Chest ACCP Member Benefits
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Guest Access | Sign In via User Name/Password
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF) Free
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Article Archive
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (5)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Hertzberg, V. S.
Right arrow Articles by Rice, C. H.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Hertzberg, V. S.
Right arrow Articles by Rice, C. H.
(Chest. 2002;122:721-728.)
© 2002 American College of Chest Physicians

Effect of Occupational Silica Exposure on Pulmonary Function*

Vicki Stover Hertzberg, PhD; Kenneth D. Rosenman, MD; Mary Jo Reilly, MS and Carol H. Rice, SM, PhD, CIH

* From the Department of Biostatistics (Dr. Hertzberg), Emory University, Atlanta, GA; the Department of Medicine (Dr. Rosenman and Ms. Reilly), Michigan State University, East Lansing, MI; and the Department of Environmental Health (Dr. Rice), University of Cincinnati, Cincinnati, OH.

Correspondence to: Vicki Stover Hertzberg, PhD, Department of Biostatistics, Rollins School of Public Health, Emory University, 1518 Clifton Rd, NE, Atlanta, GA 30322; e-mail: vhertzb{at}sph emory.edu


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Study objectives: To assess the effect of occupational silica exposure on pulmonary function.

Design: Epidemiologic evaluation based on employee interview, plant walk-through, and information abstracted from company medical records, employment records, and industrial hygiene measurements.

Participants: Drawn from 1,072 current and former hourly wage workers employed before January 1, 1986. Thirty-six individuals with radiographic evidence of parenchymal changes consistent with asbestosis or silicosis were excluded. In addition, eight individuals whose race was listed as other than white or black were excluded.

Measurements and results: Analysis of spirometry data (FVC, FEV1, FEV1/FVC) only using the test results that met American Thoracic Society criteria for reproducibility and acceptability shows decreasing percent-predicted FVC and FEV1 and decreasing FEV1/FVC in relationship to increasing silica exposure among smokers. Logistic regression analyses of abnormal FVC and abnormal FEV1 values (where abnormal is defined as < 95% confidence limit for predicted using the Knudson prediction equations) show odds ratios of 1.49 and 1.68, respectively, for occurrence of abnormal result with 40 years of exposure at the Occupational Safety and Health Administration (OSHA)-allowable level of 0.1 mg/m3. Longitudinal analyses of FVC and FEV1 measurements show a 1.6 mL/yr and 1.1 mL/yr, respectively, decline per milligram/cubic meter mean silica exposure (p = 0.011 and p = 0.001, respectively). All analyses were adjusted for weight, height, age, ethnicity, smoking status, and other silica exposures. Systematic problems leading to measurement error were possible, but would have been nondifferential in effect and not related to silica measurements.

Conclusions: There is a consistent association between increased pulmonary function abnormalities and estimated measures of cumulative silica exposure within the current allowable OSHA regulatory level. Despite concerns about the quality control of the pulmonary function measurements use in these analyses, our results support the need to lower allowable air levels of silica and increase efforts to encourage cessation of cigarette smoking among silica-exposed workers.

Key Words: epidemiology • occupational exposure • pulmonary function • silica


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
Researchers have reported conflicting results from studies1 2 3 4 5 of Vermont granite workers on whether exposures to silica within current allowable exposure limits set by the Occupational Safety and Health Administration (OSHA) are associated with a loss of pulmonary function in the absence of radiographic evidence of silicosis. Studies of granite workers in Singapore6 and Sweden,7 of grinders in the agate dust industry in India,8 of fire brick workers in China,9 and of gold miners in South Africa10 have found an association between silica exposure levels above the allowable OSHA exposure limits and pulmonary function loss in individuals without silicosis. Other investigators11 12 have reported an association between silica exposure and small airways disease.

We collected and abstracted medical and silica-exposure data on a cohort of current and retired automotive foundry workers. We previously reported the radiographic results.13 In this article, we evaluate pulmonary function test (PFT) results, assessing findings both cross-sectionally and over time, in a cohort of employees of an automotive foundry.


   Materials and Methods
TOP
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
The cohort studied is drawn from 1,072 current and former hourly wage employees of a Midwest foundry who had been employed before January 1, 1986. This group included 549 current hourly employees as of June 4, 1991; 497 retired hourly workers receiving a pension as of July 2, 1991; and 26 current salaried employees with former hourly time as of June 4, 1991. The 36 individuals with radiographic findings of parenchymal changes consistent with asbestosis (n = 8) or silicosis (n = 28) were excluded from the analyses reported in this article.

