Dynamic videoendoscopy: A new method for diagnosing equine upper airway disease

Dynamic videoendoscopy: A new method for diagnosing equine upper airway disease

Many equine practitioners find value in new imaging technology
Feb 01, 2010

On-site diagnosis: This new form of videoendoscopy allows practitioners to evaluate upper respiratory tract disorders in horses under racing conditions.
Racehorses have their own assortment of distinct veterinary needs. Two of the most common concerns and conditions for horses in the racetrack environment are upper airway disease and gastric ulceration. This article covers new developments in the diagnosis of upper airway disease. (Next month's article will discuss gastric ulceration.) Dorsal displacement of the soft palate (Photo 1), left laryngeal hemiplegia, axial deviation of aryepiglottic folds, other epiglottis abnormalities, chondritis and retro-laryngeal abscess are common disorders of the equine upper airway. Treatment varies widely depending on the type and severity of abnormality, so a definitive diagnosis of the cause of respiratory performance problems is critical. Since many of these conditions are induced by strenuous exercise, they can be especially elusive.

Photo 1: Dorsal displacement of the soft palate.
Until recently, the evaluation of equine upper respiratory tract disorders was done with a combination of physical examination and resting or high-speed treadmill endoscopy. Today, racehorses can be evaluated under racing conditions thanks to the availability of exercise videoendoscopy (Photos 1, 2) or dynamic videoendoscopy (DVE). To appreciate this new technology, it is important to understand the limitations of other available diagnostic tools.

Traditional upper airway assessment methods

For more than 30 years, James T. Robertson, DVM, DACVS, has used equine endoscopy, both in the standing horse and with the use of the high-speed treadmill, and has now become a pioneer in the use of DVE. Before high-speed treadmills were available, veterinarians like Robertson were limited to resting or immediate postexercise endoscopy. This remains the most available diagnostic procedure for racetrack and performance horse veterinarians. However, with these techniques, various dynamic obstructions are often underdiagnosed because of an inability to observe the upper respiratory tract under actual performance conditions.

"You can still make a diagnosis, in most cases, with resting endoscopy," Robertson says. "There is still room for good old-fashioned physical examination, scoping at rest and making a diagnosis, without having the sophistication of this new technology."

However, for patients that may appear normal on resting endoscopy but that have a history of respiratory noise or poor performance or for patients with an identifiable airway abnormality that does not correspond with the clinical signs and history, it is necessary to better evaluate their upper respiratory tracts during strenuous exercise. For instance, some horses are presented when they are very early in the process of developing left laryngeal hemiplegia, and it can be difficult to make a definitive diagnosis. Some dynamic conditions may not show up on resting endoscopy, even with manipulations (such as nasal occlusion) that stress the airway. Examples of this include soft palate displacement, intermittent epiglottic entrapment and nasopharyngeal collapse. Another situation that can be encountered is when a horse has already had throat surgery and yet is not performing up to expectations. It may be beneficial in these cases to further assess the airway with a dynamic examination.

In some cases, relying solely on resting endoscopy may not give the necessary confidence to elect a specific treatment. Veterinarians often have unanswered questions or feel that their observations are not yet complete. In these situations, more information can be provided by a dynamic airway examination.

"I think that there is a lot more information to be gained by examining the airway under stress, and we learned this using the high-speed treadmill," says Robertson. "We might have had an idea based on the history, clinical signs and the findings of the resting endoscopy, but with a dynamic evaluation, we can be more definitive in our assessment." The use of a high-speed treadmill allows veterinarians to assess a patient's airway during controlled exercise.

Treadmill exercise does not mimic racing precisely. Studies comparing treadmill with field conditions showed a significant variation in heart rate, exercise stride length and stride frequency. The treadmill lacks various racing factors such as ground quality, rider weight, the presence of a harness and sulky (Standardbreds) or other tack maximal achieved speed and other environmental variables. Concerns for injury on the treadmill, treadmill training sessions and expensive equipment costs are additional limitations.

"With a treadmill, it's difficult for me to believe that you can even come close to simulating having the horse on the racetrack," says Gary Priest, DVM, Harthill and Priest, Versailles, Ky. "You don't have the rider, the bit, the bridle, the tongue tie, and so on. Additionally, there is a lot of inherent danger with the use of treadmills — risks to the horse and equipment as well as the need to transport the horse to the location of the treadmill."

The advent of DVE

Photo 2: A normal view of the larynx of the horse when training.
Until recently, treadmill endoscopy was the most advanced equine upper respiratory tract diagnostic tool available. The inherent risks and limitations with treadmill exercise endoscopy have now been addressed. DVE (also known as dynamic respiratory scope [DRS]) allows for monitoring of the upper equine airway during exercise sessions on the racetrack in both Thoroughbreds and Standardbreds (Photos 3 & 4).

Photo 3: A DVE exam with a Standardbred.
"This is about as close as anything we've ever had to simulating actual racing conditions for both Standardbreds and Thoroughbreds," says Priest, who has done more bouts with the DRS than anyone in the United States. Utilizing a wireless telemetric endoscope, it provides equine practitioners with direct visualization and a reliable and safe method for imaging the equine upper respiratory tract during natural exercising conditions. With on-board endoscopes, the most common causes of upper respiratory tract disorders can be easily and accurately diagnosed during any type of performance.

With the development of exercise videoendoscope systems, horses can be examined at regular training sites and under natural training conditions. This is helpful in reaching a definitive diagnosis in many cases, as Robertson notes: "If a horse is displacing it's soft palate, it's more likely to displace under more natural conditions — on the racetrack, at the training center or wherever it trains on a day-to-day basis."

The typical DVE system consists of:

> A semirigid malleable insertion tube (9.8 mm in diameter) with an autolighting head (light-emitting diodes), which negates the need for a heavy and energy-consuming light source

Photo 4: A DVE exam with a horse at a gallop.
> A purpose-made tube fixation bridle system that fits over standard tack (Photo 5)

> A solid permanent virtual circuit (PVC) box containing all the electronics

> An integrated lavage system including pump with settings, tubing and bottle

> A remote receiver PVC video display box for real-time visualization that operates on a battery or AC.

Photo 5: DVE headshot showing the endoscopy tube inserted and affixed to tack.
Commonly, the electronics and lavage system are contained either in a rider backpack or sulky harness watertight bag. Also available is a smaller compact system in which much of the electronics are mounted to the saddle pad, making it less cumbersome to the rider (Photo 6). A system variation allows for remote control adjustment of the scope position while the horse is being exercised, using a joystick or keyboard control. Another available system enables the practitioner to directly transmit the visualization via computer to other veterinarians for consultation at sites anywhere throughout the world.