Inspiratory capacity, dynamic hyperinflation, breathlessness, and exerciseperformance during the 6-minute-walk test in chronic obstructive pulmonarydisease

Patients with severe chronic obstructive pulmonary disease (COPD) develop d ynamic lung hyperinflation (DH) during symptom-limited incremental and cons tant work exercise with cycle ergometer and treadmill. The increase in end- expiratory lung volume seems to be the best predictor of dyspnea. Quantific ation of DH is based on the relatively complex use of on-line measurement o f inspiratory capacity (IC) from flow volume loops. We reasoned that DH cou ld occur during daily activities such as walking, and that it could be simp ly measured using the spirometrically determined IC. We studied 72 men with COPD (FEV1 = 45 +/- 13.3% predicted). IC was measured at rest and after a 6-min walk test. Exertional dyspnea was evaluated using the Borg scale and dyspnea during daily activities with the modified Medical Research Council (MRC) scale. IC decreased significantly from 28.9 +/- 6.7% TLC at rest to 2 4.1 +/- 6.8% TLC after exercise (p < 0.001). Exertional dyspnea correlated with <Delta>IC (r = -0.49, p < 0.00001) and baseline MRC (r = 0.59, p < 0.0 0001). In many patients with COPD, walking leads to DH that can be easily d etermined with simple spirometric testing. DH helps explain exercise capaci ty limitation and breathlessness during simple daily activities.