CHRONIC OBSTRUCTIVE PULMONARY DISEASE

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

M M Peters, K A Webb, D E O’Donnell

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

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 (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% 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 E. With O₂, E 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 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+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.

Abbreviations: 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; CO₂, carbon dioxide output; E, minute ventilation; O₂, oxygen consumption; VT, total volume

Keywords: chronic obstructive pulmonary disease; bronchodilators; oxygen; exercise; dyspnoea; lung hyperinflation

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