Proceedings of a Workshop on - The Havemeyer Foundation

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Havemeyer Foundation Monograph Series No. 11 SPIROMETRIC AND ENDOSCOPIC ASSESSMENT OF SURGICAL TREATMENT IN HORSES WITH LARYNGEAL HEMIPLEGIA M. A. Weishaupt, R. Vogt, A. Fürst and J. A. Auer Equine Hospital, Faculty <strong>of</strong> Veterinary Medicine, University <strong>of</strong> Zurich, Switzerland INTRODUCTION The outcome <strong>of</strong> a ‘tie back’ operation is routinely judged, based on the endoscopic re-evaluation, the changes in the quality and volume <strong>of</strong> the respiratory noise and the performance history <strong>of</strong> the equine athlete. Exercise spirometry is a valuable method to quantify airflow limitation <strong>of</strong> upper airway diseases (Shappell et al. 1988; Belknap et al. 1990; Lumsden et al. 1993, 1994; Tetens et al. 1996; Weishaupt et al. 1998) and is therefore used in the authors’ clinic to assess the functional improvement after this surgical intervention. The relationship between the degree <strong>of</strong> abduction by laryngoplasty and the extent <strong>of</strong> functional improvement is poorly investigated. As over-abduction <strong>of</strong> the paralysed arytenoid may result in coughing and/or dysphagia, an optimal lateralisation aims at correcting each athlete individually in relation to its future athletic career. The aim <strong>of</strong> this study was to quantify the functional improvement <strong>of</strong> a combined laryngoplasty-ventriculectomy procedure through spirometric assessment and to correlate function with the arytenoid abduction angle determined endoscopically before and after surgery. MATERIAL AND METHODS Horses were trained to canter on a high-speed treadmill. Time and flow parameters were measured with an ultrasonic flowmeter (Spiroson Scientific ® , Isler Bioengeneering AG, Dürnten, Switzerland). The levels <strong>of</strong> exercise intensity were adjusted to the horse's individual capabilities. The left abduction angle was surveyed on endoscopic pictures using the method described by Reutter (Reutter et al. 1994). A combined laryngoplastyventriculectomy procedure was performed to correct the laryngeal hemiplegia. After a rehabilitation and retraining period <strong>of</strong> 5 months, the horses were reassessed using the identical exercise protocol. With the owner’s consent, 19 Warmblood horses with left laryngeal hemiplegia Grade 4/4 (Rakestraw et al. 1991) were assessed in this way. RESULTS Before surgery, beginning airflow limitation could be observed already at the trot; the conclusive inspiratory flow limitation occurred usually only at canter intensities <strong>of</strong> 6.0-7.5 m/s at 6% incline (heart rates 158-209/min). The inspiratory flow curve was characterised by a plateau phase and peak values were limited at 48 ± 9.9 l/s (mean ± SD; range 26–63 l/s). At expiration no limitation was obvious and peak flow reached 69 ± 9.8 l/s (range 49–94 l/s). Inspiratory time was always prolonged. Horses with severe inspiratory, dynamic collapse <strong>of</strong> the paralysed arytenoid, showed an initial flow peak with a subsequent characteristic drop <strong>of</strong> flow. At the canter, 7 <strong>of</strong> the 19 horses changed their 1:1 locomotion-torespiration coupling (LRC) intermittently or permanently to 2:1. Differences in the degree <strong>of</strong> abduction and <strong>of</strong> functional parameters after surgery are listed (Table 1). Independent <strong>of</strong> the LRC strategy, peak inspiratory flow (PIF) increased over all horses by 46.2% and thus proportional to the abduction angle. Minute ventilation (VE) increased in average by 30.9%. Comparing the increase <strong>of</strong> PIF and VE with the changes <strong>of</strong> the left abduction angle no significant correlation could be found (Pearson, 81
Equine Recurrent Laryngeal Neuropathy TABLE 1: Mean difference ± SD (percentage difference) A abd 7.1 ± 7.7 (+42.3%)* LRC 1:1 LRC 2:1 f R 0.3 ± 1.3 (+0.3%) 32 ± 14.5 (+50.1%)* t insp -3.5 ± 3.2 (-6.1%)* -10.8 ± 4.5 (-16.9%)* VT 2.5 ± 1.2 (+18.1%)* -0.4 ± 4.5 (-1.7%) VE 269 ± 108 (+18.4%)* 593 ± 265 (+54.9%)* PIF 16.4 ± 7.0 (+31.5%)* 28.9 ± 9.5 (+73%)* PEF 3.5 ± 4.7 (+5.6%) 7.5 ± 6.1 (+11.2%)* A abd , abduction angle [degree]; f R , respiratory rate [1/min]; t insp , inspiratory time fraction [%]; VT, tidal volume [l]; VE, minute ventilation [l/min]; PIF, peak inspiratory flow [l/s]; PEF, peak expiratory flow [l/s] * significant difference (paired t-test, P
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