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Combined physiological effects of bronchodilators and hyperoxia on exertional dyspnoea in normoxic COPD

2006; BMJ; Volume: 61; Issue: 7 Linguagem: Inglês

10.1136/thx.2005.053470

1468-3296

Michael Peters,

Cardiovascular and exercise physiology

Background: Studies examining the physiological interactions of oxygen (O 2 ) and bronchodilators (BD) during exercise in chronic obstructive pulmonary disease (COPD) should provide new insights into mechanisms of exercise intolerance. We examined the effects of O 2 and BD, alone and in combination, on dyspnoea, ventilation (V̇e), breathing pattern, operating lung volumes, and exercise endurance. Methods: In a randomised, double blind, crossover study, 16 patients with COPD (mean (SE) FEV 1 43(3)% predicted) performed pulmonary function tests and an incremental exercise test, then completed four visits in which they received either nebulised BD (ipratropium 0.5 mg + salbutamol 2.5 mg) or placebo (PL) with either 50% O 2 or room air (RA). After 90–105 minutes the patients performed pulmonary function tests, then breathed RA or O 2 during symptom limited constant load exercise at 75% peak work rate. Results: With BD the mean (SE) increase in inspiratory capacity (IC) was 0.3 (0.1) l (p<0.05) at rest and during exercise, permitting greater tidal volume (Vt) expansion during exercise and a greater peak V̇e. With O 2 , V̇e decreased during exercise as a result of decreased breathing frequency ( F ), with no significant change in IC. During exercise with BD+O 2 , IC and Vt increased, F decreased, and V̇e did not change. Dyspnoea decreased with all interventions at a standardised time during exercise compared with PL+RA (p<0.05). Endurance time was significantly (p<0.05) greater with BD+O 2 (10.4 (1.6) min) than with O 2 (8.5 (1.4) min), BD (7.1 (1.3) min) and PL+RA (5.4 (0.9) min). Conclusion: By combining the benefits of BD (reduced hyperinflation) and O 2 (reduced ventilatory drive), additive effects on exercise endurance were observed in patients with normoxic COPD.