Aeroacoustics of breath sounds in trachea and upper airway

Tracheal breathing sounds (TBS) are widely used in assessing respiratory disorders such as obstructive sleep apnea but a mechanistic relationship between airway morphology and aero-acoustics remains undefined. Here we use a realistic upper airway model reconstructed from a human CT scan to investigate aerodynamic and acoustic effects of velopharyngeal constriction on TBS. A hybrid aero-acoustic modeling approach was employed, combining computational fluid dynamics (CFD) with acoustic finite element simulation. The model was validated against recorded TBS and showed strong agreement in both amplitude and resonant frequencies. Simulation of four graded degrees of velopharyngeal constriction demonstrated a significant influence of geometric narrowing on airflow dynamics. Specifically, the pressure drop across the velopharyngeal segment (ΔP_velopharynx) followed a power law relationship with the percent area change (ΔA_velopharynx) with an exponent of 4.93 (R² = 0.998). Similarly, the dimensionless pressure coefficient (C_p) exhibited a strong correlation with (ΔA_velopharynx), with a power law exponent of 1.47 (R² = 0.999). Wall shear stress (WSS) at the velopharyngeal area increased dramatically with constriction severity, increasing 15-fold from 0.8 Pa to 12 Pa in the most severe case. These aerodynamic changes were closely linked to acoustic responses, leading to upward shifts in resonant frequencies within the [1000–1700] Hz range as the velopharyngeal area increased. These findings indicate a strong relationship between airway geometry and acoustic response, thus suggesting that TBS could be a valuable tool for quantitative non-invasive assessment of the upper airway in healthy and obstructive sleep apnea populations.