Small Airways Changes in Workers Exposed to Asbestos

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Abstract
Although restriction is considered the classic pulmonary function profile of asbestosis, studies suggest that obstruction of the peripheral airways not revealed by standard spirometry is equally frequent and indicative of peribronchiolar fibrosis. Flows and volumes from maximal expiratory flow volume (MEFV) curves, closing volume data and the phase 3 slope of the alveolar plateau for 610 litigants, 575 men and 35 women, exposed to asbestos for varying periods in a single workplace in northern New Jersey [USA] were recorded. Smokers (260) included current smokers and subjects who had stopped within the previous 10 yr; nonsmokers (350) had never smoked or had given up for > 10 yr. Analyses were made for both groups according to years worked. Compared to predicted, smokers and nonsmokers had significantly higher closing capacities (P < 0.01) and .DELTA.N2% [change in N2 concentration per liter] (P < 0.001) means, and lower forced vital capacity (FVC), forced expiratory volume for the 1st s (FEV1.0), maximal expiratory flow rate (MEFR) and peak expiratory flow rate (PEFR) functions (P < 0.05); the flow rate after 75% of the FVC had been exhaled (FEF75%) values were significantly reduced (P < 0.01) only for workers exposed for > 30 yr. The change from predicted was significantly more rapid for smokers, compared with nonsmokers, for FVC, FEV1.0, PEFR, MEFR and FEF75% means, while the increase in closing capacity (CC) was 2-fold as rapid for nonsmokers and the 2 groups did not differ in their mean rates of rise for .DELTA.N2%. CC and the slope of the alveolar plateau probably were the measures best able to discriminate between the data for smoking and nonsmoking asbestos workers, and their lung function prediction means. The behavior of these latter 2 indices suggested that small airways obstruction was characteristic of asbestos exposure; the data for the nonsmokers implied that these changes cannot be explained on the basis of the smoking history.

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