Observations on the mechanism of functional obstruction of the nasopharyngeal airway in the horse.

The research explores how functional pharyngeal obstruction in horses, a condition that affects their breathing during exercise, may happen due to a displacement in the nasopharyngeal and laryngeal airways. This phenomenon has been observed through endoscopy and is linked to muscular activity, particularly with sternothyrohyoid and omohyoid muscles, suggesting possible surgical intervention to prevent the condition.

Research Methodology

• The research was conducted on 10 horses demonstrating signs of functional pharyngeal obstruction during exercise. This condition is observed as temporary blockage in the upper airway of horses while exercising.
• Fibreoptic endoscopy, a non-surgical technique allowing a full view of the complexity of an organ, was used to study the movement of the larynx and pharynx in these horses when their nasal passage was blocked. This would simulate more stressful breathing conditions, similar to during exercise.
• Cine-endoscopic films, moving visual recordings of the endoscopy for deeper analysis, were filmed for three of the horses under study.

Findings

• The analysis of airway movement led researchers to view functional pharyngeal obstruction as a subluxation, or partial dislocation, of the nasopharyngeal and laryngeal airways. Essentially, the condition is caused by a shift in these airways that shouldn’t normally occur.
• One notable and consistent aspect of this airway shift was a significant caudal (rearward) retraction of the larynx, one of the airways responsible for breathing and vocalization.

Proposed Causes and Solution

• The study suggests that the caudal retraction of the larynx causing the subluxation is a result of the activity of two muscles: the sternothyrohyoid (a muscle connecting the breastbone and the larynx) and the omohyoid (another muscle that aids in lowering the larynx).
• By implication, one way of preventing this condition in horses prone to functional pharyngeal obstruction when they exercise, could be through surgical intervention acting on these muscles. This could involve removing a portion of these muscles, but the study doesn’t provide any conclusive findings about potential surgical solutions and further research would be needed to evaluate effectiveness and safety of this approach.