| Summary: | The mechanical properties of the lungs and of the small airways of 36 coalminers were investigated. Neither the miners nor the 10 control subjects had ever smoked, and all were free from symptoms of chronic bronchitis. Most of the miners had radiographic evidence of coal workers simple pneumoconiosis. Standard spirometry was performed and the transfer factor for the lung, the closing volume and the maximum expiratory flow response to breathing a helium/oxygen gas mixture were measured. The relationships between lung volume and maximum expiratory flow, static elastic recoil pressure and total airways conductance were determined. Maximum expiratory flow/static elastic recoil, total airways conductance/static elastic recoil and total airways conductance/maximum expiratory flow relationships, were constructed in order to provide information about the conductance of small airways, the collapsibility of the flow limiting segment and the radial distensibility of the tracheo-bronchial tree. The assessment of small airway function was designed to differentiate between intrinsic narrowing and loss of lung elastic recoil, since either or both of these factors may be associated with the characteristic pathophysiological lesion of coal workers simple pneumoconiosis. Extrinsic loss of elastic recoil was found to be the predominant factor giving rise to lower ventilatory capacity and maximum expiratory flow in the miners when compared with controls, and with age and height standardised normal values. An increased radiographic. category of pneumoconiosis was most strongly related to a higher volume of isoflow, and the associated pattern of change in pulmonary function suggested that this was due mainly to loss of elastic recoil. This was most marked in the miners with p-type opacities who also tended to have a slightly lower pulmonary gas transfer capability than miners with q-opacities. Longer dust exposures tended to be associated with stiffer lung tissue and narrowing of the small airways. These observations suggest that in the absence of smoking and chronic bronchitis an early reaction to coal mine dust is loss of elastic recoil leading to focal or centri-lobular emphysema. With continued exposure, fibrosis may develop or the worst affected miners leave the mining industry.
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