Airways penetration of inhaled radioaerosol: an index to small airways function?

Several reports have claimed that inhaled radioaerosol particles show diminished lung penetration in subjects with impaired small airways function. Lung penetration may be estimated from the ratio of peripheral to central deposition, from the proportion of particles retained after 24 hours, from visual classification of gamma camera images or by computer analysis of the inhomogeneity of such images. Several approaches can characterise many young symptom-free smokers, or subjects with mild asthma, as "abnormal". Yet there is no convincing evidence from review of the literature and our own work that tests based on radioaerosol deposition are superior to other "small airways tests". Studies of particle deposition are, however, vital to the use of aerosols for investigating mucociliary clearance in the small airways.