Influence of the Inhalation Route on Tracheal Flow Structures in Patient-Specific Airways using 3D PTV

TL;DR

The PTV measurements confirm that the nasal and/or oral cavity must be considered when analyzing the flow field in the lower respiratory tract, and find that the presence of both cavities significantly alters the flow field compared to idealised, fully developed inflow conditions.

Abstract

The tracheal flow field shapes particle transport into the lower airways and thus influences both the spread of inhaled pathogens and the effectiveness of aerosol-based therapies. Identifying how different inhalation routes modify the flow field is therefore crucial for understanding lower-airway disease transmission and for guiding targeted drug delivery. To gain a detailed understanding of the influence of the inhalation route on the flow structures in the human trachea, the flow field in the trachea is investigated in vitro in a non-compliant, refractive-index matched silicone model of the human respiratory tract. The investigations comprise steady inhalation, and oscillatory flow to simulate calm breathing. A realistic breathing pattern is approximated by a sinusoidal waveform for two Reynolds numbers of $Re_{Tr} = [400, 1200]$, based on the bulk velocity at maximum volume flux and the hydraulic diameter of the trachea and two Womersley numbers of $Wo = [3, 4.5]$, representing the oscillation time scales. To capture the inherently three-dimensional and asymmetric nature of the flow field, 3D particle-tracking velocimetry measurements are performed using the Shake-The-Box algorithm. Using a refractive-index matched fluid consisting of water and glycerin, the complex flow structures inside the trachea are fully resolved. The PTV measurements confirm that the nasal and/or oral cavity must be considered when analyzing the flow field in the lower respiratory tract. In particular, we find that the presence of both cavities significantly alters the flow field compared to idealised, fully developed inflow conditions. However, velocity profiles in the sagittal and coronal plane in the trachea as well as contour plots of the of the normalized velocity magnitude evidence nearly identical flow structures for oral and nasal inhalation, indicating minimal influence of the inhalation route.

Figures (14)

• Figure 1: Workflow of the lost-core method for the silicone model of the respiratory tract used during the experiments.
• Figure 2: Schematic of the setup for steady inhalation and oscillatory inhalation/exhalation, the coordinate system with corresponding planes and the silicone plugs for individual inhalation.
• Figure 3: Example of the normalized measured piston position and the corresponding prescribed sine. Points of maximum inhalation and exhalation and integration window are indicated.
• Figure 4: Comparison of the streamwise velocity profiles in the sagittal plane of the time averaged axial velocity, normalized by the axial bulk velocity $|\overline{v}| / v_{bulk}$ in the trachea at position SA $y^* = 4.2$ for $Re_{Tr} = 400$, extracted from PIV and PTV.
• Figure 5: Comparison of the mean axial velocity normalized by the bulk velocity at $y^* = 1.84$ in the trachea of 2D/2C PIV experiments johanningmeiners.2023 and a CFD simulation ruettgers.2025 with experiments using a simplified but anatomically shaped inlet trachea Groe.2007 upstream of the first bifurcation generation.