Investigations on the respiratory transport and deposition of airborne asbestos, man-made vitreous fibers (MMVFs), and carbon nanofiber/carbon nanotubes have been actively conducted in the past few decades. The elongated particles’ distinctive needle-like geometry has been identified as the main cause of extreme carcinogenicity when compared to inhaled spherical particles. Consequently, uncovering the intrinsic relationship between the particle’s unique elongated shape and its transport characteristics in human respiratory systems is crucial for understanding fiber inhalation toxicity. Currently, such information can only be provided by computational modeling. This review summarized the current state of the art of computational modeling of fiber transport in the human respiratory tract. The needed future researches were also discussed.

Exposure to ambient air pollution presents great adverse health risks to respiratory health, and assessing the respiratory exposure doses, especially in the human deep lung regions, remains difficult due to the sheer complexity of the process. To bridge this gap, an extended large-to-small conducting lung airway model was adopted in this study, which includes a broad scope containing bronchial airways up to the 15th generation. Accumulation mode particles in the size range of 100 nm to 3.0 µm representing major size spectrum of coarse diesel exhaust were released at the inlet of respiratory airway model, and both airflow and particle deposition characteristics were numerically investigated. The simulation results showed that the particle deposition in the respiratory airway is sensitive to the variation of inhalation flow rates. For inhalation exposure at lower breathing rate of 18 L/min, both deposited diffusive and inertia particles were very unevenly distributed in the lower respiratory airway. For inhalation exposure at higher breathing rate of 50 L/min, deposited diffusive and inertia particles were both scattered over the lower respiratory airway. In addition, high inhalation flow rate enabled inertia particles to be deposited further downstream of the airway with deposition hot spots observed in distal airways.