and risk for asthma and chronic bronchitis. Asthma (physician-diagnosed or undiagnosed likely) predicted lower FEV(1). Current cigarette use was associated with chronic bronchitis but not asthma. CONCLUSIONS: TWs, laborers, and OEs in HH construction are at increased risk for asthma. TWs also appear to be at increased risk for chronic bronchitis. Our data suggest that symptomatic workers are self-selecting out of their trade. Asthma was associated with lower lung function in those affected.