Stridor is the term for noisy breathing that comes from the upper airway (trachea and voice box) and can be heard without a stethoscope. The sound can be described as squeaky, grunty, shrill, coarse or many other ways. This sound represents a partial obstruction of the airway. When tissues of the airway that are close to each other have air moving through them (during breathing), they create a vibration in the tissues that creates a sound — this is how we whistle.

Different parts of the airway tend to create different types of sounds at different points in the respiratory cycle. Sometimes it occurs while breathing in and sometimes while breathing out, and sometimes both. Sometimes it only happens with coughing (e.g. barky cough). These are good clues as to the where the problem is, and it can help your airway team quickly identify the best options for evaluation. For example, laryngomalacia, which affects the voice box above the vocal cords, causes stridor only while breathing in, and tracheomalacia causes barky cough (see below).

There are also conditions that cause stridor that are not caused by a “fixed” lesion, or a lesion that is always there. In these cases, the stridor comes and goes. A good example of this is stridor in infants caused by reflux.

Inspiratory (Breathing in) Expiratory (Breathing out) Biphasic (Both)
Laryngomalacia Tracheomalacia Bilateral vocal cord paralysis
Bilateral vocal cord paralysis Vascular tracheal compression Glottic stenosis
Croup   Subglottic stenosis
Subglottic stenosis    
Reflux laryngospasm    

When a baby or child has stridor, this means that a part of the airway is narrowed and requires some investigation. Stridor is best evaluated with a thorough history and an examination that allows the team to see the affected parts of the airway. This can be done with a flexible fiberoptic camera, called a laryngoscope, which lets the team see the nose, throat and voice box, and can assess vocal cord mobility. Sometimes the area below the vocal cords, the subglottis, can be visualized, but nothing below the vocal cords can be thoroughly examined with this endoscopy. A more thorough examination of the voice box and trachea requires an examination under sedation, called a microlaryngoscopy and bronchoscopy (MLB), which is done under sedation. This examination is performed under anesthesia and allows the airway team to examine the voice box more closely and thoroughly, down into the lower airways that extend into the lungs. An examination under anesthesia also allows the team to feel and probe the structures of the airway to see if there are any gaps or holes in the airway (i.e., Laryngeal cleft or TE fistula), or if there are scarred structures that may prevent proper function. This exam is often done in partnership with a pulmonary doctor, who can examine even further down the airways and obtain samples of mucus within the lower airways for more information about the child’s lung health.

There are many causes of stridor, but the unifying factor is airway obstruction, which should be visible, in addition to audible. Please contact our Aerodigestive Clinic for more information on a multi-disciplinary appointment. 

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