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Original Research: Pulmonary Physiology |

Pleural Plaques and Their Effect on Lung Function in Libby Vermiculite MinersPleural Plaques and Their Effect on Lung Function Pleural Plaques and their Effect on Lung Function FREE TO VIEW

Kathleen A. Clark, MS; J. Jay Flynn, III, MD; Julie E. Goodman, PhD; Ke Zu, PhD, ScD; Wilfried J. J. Karmaus, MD, MPH; Lawrence C. Mohr, MD, ScD, FCCP
Author and Funding Information

From the Department of Epidemiology and Biostatistics (Ms Clark), Arnold School of Public Health, University of South Carolina, Columbia, SC; Health Network America (Dr Flynn), Tinton Falls, NJ; Gradient Corporation (Drs Goodman and Zu), Cambridge, MA; the Department of Epidemiology (Dr Goodman), Harvard School of Public Health, Boston, MA; the Division of Epidemiology, Biostatistics and Environmental Health (Dr Karmaus), School of Public Health, University of Memphis, Memphis, TN; and the Department of Medicine (Dr Mohr), the Department of Public Health Sciences (Dr Mohr), and the Environmental Biosciences Program (Dr Mohr), Medical University of South Carolina, Charleston, SC.

CORRESPONDENCE TO: Lawrence C. Mohr, MD, ScD, FCCP, Environmental Biosciences Program, Medical University of South Carolina, 135 Cannon St, Ste 405, PO Box 250838, Charleston, SC 29425; e-mail: mohrlc@musc.edu


FUNDING/SUPPORT: This work was supported by Health Network America and Gradient Corp.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2014;146(3):786-794. doi:10.1378/chest.14-0043
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BACKGROUND:  Multiple studies have investigated the relationship between asbestos-related pleural plaques (PPs) and lung function, with disparate and inconsistent results. Most use chest radiographs to identify PPs and simple spirometry to measure lung function. High-resolution CT (HRCT) scanning improves the accuracy of PP identification. Complete pulmonary function tests (PFTs), including spirometry, lung volumes, and diffusing capacity of the lung for carbon monoxide, provide a more definitive assessment of lung function. The goal of this study was to determine, using HRCT scanning and complete PFTs, the effect of PPs on lung function in Libby vermiculite miners.

METHODS:  The results of HRCT scanning and complete PFTs performed between January 2000 and August 2012 were obtained from the medical records of 166 Libby vermiculite miners. Multivariate regression analyses with Tukey multivariate adjustment were used to assess statistical associations between the presence of PPs and lung function. Adjustments were made for age, BMI, smoking history, duration of employment, and years since last occupational asbestos exposure.

RESULTS:  Nearly 90% of miners (n = 149) had evidence of PPs on HRCT scan. No significant differences in spirometry results, lung volumes, or diffusing capacity of the lung for carbon monoxide were found between miners with PPs alone and miners with normal HRCT scans. Miners with both interstitial fibrosis and the presence of PPs had a significantly decreased total lung capacity in comparison with miners with normal HRCT scans (P = .02). Age, cumulative smoking history, and BMI were significant covariates that contributed to abnormal lung function.

CONCLUSIONS:  Asbestos-related PPs alone have no significant effect on lung function in Libby vermiculite miners.

Figures in this Article

Pleural plaques (PPs) are the most common radiologic findings in individuals exposed to asbestos.1 They generally occur on the parietal pleura of the lateral or posterolateral chest wall, the dome of the diaphragm, and the mediastinum.25 Approximately two-thirds are bilateral and frequently calcified, but they may also be unilateral and uncalcified.26 On gross examination, PPs are white and firm and have sharply circumscribed borders.13 Microscopically, PPs are acellular, rarely contain asbestos bodies, and are composed of bands of interwoven collagen tissue.13

Whether PPs contribute to the loss of lung function remains controversial. Multiple previous studies have investigated this relationship, with disparate and inconsistent results.7,8 Most used chest radiographs (CXRs) to determine the presence of PPs, and relied on FVC instead of total lung capacity (TLC) to diagnose restrictive ventilatory impairment.915 In addition, many controlled inadequately for the effects of age, smoking history, and BMI.13,16,17

