Multimodality measurements of small airways disease.

S mall airways disease has long been recognised as being physiologically important in obstructive lung diseases, particularly in chronic obstructive pulmonary disease (COPD) [1]. The study of COSIO et al. [2], in which the severity of small airway inflammation and remodelling in smokers correlated with airway closure and ventilation maldistribution, as measured by single breath washout tests, is a landmark one because it linked small airways tests with pathology. Furthermore, these parameters of small airway function were more sensitive than spirometry for the presence of small airways disease. Results of more recent studies, in which small airway function was measured by the newer multiple breath nitrogen washout, showed that small airway function becomes abnormal after only 10 pack-yrs smoking, whereas spirometry becomes abnormal after 20 pack-yrs [3]. In asthma, however, the function of the small airways has been studied much less, perhaps due to the paucity of resected lung specimens on which correlations can be made between measurements of small airway function and pathology. The disease-related changes to the structural components of the airways in asthma involve both small and large airways [4]. These pathological changes, often referred to as remodelling, lead to thickening of the walls of the small airways. This is a feature that seems particularly characteristic of asthma as opposed to COPD [5].