Stertor and stridor: how to localise respiratory noise
Which statement about upper airway respiratory noises is correct?
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A. Stertor is a low-pitched, snoring-type noise originating in the nose or nasopharynx; stridor is high-pitched, whistle-like, and originates in the larynx or trachea
Correct. Stertor arises from vibration of soft tissues or secretions in the nose, nasopharynx or soft palate. Stridor indicates narrowing of a rigid airway (larynx, trachea) and is usually associated with more dangerous obstructions.
B. Stridor is a low-pitched nasopharyngeal noise and stertor a high-pitched laryngeal whistle
It is the other way round: stertor is low-pitched and high in the airway (nose and nasopharynx), and stridor is high-pitched (larynx and trachea).
C. Expiratory wheezes are the typical noise of nasal obstruction
Wheezes originate in the lower airways (bronchi), as in feline asthma or chronic bronchitis.
D. If the noise disappears when the mouth is opened, the origin is laryngeal
If the noise improves with open-mouth breathing, it points to the nose, because the mouth bypasses the nasal obstruction; a laryngeal noise persists.
lightbulb Key takeaway
Listen to the noise over the nose, larynx and trachea, and check whether it changes when the mouth is closed or each nostril is occluded. Upper airway obstructions are usually inspiratory; stridor with respiratory distress is a potential emergency.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.