Helium-
oxygen mixtures and pressure-support ventilation have been used to unload the respiratory muscles and increase exercise tolerance in
COPD. Considering the different characteristics of these techniques, we hypothesized that
helium-
oxygen would be more effective in reducing exercise-induced dynamic hyperinflation than pressure-support. We also hypothesized that patients would experience greater increases in respiratory rate and minute ventilation with
helium-
oxygen than with pressure-support. The hypotheses were tested in ten patients with severe
COPD (FEV(1) = 28 ± 3% predicted [mean ± SE]) during constant-load cycling (80% maximal workrate) while breathing 30%
oxygen-alone,
helium-
oxygen, and pressure-support in randomized order. As hypothesized,
helium-
oxygen had greater impact on dynamic hyperinflation than did pressure-support (end-exercise; p = 0.03). For the most part of exercise, respiratory rate and minute ventilation were greater with
helium-
oxygen than with pressure-support (p ≤ 0.008). During the initial phases of exercise,
helium-
oxygen caused less rib-cage muscle recruitment than did pressure-support (p < 0.03), and after the start of exercise it caused greater reduction in inspiratory reserve volume (p ≤ 0.02). Despite these different responses,
helium-
oxygen and pressure-support caused similar increases in exercise duration (
oxygen-alone: 6.9 ± 0.8 min;
helium-
oxygen: 10.7 ± 1.4 min; pressure-support: 11.2 ± 1.6 min; p = 0.003) and similar decreases in inspiratory effort (esophageal pressure-time product), respiratory drive, pulmonary resistance,
dyspnea and leg effort (p < 0.03). In conclusion,
helium-
oxygen reduced exercise-induced dynamic hyperinflation by improving the relationship between hyperinflation and minute ventilation. In contrast, pressure-support reduced hyperinflation solely as a result of lowering ventilation.
Helium-
oxygen was more effective in reducing exercise-induced dynamic hyperinflation in severe
COPD, and was associated with greater increases in respiratory rate and minute ventilation than pressure-support.