Effect of endurance training on expiratory flow limitation and dynamic hyperinflation in patients with stable chronic obstructive pulmonary disease

BackgroundExpiratory flow limitation (EFL) is the primary pathophysiological hallmark of chronic obstructive pulmonary disease (COPD). However, the effect of lower-extremity endurance training alone on EFL in patients with COPD remains largely unknown. AimThis study aims to determine the effects of endurance training on EFL and dynamic hyperinflation in patients with stable COPD. MethodsThis was a prospective, single-blinded, non-randomised controlled 12-week study recruiting Chinese patients with stable COPD in an endurance training group (n = 15) or a control group (n = 13). Before and at the end of the study, we measured the EFL, pulmonary function, peak inspiratory flow (PIF) and maximum inspiratory pressure (MIP); moreover, the patients underwent a constant work rate exercise test in which Borg dyspnoea scale, tidal breathing flow volume curves and inspiratory capacity (IC) were determined every other minute. ResultsExercise training significantly improved the exercise endurance time (7.00 3.05 vs 18.13 +/- 6.44min, P < 0.001), MIP (69.49 +/- 16.03 vs 80.18 +/- 15.97 cmH(2)O, P < 0.001) and PIF (3.96 +/- 1.01 vs 4.51 +/- 1.13L/s, P = 0.014), but not EFL (3.33 +/- 0.49 vs 3.40 +/- 0.51, P = 0.334). Subjects on training had decreased breathing frequency (26.26 +/- 7.13 vs 23.15 +/- 5.34 breaths/min, P = 0.002), minute ventilation (30.28 +/- 7.52 vs 26.85 +/- 4.17L, P = 0.013), tidal peak expiratory flow (1.53 +/- 0.22 vs 1.32 +/- 0.20 L/s, P = 0.006), mean expiratory flow (0.87 +/- 0.19 vs 0.68 +/- 0.15 L/s, P = 0.011) and Borg dyspnoea score (7.20 +/- 1.15 vs 3.93 +/- 1.39, P < 0.001), as well as increased IC (1.50 +/- 0.34 vs 1.67 +/- 0.45L, P = 0.002), expiratory time (1.47 +/- 0.62 vs 1.72 +/- 0.62s, P = 0.004) and inspiratory flow reserve (2.05 +/- 1.10 vs 2.95 +/- 1.19L/s, P = 0.002) at isotime. These changes were not observed in the control group. ConclusionEndurance training may benefit stable COPD patients in improving exercise endurance, inspiratory muscle strength, ventilatory requirements, exercise-induced hyperinflation and exertional dyspnoea.