Restrictive lung function and asbestos-induced pleural fibrosis. A quantitative approach.

To assess further the clinical significance of asbestos-induced pleural fibrosis, we used a computer algorithm to reconstruct images three dimensionally from the high-resolution computerized tomography (HRCT) scan of the chest in 60 asbestos-exposed subjects. Pulmonary function tests, chest radiographs, and HRCT scans were performed on all study subjects. The volume of asbestos-induced pleural fibrosis was computed from the three-dimensional reconstruction of the HRCT scan. Among those with pleural fibrosis identified on the HRCT scan (n = 29), the volume of the pleural lesion varied from 0.01% (0.5 ml) and 7.11% (260.4 ml) of the total chest cavity. To investigate the relationship between asbestos-induced pleural fibrosis and restrictive lung function, we compared the computer-derived estimate of pleural fibrosis to the total lung capacity and found that these measures were inversely related (r = -0.40; P = 0.002). After controlling for age, height, pack-years of cigarette smoking, and the presence of interstitial fibrosis on the chest radiograph, the volume of pleural fibrosis identified on the three-dimensional reconstructed image from the HRCT scan was inversely associated with the total lung capacity (P = 0.03) and independently accounted for 9.5% of the variance of this measure of lung volume. These findings further extend the scientific data supporting an independent association between pleural fibrosis and restrictive lung function.

Human epidemiology: a review of fiber type and characteristics in the development of malignant and nonmalignant disease.

Consideration of the human epidemiology of diseases arising from exposure to naturally occurring and man-made mineral fibers encompasses the several forms of asbestos (chrysotile, crocidolite, amosite, anthophyllite, tremolite-actinolite), other naturally occurring silicates (talc, sepiolite, erionite, attapulgite, vermiculite, and wollastonite), and man-made mineral fibers (glass continuous filament, glass/rock/slag insulation wools, ceramic and other refractory fibers, and glass microfibers). The diseases arising from exposures to some of these fibers include pleural thickening (plaques, diffuse pleural thickening, and calcification), pulmonary fibrosis, lung cancers, mesothelioma of the pleura and peritoneum, and other cancers). Risk factors important in assessing these diseases include assessment of latency, duration of exposure, cumulative exposure, fiber origin and characteristics (length and diameter), other possible confounding occupational or environmental exposures, and smoking. Methodological issues commonly presenting problems in evaluation of these data include assessment of the adequacy of environmental exposures, particularly in regard to fiber identification, distribution, and concentration over the duration of exposure, and the adequacy of study design to detect health effects (disease frequency, latency, and cohort size). Research priorities include further assessment and standardization of pleural thickening relative to fiber exposure, uniform mesothelioma surveillance, further epidemiological assessment of certain silicate and man-made mineral fiber cohorts with emphasis given to assessment of tremolite and small diameter glass and ceramic fibers. Further assessment of possible health risks of the general public should await improved definition of relevant fiber exposure in ambient air.

The use of pulmonary function testing and questionnaires as epidemiologic tools in the study of occupational lung disease.

Pulmonary function testing and questionnaires are valuable tools in epidemiologic studies of occupational lung disease. Accurate equipment and standardized methodology are vital to obtain reproducible responses. For spirometry, the FVC and FEV show the least intrasubject variability and on questionnaires, occupational and smoking history are more reproducible than symptoms. The limitations of any method used to define a lower limit of normal should be kept in mind and, whenever possible, groups should be compared by use of the distribution of observations in the two groups--not just the prevalence of "abnormal" findings.

Pleural determinants of restrictive lung function and respiratory symptoms in an asbestos-exposed population.

