Measurement of dynamic hyperinflation after a 6-minute walk test in patients with COPD

Dynamic hyperinflation (DH) develops in patients with COPD during incremental exercise with a cycle ergometer. The aims of this study were to determine whether DH can be evidenced after walking with a handheld spirometer and to determine its functional consequences.

Fifty patients with COPD (39 men; median age, 60 years [interquartile range (IQR), 54 to 69 years]; FEV(1), 45% predicted [IQR, 31 to 67% predicted]) underwent pulmonary function tests and a 6-min walk test (6MWT). Inspiratory capacity (IC) was measured with the patient in the standing position at rest and immediately after the 6MWT with a portable spirometer. Dyspnea was evaluated directly (change in Borg score during 6MWT) and indirectly (Medical Research Council scale). The first 20 patients performed an incremental exercise test with cycle ergometer that allowed for the measurement of IC at peak exercise and repeatedly during the first 3 min of recovery.

The median change in IC during the 6MWT was -210 mL (IQR, 55 to -440; n = 50), whereas the median change in IC during the exercise test was -295 mL (IQR, -145 to -515; n = 20). Both the IC and IC changes after 6MWT correlated to values after the exercise test. DH decreased rapidly after the end of the exercise test but was nonsignificantly different from the baseline value after 75 s of recovery. The percentage of decrease in IC during the 6MWT correlated with dyspnea (change in Borg score during 6MWT: r(2) = 0.21; p = 0.0006).

DH can be measured during a 6MWT with a handheld spirometer to allow for its evaluation in daily practice and its contribution to dyspnea while walking.