The functional implications of chronic bronchitis in populations exposed to dust

Studies of workers in the UK wool textile industry have shown that exposure to airborne dust is associated with symptoms of chronic bronchitis and breathlessness, though no consistent evidence has been found of an association between exposure to wool dust and chronic deficits of lung function. In other populations chronic bronchitis and breathlessness are associated with reduced lung function on average, because of their associations with smoking, and it is not known whether the symptoms associated with wool dust follow this general pattern. Furthermore studies of underground coalminers working in the industry in the 1950s, and followed up 22 years later suggest that the presence of chronic bronchitis may identify a group of people more susceptible to the effects of dust.The present study therefore investigated whether symptoms of chronic bronchitis or breathlessness in wool textile workers are associated with poor lung function and whether any association differs according to smoking habit or exposure to different airborne concentrations of dust. These questions are relevant to the general problem of occupational bronchitis and the possible influence of low toxicity dusts if inhaled in sufficient concentrations. The study reported here therefore also examines the relationships between respiratory symptoms and lung function deficits in other dust-exposed populations.The study is based on published data from six study populations which had previously been surveyed (relatively recently) by the IOM. These were 634 workers from the UK wool textile industry, 1224 current male workers in nine opencast coalmines exposed to low concentrations of quartz in mixed dust, 1110 coalminers in a Scottish colliery who attended a medical survey in 1970 and were exposed to relatively low concentrations of mixed dust with low quartz content, 549 miners (a subset of the 1110) from the same Scottish colliery who attended a follow-up survey in 1991 and had been exposed to unusually high concentrations of quartz in mixed coalmine dust, 1671 coalminers from collieries in England and Wales exposed to a range of concentrations of coalmine dust and 818 workers exposed to polyvinylchloride (PVC) dust. The concentrations of dust to which the workers were exposed varied widely between the study groups.Preliminary analyses of each of the study groups confirmed earlier results, that in coalminers in the South Wales colliery, respiratory symptoms and lung function were independently related to dust exposure. In wool textile workers and the miners in the other collieries in England, symptoms but not lung function were related to exposure. In PVC workers lung function but not symptoms were related to exposure, and in opencast workers and miners in the Scottish colliery, neither symptoms nor lung function were demonstrably related to exposure.In all six study groups, individuals with symptoms of chronic bronchitis or breathlessness had worse lung function on average, compared to standard predicted values and in comparisons internal to the study group, than individuals without such symptoms. The magnitude of the lung function deficits associated with the presence of symptoms varied between study groups, but there was no evidence that the larger deficits occurred among the study groups exposed, on average, to higher levels of dust, or to more toxic dusts (such as those containing quartz). The reduction of FEV] and FVC associated with symptoms did not vary significantly between smokers (current and ex), and non-smokers. In contrast, for three of the study groups, deficits of FEV,/FVC ratio appeared to be associated primarily with smoking-induced symptoms, suggesting that the magnitude of symptoms related functional deficits is, on average, independent of the cause.The influence of dust-related symptoms on lung function was examined by use of an interaction term in the statistical model, which represented the influence of dust exposure on lung function in those with symptoms compared to those without. In populations with demonstrable effects of exposure on symptoms, this interaction can be used to investigate whether dust-related symptoms (by definition more frequent in the more heavily dust-exposed members of the population) are associated with more or less functional deficit than non-dust related symptoms.In wood and textile workers internally consistent (but mostly not statistically significant) adverse effects of dust exposure on lung function in those with symptoms provide no positive evidence that dust-related symptoms have no influence on FEVj and FVC; indeed an adverse effect is tentatively suggested. We conclude that, while a consistent effect on lung function of exposure to wool process dust has not been demonstrated, the present evidence suggests that it would be unreliable to conclude that the respiratory symptoms associated with wool dust are definitely not associated with functional deficits.In none of the other study populations could the magnitude of the symptoms related reductions of lung function be shown to be consistently related to the degree of exposure to dust.The negative result in coalminers exposed to mixed dust is inconsistent with earlier work, possibly because of improvements in dust concentrations and study of a smaller population than previously. In any case, the separate effects of coalmine dust on symptoms and lung function are well established.In miners exposed to quartz, and PVC workers, the results are consistent with the lack of demonstrable effects of exposure on symptoms (for PVC), or on lung function (for quartz).