Combined physiological effects of bronchodilators and hyperoxia on exertional dyspnoea in normoxic COPD
- Respiratory Investigation Unit, Department of Medicine, Queen’s University, Kingston, Ontario, Canada
- Correspondence to:
Dr D E O’Donnell
102 Stuart Street, Kingston, Ontario K7L 2V6, Canada; odonnell{at}post.queensu.ca
- Received 30 September 2005
- Accepted 19 January 2006
- Published Online First 7 February 2006
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 (p<0.05) at rest and during exercise, permitting greater tidal volume (Vt) expansion during exercise and a greater peak V̇e. With O2, 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 (p<0.05). Endurance time was significantly (p<0.05) greater with BD+O2 (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.
- BD, bronchodilator
- COPD, chronic obstructive pulmonary disease
- EELV, end expiratory lung volume
- EILV, end inspiratory lung volume
- F, breathing frequency
- FEV1, forced expired volume in 1 second
- FRC, functional residual capacity
- FVC, forced vital capacity
- IC, inspiratory capacity
- IRV, inspiratory reserve volume
- O2, oxygen
- Paco2, arterial carbon dioxide tension
- Pimax, maximal inspiratory pressure
- PEFR, peak expiratory flow rate
- PL, placebo
- RA, room air
- RV, residual volume
- Sao2, oxygen saturation
- Ti, Te, inspiratory and expiratory time
- TLC, total lung capacity
- Tlco, lung carbon monoxide transfer factor
- V̇co2, carbon dioxide output
- V̇e, minute ventilation
- V̇o2, oxygen consumption
- Vt, total volume
Footnotes
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Published Online First 7 February 2006
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This study was supported by the Ontario Ministry of Health, Ontario Thoracic Society, and the William M Spear Endowment Fund, Queen’s University.
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Competing interests: none.
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Presented in part at the ALA/ATS International Conference, San Diego, May 2005 ( Peters MM, Webb KA, O’Donnell DE. The effects of supplemental oxygen and bronchodilators on exertional dyspnea and exercise performance in patients with COPD. Am J Respir Crit Care Med2005;:).
