Interspecies comparison of heat and mass transfer characteristics in monkey and human nasal cavities

Air conditioning in the nasal airways plays an important role in regulating ambient atmospheric temperature and humidity conditions of the inhaled air. Inevitably, it may alter the behaviour and fate of inhaled ambient aerosols within the human respiratory airways due to hygroscopic growth and droplet evaporation, which is a phenomena of variations in particle sizes due to physical and chemical reactions on particle surfaces in different temperature and humidity fields. Although laboratory animals have been widely used to predict health effects of human exposure to ambient substances, the nasal temperature and humidity responses in animal surrogates and human nasal cavities are still less-investigated. This paper provides a comparative study between two monkey and two human nasal subjects under the same ambient temperature and humidity conditions, where nasal models were reconstructed from CT images and the heat and mass transfer process incorporating with the intricate nose anatomy were modelled by the computational fluid dynamics (CFD) approach. Present model comparison revealed that the monkey nasal models can reach equilibrium temperature and moisture state for inhaled ambient air in a much shorter distance compared to the human models. This indicate that heat transfer in the monkey models is more effective compared to the human models due to having a higher complexity coefficient and a smaller hydraulic radius. Hence, in order to achieve comparable or similar inhalation exposure patterns in animal surrogates, corresponding adjustments such as changing the size of released particles, or the inhalation flow rates, to achieve comparable particle Stokes number are needed. The outcomes of this study would provide informative insights for future inhalation toxicology studies related to hygroscopic materials and targeted drug delivery through nasal airways.