Pneumoconiosis, lung function and exposure to airborne dust: epidemiological research to compare responses of working coalminers with responses of ex-miners. Final report on CEC Contract 6244-00/8/106

Aims: Between 1953 and 1974 the Pneumoconiosis Field Research (PFR) of the National Coal Board, and latterly of the Institute of Occupational Medicine conducted a long term epidemiological study of the respiratory health of British coalminers at selected collieries, and compared changes in respiratory symptoms, chest radiographic appearances and lung function test with calculated individual cumulative dust exposures based on environmental monitoring in these pits. Estimates, of the probability of developing pneumoconiosis during a working lifetime in various dust concentrations were calculated, on which current dust standards are based.This research included only men remaining at work in the coal industry, and it was not known whether the men who left the industry were in similar health to those who remained. The present study was designed to compare the respiratory health of miners who left the industry with that of those who remained, and to study progression or regression of disease after dust exposure ceased.Methods: Three thousand eight hundred and seventy coalminers and ex-miners, a sample of men originally examined by the Pneumoconiosis Field Research study between 1953 and 1958, have been re-examined between 1974 and 1977 by a questionnaire of respiratory symptoms, chest radiographs and measurements of lung function. Detailed occupational histories were recorded and dust levels were measured prospectively. The sample was chosen from miners examined between 1953 and 1958, working at 24 selected collieries. The sample included all men whose chest radiograph was thought at that time to show pneumoconiosis (small rounded opacities category 1 or greater), together with approximately half of the remainder, stratified by age and colliery. This report covers the first phase of the study, in which men at 12 of the 24 collieries were studied. The selected population numbered 8,727 men.Results Population Studied: Tracing procedures enabled the examination of 3,870 men (40% of whom 1,755 (20% of the original cohort) were still working in the coal industry at the time of follow-up, 2,094 (24%) had left the industry, and 21 (0.2%) were of unknown status. Of those not examined, 2,481 (28% of the original cohort) were known to have died, and 2,376 (27%) were unable or unwilling to attend or were not traced. Those who died are the subject of a separate, mortality, study.Comparison of the 3,870 men examined during the present survey with the alive non-examined men indicated that there was a preponderance of men in the younger age groups in the non-examined men, and a preponderance of men between 30 and 50 in the examined group.There was a slight consistent excess of men with simple pneumoconiosisat the time of the earlier survey among the examined group, not explained by the age differences.Comparison of the 2,094 ex-miners who were examined with the 1,755examined miners still working in the collieries showed an excess of older men among the ex-miners, and an excess of simple pneumoconiosis and progressive massive fibrosis (IMF) (at the time of the first survey) among the ex-miners, not explained by age alone.Respiratory Symptoms and Lung Function Respiratory symptoms and lung function measurements were compared in 2,414 men (1,419 working at the collieries and 995 ex-miners at the time of the present survey), who had been included in an intermediate medical survey between 1962 and 1968. Among the ex-miners, the older age groups were over-represented, and younger age group under-represented. Nevertheless, within each age range, men who subsequently left the coal industry had less dust exposure than those who stayed; more of them smoked; more had chronic cough and sputum, and more complained of breathlessness.Forced expired volume in one second (FEV..) was adversely affected by smoking and by dust exposure.Ex-miners who smoked, age for age, had lower mean levels of FEV.. than smokers who stayed in the industry. The regression of FEV.. with dust exposure was the same in these groups, suggesting that the lower mean levels of FEV.. in smoking ex-miners was not related to a greater response to dust.These preliminary results suggest that miners who have left the industry are less fit than those who remain. They have more pneumoconiosis in spite of having lower dust exposures, lower mean levels of FEV.. (among smokers), have more bronchitis, more of them smoke, and more complain of breathlessness.Changes in Chest Radiographs: Changes in the appearances of the chest radiographs were assessed in a sub-group of the study population whose dust exposure had ceased for periods of 8 to 22 years, and for whom chest radiographs had been obtained close to the date of leaving the coal industry, as well as those taken in the present survey. Seven hundred and ninety-five such pairs of radiographs were read independently in random order by three radiologists. A total of 55 cases (6.SPO of apparent regression of simple pneumoconiosis by one point on the ILO U/C 12-point scale was recorded by at least one radiologist, 15 cases (1.S00 by two radiologists and 8 (1%) by all three radiologists. Twenty-three cases (2.sp) were identified by two or more readers, and in 6 of these the regression was agreed by all three radiologists to be by two steps or more in the 12-point scale.Progression of simple pneumoconiosis was recorded in 53 cases (6.7%) by at least one radiologist, 37 (4.6% by two or more radiologists and 11 (1.4%) by all three. Forty-eight cases (6% were identified by two or more readers, and in 8 of these progression by two steps or more was agreed by all three readers.Comparison of these figures with the results of readings by the same radiologists of paired films for 2,000 miners still working in the collieries indicated that while progression of simple pneumoconiosis was commoner among men remaining at work in the collieries, regression of simple pneumoconiosis was as common among men remaining at work in the collieries as it was in those who had left the coal industry, suggesting that the apparent regression of simple pneumoconiosis in these men was related to factors other than the cessation of dust exposure.The occurrence of new cases of progressive massive fibrosis (HOT) was studied after exclusion of cases showing HIP at the earlier survey. Of the remaining 827 pairs of chest radiographs, 28 new cases of large opacities interpreted as PMF were read by at least one radiologist, comprising 9 cases read by one radiologist alone, 8 by only two radiologists and 11 by all three radiologists. The mean attack rate over a 20-22 year period after cessation of dust exposure was 34 per 1,000.Thirteen radiographs taken at the earlier survey were thought by at least one radiologist to show MF,and in none of these cases did the lesion disappear.