WHAT IS THE TRACHEA ANYWAY?
“Trachea” is the scientific name for the windpipe, the tube that connects the nose, mouth, and throat to the lungs. The trachea is meant to be a fairly rigid tube. It consists of muscle connecting a group of cartilage rings. The rings are actually not complete circles; they form a C with the open end of the C facing towards the animal's back. This muscle covering the open end of the C is called the “tracheal membrane” or sometimes the "trachealis" muscle.
When the diaphragm (the flat muscle separating the abdomen from the chest cavity) flattens and the intercostal muscles (the muscles between the ribs) move, air is sucked into the lung. When the muscles move the opposite direction, air is pushed out of the lung. The trachea serves as a pipeline bringing air into the chest. Part of the trachea is in the throat but it also extends into the chest so that we can look at the trachea as having an intrathoracic portion (inside the chest) and an extrathoracic portion (outside the chest).
WHY WOULD A TRACHEA COLLAPSE?
Tracheas collapse because the cartilage rings weaken, which is where the term "tracheomalacia" comes into play. Tracheomalacia is the condition where the cartilage becomes spongy and soft. Cartilage in this condition cannot hold its rigid C-shaped supportive structure. When the C loses its curvature, the tracheal membrane across the top stretches out and loosens, becoming floppy. Instead of being a tight muscle canopy, the now flimsy membrane moves as air passes through the trachea. When air rushes into the chest, the membrane of the intrathoracic trachea balloons outward and when air rushes out, the membrane of the intrathoracic trachea droops down into the C cartilage causing an occlusion. The tickling sensation of the membrane touching the tracheal lining generates coughing and if the obstruction interrupts breathing, the patient may become distressed. If the collapse is in the extrathoracic (also called the cervical) trachea, the opposite occurs; the collapse occurs during inhalation and the ballooning during exhalation. In the unluckiest of patients, the tracheomalacia extends down the bronchi (large airways that feed each lung). These patients have the worst prognosis and the worst coughing.
Panting or rapid breathing for any reason makes the collapse and anxiety worse, which unfortunately tends to generate more rapid breathing and a vicious cycle of distress.
Making things worse still is the inflammation generated in the trachea. The collapse creates increased secretion and inflammation thus promoting yet more coughing which creates yet more inflammation. The enzymes involved in inflammation further soften the tracheal cartilage making the collapse worse. Ultimately, the tissue of the trachea changes and loses its normal characteristics and the condition gets worse and worse.
The trachea may be collapsed along its entire length, only in the intrathoracic section, or only in the extrathoracic section. Most commonly the collapse is at its worse right where the trachea enters the chest.
Many dogs with collapsed tracheas do not show symptoms, however, until a second problem complicates matters. Factors that bring out symptoms might include:
If a secondary factor such as one of those listed above should occur and make a previously incidental collapsed trachea a problem, often removal of the secondary factor (weight loss program, getting an air filter, etc.) may clear up the symptoms of the collapsed trachea.
The following steps are often helpful in long-term management of the tracheal collapse patient:
In a recent retrospective study of 100 dogs with collapsing trachea, 71% responded to medication and management of secondary factors (obesity, irritants in the air, etc.), 7% had disease so severe that they died within one month of diagnosis, 6% had severe additional disease problems, and the other 16% were felt to be candidates for surgical treatment (see below).
The patient's distress can reach a level so severe that the normally pink mucous membranes become bluish and collapse can result. When this occurs, tranquilization is helpful to relieve the anxiety that perpetuates the heavy breathing and coughing. Oxygen therapy and cough suppressants also help. If the patient reaches the point where distress seems extreme or if collapse results, treat this an emergency and rush the pet to emergency veterinary care.
Surgical therapy of tracheal collapse requires a surgery specialist. If one is not on staff or cannot be scheduled, referral can be arranged. For more information on this procedure, the American College of Veterinary Surgeons has a web page at:
IS THERE ASSOCIATED LIVER DISEASE?
In the July/August 2006 issue of the Journal of Veterinary Internal Medicine, a group of researchers led by Natali B. Bauer pursued the common finding of enlarged liver in dogs with tracheal collapse. Her group looked at 26 dogs with tracheal collapse and compared liver function test results to 42 dogs without tracheal collapse. Ninety-two percent (92%) of dogs with tracheal collapse were found to have abnormal results. Dogs that received stent placement to assist their breathing showed improvement in these tests. It was concluded that oxygen deprivation from the collapse had resulted in significant liver disease in many tracheal collapse patients. It was further recommended that tracheal collapse patients have liver function tests periodically performed as liver supportive medications may be helpful.
Page last updated: 2/20/2020