In patients with
chronic obstructive pulmonary disease (
COPD), one of the proposed mechanisms for improving exercise tolerance, when work of breathing is experimentally reduced, is redistribution of blood flow from the respiratory to locomotor muscles. Accordingly, we investigated whether exercise capacity is improved on the basis of blood flow redistribution during exercise while subjects are breathing
heliox (designed to primarily reduce the mechanical work of breathing) and during exercise with
oxygen supplementation (designed to primarily enhance systemic
oxygen delivery but also to reduce mechanical work of breathing). Intercostal, abdominal, and vastus lateralis muscle perfusion were simultaneously measured in 10 patients with
COPD (forced expiratory volume in 1 s: 46 ± 12% predicted) by near-infrared spectroscopy using
indocyanine green dye. Measurements were performed during constant-load exercise at 75% of peak capacity to exhaustion while subjects breathed room air and, then at the same workload, breathed either normoxic
heliox (
helium 79% and
oxygen 21%) or 100%
oxygen, the latter two in balanced order. Times to exhaustion while breathing
heliox and
oxygen did not differ (659 ± 42 s with
heliox and 696 ± 48 s with 100% O2), but both exceeded that on room air (406 ± 36 s, P < 0.001). At exhaustion, intercostal and abdominal muscle blood flow during
heliox (9.5 ± 0.6 and 8.0 ± 0.7 ml · min(-1)·100 g(-1), respectively) was greater compared with room air (6.8 ± 0.5 and 6.0 ± 0.5 ml·min(-1)·100 g·, respectively; P < 0.05), whereas neither intercostal nor abdominal muscle blood flow differed between
oxygen and air breathing. Quadriceps muscle blood flow was also greater with
heliox compared with room air (30.2 ± 4.1 vs. 25.4 ± 2.9 ml·min(-1)·100 g(-1); P < 0.01) but did not differ between air and
oxygen breathing. Although our findings confirm that reducing the burden on respiration by
heliox or
oxygen breathing prolongs time to exhaustion (at 75% of maximal capacity) in patients with
COPD, they do not support the hypothesis that redistribution of blood flow from the respiratory to locomotor muscles is the explanation.