Dynamic respiratory endoscopic findings pre- and post laryngoplasty in Thoroughbred racehorses.

REASONS FOR PERFORMING STUDY To investigate laryngeal function in cases of recurrent laryngeal neuropathy pre- and post laryngoplasty (LP) using dynamic respiratory endoscopy (DRE). OBJECTIVES To compare the rima glottidis area during DRE pre- and post LP; document all forms of dynamic upper airway obstruction (DUAO) pre- and post LP and investigate the relationship between post operative abduction at rest and exercise. STUDY DESIGN Prospective case series. METHODS Thoroughbred racehorses with pre- and post LP DRE were included. Left-to-right arytenoid cartilage angle ratios and rima glottidis area ratios were used to quantify laryngeal function during rest and exercise, pre- and post LP. RESULTS In 35 horses, mean pre-LP ratios were greater during rest (left-to-right quotient angle ratio [LRQ] 0.76 ± 0.13; left-to-right arytenoid ratio [LRR] 0.72 ± 0.14; rima glottidis area ratio [RGA] 0.40 ± 0.10) than exercise (LRQ 0.39 ± 0.16, P < 0.001; LRR 0.38 ± 0.16, P < 0.001; RGA 0.15 ± 0.05, P < 0.001). Exercising ratios were larger post LP (LRQ 0.61 ± 0.13; LRR 0.60 ± 0.12; RGA 0.30 ± 0.08) than pre-LP (LRQ 0.39 ± 0.16, P < 0.001; LRR 0.38 ± 0.16, P < 0.001; RGA 0.15 ± 0.05, P < 0.001). A positive linear relationship was found between post LP resting and exercising ratios (R(2) = 0.48; P < 0.001) and post operative abduction grades (R(2) = 0.63; P < 0.001). Pre-LP all horses demonstrated left arytenoid cartilage collapse with bilateral vocal cord collapse and 37% had aryepiglottic fold collapse. Post LP 13 horses (37%) developed additional DUAOs and these horses had smaller RGAs (0.25 ± 0.08) than horses that did not develop DUAOs (0.32 ± 0.07, P = 0.01). CONCLUSIONS Multiple forms of DUAO occurred pre-LP and additional forms often developed post LP. Post LP the degree of arytenoid cartilage abduction at rest was useful to predict the degree of abduction during exercise.