Tracheal collapse is a conition characterized by incomplete formation or weakening of the cartilagenous rings of the trachea resulting in flattening of the trachea. It can be congenital or acquired, and extrathoracic or intrathoracic. Tracheal collapse is a dynamic condition. Collapse of the cervical trachea (in the neck) occurs during inspiration; collapse of the thoracic trachea (in the chest) occurs during expiration. Tracheal collapse is most commonly found in small dog breeds, including the Chihuahua, Pomeranian, Toy Poodle, Shih Tzu, Lhasa Apso, Maltese and Yorkshire Terrier. Obesity is a common contributing factor in dogs with tracheal collapse.