Evaluating Horse Airways: At Rest, During Exercise, or Both?
Veterinarians, if you’re evaluating a horse with a respiratory noise, do you reach for your standard endoscope to assess the horse at rest or arrange to have a dynamic or overground analysis performed?

As it turns out, both techniques provide invaluable information and, in most cases, should be used together.

“Start with resting endoscopy,” advised Safia Barakzai, BVSc, MSc, DESTS, Dipl. ECVS, FRCVS, an equine surgeon from Equine Surgical Referrals, in West Sussex, U.K., during her presentation at the 2017 American Association of Equine Practitioners Convention, held Nov. 17-21 in San Antonio, Texas. “Be aware, though, that even within seconds to minutes within cessation of exercise, conditions in the upper respiratory tract change, and abnormalities can rapidly disappear.”

Therefore, the goal of the resting endoscopic examination is to investigate gross structural abnormalities and potentially predict the horse’s laryngeal function during exercise.

“When possible, if the horse is not fractious, try to do the resting endoscopic examination without sedation to limit the impact of sedatives on laryngeal function,” said Barakzai. “During this resting exam, the veterinarian must induce swallowing and occlude nostrils.”

Further, she recommended veterinarians use the recommended Havemeyer System for grading throats to allow all individuals working on the horse to effectively reassess him at different times. That system, detailed in the conference proceedings, involves grading equine throats on a scale of 1-4 (with subgrades) at rest and uses an A, B, or C grading system in exercising horses.

When pursuing dynamic or overground endoscopy, Barakzai emphasized that being physically present, listening to the horse, and watching the examination, rather than simply being sent a video, is extremely valuable. Closely observing the exam can help the veterinarian differentiate between inspiratory and expiratory noises and distinguish between normal and abnormal respiratory noises during exercise.

“Trainers often push for treatment rather than overground endoscopy because of additional costs,” Barakzai said. “It’s important to relay that resting endoscopy can be incorrect or incomplete and that multiple abnormalities can occur.”

She added that “owners and trainers need to appreciate the costs associated with incorrect treatment, convalescence, and retraining, loss of earnings, and devaluation of horses that have had multiple surgeries all because they didn’t perform both resting and overground endoscopy.”

For example, nasopharyngeal collapse can occur at the walk, but this does not necessarily mean it will occur at faster gaits. At the walk, she said, horses are often pulling and dropping their head, causing the collapse.

Veterinarians perform an overground exam with the goal of reproducing competition conditions, which can be challenging, said Barakzai.

Specific examples of when using both resting and overground is beneficial include when the veterinarian suspects:

  • Vocal fold collapse, which can occur independent of arytenoid cartilage collapse (both of which are integral structural components of the larynx);
  • Arytenoid cartilage collapse, which can occur even in horses with “normal” resting laryngeal function;
  • Medial deviation of the aryepiglottic fold, blocking the smooth flow of air through the larynx and upper airways;
  • Collapse of the apex of the corniculate process of the arytenoid, located at the top end of the arytenoid cartilages in the larynx (recently renamed ventromedial luxation of the apex of the corniculate process);
  • Epiglottic entrapment and epiglottic retroversion
  • Cricotracheal ligament collapse;
  • Laryngeal dysplasia (or branchial arch defects); and
  • Palatal instability and dorsal displacement of the soft palate.

“This latter abnormality, palatal instability, can occur in all types of athletic horses, and the results of standing and dynamic endoscopic exams don’t often match up,” Barakzai said. “This highlights the need for both types of examinations.”