Pulmonary function in coal workers with Caplan's syndrome and non-rheumatoid complicated pneumosoniosis.

This retrospective study compares the pulmonary function of 24 coal workers with Caplan's syndrome with that of 36 subjects with non-rheumatoid progressive massive fibrosis (PMF). Allowing for differences in radiographical category, age, years worked underground, and smoking, obstruction to air flow as reflected in the one-second forced expiratory volume, the vital capacity, and the ratio of residual volume to total lung capacity, was significantly less in subjects with Caplan's syndrome. No significant differences in transfer factor were found. These findings may be explained by the different pathological features of the two entities. Selection bias does not appear to be responsible for the differences observed between the groups, but studies designed to eliminate this would be desirable.