Lung function changes in smokers with normal conventional spirometry.

The comparative ability to detect early abnormalities in smokers by commonly used lung function tests was studied. Sixty-five healthy male nonsmokers served as a reference group and provided standards for 1-sec forced expiratory volume, vital capacity, end-tidal spirometry, spirometric forced mid-and end-expiratory flows, single-breath diffusing capacity, static lung volumes (helium 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-sec forced expiratory volume and the ratio of 1-sec forced expiratory volume to vital capacity, to detect obstructive lung disease. In 71 smokers with normal 1-sec forced expiratory volume and ratio of 1-sec forced expiratory volume to vital capacity, the end-tidal spirometry, diffusing capacity, and residual volume indices revealed 14,20, and 21 per cent 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 per cent 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 incerse 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.