Personnel records were reviewed to construct a job history for each member of the cohort, including start and stop date, department, and job assignment for each position at the foundry. These records were also reviewed for previous employment with potential silica and asbestos exposures.

Trained interviewers administered a questionnaire to all members of the cohort regarding current health status, and medical and exposure history. The questions for respiratory symptoms were taken from the questionnaire developed by the Epidemiology Standardization Project.14 The questionnaire also included items related to tuberculosis status, other lung diseases, and exposures other than at the foundry under study. The type and length of use of respiratory protection was recorded. If unable to complete the questionnaire through an interview (due to sick leave, vacation, or retirees no longer residing in the region where the foundry was located), the questionnaire was mailed to the employee with a cover letter. Telephone follow-up was used to contact nonrespondents, with at least four telephone contacts attempted.

Existing company medical records were reviewed and abstracted for the following information: all annual PFT results since 1978 (when the company began such testing), cigarette smoking histories (where the questionnaire mentioned above was not completed), and the most recent readable chest radiograph. Radiologic results are described in a separate article.13

A standardized PFT data abstract form and written instructions were developed to collect information on each test conducted between 1978 and 1992. The form included personal identifier, test number, year of test, percent-predicted and actual FVC in liters, percent-predicted and actual FEV1 in liters, and percent-predicted and actual mid-maximal flow rate in liters per second. The mid-maximal flow rate values were not used in any analyses, however, based on recommendations of the American Thoracic Society (ATS).15 Height recorded at the time of each test was abstracted; the mode of all height values was used in the analysis. From 1978 to 1984, the company used a Volumetric Wedge-Bellow Expiratory R Model spirometer (Vitalograph; Lenaxa, KS), and from 1985 onward used a Collins Survey 2 spirometer (Warren E. Collins; Braintree, MA). Staff performing the PFTs had taken a PFT course certified by the National Institute for Occupational Safety and Health (NIOSH). However, there was no ongoing continuing education for the personnel providing the testing. Deficiencies in test performance noted were the absence of documentation of calibration, lack of variation in barometric pressure, inconsistent "end of test" determinations, and back-extrapolations > 5% or 100 mL. To address the above-mentioned quality control issues, all PFTs were reviewed as described in the following paragraph.

A standard form was also developed for the coding of PFT quality. This form included a personal identifier, test number and quality rating for FEV1, and test number and quality rating for FVC. All PFT results (including tracings) were photocopied and reviewed by a registered respiratory technician who directs a teaching hospital-based PFT laboratory in Lansing, MI. The tests were rated to ensure that they met ATS criteria for acceptable and reproducible tests.16 The ratings used were as follows: 0, not reproducible and not acceptable; 1, one effort is acceptable but not reproducible; 2, two efforts are acceptable but not reproducible; 3, three efforts are acceptable but not reproducible; 4, reproducible but not acceptable; 5, two or more efforts are reproducible, but only one is acceptable; 6, two or more efforts are reproducible, and two are acceptable; 7, two or more efforts are reproducible, and three are acceptable; 9, unable to evaluate. The ratings of FEV1 and FVC values were made separately for each test. The criteria for acceptability of the FVC measurements were as follows: (1) start of effort must be done with no hesitation, cough, or variance in flow; also the back-extrapolated volume must be < 5% of the FVC or < 100 mL, whichever is greater; and (2) end of effort must have a 6-s exhalation period with a 2-s plateau (defined as < 50 mL change per second). The criteria for the acceptability of the FVC measurements were FVC within 5% (comparing the two best/acceptable curves). The criteria for the validity of the FEV1 measurements were that start of effort must be done with no hesitation, cough, or variance in flow. Also the back-extrapolated volume must be < 5% of the FVC or < 100 mL, whichever is greater. The criteria for the reproducibility of the FEV1 measurements were FEV1 within 5% (comparing the two best/acceptable curves).

The prediction equations developed by Knudson et al17 for whites were used to calculate the 95% confidence limits. The lower 95% confidence limit of predicted was used as the cutoff for normal vs abnormal results for FVC and FEV1.15 For African-American workers, the 95% confidence limits were set at 88% of the calculated predicted value.15 For the FEV1/FVC ratio, < 70% was considered abnormal for participants < 60 years of age at testing, and < 65% was the cutoff if the individual was >= 60 years old.18 Lung function was also analyzed using average percent predicted for the most recent test available.