To further define the relationship between asbestos-induced pleural fibrosis and restrictive lung function, we investigated the pleural determinants of respiratory symptoms and restrictive physiology in 1,211 sheet metal workers. We evaluated the relationship between specific components of pleural fibrosis (costophrenic angle involvement, diaphragmatic plaques, width and length of pleural fibrosis, pleural calcification, and the type of fibrosis-circumscribed plaque or diffuse pleural thickening) and both forced vital capacity and respiratory symptoms. We found that costophrenic angle involvement, the width and length of pleural fibrosis, and the presence of either circumscribed plaque or diffuse pleural thickening were each significantly associated with a lower FVC. No consistent relationship was observed between FVC and either diaphragmatic plaques or pleural calcification. However, since the pleural abnormalities were highly collinear, none of these abnormalities alone or in combination predicted the reduction in FVC significantly better than a model that included circumscribed plaques and diffuse pleural thickening. We also investigated the relationship of each component of pleural fibrosis with cough, dyspnea, and chest pain. After controlling for appropriate confounders, a trend toward significance was observed between increased width and length of fibrosis and dyspnea with exertion. Otherwise, these pleural abnormalities were not consistently related to any of the three respiratory symptoms. Our results indicate that although pleural plaques and diffuse pleural thickening and their components are independently associated with a lower FVC, these components of pleural fibrosis do not substantially improve the previously defined relationship between FVC and both circumscribed plaques and diffuse pleural thickening. In addition, a trend toward significance was observed between the width and length of the pleural abnormality and dyspnea while hurrying.

Peak flow as a measure of airway dysfunction in swine confinement operators.

To evaluate the usefulness of a portable peak flow meter in predicting airway dysfunction in symptomatic swine confinement workers, we conducted a study using an established cohort of swine workers in Iowa. Participants were randomly selected from a group of 207 swine confinement workers and a group of nonconfinement farmers who had been followed longitudinally. Swine confinement workers with work-related symptoms were identified, and two control groups (swine confinement workers and nonconfinement workers) without work-related symptoms were frequency matched by age, sex, and smoking status to the symptomatic swine confinement workers. Peak flow measures were obtained for 7 days using a mini-Wright peak flow meter and comparisons were made between the symptomatic swine confinement farmers (n = 24) and both groups of asymptomatic workers: swine confinement workers (n = 21) and neighborhood farmer controls (n = 25). Peak flow readings were recorded by subjects five times per day for 7 days, initially on awakening, then after chores, before lunch, before dinner, and before bedtime. The actual hour of day for each measurement of peak flow was similar between the three groups. Percent changes from initial AM peak flow did not significantly differ between subject groups. However, symptomatic swine confinement workers consistently exhibited significantly lower initial and subsequent mean peak flow values compared with asymptomatic swine confinement workers and neighborhood control farmers, controlling for age, height, gender, and smoking status. These differences occurred on most of the measures of peak flow throughout the work day. The persistence of these lower values throughout the work day is remarkably consistent during the study period and is suggestive of airway disease in the symptomatic swine confinement workers. Our findings suggest that peak flow meters are a useful indicator of potential airway injury and offer an additional portable, diagnostic tool in the assessment of symptomatic workers.

Asbestos-induced pleural fibrosis and impaired exercise physiology.

To further assess the clinical significance of asbestos-induced pleural fibrosis, we performed cardiopulmonary exercise testing in 90 subjects who were exposed to asbestos. Of the 82 subjects without an abnormal resperate exercise, 35 had normal pleura, 33 had circumscribed pleural plaques, and 14 had diffuse pleural thickening. Interstitial fibrosis (International Labor Organization [ILO]. > or = 1/10) was present in 14 of 35 subjects with normal pleura, 13 of 33 subjects with circumscribed pleural plaques, and 2 of 14 subjects with diffuse pleural thickening. Although pleural fibrosis did not appear to be related to impaired respiratory function with exercise in our entire cohort, this finding was confounded by a higher proportion of interstitial fibrosis in subjects with normal pleura. In fact, among study subjects without asbestosis, significant decreases in gas exchange (higher VD/VT and increased alveolar-arterial oxygen pressure difference) were observed at maximal exercise among subjects with pleural fibrosis. Interestingly, neither a higher respiratory rate nor a lower VT/FVC ratio was observed among those with pleural fibrosis, suggesting that the mechanical effects of pleural fibrosis on the chest wall do not explain the increased VD/VT. Using multivariate analyses to control for potential confounders, regression models showed that pleural plaques (p = 0.04) and diffuse pleural thickening (p = 0.03) were independently associated with significant increases in dead space ventilation (VD/VT) with maximal exercise. These findings indicate that asbestos-induced pleural fibrosis is independently associated with decrements in gas exchange with maximal exercise and suggest that interstitial lung disease, not detected on the routine chest x-ray film, may be responsible for this abnormal response to exercise.

The relationship between HLA-A, B, DQ, and DR antigens and asbestos-induced lung disease.

