QUESTION: Does a new positive expiratory pressure device (conical-PEP) decrease lung hyperinflation during exercise in patients with chronic obstructive pulmonary disease compared to normal breathing? Does it increase the duration of exercise? DESIGN: A randomised, cross-over trial with concealed allocation. PARTICIPANTS: Thirteen patients with moderate to severe chronic obstructive pulmonary disease (mean FEV1 61% predicted). INTERVENTION: The experimental intervention was conical-PEP breathing with a positive expiratory pressure of 4 to 20 cmH2O during 30% of 1 RM alternate knee extension exercise at 70% age-predicted HRmax to fatigue. The control intervention was normal breathing. OUTCOME MEASURES: Total lung capacity (inspiratory capacity and slow vital capacity), breathlessness, and leg discomfort were measured pre and post exercise. Cardiorespiratory function was measured pre and during the last 30 s of exercise. Duration of exercise was recorded. RESULTS: After the experimental intervention, inspiratory capacity increased 200 ml (95% CI 0 to 400) and slow vital capacity increased 200 ml (95% CI 0 to 400) more than the control intervention. Participants exercised for 107 s (95% CI -23 to 238) more during the experimental intervention than the control intervention. Conical-PEP breathing during exercise resulted in 6.1 fewer breaths/min (95% CI 1.4 to 10.8) than normal breathing; it did not have any adverse effects on CO2 retention or oxygen saturation. CONCLUSION: The novel conical-PEP device decreases lung hyperinflation, is safe to use, and tends to increase the duration of exercise. TRIAL REGISTRATION: NCT00741832.

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