Tiotropium and salmeterol have been shown to reduce airflow limitation and hyperinflation but may also directly or indirectly have an effect on various aspects of lung inflammation.21,22 However, the relevance of these mechanisms to the observed differences in the end points related to exacerbations remains to be determined.Whether the observed differences might be due to differences in the aerosolizing systems, the particle size of the aerosols, or the distribution of the drug in the lung is also unknown