Relationship of emphysema and airway disease assessed by CT to exercise capacity in COPD

Abstract

Objective: To assess the association of emphysema and airway disease assessed by volumetric computed tomography (CT) with exercise capacity in subjects with chronic obstructive pulmonary disease (COPD).

Methods: We studied 93 subjects with COPD (Forced Expiratory Volume in 1 s [FEV(1)] %predicted mean +/- SD 57.1 +/- 24.3%, female gender = 40) enrolled in the Lung Tissue Research Consortium. Emphysema was defined as percentage of low attenuation areas less than a threshold of -950 Hounsfield units (%LAA-950) on CT scan. The wall area percentage (WA%) of the 3rd to 6th generations of the apical bronchus of right upper lobe (RB1) were analyzed. The 6-min walk distance (6MWD) test was used as a measure of exercise capacity.

Results: The 6MWD was inversely associated with %LAA-950 (r = -0.53, p < 0.0001) and with the WA% of 6th generation of RB1 only (r = -0.28, p = 0.009). In a multivariate regression model including CT indices of emphysema and airway disease that were adjusted for demographic and physiologic variables as well as brand of CT scanner, only the %LAA-950 remained significantly associated with exercise performance. Holding other covariates fixed, this model showed that a 10% increase of CT emphysema reduced the distance walked in 6 min 28.6 m (95% Confidence Interval = -51.2, -6.0, p = 0.01).

Conclusion: These results suggest that the extent of emphysema but not airway disease measured by volumetric CT contributes independently to exercise limitation in subjects with COPD.

Figure 1

Scatter plot of six-minute walk distance to emphysema assessed by CT defined as percentage of low attenuation areas below −950 Hounsfield units (%LAA-950) in subjects with COPD

Figure 2

Scatter plot of six-minute walk distance to wall area percentage (WA%) of the 6^th generation of the apical bronchus of the right upper lobe (RB1) assessed by CT in subjects with COPD.