Effect of mild-to-moderate airflow limitation on exercise capacity

To determine the effect of mild-to-moderate airflow limitation on exercise tolerance and end-expiratory lung volume (EELV), we studied 9 control subjects with normal pulmonary function [forced expired volume in 1 s (FFV₁) 105% pred; % of forced vital capacity expired in 1 s (FEV₁/FVC%) 81] and 12 patients with mild-to-moderate airflow limitation (FEV₁ 72% pred; FEV₁/FVC% 58) during progressive cycle ergometry. Maximal exercise capacity was reduced in patients [69% of pred maximal O₂ uptake (V̇O(₂ max))] compared with controls (104% pred V̇O(₂ max), P < 0.01); however, maximal expired minute ventilation-to-maximum voluntary ventilation ratio and maximal heart rate were not significantly different between controls and patients. Overall, there was a close relationship between V̇O(₂ max) and FEV₁ (r² = 0.62). Resting EELV was similar between controls and patients [53% of total lung capacity (TLC)], but at maximal exercise the controls decreased EELV to 45% of TLC (P < 0.01 ), whereas the patients increased EELV to 58% of TLC (P < 0.05). Overall, EELV was significantly correlated to both V̇O(₂ max) (r = -0.71, P < 0.001) and FEV₁ (r = -0.68, P < 0.001).This relationsbip suggests a ventilatory influence on exercise capacity; however, the increased EELV and associated pleural pressures could influence cardiovascular function during exercise. We suggest that the increase in EELV should be considered a response reflective of the effect of airflow limitation on the ventilatory response to exercise.