A model-based method for flow limitation analysis in the heterogeneous human lung.

Area of Science:

• Pulmonary Physiology
• Computational Biology
• Fluid Dynamics

Background:

• Airway flow limitation is crucial for maximal expiratory flow-volume curves.
• The location of this limitation is termed the choke point.
• Understanding choke point dynamics is key to respiratory mechanics.

Purpose of the Study:

• Derive expressions for critical flow calculations under different limitation regimes.
• Analyze the regime, degree, and spatial arrangement of choke points during forced expiration.
• Investigate the movement and configuration of choke points in a heterogeneous lung model.

Main Methods:

• Derived critical flow expressions for wave-speed, turbulent, and viscous limitation.
• Employed a computational model simulating forced expiration from a heterogeneous lung.
• Analyzed choke point behavior, including their arrangement (parallel vs. serial) and location.

Main Results:

• Flow limitation initiates concurrently across bronchial tree branches, forming parallel choke points.
• Airway junctions are identified as the most probable choke point locations.
• Wave-speed mechanism dominates flow choking for most of vital capacity, transitioning to viscous dissipation.

Conclusions:

• Parallel choke point arrangement is typical during forced expiration in heterogeneous lungs.
• Serial choke point configurations may occur transiently with increased airway heterogeneity.
• Wave-speed and viscous dissipation are primary mechanisms, with turbulence playing a supporting role in the transition.