title: Contrasting pressure-support ventilation and helium-oxygen during exercise in severe COPD.
abstract: 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.
authors.affiliation: Edward Hines, Jr Veterans Affairs Hospital, 111N, 5th Avenue and Roosevelt Road, Hines, IL 60141, USA.
authors.forename: Omar
authors.initials: O
authors.lastname: Hussain
authors.forename: Eileen G
authors.initials: EG
authors.lastname: Collins
authors.forename: Nalan
authors.initials: N
authors.lastname: Adiguzel
authors.forename: W Edwin
authors.initials: WE
authors.lastname: Langbein
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Tobin
authors.forename: Franco
authors.initials: F
authors.lastname: Laghi
mesh_terms: D000704:Analysis of Variance; D005081:Exercise Therapy / Q000379:methods*; D017079:Exercise Tolerance / Q000187:drug effects / Q000502:physiology*; D005260:Female; D006371:Helium / Q000008:administration & dosage* / Q000494:pharmacology; D006801:Humans; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000008:administration & dosage* / Q000494:pharmacology; D010102:Oxygen Inhalation Therapy / Q000379:methods; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology* / Q000534:rehabilitation
chemical_list: D006371:Helium; D010100:Oxygen