Since 1950, the International Labor Organization has recommended the use of CXRs to detect the presence of PPs.18 However, a CXR has relatively low diagnostic sensitivity for the detection of PPs, and subpleural fat deposits may be misinterpreted as PPs.5,19,20 CT scanning and high-resolution CT (HRCT) scanning increase PP diagnostic sensitivity to 93% and 96%, respectively.19,20 Therefore, HRCT scanning provides a more accurate basis for assessing the effects of PPs on lung function.21

From 1923 to 1990, vermiculite was mined at Zonolite Mountain, located 6 miles northeast of Libby, Montana. Libby vermiculite was contaminated with Libby amphibole asbestos (LAA), which is composed of winchite (80%), richterite (12%), tremolite (6%), and other asbestiform minerals (2%).22 In April 2000, a health benefit program known as the Libby Medical Program (LMP) was established for residents and vermiculite miners from the Libby area who were diagnosed with asbestos-related abnormalities. Of the 1,461 individuals enrolled in the LMP, 291 were former vermiculite miners with occupational exposure to LAA. Libby miners had significantly higher LAA exposures than did individuals with household or environmental exposures.23 Between January 2000 and August 2012, 180 LMP miners had thoracic HRCT scans to identify and assess the extent of any pulmonary abnormalities.23 We performed a retrospective chart review of the medical records to identify LMP miners who received at least one thoracic HRCT scan with corresponding pulmonary function tests (PFTs). The primary goal of this study was to determine the effects of PPs alone, as detected by HRCT scan, on the lung function of Libby vermiculite miners.

All LMP miner medical records were deidentified prior to investigation. The University of South Carolina Institutional Review Board approved the study protocol (ID No.: Pro00020158) prior to medical record examination.

Sample Population

Eligible participants were male LMP vermiculite miners with complete PFTs and corresponding thoracic HRCT scans performed within 3 years of each other. When miners had multiple PFTs, we analyzed the most recent one. The subject selection process and exclusion criteria are depicted in Figure 1.

Figure Jump LinkFigure 1  Flow diagram and exclusion criteria for subject selection. HRCT = high-resolution CT; LMP = Libby Medical Program; PFT = pulmonary function test.Grahic Jump Location
Radiographic Testing

All HRCT scans were reviewed by board-certified academic chest radiologists, and findings were classified into one of four groups: (1) normal HRCT scans (NCTSs), (2) PPs only (PPO), (3) PPs with interstitial fibrosis (PPIF), or (4) other HRCT scan abnormalities (OCTAs). The OCTA group consisted of miners with HRCT scan findings of rounded atelectasis, diffuse pleural thickening, pleural effusions, and pulmonary nodules > 1 cm in diameter. The severity of the PPs was determined from the interpretations of HCRT scans by study radiologists. Three categories of PP severity were defined: extensive (bilateral and diffusely distributed plaques), moderate (bilateral, but localized plaques), and mild (single plaque, unilateral plaques, or thin and sparsely distributed bilateral plaques).

Pulmonary Function Testing

PFT studies consisted of spirometry, lung volumes measured by plethysmography, and diffusing capacity of the lung for carbon monoxide (Dlco). All PFT studies were performed in accordance with the 2005 American Thoracic Society (ATS)/European Respiratory Society (ERS) guidelines.2426 National Health and Nutrition Examination Survey (NHANES) reference equations for FEV1, FVC, FEV1/FVC ratio (FEV1/FVC%), TLC, expiratory reserve volume (ERV), residual volume, Dlco, and the ratio of Dlco to alveolar volume (Dlco/Va ratio) were used to estimate % predicted values.2629 Protocol required that miners had no acute medical conditions at the time of pulmonary function testing.

Statistical Analysis

Analysis of variance or Mantel-Haenszel χ2 statistics were used to evaluate demographic differences among the HRCT scan groups. Multivariate linear regression with Tukey multiple comparison adjustment was used to determine whether NHANES % predicted FEV1, FVC, FEV1/FVC, TLC, ERV, residual volume, Dlco, and Dlco/Va ratio differed by HRCT scan group. The Dlco/Va ratio was used to identify the most likely causes for reduced Dlco. A similar analysis was performed for miners in the PPO group, to evaluate whether PFT results differed based on the extent of PPs.

Multivariate analysis with backward model selection identified covariates that were associated with statistically significant differences between observed lung function parameters and NHANES predicted values. The covariates investigated were age, BMI (kg/m2), cumulative smoking history (none, ≤ 15 pack-years, > 15 pack-years), years of employment, and years since last occupational asbestos exposure.3032 Statistical analyses were performed using SAS 9.3 (SAS Institute Inc).

