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Structure and Function of the Respiratory Tract in Dogs

By: Dr. Bari Spielman

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What Are Some Common Diseases of the Respiratory Tract?

There are many primary disorders that affect the respiratory tract. Generally speaking, coughing, sneezing, and/or difficult breathing are the most common signs seen with respiratory disease.

  • Diseases of the nasal cavity often cause nasal discharge, sneezing, and/or sterterous breathing (snoring or snorting sounds). Common diseases of the nasal cavity include:

    Rhinitis is an inflammation of the mucosa (lining) of the nasal cavity. It can be caused by infectious agents (bacteria, virus, fungal agents, parasites) or noninfectious disorders, including foreign bodies, allergies, trauma, dental disease, and environmental irritants. Sneezing and nasal discharge are commonly seen. Rhinitis may extend into the adjacent sinuses of the face, resulting in sinusitis.

    Neoplasia (tumors) may develop within the nose of dogs. Most nasal tumors are malignant cancers, such as adenocarcinomas, osteosarcoma, lymphosarcoma, and squamous cell carcinoma. Tumors may develop initially on one side of the nose, but with time may affect both nasal passages. Besides sneezing and nasal discharge, swelling of the face or around the eye may also be noted.

  • Pharyngeal disorders often present with stertor, gagging, or retching. Rarely, dogs may develop inflammatory polyps in this area. Polyps are usually benign soft tissue growths that grow from the lining of the back of the nasal passage, the pharynx, or the auditory (Eustachian) tube. They may obstruct the flow of air through the nasopharynx and cause problems within the middle ear.

  • Diseases of the larynx often cause respiratory distress and/or stridor (a high pitched audible wheezing sound). They may involve only the larynx or other parts of the upper airway as well.

    Laryngitis is inflammation of the larynx. It most commonly occurs with tracheitis and upper respiratory infections. Clinical signs may include coughing, nasal discharge, difficulty or noisy breathing and a change in voice.

    Brachycephalic syndrome is a condition of brachycephalic dogs in which several upper airway abnormalities occur together and seriously decrease the passage of air. Dogs with this syndrome may have congenitally small nostrils (stenotic nares), overly long soft palates that hang down into the nasopharynx, underdeveloped tracheas (tracheal hypoplasia), herniation of the vocal folds into the larynx (everted laryngeal saccules), and laryngeal paralysis. All of these conditions predispose the dog to respiratory difficulties, particularly if they become excited or overactive, are confined to small areas, are obese, or are exposed to heat and humidity. Clinical signs may be mild (noisy breathing, snoring, gagging or retching phlegm, exercise intolerance) to severe (respiratory distress, cyanosis, overheating, collapse, shock) with this condition.

    Laryngeal paralysis is an acquired disease of some older, large breed dogs. The cartilages that normally control the opening and closing of the larynx become paralyzed and the larynx does not open well. These dogs exhibit changes in their voice (hoarse, raspy bark), noisy breathing, and exercise intolerance. They may also overheat and collapse in respiratory distress.

    Polyps and tumors may also develop within the larynx.

  • Diseases of the trachea are most often associated with cough, respiratory distress, exercise intolerance, weakness, cyanosis (blue color to the normally pink tongue and gums) or fainting (syncope). Common disorders of the trachea include the following:

    Infectious tracheobronchitis (kennel cough) is a contagious upper respiratory disorder, and is common in dogs that have been exposed to other infected dogs, such as at a boarding facility, dog show, or playgroup. The disease is usually caused by a mixture of viruses (e.g. parainfluenza, adenovirus) and bacteria (especially Bordetella). The cough associated with kennel cough is often harsh, occurs in spasms, and may sound as though the dog is choking. At the end of the cough the dog make gag or retch. The trachea is often very sensitive, and any light manipulation of the neck results in spasms of coughing.

    Tracheitis or inflammation of the trachea may also occur with exposure to irritants such as smoke, chemicals, dust, or foreign bodies. Certain parasites may also migrate to the trachea, causing inflammation within the airway. Tracheitis occasionally develops after the use of endotracheal tubes during general anesthesia.

    Obstruction of the trachea may develop from the inhalation of foreign material, from the growth of tumors of the trachea, or from tumors or masses impinging on the trachea from surrounding tissues.

    Tracheal collapse is a disease seen most often in middle-aged to older toy breed dogs (e.g. miniature poodle, Yorkshire terrier, Pomeranian). In these dogs the soft membrane across the top of the C-cartilage of the trachea becomes weak and stretches out. This allows the C-cartilages to collapse onto themselves, making it difficult for air to pass into the lungs. The cough associated with tracheal collapse has been described as a "goose honk." It may occur with excitement, exercise, pressure on the neck from collars and leashes, and during eating or drinking. Spasms of coughing, respiratory distress, weakness and fainting are sometimes also seen with this condition.

    The most common disorder of the bronchial tree of dogs is bronchitis. Bronchitis is inflammation of the lower airways that may arise with infections (e.g. bacterial, viral, mycoplasmal, parasitic), irritants (e.g. smoke, dust, foreign material), allergies, diseases of the lungs, etc. The most common presenting sign is usually coughing. Bronchitis may either be acute or chronic in nature.

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