Article Abstract

Deposition of diesel exhaust particles in the human lungs: theoretical simulations and experimental data

Authors: Robert Sturm


Background: Based on numerous experimental and epidemiological studies diesel exhaust particles (DEPs) have been evaluated as serious health hazards, whose uptake by inhalation causes an increase of the relative risk for lung cancer. Due to this circumstance, experimental and theoretical knowledge on the transport and deposition behaviour of such particles in the respiratory tract has to be permanently improved. Here, respective support is provided by models predicting aggregate shape and transport with high accuracy.
Methods: Aggregate shape was modeled by using the computer program AGGREGATE, where respective particles are constructed from equally sized spherules by application of the random walk concept. Intrapulmonary transport and deposition of the particulate mass were simulated for a stochastic lung architecture and under the assumption of mathematically describable deposition mechanisms (Brownian motion, inertial impaction, interception, gravitational settling). Computations were conducted for particles ranging in size from 50 to 250 nm. In addition, three different breathing scenarios (sitting, light exercise, heavy exercise) were considered.
Results: According to the results of the deposition computations theoretically constructed DEP aggregates exhibit decreasing total and regional deposition with growing particle diameter. Depending on aggregate size and breathing conditions, total deposition ranges from 15.7% to 71.5%, whereas tubular deposition adopts values between 10.1% and 35.2%. Alveolar deposition may be quantified with 4.7% to 27.0%. Except for alveolar accumulation of aggregates ≤100 nm, deposition of DEPs negatively correlates with breathing intensity. Local deposition of such aggregates is commonly characterized by the development of respective modes in airway generations 20 to 22.
Conclusions: The present study leads to the conclusion that DEPs may bear the potential for an increased deposition in those lung regions, which are highly susceptible for the development of lung cancer. Thereby, the amount of particulate mass accumulated in airways and alveoli depends on both particle size and the intensity of particle uptake by inhalation.