Dynamic hyperinflation during the 6-min walk test in severely asthmatic subjects

We tested the hypothesis that dynamic hyperinflation develops in severe asthmatic subjects during exercise. Changes in inspiratory capacity (IC) were measured during the 6-min walk test (6MWT) in severe asthmatic subjects compared with chronic obstructive pulmonary disease (COPD) subjects with a similar degree of bronchial obstruction. We assessed whether changes in IC were associated with changes in dyspnoea perception. 27 severe asthmatic subjects (10 males and 17 females) and 43 COPD subjects (35 males and eight females) were recruited. The two groups performed similarly in the 6MWT (p=0.90). At the end of the test, the Borg score increased significantly in both groups (mean difference: for asthmatic subjects 1.7\ub11.6; p<0.0001; for COPD subjects 3.1\ub11.9; p<0.0001). IC measured at the beginning of 6MWT was not different between groups (2.25\ub10.47\u2005L in asthmatic subjects versus 2.38\ub10.60\u2005L in COPD subjects; p=0.32) and decreased in both groups (mean difference: for asthmatic subjects 0.160\u2005L; p=0.02; for COPD subjects 0.164\u2005L; p