Patterns of spirogram abnormality in individual smokers

Dynamic ventilatory function was measured in 147 male and 212 female smokers with a mean age of 39.3 and 42.5 yr, respectively. The results were compared with values predicted from the results of control subjects who had never smoked, and deviation from predicted was expressed as a standardized residual (SR). Although the flow indices FMF, FEF50, and FEF75 showed a substantial group change in SR for smokers, the distribution of SR indicated changes in the majority of smokers but did not favor the identification of individual subjects as being abnormal. By contrast, the distribution of SR for FEV1/FVC%, FEV3/FVC%, and the time domain indices alpha(1) 75%, MR90%, and mu favored the identification of subjects with marked abnormalities. These volume-standardized indices allowed the identification of 2 patterns of spirometric abnormality prevalent among smokers. Pattern 1 showed changes predominantly in the first 75% of FVC and Pattern 2 showed changes generally confined to the tail of the spirogram; 15% of the female and 14% of the male smokers had Pattern 1 abnormalities, with only 4% of both the female and male smokers showing Pattern 2. These results appear more consistent with the "Dutch hypothesis" and not the "small airways hypothesis" concerning the development of chronic air-flow limitation in smokers.