ORIGINAL ARTICLE
Continued Spirometry Changes After Cessation of Exposure in Asbestos-Cement Workers ´ atkowska, Beata Swi ˛ PhD, Sobala Wojciech, MSc, Zuzanna Szubert, PhD, and Neonila Szeszenia-Dabrowska, ˛ Prof
Objective: To assess further progression of spirometry parameters among former asbestos-cement plant workers. Methods: The following parameters were assessed: forced expiratory volume in 1 second (FEV1 ), forced vital capacity (FVC), and the ratio (FEV1 /FVC) using a linear regression model with mixed effects. Results: The analysis included 3005 individuals. Spirometrically defined restrictive ventilatory defects were registered in 21.6% of the patients, obstructive defects in 8.3%, whereas mixed changes in 7%. Current smokers had significantly lower levels of FEV1 , FVC, and FEV1 /FVC and a steeper decline compared with nonsmokers. More rapid progression was also observed along with increasing termination of exposure. Having higher exposure was associated with a slower decline in FEV1 and FEV1 /FVC ratios. Conclusions: This report indicates that asbestos-cement workers with higher cumulative exposure still had lower mean levels of spirometric parameters, despite cessation of asbestos exposure many years ago.
T
he pathogenic effects of asbestos on the respiratory system result from the inhalation of asbestos fibers suspended in the ambient air. The fibers accumulate in the lung tissue during the whole human lifetime, and the pathogenic effects become evident after a long period of latency. Health effects of occupational exposure to asbestos dust may reveal themselves during the time of employment as well as many years after termination of work in exposure. Despite not using asbestos for manufacturing various products in Poland for more than 16 years, the number of occupational asbestos-related diseases has remained relatively high.1 Asbestos dust because of its pathogenic properties constitutes a major health risk for the workers. As a consequence of biological effect of neoplastic changes of asbestos dust, interstitial as well as pleural changes can be observed. In addition, asbestos exposure may limit ventilation efficiency of lungs. Very few surveys on longitudinal changes in pulmonary function in asbestos-cement workers are available.2–5 Little is known about decline in both forced expiratory volume in 1 second (FEV1 ) and forced vital capacity (FVC) long after the end of exposure. In this study, we assessed further progression of spirometric parameters after termination of exposure to dust containing asbestos among the group of Polish workers who were employed in asbestoscement production plants.
MATERIAL AND METHODS Study Design Analysis included 3005 former workers of eight asbestoscement plants examined over the years 2000 to 2012. The study group comprised 78.5% of all patients employed in asbestos-cement plants who reported for examinations within the program. Periodic From the Department of Occupational and Environmental Epidemiology, Nofer Institute of Occupational Medicine, Ł´od´z, Poland. No grant funding was used to support this research. The authors declare no conflicts of interest. ´ atkowska, Address correspondence to: Beata Swi PhD, Department of Occu˛ pational and Environmental Epidemiology, Nofer Institute of Occupational Medicine, s´w. Teresy 8, 91-348 Ł´od´z, Poland ([email protected]). C 2014 by American College of Occupational and Environmental Copyright Medicine DOI: 10.1097/JOM.0000000000000117
medical examinations included general physical examination, radiograph of chest, resting spirometry, and complementary examination (eg, resting gasometry and computed tomography). Prophylactic medical examination program called “Amiantus” addressed to the former workers of asbestos-processing plants was realized in Poland since 2000. The program included the workers of asbestos-processing plants, who were employed in those plants till 1998 (ie, till introduction of the law banning the use of asbestos). Periodic medical examinations, which aim at assessment of the respiratory system, were performed by regional occupational medicine centers. For the needs of the “Amiantus” program, a standardized methodology of medical examinations and asbestos-related pathology recognition in accordance with commonly approved diagnostic criteria (Helsinki criteria, 1997) was developed.6 The clinical diagnosis of asbestos-related diseases was based on a medical interview, symptoms, radiological radiographic images, other laboratory tests, and a review of occupational asbestos exposure history. Information concerning work history in a plant (workstation, length of service, employment period), number of cigarettes smoked now and in the past, and diagnosis of the respiratory system diseases was collected on the developed detailed questionnaires. Monitoring of health effects in the whole study population, coordination of the study, and supervision of institutions performing periodic medical examinations have been realized by the Reference Centre of Asbestos Exposure and Health Risk Assessment at Nofer Institute of Occupational Medicine in Lodz.7
