Nonuniformity of diffusing capacity: RESULTS (1)

The characteristics of the smoking and nonsmoking groups, which have been previously reported , were similar in terms of sex distribution (smokers: 12 women and nine men; nonsmokers: 10 women and 11 men), age (smokers 39±8 years; nonsmokers 38±7 years, mean ± SD) and height (smokers 172±10 cm; nonsmokers 174±10 cm). There were no significant differences in FVC (smokers 105±10% predicted; nonsmokers 101±8% predicted) or FEV1 (smokers 100±9% predicted; nonsmokers 102±8% predicted). The FEF25-75 was smaller (P<0.05) in smokers (90±24% predicted) than in nonsmokers (106±21% predicted). The smokers had a mean of 21 ±12 pack-years of cigarette smoking (range of four to 55 pack-years). There were no differences in the expired volume, maximum end-inspired volume, preinspiratory lung volume or breath hold time for comparable manoeuvres between smokers and nonsmokers (Table 1).

SBWsm atOsof breath holding: DLcoSb-3EQ from the total alveolar sample was slightly reduced in smokers (Table 1; P<0.05). DLcoSb-3EQ measured from small alveolar gas samples was reduced in the first alveolar sample, measured at high lung volumes just after alveolar dead space clearance, but increased progressively in subsequent samples (Figure 2, left graph). Di was therefore greater in smokers (42±29%) than in nonsmokers (18±7%) (Table 1; P<0.001). Di correlated with age in smokers (Figure 3; r2=0.23; P=0.026) and pack-years of smoking (Figure 3; r2=0.36; P=0.004). Sn, but not Emix, was also markedly increased in smokers (Table 1; P<0.001). Di at 0 s of breath holding correlated significantly with Sn at 0 s of breath holding in both smokers (r2=0.63; P<0.001) and nonsmokers (r2=0.38; P<0.01) (Figure 4). The day-to-day coefficient of variation of Di for this manoeuvre was 8.0±4.6% in 10 normal subjects whose value were repeated on five successive days .

Table 1. Group mean values (± SD) of single breath washout manoeuvres for nonsmokers and smokers during conventional vital capacity manoeuvres without breath holding (SBWvc) and submaximal (SBWsm) manoeuvres at 0 and 10 s of breath holding

Significance of comparisons between smokers and nonsmokers.:*P<0.05, **P<0.01, ***P<0.001. DLCOsb-3EQ Three equation diffusing capacity for carbon monoxide; Di Degree of uniformity, root mean square difference of DLCOsb-3EQ calculated from the four equal alveolar gas samples that are normalized by expressing them as a percentage of DLCOSB-3EQ measured from the total alveolar gas sample; Sn Normalized phase ill slope for the tracer gas helium

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Category: Increased in smokers

Tags: Diffusion index, Inhomogeneity, Slope of phase III, Small airways, Three-equation diffusing capacity, Tobacco smoking