Failure of subtotal arytenoidectomy to improve upper airway flow mechanics in exercising standardbreds with induced laryngeal hemiplegia.

This research studied the effectiveness of a surgical procedure called subtotal arytenoidectomy on Standardbred horses suffering from induced left laryngeal hemiplegia. The results suggest that this treatment does not improve the impaired upper airway flow mechanics and blood gas measurements typically associated with this condition.

Overview of the Study

The study went through several stages:

• Baseline measurements were collected after exteriorization of the right common carotid artery, with the horses at rest, and while performing various levels of physical activity on a treadmill.
• Following this baseline data collection, left recurrent laryngeal neurectomy (LRLN) was performed on the horses, and measurements were taken again.
• Finally, the horses underwent a surgical procedure known as left subtotal arytenoidectomy and measurements were once again taken.

Results of the Study

• Baseline measurements showed that increasing the speed of the treadmill resulted in increased peak inspiratory and expiratory flow, peak inspiratory and expiratory transupper airway pressure, respiratory frequency, tidal volume, minute volume, and heart rate. Inspiratory and expiratory times decreased with increased treadmill speed, as did arterial oxygen tension. Inspiring and expiratory impedance did not change with treadmill speeds.
• After the LRLN procedure, peak inspiratory flow, respiratory frequency, and arterial oxygen tension significantly decreased during exercise, while peak inspiratory transupper airway pressure, inspiratory time and inspiratory impedance all significantly increased. Minute volume decreased at exercise after LRLN but not significantly. LRLN had no effect on peak expiratory flow, expiratory transupper airway pressure, expiratory impedance, heart rate, arterial carbon dioxide tension or tidal volume.
• The key result from this study was that the final surgery, subtotal arytenoidectomy, had no effect on improving impaired upper airway flow mechanics or blood gas measurements associated with left laryngeal hemiplegia.

Implications of the Study

• These results suggest that while LRLN surgery impacts several aspects of upper airway flow mechanics and arterial blood gas levels, subtotal arytenoidectomy does not appear to have the desired effect of improving those parameters for horses suffering from left laryngeal hemiplegia.
• This indicates that alternative treatments or surgical procedures may need to be considered for this condition in horses.