To evaluate the relationship between human leukocyte antigen (HLA) and both asbestos-induced pulmonary fibrosis and pleural fibrosis, we obtained HLA-A, B, C, DQ, and DR phenotypes in 42 long-term asbestos-exposed workers. Among these exposed workers, 15 had asbestosis (ILO > or = 1/0) on the chest radiograph and 18 had asbestos-induced pleural fibrosis. We found that there was an increased percentage of HLA-A29, HLA-B44, and HLA-Bw4 in the subjects with asbestosis. In addition, we observed a marginally positive relationship between HLA-A29 and the severity of pulmonary fibrosis. Similarly, there was a higher prevalence of HLA-DRw53 and DQ2 in the subjects with asbestos-induced pleural fibrosis. The presence of HLA-DQ2 was significantly related to the extent and type of asbestos-induced pleural fibrosis while HLA-DRw53 was not consistently related to the type or extent of pleural disease. Importantly, we observed that HLA-A29, HLA-B44, HLA-Bw4, HLA-DRw53, and HLA-DQ2 do not have a significantly shorter duration or latency of asbestos exposure. Moreover, none of the HLA haplotypes (A29, B44, Bw4, DRw53, and DQ2) that we found to be associated with radiographic manifestations of asbestos-induced lung disease were associated with the physiologic abnormalities that have been traditionally associated with asbestos-induced lung disease. The only exception was an isolated decrease in the residual volume associated with the presence of HLA-A29. These results suggest that the HLA-A29 phenotype may be associated with the development of asbestosis and the HLA-DQ2 phenotype may be associated with the development of asbestos-induced pleural fibrosis. However, these associations are not particularly strong, physiologic correlation is lacking, and previous studies do not support our findings.

The detection of thoracic abnormalities using posterior-anterior (PA) vs PA and oblique roentgenograms.

A reading trial was conducted as part of the 1978 Bay Area Asbestos Screening Project to evaluate the utility of adding oblique-view roentgenograms to standard posterior-anterior (PA) views. Chest films from a sample of 555 workers with histories of long-term asbestos exposure were read twice as PA and twice as PA + oblique sets, providing a basis for assessing reliability through intrareader, interreader, and intermethod agreement. The ancillary use of oblique view films resulted in higher rates of detection of asbestos-related abnormalities than with PA films alone, but the increased rates were gained at the expense of reliability in the interpretation process. Depending on the source of this unreliability, which requires further study, different remedial actions might be indicated. A reader's lack of experience could indicate the need for additional training, the use of several readers, an average over several reader judgements, or the development of standards for evaluating obliques. If, on the other hand, no way is found to reduce the unreliability, the use of oblique films in routine screening programs ought to be discouraged on the basis of measurement theory, since reliability is a prerequisite to validity.

Determinants of restrictive lung function in asbestos-induced pleural fibrosis.

We evaluated whether restrictive lung function among asbestos-exposed individuals with pleural fibrosis was caused by radiographically inapparent parenchymal inflammation and/or parenchymal fibrosis. All 24 study participants were sheet metal workers who were nonsmokers with normal parenchyma on posteroanterior chest radiograph. These subjects had either normal pleura (n = 7), circumscribed plaques (n = 9), or diffuse pleural thickening (n = 8). After controlling for age, years in the trade, and pack-years of smoking, we found that sheet metal workers with diffuse pleural thickening had a lower forced vital capacity (P less than 0.001), total lung capacity (P less than 0.01), and CO-diffusing capacity of the lung (P less than 0.05) than those with normal pleura. Similarly, sheet metal workers with circumscribed plaques were found to have a reduced forced vital capacity; however, because of the small number of study subjects, this difference (regression coefficient = -11.0) was only marginally significant (P = 0.06). Although circumscribed plaque and diffuse pleural thickening were both associated with a lymphocytic alveolitis and a higher prevalence of parenchymal fibrosis on high-resolution computerized tomography (HRCT) scan, neither a lymphocytic alveolitis nor the finding of parenchymal fibrosis on HRCT scan influenced the relationship between pleural fibrosis and restrictive lung function. We conclude that pleural fibrosis is associated with restrictive lung function and abnormally low diffusion that appears to be independent of our measures of parenchymal injury (chest X-ray, bronchoalveolar lavage, and HRCT scan).(ABSTRACT TRUNCATED AT 250 WORDS)

High-resolution CT-derived measures of lung density are valid indexes of interstitial lung disease.

