Low DLCO, reduced pulmonary blood volume and ventilatory inefficiency in smokers with mild emphysema

Abstract

<b>Background:</b> D_LCO is modestly associated with emphysema in mild-moderate COPD. Whether low D_LCO is associated with reduced pulmonary total blood volume (TBV) and ventilatory inefficiency, independent of emphysema, is unknown. <b>Methods:</b> We performed lung function, incremental exercise test and quantitative chest computed tomography (QCT) in 65 smokers with no or mild-moderate airflow obstruction. TBV was calculated for the entire segmented vascular tree (VIDA Apollo). Smokers were dichotomized based on emphysema extent using the median CT low attenuation percent: trace (0.1-2.1% (&lt;-950 HU)) and mild (2.2-19.5%). Each subgroup was evaluated for low and normal D_LCO (GLI equation). <b>Results:</b> Groups were matched for age, sex, and FEV₁. Smoking history (pack-years) was 39±30 vs. 49±7 and 35±20 vs. 30±19 (mean±SD), for normal vs. low D_LCO in trace and mild emphysema subgroups, respectively. Within emphysema subgroups (Figure), low D_LCO was associated with greater ventilatory equivalent for CO2 (⩒_E/⩒CO₂) nadir during exercise and lower TBV on QCT (p&lt;0.05). In all smokers, D_LCO (but not emphysema extent) was associated with TBV (r=0.23, p=0.04) and ⩒_E/⩒CO₂ nadir (r=-0.62, p&lt;0.01). <b>Conclusion:</b> In smokers with “largely mild" emphysema, low resting D_LCO was associated with reduced CT pulmonary blood volume and increased exercise ventilatory inefficiency, independent of airflow obstruction and emphysema severity.