ABSTRACT Airflow obstruction in chronic obstructive pulmonary disease (COPD) is due to the combination of airway disease and emphysema, may be accompanied by airway reactivity, and may be partially reversible. Aerosol deposition is affected by airway geometry. Deposition patterns in COPD are increasingly abnormal as the forced expiratory volume in 1 second (FEV1) percentage deteriorates. More advanced COPD is characterized by the formation of multiple impactions in the central airways and a marked reduction in peripheral deposition. Vagal innervation is most prominent in the central airways, although beta-adrenergic receptors are more widely distributed in small airways. Anticholinergics and beta agonists are effective bronchodilators in COPD. With large doses of either ipratropium or beta agonists, most studies have demonstrated equivalent bronchodilation in stable COPD. Small, conventional doses of the two agents are additive, and large doses are not. In COPD patients with acute exacerbation, nebulized ...