Pleural thickening and gas transfer in asbestosis.

Anomalies in the ratio of transfer factor to effective alveolar volume as an indicator of pulmonary gas exchange in cases of asbestosis may be related to diffuse pleural thickening. To examine the effect of pleural disease on gas transfer the plain chest radiographs of patients with asbestosis were assessed by two observers for profusion of parenchymal opacities and extent of pleural disease and the results were related to lung function. In 30 cases of category 1 profusion of parenchymal abnormality (according to the ILO international classification of radiographs for pneumoconiosis) transfer factor was independent of the degree of pleural thickening. The ratio of transfer factor to effective alveolar volume correlated directly with the degree of pleural thickening as alveolar volume fell with increasing severity of pleural disease. The results indicate that correcting transfer factor for alveolar volume does not provide an accurate reflection of severity of diffuse parenchymal fibrosis in patients with asbestosis and even minor pleural disease.