Flat Nose Breeds & Obstructive Airway Syndrome

French bulldog, bulldog, pug, pekingese, shih tzu, Japanese chin, boxer and Boston terrier are all examples of flat nose breeds.


BOAS (Brachycephalic obstructive airway syndrome) affect all flat nose dogs to some degree. The more affected ones show various degrees of respiratory distress or digestive troubles, ranging from occasionally short of breath to collapsing on moderate exercise.


Following shows the 4 nostril opening grading(open, mild, moderate and severe) for Pugs, French bulldogs and Bulldogs

BOAS Nostril Stenosis for pugs, french bulldogs and bulldogs

Based on research, the following physical attributes are linked to higher BOAS risk for bulldogs, French bulldogs and pugs   

Conformational risk factors for BOAS Bulldogs


Conformational risk factors for BOAS in french bulldogs


Conformation risk factors for BOAS in pugs


Clinical signs dog parents should recognize 

(Your vet can perform professional respiratory function test)
  • Respiratory noise - There are different types of noise depending on the location of the obstruction: pharynx, larynx, and/or nasal cavity

  • Nostrils - Excessively narrow and often collapse inward during inspiration, making it difficult for the dog to breathe through the nose properly. The narrowing can affect the inner nasal wing as well.

  • Gastrointestinal signs such as regurgitation. The opening of the esophagus is located near the airway opening

  • Obstructive sleep apnea / sleep-disordered breathing

  • Heat intolerance

  • Cyanosis and collapse - When blood is inadequately oxygenated, you may see bluish discoloration (cyanosis) in the dog’s tongue and tongue and gums. The dog may collapse if the oxygen levels are not stabilized immediately.

There are 4 Grades of BOAS 

  • Grade 0: Clinically unaffected and is currently free of respiratory signs 

  • Grade 1: Clinically unaffected but does have mild respiratory signs. These signs do not affect exercise performance. 

  • Grade 2: Clinically affected and has moderate respiratory signs that should be monitored and may require veterinary treatment

  • Grade 3: Clinically affected and has severe respiratory signs and should be seen by your vet 

If your dog is young, please bear in mind, BOAS can develop later in life. 

Distribution of the 4 function grade among study participants

(Participant size: 189 pugs, 214 French bulldogs and 201 bulldogs)

BOAS Grade Pug French Bulldog Bulldogs
Grade 0 5% 11% 11%
Grade 1 31% 30% 38%
Grade 2 45% 44% 39%
Grade 3 19% 15% 12% 


Source: University of Cambridge Veterinary, Department of Veterinary Medicine, Cambridge BOAS Research Group 

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