Data collected from plant walk-through surveys, company and union industrial hygiene files, and employee interviews were used to estimate silica exposures throughout the operating history of the foundry. Estimated levels of exposure by date, department, and job function were merged with personnel records to calculate the cumulative exposure level for each employee. More details on the methods applied to develop these exposure indexes are given in Rosenman et al.13 From employee work histories and the questionnaire, employment in other foundries or silica-related industries was determined.

Exposure measurements were found for 26 of the 30 years covered by this study. The early data reported as dust counts were converted to an estimate of the mass concentration of silica exposure, and used to calculate time-weighted average exposures for the various jobs at the foundry. These data were merged with the results of 8-h mass-respirable sampling. Cumulative exposure was calculated as the product of exposure intensity and duration at each job for each participant.

Cumulative exposure categories were selected a priori following the general guidelines of Lynch and Ayer19 for the formation of categories from data that are log-normally distributed. The mean of each group was statistically different (p < 0.001) from the other means, as tested by analysis of variance. Over a 40-year working lifetime, 286 workdays per year, the average daily exposure for each of the four groups is 0.006 mg/m3 (n = 172), 0.04 mg/m3 (n = 357), 0.12 mg/m3 (n = 346), and 0.28 (n = 167) mg/m3, respectively. The average exposure in category 2 is approximately equal to the recommended limit from NIOSH of 0.05 mg/m3; the average exposure in category 3 is slightly greater than the current OSHA limit of 0.10 mg/m3 for dust composed of pure silica. Thus, these groups provide useful benchmarks for comparison with exposure guidelines and standards.

Contingency table methods were used to assess relationships between discrete variables (for instance, smoking status, categorized as current, former, and never, vs normal or abnormal FEV1 result). Logistic regression analysis20 was used to assess the relationships between normal/abnormal PFT results and exposures after adjusting for other factors such as smoking status. In addition, longitudinal data analysis methods21 were applied to assess exposure-response relationships between the silica-exposure metrics and changes in PFT results over time.


   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
There were 1,028 individuals without evidence of parenchymal changes from exposure to asbestos (n = 8) or silica (n = 28). Of the 575 current employees (includes 26 salary employees who were former hourly employees), 55.8% were African American, 44.2% were white, and 99.5% were men. One individual was Hispanic, and two individuals were categorized as other. There were 60.1% African Americans, 39.9% whites, and 93.8% men among the 497 retirees. Ethnicity was unknown for three retirees, was categorized as Hispanic for one retiree, and categorized as other for one retiree. The average age, average latency of exposure, and average duration of exposure are given in Table 1 (time from first exposure to silica to times of last exposure to silica; the last exposure end point for current employees was June 4, 1991, and for retirees was last date worked; layoffs were subtracted from the duration calculation). Table 2 shows the availability of medical data used for this analysis by employment status (current vs retired). The cigarette smoking status for the cohort is described in Table 3 . The eight individuals whose race was listed as other than white or African American were excluded from the analysis of PFT results (Table 4 ) due to lack of accuracy from small numbers. While the total cohort consists of 1,072 individuals, the result reported for this article is limited to 1,028 of those individuals.


View this table:
[in this window]
[in a new window]

  		Table 1. Demographic and Exposure Characteristics by Employment Status*

 

View this table:
[in this window]
[in a new window]

  		Table 2. Availability of Medical Data by Employment Status*

 

View this table:
[in this window]
[in a new window]

  		Table 3. History of Cigarette Smoking by Employment Status*

 

View this table:
[in this window]
[in a new window]

  		Table 4. Workers With Acceptable PFT Results by No. of Years Such Tests Were Available*

 
Spirometry results were available for 815 individuals who were either white or African American, of whom 762 had PFTs done for >= 2 years. Six hundred ninety-six individuals had one or more tests for which two or more efforts were adjudged to be acceptable and reproducible for FEV1 and who also had smoking status and exposure levels known. Moreover, 523 individuals had one or more tests for which two or more efforts were adjudged to be acceptable and reproducible for FVC and also had smoking status and exposure level known. The number of individuals with 0, 1, 2, or more years in which testing was done and for which two or more efforts were adjudged to be acceptable and reproducible for FEV1 and FVC is shown in Table 4 . The relationship between abnormal FVC and cumulative silica exposure by smoking status is shown in Table 5 . There is no association among nonsmokers; however, there is a statistical trend among smokers of an increasing percentage of individuals with a decreased FVC with increasing cumulative exposure (p = 0.042). The mean percent-predicted FVC levels by cumulative silica exposure and smoking status are also given in Table 5 . Again, there is no relationship between percent-predicted FVC and cumulative silica exposure among nonsmokers, while there is a clear relationship of decreasing percent-predicted FVC with increasing cumulative silica exposure (p = 0.0013) in smokers.


