Pathophysiology of dorsal displacement of the soft palate in horses.

The research explores the causes of dorsal displacement of the soft palate in horses, a condition affecting the upper airways during intense exercise. The study specifically investigates the role of various factors in this condition, by conducting three separate experiments on exercising horses.

Experiment 1: Evaluating the Role of Hypoglossal and Glossopharyngeal Nerves

• The first experiment looked at the effect of blocking the bilateral hypoglossal and glossopharyngeal nerves on epiglottic function in horses during exercise.
• The nerve block caused epiglottic retroversion, leading to an inspiratory upper airway obstruction. However, this did not result in Dorsal Displacement of the Soft Palate (DDSP), suggesting these nerves do not significantly contribute to DDSP.

Experiment 2: Looking into Tensor Veli Palatini Muscle Dysfunction

• In the second experiment, the researchers studied the hypothesis that dysfunction in the tensor veli palatini muscle, a small muscle in the upper throat, could be linked to the onset of DDSP.
• Surprisingly, the bilaterally removed tensor veli palatini did not cause DDSP. Instead, it led to instability of the rostral half of the soft palate and caused a minor inspiratory upper airway obstruction. Hence, the dysfunction of this muscle might not directly result in DDSP, but it seems to influence other symptoms.

Experiment 3: Exploring the Involvement of Palatinus and Palatopharyngeal Dysfunction

• The third experiment hypothesised that dysfunction in the palatinus and palatopharyngeal muscles could cause DDSP. To test this, the researchers blocked the pharyngeal branch of the vagus nerve in the guttural pouch bilaterally.
• This nerve block caused DDSP in all subjects within a timeframe of 2-15 minutes post nerve block. Additionally, DDSP resulted in expiratory nasopharyngeal obstruction.
• The results indicate that the pharyngeal branch of the vagus nerve, located near the retropharyngeal lymph node chain, can be a major contributing factor in the development of DDSP. Therefore, it is suggested that retropharyngeal lymphadenopathy, a condition involving the swelling of lymph nodes, may cause neural dysfunction and contribute to the onset of clinical DDSP in horses.