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Comparative quantitative evaluation of pleural fibrosis and its effects on pulmonary function in two large asbestos-exposed occupational groups—Insulators and sheet metal workers

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Comparative quantitative evaluation of pleural fibrosis and its effects on pulmonary function in two large asbestos-exposed occupational groups—Insulators and sheet metal workers
  ENVIRONMENTAL RESEARCH 59, 49--66 (1992) Comparative Quantitative Evaluation of Pleural Fibrosis and Its Effects on Pulmonary Function in Two Large Asbestos Exposed Occupational Groups Insulators and Sheet Metal Workers RUTH LILIS, *'1 ARTHUR MILLER,t JAMES GODBOLD,* STEVEN BENKERT,* XIAOCHU Wu,* AND IRVING J. SELIKOFF* *Division of Environmental and Occupational Medicine Community Medicine) and ?Division of Pulmonary Disease Medicine), Mount Sinai School of Medicine of the City University of New York, New York Received May, 22, 1992 Two large (N = 1584 and N = 1330) population groups of workers exposed to asbestos as insulators (I) or sheet metal workers (SM) were compared. Prevalence rates of radio- graphic changes including pleural fibrosis (circumscribed and diffuse) were found to be much higher in I than SM. An integrative index of pleural fibrosis (INDEX) showed similar distribution patterns in the two groups; the effect of INDEX on FVC% predicted was more marked in insulators. Factors that could contribute to this difference are thought to be the higher prevalence of interstitial pulmonary fibrosis (probably including that which is not yet radiologically detectable) in I than in SM, the possibility of more extensive pleupal fibrosis in areas not accessible to the standard chest X ray (and thus not affecting INDEX) and a higher proportion of diffuse pleural fibrosis in the I group. © 1992 Academic Press, Inc. INTRODUCTION The recognition of relatively high prevalence rates of pleural fibrosis, when compared to interstitial pulmonary fibrosis, in various occupational groups (Fel- ton et al. 1980; Lilis et al. 1980; Baker et al. 1985; Oliver et al. 1985; Sprince et al. 1985; Jarvholm and Sanden, 1986; Lundorf et al. 1987; Rosenstock et al. 1988; Bourbeau et al. 1990; Schwartz et al. 1990, 1991; Fischbein et al. 1991) with relatively lower or intermittent asbestos exposure has focused attention on two major issues: the clinical and functional significance of pleural fibrosis and the possibly different dose-response relationship for the two fibrogenic effects of asbestos, i.e., pleural versus pulmonary parenchymal fibrosis. We have recently investigated the quantitative relationships between an inte- grative index of pleural fibrosis (Lilis et al. 1991b,c) and restrictive respiratory dysfunction, i.e., forced vital capacity (FVC% predicted) in a large population of insulation workers with long-term asbestos exposure. The size of the studied population allowed the characterization of the differential distribution patterns of the integrative index of pleural fibrosis (INDEX) in the subgroup with circum- scribed pleural changes as compared to that with diffuse pleural fibrosis (defined 1 To whom reprint requests should be addressed at Mount Sinai School of Medicine, Box 1057, 1 Gustave Levy Place, New York, NY 10029. 49 0013-9351/92 $5.00 Copyright © 1992 by Academic Press, Inc. All rights of reproduction n any form reserved.  50 LILIS ET AL. as including the blunting of the costophrenic angle). Multiple regression analysis showed that the pleural INDEX had a statistically significant and independent (of profusion of small opacities) effect on FVC% predicted in the subgroup with circumscribed pleural fibrosis. Decrements in FVC were more marked in those with diffuse pleural fibrosis, although the magnitude of the INDEX in the case of diffuse pleural fibrosis did not significantly affect FVC; it was the blunting of costophrenic angles, even when accompanied by only very limited pleural fibro- sis, that had the most decisive effect in reducing FVC% predicted. Thus, a sig- nificant quantitative relationship between the magnitude of the integrative index of pleural fibrosis and the decrement in FVC% predicted was demonstrated for circumscribed pleural fibrosis, which represents, in most exposed populations, about 80% of all pleural fibrosis. PRESENT STUDY: POPULATION AND METHODS We have subsequently investigated the adverse health effects of asbestos ex- posure in a large group of sheet metal workers; characteristics of the population studied and major findings have been reported (Selikoff and Lilis, 1991). The chest X rays have