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Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

Incomplete obstruction to airflow within the upper respiratory tract leads to turbulence and the intense musical sound of stridor. It may be difficult to distinguish from a monophonic wheeze.

The larynx is particularly predisposed to obstruction because it is the only part of the respiratory tract that has an entire circle of non-compliant cartilage - the cricoid cartilage. In addition, the subglottis - the area just below the vocal cords - is also the narrowest part of the upper respiratory tract. Hence, pathology in the larynx, e.g. inflammation or a foreign body, may lead to airflow obstruction.

Stridor may be of three types according to the location of the airway obstruction:

  • inspirational: most common; obstruction at, or above, the level of the cords
  • biphasic: inspirational and expirational; obstruction in the subglottis or trachea
  • expirational - obstruction in the small airways, e.g. asthma

With advancing obstruction, inspirational stridor may develop into the biphasic form.

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