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

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.

On-site diagnosis: This new form of videoendoscopy allows practitioners to evaluate upper respiratory tract disorders in horses under racing conditions.

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.

Photo 1: Dorsal displacement of the soft palate.

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

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 2: A normal view of the larynx of the horse when training.

"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.

Photo 3: A DVE exam with a Standardbred.

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

> A purpose-made tube fixation bridle system that fits over standard tack (Photo 5)

Photo 4: A DVE exam with a horse at a gallop.

> 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.

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.

Photo 5: DVE headshot showing the endoscopy tube inserted and affixed to tack.

"Dynamic respiratory endoscopy is very exciting," says Jennifer Smith, DVM, DACVS, New Jersey Equine Clinic. "I really do believe it is going to change how we look at upper airway disorders in horses. My experience with the DRS has completely changed the way I interpret upper airway disorders in horses. Basically, what I have found is that it is impossible to predict how a horse's upper airway will function during exercise based on its appearance on a resting endoscopic exam alone. Horses with normal-looking airways at rest can experience severe dynamic obstructions during high-intensity exercise, or vice versa — a horse appears abnormal at rest (ex-asymmetry of the arytenoid cartilages, intermittent displace the soft palate) and maintains normal function during exercise. I no longer feel comfortable recommending a surgical treatment based on a resting exam alone or without a dynamic respiratory examination to document the airway disorder."

Photo 6: DVE equipment affixed to a saddle pad.

DRS examination gives veterinarians a way to evaluate patients both for initial diagnostic purposes, pre-purchase examinations, as well as for treatment follow-up. With DRS, veterinarians are able to compare a horse before and after surgery and provide objective documentation that the surgical procedure performed either corrected or failed to correct the airway disorder. Ideally, by having a definitive diagnosis on DRS examination to begin with, practitioners can make better treatment recommendations and have more favorable outcomes.

There are additional unique advantages to the use of DRS over traditional treadmill endoscopy. For horses that only develop abnormal noise or exercise intolerance at higher speeds over longer distances or when they are challenged in the company of other horses, DRS is likely to be more diagnostic than traditional treadmill endoscopy. "You can breeze the affected horse longer distances or alongside other horses to try to best replicate the conditions in which the horse typically demonstrates the dysfunction," says Smith. "You cannot do that with treadmill exams."

Scott Hay, DVM, of Teigland, Franklin and Brokken, Fort Lauderdale, Fla., who practices at Calder and various south Florida racetracks, has had DVE available in his practice for about 9 months. "It's a lot less traumatic for the horse," says Hay. "For owners or trainers, it's easier to consider using DVE at their home track or training center and not have to ship their horse to a facility where they could get a treadmill exam done."

Hay says that in south Florida, the nearest treadmill is a five-hour van ride away to the University of Florida School of Veterinary Medicine. "The other advantage to using this piece of equipment is that it more closely mimics the racing or the training experience — having the horses go naturally on a racetrack, rather than on a treadmill," says Hay.

Despite the many advantages, there are some minor concerns with the use of DVE. "There are things that can go wrong when you do it, and I've experienced most of them," Hay says. "It's a somewhat sensitive piece of equipment, so you have to make sure that everything is hooked up right and that all your pieces are functioning properly. There can be issues with mucus accumulation on the end of the scope, but this is reported as more of an annoyance than a true problem. Additionally, scope placement can result in difficulties. Problems have been experienced if the scope is placed improperly or slips during the examination."

During Priest's experience with DVE, there has not been a problem with mucus accumulation or the automatic lavage system, which rinses the lens. "Once the water is pumped across the lens, you might lose a few frames of video, but it is inconsequential," he says. Priest suggests that if you regulate the water and adjust it properly, the mucus causes minimal problems, However, he does admit that the visual disturbance is variable since some horses produce more mucus discharge than others.

There appears to be a definite learning curve in getting the right positioning of the scope in the horse's airway, but if you take the time to ensure that it is placed correctly to start with, then the other issues can usually be avoided.

Veterinarians using DVE have also experienced signal abnormalities on some racetracks, preventing continuous visualization on the monitor. However, the recording system allows the veterinarian to go back and view the examinations later.

"The main thing I tell most people is that we are probably not going to make a solid diagnosis while we are sitting there watching the horse train," says Hay. "We are going to take the images back to the computer and see what we've got."

Being able to save and send the images to others in the diagnostic and patient loop, including clients, trainers, referring veterinarians or other specialists, is an important feature to this new technology. "Seeing is believing, as the saying goes," says Smith. "And with most of the upper airway disorders, even an untrained eye can appreciate the difference in the size of a normal airway versus an airway experiencing a dynamic obstruction."

The DVE equipment is still new to most veterinarians, and both the systems and technology are likely to continue to develop in the future. However, the currently available systems are proving to be reliable, well-tolerated by patients and generally user-friendly. The clinicians making use of DVE have found that experience with the equipment is invaluable.

While DVE is not designed to replace the use of standing endoscopy and other diagnostic tools, it is another resource for diagnosing some of the more difficult upper respiratory abnormalities in performance horses.

Racetrack veterinarians may be concerned about the cost and usefulness of this device. Bryan Young, DVM, Young Equine Services, Cypress, Texas, has some of these concerns. "We have to have a unit that is portable and affordable," he says. "Obviously it has great application. We'd love to be able to see what these horses' throats look like under tack and at speed. I think the technology is very exciting, and I'd love to have it. It's just a question of getting it down to where we can afford it and where we would be able to set it up and use it effectively in a racetrack environment."

An exciting future

Several of the veterinarians currently using DVE systems are enthusiastic about the future of this technology.

"The actual endoscope and the quality of the images are so good now, and the stability of the images is far better than with the fiberoptic scope that is used on the treadmill," Priest says. "As with all technologies, there might be room for improvement, but the image quality is very good at this time."

Robertson says, "I think we are going to see some improvements through generations of development."

According to Robertson, audio is currently available on some of the equipment, including audio analysis of recordings, spectrographic analysis, and graphic analysis of noise frequency. In the near future, an audio component to the video is likely to be a standard feature, which will allow the practitioner to evaluate sounds that have been heard by jockeys or exercise riders on the racetrack to determine how significant those sounds are. There is also discussion of incorporating a global positioning system to monitor the speed and position of the horse on the racetrack when respiratory tract events such as a dorsal displacement of the soft palate occur.

Veterinarians would also like to know additional data about these patients at the time of respiratory compromise, including heart rate and respiratory rate. The goal is to provide practitioners with a safe, easy, useful and comprehensive tool that is affordable to purchase and maintain in private practice.

According to Robertson, the true benefit of DVE is that it is really helping equine patients.

Ed Kane, PhD, is a researcher and consultant in animal nutrition. He is an author and editor on nutrition, physiology and veterinary medicine with a background in horses, pets and livestock. Kane is based in Seattle.