RESEARCH ARTICLE Correlation of a Decline in Aerobic Capacity with Development of Emphysema in Patients with Chronic Obstructive Pulmonary Disease: A Prospective Observational Study

In patients with COPD, CT assessment of emphysema and airway disease is known to be associated with lung function and 6-minute walk distance. However, it remains to be deter-mined whether low attenuation area (LAA) on CT is associated with aerobic capacity as-sessed using cardiopulmonary exercise testing (CPET). In this prospective observational study, we repeatedly conducted high-resolution CT and CPET using a treadmill in 81 COPD patients over a median interval of 3.5 years. Two investigators independently scored LAA on images obtained at the aortic arch level, tracheal bifurcation level, and supradiaphrag-matic level. Grades for the images of each lung were added to yield the total LAA score. Total LAA score was negatively correlated with peak aerobic capacity (V_O2) (p<0.001, r =-0.485). LAA scores of the upper (aortic arch level) and the lower (supradiaphragmatic level) lungs were both significantly associated with peak V_O2. There was a significant corre-lation between total LAA score and peak CO2 output (V_CO2) (p<0.001, r =-0.433). Total LAA score was correlated with oxygen saturation at peak exercise (p<0.001, r =-0.634) and the estimated dead space fraction (p<0.001, r = 0.416). The mean annual change in total LAA score was significantly correlated with those in peak V_O2 (p<0.001, r =-0.546) and peak V_CO2 (p<0.001, r =-0.488). The extent of emphysema measured by CT was associat-ed with the results of CPET. The time-dependent changes in CPET data were also correlat-ed with that in total LAA score. CT assessment could be a non-invasive tool to predict aerobic capacity in patients with COPD