Effects of hyperoxia on ventilatory limitation during exercise in advancedchronic obstructive pulmonary disease

We studied interrelationships between exercise endurance, ventilatory deman d, operational lung volumes, and dyspnea during acute hyperoxia in ventilat ory-limited patients with advanced chronic obstructive pulmonary disease (C OPD). Eleven patients with COPD (FEV1.0 = 31 +/- 3% predicted, mean +/- SEM ) and chronic respiratory failure (Pa-O2 52 +/- 2 mm Hg, Pa-CO2 48 +/- 2 mm Hg) breathed room air (RA) or 60% O-2 during two cycle exercise tests at 5 0% of their maximal exercise capacity, in randomized order. Endurance time (T-lim), dyspnea intensity (Borg Scale), ventilation ((V) over dot E), brea thing pattern, dynamic inspiratory capacity (ICdyn), and gas exchange were compared. Pa-O2, at end-exercise was 46 +/- 3 and 245 +/- 10 mm Hg during R A and O-2, respectively. During O-2, T-lim increased 4.7 +/- 1.4 min (p < 0 .001); slopes of Borg, (V) over dot E, (V) over dot CO2, and lactate over t ime fell (p < 0.05); slopes of Borg-(V) over dot E, (V) over dot E-(V) over dot E-lactate were unchanged. At a standardized time near end-exercise, O- 2 reduced dyspnea 2.0 +/- 0.5 Borg units, (V) over dot CO2 0.06 +/- 0.03 L/ min, (V) over dot E 2.8 +/- 1.0 L/min, and breathing frequency 4.4 +/- 1.1 breaths/min (p < 0.05 each). ICdyn and inspiratory reserve volume (IRV) inc reased throughout exercise with O-2 (p < 0.05). Increased ICdyn was explain ed by the combination of increased resting IRV and decreased exercise breat hing frequency (r(2) = 0.83, p < 0.0005). in conclusion, improved exercise endurance during hyperoxia was explained, in part, by a combination of redu ced ventilatory demand, improved operational lung volumes, and dyspnea alle viation.