In a longitudinal study of a sample of firemen in London 1006 firemen were interviewed and examined in 1976 and 895 were seen a second time 12 months later. On each occasion a Medical Research Council respiratory questionnaire was administered and forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) were measured. The average levels of FEV1, FVC, and FEV1/FVC in both years compared favourably with conventional predicted values. Separate multiple regression analysis for the two years indicated that the FEV1 and FVC fell more rapidly in those aged over 40, and that cigarette smoking had a strong harmful effect on these measures of function. Only among men with over 20 years' service was there possibly any evidence (not statistically significant) of an effect from duration of employment. The comparatively large fall in FEV1 and FVC from 1976 to 1977 was due mainly to instrumental variation. The prevalence of respiratory symptoms was higher in smokers than non-smokers and increased with the number of cigarettes smoked.
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