View this table:
[in this window]
[in a new window]

  		Table 5. Analysis of FVC by History of Smoking and Cumulative Silica Exposure*

 
The relationship between abnormal FEV1 and cumulative silica exposure by smoking status is shown in Table 6 . There is no association among nonsmokers; however, there is a suggestion of a trend among smokers (p = 0.062). The mean percent- predicted FEV1 levels by cumulative silica exposure and smoking status are also given in Table 6 . Again, there is no relationship between percent-predicted FEV1 and cumulative silica exposure among nonsmokers; however, there is a pattern of decreasing percent-predicted FEV1 with increasing cumulative silica exposure which emerges (p = 0.011) among smokers.


View this table:
[in this window]
[in a new window]

  		Table 6. Analysis of FEV1 < 95% by History of Smoking and Cumulative Silica Exposure*

 
The relationship between abnormal FEV1/FVC and cumulative silica exposure by smoking status is shown in Table 7 . There is no association among nonsmokers; however, a significant trend is seen among smokers (p = 0.011). The mean FEV1/FVC levels by cumulative silica exposure and smoking status are also given in Table 7 . Again, there is no relationship between FEV1/FVC and cumulative silica exposure among nonsmokers; however, there is a pattern of decreasing FEV1/FVC at the highest cumulative silica exposure (p = 0.0013).


View this table:
[in this window]
[in a new window]

  		Table 7. Analysis of Abnormal FEV1/FVC by History of Smoking and Cumulative Silica Exposure*

 
The results of multiple linear regression analyses of PFT results (FEV1, FVC, FEV1/FVC) on cumulative silica exposure, pack-years of cigarette smoking, ethnicity, age, height, and exposure to silica at another job are given in Table 8 . For each PFT end point, there is a significant relationship between decreasing PFT results and increasing cumulative silica exposure (p = 0.0001, 0.0009, and 0.0276 for FEV1, FVC, and FEV1/FVC, respectively). Table 9 shows expected decrements in FEV1, FVC, and FEV1/FVC for 20 years and 40 years of silica exposure at a variety of daily time-weighted average exposure levels, after adjustment for the effects of each confounding variable listed above. No adjustment was made for respiratory protection, since compliance with voluntary use of respirators was low.


View this table:
[in this window]
[in a new window]

  		Table 8. Linear Regression of Changes in PFT Results Controlling for Silica, Pack-Years of Cigarettes, Ethnicity, Age, Height, and Exposure to Silica at Job Other Than This Foundry

 

View this table:
[in this window]
[in a new window]

  		Table 9. Decrements in Pulmonary Function by Time-Weighted Average of Silica Exposure, Controlling for Effects of Cigarette Pack-Years, Ethnicity, Age, Height, and Silica Exposure at Job Other Than This Foundry

 
The odds ratios for the incidence of an abnormal pulmonary function test (FEV1 < 95% confidence limit; FVC < 95% confidence limit) for 20 years and 40 years of exposure at a variety of time-weighted average levels were calculated from a logistic regression analysis of abnormal PFT results on cumulative exposure, pack-years smoked, and ethnicity. The values ranged from 1.02 to 2.17 times a risk of developing an abnormal FEV1 and an abnormal FVC of 1.02 times to 1.7 times for 20 years worked at a constant time-weighted average level of 0.01 to 0.30 mg/m3, respectively. For 40 years at this range of exposures, the risk of developing an abnormal FEV1 varied from 1.05 times to 4.72 times, and the risk of developing an abnormal FVC varied from 1.04 to 2.89 times.

Longitudinal data analysis of FEV1 results over time (among the 242 individuals with five or more acceptable FEV1 results) showed a 1.1 mL/yr decline in FEV1 for each milligram per cubic meter of mean silica exposure (p = 0.001), after adjusting for ethnicity and pack-years smoked. Similar analyses revealed a 1.6 mL/yr decline in FVC for each milligram per cubic meter of mean silica exposure (p = 0.0108).