Spirometry Spirometry was carried out in accordance with the standards determining requirements concerning the used apparatus and the way of conducting medical examination as well as with training of people responsible for medical examination performance. In case of doubts about whether the spirometry was performed correctly (eg, a note in the card of functional respiratory system examination informing about the lack of cooperation on the side of the patient), such results were excluded from the analysis. As part of clinical examination, the following spirometric parameters were measured: FEV1 , FVC, and FEV1 /FVC— (pseudo)Tiffeneau indicator. Ventilation disorders were defined as follows: normal FVC 80% or more and FEV1 /FVC 70% or more; restrictive FVC less than 80% and FEV1 /FVC 70% or more; obstructive FVC 80% or more and FEV1 /FVC less than 70%; and mixed FVC less than 80% and FEV1 /FVC less than 70%. The measured values of lung function parameters were compared with the reference values for a given patient calculated on the basis of the suitable Falaschetti predictive equations.8
Exposure Assessment Manufacturing of asbestos-cement products in Poland lasted from 1945 to 1998 (in individual plants from 14 to 46 years). These products contained 9% to 12% of asbestos in terms of dry weight. In all eight plants, the process of board production was similar; the differences mainly regarded the production size and the type of asbestos used. Typical pure Portland cement without any additives and chrysotile were used. Occasionally, small amounts (up to 5%) of crocidolite were added to chrysotile asbestos. Since the mid-80s, the use of crocidolite has been banned.
JOEM r Volume 56, Number 4, April 2014 Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
403
JOEM r Volume 56, Number 4, April 2014
´ ˛tkowska et al Swia
Assessment of exposure to dust containing asbestos was carried out on a basis of a developed job exposure matrix in the plants manufacturing asbestos-cement products.9 Exposure was determined on a basis of data obtained from the workplaces or archives in the case of closed down industrial plants, data from sanitary– epidemiological stations as well as data obtained during measurements taken by the Nofer Institute of Occupational Medicine. The workstation of an examined individual was specified on a basis of a questionnaire interview. Individual measurements of respirable dust in the air at the workstations and stationary measurements were performed by the use of the gravimetric method. Respirable dust measurement results were obtained from the years 1960 to 1997. We have a total of 1958 measurements in eight asbestos factories. The highest concentrations of dust were reported at workstations of burying the material, crushing wheels as well as cutting and polishing of products. The highest concentration of dust containing asbestos reported in 1960 amounted to 52 mg/m3 , then in 1973 to 26.9 mg/m3 , and in 1984 to 11.6 mg/m3 . The lowest mean concentration occurred in 1996, and it amounted to 1.2 mg/m3 . The indicator of cumulative exposure to dust containing asbestos was expressed in mg/m3 ·yr. The method for determination of the number of asbestos fibers in cm3 of the air was introduced only in the mid-80s. A total of 754 fiber measurements were taken in six factories. Spearman correlation coefficient for both measurement methods is 0.184 (P < 0.001; n = 599).
Radiographic Evaluation The chest radiographs were read epidemiologically according to the International Labour Organization (ILO, Geneva 1980) classification.10 Radiographs of the fourth degree of technical quality were excluded from analysis. Each patient included in the study had full-dimensional chest radiograph taken both in the posterior– anterior and lateral view, which was assessed by two specialist radiologists having long experience in diagnosis of dust diseases and using the most recent chest radiographs and ILO standard films. In discordant cases, a consensus reading was conducted. The ILO classification scheme was used to record density of small irregular opacities, and the presence of pleural plaques, diffuse pleural thickening, and diaphragmatic pleural plaques. Subjects who had been classified as 0/1 or more were included into a group with the presence of small opacities.
