A Proof-of-Concept CFD Study of Intranasal Airflow Under Different Breathing Routes and Airway Collapse Conditions

Obstructive sleep apnea (OSA) is closely associated with nasal obstruction, breathing route, and upper-airway collapsibility, yet how changes in breathing route interact with airway collapse to redistribute aerodynamic loading remains incompletely understood. This proof-of-concept study developed a patient-specific computational fluid dynamics (CFD) framework to compare nasal and oronasal breathing under baseline and simulated collapsed upper-airway conditions. Airflow velocity, regional pressure drop, and wall shear stress (WSS) were evaluated across the nasal cavity and downstream pharyngeal regions. Switching from nasal to oronasal breathing consistently reduced intranasal airflow velocity and nasal pressure drop under both airway conditions. Oronasal breathing reduced the cycle-maximum local WSS within the nasal cavity by approximately 42–45%, with reductions exceeding 50% across most turbinate regions. In contrast, the pressure response was strongly region-dependent: oronasal breathing reduced pressure loss across the nasal cavity and uvular region but increased pressure drop at the tongue root. Airway collapse produced a more localized aerodynamic response, most notably increasing posterior nasal velocity and markedly increasing the pressure drop across the uvular region during nasal breathing. These findings indicate that breathing-route alteration and airway collapse do not uniformly increase or decrease upper-airway aerodynamic loading; instead, they redistribute airflow and pressure losses among different anatomical regions. Although based on a single patient-specific model, the proposed CFD framework demonstrates the feasibility of quantifying breathing-route-dependent nose–pharynx aerodynamic interactions and provides a methodological basis for future patient-specific and cohort-based investigations of OSA.