The larynx (sometimes called the voice box) is a muscular and cartilaginous structure that connects the pharynx (throat) and trachea (windpipe). The larynx contains the vocal cords. These are the muscular structures within the airway that vibrate when air passes by them allowing us to talk, bark or meow. The opening to the larynx is covered by the epiglottis, a large muscular flap that covers the windpipe when we swallow, to prevent food from entering the trachea. The larynx itself also closes to prevent aspiration of food and water. This function is so important that, of the eight muscles of the larynx, seven of them are responsible for closure. The remaining muscle (cricoarytenoideus dorsalis) functions to open the laryngeal portion of the airway by abducting (pulling open) the arytenoid cartilages when we inspire. If the muscle stops functioning properly, the airway cannot remain open as we breathe, causing roaring, gasping episodes which may become life-threatening.
Laryngeal Paralysis refers to a failure of the laryngeal cartilages to open during inspiration, creating a partial or complete upper airway obstruction. It is usually caused by dysfunction of the nerve (recurrent laryngeal) that controls the laryngeal musculature. This can be secondary to a disease process that affects all of the nerves of the body (polyneuropathy) or a traumatic event that affects only the laryngeal innervation. Generalized neuromuscular or muscular disease can also result in laryngeal paralysis. Most of these processes, with the exception of a traumatic episode, are slowly progressive, until an acute exacerbation causes a life-threatening crisis. A temporary tracheotomy may be necessary to bypass the compromised airway as an emergency procedure until definitive surgical correction can be performed.
The signs of laryngeal paralysis most commonly begin as a vague change in the quality of the voice, then progress to noisy breathing sometimes called "roaring", inspiratory dyspnea (difficulty breathing in), and stridor (noisy gagging or coughing). Cyanosis (a blue tinge to the tongue due to lack of oxygen) may also be present. This predisposes the patient to a life-threatening collapse, asphyxia and death. The signs of laryngeal paralysis are often made worse by exercise, hot and humid weather, and obesity. Aspiration pneumonia can also occur during violent gasping and gagging episodes.
The diagnosis of laryngeal paralysis involves direct observation of arytenoid function during respiration. This is usually performed under heavy sedation or light anesthesia. When we breathe normally, we abduct (pull open) the larynx and decrease the pressure in our lungs by expanding our chests. These actions allow air to flow down our trachea and into our lungs (just like the way that we make liquid travel up a straw). Dogs with compromised airflow through the larynx must work harder to fill their lungs with air. This decreases the airway pressure even more, which literally pulls the laryngeal wall into the airway (just like the way a straw collapses if you suck hard enough). When collapsed, the paralyzed laryngeal wall closes in front of the opening to the trachea and blocks the flow of air. Thus, the paralyzed larynx is sucked closed when we need air the most, creating the anxious and terrifying noisy breathing, gagging and gasping for air with exercise or periods of excitement.
While emergency procedures ranging from sedation, oxygen, and corticosteroids to tracheotomy may be required for initial stabilization, SURGERY is the only permanent correction. An arytenoid lateralization is a procedure that uses sutures to hold the laryngeal portion of the airway open. This can be performed either unilaterally (one side) or bilaterally (both sides). The suture is passed through the arytenoid cartilage to the outside of the larynx and tied. This abducts (pulls out) the arytenoid process, preventing collapse. This procedure also, in effect, debarks dogs, preventing the air turbulence necessary to create a high pitched sound.
Postoperative hospitalization for 24 to 72 hours is required due to the potential for aspiration and laryngeal swelling. Broad spectrum antibiotics and anti-inflammatory medications are utilized for 5-10 days along with a cool, calm atmosphere for recuperation. Occasionally, sedatives may be required. It is also important to avoid heavy exercise during hot or humid weather and to avoid excessive weight gains.
Copyright 1998, Southern
California Veterinary Surgical Group