Relation between content and composition of coalworkers' lungs and radiological appearances.

31-44. The relation between radiological category of simple pneumoconiosis and dust content of the lung has been studied on a mixed group of 221 miners, of whom 76 had progressive massive fibrosis radiologically. The average radiological scores based on 11 independent readings for the films showing simple pneumoconiosis only were related, by multiple regression, to the coal, mineral, quartz, and iron contents of the lungs. Three subgroups were found which showed differing relations. Films of poor technique tended to be read in the middle categories whatever the content of the lungs. The lungs of Scottish miners all contained soot, from working in naked light pits, and their radiological scores were much higher than expected from the lung dust contents. The few films showing nodular sized small opacities were also over-read, suggesting that nodularity may be some response to dust other than simple accumulation. There were 98 subjects in the resulting homogeneous group of cases with simple pneumoconiosis only. On a revised scale to correct for slight non-linearity, the regression coefficients of radiological score on the total mineral and coal contents of the lung were in the ratio of 3·8 to 1. The iron content did not add much to this regression relation even though by itself it correlated well with the amount of simple pneumoconiosis. Probably most of the variation of radiological appearance with iron reflects variation with coal and mineral. The mineral and quartz contents were highly correlated (r = 0·96), but relations including quartz were not as close fitting as those including mineral. There was a small, but significant, residual relation of radiological score to years in coalmining. The background categories of simple pneumoconiosis in the 76 radiographs showing some evidence of progressive massive fibrosis were generally read higher than expected from the relation to dust content derived from the simple pneumoconiosis cases only. This was most true for those showing most evidence of progressive massive fibrosis.