Of the180 Libby miners who underwent HRCT scans between January 2000 and August 2012, 166 met the inclusion criteria (Fig 1). Demographic characteristics are presented in Table 1. All miners were adult white men; 50% were obese (mean BMI, 30.3 kg/m2; 95% CI, 29.5-31.2). More than 70% of the miners were current or former smokers, with an average smoking history of 33.8 pack-years. The average time since last occupational LAA exposure was 31.4 years. Significant HRCT scan group differences were seen for age (P < .0001) and time since last employment (P = .05) (Table 1).

Table Graphic Jump Location
TABLE 1  ] Characteristics of Libby Medical Program Vermiculite Miners by HRCT Scan Outcome

HRCT = high-resolution CT; NCTS = normal HRCT scan; OCTA = other HRCT scan abnormality; PPIF  = pleural plaques with coexisting interstitial fibrosis; PPO = pleural plaques only.

a 

P values were calculated by analysis of variance or Mantel-Haenszel tests.

b 

Mean and median pack-y were calculated among current and ex-smokers.

Sixteen miners (9.6%) had NCTSs. Nearly 90% of miners (n = 149) showed HRCT scan evidence for PPs, the majority of which were bilateral and calcified. PPs alone, with no other HRCT scan findings (PPO), were present in 89 miners (53.6%). Additionally, 26 miners (16.3%) were in the PPIF group, and 35 miners (20.5%) were in the OCTA group. All miners in the PPIF group had mild to moderate interstitial fibrosis. Only one miner in the OCTA group did not have PPs in conjunction with other HRCT scan findings. The HRCT scan findings for each group of miners are shown in Table 2.

Table Graphic Jump Location
TABLE 2  ] HRCT Scan Findings for Each HRCT Scan Miner Group (N = 166)

Data are presented as No. (%). See Table 1 legend for expansion of abbreviations.

There were no statistically significant differences in lung function between the PPO group of miners and those miners with NCTSs. The PPO group had slightly lower mean values for TLC, FEV1, FVC, FEV1/FVC%, and Dlco compared with the NCTS group (P = .2, P = .5, P = .3, P = .7, P = .2, respectively). However, none of these differences was statistically significant, and all parameters were well within the accepted ATS limits of normal (Table 3). Furthermore, the severity of PPs had no effect on lung function within the PPO group (Table 4). Significant group differences in lung function were found for the PPIF and OCTA groups of miners when compared with miners with NCTSs. Miners in the PPIF group had a significantly lower mean value for TLC (P = .02), with no other differences in lung function parameters. Miners in the OCTA group had significantly lower mean values for TLC, FEV1, FVC, and Dlco (P = .05, P = .01, P = .03, and P = .006, respectively) (Table 3).

Table Graphic Jump Location
TABLE 3  ] Multivariate Linear Regression Results for Individual Lung Function Parameters by HRCT Scan Miner Group (N = 166)

Data were adjusted for age, BMI, cumulative smoking (none, ≤ 15 pack-y, > 15 pack-y), duration of employment, and latent years. P values for overall ANOVAs, as well as between-subgroup comparisons, were calculated. Covariates: FVC: BMI (F = 12.3, P = .0006); FEV1: smoking > 15 pack-y (F = 9.94, P < .0001); FEV1/FVC: smoking > 15 pack-y (F = 15.2, P < .0001), BMI (F = 8.03, P = .005); TLC: age (F = 6.37, P = .01), BMI (F = 4.72, P = .03); Residual volume: smoking > 15 pack-y (F = 4.95, P = .008); ERV: age (F = 3.93, P = .05), BMI (F = 8.86, P = .003); Dlco: smoking > 15 pack-y (F = 14.6, P < .0001), age (F = 13.68, P = .0003), BMI (F = 6.77, P = .01); Dlco/Va ratio: no significant type 3 fixed effect covariates. ANOVA = analysis of variance; Dlco = diffusing capacity of the lung for carbon monoxide; Dlco/Va ratio = ratio of diffusing capacity of the lung for carbon monoxide and alveolar volume; ERV = expiratory reserve volume; TLC = total lung capacity. See Table 1 legend for expansion of other abbreviations.

