Effects of stylopharyngeus muscle dysfunction on the nasopharynx in exercising horses.
BACKGROUND
Nasopharyngeal collapse has been observed in horses as a potential cause of exercise intolerance and upper respiratory noise. No treatment is currently available and affected horses are often retired from performance.


OBJECTIVE
To determine the effect of bilateral glossopharyngeal nerve block and stylopharyngeus muscle dysfunction on nasopharyngeal function and airway pressures in exercising horses.


METHODS
Endoscopic examinations were performed on horses at rest and while running on a treadmill at speeds corresponding to HRmax50, HRmax75 and HRmax, with upper airway pressures measured with and without bilateral glossopharyngeal nerve block.


RESULTS
Bilateral glossopharyngeal nerve block caused stylopharyngeus muscle dysfunction and dorsal nasopharyngeal collapse in all horses. Peak inspiratory upper airway pressure was significantly (P = 0.0069) more negative at all speeds and respiratory frequency was lower (P = 0.017) in horses with bilateral glossopharyngeal nerve block and stylopharyngeus muscle dysfunction compared to control values.


CONCLUSIONS
Bilateral glossopharyngeal nerve anaesthesia produced stylopharyngeus muscle dysfunction, dorsal pharyngeal collapse and airway obstruction in all horses.


CONCLUSIONS
The stylopharyngeus muscle is probably an important nasopharyngeal dilating muscle in horses and dysfunction of this muscle may be implicated in clinical cases of dorsal nasopharyngeal collapse. Before this information can be clinically useful, further research on the possible aetiology of stylopharyngeus dysfunction and dysfunction of other muscles that dilate the dorsal and lateral walls of the nasopharynx in horses is needed.
Tessier
C
C
Department of Large Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan 48824, USA.
Holcombe
S J
SJ
Derksen
F J
FJ
Berney
C
C
Boruta
D
D
D000402:Airway Obstruction / Q000209:etiology / Q000503:physiopathology / Q000662:veterinary*; D000818:Animals; D005080:Exercise Test / Q000662:veterinary; D005260:Female; D005540:Forced Expiratory Flow Rates; D005930:Glossopharyngeal Nerve / Q000502:physiology; D006734:Horse Diseases / Q000209:etiology / Q000503:physiopathology*; D006736:Horses; D008297:Male; D009305:Nasopharynx / Q000503:physiopathology*; D009407:Nerve Block / Q000379:methods / Q000662:veterinary; D010609:Pharyngeal Muscles / Q000294:innervation / Q000503:physiopathology*; D010805:Physical Conditioning, Animal / Q000502:physiology*; D011312:Pressure; D012119:Respiration; D012135:Respiratory Sounds / Q000209:etiology / Q000503:physiopathology / Q000662:veterinary; D012420:Running