Particles in the lungs of patients with chronic bronchitis—part 1: deposition modeling

Robert Sturm


Background: Chronic bronchitis represents a lung disease which is characterized by a non-reversible reduction of the airway calibers and, as a consequence of that, by a continuous widening of the terminal lung structures. In the present contribution the behavior of inhaled particles in bronchitis lungs is submitted to a detailed theoretical investigation, thereby using a well-validated deposition model.
Methods: Any changes of the bronchial airway architecture and alveolar region were modeled by application of well-defined scaling procedures, where random reductions of tubular and spherical diameters are considered. Transport and deposition of particles were simulated by using a random-walk approach including the Monte Carlo method. For the computation of random particle paths a stochastic lung architecture was assumed. Particle deposition was modeled with the help of empirical and analytical formulae describing the physical mechanisms exerting on the particulate substances. Simulations were carried out for male adult lungs and two different breathing conditions.
Results: With regard to submicron particles differences of total deposition between bronchitis patients and healthy controls range from 5% to 10%. In the case of particles exceeding a size of 1 µm these discrepancies may be increased to 20%. For most particle sizes chronic bronchitis results in a significant enhancement of tubular (= bronchial + ductal) and alveolar deposition. A change of the breathing conditions from sitting inhalation to light-work inhalation has only minor consequences for total and regional deposition, whereby small particles (<100 nm) are increasingly accumulated in the alveolar compartment.
Conclusions: Based on the theoretical results presented in this study it may be concluded that particle deposition is remarkably increased in bronchitis patients with respect to healthy controls. Detailed knowledge of these modifications may be regarded as essential basis for the optimization of inhalation therapies, where high amounts of inhaled aerosol particles have to be delivered to respective target regions.