Heliox Improves Oxygen Delivery and Utilization during Dynamic Exercise in Patients with Chronic Obstructive Pulmonary Disease

Rationale: Normoxic heliox (mixture of 79% He and 21% O-2) may enhance exercise tolerance in patients with chronic obstructive pulmonary disease (COPD). It remains to be determined whether part of these beneficial effects could be ascribed to increased O-2 delivery (O2DEL) to locomotor muscles. Objectives: To investigate the effects of heliox on peripheral O2DEL and utilization during exercise in moderate to severe COPD. Methods: Twelve mildly hypoxic or nonhypoxemic men (FEV1 = 45.0 +/- 13.0% predicted) underwent constant-work rate tests (70-80% peak) to the limit of tolerance while receiving heliox or room air. Near-infrared spectroscopy determined changes (Delta) in leg muscle deoxygenation (deoxyhemoglobin concentration [HHb], an index of fractional O-2 extraction), and surface electromyography estimated muscle fiber recruitment (n = 5). Q and Spo(2) were monitored by impedance cardiography and pulse oximetry, respectively. Measurements and Main Results: Heliox significantly decreased dynamic hyperinflation and increased exercise tolerance compared with room air (640 +/- 95 s vs. 371 +/- 100 s; P < 0.01). Heliox also accelerated on-exercise dynamics of (, which were accompanied by faster O-2 uptake kinetics and slower Delta[HHb] responses (P < 0.05). During steady-state exercise, Spo(2)-corrected Delta[HHb] values decreased with heliox despite no significant changes in cardiac output. Muscle fiber recruitment and leg effort scores were also diminished (P < 0.05). On a multiple regression analysis, reductions in dynamic hyperinflation, dyspnea, and Delta[HHb] were independently related to improvements in exercise tolerance with heliox (R-2 = 0.91; p < 0.01). Conclusions: Heliox increases lower limb O2DEL and utilization during dynamic exercise in patients with moderate to severe COPD. These effects enhance exercise tolerance in this patient population.