Table Graphic Jump Location
TABLE 4  ] Multivariate Linear Regression Lung Function Results for PPO Miners and Severity of PPs (N = 87)

FEF25%-75% = forced expiratory flow, midexpiratory phase; PP = pleural plaque. See Table 1 and 3 legends for expansion of other abbreviations.

In addition to HRCT scan groups, we identified three additional independent predictors of lung function (Table 3). Age significantly contributed to differences in TLC, ERV, and Dlco (P = .01, P = .05, and P = .0003, respectively). Smoking for > 15 pack-years contributed to significant differences in FEV1, FEV1/FVC%, residual volume, and Dlco (P < .0001, P < .0001, P = .008, and P < .0001, respectively). BMI contributed to significant differences in FVC, FEV1/FVC%, TLC, and Dlco (P = .0006, P = .005, P = .03, and P = .01, respectively).

Of the 56 miners with reduced Dlco (< 75% predicted), 38 (68%) had recorded Dlco/Va ratios. Eighteen miners (47%) had Dlco/Va ratios that indicated that their Dlco reduction was most likely related to decreased lung volumes or parenchymal changes. Twenty miners (53%) had Dlco/Va ratios that indicated that their Dlco reduction was most likely attributable to airway obstruction with increased alveolar dead space. There were no significant differences in Dlco/Va ratios among miner groups when compared with miners with NCTSs (Table 3).

We observed no significant differences in spirometry results, TLC, ERV, residual volume, Dlco, or Dlco/Va ratio between the PPO group miners and those miners with NCTSs. Mean % predicted values for FEV1, FVC, TLC, and Dlco were slightly lower in the PPO group, but none was statistically significant, and group means were well within ATS/ERS limits of normal.29 We also found a statistically significant decrease in TLC in the group of miners in the PPIF group in comparison with the group of miners with NCTSs. These results indicate that PPs alone have no effect on lung function in Libby vermiculite miners. They also demonstrate that the observed reduction in TLC in the group of miners in the PPIF group can be attributed to the interstitial fibrosis and not to the PPs. These findings are consistent with comments in previous reports that suggested that decreases in FVC among individuals with PPs detected by CXRs are probably associated with occult, subradiographic interstitial fibrosis, which is not detectable on CXRs, rather than with the PPs per se.8,10,11

Our study also demonstrated that the miners in the OCTA group had lower mean values for TLC, FEV1, FVC, and Dlco that were statistically significant when compared with the group of miners with NCTS (P = .05, P = .01, P = .03, and P = .006, respectively). The OCTA group of miners was heterogeneous, with HRCT scan findings of rounded atelectasis, diffuse pleural thickening, pleural effusions, and pulmonary nodules > 1 cm in diameter. Miners with these findings were categorized into a single group, because the number of miners with each specific HRCT scan abnormality was too small to achieve sufficient power for statistical analysis. All but one miner in the OCTA group had PPs in addition to one of the other specified abnormalities. Based on our previous observation that PPs alone have no significant effect on the lung function of Libby vermiculite miners, we conclude that the decrements in lung function parameters observed in the OCTA group were most likely caused by the combined pathophysiologic effects of the various other HRCT scan abnormalities.

In 2009, the American College of Chest Physicians (CHEST) published the results of a Delphi study that assessed and quantified the opinions of 71 experts in asbestos-related disease about various clinical issues related to asbestos-induced lung disease.33 This study reported that there was strong disagreement with the statement, “Pleural plaques alter lung function to a clinically significant degree.” That is, 71 experts in asbestos-related disease strongly disagreed with the assertion that asbestos-related PPs cause any significant alteration of lung function.33 There was good consensus for this disagreement among the 71 experts. These expert opinions are consistent with the results of our study, which show that PPs alone have no significant effect on lung function among Libby vermiculite miners.

There are several significant strengths of our study: (1) All miners were exposed to the same type of asbestos (LAA) in the same location; (2) PPs were determined by HRCT scan rather than by CXR; (3) lung volumes, Dlco, and Dlco/Va ratios were obtained, in addition to spirometry; (4) all PFT studies were reviewed for quality standards; (5) numerous potential confounding variables were investigated; and (6) statistical adjustments were made for covariates that were associated with significant effects on lung function parameters. In addition, the NCTS group acted as an ideal reference group for comparison with miners in the other HRCT scan groups. Also, HRCT scanning is much more sensitive than CXR in identifying PPs and in distinguishing PPs from subpleural fat.13 This helped reduce misclassification bias within the PPO group.

