Stridor in children (Causes, Inspiratory and Expiratory Stridor, Pathophysiology)

Stridor is a sound predominantly heard during inspiration. It is caused by partial obstruction of the large airways that results in turbulent airflow in the respiratory passage. Stridor is defined as high-pitched, monophonic sound and is usually loud and can be heard without a stethoscope. The differential diagnosis of stridor is vast with croup being the most common cause of acute stridor and laryngomalacia being the most common chronic or congenital cause of stridor congenital.

When thinking about pathophysiology of stridor it’s good to think of the respiratory tract in terms of extrathoracic region and intrathoracic region.

As a general rule inspiratory stridor occurs in the extrathoracic region and expiratory stridor occurs from obstruction in the intrathoracic region.

During inspiration, air flows from the extrathoracic region into the intrathoracic region. When there is some airway obstruction anywhere in the extrathoracic region this will cause an inspiratory stridor because of the turbulent flow through respiratory tube. Most causes of stridor are found in the extrathoracic region.

During expiration air flows from the intrathoracic region through the extrathoracic region. If there is any obstruction in the small airways of the intrathoracic region it causes expiratory stridor. Expiratory stridor is much less common.