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

¹ Pulmonary Function and Clinical Exercise Physiology Unit (SEFICE), Division of Respiratory Diseases, Department of Medicine, Federal University of São Paulo (UNIFESP), São Paulo, Brazil; ² Department of Physiology, University of Kentucky, Lexington, Kentucky; and ³ Exercise Research Laboratory, School of Physical Education, Federal University of Rio Grande do Sul, Porto Alegre, Brazil

Correspondence and requests for reprints should be addressed to J.A. Neder, M.D., Ph.D., Respiratory Division, Department of Medicine, Federal University of São Paulo (UNIFESP), Rua Professor Francisco de Castro 54, Vila Clementino, 04020-050 São Paulo, Brazil. E-mail: albneder{at}pneumo.epm.br

Rationale: Normoxic heliox (mixture of 79% He and 21% O₂) 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 O₂ 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 () in leg muscle deoxygenation (deoxyhemoglobin concentration [HHb], an index of fractional O₂ extraction), and surface electromyography estimated muscle fiber recruitment (n = 5). and Sp_O2 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 O₂ uptake kinetics and slower [HHb] responses (P < 0.05). During steady-state exercise, Sp_O2-corrected [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 [HHb] were independently related to improvements in exercise tolerance with heliox (R² = 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.

Key Words: chronic obstructive pulmonary disease • helium • exercise tolerance • oxygen consumption • near-infrared spectroscopy

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject Expiratory flow limitation and increased operational lung volumes are centrally related to exercise intolerance in patients with chronic obstructive pulmonary disease (COPD). There is renewed interest in determining whether such abnormalities might reduce the convective delivery of oxygen to the exercising muscles and thereby decrease patients' ability to sustain whole-body exercise. What This Study Adds to the Field This study demonstrates that a strategy able to ammeliorate expiratory flow limitation and dynamic hyperinflation (heliox) accelerates the dynamics of peripheral muscle utilization of oxygen as a consequence of improved delivery during high-intensity exercise in patients with moderate to severe COPD. Our data provide a scientific rationale for respiratory–mechanical interventions aiming to enhance oxygen delivery to the lower limb muscles during dynamic exercise in this patient population.