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

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 (V-E), 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% 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) I (p < 0.05) at rest and during exercise, permitting greater tidal volume (V-T) expansion during exercise and a greater peak V-E. With O-2, V. E 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 V-T increased, F decreased, and V-E 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.