[Relationship between smoking habits and lung function changes with conventional spirometry].

Maximal expiratory flow and volume parameters derived from simultaneous maximal expiratory flow-volume and volume-time curves obtained by the forced vital capacity maneuver were studied in 311 healthy normal Chinese men, consisting of 180 nonsmokers and 131 smokers of 20 to 78 years of age. Six maximal expiratory parameters--FVC, FEV1, FEV1/FVC, PEFR, FEF25-75% and Vmax75, both unadjusted and adjusted for age and body height, were compared between nonsmokers and smokers to study the effects of smoking on ventilatory function and to detect early abnormal changes. In current smokers and ex-smokers, the FEV1/FVC was significantly lower than that of nonsmokers. However, no such differences were noted for FVC and FEV1. Among FVC, FEV1 and FEV1/FVC, a low FEV1/FVC appeared to be the earliest discriminative index in normal asymptomatic smokers. With increasing quantity and duration of smoking, a higher incidence of abnormally low FEV1 and FVC compared to those who smoked a lesser amount or for a shorter period of time, were observed in sequence. Current smokers over the first 5 pack-yrs of smoking did not show any abnormality in FVC, FEV1 and FEV1/FVC. It is concluded that cigarette smoking is associated with a decrease in pulmonary function although the effects take some time to develop and are not immediately apparent after beginning the smoking habit. There is an irreversible decrease in FEV1/FVC with cumulative cigarette consumption, but smoking cessation will prevent further deterioration in FEV1 and FVC.