Imaging of ventilation in chronic obstructive pulmonary disease.

Patterns of radioaerosol deposition in patients with COPD may be interpreted on the basis of derangements in convective ventilation. Thus, in patients with asthma, central deposition is consistently associated with increased airway resistance, in the absence of acute attack, indicating that in this condition major airways are usually the site of bronchial constriction. In patients with chronic bronchitis, inhomogeneous and spotty deposition patterns are strongly associated with indexes of uneven and wasted ventilation and may be explained on the basis of destruction or obstruction of peripheral airways. Spotty deposition is ascribed to very uneven convective ventilation reduced to a limited number of air streams, as opposed to the normal situation of a very high number of air streams giving rise to the uniform pattern of radioaerosol deposition. Patients with emphysema show less distinctive patterns of deposition and may resemble those of the patients with asthma and chronic bronchitis. Nevertheless, the deposition features are very useful to better characterize the patient even in the emphysematous group. From the practical point of view, the features of aerosol deposition provide useful information for evaluation and treatment of the patient with COPD. They may also prove useful to better define and characterize the different disease entities grouped as COPD.