Cricothyroid muscle function and vocal fold stability in exercising horses.
OBJECTIVE
To determine (1) if the cricothyroid muscle had respiratory-related electromyographic (EMG) activity that increased with respiratory effort and (2) if bilateral cricothyroid myotomy resulted in vocal fold instability and collapse in exercising horses.


METHODS
Experimental.


METHODS
Seven (3 EMG; 4 cricothyroid myotomy) Standardbred horses.


METHODS
Three horses exercised on a treadmill at speeds corresponding to the speed that produced maximum heart rate (HR(max)), 75% of maximum heart rate (HR(75%max)), and 50% of maximum heart rate (HR(50%max)) for 60 seconds at each speed while EMG activity of the cricothyroid muscle and nasopharyngeal pressures were measured. Another 4 normal horses were exercised on the treadmill at HR(max) and HR(75%max) for 60 seconds at each speed before and after bilateral cricothyroid myotomy. Upper airway pressures were measured and videoendoscopic examinations were performed and videotaped at each speed.


RESULTS
Peak phasic EMBG activity of the cricothyroid muscle was coincident with inspiration and increased with treadmill speed. Bilateral cricothyroid myotomy resulted in vocal fold collapse in all horses. Mean peak inspiratory pressures were significantly more negative compared with control values at both HR(max) and HR(75%max).


CONCLUSIONS
Cricothyroid muscle dysfunction may be implicated in vocal fold collapse and likely causes inspiratory airway obstruction in exercising horses.


CONCLUSIONS
Conditions compromising cricothyroid muscle function or motor innervation could result in vocal fold collapse.
Holcombe
Susan J
SJ
Department of Large Animal Clinical Sciences, Michigan State University, College of Veterinary Medicine, East Lansing, 48824, USA. Holcombe@cvm.msu.edu
Rodriguez
Katie
K
Lane
Jennifer
J
Caron
John P
JP
D000402:Airway Obstruction / Q000209:etiology / Q000503:physiopathology / Q000662:veterinary*; D000818:Animals; D004576:Electromyography / Q000379:methods / Q000662:veterinary; D004724:Endoscopy / Q000662:veterinary; D049631:Esophageal Sphincter, Upper / Q000502:physiology* / Q000503:physiopathology / Q000601:surgery; D005080:Exercise Test / Q000662:veterinary; D005260:Female; D006339:Heart Rate; D006734:Horse Diseases / Q000209:etiology / Q000503:physiopathology*; D006736:Horses; D008297:Male; D010101:Oxygen Consumption; D010609:Pharyngeal Muscles / Q000502:physiology* / Q000503:physiopathology / Q000601:surgery; D010805:Physical Conditioning, Animal / Q000502:physiology*; D011312:Pressure; D012119:Respiration; D012420:Running; D014741:Video Recording