Effects of Beta-Agonists on Breathlessness and Exercise Tolerance in Patients with Chronic Obstructive Pulmonary Disease

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Abstract
In a single-blind placebo-controlled trial in 12 patients with advanced chronic obstructive pulmonary disease (COPD) we compared the effects of nebulized sulbutamol (1 mg), clenbuterol (30 .mu.g) and placebo (4 ml of normal saline) on spirometric indices (FVC, FEV1), maximal expiratory flows (.ovrhdot.Vmax 50) and .ovrhdot.Vmax 25), the distance walked in 6 min (6 MD), assessment of breathlessness by visual analogue scale (VAS), and estimates by the patients of perceived exertion (RPE). Both clenbuterol and salbutamol produced significant increases in FEV1, FVC, .ovrhdot.Vmax 50 and .ovrhdot.Vmax 25. With both drugs, 6MD increased significantly (p < 0.01) and breathlessness decreased significantly without an appreciable increase in RPE after exercise despite the extra distance covered. The absolute improvements in FEV1 and 6MD after clenbuterol were correlated (r = 0.763, p < 0.01), but these indices were not correlated after salbutamol (r = 0.121, p > 0.1). The lack of correlation between the changes in 6MD and FEV1 after sulbutamol might indicate that relief of airways obstruction is not the only explanation for the effects on distance walked, at least with salbutamol.