The PPFEV, and PPFVC were lower in smokers compared with non-smokers across all fibre groups, and the regression analysis ranked smoking pack-years as the strongest predictor variable for both PPFEV, and PPFVC. The exact relation between smoking and lung function abnormalities in the presence of exposure to cotton dust remains controversial. Early epidemiological studies tended not to include information on smoking habit. Merchant et al documented decrement in lung function in smokers compared with non-smokers, although men who smoked and had occupations exposed lightly to dust had
significantly better lung function than those in heavily exposed occupations.'2 Their subsequent work indicated that smoking and dust exposure may act independently to influence loss in lung volume.20 Imbus concluded that smoking was far more important than dust exposure in causing loss of FEV,.2' When dust exposure was considered in this study, division of operatives into high and low exposures
seemed to suggest an effect of current exposure on measured lung function. The regression analysis, however, did not identify a relation between current or past dust measurements and lung function. This is contrary to the findings of Jones et al who studied lung function variables in cotton operatives and man made fibre control workers.22 Mill of work, current dust concentrations, and occupation had no bearing on impairment of FEV, and FVC although an association was found between increased duration of exposure to cotton dust and impaired FVC.