Numerical comparison of inspiratory airflow patterns in human nasal cavities with distinct age differences

As a primary determinant of nasal physiological functions, the nasal morphology and its effects on the airflow dynamics have been extensively studied in literature. However, gross flow features reported in literature are mostly obtained from subjects at similar ages, while studies focusing on nasal subjects with distinct age differences are significantly less. To advance current understandings of nasal airflow dynamics in the context of age diversity, this study employed three anatomically accurate nasal cavity models with distinct age features (5-, 24- and 77-year-old models) and numerically compared the physiological nasal airflow fields within these nasal cavity models. To demonstrate the validity of the present numerical models, in vivo rhinomanometry measurement was conducted on the 24-year-old female nasal model, and key anatomical features and pressure-flow curves of all three models were compared with models with similar age features in literature work. Apart from results comparison based on conventional velocity flow fields and wall shear stress distributions, a method for quantifying flow partitions in confined airway spaces was developed to reveal the proportions of fractional flow that enters the olfactory region. Our results revealed dramatic intersubject discrepancies between considered nasal cavity models, especially for the fractional flow that enters the olfactory region. Specifically, the 5-year-old girl nasal model received the highest proportion of fractional flow, which accounts for 13.3% ~ 15% of overall inhalation flow rates under different activity levels. For the 24-year-old female model, on the contrary, the olfactory fractional flow was dramatically reduced (with a local to overall percentage around 4.3%-7.7%). Finally, for the elderly subject-77-year-old male model, minimum level of olfactory flux was observed with a local to overall percentage ranging between 3.1% and 4.9% for considered wide range of inhalation flow rates. Therefore, the local flow intersubject variation can reach nearly fourfold. The vast local flow difference is mainly due to the inherent anatomical features (e.g., immature nasal turbinate structure in the child model, the partial narrowing superior nasal valve in the elder model). The results may further lead to discrepant health effects associated with inhalation exposure to airborne particles.