Three-dimensional flow patterns in the upper human airways.

Area of Science:

• Fluid dynamics
• Respiratory physiology
• Biomedical engineering

Background:

• Understanding airflow dynamics in human lung airways is crucial for optimizing mechanical ventilation strategies.
• Previous studies have often simplified airway geometry or flow conditions.

Purpose of the Study:

• To numerically investigate flow dynamics in a detailed 3D human lung airway model.
• To compare airflow behavior under conventional mechanical ventilation (CMV) and high-frequency oscillatory ventilation (HFOV).
• To analyze velocity profiles and secondary flow structures during different ventilation phases.

Main Methods:

• A 3D human lung airway model based on Horsfield and Weibel data, bifurcating to the sixth generation.
• Numerical simulation of airflow dynamics.
• Comparison of numerical results with experimental data from the identical model.

Main Results:

• Excellent agreement between numerical and experimental data validates the model.
• Velocity profiles at peak inspiration/expiration were similar for CMV and HFOV.
• Bidirectional mass flow zones emerged at flow reversal, increasing in amplitude with higher frequencies.
• Secondary flow structures were primarily influenced by local curvature and branch orientation, independent of adjacent generations.

Conclusions:

• The validated model provides reliable insights into lung airway flow dynamics.
• CMV and HFOV exhibit similar peak velocity profiles, suggesting limited frequency-dependent development in this model.
• Higher frequencies induce frequency-dependent bidirectional flow zones and localized secondary flow structures.