Stertor is an abnormal, noisy breathing sound originating in the upper airway. It is produced by the turbulent flow of air encountering a partial obstruction in the passageways above the voice box. This distinct sound signals an underlying issue causing restricted airflow, which can range from minor and temporary to more significant anatomical problems.
The Sound and Anatomy of Stertor
The sound of stertor is typically described as low-pitched, often resembling a heavy snore, snorting, or a rattling noise. This characteristic sound is produced by the vibration of soft tissues within the upper airway, specifically the nasal passages and the pharynx (the back of the throat). When the airway is partially narrowed, the air moving through it becomes turbulent. This turbulence causes relaxed tissues, such as the soft palate or pharyngeal walls, to oscillate, generating the low-frequency sound. Because the obstruction is supralaryngeal (above the larynx), the sound is often heard most prominently during inhalation.
How Stertor Differs from Stridor
It is important to differentiate stertor from stridor, as both are forms of noisy breathing but originate from different anatomical locations and have distinct sound qualities. Stertor is a low-pitched, snoring-type sound that arises from partial obstruction in the nasal cavity or pharynx, the uppermost part of the airway. The sound is generated by the vibration of relatively soft tissues in this area.
Stridor, in contrast, is a high-pitched, harsh, or musical noise, sometimes described as a whistling sound. This sound is produced when the obstruction is located lower in the upper airway, specifically at the level of the larynx (voice box) or the trachea (windpipe). Because stridor involves the vibration of more rigid tissues, the sound produced is higher in pitch.
Conditions That Cause Stertor
Stertor is caused by any condition that creates a partial blockage or narrowing in the nasal passages or the pharynx, leading to soft tissue vibration. Structural issues are common causes, particularly in certain animal breeds, such as brachycephalic dogs like Pugs and Bulldogs. These breeds often suffer from Brachycephalic Obstructive Airway Syndrome (BOAS), which includes an elongated soft palate extending too far back into the throat and stenotic nares (narrowed nostrils). The elongated soft palate bulges into the airway, creating significant resistance and generating the sound.
Temporary obstructions can also cause stertor. These include excessive mucus from an upper respiratory infection or severe allergic reactions that cause tissue swelling. Enlarged tonsils or adenoids, often due to infection or inflammation, can physically obstruct the nasopharynx and oropharynx, leading to the characteristic snoring sound. Growths in the nasal cavity or pharynx, such as polyps or tumors, are other mechanical causes that decrease the airway lumen. Pharyngomalacia, or floppy tissues in the pharynx, can collapse during the negative pressure of inhalation, contributing to the partial obstruction.
When to Seek Help and Treatment Options
While mild, intermittent stertor, such as common snoring, may not be an immediate concern, a sudden onset, worsening, or persistent stertor warrants medical evaluation. Seek immediate veterinary attention if the animal shows signs of severe respiratory distress, such as labored breathing, blue or pale gums or tongue (cyanosis), or collapse. These signs indicate a severe airway compromise requiring emergency intervention.
The medical investigation typically begins with a thorough physical examination to assess respiratory effort and localize the sound. Diagnostic tools may include X-rays or computed tomography (CT) scans to visualize the nasal passages and pharynx, and endoscopy to directly examine the upper airway structures. Treatment focuses on addressing the underlying cause of the obstruction.
Treatment Options
For temporary issues, such as inflammation or infection, medications like anti-inflammatories or antibiotics may be used. Structural issues, like an elongated soft palate or stenotic nares, often require surgical correction to widen the airway and prevent further tissue damage. Weight management is also a common recommendation, as excess weight can exacerbate the soft tissue obstruction in the throat.