been interpreted according to the ILO International Classification of Radiographs of Pneumoconioses by the same NIOSH-certified B reader (RL); pulmonary function tests were performed by the same team (Miller et al. 1992) and using the same methodology as previously described. The same question- naires were used for recording demographic data, occupational history, smoking history, past medical history, and symptoms (Lilis et al. 1991a,b; Miller et al. 1992). An integrative index of pleural fibrosis was calculated using the following ap- proach: For each hemithorax, for pleural thickening in profile, the width A, B, or C was coded 1, 2, or 3, respectively. The extent score (1, 2, or 3) was multiplied by the figure for width. For pleural face on, the extent (1, 2, or 3) was multiplied by a factor of 2 (since width of pleural face on cannot be measured, the median possible width was assumed); the product was added to that obtained for pleural thickening in profile. Diaphragmatic plaques were given a score of 1 (if measuring less than 2 cm) or 2 (more than 2 cm); this figure, as well as the grading for pleural calcifications (1, 2, or 3), was added to the score obtained for chest wall pleural thickening. The totals obtained for the right and left hemithorax were added, to give the Integrative Index of Pleural Fibrosis (possible maximum value of 40). Diffuse pleural fibrosis, defined as that which includes blunting of the ipsilateral costophrenic angle, was indicated with the symbol D. For certain analyses, circumscribed pleural fibrosis was treated separately from diffuse pleural fibrosis. Asbestos exposure of sheet metal workers has occurred as a result of the extensive use, in the past, of asbestos insulation in the construction industry (Baker et al. 1985; Drucker et al. 1987). Adverse effects of this exposure have been reported (Owen, 1964; Dach et al. 1980; Baker et al. 1985; Zoloth and Michaels, 1985; Michaels and Zoloth, 1988; Schwartz et al. 1990). Although  EVALUATION OF PLEURAL FIBROSIS 51 quantitative measurements of airborne asbestos concentrations to which sheet metal workers have been exposed are not available, it is generally accepted that exposures were intermittent, due in part to their own occasional use of asbestos material or removal of such materials when performing repair work, but mostly because of work areas contaminated with asbestos due to activities of other trades, mainly insulators. There is general agreement that sheet metal workers have been exposed to relatively lower levels of asbestos than insulators. This paper presents comparative data on prevalence rates of parenchymal in- terstitial pulmonary fibrosis and of pleural fibrosis in insulation workers (N = 1584) and sheet metal workers (N = 1330), the comparative distribution patterns of the integrative index of pleural fibrosis and comparison of the relationships between INDEX and FVC% predicted in these two populations. The working hypothesis, in initiating this study, was that the quantitative relationship between the integrative index of pleural fibrosis and decrements in pulmonary function would not differ significantly in populations with different asbestos exposure levels. STATISTICAL METHODS Multiple regression methods were used to examine the relationships between forced vital capacity and explanatory variables such as pleural index, smoking history, duration since onset of exposure to asbestos, and profusion of small opacities. In these analyses, the pleural index was transformed into a logarithmic scale because the distribution of pleural index in these groups was skewed to the right. The regression models developed by Godbold and co-workers (Lilis et al. 1991b) for the population of insulators occupationally exposed to asbestos were used in the study of sheet metal workers so that the magnitude of an effect for a given variable could be compared between the populations within the context of the same model. The rationale for developing the srcinal models is given in the earlier report. Thus, models including nonsignificant variables are presented for conformity with models developed for insulators. Reasons for the similarities and differences between the statistical significance found to be associated with vari- ables for the insulators and that associated with the same variables for the sheet metal workers are presented under Results. To further explore the reasons for differences between the two populations, additional regression models were de- veloped in subgroups defined by restricting the duration since onset of exposure and the degree of parenchymal abnormalities. Multiple regression methods were also used to quantify the effects of occupa- tion (sheet metal workers vs insulators), cigarette smoking, and INDEX on FVC% predicted. This analysis was performed using the subgroup of workers with pleural abnormalities only (i.e., no parenchymal abnormalities) in the com- bined data set insulators and sheet metal workers. There were 452 insulators and 324 sheet metal workers in this subgroup. The dependent variable was FVC% predicted and the independent variables were occupational group, smoking status, interaction between occupation and smoking, pleural index (measured on the log scale), and the square of pleural index (also measured on the log scale).  