   Discussion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
An initial cross-sectional study of PFT results among a cohort of 729 currently employed Vermont granite workers reported a decrease in FVC and FEV1 of 1.6 mL/dust-year.22 Four years later, 668 of these workers were restudied.4 They reported a decrease in FVC of 70 to 80 mL/yr with no association with level of dust. Four hundred eighty-seven of these individuals were tested by another group of investigators who found improvements in FVC and FEV1.3 23 Differences between the two groups of investigators were ascribed to technical quality issues in the initial two studies. A follow-up study24 by this second group of investigators found only an 18 mL/yr decrease in FVC and a 30-mL annual loss in FEV1, appreciably less than that reported by Musk et al.4 The most recent publication on this cohort has described an appreciably greater loss of FEV1 among workers who dropped out of the study, with a 65 mL/yr decrease in FEV1.2 Among the individuals who dropped out, there was a 4 mL/yr loss in FEV1 per milligram per cubic meter-year of cumulative exposure to silica. In our study we found a 1.1-mL/yr loss in FEV1 per milligram per cubic meter of mean silica exposure and 1.6-mL decline in FVC per milligram per cubic meter of mean silica exposure. These results are similar to the initial results of the study of Vermont granite workers.22

Most other studies7 8 9 12 that have reported an association between silica exposure and pulmonary function loss have used either surrogates of exposure (ie, duration) or qualitative estimates of exposure (ie, low, medium, high). One study6 that calculated a dust exposure index for individuals found only a borderline association with cumulative silica exposure of 0.69 mg/m3/yr.

We used multivariate analyses to model the predicted consequence over a working lifetime of the longitudinal loss in pulmonary function. Controlling for cigarette pack-years, age, height, ethnicity, and silica exposure at another job besides this foundry, we calculated that there would be a loss of 104.4 mL of FEV1, 137.7 mL of FVC, and 1.49% of FEV1/FVC for 40 years of exposure of silica at the allowable OSHA exposure level of 0.1 mg/m3. These results are less than but comparable to smoking a pack of cigarettes a day for 40 years, which would result in a loss of 312 mL of FEV1, 232 mL of FVC, and 3.4% of FEV1/FVC. The adverse results of cigarettes would be additive to silica and explain the increased abnormalities and symptoms among cigarette smokers (Tables 4 5 6) . Work for 20 years at the current OSHA standard increased the risk of developing an abnormal FEV1 to 1.3 times and an abnormal FVC to 1.19 times. At 40 years, the risk of an abnormal FEV1 was 1.68 times and an abnormal FVC was 1.42 times. The analysis for increases in abnormal PFT results controlled for pack-years of cigarettes smoked, ethnicity, and silica exposure at another job besides this foundry. The risk was reduced to 1.14 for FEV1 and 1.09 for FVC for 20 years, and 1.3 for FEV1 and 1.19 for FVC for 40 years of exposure at the recommended NIOSH level of 0.05 mg/m3.

The finding of "other silica exposure" as a significant variable in the multivariate analysis for FVC indicates that exposure has been underestimated for a number of study subjects. Since exposure status was determined independent of health status, the resulting misclassification is likely to be nondifferential. In addition to other silica exposure, the other variables determined from the questionnaire may also be affected by selection bias, in that about 25% of the cohort chose not to complete the questionnaire. Encouraging, however, is the fact that the response rate for completing the questionnaire for the current and retired groups (77% and 72%, respectively) was equivalent. Selection bias, however, would not affect objective measures such as height, weight, and PFT results, nor the determinations of exposure levels taken from corporate personnel records and industrial hygiene data.

Another limitation of our study was that the PFTs were performed as part of the medical screening function of the company without emphasis on quality control. To address this problem, we reviewed all PFT tracings and used only results that met ATS criteria for reproducibility and acceptability. This review, however, would not address systemic problems such as lack of documentation of calibration, which could result in measurement error. Such systemic problems would be nondifferential and not related to silica exposure measurements, and therefore should not bias our findings.

