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

Reduced lung diffusing capacity for carbon monoxide (DL CO ) at rest and increased ventilation ( ⩒ E )-carbon dioxide output ( ⩒ CO 2 ) during exercise are frequent findings in dyspneic smokers with largely preserved FEV 1 . It remains unclear whether low DL CO and high ⩒ E - ⩒ CO 2 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, FEV 1 = 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 - ⩒ CO 2 , 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.