Accurate Diagnosis of Upper Airway Dynamic Obstructions: A Critical Guide to Surgical Success

Whatever the equestrian discipline, age or breed, the respiratory system represents the main limiting factor to exercise in the healthy horse. Respiratory diseases are the second most common cause of wastage in sport horses and racehorses. The upper airways (UA) are involved in the high prevalence of respiratory problems as a cause of poor performances. The advent of overground endoscopes has revolutionized our diagnosis of UA disorders in practice: we can now recreate “real-life” conditions and observe UA function in situations similar to work or competition. We can also account for important factors that interfere with upper airway stability or patency during work such as rider, equitation and tack.

Whatever the clinical signs of UA dysfunction we observe during exercise, these are linked to a primary cause: identifying that underlying cause is of paramount importance to propose an adapted treatment be it medical or surgical. Missing the proper diagnosis inevitably leads to poor therapeutic success rate.

A few elements of physiology

To provide the lowest resistance due to inertance, friction and turbulence, the horse’s upper airway should ideally have been be short, large, straight and rigid. However, they are long, narrow in some critical areas such as the larynx, bent and compliant in others such as the pharynx. The pharyngeal and laryngeal sections of the UA is made of soft tissue and only sustained by muscles or mobile cartilages, making them highly susceptible to dynamic collapse when submitted to important transmural pressures, such as those physiologically encountered during exercise.

Any abnormality that would reduce the airway section would be a potential factor of impaired ventilation and consequently impaired performance. Complex obstructions, where more than one structure collapses into the airway, or combinations of upper and lower airway disorders occur frequently. Multiple abnormalities will more commonly be associated with significant gas exchange impairment than single disorders.  [...]