Laryngeal or tracheal stridor
In one sentenceA continuous sound that arises from the larynx or a central airway and is loudest over the neck.
Listen to the same sound in another patient. Breathing rate, chest wall, the pitch of the sound and the number of adventitious sounds vary within realistic limits.
What does it sound like?
Loud, harsh and musical. Its rich harmonics usually make it sound high-pitched. It may be audible at a distance, without a stethoscope.
Where is it heard?
Loudest over the neck and trachea. It may be transmitted to the chest.
What causes it?
Air passes very fast through a narrowing in the larynx or trachea, and a strong tone forms. The source is in the neck, so the sound is much louder over the neck than over the chest. During inspiration, the airway in the neck collapses inwards. For this reason, a dynamic narrowing outside the chest produces sound mainly during inspiration.
Quantitative criteria
- No frequency threshold is diagnostic on its own. Phase, intensity and recording site are more informative than frequency.
- On the spectrogram, a fundamental tone runs without a break through inspiration, with a strong series of harmonics. The sound stands well above the breath sound.
Clinical meaning
Inspiratory stridor usually suggests extrathoracic (laryngeal) obstruction. Expiratory stridor more often suggests intrathoracic obstruction. Biphasic stridor suggests a fixed glottic, subglottic or proximal tracheal narrowing. Causes include laryngeal oedema after extubation, foreign body, tumour, stenosis and inducible laryngeal obstruction. It is a finding that may need urgent assessment.
Sounds it can be confused with
A wheeze is louder over the chest, stridor over the neck. Stridor is mostly inspiratory.
The normal tracheal sound contains no musical tone.
Place the stethoscope first on the neck, then on the chest. If the sound is clearly louder over the neck, the source is the upper airway.
See the reference list for sources.