Our study has several potential limitations. HRCT scan examinations and PFT studies were not performed at exactly the same time for all miners. Given the long latency period between asbestos exposure and pleuropulmonary abnormality development, we considered a 3-year interval between HRCT scanning and PFT studies to be acceptable. That said, 53 HRCT scans and PFT studies were performed on the same day, 73 were performed within the same week, and 139 were performed within 1 year of each other. Only 12 PFT studies were performed between 1 and 3 years after HRCT scanning. A second potential limitation is that we did not have an exact quantification of PP severity.15 However, our classification of PPs as extensive, moderate, or mild based on HRCT scan interpretations provided a reasonable basis for the statistical analysis of the effect of PP severity on lung function. Also, because the extent of PPs is related to the amount of asbestos exposure and there is a long latency period between initial exposure and PP development, we believe that our statistical adjustment for length of employment and time since last occupational exposure adequately accounted for the variation of PPs among individual miners. A third potential limitation is that the reference group (NCTS) was small (n = 16). Nevertheless, we did have enough power to detect statistically significant lung function differences between the reference group (NCTS) and both the PPIF and the OCTA groups. Given that the PPO group of miners had a much greater sample size than all other miner groups, we are confident that the potential for type 2 error was minimal, and conclusions regarding differences in lung function between the PPO and the NCTS group are robust.

To our knowledge, we are the first to investigate the effects of PPs on the lung function of Libby vermiculite miners by using HRCT scanning, plethysmography-determined lung volumes, Dlco, and Dlco/Va ratios.15,23,3436 We are aware of several other studies that used similar techniques to investigate the effect of PPs on lung function in various different asbestos-exposed populations.3739 For example, one study found no significant effect for isolated PPs on lung function in 73 asbestos-exposed cement factory workers.37 Another study used a validated CT scan scoring system to assess the extent of various pleural abnormalities in a cohort of 50 subjects and found that that PPs alone were not significantly associated with a deficit in lung function.38 A third study investigated the effect of PPs on lung function in a cohort of 2,743 individuals who were occupationally exposed to various forms of asbestos from different sources. They reported a slight, but statistically significant, trend toward restrictive ventilatory impairment among subjects with isolated PPs.39 However, all lung function parameters remained well within ATS/ERS normal limits in the group of subjects with isolated PPs, and the authors stated that the observed decrease in TLC and FVC was unlikely to be of real clinical relevance for the majority of subjects.39 Thus, the results of our study add significant weight to the body of scientific evidence that suggests that asbestos-related PPs alone have no significant effect on lung function.

Asbestos-related PPs alone have no significant effect on lung function in Libby vermiculite miners.

Author contributions: K. A. C., J. J. F., and L. C. M. had full access to all data used in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. L. C. M. is the guarantor of this study. K. A. C. and J. J. F. contributed to the data collection; K. A. C., J. J. F., and L. C. M. contributed to data review; K. A. C., J. J. F., J. E. G., K. Z., and L. C. M. contributed to study design; K. A. C., J. E. G., K. Z., W. J. J. K., and L. C. M. contributed to data analysis and interpretation; J. J. F. contributed data interpretation; W. J. J. K. contributed to the critical review of data analysis and interpretation; K. A. C., J. J. F., J. E. G., and L. C. M. contributed to preparation of the manuscript; and K. A. C., J. J. F., J. E. G., K. Z., W. J. J. K., and L. C. M. contributed to the critical review of the manuscript, and approval of the final version to be published.

