stridor

Stridor is a harsh, single-pitched, often crowing sound caused by air rushing through a narrowed upper airway — the larynx, the windpipe just below it, or the throat. Where a wheeze sounds musical and comes from deep in the chest, stridor is louder, rougher and seems to come from the neck.

It is classically heard on inspiration, when the negative pressure of breathing in pulls the soft tissues of the upper airway inward and narrows them further. Stridor present on both breathing in and out, or mainly on breathing out, suggests a tighter or lower obstruction, which is often more serious.

Because the upper airway is a single shared passage, narrowing there threatens the whole supply of air. Causes include croup and other infections in children, inhaled foreign bodies, allergic swelling of the throat, vocal cord problems, and tumors or scarring of the windpipe. In an adult, new stridor is treated as a potential airway emergency until proven otherwise, because the channel can close quickly.

Stridor is therefore less a diagnosis than an urgent localizing sign: it tells the listener the trouble is high in the airway and that the margin for safe breathing may be small.