Effect of heliox on lung dynamic hyperinflation, dyspnea, and exercise endurance capacity in COPD patients.

We tested the hypothesis that heliox breathing, by reducing lung dynamic hyperinflation (DH) and dyspnea (Dys) sensation, may significantly improve exercise endurance capacity in patients with chronic obstructive pulmonary disease [n = 12, forced expiratory volume in 1 s = 1.15 (SD 0.32) liters]. Each subject underwent two cycle ergometer high-intensity constant work rate exercises to exhaustion, one on room air and one on heliox (79% He-21% O2). Minute ventilation (VE), carbon dioxide output, heart rate, inspiratory capacity (IC), Dys, and arterial partial pressure of CO2 were measured. Exercise endurance time increased significantly with heliox [9.0 (SD 4.5) vs. 4.2 (SD 2.0) min; P < 0.001]. This was associated with a significant reduction in lung DH at isotime (Iso), as reflected by the increase in IC [1.97 (SD 0.40) vs. 1.77 (SD 0.41) liters; P < 0.001] and a decrease in Dys [6 (SD 1) vs. 8 (SD 1) score; P < 0.001]. Heliox induced a state of relative hyperventilation, as reflected by the increase in VE [38.3 (SD 7.7) vs. 35.5 (SD 8.8) l/min; P < 0.01] and VE/carbon dioxide output [36.3 (SD 6.0) vs. 33.9 (SD 5.6); P < 0.01] at peak exercise and by the reduction in arterial partial pressure of CO2 at Iso [44 (SD 6) vs. 48 (SD 6) Torr; P < 0.05] and at peak exercise [46 (SD 6) vs. 48 (SD 6) Torr; P < 0.05]. The reduction in Dys at Iso correlated significantly (R = -0.75; P < 0.01) with the increase in IC induced by heliox. The increment induced by heliox in exercise endurance time correlated significantly with resting increment in resting forced expiratory in 1 s (R = 0.88; P < 0.01), increase in IC at Iso (R = 0.70; P < 0.02), and reduction in Dys at Iso (R = -0.71; P < 0.01). In chronic obstructive pulmonary disease, heliox breathing improves high-intensity exercise endurance capacity by increasing maximal ventilatory capacity and by reducing lung DH and Dys.