Financial/nonfinancial disclosures: The authors have reported to CHEST the following conflicts of interest: Ms Clark received a graduate student research grant from Health Network America for the collection and analysis of medical surveillance data from the LMP. Funding for this research grant was provided to Health Network America by W.R. Grace and Co. Dr Goodman is a Principal at Gradient Corp, an independent environmental and risk science consulting firm, in Cambridge, MA. Dr Zu is a research associate at Gradient Corp. Through a contract with Gradient Corp, Drs Goodman and Zu have served as scientific consultants to W. R. Grace and Co on issues related to asbestos exposure and asbestos-related health risks. They both contributed to the data analyses reported in this manuscript with funding received through the Gradient consulting contract with W. R. Grace and Co. W. R Grace and Co has recently provided research funding to Gradient Corp for a preliminary weight-of-evidence study related to associations between PPs and lung function. Dr Goodman has served as an expert witness on cases involving chrysotile asbestos and cancer risk and has received funding from Tucker Ellis & West LLP for the preparation of scientific manuscripts regarding radiation, mesothelioma, and lung cancer. She previously received funding from the National Cancer Institute as a Cancer Prevention Fellow. Dr Flynn is an independent physician contractor for Health Network America, a health-care consulting company, in Eatontown, NJ. He served as Medical Director of the LMP from January 2001 to January 2013, as a Health Network America employee. Health Network America received fees from W.R. Grace and Co for providing administrative services to the LMP. Dr Flynn participated in all public comment sessions for the Environmental Protection Agency Toxicological Review of Libby Amphibole Asbestos in 2011 and 2012, in his capacity as Medical Director of the LMP. Dr Karmaus has received no funding for his work on this project and has no potential conflict of interest; he has received research funding from the National Institutes of Health for work on other projects in collaboration with Ms Clark and Dr Mohr. Dr Mohr has served as a research consultant to Exponent and Health Network America, scientific research and consulting firms, which received funding from W.R. Grace Co for research and scientific consultation on asbestos-related health risks. He has also received funding through a research contract with Gradient Corp for a literature review and preliminary weight-of-evidence study related to associations between PPs and lung function. He has submitted public commentary reports to the Scientific Advisory Board of the US Environmental Protection Agency on the Draft Toxicological Review Pertaining to Libby Amphibole Asbestos (2011) and the Association Between Localized Pleural Thickening (Pleural Plaques) and Lung Function; both reports were submitted in his capacity as a research consultant to Exponent, which received funding from W.R. Grace and Co for this work. Dr Mohr has received research grant funding from the National Institutes of Health, the National Cancer Institute, the US Department of Energy, the Agency for Healthcare Research and Quality, the Health Resources and Services Administration, the South Carolina Universities Research and Education Foundation, and the North Atlantic Treaty Organization for work on other research projects. He has served on scientific advisory boards for Marine Polymer Technologies, Inc and Entegrion. The authors wish to report that W.R. Grace and Co operated the Libby Vermiculite mine from 1963 to 1990.

Role of sponsors: None of the aforementioned sponsors or funding sources for any of the authors participated in data collection, had access to data used in the study, participated in data review, contributed to study design, contributed to data analysis, participated in data interpretation, participated in preparing the manuscript, participated in review of the manuscript, participated in the decision to submit the manuscript for peer-reviewed publication, or participated in approval of the final version to be published.

Other contributions: The authors acknowledge and thank the following chest radiologists who peer reviewed the chest CT scans used in our study: Daniel A. Henry, MD, Virginia Commonwealth University and Medical Center; Paul L. Molina, MD, University of North Carolina School of Medicine; and Ralph T. Shipley, MD, University of Cincinnati College of Medicine.

ATS

American Thoracic Society

CXR

chest radiograph

Dlco

diffusing capacity of the lung for carbon monoxide

Dlco/Va ratio

ratio of diffusing capacity of the lung for carbon monoxide and alveolar volume

ERS

European Respiratory Society

ERV

expiratory reserve volume

HRCT

high-resolution CT

LAA

Libby amphibole asbestos

LMP

Libby Medical Program

NCTS

normal high-resolution CT scan

NHANES

Third National Health and Nutrition Examination Survey

OCTA

other high-resolution CT scan abnormality

PFT

pulmonary function test

PP

pleural plaque

PPIF

pleural plaques with coexisting interstitial fibrosis

PPO

pleural plaques only

TLC

total lung capacity

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Macintyre N, Crapo RO, Viegi G, et al. Standardisation of the single-breath determination of carbon monoxide uptake in the lung. Eur Respir J. 2005;26(4):720-735. [CrossRef] [PubMed]
 
Hankinson JL, Odencrantz JR, Fedan KB. Spirometric reference values from a sample of the general US population. Am J Respir Crit Care Med. 1999;159(1):179-187. [CrossRef] [PubMed]
 
American Thoracic Society. Lung function testing: selection of reference values and interpretative strategies. Am Rev Respir Dis. 1991;144(5):1202-1218. [CrossRef] [PubMed]
 
