The Influence of Silicosis on Deteriorating Lung Function in Gold Miners

doi:10.1378/chest.113.2.340

Chest

Volume 113, Issue 2, February 1998, Pages 340-343

https://doi.org/10.1378/chest.113.2.340 Get rights and content

Study objective

To reexamine the symptoms, lung function, and chest radiographs of older gold miners who continued to work in or around gold mines 5 years after their enrollment in the cohort.

Design

A follow-up study of a stratified sample of a cohort of gold miners.

Setting

A health-care center for 24 gold mines in Welkom, South Africa.

Population

A stratified, random sample of 242 miners who were part of a cohort of 1,197 gold miners who had been employed underground in gold mines for a mean period of 29 years. No silicosis was apparent on entry in 59 men, 78 had silicosis with category 1 nodule profusion, 73 had category 2, and 32 had category 3.

Measurements

The men were assessed with questionnaires, lung function tests, and chest radiographs approximately 4.5 years after their initial assessment.

Results

Radiologic features of silicosis had progressed an average of one subcategory (eg, 2/1 to 2/2) in the follow-up period. Lung function deteriorated more rapidly in the men with silicosis and the deterioration increased in proportion to the degree of silicosis at the start of the study. Thus, the annual loss of FEV₁ was 37 mL in those without silicosis, 57 mL in those with category 1, 100 mL with category 2, and 128 mL in the men with category 3 nodule profusion (p=0.000001). A similar pattern of loss was noted for the FVC (p=0.00003) and the single-breath lung diffusion (p=0.004). These changes remained significant after controlling for age, original lung function, and for smoking.

Conclusions

The men with silicosis suffered a substantial loss of lung function during the period of follow-up that was directly in proportion with the nodule profusion on their initial chest radiographs.

Section snippets

Materials and Methods

The study was conducted in the goldfields of the Free State Province of South Africa. The development of the cohort of 1,197 older gold miners with and without silicosis has been described previously.³ In summary, a sampling frame was created by selecting men whose routine screening chest radiographs showed changes in keeping with silicosis and matching each of these men with a similarly aged man without silicosis whose radiograph was read on the same day by the same radiograph reader. Men were

Results

Twenty-five (9%) of the 267 men selected for this follow-up study were unable to participate as they were away from the mine on leave. The remaining 242 men did not differ from the total cohort of 1,197 men with regard to their age or length of underground exposure. The smokers in the sample had a smoking history that was similar to that of the cohort but the proportion of never-smokers was 24% in the sample and 37% in the original cohort (χ² df1=12.7, p=0.005).

The follow-up assessment occurred

Discussion

It was not possible to examine the entire cohort of 1,197 men in this unfunded study nor did resources exist to include the men who were no longer employed as miners. The men who were selected for this follow-up study were chosen in a random fashion after stratification into their original silicosis nodule profusion category. The sample studied did not differ with regard to any of the measured characteristics from the members of the cohort who remained employed as miners. The men who had left

ACKNOWLEDGMENTS

I wish to thank Salmon Mabena who performed all the lung function tests and conducted the questionnaires in each man's own language reflecting his fluency in at least four African languages. I gratefully acknowledge the expertise and assistance of Dr. Mike van Schalkwyk who constructed the initial sample frame from his readings of the routine miniature radiographs of the miners and who was the second reader of the radiographs in this study.

