Stertor and Stridor in Dogs
Unusually loud breathing sounds are often the result of air passing through abnormally narrowed passageways, meeting resistance to airflow because of partial blockage of these regions. The origin may be the back of the throat (nasopharynx), the throat (pharynx), the voice box (larynx), or the windpipe (trachea). Abnormal breathing sounds of this type can be heard without using a stethoscope.
Stertor is noisy breathing that occurs during inhalation. It is a low-pitched, snoring type of sound that usually arises from the vibration of fluid, or the vibration of tissue that is relaxed or flabby. It usually arises from airway blockage in the throat (pharynx).
Stridor is high-pitched, noisy breathing. The higher-pitched sounds result when relatively rigid tissues vibrate with the passage of air. It often occurs as the result of partial or complete blockage of the nasal passages or voice box (larynx), or collapse of the upper part of the windpipe (known as cervical tracheal collapse).
The upper respiratory tract or upper airways includes the nose, nasal passages, throat (pharynx), and windpipe (trachea).
Noisy breathing is common in short-nosed, flat-faced (brachycephalic) dog breeds. Inherited paralysis of the voice box, known as laryngeal paralysis, has been identified in Bouviers des Flandres, Siberian huskies, bulldogs, and Dalmatians.
Acquired paralysis of the voice box (laryngeal paralysis) is more common in certain giant-breed dogs, such as St. Bernards and Newfoundlands, and in large-breed dogs, such as Irish setters, Labrador retrievers, and golden retrievers, than other breeds.
Affected short-nosed, flat-faced dogs with inherited paralysis of the voice box typically are younger than one year of age when breathing problems are first detected. Acquired paralysis of the voice box typically occurs in older dogs. Inherited paralysis of the voice box has a 3:1 male-to-female ratio.
Symptoms and Types
- Change or loss of voice – inability to bark
- Partial blockage of the upper airways produces an increase in airway sounds before producing an obvious change in breathing pattern
- Unusually loud breathing sounds may have existed for as long as several years
- Breathing sounds can be heard from a distance without the use of a stethoscope
- Nature of the sounds range from abnormally loud to obvious fluttering to high-pitched squeaking, depending on the degree of airway narrowing
- May note increased breathing effort; breathing often accompanied by obvious body changes (such as extended head and neck and open-mouth breathing)
- Condition of abnormal breathing passages in short-nosed, flat-faced animals (a condition known as brachycephalic airway syndrome), characterized by any combination of the following conditions: narrowed nostrils (stenotic nares); overly long soft palate; turning inside-out of a portion of the voice box or larynx (everted laryngeal saccules), such that the space for air to pass through the larynx is decreased; and collapse of the voice box or larynx (laryngeal collapse), and fluid build up (edema) of the voice box or larynx
- Narrowing of the back of the nose and throat (nasopharyngeal stenosis)
- Paralysis of the voice box or larynx (laryngeal paralysis) - may be inherited or acquired
- Tumors of the voice box or larynx - may be benign or malignant (cancer)
- Nodular, inflammatory lesions of the voice box or larynx (granulomatous laryngitis)
- Reduction in the diameter of the lumen of the windpipe (trachea) during breathing (tracheal collapse)
- Narrowing of the windpipe (trachea; tracheal stenosis)
- Tumors of the windpipe (trachea)
- Foreign bodies in the windpipe (trachea) or other parts of the airway
- Inflammatory masses that develop from the middle ear or eustachian tube (nasopharyngeal polyps)
- Condition caused by excessive levels of growth hormone, leading to enlargement of bone and soft-tissues in the body (acromegaly)
- Nervous system and/or muscular dysfunction
- Anesthesia or sedation - if certain anatomy exists (such as a long soft palate) that increases susceptibility to abnormal, loud breathing sounds
- Abnormalities or tumors of the soft palate (the soft portion of the roof of the mouth, located between the hard palate and the throat)
- Excessive tissue lining the throat (redundant pharyngeal mucosal fold)
- Tumor in the back of the throat (pharynx)
- Fluid build-up (edema) or inflammation of the palate, throat (pharynx), and voice box (larynx) - secondary to coughing, vomiting or regurgitation, turbulent airflow, upper respiratory infection, and bleeding
- Discharges (such as pus, mucus, and blood) in the airway lumen – may occur suddenly (acutely) after surgery; a normal conscious animal would cough out or swallow them
- High environmental temperature
- High metabolic rate - as occurs with increased levels of thyroid hormone (hyperthyroidism) or a generalized bacterial infection (sepsis)
- Anxiety or excitement
- Any breathing or heart disease that increases movement of air into and out of the lungs (ventilation)
- Turbulence caused by the increased airflow may lead to swelling and worsen the airway obstruction
- Eating or drinking
You will need to provide a thorough history of your pet's health leading up to the onset of symptoms. Your veterinarian will use a stethoscope to listen to the entire area from the pharynx to the trachea. If the sound persists when your pet opens its mouth, a nasal cause can virtually be ruled out. If the sound occurs only during expiration, it is likely that airway narrowing is the cause. If the abnormal sounds are loudest during inspiration, they are from disease other than in the chest. If you have noticed a change in your dog's voice, the larynx is the likely abnormal site. Your veterinarian will systematically listen with the stethoscope over the nose, pharynx, larynx, and trachea to identify the point of maximal intensity of any abnormal sound and to identify the phase of respiration when it is most obvious. It is important to identify the location from which the abnormal sound arises and to seek aggravating causes.
Internal imaging techniques, such as radiography and fluoroscopy, are important for assessing the cardiorespiratory system and to rule out other or additional causes of respiratory difficulty. Such conditions may add to an underlying upper airway obstruction, causing a subclinical condition to become clinical. X-rays of the head and neck may help to identify abnormal soft tissues of the airway. A computed tomography (CT) scan may also be used to provide additional anatomic detail.
In some cases, your dog's physiological inheritance can make the diagnosis more apparent, such as with dogs that are brachycephalic. In these situations, your veterinarian will determine the location that is being most affected by your dog's conformation and decide where to go from there.