Fluoroscopically measured bronchial collapse in healthy dogs during cough exceeds 25%, and a cutoff of 60% bronchial collapse can be used to distinguish healthy from chronically coughing dogs.

Bronchomalacia, the weakening of bronchial cartilage, is a common cause of cough in dogs. The gold standard for diagnosis of bronchomalacia is bronchoscopy; however, fluoroscopy is often used as a preliminary diagnostic test due to its noninvasiveness. The normal amount of bronchial collapse in healthy dogs using fluoroscopy has not been previously established, with some authors citing <25%. The aims of this prospective and retrospective analytical observational study were to determine the normal amount of airway collapse in healthy animals, the amount of airway collapse in dogs with chronic cough and presumed bronchomalacia, and cut-off values of airway collapse during expiration and cough to distinguish between the two groups. Thoracic fluoroscopy was performed in right and left lateral recumbency during inspiration, expiration, and cough to evaluate the percentage collapse of the trachea and lobar bronchi in 45 healthy and 76 chronically coughing dogs. The bronchi of chronically coughing dogs exhibited a significantly greater amount of collapse during both expiration and cough compared with healthy dogs. Chronically coughing dogs exhibited up to 31.7 ± 26.6% collapse in expiration and 87.5 ± 23.7% collapse during cough, whereas healthy dogs exhibited 14.9 ± 6.1% collapse in expiration and 35.0 ± 13.7% collapse during cough. Based on ROC curves, the authors suggest using cut-off values of 30% during expiration and 60% during cough to distinguish between healthy dogs and those with presumed bronchomalacia. Findings suggest that though healthy dogs can exhibit a greater degree of airway collapse than previously thought, fluoroscopy can be used to distinguish between healthy and presumed bronchomalacic dogs.