Small airway dysfunction is associated with poorer asthma control.

The clinical relevance of the small airways in persistent asthma has been gaining greater recognition in recent years [1]. Studies have shown that a significant proportion of asthmatics on standard treatment fail to achieve satisfactory asthma control. For example, in one study of 3421 asthmatic subjects who underwent guideline-driven dose titration with standard inhaled corticosteroids (ICS)/long-acting b-agonist (LABA) combination therapy over 1 year, only 41% achieved total control of their asthma while 71% were well controlled [2]. ANDERSON et al. [3] found a high prevalence of adult patients with persistent small airway dysfunction determined by impulse oscillometry (IOS) (assessed as the difference between the resistance at 5 Hz (R5) and that at 20 Hz oscillation (R20)) and spirometry (assessed as the forced expiratory flow at 25–75% of forced vital capacity (FEF25–75%)) across British Thoracic Society (BTS) treatment steps for asthma, many of whom had a preserved forced expiratory volume in 1 s (FEV1). This, in turn, suggests an unmet clinical need in terms of patients who may have a small airway asthma phenotype.