Effect of 10 s of breath holding on SBWsm: DLcoSb-3EQ from the total alveolar gas sample was similar between smokers and nonsmokers (Table 1). For DLcoSb-3EQ measured from small alveolar gas samples there was markedly less deviation of all four samples from DLcoSb-3EQ measured from the total sample (Figure 2). However, the pattern of change remained similar to that observed at 0 s of breath SB holding with DLco -3EQ being lower for sample 1 but higher for sample 4. Whereas Di was markedly reduced, compared with those measured at 0 s of breath holding, it remained slightly, but significantly higher in smokers (5±3%) than nonsmokers (3±1%) (Table 1) and correlated with pack-years of smoking (r =0.51; P<0.001) and with Sn (r2=0.22; P<0.05).
Change in Di with breath holding for SBWsm: The decrease in Di from 0 s to 10 s of breath holding correlated with Sn measured at 0 s of breath holding in both nonsmokers (r2=0.37; P<0.01) and smokers (r2=0.61; P<0.01), but did not correlate with Sn at 10 s of breath holding in either group. In smokers the decrease in Di with breath holding time (ADi) was significantly greater in smokers than nonsmokers (Table 1) and correlated with the corresponding change in Sn (ASn) (Figure 5, r2=0.51; P<0.001). In nonsmokers ADi and ASn were both less than in smokers, but the correlation between them was also significant (r =0.31; P<0.01).
Figure 2) Group mean values for the four normalized three-equation diffusing capacity for carbon monoxide (DLcosb-3EQ) values (error bars, ± SD) for nonsmokers (O) and smokers at 0 s of breath holding (left diagram) and after 10 s of breath holding (right diagram). Because the DLcosb-3EQ values deviate more from DLcosb-3EQ measured from the whole sample in smokers, degree of nonuniformity (Di) is larger in this group (42±29%, mean ± SD) than in nonsmokers (18±6%) at 0 s of breath holding. At 10 s of breath holding the four samples are almost identical to DLcoSB-3EQfrom the total alveolar gas sample. The degree of uniformity dramatically decreases with breath holding in both groups, but remains significantly higher in smokers