Hyperventilation with He-O2 breathing is not decreased by superimposed external resistance

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 (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.

Impaired exercise ventilatory mechanics with the self-contained breathing apparatus are improved with heliox

The effect of the self-contained breathing apparatus (SCBA) with compressed air (BA-A) on ventilatory mechanics, work of breathing (WOB), pulmonary function, and respiratory muscle fatigue, was compared with that of a low resistance breathing valve (LRV). Further, the effect of unloading the respiratory muscles with heliox with the SCBA (BA-H) was compared with BA-A and LRV. Twelve men completed three randomized exercise trials on separate days, each consisting of three 10 min bouts of stepping exercise (Bouts 1, 2, and 3) separated by a 5 min recovery. Subjects wore firefighter protective equipment including the SCBA. At rest, FEV(1) and peak expiratory flow rates were lower with BA-A than with LRV, but were higher with BA-H than either with BA-A or LRV. After Bout 3, expiratory reserve volume, expiratory resistive WOB, and inspiratory elastic WOB were increased in BA-A compared to LRV but these were lower with BA-H compared to BA-A. After Bout 3, maximal inspiratory and expiratory pressures were reduced with BA-A, but not with LRV or BA-H. In summary, we found that the SCBA reduced resting pulmonary function, and increased expiratory reserve volume, work of breathing, and respiratory muscle fatigue during stepping exercise, and these changes can be reduced with the use of heliox.