Ventilation and respiratory mechanics during exercise in younger subjects breathing CO 2 or HeO 2

Abstract

To determine if ventilation (V̇ e) during maximal exercise would be increased as much by 3% CO 2 loading as by resistive unloading of the airways, we studied seven subjects (39±5 years; mean±S.D.) during graded cycle ergometry to exhaustion while breathing: (1) room air (RA); (2) 3% CO 2, 21% O 2, and 76% N 2; or (3) 79% He and 21% O 2). V̇ e and respiratory mechanics were measured during each 1-min increment (20 or 30 W) in work rate. V̇ e during maximal exercise was increased 21±17% when breathing 3% CO 2 and 23±16% when breathing HeO 2 ( P<0.01). Further, the ventilatory response to exercise above ventilatory threshold (VTh) was increased ( P<0.05) when breathing HeO 2 (0.89±0.26 L/min/W) as compared with breathing RA (0.65±0.12). When breathing HeO 2, end-expiratory lung volume (%total lung capacity, TLC) was lower during maximal exercise (46±7) when compared with RA (53±6, P<0.01). In conclusion, V̇ e during maximal exercise can be augmented equally by 3% CO 2 loading as by resistive unloading of the airways in younger subjects. This suggests that in younger subjects with normal lung function there are minimal mechanical ventilatory constraints on V̇ e during maximal exercise.