Role of the hypoglossal nerve in equine nasopharyngeal stability.

The research explores the role of the hypoglossal nerve in maintaining the stability of the upper airway in horses, particularly during strenuous exercise. The study found that disturbance to the nerve’s function can cause respiratory issues similar to a naturally occurring equine disease.

Background and Purpose of the Study

• This study targets understanding the role of the hypoglossal nerve in the stability of the equine upper airway, which provides a high oxygen demand during strenuous aerobic exercise in horses.
• While it is known that the tongue musculature, which the hypoglossal nerve innervates, plays an essential role in human airway stability, its role in equine upper airway stability has not been previously established.
• The researchers aim to provide insight into respiratory functioning that could potentially be applied to humans.

Methodology

• The research used isolated tongues from eight mature horses to determine the distal anatomy and branching of the equine hypoglossal nerve.
• Using the collected data, a peripheral nerve location technique was used to perform bilateral block of the common trunk of the hypoglossal nerve in 10 horses.
• Each horse was subjected to two trials with the bilateral hypoglossal nerve block and two control trials (unblocked). The upper airway stability during exercise was then measured using videoendoscopy and measurement of tracheal and pharyngeal pressure.

Findings

• Three primary nerve branches were identified: medial and lateral branches and a discrete branch that innervated the geniohyoid muscle alone.
• The bilateral hypoglossal block induced nasopharyngeal instability in more than half the trials, while none of the control trials resulted in instability.
• This instability persisted until the end of the treadmill test, resulting in an expiratory obstruction similar to a naturally occurring equine disease known as dorsal displacement of the soft palate (DDSP).

Implications

• The data suggests that the hypoglossal nerve mediates the stability of the equine upper airway during exercise.
• This research can contribute to shedding light on how the upper airway functions in species with extreme respiratory adaptation, potentially providing insights that could be applied to human respiratory functioning.
• The researchers also noted similarities between DDSP in horses and obstructive sleep apnea in humans. As such, further studies of equine respiratory functioning could potentially contribute to understanding and treating sleep-related breathing disorders in humans.