Functional electrical stimulation of intrinsic laryngeal muscles under varying loads in exercising horses.
Authors: Cheetham Jon, Regner Abby, Jarvis Jonathan C, Priest David, Sanders Ira, Soderholm Leo V, Mitchell Lisa M, Ducharme Norm G
Journal: PloS one
Summary
Bilateral vocal fold paralysis represents a significant clinical challenge in equine medicine, compromising airway patency during exercise with potentially fatal consequences, and functional electrical stimulation (FES) of the posterior cricoarytenoid muscle offers a promising therapeutic avenue despite technical difficulties relating to the muscle's small size and deep anatomical location. Cheetham and colleagues implanted bipolar intramuscular electrodes into the left PCA muscle of six horses and characterised the electrical properties of this innervated muscle (rheobase 0.55±0.38 V; chronaxie 0.38±0.19 ms), establishing baseline parameters for safe and effective stimulation. Direct electrical stimulation of the PCA muscle successfully restored arytenoid abduction across all exercise intensities, with stimulation-induced abduction matching naturally-occurring control values under moderate workloads. For equine practitioners managing horses with laryngeal paralysis, these findings suggest that intramuscular FES could maintain functional airway diameter during athletic activity, potentially offering an alternative to conventional surgical approaches such as tie-back procedures. The equine larynx's anatomical and physiological similarities to human laryngeal innervation indicate that this work has translational relevance beyond equine medicine, whilst establishing essential groundwork for clinical FES system development in horses with paralysis-related respiratory obstruction.
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Practical Takeaways
- •FES shows promise as a potential future treatment option for horses with laryngeal paralysis, offering an alternative approach to maintain airway patency during exercise
- •The technical feasibility of stimulating small, inaccessible muscles like the PCA has been demonstrated, though further development is needed before clinical application
- •This research may eventually provide therapeutic options for performance horses affected by recurrent laryngeal neuropathy, potentially avoiding the need for prosthetic laryngoplasty
Key Findings
- •Rheobase and chronaxie values for the posterior cricoarytenoid (PCA) muscle were within normal ranges (0.55±0.38 V and 0.38±0.19 ms respectively)
- •Intramuscular electrical stimulation of the PCA muscle significantly improved arytenoid abduction at all exercise intensities
- •Direct muscle stimulation achieved arytenoid abduction levels equivalent to control values under moderate exercise loads
- •Functional electrical stimulation is feasible as a potential therapeutic approach for equine vocal fold paralysis