The most remarkable finding in this study was that Di was significantly higher in smokers for SBWSM at 0 s of breath holding and correlated with cumulative pack-years of smoking. The fact that, for these manoeuvres, Di correlated with both age and pack-years of smoking in smokers, but was not affected by age in nonsmokers (Figure 3), implied a specific effect of smoking on Di that could not be explained by ageing. Although the precise pathological changes responsible for the increase in Di in smokers for SBWSM manoeuvres at 0 s of breath holding must await future structure-function correlations, the effects of breath holding on both Di and simultaneous measurements of ventilation inhomogeneity allow us to draw some inferences about the possible mechanisms for the effects of smoking on Di.
Figure 3) For submaximal single breath washout manoeuvres degree of diffusion nonuniformity (Di) correlates with pack-years of smoking (left diagram) in smokers (r2=0.36; P=0.004) and with age in smokers (r2=0.23; P=0.026), but not in nonsmokers (right diagram, r2=0.12). O with dashed line Nonsmokers; 0 with solid line smokers