Upper airway abnormalities are common causes for poor performance in the equine athlete. Racehorses are not the only equine athletes that suffer performance problems related to upper airway problems. Horses of all breeds and disciplines can be and are affected with upper respiratory problems.
If you have a performance horse that is making abnormal noises at exercise, or is becoming exercise intolerant, then you might need to investigate dynamic endoscopy. J. Brett Woodie, DVM, MS, Dipl. ACVS, explains what this examination entails and what this procedure can do to help diagnose upper respiratory problems.
The horse is an obligate nasal breather, so all the air needed for oxygenation must pass through the upper airway. The upper airway of the horse must accommodate a very large increase in airflow during exercise.
During maximal exertion the upper airway must handle more than a 20-fold increase in airflow compared to airflow at rest. The upper airway also must withstand significant negative pressure that is generated during exercise. There is a nine-fold increase in the amount of negative pressure generated in the upper airway at exercise compared to resting conditions.
It is easy to understand that what may seem like a minor abnormality at rest can be a big problem at exercise.
An endoscopic examination is the primary diagnostic tool used by veterinarians to evaluate the upper airway. Numerous upper airway abnormalities can be diagnosed from a resting endoscopic examination. However, endoscopy of the upper airway while the horse is exercising is an invaluable tool for diagnosing dynamic problems the equine athlete may experience.
A dynamic problem is only present during exercise and will not be evident at rest or during an endoscopic examination immediately after strenuous work. Often a dynamic examination will clarify multiple problems of the upper airway. This is vital information so that all problems can be addressed.
Case selection for an endoscopic examination while exercising includes horses that are experiencing unexplainable poor performance; those making abnormal respiratory noise with a normal resting endoscopic examination; horses that have an abnormal finding on resting endoscopy but the effect still needs to be assessed at exercise; and cases in which there is a concern for a dynamic upper airway problem.
There are two methods that can be used to evaluate the upper airway during exercise. One is a treadmill examination and the second is over-ground endoscopy. Over-ground endoscopy uses endoscopic equipment that is attached to the horse so that the upper airway can be examined while the horse is working under their natural conditions.
Once the decision has been made to evaluate the horse using a dynamic examination, we must make sure that the horse is as fit as it is for competition. If the horse has been out of work, it may not be able to withstand strenuous work and the problem may go undiagnosed. The horse may be at greater risk to sustain an injury if it is not fit and is subjected to a strenuous workout.
If fit for the exam, the horse then is subjected to an exercise test that mimics the type of work that the horse typically performs. It is very important to have the exercising conditions simulate the horse’s normal working conditions as closely as possible not only in intensity, but also in distance, as well as head and neck carriage. The position of the head and neck changes the amount of airway resistance that is present, so it is important to have the horse’s head and neck positioned properly during the examination or the upper airway abnormality may go undiagnosed.
Over-ground endoscopy allows the clinician to replicate the exact type of work that the horse performs. Often there are influences of the rider/jockey/driver and movements of the horse that exacerbate an upper airway problem. It is not always possible to simulate these factors during a treadmill examination. The endoscopic examination is recorded so that it can be reviewed. The over-ground endoscopic equipment has a distinct advantage when examining horses that must be shown with a certain head and neck carriage (“collection”) or when a horse needs to be ridden or driven in order to create the upper airway problem.
Once the horse has completed the exercise test, the endoscope is removed from the nasal passage and the horse is cooled out appropriately. While the horse is being cooled out, the upper airway video is reviewed in real time, as well as in slow motion, to look for any abnormalities. It is very important to review the video in slow motion so the full extent of any airway abnormality can be assessed.
A dynamic examination of the upper airway is an invaluable tool that is necessary in order to diagnose many upper airway abnormalities. Predicting upper airway function based on a resting endoscopic examination is very difficult if not impossible. There are numerous abnormalities that occur only during exercise therefore a resting examination will not allow the veterinarian to make the diagnosis.
By J. Brett Woodie, DVM, MS, Dipl. ACVS