Statistical Analysis Statistical inference was performed on the basis of significance tests at the significance level of 0.05. Relationship between the results of spirometric parameters was analyzed by the use of a linear regression model with mixed effects. Sex and age were included as random effects. All three multivariate models (for FEV1 , FVC, and FEV1 /FVC ratio) included all the examined predictors (cumulative concentration, cigarette smoking, duration of time from exposure termination, as well as changes in the chest radiographic image—small, irregular opacities, pleural plaques, diffuse pleural thickening, and also age, height, and sex) and its interactions with age at examination as fixed terms in regression models. In models for FEV1 and FVC, sex was included as a predictor of residual variance. R programme, version 2.15.3, was used for statistical analysis. The model with mixed effects was fitted by the use of Ime function from the nlme package.
RESULTS The analysis included 3005 individuals (among them 864 women) (Table 1). The most numerous group comprised individuals aged 51 to 60 years (39.3%), whereas about 28.4% were patients younger than 50 years. Individuals who declared current smoking 404
TABLE 1. Characteristics of the Former Asbestos-Cement Workers (n = 3005), Poland Variable Age at the time of the first spirometry test, yrs 24–50 51–60 61–70 >71 Height, cm—mean (SD) Weight, kg—mean (SD) Smoking, cigarette/d* No 1–10 11–50 Time between the first and last examination, yrs† 1–3 4–6 7–9 >9 Time since termination of employment, yrs 2–10 11–30 >30 Cumulative exposure index, mg/m3 ·yr 60 Radiographic abnormalities Small opacities Pleural plaques Diffuse pleural thickening Spirometry measurements FEV1 , L—mean (SD) FVC, L—mean (SD) FEV1 /FVC ratio, %—mean (SD)
N (%)
853 (28.4) 1182 (39.3) 672 (22.4) 298 (9.9) 167.4 (8.6) 78.2 (14.9) 2206 (73.4) 379 (12.6) 420 (14.0) 480 (16.0) 531 (17.7) 671 (22.3) 529 (17.6) 1006 (33.5) 1649 (54.9) 350 (11.6) 1519 (50.5) 978 (32.5) 508 (16.9) 1903 (63.3) 330 (11.0) 1683 (56.0) 2.8 (0.9) 3.5 (1.1) 79.8 (10.7)
*Those who declared current smoking. † A total of 794 (26.4%) patients had spirometry performed only once. FVC, forced vital capacity; FEV1 , forced expiratory volume in 1 second; FEV1 /FVC, the ratio of FEV1 to FVC expressed as a percentage; SD, standard deviation.
amounted to 26.6% of the group. In the study group of 3005 patients, 794 (26.4%) had only one spirometry performed, 706 (23.5%) had between five and eight tests, and more that eight spirometry tests were reported in 198 (6.6%) of the patients. Considerable part of the individuals (n = 1307; 43.5%) included in the analysis had between 2 and 4 spirometric examinations performed. For majority of the individuals included in the analysis, an interval between the first and last examination ranged from 7 to 9 years. The mean duration of employment was 11.5 years. Of all the individuals included in the analysis, the workers employed before 1966 comprised 16.4%; over 1966 to 1975, 37.3%; over 1976 to 1985, 29.4%; while those employed after 1985 comprised 16.9%. The average time that has passed from exposure termination amounted to 16.5 years. For the majority of the patients (44.7%), time that passed from the moment of being employed to the first examination amounted to 16 to 30 years and the period shorter than 16 years was reported in 10.7% of the former workers The mean cumulative exposure to dust containing asbestos for the workers employed in asbestos-cement plants
C 2014 American College of Occupational and Environmental Medicine
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
JOEM r Volume 56, Number 4, April 2014
Lung Function in Former Asbestos-Cement Workers
amounted to 31.5 mg/m3 ·yr (standard deviation = 31.7). About a half of the examined individuals (49.5%) worked above currently applying maximum admissible concentration. Ventilation disorders of restrictive type were observed in 21.6% of the individuals from the examined population; obstructive changes were observed in 8.3% of the patients, whereas those of mixed nature in 7%.
