The term tracheal collapse tends to imply
an 'all-or-nothing' effect, but in the majority of cases dorso-ventral flattening
of the trachea and flaccidity of the dorsal membrane are the major problems and the
trachea may only develop a partial collapse.
The dog trachea consists of a series
of incomplete cartilagenous rings connected together by a fibroelastic ligament
The dorsal gap between the ends of the
cartilage rings is bridged by a membrane consisting of smooth muscle (trachealis)
and connective tissue.
In some dogs the tracheal cartilage is
weak and lacks structural rigidity, and the dorsal membrane is flaccid and wide.
These anatomical deformities are usually seen in small toy breeds, particularly
the Yorkshire terrier and the miniature poodle.
Mechanics of tracheal collapse
By understanding the mechanical forces
exerted on the trachea during the different phases of the respiratory cycle we
can appreciate the problems that may occur with this condition and the different
forms of the condition that are seen (
During inspiration the extrathoracic
trachea tends to collapse causing inspiratory difficulty. The intrathoracic trachea
is passively opened during inspiration and so is not affected.
During expiration the extrathoracic trachea
is passively opened and is not affected, whereas the intrathoracic trachea is
actively compressed causing expiratory difficulty and coughing.
Animals prone to tracheal collapse have
an excessively flaccid dorsal membrane and dorsoventral flattening of the tracheal
Obstruction to airflow can occur in the
extrathoracic (cervical) trachea (inspiratory phase), at the thoracic inlet (inspiratory
and expiratory phase) or in the intrathoracic trachea (expiratory phase).
TRACHEAL COLLAPSE: Clinical features
TRACHEAL COLLAPSE: Diagnosis
TRACHEAL COLLAPSE: Therapy
TRACHEAL COLLAPSE: Prognosis
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