LUNG-FUNCTION CHANGES IN SMOKERS WITH NORMAL CONVENTIONAL SPIROMETRY

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Abstract
The comparative ability to detect early abnormalities in smokers by commonly used lung function tests was studied. Healthy male nonsmokers (65) served as a reference group and provided standards for 1 s forced expiratory volume, vital capacity, end-tidal spirometry, spirometric forced mid- and end-expiratory flows, single-breath diffusing capacity, static lung volumes (He method), and single-breath N2 closing volume measurements. In the present series of 80 male smokers, the measurements of forced mid-expiratory flow and forced end-expiratory flow did not improve the ability of the more conventional indices, 1 s forced expiratory volume and the ratio of 1 s forced expiratory volume to vital capacity, to detect obstructive lung disease. In 71 smokers with normal 1 s forced expiratory volume and ratio of 1 s forced expiratory volume to vital capacity, the end-tidal spirometry, diffusing capacity and residual volume indices revealed 14, 20 and 21% of abnormalities, respectively. The single-breath N2 closing volume test (Phase IV/vital capacity and slope of Phase III) detected the greatest number of subtle changes in lung function; this was abnormal in 32% of smokers with normal conventional spirometry. In young or light smokers, Phase IV/vital capacity was more frequently increased than the slope of Phase III; an inverse trend was observed in older or heavier smokers. The single-breath N2 closing volume test also provided the greatest number of abnormal results when other indices were impaired in the same subjects.