Wall motion in expiratory flow limitation: choke and flutter.

Area of Science:

• Physiology
• Biophysics
• Fluid Dynamics

Background:

• Current understanding of expiratory airflow limitation in mammalian airways relies on wave-speed theory.
• A key limitation of wave-speed theory is the absence of an energy dissipation mechanism when effort exceeds maximal flow requirements.

Purpose of the Study:

• To investigate the relationship between expiratory airflow limitation and airway wall oscillation.
• To identify a potential mechanism for energy dissipation during flow limitation.

Main Methods:

• Observation of substantial wall motion in a physical model of a trachea during flow limitation.
• Examination of a two-dimensional mathematical model simulating tracheal behavior.
• Comparison of model predictions with wave-speed theory.

Main Results:

• The mathematical model aligns with wave-speed predictions for long waves.
• The model predicts aerodynamic flutter in the supercritical flow zone.
• Aerodynamic flutter offers a mechanism for energy dissipation and explains observed pure tones.

Conclusions:

• Aerodynamic flutter in supercritical flow is a plausible mechanism for energy dissipation during airway flow limitation.
• This mechanism reconciles wave-speed theory with observed phenomena like pure tone generation.