RELATION OF SPIROMETRIC FUNCTION TO RADIOGRAPHIC INTERSTITIAL FIBROSIS IN 2 LARGE WORKFORCES EXPOSED TO ASBESTOS - AN EVALUATION OF THE ILOPROFUSION SCORE

Objectives-To analyse quantitatively the relations of spirometric lung function (forced vital capacity (FVC)) to radiographic interstitial p ulmonary fibrosis (assessed by the International Labour Organisation ( ILO) profusion score of small irregular opacities) in two large workfo rces exposed to different intensities of asbestos. These analyses cons ider the question whether a similar profusion score in differently exp osed workers is associated with a similar effect on lung function. Met hods-Surveys of two workforces, insulators (n = 2611) and sheet metal workers (n = 1245), by the same investigators allowed comparison of th e effects of the two levels of exposure to asbestos. The two groups we re of similar age and had similar percentages of non-smokers and smoke rs. All radiographs were read by the same expert reader. Results-Consi stent with their less continuous and less intense exposure to asbestos , metal workers had: (a) far less frequent radiographic asbestosis (pr ofusion score greater than or equal to 1/0, 17.5% v 59.6% for insulato rs); (b) less severe radiographic asbestosis (only 1.1% had scores gre ater than or equal to 2/1 v 13.3% of insulators); (c) a similar slope to that seen in insulators for the relation between FVC and profusion score when pleural thickening was absent; (d) less frequent pleural fi brosis (36% v 75%); and (e) less frequent restrictive impairment (23% v 33%). In both insulators and metal workers, lung function was below normal even when lung fields were normal, FVC fell. with increasing pr ofusion, it was lower in smokers and in those with pleural thickening at comparable profusion scores, and there was no difference in FVC bet ween scores 0/1 and 1/0. Conclusion-The decrease in FVC with increasin g profusion score in both workforces as well as the similar slopes for the relation between FVC and profusion score and the similar FVC at s imilar scores in the absence of pleural thickening confirm the ILO pro fusion score as an acceptable assessment of pulmonary fibrosis.