Thermogenic effect of bronchodilators in patients with chronic obstructive pulmonary disease

Background - Patients with chronic obstructive pulmonary disease (COPD) are frequently malnourished and have increased resting energy expenditure (REE). An increase in the work of breathing is generally considered to be the main cause of this hypermetabolism, but other factors may also be implicated. Bronchodilators may decrease the work of breathing by reducing airway obstruction, but beta(2) adrenergic agents have a thermogenic effect. The aim of this study was to determine the effect of salbutamol and ipratropium bromide administration on REE in patients with COPD. Methods - Thirteen patients (10 men) of mean (SD) age 68.3 (7.3) years and forced expiratory volume in one second (FEV(1)) 39.0 (17.0)% predicted were studied on three consecutive days. The REE was measured by indirect calorimetry at 30, 60, 120, and 180 minutes after double blind nebulisation of either salbutamol, ipratropium bromide, or placebo in random order. Results - FEV(1) increased both after salbutamol and after ipratropium. The difference in the mean response between salbutamol and placebo over 180 minutes was + 199 ml (95% CI + 104 to + 295). The difference in mean response between ipratropium and placebo was + 78 ml (95% CI + 2 to + 160). REE increased after salbutamol but was not changed after ipratropium. The difference in mean response between salbutamol and placebo was + 4.8% of baseline REE (95% CI + 2.2 to + 7.4). Heart rate increased after salbutamol but not after ipratropium. The difference in the mean response between salbutamol and placebo was + 5.5 beats/min (95% CI + 2.6 to + 8.4). Conclusion - Salbutamol, but not ipratropium bromide, induces a sustained increase in the REE of patients with COPD despite a reduction in airway obstruction.