Functional Electrical Stimulation of Intrinsic Laryngeal Muscles under Varying Loads in Exercising Horses

Bilateral vocal fold paralysis (BVCP) is a life threatening condition and appears to be a good candidate for therapy using functional electrical stimulation (FES). Developing a working FES system has been technically difficult due to the inaccessible location and small size of the sole arytenoid abductor, the posterior cricoarytenoid (PCA) muscle. A naturally-occurring disease in horses shares many functional and etiological features with BVCP. In this study, the feasibility of FES for equine vocal fold paralysis was explored by testing arytenoid abduction evoked by electrical stimulation of the PCA muscle. Rheobase and chronaxie were determined for innervated PCA muscle. We then tested the hypothesis that direct muscle stimulation can maintain airway patency during strenuous exercise in horses with induced transient conduction block of the laryngeal motor nerve. Six adult horses were instrumented with a single bipolar intra-muscular electrode in the left PCA muscle. Rheobase and chronaxie were within the normal range for innervated muscle at 0.55±0.38 v and 0.38±0.19 ms respectively. Intramuscular stimulation of the PCA muscle significantly improved arytenoid abduction at all levels of exercise intensity and there was no significant difference between the level of abduction achieved with stimulation and control values under moderate loads. The equine larynx may provide a useful model for the study of bilateral fold paralysis

A sequential double labeling technique for studying changes in motoneuronal projections to muscle following nerve injury and reinnervation.

Elsevier, Akihiro, Katada ; Jeremy D. Vosa ; Brad B. Swelstada ; David L. Zealear, Journal of neuroscience methods, 155(1), 2006, 20-27. authorThe purpose of this study was to develop an anatomical technique that could directly demonstrate the motoneuron projections to the muscle both before injury and again following reinnervation. Investigation focused on the identification of a long-term retrograde fluorescent tracer that would label original motoneurons and persist long enough for reinnervating motoneurons to become labeled by a second fluorescent tracer. True Blue (TB) was evaluated as a potential long-term tracer, Fluoro-ruby (FR) and Fluoro-emerald (FE) were tested as potential short-term tracers in 45 adult Sprague-Dawley rats. In the initial phase of the study, TB was injected into the tibialis anterior (TA) muscle in 16 rats and sacrificed 1 week to 6 months later, to study its persistence. During the second stage, a short-term tracer was injected into the TA muscles bilaterally in 15 rats with survival time ranging from 4 to 28 days. Sequential double labeling was subsequently performed using the combination of TB and FR in 14 rats. The number and brightness of TB cells did not change over 6 months time, a period sufficient for complete reinnervation. FR and FE showed maximum labeling of motoneurons at 1 week after tracer application. In the double labeling study, we could easily distinguish double-labeled cells from those labeled only by TB or FR. These results suggest that sequential double labeling of TB and FR is a valuable method for long-term muscle reinnervation studies

Functional electrical stimulation of laryngeal adductor muscle restores mobility of vocal fold and improves voice sounds in cats with unilateral laryngeal paralysis.

Elsevier, Katada, Akihiro ; Nonaka, Satoshi ; Adachi, Masaaki ; Kunibe, Isamu ; Arakawa, Takuya ; Imada, Masanobu ; Hayashi, Tatsuya ; Zealear, David L. ; Harabuchi, Yasuaki, Neuroscience Research, 50(2), 2004, 153-159. authorFunctional electrical stimulation (FES) has been proposed as a potential treatment for restoring motor functions of denervated motor systems. We investigated whether FES of paralyzed laryngeal adductor muscles could restore adduction to the vocal folds. In addition, we studied the effect of stimulated vocal fold adduction on the intensity and overall quality of voice production. We recorded movement of the vocal fold, electromyographic activity of muscles recruited for vocalization, and sound production in unanesthetized decerebrate cats during FES of the paralyzed thyroarytenoid (TA) muscle. FES of the paralyzed TA muscle induced adduction of the vocal fold. Appropriate stimulus parameters for induction was 1.5–3.0 mA intensity pulses delivered at a frequency of 30–50 pulses per second (pps). FES of the paralyzed TA muscle prolonged phonation time and increased intensity of voice sounds during vocalization induced by electrical stimulation (0.2 ms, 20–50 μA, 50 pps) of the periaqueductal gray (PAG). The quality of voice sounds evaluated by sound spectrography was shown to improve during vocalization with FES. We conclude that FES of the paralyzed laryngeal adductor muscle was effective in restoring adduction of the vocal fold and improving voice sounds impaired by unilateral laryngeal paralysis