BACKGROUND: People with chronic obstructive pulmonary disease (COPD) have reduced pulmonary diffusing capacity for carbon monoxide (DLCO) compared to healthy controls, likely due to lower pulmonary capillary blood volume (Vc) or membrane diffusing capacity (Dm). Previous work has shown reduced pulmonary vascular volumes measured by computed tomography (CT) in COPD compared to controls. The purpose of this study was to explore the potential associations between CT measured pulmonary vascular structure with DLCO, Vc and Dm. We hypothesized that those with greater pulmonary vascular volumes would show higher DLCO, Vc and Dm.

METHODS: Day 1: Enrollment and pulmonary function test. Day 2: Chest CT scan to quantify emphysema severity, total vessel volume (TVV), volume of vessels with a cross-sectional area <5mm2 (BV5), and between 5-10mm² (BV5-10). Day 3: Multiple fraction of inspired O₂ DLCO technique to determine Vc and Dm. Potential associations were evaluated by Pearson correlation.

RESULTS: To date, 35 people with COPD (18 females, mean FEV₁ 65±16% predicted; 69±7 years) have been recruited. DLCO adjusted for alveolar volume was correlated with TVV (r= 0.55, p<0.001), BV5 (r=0.47, p=0.006) and BV5-10 (r=0.48, p=0.004). Exploratory analyses revealed that among CT variables, Dm was associated with BV5-10 (r=0.46, p=0.006) and TVV (r=0.37, p=0.03), while Vc was not associated with any CT pulmonary vascular measurements.

CONCLUSIONS: Our results suggest that DLCO and Dm are related to CT-measured pulmonary vascular volumes in COPD; supporting an association between pulmonary vascular function and structure.