To assess the validity of computer-assisted methods in analyzing the lung parenchyma imaged with high-resolution computed tomography (HRCT), we compared computer-derived estimates of lung density to other, more traditional, measures of parenchymal injury in 24 subjects with idiopathic pulmonary fibrosis (IPF) and 60 subjects with extensive occupational exposure to asbestos. Gray scale density histograms were constructed from the HRCT images. The gray scale histogram of both study groups was of a skewed unimodal distribution. However, compared with the asbestos-exposed subjects, the patients with IPF had a gray scale distribution that was significantly shifted to the right (greater density) and flatter. In a multivariate analysis, after controlling for age and cigarette smoking, we found that the mean and median gray scale densities were independently associated with the presence of moderate-to-severe dyspnea, a higher International Labour Office chest X-ray category, a lower forced vital capacity, and a higher concentration of macrophages and eosinophils in the bronchoalveolar lavage fluid. These factors accounted for > 70% of the variance of the mean and median gray scale densities. Interestingly, no differences in gray scale density measures were noted between patients with IPF and patients with asbestosis when these other factors were taken into account. Our results suggest that computer-derived density analysis of the lung parenchyma on the HRCT scan is a valid, clinically meaningful, and objective measure of interstitial lung disease.

Risk factors for injury in rural Iowa: round one of the Keokuk County Rural Health Study.

BACKGROUND: Unintentional injuries represent a major cause of morbidity and mortality in rural communities. This study aimed to determine the distribution of injury risk factors in a rural Iowa community and to identify the rural subgroups at highest risk for injury. METHODS: We reported on 1583 participants, aged > or =25 years, from Round One of the Keokuk County Rural Health Study, a longitudinal panel study of a rural community. The self-reported data were collected during face-to-face interviews. RESULTS: Our data suggested that several risk factors for injury are not uniformly distributed among rural populations. Male farmers were significantly less likely to wear their seatbelts than townspeople or rural nonfarmers. However, farm women were as likely to wear seatbelts as other women. Both male and female farmers were more likely to use all-terrain vehicles than townspeople or rural nonfarmers. In contrast, townspeople were more likely to ride bicycles than either farmers or rural nonfarmers. Townspeople were less likely to have firearms in their homes than either farmers or rural nonfarmers. Farmers were most likely to have fired a gun in the last year. Male farmers aged <65 years were less than half as likely as other men the same age to report a history of alcohol abuse. Binge drinking was equally frequent among farmers, rural nonfarmers, and townspeople. CONCLUSIONS: These differences in risk behavior in a rural county suggest the possibility of targeting specific rural injury prevention interventions at those with the highest risk for dangerous behavior.

Dose-response relationships between occupational aerosol exposures and cross-shift declines of lung function in poultry workers: recommendations for exposure limits.

Numerous articles have been published regarding the adverse respiratory health consequences of working in intensive livestock and poultry housing. Threshold limit exposure guidelines are not currently applied to this environment, but they are essential to implement and monitor effective environmental controls. Previous dose-response research work with swine workers has resulted in exposure limit recommendations of 2.5 mg/m3 total dust, 0.23 mg/m3 respirable dust, 100 EU/m3 endotoxin, and 7 ppm ammonia. No similar recommendations have been reported previously for poultry workers. Therefore, an industry-wide study was conducted to examine dose-response relationships of bioaerosol exposures and worker respiratory health. A total of 257 poultry workers were studied for respiratory symptoms, pulmonary function, and exposure to dust (total and respirable), endotoxin (respirable and total), and ammonia. Details of the sampling plan and environmental assessment are described elsewhere. Relationships between exposures and response were studied by correlation and multiple regressions. Significant dose-response relationships were observed between exposures and pulmonary function decrements over a work shift. Exposure concentrations associated with significant pulmonary function decrements were as follows: 2.4 mg/m3 total dust, 0.16 mg/m3 respirable dust, 614 EU/m3 endotoxin, and 12 ppm ammonia.

Self-reported postwar injuries among Gulf War veterans.

