Quantification of inhaled cigarette smoke movement and deposition in human nasal airways

Background: There are nearly one billion smokers worldwide, and cigarette smoke is not only a physical and chemical damage factor but also an allergen. Due to technical and ethical barriers, few studies have quantitatively measured the deposition of cigarette particles on the nasal mucous membranes of humans or animals. 

Methods: CT data of nine healthy adults were recruited to construct nasal airway models and conduct numerical simulation using Computational Fluid Particle Dynamics (CFPD) approach. Deposition fractions in each nasal regions under different breathing conditions were analyzed, and the transport process of cigarette particles from the initial releasing locations at the nostrils to the final deposited sites were traced.

Results: 1) For sub-micron particles like cigarette smoke, their deposition due to the nasal filtration function in nasal airways is very limited, about 3.45% of the particles are deposited in the nasal cavity under the rest inhalation condition, with the majority being inhaled into the downstream airways. 2) Increased particle collision and deposition were observed in the nasal airway under intense inhalation condition. 3) Cigarette particles deposited in the paranasal sinuses and the olfactory region were inhaled from the inner superior corner of the nostrils (covering 1/3 or even 1/2 of the nostril plane). In contrast, particles deposited in other nasal regions showed no clear release pattern, as the initial inhaled locations were more dispersed across the nostrils. 

Conclusion: This study advances the current understanding of secondhand smoke exposure characteristics in human nasal passages. (1) The vast majority of cigarette smoke particles go straight into the downstream airways. (2) Smoke particles deposition pattern in the nasal airway was widespread and evenly distributed, and those deposited in the paranasal sinuses and the olfactory region were inhaled from the inner superior corner of the nostrils. (3) This study highlighted the damage caused by the secondhand smoke, emphasized the need for strengthened smoke management and education, and suggested the implement of proactive allergen protection measures under smoke exposure scenarios.