Brachycephalic upper airway obstructive syndrome

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Brachycephalic upper airway obstructive syndrome (BAOS) is a combination of nasal and oropharyngeal anatomic abnormalities resulting from selective breeding to reduce the length of the maxilla without concurrent reduction in the soft tissue of the nose, palate, and pharynx[1].

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 and laryngeal collapse.

Brachycephalic dogs can present other respiratory tract abnormalities such as tracheal hypoplasia, bronchial collapse, macroglossia, reduced buccal opening, nasopharyngeal collapse and nasopharyngeal turbinates [2].

Dogs such as the English Bulldog have snoring and fragmented sleep with mild hypoxemia and apneas only during rapid eye movement[3].

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[4][5].


  1. Wykes PM (1991) Brachycephalic airway obstructive syndrome. Probl Vet Med 3:188–197
  2. De Lorenzi D et al (2009) Bronchial abnormalities found in a consecutive series of 40 brachycephalic dogs. J Am Vet Med Assoc 235:835–840
  3. Hendricks JC et al (1987) The English bulldog: a natural model of sleep-disordered breathing. J Appl Physiol 63:1344–1350
  4. Poncet CM et al (2005) Prevalence of gastrointestinal tract lesions in 73 brachycephalic dogs with upper respiratory syndrome. J Small Anim Pract 46:273–279
  5. Poncet CM et al (2006) Long-term results of upper respiratory syndrome surgery and gastrointestinal tract medical treatment in 51 brachycephalic dogs. J Small Anim Pract 47:137–142