SMOKING AND LUNG-FUNCTION

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Abstract
In a cross-sectional survey of 3 separate communities, white residents 7 yr of age and older were studied to determine the relation between cigarette smoking and lung function. Identifed were 2817 nonsmokers, 664 ex-smokers and 1209 smokers who were classified as light smokers (1-20 cigarettes/day), and heavy smokers (> 20 cigarettes/day). Residual lung function (observed-predicted) was examined in these groups for forced expiratory volume in 1 sec (rFEV1), and for maximal expiratory flow rates at 50% and 25% of vital capacity (r.ovrhdot.Vmax50% and r.ovrhdot.Vmax25%). Mean residuals by sex, age and smoking category were compared and revealed an increasing progression of lung function loss with advancing age in males and females in all smoking categories. Age-related trends were primarily due to the amount smoked by persons in each group. Age of onset of these abnormalities was as early as 15-24 yr. Abnormalities were greater in smokers than ex-smokers, even when the amount smoked was taken into account. This suggested an improvement in lung function after cessation of smoking. Men and women experienced the same relative degree of gain. Contribution of various smoking habits to lung function loss was assessed, using regression analyses, and accounted for no more than 15% of variation of residual lung function. Combinations of variables explained only slightly more variation than a single variable. The 2 most important variables were duration of smoking and pack-years. Inhalation and use of filters were not significant. Although amount of variation explained by smoking variables after accounting for age, height, weight and sex was small, this variation accounted for almost all decrease, over age, in residual lung function for smokers and ex-smokers.