Brachycephalic upper airway obstructive syndrome
Brachycephalic upper airway obstructive syndrome (BAOS) is a combination of nasal and oropharyngeal anatomic abnormalities due to reduced length of the maxilla with concurrent reduction in the soft tissue of the nose, palate, and pharynx.
In brachycephalic dogs, the skull bone shortening is not paralleled by a decreased development of soft tissues. Relatively longer soft palate is one of the main factors contributing to pharyngeal narrowing during normal respiratory activity of these dog breeds. The elongated brachycephalic soft palate shows a number of peculiar features such as thickened superficial epithelium, extensive oedema of the connective tissue, and mucous gland hyperplasia.
The resulting excess of soft tissue causes airway obstruction in affected animals, with clinical signs that may include inspiratory stertor and stridor, exercise and heat intolerance, cyanosis, respiratory distress, regurgitation, and vomiting.
The primary abnormalities of BAOS are stenotic nares and an elongated soft palate. Secondary changes that occur as a result of chronic upper airway obstruction include eversion of laryngeal saccules, pharyngeal edema, laryngeal collapse and excessive mobility of the epiglottis.
Brachycephalic dogs can present other respiratory tract abnormalities such as tracheal hypoplasia, bronchial collapse, macroglossia, reduced buccal opening, nasopharyngeal collapse and nasopharyngeal turbinates .
The presence of digestive signs in dogs with BAOS is relatively common, due to the exaggerated repetitive variation of diaphragmatic pressure, present in patients with obstructive breathing, which causes gastroesophageal reflux and inflammation of the oropharyngeal areas that, in turn, worsen respiratory signs.
Treatment usually requires surgical shortening of the soft palate and in some cases, tonsilectomy.
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