It has been suggested that the pathophysiology of chronic obstructive pulmonary disease is characterized by a centrally mediated increase in cholinergic tone. β-Agonists act by binding to adrenergic receptors, which stimulate bronchodilation through the mediation of the cyclic AMP (cAMP) second messenger system. Theophylline is postulated to stimulate bronchodilation by inhibiting phosphodiesterase and adenosine. Phosphodiesterase inhibition prolongs the actions of cAMP and results in bronchodilation. Inhaled long-acting anticholinergics work by antagonizing the actions of acetylcholine, producing relaxation of airway smooth muscle.