FEV1 Table 2 shows the mean values for FEV1 , FVC, and FEV1 /FVC from the mixed models. In the multivariate model, the mean FEV1 value was significantly lower among women than among men participating in the study. The carried out multivariate analysis of progression of the FEV1 value (Table 3) shows that this parameter reduces more slowly in women (P < 0.001). Comparison of FEV1 levels among smokers and nonsmokers revealed that, for the individuals who smoke, the value of this parameter was lower compared the nonsmokers. The average 10-year decrease of this parameter is by 0.091 L higher in the individuals who smoke from 11 to 50 cigarettes a day (P < 0.001) in comparison with the nonsmokers. In addition, the analysis results indicate lower mean values of FEV1 with increasing levels of cumulative exposure (Table 2). It was observed that reduction of FEV1 indicator was more slowly, by 0.046 L per 10 years (P = 0.053) in the individuals with the cumulative exposure index more than 60 mg/m3 ·yr in comparison with the exposure group less than 21 mg/m3 ·yr (Table 3). Subjects with asbestosis had lower levels of FEV1 than those without asbestosis (Table 2). The decrease in FEV1 in the group of the examined patients proceeds more slowly in the individuals with interstitial changes, for shadows density category 2/1 and higher by 0.160 L per 10 years (P = 0.036) in comparison with the individuals without such a type of changes in the radiographic image (category 0/0 to 0/1) (Table 3).
FVC People with higher index of cumulative exposure and subjects with asbestosis and diffuse pleural thickening had significantly lower FVC mean values (Table 2). On the basis of the multivariate progression model for FVC value, it has been reported that changes of this parameter proceed more slowly among women than in examined men (P < 0.001) (Table 3). The average 10-year decline of this parameter is higher among the individuals who smoke more than 10 cigarettes a day, by 0.064 L (P = 0.030), compared with the nonsmokers.
FEV1 /FVC The multivariate analysis of progression of (pseudo)Tiffeneau indicator decreases in the examined group (Table 3) has shown that this parameter drops faster in smokers, by 1.01% per 10 years (P = 0.028) for the individuals who smoke up to 10 cigarettes a day and by 1.45% per 10 years (P < 0.001) for those smoking more than 10 cigarettes a day, in comparison with the nonsmokers. The value of this parameter reduces along with the lengthening of time from exposure termination—from 1.27% per 10 years (P < 0.001) for the individuals for whom this period amounted to 11 to 30 years to 2.62% per 10 years (P < 0.001) for longer than 30 years in comparison with the time of exposure termination shorter than 11 years. People with higher index of cumulative exposure had significantly lower FEV1 /FVC levels and a slower decline over time. The average 10-year decline of this parameter is by 1.02% lower among the workers with cumulative asbestos exposure more than 60 mg/m3 ·yr in comparison with those with less than 21 mg/m3 ·yr. Presence of asbestosis was associated with lower levels of FEV1 /FVC (Table 2). Changes of this parameter proceeded more slowly by 3.17% per 10 years (P = 0.031) in the case of individuals who had shadows density category 2/1 and higher in comparison with the subjects without such a diagnosis.
