title: Dynamic pharyngeal collapse in racehorses.
abstract: BACKGROUND
  Dynamic pharyngeal collapse (PC) is a condition seen in racehorses that can be career-ending.
  
  
  OBJECTIVE
  To characterise and grade PC and describe the effects of PC on athletic performance.
  
  
  METHODS
  Medical records were reviewed for 828 horses, of which 49 (6%) records were identified as horses with a primary diagnosis of PC. Tapes of video-endoscopy of the pharynx during exercise were reviewed. Each video recording was assigned a grade (0-4) reflecting the degree of PC and a classification for severity of upper airway obstruction. Earnings per race prior to diagnosis of PC were compared to earnings per race after diagnosis of PC for all horses, as well as performance index (PI). Available exercising arterial blood gases were reviewed for horses with PC.
  
  
  RESULTS
  There were 35 (80%) Thoroughbreds (TB), and 9 (20%) Standardbreds (STD). 32 (73%) had a history of making an upper respiratory noise. 4 (9%) grade 1 PC, 8 (18%) grade 2 PC, 26 (59%) grade 3 PC, and 6 (14%) grade 4 PC. Seven (16%) horses were classified as mild PC, 18 (41%) as low-moderate PC, 14 (32%) as high-moderate PC, and 5 (11%) as severe PC. Of 30 horses 11 had abnormally decreased PaO2 and 8 horses had abnormally elevated PaCO2. A significant decrease was found in earnings per race prediagnosis when compared to post diagnosis earnings per race in horses > or =4 years of age (P = 0.003). A significant decrease was also observed for earnings per race prediagnosis when compared to post diagnosis earnings per race in horses with grade 3 PC (P = 0.03) No significant differences were observed in PI before or after diagnosis of PC.
  
  
  CONCLUSIONS
  There was a trend for PC to be observed in more TB than STD, and more males than females compared to the general hospital population. Horses with PC significant had decreases in arterial oxygenation. Racing records after a diagnosis of PC in all horses > or = 4 years of age suggesting that older horses have a guarded prognosis for continued success.
  
  
  CONCLUSIONS
  This study provides a classification system for dynamic pharyngeal collapse and suggests that older racehorses (> or = 4 years of age) diagnosed with PC and all horses with grade 3 PC have a poor prognosis for return to previous level of performance.
authors.affiliation: Department of Clinical Studies, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, 382 W Street Road, Kennett Square, Pennsylvania 19348, USA.
authors.forename: A G
authors.initials: AG
authors.lastname: Boyle
authors.forename: B B
authors.initials: BB
authors.lastname: Martin
authors.forename: E J
authors.initials: EJ
authors.lastname: Davidson
authors.forename: M M
authors.initials: MM
authors.lastname: Durando
authors.forename: E K
authors.initials: EK
authors.lastname: Birks
mesh_terms: D000367:Age Factors; D000818:Animals; D001947:Breeding; D005260:Female; D006734:Horse Diseases / Q000175:diagnosis / Q000473:pathology* / Q000503:physiopathology; D006736:Horses; D008173:Lung Diseases, Obstructive / Q000175:diagnosis / Q000473:pathology / Q000503:physiopathology / Q000662:veterinary*; D008297:Male; D010100:Oxygen / Q000097:blood; D010614:Pharynx / Q000473:pathology*; D010805:Physical Conditioning, Animal / Q000502:physiology*; D011379:Prognosis; D012720:Severity of Illness Index; D012737:Sex Factors; D014741:Video Recording
chemical_list: D010100:Oxygen