Di described the degree to which the four DLcoSb-3EQ values measured from the four alveolar gas samples deviated from the single DLcoSb-3EQ value measured from the entire alveolar gas sample by calculating the root-mean-square difference of the normalized DLcoSb-3EQ values (Figure 1). Di quantified the degree of nonuniformity of DLcoSb-3EQ measured from the four small samples, each normalized by DLcoSb-3EQ measured from the total sample.
As previously reported the phase III helium slope (AHe/L) between 33% and 67% of the exhaled volume was measured, and the phase III slope (Sn) was normalized by dividing AHe/L by the predicted ideal, mean end-inspired alveolar helium concentration ([He]A preD) . The mixing efficiency (Emix) was calculated using a previously described computer algorithm .
Statistics: Group mean data for smokers and nonsmokers were compared using unpaired Student’s t tests. Differences due to the SBW manoeuvre and to breath hold time were assessed using paired Student’s t tests in both smokers and nonsmokers. correlations were performed using linear regression analysis.
Figure 1) Three-equation diffusing capacity for carbon monoxide (DLcosb-3EQ) values measured from the four equal alveolar gas samples are normalized by expressing them as a percentage of DLcosb-3EQ measured from the total alveolar gas sample (y axis). Values (sample 1 to 4) are shown for a representative submaximal single breath washout manoeuvre at 0 s of breath holding. DLcosb-3EQ value for sample 1, measured at high expired lung volumes, is below 100% whereas subsequent DLcosb-3EQ values rise progressively above 100%. For each of the four normalized DLcosb-3EQ values measured from the four equal alveloar gas samples, the difference between each of the small samples and the normalized DLcosb-3EQ from the total aveloar gas sample was calculated (A, B, C, D). The root mean square difference of the four samples, the degree of diffusion nonuniformity (Di) is calculated using A, B, C and D as shown in the insert. Di is 27% in this example.