Arytenoid cartilage movement in resting and exercising horses.

The research examines the movement of the arytenoid cartilage in horses both at rest and while exercising and finds that horses with arytenoid asynchrony at rest do not exhibit any progressive collapse of this cartilage during exercise, thus questioning the need for surgical intervention in certain cases.

Methodology

• The study was conducted on 49 horses where endoscopic examinations of their larynx were carried out both while they were at rest and while exercising.
• The exercise involved running on a 5% inclined high-speed treadmill for 8 minutes at a maximum speed of 8.5 m/sec.

Laryngeal Function Scores

• The horses were subjected to laryngeal function scores at rest and while exercising. This was based on the degree and synchrony of arytenoid abduction.
• The arytenoid abduction refers to the movement of the arytenoid cartilages located in the larynx that control the opening and closing of the larynx during breathing and noise production.
• The abduction was expressed as a left:right ratio of measurements of the rima glottidis, the opening between the vocal cords.

Findings

• Horses with arytenoid cartilage asynchrony at rest, defined as grade 2, could not be differentiated from normal horses when exercising as they maintained full abduction.
• Out of six horses with incomplete left arytenoid abduction at rest, defined as grade 3, five maintained full abduction during exercise, with one developing a dynamic collapse of the left side of the larynx.
• All horses with laryngeal hemiplegia at rest, that is, paralysis of one side of the larynx, defined as grade 4, developed dynamic collapse of the left side of their larynx during exercise.
• Horses with a resting left:right arytenoid abduction ratio greater than or equal to .71 consistently had complete arytenoid abduction at exercise. Seven horses with a left:right ratio less than .71 consistently showed dynamic collapse at exercise.

Implications of the Research

• The research suggests that horses with arytenoid asynchrony at rest do not suffer progressive collapse of the rima glottidis during exercise. Therefore, incomplete arytenoid abduction at rest is an unreliable predictor of such collapse.
• Furthermore, the results question the need for surgical treatment for all grade 2 horses and some grade 3 horses, which may otherwise be considered.