TABLE 2. Results From the Linear Mixed Model for Dependent Variables FEV1 , FVC, and FEV1 /FVC* FEV1 , L Selected Factors
Estimate (SE)
Women (ref.: male) − 0.319 (0.030) Cigarette smoking (ref.: no) 1–10 cigarettes/d − 0.075 (0.030) 11–50 cigarettes/d − 0.227 (0.032) Time since termination of employment (ref.: 30 yrs − 0.059 (0.024) Cumulative exposure index (ref.: 60 mg/m3 ·yr − 0.109 (0.030) Categories of small, irregular opacities (ref.: 0/0–0/1) 1/0–1/2 − 0.078 (0.023) ≥2/1 − 0.337 (0.107) Pleural plaques (ref.: no) − 0.041 (0.037) Diffuse pleural thickening (ref.: no) − 0.163 (0.022) 0.47 σ bw 0.16 σ age 0.34 σ res
FVC, L
FEV1 /FVC, %
P Value
Estimate (SE)
P Value
Estimate (SE)
P Value
Continued Spirometry Changes After Cessation of Exposure in Asbestos-Cement Workers ´ atkowska, Beata Swi ˛ PhD, Sobala Wojciech, MSc, Zuzanna Szubert, PhD, and Neonila Szeszenia-Dabrowska, ˛ Prof
Objective: To assess further progression of spirometry parameters among former asbestos-cement plant workers. Methods: The following parameters were assessed: forced expiratory volume in 1 second (FEV1 ), forced vital capacity (FVC), and the ratio (FEV1 /FVC) using a linear regression model with mixed effects. Results: The analysis included 3005 individuals. Spirometrically defined restrictive ventilatory defects were registered in 21.6% of the patients, obstructive defects in 8.3%, whereas mixed changes in 7%. Current smokers had significantly lower levels of FEV1 , FVC, and FEV1 /FVC and a steeper decline compared with nonsmokers. More rapid progression was also observed along with increasing termination of exposure. Having higher exposure was associated with a slower decline in FEV1 and FEV1 /FVC ratios. Conclusions: This report indicates that asbestos-cement workers with higher cumulative exposure still had lower mean levels of spirometric parameters, despite cessation of asbestos exposure many years ago.
T
he pathogenic effects of asbestos on the respiratory system result from the inhalation of asbestos fibers suspended in the ambient air. The fibers accumulate in the lung tissue during the whole human lifetime, and the pathogenic effects become evident after a long period of latency. Health effects of occupational exposure to asbestos dust may reveal themselves during the time of employment as well as many years after termination of work in exposure. Despite not using asbestos for manufacturing various products in Poland for more than 16 years, the number of occupational asbestos-related diseases has remained relatively high.1 Asbestos dust because of its pathogenic properties constitutes a major health risk for the workers. As a consequence of biological effect of neoplastic changes of asbestos dust, interstitial as well as pleural changes can be observed. In addition, asbestos exposure may limit ventilation efficiency of lungs. Very few surveys on longitudinal changes in pulmonary function in asbestos-cement workers are available.2–5 Little is known about decline in both forced expiratory volume in 1 second (FEV1 ) and forced vital capacity (FVC) long after the end of exposure. In this study, we assessed further progression of spirometric parameters after termination of exposure to dust containing asbestos among the group of Polish workers who were employed in asbestoscement production plants.
MATERIAL AND METHODS Study Design Analysis included 3005 former workers of eight asbestoscement plants examined over the years 2000 to 2012. The study group comprised 78.5% of all patients employed in asbestos-cement plants who reported for examinations within the program. Periodic From the Department of Occupational and Environmental Epidemiology, Nofer Institute of Occupational Medicine, Ł´od´z, Poland. No grant funding was used to support this research. The authors declare no conflicts of interest. ´ atkowska, Address correspondence to: Beata Swi PhD, Department of Occu˛ pational and Environmental Epidemiology, Nofer Institute of Occupational Medicine, s´w. Teresy 8, 91-348 Ł´od´z, Poland ([email protected]). C 2014 by American College of Occupational and Environmental Copyright Medicine DOI: 10.1097/JOM.0000000000000117
medical examinations included general physical examination, radiograph of chest, resting spirometry, and complementary examination (eg, resting gasometry and computed tomography). Prophylactic medical examination program called “Amiantus” addressed to the former workers of asbestos-processing plants was realized in Poland since 2000. The program included the workers of asbestos-processing plants, who were employed in those plants till 1998 (ie, till introduction of the law banning the use of asbestos). Periodic medical examinations, which aim at assessment of the respiratory system, were performed by regional occupational medicine centers. For the needs of the “Amiantus” program, a standardized methodology of medical examinations and asbestos-related pathology recognition in accordance with commonly approved diagnostic criteria (Helsinki criteria, 1997) was developed.6 The clinical diagnosis of asbestos-related diseases was based on a medical interview, symptoms, radiological radiographic images, other laboratory tests, and a review of occupational asbestos exposure history. Information concerning work history in a plant (workstation, length of service, employment period), number of cigarettes smoked now and in the past, and diagnosis of the respiratory system diseases was collected on the developed detailed questionnaires. Monitoring of health effects in the whole study population, coordination of the study, and supervision of institutions performing periodic medical examinations have been realized by the Reference Centre of Asbestos Exposure and Health Risk Assessment at Nofer Institute of Occupational Medicine in Lodz.7