The PFT results from our study are consistent with the classical association of silica exposure with restrictive lung disease, as well as the more recent recognition of the occurrence of obstructive changes with silica exposure.25 26 27 28 29 30 31 32 33 34 However, we only found an association between obstructive changes and cumulative silica exposure in individuals who also smoked cigarettes. The absence of significant obstructive changes in nonsmokers with silica exposure has been reported in some of the studies of South African gold miners,31 while not in others.27 30 Some studies26 35 have reported obstructive changes among nonsmokers with silica exposure only in the presence of advanced silicosis. We excluded all individuals with radiographic changes of silicosis from this analysis of PFT results. The results of all the studies have concurred that occurrence of obstructive disease is significantly greater among individuals with both silica and tobacco exposure in comparison with either one separately. Our study supports the initial results of the Vermont granite workers study, which found a decrement in pulmonary function results within the existing allowable air levels for silica,4 5 22 23 which were not confirmed by later findings from other investigators.3 23 24

We have presented our results using both the prevalence of PFT results below those commonly used as clinical cutoffs of normal and abnormal, and as differences in the means of the pulmonary functions. There is a consistent association with increased pulmonary function abnormalities and estimated measures of cumulative silica exposure within the current allowable OSHA regulatory level. The results of our study support the need to lower the allowable air levels of silica and to increase efforts to encourage cigarette smoking cessation among silica-exposed workers.


   Footnotes
 
Abbreviations: ATS = American Thoracic Society; NIOSH = National Institute for Occupational Safety and Health; OSHA = Occupational Safety and Health Administration; PFT = pulmonary function test

This project was funded in whole by funds from the United Auto Workers-Chrysler National Joint Committee on Health and Safety.

Received for publication February 14, 2001. Accepted for publication January 8, 2002.


