Article Abstract

Theoretical model of clearance in the tracheobronchial airways of healthy subjects and smokers

Authors: Robert Sturm


Background: According to experimental and theoretical studies long-term inhalation of tobacco smoke is associated with serious health effects, among which impairment of tracheobronchial clearance plays an important role. The present contribution presents a theoretical model enabling a comparison of mucociliary clearance in healthy subjects with that in heavy smokers.
Methods: Clearance simulations were carried out with a multi-compartment model including all those cellular and non-cellular structures of the tracheobronchial tree that are capable for the intake and storage of deposited particulate mass. Hypothetical mass transfer between the structures was computed after definition of rate constants. Since airways of heavy smokers are characterized by significant epithelial modifications with respect to healthy structures, the related compartment model was changed in several aspects (omission of compartments and rate constants).
Results: Theoretical predictions of tracheobronchial clearance in healthy probands and smokers were restricted to spherical particles with a uniform diameter of 1 µm and a density of 1 g·cm−3. According to the model 93% of inhaled particles deposited in healthy bronchial airways are cleared within the first ten days following aerosol exposure. In this case the gastrointestinal tract represents the main accumulation site of the removed particulate mass. In heavy smokers mucociliary transport is significantly replaced by slow clearance, resulting in a removal of 36% of all particles within ten days.
Conclusions: Lung airways modified by extensive impaction of cigarette smoke particles are marked by considerable changes of their clearance behaviour with respect to healthy bronchial structures. This is mainly expressed by the circumstance that the lymphatic and vascular systems take over the role of accumulation compartments in the diseased lungs.