Spirometry Spirometry was carried out in accordance with the standards determining requirements concerning the used apparatus and the way of conducting medical examination as well as with training of people responsible for medical examination performance. In case of doubts about whether the spirometry was performed correctly (eg, a note in the card of functional respiratory system examination informing about the lack of cooperation on the side of the patient), such results were excluded from the analysis. As part of clinical examination, the following spirometric parameters were measured: FEV1 , FVC, and FEV1 /FVC— (pseudo)Tiffeneau indicator. Ventilation disorders were defined as follows: normal FVC 80% or more and FEV1 /FVC 70% or more; restrictive FVC less than 80% and FEV1 /FVC 70% or more; obstructive FVC 80% or more and FEV1 /FVC less than 70%; and mixed FVC less than 80% and FEV1 /FVC less than 70%. The measured values of lung function parameters were compared with the reference values for a given patient calculated on the basis of the suitable Falaschetti predictive equations.8
Exposure Assessment Manufacturing of asbestos-cement products in Poland lasted from 1945 to 1998 (in individual plants from 14 to 46 years). These products contained 9% to 12% of asbestos in terms of dry weight. In all eight plants, the process of board production was similar; the differences mainly regarded the production size and the type of asbestos used. Typical pure Portland cement without any additives and chrysotile were used. Occasionally, small amounts (up to 5%) of crocidolite were added to chrysotile asbestos. Since the mid-80s, the use of crocidolite has been banned.
JOEM r Volume 56, Number 4, April 2014 Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
403
JOEM r Volume 56, Number 4, April 2014
´ ˛tkowska et al Swia
Assessment of exposure to dust containing asbestos was carried out on a basis of a developed job exposure matrix in the plants manufacturing asbestos-cement products.9 Exposure was determined on a basis of data obtained from the workplaces or archives in the case of closed down industrial plants, data from sanitary– epidemiological stations as well as data obtained during measurements taken by the Nofer Institute of Occupational Medicine. The workstation of an examined individual was specified on a basis of a questionnaire interview. Individual measurements of respirable dust in the air at the workstations and stationary measurements were performed by the use of the gravimetric method. Respirable dust measurement results were obtained from the years 1960 to 1997. We have a total of 1958 measurements in eight asbestos factories. The highest concentrations of dust were reported at workstations of burying the material, crushing wheels as well as cutting and polishing of products. The highest concentration of dust containing asbestos reported in 1960 amounted to 52 mg/m3 , then in 1973 to 26.9 mg/m3 , and in 1984 to 11.6 mg/m3 . The lowest mean concentration occurred in 1996, and it amounted to 1.2 mg/m3 . The indicator of cumulative exposure to dust containing asbestos was expressed in mg/m3 ·yr. The method for determination of the number of asbestos fibers in cm3 of the air was introduced only in the mid-80s. A total of 754 fiber measurements were taken in six factories. Spearman correlation coefficient for both measurement methods is 0.184 (P < 0.001; n = 599).
Radiographic Evaluation The chest radiographs were read epidemiologically according to the International Labour Organization (ILO, Geneva 1980) classification.10 Radiographs of the fourth degree of technical quality were excluded from analysis. Each patient included in the study had full-dimensional chest radiograph taken both in the posterior– anterior and lateral view, which was assessed by two specialist radiologists having long experience in diagnosis of dust diseases and using the most recent chest radiographs and ILO standard films. In discordant cases, a consensus reading was conducted. The ILO classification scheme was used to record density of small irregular opacities, and the presence of pleural plaques, diffuse pleural thickening, and diaphragmatic pleural plaques. Subjects who had been classified as 0/1 or more were included into a group with the presence of small opacities.
