Theoretical deposition of diesel exhaust particles in the respiratory tract of children

Robert Sturm


Background: According to a multitude of scientific investigations diesel exhaust particles (DEP) have to be regarded as serious health hazards. After their uptake from the ambient air by inhalation, they may act as triggers for various pulmonary diseases, among which lung cancer deserves special reference. Until now, deposition scenarios of DEP in the respiratory tract have been mainly studied for adults, although children with different ages are also exposed to these airborne substances to a certain extent. In the present study, DEP deposition in children’s lungs was subjected to a comprehensive theoretical approach.
Methods: Geometry of DEP, which occur as complex particulate aggregates, was approximated by means of the computer program AGGREGATE. Here, single particulate objects are constructed by using equally sized spherules as basic elements that are arranged according to a random walk algorithm. Children’s lungs were assigned to two different age categories (5 y, 10 y), whereby size of the respiratory systems was determined by application of well validated airway scaling procedures. Intrapulmonary transport and deposition of DEP (size: 100–250 nm) was simulated by assuming (I) a stochastic lung architecture, (II) four mathematically describable deposition mechanisms and (III) two different breathing scenarios.
Results: Within both age categories, total and regional deposition of DEP is characterized by a remarkable decrease with rising aggregate size. Under sitting breathing conditions total deposition ranges from 24.1% to 41.5% in 5-year-old children and from 16.6% to 29.5% in 10-year-old children. Tubular and alveolar depositions adopt values of 13.6–24.8% and 3.5–5.6% (5 y) as well as 14.3–25.4% and 4.7–8.7% (10 y). Any increase of breathing intensity results in a decline of deposition per breath-cycle. Airway-specific deposition of DEP is commonly marked by the development of modes in airway generations 19 to 21.
Conclusions: The theoretical results presented in this study lead to the conclusion that also in children of different age mainly those lung sites being highly susceptible for diverse pulmonary diseases are targeted by DEP. Thereby, the amount of particulate mass accumulated in single pulmonary compartments mainly depends on aggregate size and breathing intensity.