Targeting small airways, a step further in asthma management

During the last decade, small airway (SA) involvement in asthma and Chronic Obstructive Pulmonary Disease (COPD) have reached increasing attention. Originally referred to as the 'silent zone', SA may not be that silent after all. Important clinical correlates are asthma exacerbations and airways remodelling, exercise asthma and nocturnal asthma. Thus, to control pathology in the SA has become a desirable goal in asthma management.

The scope of this review is to give a brief overview of the current status on SA in asthma, how to monitor and to diagnose SA inflammation and finally highlight some important treatment strategies.

New tools have been developed to monitor SA function; these implies the use of imaging techniques and respiratory physiology, targeting SA function. Fractional exhaled nitric oxide and the combined use of hyperresponsiveness testing with impulsoscillometry is another option. The introduction of ultrafine aerosols has provided new tools for to treat SA inflammation. The challenge for the future will be to define the optimal particle size and device for maximal deposition in entire lung, including the small airways. Moreover, we also need strategies for increasing the therapeutic ratio, i.e. increasing lung deposition without increasing systemic side effects. Another challenge is to design and to perform clinical trials, targeting effects in SA, proving the clinical importance of SA treatment in a large number of patients. The latter also imply education of our medical authorities, communicating that asthma is more than a beta-2 agonist responsive central airway disorder of the lungs.