Part III: Location of asthma inflammation and the distal airways: clinical implications.

Accumulating evidence suggests that the airway inflammation and remodeling characteristic of asthma occur not only in the central airways, but also in the distal lung and the lung parenchyma. The distal airways are increasingly being recognized as important sites of airflow obstruction. Research indicates that distal inflammation may play a crucial role in airway hyperresponsiveness, nocturnal asthma, and spontaneous exacerbations of asthma symptoms. Although the effectiveness of inhaled corticosteroids in improving asthmatic symptoms and preventing exacerbations is well established, the ability of conventional formulations to reach the distal airways is limited. The impaired ability of these formulations to reach the distal airways may contribute to the observation that inhaled corticosteroids do not always provide adequate control of asthma symptoms. Newer formulations of inhaled corticosteroids that use hydrofluoroalkane (HFA) propellants in solution have greater access to the distal airways and produce beneficial changes in lung function. Due to their highly targeted delivery systems, newer HFA-based formulations have the potential to effectively treat asthma at reduced doses.