Modeling and simulation of conducting airways during continuous high-frequency oscillation therapy

Area of Science:

• Biomedical Engineering
• Fluid Dynamics
• Respiratory Physiology

Background:

• Continuous high-frequency oscillation (CHFO) is a clinical tool for airway clearance and lung expansion.
• Quantifying pressure and shear distribution in human airways during CHFO is crucial for understanding its efficacy.
• Existing knowledge lacks detailed analysis of CHFO's mechanical loading within patient-specific airway geometries.

Purpose of the Study:

• To quantify the pressure and shear stress distribution within a patient-specific human conducting airway model during CHFO.
• To compare the effects of standard and high-pressure CHFO modes on airway mechanics.
• To identify anatomical regions susceptible to mechanical loading during CHFO.

Main Methods:

• Developed a patient-specific, CT-derived airway model from the nasal cavity to the 13th lung generation.
• Performed transient Reynolds-averaged Navier-Stokes (RANS) simulations with k-ω SST turbulence closure on a 7.75 million cell hybrid mesh.
• Combined a slow-breathing waveform with 3Hz oscillatory pressure input, simulating two CHFO therapeutic settings.

Main Results:

• Anatomical features create persistent "hot spots" of mechanical loading, such as a laryngeal jet causing pressure minima and elevated shear.
• The nasal and pharyngeal cavities experience the highest global wall-normal forces.
• Distal airway generations exhibit tightly phase-locked pressures with minimal proximal-to-distal gradients, showing limited axial attenuation of oscillatory forcing.
• High-pressure CHFO increases mean and RMS airway pressures and wall-normal forces but preserves the spatial hierarchy of pressure and shear.

Conclusions:

• CHFO significantly reshapes pressure, shear, and wall-normal loading within the conducting airways.
• Anatomical structures dictate the spatial distribution of mechanical loading during CHFO.
• High-pressure CHFO leads to more tonic loading compared to standard CHFO, while maintaining the anatomy-defined loading hierarchy.