Considerations for pacing of the cricoarytenoid dorsalis muscle by neuroprosthesis in horses.

The research aims to define the optimal parameters for effectively using electrical stimulation on the recurrent laryngeal nerve in horses in order to improve laryngeal movement. The study found that such stimulation could lead to the full abduction of the arytenoid cartilage in horses, potentially providing a treatment modality for horses with recurrent laryngeal neuropathy.

Study Objective

• The goal of the study was to identify the best parameters for functional electrical stimulation of the recurrent laryngeal nerve (RLN) in horses. This was carried out with a view to improve prosthetic laryngoplasty outcomes in horses and repair impaired laryngeal function.

Methodology

• The research was conducted on 7 mature horses, with an age range from 2 to 21 years. Each animal had a nerve cuff placed on the distal end of the RLN’s common trunk.
• In order to evaluate the effectiveness of the electrical nerve stimulation, the ipsilateral adductor branch of RLN in six horses was transected. The electrodes from the nerve cuff were connected to an internal programmable stimulator.
• The optimal parameters of stimulation were explored by using cathodic phase and biphasic pulses at 24 Hz with a specific pulse duration (0.427 ms).
• Experiments to observe the response from this stimulation were performed at monthly intervals, starting from one week after the implantation, and continued for up to one year.

Results

• The researchers found that excellent movement of arytenoid cartilage (with an average angle of abduction of 52.7 degrees) was achieved in six horses. However, two of the horses which had grade IV laryngeal function exhibited poor abduction.
• Successful arytenoid abduction was maintained for up to a year in one horse, while technical difficulties with the implant resulted in loss of abduction in six horses at varying stages post-operation.
• The study also revealed the minimal amount of stimulation required for achieving maximum abduction, and uncovered no electrical leakage during the experiment process. Importally, continuous electrical stimulation of the RLN for 60 minutes did not lead to muscle fatigue.

Conclusion

• The study concluded that functional electrical stimulation of the RLN can lead to full arytenoid abduction in horses.
• Furthermore, the study suggested that this type of treatment could be applicable for horses suffering from recurrent laryngeal neuropathy – a condition characterized by the gradual damage of the RLN that leads to voice changes and difficulty in breathing.