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 (O(2)DEL) to locomotor muscles.
Objectives: To investigate the effects of heliox on peripheral O(2)DEL and utilization during exercise in moderate to severe COPD.
Methods: Twelve mildly hypoxic or nonhypoxemic men (FEV(1) = 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 Sp(O(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 Q, which were accompanied by faster O(2) uptake kinetics and slower Delta[HHb] responses (P < 0.05). During steady-state exercise, Sp(O(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 O(2)DEL and utilization during dynamic exercise in patients with moderate to severe COPD. These effects enhance exercise tolerance in this patient population.