OBJECTIVE: From September 1995 to May 1996, the authors conducted a telephone survey of Iowa military personnel who had served in the regular military or activated National Guard or Reserve during the Gulf War period. To assess the association between military service in a combat zone and subsequent traumatic injury requiring medical consultation, the authors analyzed veterans' interview responses. METHODS: Using data from the larger survey, the authors compared rates of self-reported postwar injuries requiring medical consultation in a sample of Iowa Gulf War veterans to the rates in a sample of Iowa military personnel who served at the same time, but not in the Persian Gulf. RESULTS: Of 3695 veterans, 605 (16%) reported a traumatic injury in the previous three months requiring medical consultation. Self-reported injuries were associated with service in the Persian Gulf (odds ratio 1.26; 95% confidence interval 1.02, 1.55). CONCLUSION: This finding is consistent with the results of earlier studies of traumatic injury mortality rates among war veterans.

Physician visits in a farming-dependent county.

Physician visits in a farming-dependent county in the upper-Midwest were studied using a mail questionnaire. A 16 percent random sample of households yielded 426 surveys (60 percent response rate). The dependent variable was the natural log (plus one) of the number of times the respondent had seen a physician in the prior 12 months. Predisposing, enabling, and medical need variables were tested as potential predictors of medical care usage. Self-rated health status proved to be an important predictor, as was a history of hospitalization and being married. However, health insurance coverage and family income were not associated with increased physician visits. Implications for modifying the conceptual model employed to analyze medical care utilization in similar populations are discussed.

Respiratory symptoms and lung function among workers in swine confinement buildings: a cross-sectional epidemiological study.

To study possible chronic respiratory problems of people working in swine confinement buildings, a cross-sectional epidemiological study was initiated. A cohort of swine confinement workers was matched for age, sex, and smoking history with nonconfinement swine producers. Pulmonary function studies and a survey questionnaire for chronic respiratory disease symptoms (the American Thoracic Society, Epidemiologic Standardization Project Questionnaire) were performed on both groups. Compared to controls, the confinement workers experienced significantly higher prevalence of chronic bronchitis and wheezing, (odds ratio 7 and 4, respectively). There were, however, no significant differences in baseline pulmonary functions. Based on the high prevalence of chronic respiratory disease symptoms, this study emphasizes an emerging occupational concern in agriculture to the estimated 500,000 persons working in swine confinement operations and the estimated 500,000 additional persons who work in poultry, veal, beef, or dairy confinement operations. It is important to study a representative population of these workers prospectively to determine if a progressive loss in lung function is evident.

Responses to cotton dust.

Twelve cotton textile workers were studied: (1) to compare standard measures of volume and expiratory flow, maximal expiratory flow volume (MEFV) curves, closing volume (CV), and closing capacity (CC) in detection of airway narrowing with cotton dust exposure; (2) to evaluate the response of arterial blood gases to exposure; (3) to measure changes in leukocytes in peripheral blood and airway secretions; and (4) to assess the temporal relationships and correlations between measures. Change in expiratory flow (FEV) most consistently and significantly discriminated between the control and cotton dust exposures. Vmax50%FVC was a more sensitive indicator, but variance was increased proportionately. CV and CC changed inconsistently with relatively large variances. The PaO-2 decreased overall and two subjects had large decrements. Peripheral blood and polymorphonuclear cell counts increased with exposure to cotton dust and polymorphonuclear leukocytes were recruited to the nasal mucosa. Chest tightness and decreased flow were temporally correlated with leukocyte recruitment that may be important in respiratory disease among cotton textile workers and therefore deserves further investigation.

WORKSAFE IOWA Occupational Medicine Associates Network: a university--community partnership in occupational safety and health.

The WORKSAFE IOWA Occupational Medicine Associates Network is a unique health care model for dispensing regional occupational medicine services in the state of Iowa, USA. WORKSAFE IOWA is an educational, informational, and consultation service of the College of Public Health at The University of Iowa. WORKSAFE IOWA includes a fee-for-service industrial hygiene program, the Occupational Medicine Associates Network, and educational and informational services. The Associates Network provides education, information, and consultation in exchange for an annual fee paid by each Associate to the university-based network. The Associates clinics provide comprehensive occupational medicine services to up to 1,500 clients through 66,000 annual clinic visits in their respective communities. The Associates Network has been financially self-sustaining over a period of 10 years, and has proven to provide valuable services to the community-based Associates, and to provide excellent training opportunities for the University students in several occupational safety and health disciplines.