In Depth: Evaluating the Upper Respiratory Tract (AAEP 2011)
Woodie said that to perform a dynamic examination and achieve accurate results, it's important to reproduce the horse's usual work routine--including tack, headset, duration, speed, and gaits performed--as seen here.
Photo: Anne M. Eberhardt/The Horse
Performance horses can develop a host of upper respiratory problems that can cause exercise intolerance, abnormal respiratory sounds, and poor performance. Fortunately, veterinarians have fine-tuned numerous methods for evaluating the upper respiratory tract for abnormalities. An equine surgeon recently reviewed these in a presentation to veterinarians at the 2011 American Association of Equine Practitioners Convention, held Nov. 18-22 in San Antonio, Texas.
When to Evaluate
Brett Woodie, DVM, MS, Dipl. ACVS, a surgeon and owner at Rood & Riddle Equine Hospital, in Lexington, Ky., noted the veterinarian first must decide when an upper respiratory examination is indicated. Consultation with the horse's owner or trainer is important, he added, as the veterinarian needs a complete history is to determine next steps.
Owners, riders, or trainers should be prepared to answer questions including:
- Is the horse exercise intolerant, and how is his recent race or performance record?
- Have you noticed any unusual noises--consistent or intermittent--when the horse works, and when during the work is the noise most common?
- Has he previously had an endoscopic examination or surgery on the upper respiratory tract?
Answers to these questions will help a veterinarian determine the best course of diagnostic action, Woodie explained.
Next, he recommended the horse undergo a physical examination. He suggests veterinarians "take a step back" and examine the horse thoroughly with these techniques:
- Look and feel for any decrease or asymmetry in airflow from the nostrils, and look for any nasal discharge;
- Evaluate the heart and lungs ("Remember that diseases of the lower airways and lungs do not cause upper respiratory noise," he cautioned);
- Palpate both jugular veins, the trachea, and the larynx; and
- Examine the head and eyes carefully, and look closely for any asymmetry in the shape or carriage of the horse's head.
- Woodie said he subsequently turns to endoscopic examinations--resting and/or dynamic--if indicated by one or more of the following clinical signs:
- Exercise intolerance and/or poor performance;
- Upper respiratory noise;
- Nasal discharge; and
- Abnormal swelling of the head or neck.
"The resting endoscopic examination is very important to determine if there are any structural or anatomic abnormalities present" that are causing the above clinical signs, Woodie explained.
Veterinarians have several resting endoscopy options:
- Video endoscopes, which allow live review of the images on a screen large enough for several people to observe, all while recording the examination;
- Fiber-optic endoscopes, which only allow the veterinarian performing the evaluation to view the results; and
- Portable video endoscopes, which are smaller in size but have similar capabilities to larger video endoscopes.
Woodie noted that when preparing the horse for examination, restrain but do not sedate him, . Sedation can interfere with the function of the upper airway, especially when evaluating laryngeal function ("Sedation can affect the function of the larynx, thus making assessment difficult," Woodie noted).
A veterinarian passes the endoscope into the airway to look for the following anatomic or functional anomalies:
- Laryngeal hemiplegia, also known as "roaring" ( paralysis of one or both arytenoid cartilages whereby the horse cannotfully abduct these structures during respiration);
- Ethmoid Hematoma (a potentially destructivemass located in the ethmoid region of a horse's nasal passage);
- Masses (including chronic inflammatory lesions like granulomas, cysts, and tumors);
- Arytenoid chondritis (inflammation or infection involving one or both arytenoid cartilages)
- Nasal septum swelling (when the bony structure dividing the nasal cavity thickens and, in turn, narrows the nasal passages);
- Nasopharynx narrowing (the region extending from the nasal passages to the trachea);
- Dorsal displacement of the soft palate (when the epiglottis--which normally lies on top of the soft palate--becomes displaced below the soft palate); and
- Epiglottic entrapment (when the epiglottis--a movable, leaf-shaped piece of cartilage located at the base of the tongue and above the soft palate--becomes trapped by the nearby aryepiglottic folds of tissue).
Diagnosis with some of those conditions means a very poor prognosis to resume athletic activity, noted Woodie.
He cautioned, however, that multiple scientific research papers have shown resting endoscopy isn't always able to predict abnormalities that arise only during exercise.
To this end, Woodie discussed the relatively new concept of using laryngeal ultrasound to help predict laryngeal function during exercise. Laryngeal ultrasound is a useful tool when evaluating horses with arytenoid chondritis and other anatomic abnormalities of the laryngeal cartilages, he said. He noted that clinical studies have suggested this tactic could be effective.
If the veterinarian detects no major problems during a resting exam, Woodie said that a dynamic endoscopic examination--in which the horse undergoes the exam while exercising on a high speed treadmill or working under saddle--is the next step in the diagnostic procedure.
Most often veterinarians employ these exams if the horse has a history of poor performance or emits a noise while working, or if there are abnormal findings--or no problems at all--on his resting exam.
Woodie said that to perform a dynamic examination and achieve accurate results, it's important to reproduce the horse's usual work routine--including tack, headset, duration, speed, and gaits performed. For example, some horses' abnormalities are only evident when working in a very collected frame. Conversely, other horses could have questionable upper airway function at rest that turns out to be normal during exercise.
Some anomalies that veterinarians typically only diagnose during dynamic endoscopic evaluations include axial deviation (collapse) of the aryepiglottic folds, epiglottic retroversion, and pharyngeal collapse.
Epiglottic retroversion is a relatively uncommon condition that involves a dysfunction of the hyoepiglottis muscle; this renders the epiglottis unable to maintain its correct position on the soft palate. In turn, the epiglottis is sucked into the larynx during inspiration.
Pharyngeal collapse occurs in various areas of the pharynx, with lateral (side) wall collapse being the most difficult to treat. The pharynx essentially collapses during exercise, limiting the horse's ability to breathe.
By making use of both the horse's clinical history and the available technology, veterinarians are often able to make an accurate diagnosis before deciding on a course of action. Upon reaching a diagnosis, Woodie said a veterinarian will begin planning treatment. He or she will consider both surgical and nonsurgical options before implementing a treatment plan.
Should your horse develop signs possibly indicative of upper respiratory tract issues, work with your veterinarian to determine exactly what's going wrong. An accurate diagnosis often leads to successful treatment and return to athletic function.
About the Author
Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.
POLL: Mosquito-Borne Diseases