Pellegrino R, Viegi G, Brusasco V, et al. Interpretative strategies for lung function tests. Eur Respir J. 2005;26(5):948-968. [CrossRef] [PubMed]
 
Rui F, De Zotti R, Negro C, Bovenzi M. A follow-up study of lung function among ex-asbestos workers with and without pleural plaques [in Italian]. Med Lav. 2004;95(3):171-179. [PubMed]
 
Jones RL, Nzekwu MM. The effects of body mass index on lung volumes. Chest. 2006;130(3):827-833. [CrossRef] [PubMed]
 
Salome CM, King GG, Berend N. Physiology of obesity and effects on lung function. J Appl Physiol (1985). 2010;108(1):206-211. [CrossRef] [PubMed]
 
Banks DE, Shi R, McLarty J, et al. American College of Chest Physicians consensus statement on the respiratory health effects of asbestos. Results of a Delphi study. Chest. 2009;135(6):1619-1627. [CrossRef] [PubMed]
 
Larson TC, Meyer CA, Kapil V, et al. Workers with Libby amphibole exposure: retrospective identification and progression of radiographic changes. Radiology. 2010;255(3):924-933. [CrossRef] [PubMed]
 
Winters CA, Hill WG, Rowse K, Black B, Kuntz SW, Weinert C. Descriptive analysis of the respiratory health status of persons exposed to Libby amphibole asbestos. BMJ Open. 2012;2(6):e001552. [PubMed]
 
Antao VC, Larson TC, Horton DK. Libby vermiculite exposure and risk of developing asbestos-related lung and pleural diseases. Curr Opin Pulm Med. 2012;18(2):161-167. [CrossRef] [PubMed]
 
Van Cleemput J, De Raeve H, Verschakelen JA, Rombouts J, Lacquet LM, Nemery B. Surface of localized pleural plaques quantitated by computed tomography scanning: no relation with cumulative asbestos exposure and no effect on lung function. Am J Respir Crit Care Med. 2001;163(3 pt 1):705-710. [CrossRef] [PubMed]
 
Copley SJ, Wells AU, Rubens MB, et al. Functional consequences of pleural disease evaluated with chest radiography and CT. Radiology. 2001;220(1):237-243. [CrossRef] [PubMed]
 
Clin B, Paris C, Ameille J, et al. Do asbestos-related pleural plaques on HRCT scans cause restrictive impairment in the absence of pulmonary fibrosis? Thorax. 2011;66(11):985-991. [CrossRef] [PubMed]
 

Figures

Figure Jump LinkFigure 1  Flow diagram and exclusion criteria for subject selection. HRCT = high-resolution CT; LMP = Libby Medical Program; PFT = pulmonary function test.Grahic Jump Location

Tables

Table Graphic Jump Location
TABLE 1  ] Characteristics of Libby Medical Program Vermiculite Miners by HRCT Scan Outcome

HRCT = high-resolution CT; NCTS = normal HRCT scan; OCTA = other HRCT scan abnormality; PPIF  = pleural plaques with coexisting interstitial fibrosis; PPO = pleural plaques only.

a 

P values were calculated by analysis of variance or Mantel-Haenszel tests.

b 

Mean and median pack-y were calculated among current and ex-smokers.

Table Graphic Jump Location
TABLE 2  ] HRCT Scan Findings for Each HRCT Scan Miner Group (N = 166)

Data are presented as No. (%). See Table 1 legend for expansion of abbreviations.

Table Graphic Jump Location
TABLE 3  ] Multivariate Linear Regression Results for Individual Lung Function Parameters by HRCT Scan Miner Group (N = 166)

Data were adjusted for age, BMI, cumulative smoking (none, ≤ 15 pack-y, > 15 pack-y), duration of employment, and latent years. P values for overall ANOVAs, as well as between-subgroup comparisons, were calculated. Covariates: FVC: BMI (F = 12.3, P = .0006); FEV1: smoking > 15 pack-y (F = 9.94, P < .0001); FEV1/FVC: smoking > 15 pack-y (F = 15.2, P < .0001), BMI (F = 8.03, P = .005); TLC: age (F = 6.37, P = .01), BMI (F = 4.72, P = .03); Residual volume: smoking > 15 pack-y (F = 4.95, P = .008); ERV: age (F = 3.93, P = .05), BMI (F = 8.86, P = .003); Dlco: smoking > 15 pack-y (F = 14.6, P < .0001), age (F = 13.68, P = .0003), BMI (F = 6.77, P = .01); Dlco/Va ratio: no significant type 3 fixed effect covariates. ANOVA = analysis of variance; Dlco = diffusing capacity of the lung for carbon monoxide; Dlco/Va ratio = ratio of diffusing capacity of the lung for carbon monoxide and alveolar volume; ERV = expiratory reserve volume; TLC = total lung capacity. See Table 1 legend for expansion of other abbreviations.

