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

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Abstract
Background: Studies examining the physiological interactions of oxygen (O2) 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 O2 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) FEV1 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% O2 or room air (RA). After 90–105 minutes the patients performed pulmonary function tests, then breathed RA or O2 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 (p2, V̇e decreased during exercise as a result of decreased breathing frequency (F), with no significant change in IC. During exercise with BD+O2, 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 (p2 (10.4 (1.6) min) than with O2 (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 O2 (reduced ventilatory drive), additive effects on exercise endurance were observed in patients with normoxic COPD.

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