Experimental Study On Reinnervation Of Bilateral Vocal Cord Paralysis

Objectives To explore the feasibility of restoring laryngeal motor function with a surgical reinnervation technique. For this purpose experimental animal model in dogs were used.MethodsTwenty beagle dogs were divided into four groups randomized, 6 dogs for group A, B and C, 2 dogs as control group.Group A Dogs underwent a reanastomosis of the sectioned bilateral RLN. At a distance of 2.0 cm from the cricothyroid joint the bilateral RLN was cut and the ends reanastomosed using ipsilateral ansa cervicalis. The intralaryngeal adductor branch was cut and sutured into the belly of the ipsilateral PCA muscle.Group B The left RLN underwent selective abductor reinnervation with ipsilateral phrenic nerve transfer.Group C Dogs underwent reinnervation of both sides. The distal stump of the left RLN anastomosed to ipsilateral phrenic nerve. The left intralaryngeal adductor branch were transected and sutured to the distal stump of the right RLN, which was carried contralaterally through a retrolaryngeal tunnel. The adductor branch of the right RLN was sutured into the posterior cricoarytenoid (PCA) muscle.In two dogs, the left RLN were cut and ligated to prevent the reinnervation of the thyroarytenoid, lateral cricoarytenoid, and interarytenoid muscles.All animals were anesthetized and underwent transections of the bilateral RLN, followed by one of three surgical reinnervation procedures or as control. After operation a tracheostomy through rings 10 to 13 was performed.To assess laryngeal abductor function, videolaryngoscopy and electromyography (EMG) were performed, using the same anesthesia that was used for the surgical procedure. After completion of physiologic testing, the PCA muscles of both sides were excised and stained by Hematoxylin and Eosin immunohistochemical (IHC) system for classifying laryngeal muscle fiber.ResultsLaryngeal abductor function was comparable with the two unreconstructed dogs. During quiet respiratory and forced respiratory. Evidence of reinnervation of both muscle groups was established and assessed with videolaryngoscopy, electromyography, and Hematoxylin and Eosin IHC system.Laryngeal Abductor Function AssessmentResults of laryngeal abductor function seen by in each group during quiet breathing and respiratory distress are recorded and assessed.without-reinnervation. In two dogs in the control denervation group there was no movement of the left vocal cords both during quiet respiration and forced respiration. Group A. The five sixth dogs reinnervated by the ansa cervicalis nerve there were apparent excursions during both quiet breathing and respiratory distress on both vocal cords.Group B. In the group reinnervated by the bilateral phrenic nerve, The excursions of the 6 dogs were apparent during both quiet breathing and respiratory distress on both vocal cords.Group C. The five sixth dogs underwent a bilateral reanastomosis using unilateral phrenic nerve showed further apparent excursions of bilateral vocal cord at 6 months later than Group A during both quiet breathing and respiratory distress on both vocal cords.Electromyographywithout-reinnervation. In two dogs in the control denervation group there was no EMG activity pattern is seen in the bilateral PCA muscles, and an uncoordinated pattern of single motor unit potentials is seen.Group A. In the group of dogs reinnervated by the ansa cervicalis nerve, spontaneous electrical activities of the reinnervated PCA muscles could be recorded in all cases during whining and showed a typical phonatory high-frequency discharge. The activities of these muscles were low during normal inspiration. Stronger activities were recorded during obstructive respiratory dyspnea, but they were still lower than discharge during whining.Group B. In the 6 dogs reinnervated by the left phrenic nerve, spontaneous an inspiratory activity pattern has occurred in the left PCA muscles.Group C. In the group 5 dogs underwent a bilateral reanastomosis spontaneous an inspiratory activity pattern has occurred in the both PCA muscles. The pattern is almost synchronous with the normal inspiratory activity of the reinnervated PCA muscles.ImmunohistochemistryThe expression of MHC isoforms in individual muscle fibers was also studied using immunohistochemistry. In PCA muscle two major fiber types were clearly identified。 The expression of MHC isoforms in individual muscle fibers was also studied. In PCA muscle two major fiber types were clearly identified。In Group A the ratio of type I fiber in the PCA is 46.34±7.97%.In Group B the ratio of type I fiber in the PCA is 45.38±9.11%.In Group C the ratio of type I fiber in the PCA is 43.92±5.35%.There were no significant statistics in the number of type I fiber in the PCA muscles among the Group B, Group B and Group C. Other changes were not significant.ConclusionsOf the three types operation, recovery of abductory was all obtained. However, the approach (Group B and C) using phrenic nerve to anastomosis RLN could be more effective. Reinnervation by ansa cervicalis appears to be a moderate type for abductor reinnervation of the larynx. While in some situation the PN should not be adopted, the ansa cervicalis could be chosen.