Table 1. Functional grading system of brachycephalic obstructive airway syndrome (BOAS) based on respiratory signs before and after an exercise tolerance test (ETT).

		Respiratory noise a	Inspiratory effort b	Dyspnoea/ Cyanosis/ Syncope c
Grade 0	Pre-ETT	Not audible	Not present	Not present
	Post-ETT	Not audible	Not present	Not present
Grade I	Pre-ETT	Not audible or mild	Not present	Not present
	Post-ETT	Mild	Not present to mild	Not present
Grade II	Pre-ETT	Mild to moderate	Mild to moderate	Not present
	Post-ETT	Moderate to severe	Moderate to severe	Mild dyspnoea; cyanosis or syncope not present
Grade III	Pre-ETT	Moderate to severe	Moderate to severe	Moderate to severe dyspnoea; may or may not present cyanosis. Inability to exercise.
	Post-ETT	Severe	Severe	Severe dyspnoea; may or may not present cyanosis or syncope.

The clinical grading was based on respiratory signs before (pre-ETT) and immediately after the exercise tolerance test (post-ETT) as described in the methods section.

^a Respiratory noise was diagnosed by pharyngolaryngeal auscultation. Mild: only audible under auscultation; moderate: intermittent audible noise that can be heard without stethoscope; severe: constant audible noise that can be heard without stethoscope.

^b An abnormal respiratory cycle characterized by evidence of increased effort to inhale the air in with the use of diaphragm and/or accessory muscles of respiration and/or nasal flaring with an increase in breathing rate. Mild: regular breathing patterns with minimal use of diaphragm; moderate: evidence of use of diaphragm and accessary muscles of respiration; severe: marked movement of diaphragm and accessary muscles of respiration.

^c Dogs that have had episodes of syncope and /or cyanosis as documented by owner’s report are classified into Grade III without ETT. Mild dyspnoea: presents sign of discomfort; Moderate dyspnoea: irregular breathing, signs of discomfort; severe dyspnoea: irregular breathing with signs of breathing discomfort and difficulty in breathing.