   References
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

  1. Eisen, EA, Wegman, DH, Louis, TA (1983) Effects of selection in a prospective study of forced expiratory volume in Vermont granite workers. Am Rev Respir Dis 29,587-591
  2. Eisen, EA, Wegman, DH, Louis, TA, et al Healthy work effect in a longitudinal study of one-second forced expiratory volume (FEV1) and chronic exposure to granite dust. Int J Epidemiol 1995;24,1154-1162[Abstract/Free Full Text]
  3. Graham, WGB, Weaver, SL, Ashikaga, T, et al Longitudinal pulmonary function losses in Vermont granite workers: a reevaluation. Chest 1994;106,125-130[Abstract/Free Full Text]
  4. Musk, AW, Peters, JM, Wegman, DH, et al Pulmonary function in granite dust exposure: a four year follow-up. Am Rev Respir Dis 1977;115,769-776[ISI][Medline]
  5. Theriault, GP, Peters, JM, Fine, LJ Pulmonary function in granite shed workers in Vermont. Arch Environ Health 1974;28,18-22[ISI][Medline]
  6. Ng, TP, Chan, SL Lung function in relation to silicosis and silica exposure in granite workers. Eur Respir J 1992;5,986-991[Abstract]
  7. Malmberg, P, Hedenstrom, H, Sundblad, BM Changes in lung function of granite crushers exposed to moderately high silica concentrations: a 12 years follow up. Br J Ind Med 1993;50,726-731[ISI][Medline]
  8. Rastogi, SK, Gupta, BN, Neeraj, M, et al Pulmonary function study in female grinders exposed to agate dust. Toxicol Ind Health 1990;6,145-154[ISI][Medline]
  9. Liou, SH, Chen, YP, Shih, WY, et al Pneumoconiosis and pulmonary function defects in silica-exposed fire brick workers. Arch Environ Health 1996;51,227-233[ISI][Medline]
  10. Irwig, LM, Rocks, P Lung function and respiratory symptoms in silicotic and non-silicotic gold miners. Am Rev Respir Dis 1978;17,429-435
  11. Choudat, D, Frisch, C, Barrat, G, et al Occupational exposure to amorphous silica dust and pulmonary function. Br J Ind Med 1990;47,763-766[ISI][Medline]
  12. Chia, KS, Ng, TP, Jeyaratnam, J Small airways function of silica-exposed workers. Am J Ind Med 1992;22,155-162[ISI][Medline]
  13. Rosenman, KD, Reilly, MJ, Rice, C, et al Silicosis among foundry workers: implication for the need to revise the OSHA standard. Am J Epidemiol 1996;144,890-900[Abstract/Free Full Text]
  14. Ferris, BG Epidemiology Standardization Project. Am Rev Respir Dis 1978;118,1-120[ISI][Medline]
  15. American Thoracic Society. Lung function testing: selection of reference values and interpretative strategies. Am Rev Respir Dis 1991;144,1202-1218[ISI][Medline]
  16. American Thoracic Society. Standardization of spirometry, 1987 update. Am Rev Respir Dis 1987;136,1285-1298[ISI][Medline]
  17. Knudson, RJ, Lebowitz, MD, Holberg, CJ, et al Changes in the normal maximal expiratory flow-volume curve with growth and aging. Am Rev Respir Dis 1983;127,725-734[ISI][Medline]
  18. Miller, A, Warshaw, R, Thorton, JC Prevalence of spirometric abnormalities in a representative sample of the population. Am J Ind Med 1991;19,473-485[ISI][Medline]
  19. Lynch, JR, Ayer, HE Measurement of dust exposures in the asbestos textile industry. Am Ind Hyg J 1966;27,431-437
  20. Breslow NE, Day NE. Statistical methods in cancer research (vol 1): The analysis of case-control studies. Lyon, France: IARC Scientific Publications, 1980. No. 32
  21. Laird, NM, Ware, JH Random effects models for longitudinal data. Biometrics 1982;38,963-974[CrossRef][ISI][Medline]
  22. Theriault, GP, Peters, JM, Johnson, WM Pulmonary function and roentgenographic changes in granite dust exposure. Arch Environ Health 1974;28,23-27[ISI][Medline]
  23. Graham, WGB, O’Grady, RV, Dubuc, B Pulmonary function loss in Vermont granite workers: a long term follow-up and critical reappraisal. Am Rev Respir Dis 1981;123,25-28[ISI][Medline]
  24. Graham, WGB, Ashikaga, T, Hemenway, D, et al Radiographic abnormalities in Vermont granite workers exposed to low levels of granite dust. Chest 1991;100,1507-1514[Abstract/Free Full Text]
  25. Becklake, MR Chronic airflow limitation: its relationship to work in dusty occupations. Chest 1985;88,608-617[Abstract/Free Full Text]
  26. Begin, R, Filion, R, Ostiguy, G Emphysema in silica and asbestos-exposed workers seeking compensation. Chest 1995;108,647-655[Abstract/Free Full Text]
  27. Cowie, RL, Mabena, SK Silicosis, chronic airflow limitation, and chronic bronchitis in South Africa gold miners. Am Rev Respir Dis 1991;143,80-84[ISI][Medline]
  28. Cowie, RL, Hay, M, Thomas, RG Association of silicosis, lung dysfunction, and emphysema in gold miners. Thorax 1993;48,746-749[Abstract]
  29. Hnizdo, E Health risks among white South African gold miners: dust, smoking and chronic obstructive pulmonary disease. S Afr Med J 1992;81,512-517[ISI][Medline]
  30. Hnizdo, E Loss of lung function associated with exposure to silica dust and with smoking and its relation to disability and mortality in South African gold miners. Br J Indust Med 1992;49,472-479[ISI][Medline]
  31. Hnizdo, E, Baskind, E, Sluis-Cremer, GK Combined effect of silica dust exposure and tobacco smoking on the prevalence of respiratory impairments among gold miners. Scand J Work Environ Health 1990;16,411-422[ISI][Medline]
  32. Hnizdo, E, Sluis-Cremer, GK, Baskind, E, et al Emphysema and airway obstruction in non-smoking South African gold miners with long exposure to silica dust. Occup Environ Med 1994;51,557-563[Abstract]
  33. Neukirch, F, Cooreman, J, Korobaeff, M, et al Silica exposure and chronic airflow limitation in pottery workers. Arch Environ Health 1994;49,459-464[ISI][Medline]
  34. Oxman, AD, Muir, DCF, Shannon, HS, et al Occupational dust exposure and chronic obstructive pulmonary disease. Am Rev Respir Dis 1993;148,38-48[ISI][Medline]
  35. Kinsella, M, Muller, N, Vedal, S, et al Emphysema in silicosis. Am Rev Respir Dis 1990;141,1497-1500[ISI][Medline]



This article has been cited by other articles:


Home page
 Toxicol Ind HealthHome page
I. Mohebbi and I. A. Rad
Secondary spontaneous pneumothorax in rapidly progressive forms of silicosis: characterization of pulmonary function measurements and clinical patterns
Toxicology and Industrial Health, April 1, 2007; 23(3): 125 - 132.
[Abstract] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF) Free
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Article Archive
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (5)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Hertzberg, V. S.
Right arrow Articles by Rice, C. H.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Hertzberg, V. S.
Right arrow Articles by Rice, C. H.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS