Pneumoconiosis, lung function and exposure to airborne dust: epidemiological research to compare responses of working coalminers with responses of ex-miners: Part II. Final report on CEC Contract 7246-16/8/002

Present estimates of the relationships between exposure to mixed respirahle duct in British coalmines and risk of developing lung disease are based on studies of working miners, and it has not been clear whether these estimates also apply to all men who have been miners, whether or not they have continued to work in the mining industry.In this report we describe the results of a study in which the dust/disease relationships in men who have been miners but who have left the industry are compared with those found in men who have retrained in it. A sample of 17,738 men who were first examined when working in 24 British collieries in the 1950s have been followed up approximately 22 years later. It has been possible to examine 40% of the original sample. The major reason for non-examination was death in the intervening period (34% of the original sample), the remainder having moved away or being unable or unwilling to attend. Sixty-one per cent of the survivors were examined.On attending, each man answered a questionnaire of respiratory symptoms and smoking habit, performed lung spirometry and had a chest radiograph taken. Where appropriate, detailed occupational histories were obtained by interview. The appearances of chest radiographs were interpreted according to the 11,0 classification of the appearances of pneumoconiosis by a self-trained panel of readers.Detailed records of daily occupation and place of work in each colliery for each man had been kept from the 1950s for the first 10 years of the period. Thereafter these records were continued at 10 collieries but discontinued at the other 14. Occupational histories for the period before the research, and in the 14 collieries for the period after the occupational recording system ceased were obtained by interview.Detailed measurements of the respirable dust exposure of the various occupations in the collieries were made throughout the first 10 years of the research, and for the remaining years in the 10 collieries, and personal cumulative respirable dust exposures were calculated for each man from the occupational records and dust measurements. Dust concentrations occurring before the period of the research were estimated to be the same as the mean values measured for each of six broad categories of occupation in each colliery during the first 10 years of measurement. Dust concentrations in the 14 collieries in which the research measurements ceased after the first 10 years were derived for the subsequent period from routine sampling, and used to calculate exposures during this period.Seven thousand and seventy-three men were included in the analysis of chest radiographic appearances, 2,202 still working in the coal industry, and 4,871 men who had left. Prevalences of simple pneumoconiosis at follow-up were generally higher among men who had left than in those who stayed: for instance, prevalence of simple pneumoconiosis category 2/1 or greater was higher in men under the age of 65 who had left the industry than in men who stayed by a factor of nearly 1.8. These differences were partly accounted for by higher dust exposures among those who left, and the quantitative relationship between dust exposure and simple pneumoconiosis was not in general shown to be different for men who left and men who stayed. We conclude from this that previously published estimates of risk of pneumoconiosis in relation to dust exposure are appropriate for all men who have worked in the research collieries, whether they have left the industry or stayed in it. There were large differences between collieries in the dust/disease relationships, and these require further investigation.The attack rate of progressive massive fibrosis after dust exposure ceased was assessed in a subgroup of the men who had left the coal industry. The attack rates were 82 per 1,000 over an 11-year period and 118 per 1,000 over a 17-year period. Attacks were related to age and to previous category of simple pneumoconiosis: for instance, the attack rate of progressive massive fibrosis over an 11-year period after dust exposure ceased in men with categories O/-, 0/0 and 0/1 small rounded opacities at the time of leaving the industry was 37 per 1,000, while that for men with categories 1/0, 1/1 and 1/2 was 168 per 1,000 and that for men with categories 2/1, 2/2 and 2/3 was 205 per 1,000. In the whole follow-up population, the attack rates of progressive massive fibrosis were also found to be much higher in men who had left the industry than those who remained within it. For instance, the overall attack rates of progressive massive fibrosis over 22 years in men of all ages who had no simple pneumoconiosis at first survey were 11 per 1,000 in men who remained in the industry and 49 per 1,000 in men who left, and the rates for men with category 2 simple pneumoconiosis were 200 per 1,000 for men who stayed in the industry and 346 per 1,000 for men who left. These findings indicate much higher unadjusted attack rates than those previously found over a five-year period in working miners, probably because of the longer .period of observation and the inclusion of men in this study who had left the industry. Methodological differences in the selection of men and in reading the chest radiographs may also have contributed to these differences to a small extent.There was little evidence of progression or regression of simple pneumoconiosis after dust exposure ceased. These findings suggest that progression of simple pneumoconiosis is related principally to further dust exposure, while the development of progressive massive fibrosis is related to changes in the biological response to dust already present in the lungs.Relationships between lung function and dust exposure were examined in men who were working in the industry at the time of the first medical survey in the 1950s, and also the third survey 10 years later. These men were therefore to this extent asurvivor population within the industry, though many of them left the industry subsequently. Levels of lung function at third survey and at follow-up were inversely related to cumulative dust exposure after allowing for other factors, and the longitudinalloss of lung function over the 11-year period between third and follow-up surveys was also related to cumulative exposure to respirable dust. Men under 65 who left the industry tended to have lower levels of lung function than men who stayed after allowing for age, height, weight, smoking and differences between geographical regions. They also had higher dust exposures on average, but this alone did not account for their lower lung function. There was no evidence that the men who left had shown a more severe response in proportion to their dust exposure than the men who stayed in the industry.The patterns of the relationships of lung function with dust exposure suggested that the dust caused a mixed type of lung functional abnormality, restrictive predominating over obstructive features. By contrast smoking was related to a classical obstructive pattern.The magnitude of the loss of forced vital capacity related to the mean cumulative dust exposure for men who stayed was estimated to be 146 ml on average for the cross-sectional analysis at follow-up, or an excess loss of 43 ml on average over the 11-year period for the longitudinal analysis related to mean cumulative dust exposure up to the start of the period, while the relationship for forced expired volume in one second with smoking at the mean age for men who stayed was estimated to be – 235 ml, and the excess loss over 11 years was 112 ml.We conclude from this that exposure to mixed respirable coalmine dust causes a loss of lung function of different type from losses attributable to smoking, and unrelated to the presence of pneumoconiosis. “”