Effects of oxygen on lower limb blood flow and O-2 uptake during exercise in COPD

Purpose: To quantify the effects of acute oxygen supplementation on lower l imb blood flow ((Q)over dotLEG), O-2 delivery ((Q)over dotO(2)LEG), and O-2 uptake ((V)over dotO(2)LEG) during exercise and to determine whether the m etabolic capacity of the lower limb is exhausted at peak exercise during ro om air breathing in patients with COPD. Methods: Oxygen (FIO2 = 0.75) and a ir were randomly administered to 14 patients with COPD (FEV1: 35 +/- 2% pre d, mean +/- SEM) during two symptom-limited incremental cycle exercise test s. Before exercise, a cannula was installed in a radial artery and a thermo dilution catheter inserted in the right femoral vein. At each exercise step , five-breath averages of respiratory rate, tidal volume, and ventilation ( (V)over dotE), dyspnea and leg fatigue scores, arterial and venous blood ga ses, and (Q)over dotLEG were obtained. From these measurements, Tio,LEG was calculated. Results: Peak exercise capacity increased from 46 +/- 3 W in r oom air to 59 +/- 5 W when supplemental oxygen was used (P < 0.001). (Q)ove r dotLEG, (Q)over dotO(2)LEG, and (V)over dotO(2)LEG were greater at peak e xercise with O-2 than with air (P < 0.05). During submaximal exercise, dysp nea score and (V)over dotE were significantly reduced with O-2 (P < 0.05), whereas (Q)over dotLEG, (V)over dotO(2)LEG, and leg fatigue were similar un der both experimental conditions. The improvement in peak exercise work rat e correlated with the increase in peak (Q)over dotO(2)LEG (r = 0.66, P < 0. 01), peak (V)over dotO(2)LEG (r = 0.53, P < 0.05), and reduction in dyspnea at iso-exercise intensity (r = 0.56, P < 0.05). Conclusion: The improvemen t in peak exercise capacity with oxygen supplementation could be explained by the reduction in dyspnea at submaximaI exercise and the increases in (Q) over dotO(2)LEG and (V)over dotO(2)LEG, which enabled the exercising muscle s to perform more external work. These data indicate that the metabolic cap acity of the lower Limb muscles was not exhausted at peak exercise during r oom air breathing in these patients with COPD.