In this BoardsCast episode, we continue Tobias Chapter 102 — Trachea and Bronchi by solving the “impossible” airway riddle:

The airway is open… there’s no mass… and it still collapses.

That’s because airway collapse isn’t a blockage problem; It’s a physics problem — specifically a pressure problem. 

This episode builds the dominant mental model that makes tracheal collapse predictable:

Airway diameter is dictated by transmural pressure
(inside pressure − outside pressure).
Positive transmural pressure = airway stays open.
Negative transmural pressure = airway collapses. 

You’ll learn:

• Why the trachea is a reinforced vacuum hose, not a rigid pipe 
• The pressure rule that decides everything: transmural pressure (intraluminal − extraluminal) 
• Why cartilage degeneration turns “armored rings” into a floppy tube (small-breed collapse setup) 
• Why does cervical collapse happen on inspiration (vacuum effect) 
• Why does intrathoracic collapse happen on expiration (pleural pressure crush) 
• Why static radiographs miss dynamic collapse (you’re filming a movie with a single photo) 
• The grading framework: 25% / 50% / 75% / 100% lumen loss (Grades I–IV) 

Key takeaway: Stop asking “what’s narrowing the airway?” and start asking “when does it collapse?”

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