Abstract

To assess changes in the mechanical properties of the lungs in pneumoconiosis, the “elastance” (coefficient of elastic resistance, the reciprocal of compliance) of the lung and resistance of the airways were measured by the method of Mead and Whittenberger (1953) in 97 coal-miners and 17 men who had never worked underground. Ages ranged from 24 to 57. The work done on the lung was measured in 66 of these subjects, and the maximum voluntary ventilation (M.V.V.) was measured in all. The subjects were obtained by random selection from hospital out-patients and by random selection from a radiological survey of over 5,000 coal-miners. The M.V.V. was reduced in coal-miners with progressive massive fibrosis (P.M.F.), and in those without pneumoconiosis, but was not significantly reduced in simple pneumoconiosis. Elastance of the lung was unaltered in young miners but was slightly, and significantly, increased in all elderly faceworkers whatever the radiological category. This change appeared to be due to long years of work underground rather than to the radiological abnormality of pneumoconiosis. This slight change in the pulmonary elastance cannot be the cause of the reduction in M.V.V., since the two are unrelated. Inspiratory resistance was normal in all coal-miners, suggesting that pneumoconiosis is not associated with any fixed distortion of the airways. The non-elastic work of breathing, however, was frequently above normal and this suggests that bronchial obstruction develops rather commonly during expiration. This change appears to be the cause of reduction of M.V.V. in the majority of cases, as a negative correlation between M.V.V. and non-elastic work was established. Mean non-elastic work was not, however, unduly high in those radiological groups in which a significant reduction of M.V.V. was recorded. It is suggested that this discrepancy may be due to excessive frictional resistance in the chest wall of miners with P.M.F. and those with no radiological abnormality. The findings are consistent with the hypothesis that emphysema is abnormally common in elderly coal-miners, and that it, rather than pneumoconiosis, is the cause of their reduced ventilatory ability.