Dynamic videoendoscopy: A new method for diagnosing equine upper airway disease
Traditional upper airway assessment methodsFor 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
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 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.