Statistical Analysis Statistical inference was performed on the basis of significance tests at the significance level of 0.05. Relationship between the results of spirometric parameters was analyzed by the use of a linear regression model with mixed effects. Sex and age were included as random effects. All three multivariate models (for FEV1 , FVC, and FEV1 /FVC ratio) included all the examined predictors (cumulative concentration, cigarette smoking, duration of time from exposure termination, as well as changes in the chest radiographic image—small, irregular opacities, pleural plaques, diffuse pleural thickening, and also age, height, and sex) and its interactions with age at examination as fixed terms in regression models. In models for FEV1 and FVC, sex was included as a predictor of residual variance. R programme, version 2.15.3, was used for statistical analysis. The model with mixed effects was fitted by the use of Ime function from the nlme package.
RESULTS The analysis included 3005 individuals (among them 864 women) (Table 1). The most numerous group comprised individuals aged 51 to 60 years (39.3%), whereas about 28.4% were patients younger than 50 years. Individuals who declared current smoking 404
TABLE 1. Characteristics of the Former Asbestos-Cement Workers (n = 3005), Poland Variable Age at the time of the first spirometry test, yrs 24–50 51–60 61–70 >71 Height, cm—mean (SD) Weight, kg—mean (SD) Smoking, cigarette/d* No 1–10 11–50 Time between the first and last examination, yrs† 1–3 4–6 7–9 >9 Time since termination of employment, yrs 2–10 11–30 >30 Cumulative exposure index, mg/m3 ·yr 60 Radiographic abnormalities Small opacities Pleural plaques Diffuse pleural thickening Spirometry measurements FEV1 , L—mean (SD) FVC, L—mean (SD) FEV1 /FVC ratio, %—mean (SD)
N (%)
853 (28.4) 1182 (39.3) 672 (22.4) 298 (9.9) 167.4 (8.6) 78.2 (14.9) 2206 (73.4) 379 (12.6) 420 (14.0) 480 (16.0) 531 (17.7) 671 (22.3) 529 (17.6) 1006 (33.5) 1649 (54.9) 350 (11.6) 1519 (50.5) 978 (32.5) 508 (16.9) 1903 (63.3) 330 (11.0) 1683 (56.0) 2.8 (0.9) 3.5 (1.1) 79.8 (10.7)
*Those who declared current smoking. † A total of 794 (26.4%) patients had spirometry performed only once. FVC, forced vital capacity; FEV1 , forced expiratory volume in 1 second; FEV1 /FVC, the ratio of FEV1 to FVC expressed as a percentage; SD, standard deviation.
amounted to 26.6% of the group. In the study group of 3005 patients, 794 (26.4%) had only one spirometry performed, 706 (23.5%) had between five and eight tests, and more that eight spirometry tests were reported in 198 (6.6%) of the patients. Considerable part of the individuals (n = 1307; 43.5%) included in the analysis had between 2 and 4 spirometric examinations performed. For majority of the individuals included in the analysis, an interval between the first and last examination ranged from 7 to 9 years. The mean duration of employment was 11.5 years. Of all the individuals included in the analysis, the workers employed before 1966 comprised 16.4%; over 1966 to 1975, 37.3%; over 1976 to 1985, 29.4%; while those employed after 1985 comprised 16.9%. The average time that has passed from exposure termination amounted to 16.5 years. For the majority of the patients (44.7%), time that passed from the moment of being employed to the first examination amounted to 16 to 30 years and the period shorter than 16 years was reported in 10.7% of the former workers The mean cumulative exposure to dust containing asbestos for the workers employed in asbestos-cement plants
C 2014 American College of Occupational and Environmental Medicine
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
JOEM r Volume 56, Number 4, April 2014
Lung Function in Former Asbestos-Cement Workers
amounted to 31.5 mg/m3 ·yr (standard deviation = 31.7). About a half of the examined individuals (49.5%) worked above currently applying maximum admissible concentration. Ventilation disorders of restrictive type were observed in 21.6% of the individuals from the examined population; obstructive changes were observed in 8.3% of the patients, whereas those of mixed nature in 7%.