52 LILIS ET AL. TABLE 1 CHEST X-RAY FINDINGS IN WORKERS WITH LONG-TERM ASBESTOS EXPOSURE Radiologic abnormalities N % Insulation workers (N = 1584) Normal chest X ray 262 16.5 Parenchymal only 137 8,6 Pleural only 460 29.0 Parenchymal and pleural 725 45.8 Total parenchymal abnormalities 862 54.4 Total pleural abnormalities 1185 74.8 Sheet metal workers (N = 1330) Normal chest X ray 767 57.7 Parenchymal only 84 6.3 Pleural only 332 25.0 Parenchymal and pleural 147 11.1 Total parenchymal abnormalities 231 17,4 Total pleural abnormalities 479 36.0 RESULTS The prevalence rates of abnormalities on chest X-ray films are presented in Table 1. All radiographic changes were present with higher prevalence in insula- tion (I) workers than sheet metal (SM) workers; it is noteworthy that the differ- ence was proportionally greater for parenchymal changes (54,4% in I versus 17.4% in SM) than for pleural abnormalities (75% in I versus 36% in SM). These findings confirm the observations of relatively higher prevalence rates of pleural fibrosis than of parenchymal fibrosis in populations with lower asbestos exposure. There was a steady increase in prevalence of radiographic abnormalities with duration from onset of asbestos exposure (Table 2) in both I and SM workers (Table 3); the only category for which the prevalence decreased with time from onset of exposure was that of parenchymal changes only reflecting the signif- icant increase in the category parenchymal and pleural changes. In insulators TABLE 2 RADIOLOGIC CHANGES AND DURATION FROM ONSET OF ASBESTOS EXPOSURE IN ASBESTOS INSULATION WORKERS (N = 1584) Radiologic abnormalities Time from onset of asbestos exposure (years) Less than 30 30-39 40 and over (N = 238) (N = 939) (N = 407) N % N % N % Parenchymal only 25 Pleural only 81 Parenchymal and pleural 51 Total pleural abnormalities 132 Total parenchymal abnormalities 76 Normal chest X ray 81 10.5 88 9.4 24 5.9 34.0 273 29.1 106 26.0 21.4 436 46.4 238 58.5 55.4 709 75.5 344 84.5 31.9 524 55.8 262 64.4 34.0 142 15.1 39 9.6  EVALUATION OF PLEURAL FIBROSIS 53 TABLE 3 RADIOLOGIC CHANGES AND YEARS FROM ONSET OF ASBESTOS EXPOSURE IN SHEET METAL WORKERS (N = 1330) Time from onset of asbestos exposure (years) Less than 30 30-39 40 and over (N = 86) (N = 641) (N = 603) Radiologic abnormalities N % N % N % Parenchymal only 8 9.3 39 6.1 37 6.1 Pleural only 13 15.1 147 22.9 172 28.5 Parenchymal and pleural 4 4.7 59 9.2 84 13.9 Total pleural abnormalities 17 19.8 206 32.1 256 42.5 Total parenchymal abnormalities 12 14.0 98 15.3 121 20.1 Normal chest X ray 61 70.9 396 61.8 310 51.4 there was also a slight decrease in the prevalence of pleural changes only with longer duration from onset of exposure. The prevalence of pleural changes only steadily increased in SM, from 15% in those less than 30 years from onset of asbestos exposure to 28.5% of those with over 40 years from onset. In the I group the prevalence of pleural changes only did not increase with time from onset of exposure. This difference is explained by the fact that in the I group there was a major increase in prevalence of the category parenchymal and pleural abnormalities which reached 58.5% of those over 40 years of exposure (Table 2), while in the SM group the corresponding proportion was only 14% (Table 3). Thus, the major radiographic differences between the two occupational groups are the higher prevalence rates for parenchymal abnormalities (about three times TABLE 4 PARENCHYMAL ABNORMALITIES Profusion of small opacities Sheet metal workers Insulation workers (N = 1330) (N = 1584) Profusion N % Profusion N % 0/0-0/1 t 099 82.6 0/0-0/1 722 45.6 1/0-1/2 216 16.2 1/0-1/2 707 44.6 2/1-2/3 14 1.1 2/1-2/3 131 8.3 3/2-3/4 1 0.1 3/2-3/4 24 1.5 Profusion scores of 1/0, 1/1, 1/2 Sheet metal workers Insulation workers (N = 216) (N = 707) Profusion N % Profusion N % 1/0 98 45.4 1/0 276 39.0 1/1 102 47.2 1/1 337 47.7 1/2 16 7.4 1/2 94 13.3
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