Stochastic simulation of alveolar particle deposition in lungs affected by different types of emphysema

In the present study, disease-specific stochastic models were developed for the computation of particle deposition in lungs affected by COPD, emphysema, or both, distinguishing between four types of pulmonary emphysema-centriacinar, paraseptal, panacinar, and bullous. To simulate COPD, airway calibers of the tracheobronchial tree were randomly reduced between 20% and 50% in each airway. For the study of pure COPD ("blue bloaters"), alveolated airway dimensions of the healthy lung were used, while for the simulation of emphysema without COPD ("pink puffers"), normal conductive airway diameters were assumed. Deposition calculations in diseased lungs were carried out by assuming (a) identical inspiration and expiration times (no breath-hold time) and (b) a continuous increase of the functional residual capacity (from 3,300 to 5,000 mL), accompanied by a simultaneous drop of the tidal volume (from 1,000 to 500 mL). Independent of particle size, total alveolar deposition in emphysematous lungs was significantly decreased relative to normal lungs. In particular, the deposition maximum at large particle sizes, which is a characteristic for healthy subjects, completely disappeared. Among the various emphysema models, deposition was smallest in lungs with bullous emphysema due to strongly enhanced settling and diffusion distances within the alveolar structures. A change of the lung volume caused a further decrease in particle deposition. Alveolar deposition in "blue bloaters" and "pink puffers" was very similar to the deposition in patients suffering from COPD and emphysema. Alveolar deposition per acinar airway generation was also strongly reduced in diseased lungs compared to normal lungs. Besides this reduction, deposition patterns became more uniform throughout the alveolar region.