FEV1 Table 2 shows the mean values for FEV1 , FVC, and FEV1 /FVC from the mixed models. In the multivariate model, the mean FEV1 value was significantly lower among women than among men participating in the study. The carried out multivariate analysis of progression of the FEV1 value (Table 3) shows that this parameter reduces more slowly in women (P < 0.001). Comparison of FEV1 levels among smokers and nonsmokers revealed that, for the individuals who smoke, the value of this parameter was lower compared the nonsmokers. The average 10-year decrease of this parameter is by 0.091 L higher in the individuals who smoke from 11 to 50 cigarettes a day (P < 0.001) in comparison with the nonsmokers. In addition, the analysis results indicate lower mean values of FEV1 with increasing levels of cumulative exposure (Table 2). It was observed that reduction of FEV1 indicator was more slowly, by 0.046 L per 10 years (P = 0.053) in the individuals with the cumulative exposure index more than 60 mg/m3 ·yr in comparison with the exposure group less than 21 mg/m3 ·yr (Table 3). Subjects with asbestosis had lower levels of FEV1 than those without asbestosis (Table 2). The decrease in FEV1 in the group of the examined patients proceeds more slowly in the individuals with interstitial changes, for shadows density category 2/1 and higher by 0.160 L per 10 years (P = 0.036) in comparison with the individuals without such a type of changes in the radiographic image (category 0/0 to 0/1) (Table 3).
FVC People with higher index of cumulative exposure and subjects with asbestosis and diffuse pleural thickening had significantly lower FVC mean values (Table 2). On the basis of the multivariate progression model for FVC value, it has been reported that changes of this parameter proceed more slowly among women than in examined men (P < 0.001) (Table 3). The average 10-year decline of this parameter is higher among the individuals who smoke more than 10 cigarettes a day, by 0.064 L (P = 0.030), compared with the nonsmokers.
FEV1 /FVC The multivariate analysis of progression of (pseudo)Tiffeneau indicator decreases in the examined group (Table 3) has shown that this parameter drops faster in smokers, by 1.01% per 10 years (P = 0.028) for the individuals who smoke up to 10 cigarettes a day and by 1.45% per 10 years (P < 0.001) for those smoking more than 10 cigarettes a day, in comparison with the nonsmokers. The value of this parameter reduces along with the lengthening of time from exposure termination—from 1.27% per 10 years (P < 0.001) for the individuals for whom this period amounted to 11 to 30 years to 2.62% per 10 years (P < 0.001) for longer than 30 years in comparison with the time of exposure termination shorter than 11 years. People with higher index of cumulative exposure had significantly lower FEV1 /FVC levels and a slower decline over time. The average 10-year decline of this parameter is by 1.02% lower among the workers with cumulative asbestos exposure more than 60 mg/m3 ·yr in comparison with those with less than 21 mg/m3 ·yr. Presence of asbestosis was associated with lower levels of FEV1 /FVC (Table 2). Changes of this parameter proceeded more slowly by 3.17% per 10 years (P = 0.031) in the case of individuals who had shadows density category 2/1 and higher in comparison with the subjects without such a diagnosis.
TABLE 2. Results From the Linear Mixed Model for Dependent Variables FEV1 , FVC, and FEV1 /FVC* FEV1 , L Selected Factors
Estimate (SE)
Women (ref.: male) − 0.319 (0.030) Cigarette smoking (ref.: no) 1–10 cigarettes/d − 0.075 (0.030) 11–50 cigarettes/d − 0.227 (0.032) Time since termination of employment (ref.: 30 yrs − 0.059 (0.024) Cumulative exposure index (ref.: 60 mg/m3 ·yr − 0.109 (0.030) Categories of small, irregular opacities (ref.: 0/0–0/1) 1/0–1/2 − 0.078 (0.023) ≥2/1 − 0.337 (0.107) Pleural plaques (ref.: no) − 0.041 (0.037) Diffuse pleural thickening (ref.: no) − 0.163 (0.022) 0.47 σ bw 0.16 σ age 0.34 σ res
FVC, L
FEV1 /FVC, %
P Value
Estimate (SE)
P Value
Estimate (SE)
P Value
