Causes of disability in coalminers: a clinico-pathological study of emphysema, airways obstruction and massive fibrosis. Final report on CEC Contract 7248/31/030

This report is based on autopsy studies of coalworkers’ lungs drawn from a collection of almost 1400 lungs made between 1972 and 1986. All the men had taken part, at some stage in their working life, in the Pneumoconiosis Field Research (PFR), which included 24 collieries representing the range of mining experience in the British coalfields. Examination of cause of death in the autopsy group, of whom 79% were included in a mortality study based on the PFR population, showed that the autopsy group included higher proportions of men dying from bronchitis, emphysema and pneumoconiosis than did the parent mortality population.The prevalence of emphysema was examined in 503 men. Both panacinar and centriacinar emphysema were more common in smokers than non-smokers and were more likely to occur in men whose lungs also showed dust-related fibrosis. Prevalence of emphysema increased with increasing age, although, for men with PMF, neither age nor smoking habit contributed significantly to the presence of centriacinar emphysema in regression analyses and more than 60% showed some emphysema at all ages. Emphysema was rare in non-smokers under the age of 65 unless they also had PMF.There was no association between dust exposure and the likelihood of showing panacinar emphysema. However, there was a clear association between the occurrence of centriacinar emphysema and the amount of dust to which a man had been exposed during life, after allowing for the effects of age and smoking. This association could be demonstrated unequivocally only for men whose lungs showed some dust-related fibrosis, and was dependent on the composition of that dust in such a way that emphysema was more likely to occur the greater the coal content of the dust. Once a man had developed PMF, dust composition played a dominant role as far as exposure was concerned, with the coal and ash components having opposite effects. For all men any long-term pathological response will be to the dust which is retained in the lung, and for men with any dust-related fibrosis (presenting as either simple or complicated pneumoconiosis) there was a significant association between the amount of coal in the lungs and the likelihood of showing centriacinar emphysema.An examination of 95 non-smokers showed that the prevalence of centriacinar emphysema in men without PMF was associated with increasing exposure to dust. The prevalence of centriacinar emphysema for men with PMF was mugh higher at all levels of exposure. Only 2 of the 21 non-smokers who had no fibrosis in their lungs showed centriacinar emphysema; this number was too small to allow any comment on the effect of dust in men who neither smoke nor have pneumoconiosis. The relationship between respiratory function and pathological changes in the lung was explored in a group of 257 miners selected by the availability of function measurements within 5 years of death. This group was a sub-set of that examined for emphysema. For the group as a whole there were positive associations between both FEV, and FVC and height, and a significant decrease of FEV, and FVC with increasing age amounting to just over 30mls/year for both variables. Non-smokers had, on average, significantly higher levels of FEV, and FVC than smokers.Both the presence and the amount of emphysema were associated with reductions in FEV, and FVC. In mean terms FEV, and FVC were around 200mls lower for men with emphysema than for those without emphysema other factors being equal. Involvement of one third of the lung in emphysematous change was predicted to reduce FEV, by a further SOOmls and FVC by 300mls.Increasing dust exposure was associated with decreases in FEV, and FVC. This effect was considerably reduced by the inclusion of emphysema in the regression model, reflecting the association between dust and emphysema described earlier. Increase in the mean Reid Index, scoring the extent of bronchial mucus secreting glands, was particularly associated with a decrease in FEV, and in the FEV,/FVC ratio. After adjustment for explanatory variables men with PMF showed, on average, higher values for the measures of respiratory function. This result may be attributed to the different selection procedures that may have operated for men with PMF compared to those without.A small study of the alveolar attachments to small airways showed, in 13 men without emphysema, a significant negative association between both FEV, and FVC and the distance between such attachments; no association could be shown for 12 men who had emphysema.The development of PMF, and its radiographic and pathological appearances, were studied in 173 men. PMF was typed, according to a published classification, both on the radiograph which first showed PMF and on the latest available radiograph. The results indicated that, while at least two thirds of PMF lesions eventually presented as radiographically homogeneous shadows, a proportion of these showed formation by aggregation of smaller lesions at an earlier stage of development. Such aggregation of small opacities or an increase in their density, featured prominently in the descriptions of pre-PMF appearances. No association was demonstrated consistently between the type of PMF observed and either dust ash or quartz in exposure, or lung dust content and composition.Around one fifth of subjects showed PMF in one lung only; this was likely to be on the right side in 80% of cases. When PMF was bilateral it first appeared in the right lung in around 60% of subjects, and arose in both lungs simultaneously in one third.Increase in the extent of PMF in the lungs was examined by tracing lesions � on radiographs at intervals of approximately five years from first development. Areas were recorded using a semi-automatic digitising system. Each subject was then assigned to a “”growth pattern”” group determined by the relationship between area and time. For 44% of subjects increase in lesion size was minor or absent; a similar proportion (although varying from 38% to 53% according to the observer) showed quite rapid increase in PMF size directly related to time. There was no obvious association between radiographic type of PMF and growth pattern. Rapid “”growth”” was associated with multiple lesions in the lung and, in logistic analysis, the amount of quartz retained in the lung was clearly related to rapid growth patterns.While it was found that PMF lesions which appeared, radiographically, to be formed by aggregation of smaller lesions were likely to show pathological evidence of such aggregation, this was not universally so. Lungs showing a microscopic pattern of PMF formation from nodules without other tissue intervening were noted to have a lower dust content with a higher proportion of quartz than was found for other patterns. An examination of the spatial arrangements of nodules in non-PMF lungs from 9 subjects with unilateral PMF showed nodules to be concentrated in the upper regions of the lung as expected, and also possibly to show aggregation within those regions.PMF lesions which increased rapidly in size were likely to involve the hilum of the lung at post-mortem; there was little to indicate a specific lung site for the origin of such lesions. The evidence from lymph node studies suggests that nodes are involved in dust clearance, particularly the preferential removal of quartz, even in subjects who were not occupationally exposed. For such subjects, and for miners without dust-related fibrosis, there was no strong association between the proportion of quartz in lung and lymph nodes. There was evidence, in the small number of coalworkers with considerable amounts of quartz in their lungs that a compositional equilibrium might be achieved between lung and lymph node dust.We conclude that control of dust exposure continues to be an important goal for the containment of both the development of massive fibrosis and the occurrence of emphysema. It is clear also that smoking is a major contributor to respiratory ill-health and should be tackled by appropriate educational measures. Early detection of PMF may be aided by the recognition of opacity clustering on radiographs and monitoring should continue into retirement as increase in lesion size may continue after exposure ceases. In addition, particular vigilance is required in mining environments where quartz exposure is likely to be high as the results suggest that any fibrosis which may develop under such conditions will deserve the title “”progressive””. “”