Why does air way collapse when pressure outside exceeds pressure inside?

[scilearner]

Ok this makes sense but pressure inside an airway is determined by hydrostatic pressure and when air moves fast hydrostaic pressure is decreased and converted to kinetic energy. So this collapses the airway. My question is doesn't kinetic energy of moving molecules exert a pressure on the walls of the airways. Why is it that only hyrdostatic pressure determines the pressure inside an airway? Thanks!!

[Mokele]

It's pretty simple - you have hydrostatic pressure pushing out, and outer pressures pushing in. If the hydrostatic pressure gets lower for any reason (faster airflow, lack of air) or the outer pressure rises, the airway collapses simply because there's not enough force on the inside to oppose the force on the outside.