Inspiratory stridor. The sound happens when you inhale or breathe in. It may be because of floppy tissue around the vocal cords, especially in children. Expiratory stridor. The sound happens when you exhale, or breathe out. The cause could be a problem farther down your airway.

Inspiratory stridor occurs when your child breathes in and it indicates a collapse of tissue above the vocal cords. Expiratory stridor occurs when your child breathes out and it indicates a problem further down the windpipe.

Stridor is a sign of upper airway obstruction. In children, laryngomalacia is the most common cause of chronic stridor, while croup is the most common cause of acute stridor. Generally, an inspiratory stridor suggests airway obstruction above the glottis while an expiratory stridor is indicative of obstruction in the lower trachea.