Exercise capacity and breathing mechanics in patients with airflow limitation.

To investigate the impact of expiratory airflow limitation on ventilation during exercise, we studied six control subjects with normal lung function (FEV1/FVC = 79 +/- 6%) and eight patients with borderline-to-mild airflow limitation (FEV1/FVC = 68 +/- 4%) during cycle ergometry. VO2, HR, and VE/MVV were not different between the control subjects or patients during maximal or submaximal exercise. In contrast, five of the eight patients achieved maximal expiratory flow over a large portion (37%) of their tidal volume (VT) during submaximal exercise, whereas none of the control subjects achieved maximal expiratory flow. To estimate the fraction of expiratory capacity used by the control subjects and the patients, we calculated a mechanical ventilatory maximum (VEmaxCal) for each level of exercise using the individual's VT, end-expiratory lung volume (EELV), and maximal expiratory flow-volume curve. The patients used a greater fraction of their VEmaxCal at each level of submaximal exercise (P less than 0.03). Despite the flow limitation during submaximal exercise, EELV was similar between the control subjects and patients. In conclusion, even patients with borderline-to-mild airflow limitation achieve maximal expiratory flow during submaximal exercise and these restrictions are not reflected by VE/MVV nor by EELV.