Dynamic hyperinflation and tolerance to interval exercise in patients with advanced COPD

Dynamic hyperinflation (DH) contributes importantly to the limitation of constant-load exercise (CLE) in patients with chronic obstructive pulmonary disease (COPD). However, its role in the limitation of interval exercise (IE) remains to be explored. The change (Δ) in inspiratory capacity (IC) was measured to reflect changes in DH in 27 COPD patients (forced expiratory volume in one second mean±SEM % predicted: 40±3) at the end of a symptom-limited CLE test at 80% of peak work capacity (WRmax) and an IE test at 100% WRmax (30 s of work, alternated with 30 s of unloaded pedalling). At the limit of tolerance in both IE and CLE, patients exhibited similar DH (ΔIC: 0.39±0.05 L and 0.45±0.05 L, respectively). However, exercise endurance time (tend) for IE (32.7±3.0 min) was significantly greater than for CLE (10.3±1.6 min). The IE tend correlated with resting IC, expressed as % pred normal. At 30 and 90%, of total IE tend, ΔIC (0.43±0.06 and 0.39±0.05 L, respectively) and minute ventilation (31.1±1.6 and 32.7±2.2 L·min^-1, respectively) were not significantly different. Resting hyperinflation helps to explain the limitation of interval exercise. Implementation of interval exercise for rehabilitation should provide important clinical benefits because it prolongs exercise endurance time and allows sustaining higher stable ventilation.