Control of breathing during exercise in patients with chronic airflow limitation with or without hypercapnia

Twenty-four patients suffering from chronic obstructive pulmonary disease (COPD) exercised on a bicycle with a progressive increase in load (30 W/min) until dyspnea or exhaustion occurred. Seven subjects were CO2 retainers: PaCO2 greater than or equal to 45 mm Hg at rest and/or during exercise. Fifteen normal subjects were submitted to the same protocol. To make comparison possible, all the parameters studied were calculated at 60 watts. It was concluded that CO2 retention during exercise is not secondary to a decreased respiratory drive but mainly to a lesser increase in VE and to higher VD/VT ratios.