Exercise capacity and lobar hyperinflation in patients with COPD

Introduction Reduced exercise capacity in COPD patients can be due to lung hyperinflation. Until recently, this could only be measured by pulmonary function tests (PFT) which are not capable to measure regional lung changes. However, CT based Functional Respiratory Imaging (FRI) is able to quantify hyperinflation on a lobar level. These regional lung changes and their relationship with exercise capacity remained so far unexplored. Objective To evaluate the relationship between lobar hyperinflation and exercise capacity. Methods A retrospective analysis of baseline data on 26 COPD patients was performed. Patients underwent PFT. Exercise capacity was measured by 6 minute walking test. Lobar hyperinflation was measured by FRI. Based on CT, three dimensional models of the lobes were extracted and hyperinflation was calculated at functional residual capacity. Results Lung hyperinflation by PFT, expressed as the ratio between residual volume and total lung capacity (RV/TLC), is inversely correlated with 6 minute walking distance (6MWD)(Spearman r=-0.591; p=0.001), whereas lobar hyperinflation of only the left upper lobe is correlated with the 6MWD (Spearman r=0.422; p=0.032). ![Figure][1] Conclusions FRI is more sensitive to measure the regional changes in the lung than PFT (De Backer, L. et al. ERJ 2012; 40:298-305), however lobar hyperinflation does not contribute to exercise capacity. It seems that exercise capacity is more related to global changes in lung impairment. [1]: pending:yes