Table Graphic Jump Location
TABLE 4  ] Multivariate Linear Regression Lung Function Results for PPO Miners and Severity of PPs (N = 87)

FEF25%-75% = forced expiratory flow, midexpiratory phase; PP = pleural plaque. See Table 1 and 3 legends for expansion of other abbreviations.

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Miller MR, Hankinson J, Brusasco V, et al; ATS/ERS Task Force. Standardisation of spirometry. Eur Respir J. 2005;26(2):319-338. [CrossRef] [PubMed]
 
Wanger J, Clausen JL, Coates A, et al. Standardisation of the measurement of lung volumes. Eur Respir J. 2005;26(3):511-522. [CrossRef] [PubMed]
 
Macintyre N, Crapo RO, Viegi G, et al. Standardisation of the single-breath determination of carbon monoxide uptake in the lung. Eur Respir J. 2005;26(4):720-735. [CrossRef] [PubMed]
 
Hankinson JL, Odencrantz JR, Fedan KB. Spirometric reference values from a sample of the general US population. Am J Respir Crit Care Med. 1999;159(1):179-187. [CrossRef] [PubMed]
 
American Thoracic Society. Lung function testing: selection of reference values and interpretative strategies. Am Rev Respir Dis. 1991;144(5):1202-1218. [CrossRef] [PubMed]
 
Pellegrino R, Viegi G, Brusasco V, et al. Interpretative strategies for lung function tests. Eur Respir J. 2005;26(5):948-968. [CrossRef] [PubMed]
 
Rui F, De Zotti R, Negro C, Bovenzi M. A follow-up study of lung function among ex-asbestos workers with and without pleural plaques [in Italian]. Med Lav. 2004;95(3):171-179. [PubMed]
 
Jones RL, Nzekwu MM. The effects of body mass index on lung volumes. Chest. 2006;130(3):827-833. [CrossRef] [PubMed]
 
Salome CM, King GG, Berend N. Physiology of obesity and effects on lung function. J Appl Physiol (1985). 2010;108(1):206-211. [CrossRef] [PubMed]
 
Banks DE, Shi R, McLarty J, et al. American College of Chest Physicians consensus statement on the respiratory health effects of asbestos. Results of a Delphi study. Chest. 2009;135(6):1619-1627. [CrossRef] [PubMed]
 
Larson TC, Meyer CA, Kapil V, et al. Workers with Libby amphibole exposure: retrospective identification and progression of radiographic changes. Radiology. 2010;255(3):924-933. [CrossRef] [PubMed]
 
Winters CA, Hill WG, Rowse K, Black B, Kuntz SW, Weinert C. Descriptive analysis of the respiratory health status of persons exposed to Libby amphibole asbestos. BMJ Open. 2012;2(6):e001552. [PubMed]
 
Antao VC, Larson TC, Horton DK. Libby vermiculite exposure and risk of developing asbestos-related lung and pleural diseases. Curr Opin Pulm Med. 2012;18(2):161-167. [CrossRef] [PubMed]
 
Van Cleemput J, De Raeve H, Verschakelen JA, Rombouts J, Lacquet LM, Nemery B. Surface of localized pleural plaques quantitated by computed tomography scanning: no relation with cumulative asbestos exposure and no effect on lung function. Am J Respir Crit Care Med. 2001;163(3 pt 1):705-710. [CrossRef] [PubMed]
 
Copley SJ, Wells AU, Rubens MB, et al. Functional consequences of pleural disease evaluated with chest radiography and CT. Radiology. 2001;220(1):237-243. [CrossRef] [PubMed]
 
Clin B, Paris C, Ameille J, et al. Do asbestos-related pleural plaques on HRCT scans cause restrictive impairment in the absence of pulmonary fibrosis? Thorax. 2011;66(11):985-991. [CrossRef] [PubMed]
 
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