Comparative modelling of inspiratory airflow and micron particle deposition patterns in monkey and human nasal airways

Laboratory animals have historically performed a vital function in evaluating health effects of human exposure to ambient particulate matter (PM). Due to the complexity of particle-laden flows and airway interactions that involve multiple species, in-depth knowledge of airflow and particle transport in both the non-human primate surrogates and human airways is still lacking. To advance the understanding in this field, this paper presents a numerical study that investigated the airflow and particle deposition characteristics of inhaled PMs in monkey and human nasal airways. Anatomically accurate macaca fuscata monkey and human nasal cavity models were reconstructed from CT images, micron particles with diameters less than 10 mu m were included to conduct in silico exposure studies. Resultant particle deposition patterns were quantified by deposition enhancement factor (DEF) and deposition intensity (DI) along the airways to provide profound understanding of the similarities and differences in particle inhalation exposure characteristics across species. Anatomy comparison showed that the convoluted nasal passage of the monkey airway possessed higher level of complexity in terms of the surface-area-to-volume ratio compared to the two human nasal models, which could lead to higher evaluated nasal exposure to airborne particulate matter. Similar airflow patterns were observed from streamlines and wall shear stress distributions in all three nasal cavities of two species, with bulk air concentrated mainly in the middle and inferior meatuses in the nasal chambers. Despite the evidenced intersubject deposition variations presented in all considered nasal cavity models, strong and similar micron particle deposition preferences with comparable DEF and DI levels were observed along the floor region of middle and inferior meatuses for both species. The methods and research findings presented in this work represent critical, initial steps towards establishing high-fidelity qualitative and quantitative linkages between the two species that enable more effective laboratory data extrapolations, improve study design, and facilitate validations of in vitro techniques currently being developed as part of international efforts to reduce or replace the use of animals in toxicity assessments for aerosol exposures.