Ventriculocordectomy reduces respiratory noise in horses with laryngeal hemiplegia

Reasons for performing study: Show and performance horse with laryngeal hemiplegia (LH) often present for excessive respiratory noise rather than significant exercise intolerance. Therefore, the goal of surgery in these horses is to reduce respiratory noise but there are no quantitative studies evaluating the effect of any upper-airway surgery in LH-affected horses. Objective: To determine whether bilateral ventriculocordectomy (VC) reduces respiratory noise in exercising horses with laryngeal hemiplegia. Methods: Six Standardbred horses with normal upper airways were used in this study. Respiratory sounds and inspiratory trans-upper airway pressure (P-ui) were measured in all horses before and after induction of LH, and 30, 90 and 120 days after VC. In horses with LH, spectrogram analysis revealed 3 inspiratory sound formants centred at approximately 400, 1700 and 3700 Hz. Inspiratory sound levels (SL) and the sound intensity of the 3 inspiratory formants (F-1, F-2, F-3 respectively) were measured using a computer-based sound analysis programme. Results: In LH-affected horses, P-ui, inspiratory SL and the sound intensity of F-2 and F-3 were significantly increased compared to baseline values. At 90 and 120 days after VC the sound intensities of F-2 and F-3 returned to baseline values. The P-ui and SL, were significantly decreased compared to LH values, but remained different from baseline. Conclusions: VC effectively reduces inspiratory noise in LH-affected horses by 90 days following surgery. Inspiratory trans-upper airway pressures are improved 30 days following VC, but do not return to baseline values. Potential relevance: VC can be recommended as a surgical treatment of LH-affected horses if reduction of respiratory noise is the primary objective of surgery. Further studies are required to determine if variations of the surgical technique used in this study will have similar results.