Experiments in laryngeal reinnervation

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Abstract
Laryngeal reinnervation surgical procedures were performed in 26 dogs. Nineteen animals comprise the data reported in this thesis. Two different operative procedures were investigated, the ansa hypoglossi neuromuscular pedicle in 5 dogs, and the split phrenic nerve graft in 14 dogs. The studies were designed to evaluate whether either procedure resulted in inspiratory abduction of the vocal cord; and, if so, the mechanism by which abduction was produced. Five dogs in Experiment 1 demonstrated similar results from the ansa hypoglossi neuromuscular pedicle procedure. Apparent vocal cord abduction was seen during hyperpnea from airway obstruction, but was abolished by superior laryngeal nerve transection, or detachment of the sternothyroid muscle. None of the nerves in the neuromuscular pedicles was electrically excitable. Fourteen dogs in Experiment 2 underwent the split phrenic nerve graft operation. Vocal cord abduction, synchronized with inspiration, was noted in 5 animals. Two dogs had inspiratory abduction in quiet respiration. Electromyography, nerve action potentials, endoscopic motion pictures, and histologic study confirmed that posterior cricoarytenoid muscle reinnervation had occurred via the nerve graft from the phrenic nerve. Vocal cord abduction and electromyographic activity in the posterior cricoarytenoid muscle were abolished by transection of the nerve graft or the phrenic nerve. Conclusions of the study include the following: 1. the neuromuscular pedicle procedure does not result in reinnervation of the posterior cricoarytenoid muscle the pedicle's nerve and muscle block. 2. The phrenic nerve procedure may result in reinnervation of the posterior cricoarytenoid via the nerve graft, and inspiratory abduction of the paralyzed vocal cord. Failure of the phrenic procedure to produce reinnervation appeared to be due to a. recurrent laryngeal nerve regeneration, or b. avulsion of the nerve graft due to swallowing and other laryngeal movements.