Proceedings of a Workshop on - The Havemeyer Foundation

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,
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