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 (e), 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 e. With O(2), 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 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+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).


CONCLUSIONS
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.
Peters
M M
MM
Department of Medicine, Respiratory Investigation Unit, Queen's University, Kingston, Ontario, Canada.
Webb
K A
KA
O'Donnell
D E
DE
D001993:Bronchodilator Agents / Q000627:therapeutic use*; D003131:Combined Modality Therapy / Q000379:methods; D018592:Cross-Over Studies; D004311:Double-Blind Method; D004417:Dyspnea / Q000503:physiopathology / Q000628:therapy*; D005081:Exercise Therapy / Q000379:methods; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000627:therapeutic use*; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology / Q000628:therapy*; D012129:Respiratory Function Tests; D016896:Treatment Outcome
D001993:Bronchodilator Agents; D010100:Oxygen