Dynamic obstructions of the equine upper respiratory tract. Part 2: comparison of endoscopic findings at rest and during high-speed treadmill exercise of 600 Thoroughbred racehorses.
BACKGROUND
The reliability of diagnoses of obstructive conditions of the upper respiratory tract (URT) based on examinations performed at rest vs. at exercise is controversial.


OBJECTIVE
To compare diagnosis of URT by endoscopy at rest with that achieved during high-speed treadmill exercise (HSTE).


OBJECTIVE
Endoscopy of URT at rest, when performed in isolation from other simpler techniques is unreliable in the prediction of dynamic respiratory obstructions.


METHODS
Endoscopic findings of 600 Thoroughbred racehorses during quiet breathing were compared with findings during high-speed treadmill exercise. Other parameters were also assessed for their specificity in diagnosis.


RESULTS
Endoscopy of the resting horse showed low sensitivity (0.15) in the diagnosis of dorsal displacement of the soft palate (DDSP) and palatal instability (PI). When endoscopy and reported noises were taken together there was still a 35% misdiagnosis rate. Although there was significant association between resting laryngeal function score (LFS) and dynamic vocal cord and/or arytenoid cartilage collapse at exercise, 19% of horses with a grade 4/5 LFS were able to attain and maintain full abduction during exercise and 7% of those with 'normal' grades 1 or 2 LFS at rest showed dynamic laryngeal collapse when exerted. Sensitivity of the diagnostic model was greatly increased (80%) when a history of inspiratory noise and palpable intrinsic muscle atrophy were included.


CONCLUSIONS
Endoscopy of the upper respiratory tract of static horses is unreliable in the diagnosis of dynamic obstructions of the URT and should not be used in isolation in surgical decision-making or in the assessment of horses at the time of sale.
Lane
J G
JG
Department of Clinical Veterinary Science, University of Bristol, Langford, UK.
Bladon
B
B
Little
D R M
DR
Naylor
J R J
JR
Franklin
S H
SH
D000367:Age Factors; D000402:Airway Obstruction / Q000175:diagnosis / Q000209:etiology / Q000662:veterinary*; D000818:Animals; D001193:Arytenoid Cartilage / Q000503:physiopathology; D003937:Diagnosis, Differential; D004724:Endoscopy / Q000379:methods / Q000662:veterinary*; D005080:Exercise Test / Q000662:veterinary; D005260:Female; D006734:Horse Diseases / Q000175:diagnosis* / Q000209:etiology; D006736:Horses; D007830:Larynx / Q000002:abnormalities / Q000503:physiopathology; D008297:Male; D009305:Nasopharynx / Q000002:abnormalities / Q000503:physiopathology; D010160:Palate, Soft / Q000002:abnormalities / Q000503:physiopathology; D010805:Physical Conditioning, Animal / Q000502:physiology*; D012135:Respiratory Sounds / Q000175:diagnosis / Q000503:physiopathology / Q000662:veterinary; D015619:Respiratory System Abnormalities / Q000175:diagnosis / Q000503:physiopathology / Q000662:veterinary*; D012146:Rest / Q000502:physiology*; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D014741:Video Recording