Electrical stimulation to promote selective reinnervation of denervated laryngeal muscles
Vocal fold paralysis (VFP) that results from injury to motor axons in the recurrent laryngeal nerve (RLN) is a common clinical problem. In the majority of these patients, misdirected regeneration of neural fibers in the RLN leads to a synkinetic larynx. Evidence has indicated that electrical stimulation (ES) of the denervated posterior cricoarytenoid (PCA) muscle with a low frequency may reduce synkinetic vocal fold motion. The current study was designed to investigate the mechanism of selective reinnervation promoted by ES (Specific aim 1), and to find out the best stimulation frequency to avoid synkinesis (Specific aim 2). To achieve the first specific aim, an implantable system was developed to obtain chronological EMG recordings from both abductor (PCA) and adductor (thyroarytenoid, TA) muscles in canine’s larynx. The system was implanted in 8 canines for up to 41 weeks. It showed good compatibility and consistent EMG signals were recorded. The reinnervation process was better understood with this system. For the second specific aim, eleven canines were implanted with a stimulation system to condition the denervated PCA muscles with different stimulation frequencies. Spontaneous vocal fold movement and rectified integrated EMG potentials were recorded in anesthetized animals. Exercise tolerance was measured on a treadmill in the awake animals. Results showed that ES of the denervated PCA muscle with a frequency of 10Hz, characteristic of the intrinsic activity of PCA inspiratory motoneurons, inhibited synkinetic reinnervation by RGC motoneurons, promoted selective reinnervation by its original inspiratory motoneurons, and improved functional recovery.