Stridor is a harsh, high-pitched respiratory sound that signals turbulent airflow through a narrowed upper airway. This symptom is not a diagnosis in itself, but it is an immediate indicator of a partial obstruction that demands prompt assessment to determine the severity and underlying cause. Even minor swelling or obstruction can significantly reduce the internal diameter of the rigid upper airway, leading to this characteristic turbulent flow.
Identifying the Type of Stridor
Inspiratory stridor, heard when breathing in, usually points to an obstruction above the vocal cords in the extrathoracic region, such as the larynx. The timing of the stridor sound during the breathing cycle offers a valuable clue regarding the anatomical location of the obstruction. During inhalation, the negative pressure in the chest cavity tends to collapse the flexible tissue in the upper airway, amplifying the sound. Common causes include conditions like laryngomalacia or croup.
Expiratory stridor, occurring upon breathing out, suggests an obstruction further down the airway, typically below the vocal cords in the intrathoracic trachea or bronchi. During exhalation, the positive pressure in the chest can squeeze the walls of the lower airway, making the narrowed segment smaller. This type of stridor may indicate issues like tracheomalacia or a foreign body.
When the sound is heard during both inhalation and exhalation, it is classified as biphasic stridor. This pattern suggests a fixed obstruction at the level of the vocal cords or just below them, in the subglottic area. A rigid blockage, such as from subglottic stenosis, causes turbulent flow regardless of the pressure changes throughout the breath cycle.
Specific Areas for Auditory Assessment
Stridor is often loud enough to be heard clearly without the aid of a stethoscope. The most effective physical location to listen for stridor is directly over the anterior neck, where the larynx and trachea are located. Since the sound is generated at the source of the obstruction, proximity to the windpipe is the optimal listening point.
The bare ear placed near the mouth and nose can easily detect the sound’s quality and timing for a quick determination. If a stethoscope is available, placing the diaphragm gently over the voice box or the upper sternum area provides the clearest transmission of the turbulent sound. Listening to the chest and lungs is less effective because the sound originates higher up and may be muffled by the time it reaches the lower airways.
Stridor Versus Similar Breathing Sounds
Stridor is a high-pitched, turbulent sound that is non-musical in quality, and it always originates from the upper respiratory tract: the larynx or trachea. The harsh sound is a result of air being forced through a significantly narrowed passage.
Wheezing, in contrast, is a high-pitched, musical, or whistling sound that typically occurs during exhalation. This sound is generated by the vibration of air passing through narrowed lower airways, such as the bronchi, and is best heard by listening over the chest and lungs. The musical quality of wheezing sets it apart from the harsh, turbulent sound of stridor.
Another sound, stertor, is a low-pitched, snorting, or gurgling noise, often compared to snoring. Stertor arises from the vibration of soft tissues in the nasopharynx or oropharynx, the area of the nose and back of the throat. Because stertor originates higher up and is lower in pitch, it is distinct from the high-pitched stridor that signals a laryngeal or tracheal problem.
When Immediate Medical Help is Needed
The presence of stridor always warrants professional medical evaluation, but certain accompanying signs indicate a rapidly worsening or severe airway obstruction that requires immediate emergency intervention. These red flags demand an immediate call for emergency medical services:
- Inability to speak or cry effectively, suggesting the obstruction is significantly affecting the vocal cords.
- A change in skin or lip color to blue or gray (cyanosis), signaling dangerously low oxygen levels in the blood.
- The presence of retractions, where the skin is visibly sucked in between the ribs, above the collarbone, or at the sternum, shows the body is using accessory muscles to forcefully pull air in.
- Drooling, a rapid breathing rate, or an altered mental status, such as being excessively sleepy or agitated.