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Exposure to silica can accelerate decrements to lung function, which can occur even in the absence of such opacities on a chest x-ray. Silicosis has been shown to accelerate substantial pulmonary function loss among miners, with the degree of the decrease proportional to the severity of silicosis (Ehrlich et al., 2011; Cowie, 1998). ASGM sites are often situated in resource-limited, rural settings, and thus workers and community members may be exposed to biomass fuel (BMF) smoke.
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A similar tendency was also observed in this respiratory function test at baseline and 5th year. Various indices of longitudinal observation for the respiratory function test have been reported [11–14]; the indices of PEFR, VC, %VC, FEV1, and FEV1% were used in this study. In order to examine the effects of continuous smoking on respiratory functions, our study compared the time-course of respiratory function among three groups, including the group that continued smoking for 4 years, the group that continued not smoking for 4 years, and the other group that started smoking again in our study.
Focusing on the respiratory function for health effect indices, we conducted a cross-sectional study on workers who did and did not handle toner to compare the longitudinal changes.
Among 116 individuals who worked for a Japanese business equipment manufacturer and participated in the study, the analysis included 69 male workers who we were able to follow up for 4 years. We categorized the 40 workers engaged in toner-handling work as the exposed group and the 29 workers not engaged in these tasks as the referent group, and compared their respiratory function test results: peak expiratory flow rate (PEFR), vital capacity (VC), predicted vital capacity (%VC), forced expiratory volume in 1 second (FEV₁), and forced expiratory volume in 1 second as a percent of forced vital capacity (FEV₁%).
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Our study does not suggest any toner exposure effects on respiratory function. However, the number of subjects was small in our study; studies of larger populations will be desired in the future.
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Foram estudados 194 casos de fumadores e exfumadores (≥ 1 UMA), de ambos os sexos e idades compreendidas entre os 20 e os 82 anos, tendo sido excluídos doentes detentores de patologias ou antecedentes profissionais de risco. Apresentavam grau variado de sintomatologia e exame pletismográfico normal, mas com valores anormais do factor de transferência alvéolo-capilar, determinados pelo método de single breath com CO (TL_CO SB e TL_CO /VA). Dos 194 casos avaliados, 136 (70,1%) tinham valores anormais de um ou dos dois parâmetros referidos. No tratamento estatístico da amostra (teste do qui-quadrado), a diferença da sensibilidade entre ambos os parâmetros foi significativa (p = 0,0001). As eventuais limitações do método de avaliação usado (single breath) foram, no presente estudo, minimizadas (restrição ventilatória com capacidade vital < 1,5 litros), pela normalidade referida do exame pletismográfico. De igual modo, a presença de alterações da distribuição ventilatória foi, em princípio, excluída pela ausência de valores da relação CPT-sb/CPTplet inferiores a 0,85.
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The prevalence of a restrictive abnormal pattern on spirometric test results increased with increasing profusion abnormalities on the chest radiographs and latency from first exposure to silica but not with duration of exposure to silica (Tables3–5). The association of increasing spirometric abnormalities with ILO radiographic profusion has been reported in a number of silicosis cohorts.12–17 Controlling for age, duration of silica exposure, and cigarette-smoking status, restrictive changes were significantly increased in individuals with profusion category 3, and obstructive and mixed changes in individuals with PMF compared with individuals with profusion category 1 (Table 6).
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Few if any studies of the association between pulmonary tuberculosis (TB) and lung function loss have had access to premorbid lung function values.
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: revision accepted July 18.

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Chest

Clinical Investigations: Inhalation/PneumoconiosisThe Influence of Silicosis on Deteriorating Lung Function in Gold Miners

Study objective

Design

Setting

Population

Measurements

Results

Conclusions

Section snippets

Materials and Methods

Results

Discussion

ACKNOWLEDGMENTS

Chest

Silicosis

Am Rev Respir Dis

Lung function and respiratory symptoms in silicotic and non-silicotic gold miners

Am Rev Respir Dis

Silicosis, chronic airflow limitation, and chronic bronchitis in South African gold miners

Am Rev Respir Dis

Symptoms and clinical findings in patients with silicosis

Scand J Work Environ Health

Lung function in relation to silicosis and silica exposure in granite workers

Eur Respir J

Emphysema and airway obstruction in non-smoking South African gold miners with long exposure to silica dust

Occup Environ Med

Clinical Investigations: Inhalation/Pneumoconiosis
The Influence of Silicosis on Deteriorating Lung Function in Gold Miners