Effects of Functional Electrical Stimulation on Denervated Laryngeal Muscle in a Large Animal Model.

This research study investigates the impact of Functional Electrical Stimulation (FES) on denervated laryngeal muscles, particularly the posterior cricoarytenoid (PCA) muscle, in horses suffering from Recurrent Laryngeal nerve (RLn) injury. The study found that FES could prevent muscle fiber from deteriorating even after complete denervation.

Investigating Functional Electrical Stimulation (FES)

• The research centralizes around the therapeutic use of Functional Electrical Stimulation. FES is a technique that employs electrical currents to activate motor, i.e. movement-related, functions, that have been damaged due to nerve lesions.
• The researchers aimed to study the effects of FES on the posterior cricoarytenoid (PCA) muscle, which plays a key role in controlling vocal folds. Bilateral vocal fold paralysis (BVCP), which results from Recurrent Laryngeal nerve (RLn) injury, can render the affected person or animal unable to control their vocal folds.

Methodology and Results

• For this study, ten horses were fitted with two quadripolar intramuscular electrodes in their left posterior cricoarytenoid muscle. The electrodes were meant to deliver the functional electrical stimulation.
• Out of the ten horses, seven were given daily FES treatment for 8 weeks after a 3-month period of denervation. The remaining three horses served as control subjects and did not receive any FES treatment.
• The researchers observed that the denervation process significantly increased the rheobase (the minimum current required to cause muscle fiber contraction).
• Electrical stimulation via FES led to a 30% increase in muscle fiber diameter in the treated group, compared to the untreated control group. The implication here is that FES could help counteract atrophying of muscles due to denervation.
• The researchers also noticed a possible decrease in slow (type 1) muscle fibers and a simultaneous increase in fast (type 2a) muscle fibers, though these changes didn’t result in any noticeable improvements in the rest function of the PCA muscle.

Conclusion

• Despite the lack of improvement in the muscle function, the significant increase in muscle fiber diameter indicates that the FES can potentially reverse the muscle atrophy caused by complete denervation.
• The potential shift from slow to fast muscle fibers also indicates the possible muscle adaptation following the electrical stimulation intervention.