Stridor & Wheezing

Figure 1: Cross-sectional anatomy of the airway from mouth to alveoli. Structures located above the chest cavity compose the upper airway. Those structures within the chest cavity are considered part of the lower airway.

Stridor is a noise heard on inspiration and is caused by the narrowing of the extrathoracic upper airway.

In extrathoracic obstruction, pressure distal to the point of obstruction will become -ve in order to overcome the airway resistance. Thus, the airways will collapse. So, during the inspiration, there will be increase in turbulence of air moving through the obstructed airways. Thus, this produces audible sound during inspiration called STRIDOR.

Wheezing is a whistling-like sound and is caused by the narrowing of the intrathoracic airway.

In intrathoracic airway obstruction, intrapleural pressure will become more positive during expiration because of the air trapped inside. So, there will be collapse of the intrathoracic airways. When air is expired out, it will pass through this collapsed airways. Thus, producing WHEEZING sound during expiration.

Sources:

1) Essentials of Pathophysilogy (Lippincott Williams & Wilkins)

2) Paediatrics and Child Health (Blackwell Publishing)

3) http://publicsafety.com/article/article.jsp?id=2115&siteSection=8

Wassalam.