Effects of Head Posture on Inhaled Particle Deposition and Upper-Airway Penetration

Targeted drug delivery in the respiratory tract must overcome inertial impaction at the oropharyngeal bend which typically captures the majority of inhaled particles before they reach the larynx or lungs. We investigated whether head posture can be used to control that impaction by altering upper-airway curvature. Four head postures of a simplified airway (flexion at 30°, neutral (0°), and extension at 30° and 60°) were simulated at inhalation flow rates of 10 L min−1 (laminar) and 30 L min−1 (k− ω SST turbulence), with particle trajectories tracked across aerodynamic diameters from 3 μm to 29 μm. The Dean number at the bend decreased from 1608 in flexion to 835 at 60° extension at 30 L min−1. Regional particle deposition followed bend curvature rather than the head tilt angle. As the bend opened with extension, preferential deposition sites shifted 50 mm downstream toward the glottis. Total airway deposition varied with posture, peaking at 30° extension and reducing at 60° extension, where over 40% of coarse particles exited through the tracheal outlet. The posture-specific maximum in laryngeal deposition, each attained at its own optimal particle size, was highest at 30° extension and 30 L min−1 (26% at 9 μm), compared with 16% at 11 μm for the neutral posture and 11% at 13 μm in flexion. Head extension could therefore roughly double laryngeal drug delivery relative to neutral posture when paired with appropriate particle sizes, while extreme extension straightens the airway and allows a larger fraction of the inhaled dose to penetrate beyond the upper airway toward the lungs.