Question

In a case of extra-thoracic airway obstruction, where does the airway collapse occur and during which phase of respiration?

• A. Collapse occurs above the level of obstruction during Inspiration
• B. Collapse occurs above the level of obstruction during expiration
• C. Collapse occurs below the level of obstruction during Inspiration
• D. Collapse occurs below the level of obstruction during expiration

Hint:

Extrathoracic obstruction (e.g., Croup, Laryngomalacia) $\rightarrow$ dynamic collapse during Inspiration (Stridor). Intrathoracic obstruction (e.g., Asthma, Tracheomalacia) $\rightarrow$ dynamic collapse during Expiration (Wheeze).

Answer 1

The Correct Option is A

Concept:
The mechanics of airway collapse during the respiratory cycle depend heavily on whether the obstruction is extrathoracic (e.g., larynx, upper cervical trachea) or intrathoracic (e.g., intrathoracic trachea, bronchi).
Dynamic pressure differentials between the intraluminal airway pressure and surrounding atmospheric or pleural pressure dictate the phase and site of dynamic airway narrowing.
Explanation:
• In an extrathoracic airway segment (above the thoracic inlet), the outer surface of the airway is exposed to atmospheric pressure ($P_{\text{atm}}$).

• During inspiration, the generation of negative intrathoracic pressure by the diaphragm creates subatmospheric intraluminal pressure within the extrathoracic airway ($P_{\text{luminal}} < P_{\text{atm}}$).

• When the intraluminal pressure drops below the surrounding atmospheric pressure, a positive transmural pressure gradient acts inward across the compliant airway walls, leading to dynamic narrowing/collapse during inspiration.

• By contrast, during expiration, the airway pressure inside the extrathoracic lumen increases above atmospheric pressure ($P_{\text{luminal}} > P_{\text{atm}}$), which forces the extrathoracic airway open.

• Consequently, extrathoracic lesions characteristically manifest with dynamic collapse and inspiratory stridor, whereas intrathoracic airway lesions collapse during expiration to produce expiratory wheeze.
Final Answer:
In extrathoracic airway obstruction, dynamic collapse occurs prominently during inspiration.