wheeze

A wheeze is a high-pitched, musical, whistling sound made as air squeezes through airways that have become too narrow. The mechanism is much like a reed instrument or like pinching the neck of a balloon: force air through a tight channel and the walls vibrate, producing a continuous tone.

Wheezes are usually loudest during expiration, when the airways naturally narrow further, and they tend to be heard over both lungs in widespread airway disease. The pitch reflects how tight and how stiff the airway is, not how much air is moving. Counterintuitively, a very severe asthma attack can become quiet — the so-called silent chest — because so little air is flowing that no sound is generated, a more dangerous sign than loud wheezing.

The commonest causes are asthma and COPD, where airway muscle tightening, inflammation and secretions all reduce the channel. But a localized, single-pitched wheeze that does not clear with coughing can signal one airway narrowed by a tumor or an inhaled object, and deserves separate attention from the widespread, many-toned wheeze of diffuse airway disease.