Cross-sectional studies of respiratory disease in British coalminers. Final report on CEC Contract 7248-31/009

The influence of exposure to respirable coalmine dust on syndromes of respiratory disease other than pneumoconiosis has been examined in cross-sectional studies of coalminers in three collieries in Britain (S. Wales, Yorkshire and Tyne and Wear). Nearby telecommunications workers and postmen were included also to permit comparisons with non-coalmining populations. The sample was selected from those who had worked in their industries between 1970 (when new coalmine dust control regulations were introduced in the coalmining industry) and the date of survey (between 1981 and 1986). Data collected at medical survey included questionnaires of respiratory symptoms, smoking habit and detailed occupational histories, measurement of lung function by forced expiratory flow volume loops and single breath gas transfer, and full size chest radiographs. Detailed records of miners’ lifetime exposure to respirable dust, recorded in detail as part of British Coal’s long term Pneumoconiosis Field Research, were updated by reference to the occupational histories recorded at survey.Response rates among current workers were on average 83%, 74% and 61% respectively for miners, telecommunications workers and postmen; rates among men who had left their industry were 37%, 20% and 28% respectively, in spite of considerable efforts to encourage response. Frequencies of respiratory symptoms were greater in current miners than current telecommunications workers or postmen in each area, and a similar pattern was observed in those who had left. Evidence from sickness absence records suggested that the frequencies of respiratory disease in the non-mining subjects who attended the surveys, could be underestimates of the true frequencies.The analysis concentrated on lung function; on the one hand identifying different types of functional defect, and relating them to possible causative factors; and, on the other hand, using FEV1 as a convenient summary of lung function, expressing the risks of specified lung function losses in relation to exposure to dust.A principal components analysis, based on seven lung function variables from the flow-volume curve and single breath gas transfer manoeuvre described the way these functional measurements varied in relation to each other, and enabled the recognition and quantification of three qualities of lung function in each subject; a general measure of lung size; a measure of the obstructive or restrictive quality; and a measure of gas transfer ability. In a small subset of men comparisons of total lung capacity, measured from the chest radiographs, with principal components were consistent with this interpretation of the components. The principal component analysis, when applied separately to the three coalmining and five non-coalmining populations, gave very similar values for the coefficients of the components, indicating that the analysis is applicable generally. Scores for each of these principal components could be calculated for each man, describing his lung function. Comparison of these scores with possible causative factors confirmed that age was associated with defects of all three components; height was associated with large lungs, high gas transfer and airflow obstruction; and weight (after allowing for height and age) was associated with large lungs, less airflow obstruction, and high gas transfer ability. Smoking was associated with all three components.After allowing for these factors, lifetime exposure to respirable dust (in S. Wales miners) was associated with smaller lungs, but the lack of a relationship with the second principal component indicated that the defect was intermediate between obviously obstructive and restrictive types. A relationship between dust exposure and lung gas transfer ability was not demonstrated.The presence of the large opacities of progressive massive fibrosis was associated with defects characterised by all three principal component scores (small lungs, airflow obstruction and impaired gas transfer), and this would be consistent both with direct destruction of lung by the fibrosis, and also the presence of associated emphysema.An adverse influence on lung function of lifetime exposure to respirable dust was demonstrated in the S. Wales miners but could not be confirmed in the miners in the other two collieries. This was partly because of confounding of the effects of age and exposure. Evidence is presented that these negative results might be the result of a combination of factors; a narrow range of exposures and marginally small study populations for the range of exposures.Inverse relations between exposure and lung function in a different population of men in these three collieries have been confirmed by reexamination of data from earlier studies.Deficits of FEV, from predicted values of probable clinical relevance were chosen after comparisons with symptoms of breathlessness reported on the MRC questionniare. The average deficit of FEV, of those admitting to the first level of breathlessness was -422 ml in S. Wales miners, -343 ml in Yorkshire and -215 ml in Tyne and Wear. The average deficits of those admitting to the third (most severe) level of breathlessness were -942 ml, -812 ml and -800 ml respectively for these areas. Men whose FEV, was less by these amounts or greater than that predicted on the basis of their age, height and weight, corresponding to breathlessness levels 1, 2 and 3, were designated cases, groups 1, 2 and 3. The influence of smoking and dust exposure on risk of being a case was examined by logistic regression analysis. The risks of being a case in any of the three case groups in each area were related to smoking habit, and was greater in men who left mining than those who stayed. After allowing for these factors, risks for all three case groups were related to lifetime exposure to respirable dust in the S. Wales miners, though this relationship was not demonstrable in miners in the other two collieries. The estimated risks of having an FEV, deficit of -422 ml in the S. Wales colliery in non-smokers aged 55, for example, was 28% at zero dust exposure rising to 57% at 400 ghm-3 exposure (a high exposure for this population). In smokers the corresponding risks were 36% and 66% respectively. The estimated risks of having an FEV, deficit of -942 ml at these dust exposures were respectively 4% and 21% for non-smokers and 12% and 46% for smokersThis way of describing the risks of functional loss will be helpful in consideration of dust standards, though some comparisons between the results from this colliery and existing data from others in the Pneumoconiosis Field Research would be desirable to place these results in context. “”