Pulmonary Vascular Volume by Quantitative CT in Dyspneic Smokers with Minor Emphysema

Abstract

Reduced lung diffusing capacity for carbon monoxide (DL_CO) at rest and increased ventilation (⩒_E)-carbon dioxide output (⩒CO₂) during exercise are frequent findings in dyspneic smokers with largely preserved FEV₁. It remains unclear whether low DL_CO and high ⩒_E-⩒CO₂ are mere reflections of alveolar destruction (i.e. emphysema) or impaired pulmonary perfusion in non-emphysematous tissue contributes to these functional abnormalities. Sixty-four smokers (41 males, FEV₁= 84 ± 13%predicted) underwent pulmonary function tests, an incremental exercise test, and quantitative chest computed tomography. Total pulmonary vascular volume (TPVV) was calculated for the entire segmented vascular tree (VIDA Vision™). Using the median % low attenuation area (-950 HU), participants were dichotomized into "Trace" or "Mild" emphysema (E), each group classified into preserved versus reduced DL_CO. Within each emphysema subgroup, participants with abnormally low DL_CO showed lower TPVV, higher ⩒_E-⩒CO₂, and exertional dyspnea than those with preserved DL_CO (p < 0.05). TPVV (r = 0.34; p = 0.01), but not emphysema (r = -0.05; p = 0.67), correlated with lower DL_CO after adjusting for age and height. Despite lower emphysema burden, Trace-E participants with reduced DL_CO had lower TPVV, higher dyspnea, and lower peak work rate than the Mild-E with preserved DL_CO (p < 0.05). Interestingly, TPVV (but not emphysema) correlated inversely with both dyspnea-work rate (r = -0.36, p = 0.004) and dyspnea-⩒_E slopes (r = -0.40, p = 0.001). Reduced pulmonary vascular volume adjusted by emphysema extent is associated with low DL_CO and heightened exertional ventilation in dyspneic smokers with minor emphysema. Impaired perfusion of non-emphysematous regions of the lungs has greater functional and clinical consequences than hitherto assumed in these subjects.

Keywords: CT; DLCO; Smoking; dyspnea; emphysema; pulmonary vascular volume.