To investigate the high death rates for bronchitis in South Wales miners a survey of respiratory symptoms and ventilatory capacity in 90% of a random sample of 600 men between the ages of 35 and 64 and 200 women between 55 and 64 living in the Rhondda Fach was carried out. The sample of men was stratified by age and occupation, 100 miners and ex-miners, and 100 non-miners being studied in each decade.
The higher prevalence of symptoms and lower mean indirect maximum breathing capacity (I.M.B.C.) of the miners and ex-miners, observed previously, was confirmed and within the mining group there was little relation of symptoms to radiological category of pneumoconiosis. Miners and ex-miners with progressive massive fibrosis had a lower mean I.M.B.C. than the rest at all ages.
Analysis of symptoms and I.M.B.C. by length of time spent working on the coal-getting shift in both miners and ex-miners did not suggest that the total dust dosage to which a man had been exposed during his working life was closely related to chronic respiratory disease. A lower prevalence of symptoms and a higher mean indirect M.B.C. was found in those who had worked for under one year on the coal-getting shift. Above one year no clear pattern of symptom prevalence was discerned although there was a slight downward trend in the mean indirect M.B.C. with increased time spent working on the coal-getting shift. When working miners alone were considered the reduction in ventilatory function with increasing duration of work was slightly greater.
Dust exposure alone seemed unlikely to account for all the excess respiratory disease in miners compared with the rest of the community and other possible explanations are discussed.
The women recorded a lower prevalence of symptoms than the men who had never worked in mining. This prevalence was, however, higher than that previously found in rural areas in Wales and Scotland. The mean indirect M.B.C. recorded for the women in this survey was also lower than that observed in Scots women.
Analysis of the findings in the women according to the occupation of their husbands showed that miners' wives recorded a higher prevalence of symptoms and lower mean indirect M.B.C. than non-miners' wives, suggesting the importance of social rather than occupational factors in miners.
Smoking was associated with an increased prevalence of symptoms and lower indirect M.B.C. in the men but not in the women. Differnces in smoking habits could not, however, account for the differences between miners and non-miners, as these remained after standardization for smoking.