4-YEAR FOLLOW-UP-STUDY OF LUNG-MECHANICS IN SMOKERS

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Abstract
A prospective study of pulmonary function was performed in 21 smokers, 9 ex-smokers and 12 non-smokers. The smokers and ex-smokers were preselected, because they were participants in a smoking cessation clinic. An average interval of 4 yr separated the 1st and 2nd (follow-up) studies. The smoking group showed a significant decrease in maximal expiratory flow measured at low lung volume, loss of elastic recoil, increase in lung compliance, increase in total lung capacity; increase in the ratio of residual volume to total lung capacity, and an increase in the ratio of functional residual capacity to lung capacity. The ex-smokers showed changes similar to the smokers, but of lesser magnitude. The nonsmoking group demonstrated few changes in function during the study interval. Commonly measured parameters of function, including the ratio of the forced expiratory volume in 1 s to the forced vital capacity and the maximal expiratory flow after exhalation of 50% of the vital capacity, did not change significantly in any group. Sensitive tests of lung function were abnormal in a high percentage of the combined group of smokers and ex-smokers when measured at the time of the 2nd study; only a small number of abnormalities in these parameters were noted in the nonsmoking group. There was a deterioration of lung function in smokers far in excess of that predicted by age. These changes suggest the development of emphysema and were predictable for the group as a whole by a high prevalence of abnormality of dynamic compliance, closing volume, maximal mid-expiratory flow and residual volume at the time of the initial study.