If a horse is unable to properly move air in and out of its lungs, it is no surprise that it is is unable to perform to the best of its athletic abilities. There are a variety of conditions that can affect the upper airway of our equine athletes.
The upper airway consists of the nostrils, nasal passages, nasopharynx and larynx. It is possible to have conditions that affect one or more structures within this portion of the airway which can affect the movement of air in or out.
Endoscopic examination of the upper airway involves passing a scope up one or both nostrils to visualize the entire nasal passage, nasopharynx and larynx. These structures can be assessed for anatomic and functional defects. For horses that are suspected to have an upper airway abnormality but have a normal resting airway exam, a dynamic airway exam may be necessary. This involves the same principle as the resting exam with a scope passed up the nose to visualize the nasopharynx and larynx, but instead, this special scope is secured in place and the horse is asked to perform its usual activity. Horses can do dressage, jump and even gallop at full speed with the scope in place. This allows the veterinarian to assess the function of the airway during the horse’s most intense activity.
Perhaps the most commonly seen upper airway condition in performance horses is laryngeal hemiplegia, more commonly known as roaring. This condition occurs due to paralysis of one side of the larynx. Most commonly, the left side is affected due to the longer route in which that nerve takes to innervate it’s laryngeal structures. This paralysis allows a portion of the laryngeal cartilage to protrude into the airway. When exercising, the airway is under increased negative pressure and this cartilage, as well as the vocal cord, are pulled into the airway, creating a dynamic obstruction to airflow. The vocal cord fluttering in the wind creates the characteristic roaring sound. This condition is most frequently corrected via a surgical procedure, known as a tie back. Here, a suture is placed through the paralyzed cartilage and tied back to hold that structure out of the airway. Most commonly, this procedure is combined with a resection of the vocal cord to further prevent any future obstruction.
Another important condition to consider is known as dorsal displacement of the soft palate. The soft palate is a soft flap of tissue that extends off the back edge of the hard palate towards the larynx. In horses, this structure usually sits underneath the epiglottis and is thus out of the way of normal air flow into the trachea. In some horses, the back edge of the soft palate displaces upwards and the epiglottis becomes trapped underneath it. The free edge of the soft palate then creates an obstruction to airflow as the horse breathes out. When they are unable to expel the entire breath of air, they are subsequently unable to take a full breath back in. This results in the horse having to take smaller breaths when its oxygen demands are highest. They are unable to meet their needs and their performance suffers. This condition is characterized by a gurgling sound on expiration as the free edge of the soft palate flutters as the expired air passes over it. This is of high suspicion in horses that are performing appropriately but suddenly begin having trouble and may even stop on course. It is extremely common for these horses to have normal resting endoscopic examinations and thus, a dynamic examination should be considered when the level of suspicion is high. Surgical correction is achieved via a tie forward procedure in which the entire larynx is pulled forward and secured in place to prevent the epiglottis from being pulled backwards allowing it to slip under the edge of the soft palate.
If you hear an abnormal sound while your horse is exercising or you find that your horse is unable to perform at the level that it was previously able, consider having a complete airway examination performed by your veterinarian. This may include an under saddle evaluation, resting endoscopy and, potentially, dynamic endoscopy. Identifying the cause of the problem will help you and your horse breathe easier.