Anastomosis of Recurrent Laryngeal to Phrenic Nerves: Some Recovery of Function

Reinnervation of the Canine Posterior Cricoarytenoid Muscle with Sympathetic Preganglionic Neurons

This experiment investigated the reinnervation of the canine posterior cricoarytenoid (PCA) muscle with preganglionic neurons of the sympathetic nervous system. Six dogs had their right recurrent laryngeal nerve (RLN) sectioned. Four of these dogs had the sympathetic cervical trunk (SCT) implanted into the right PCA muscle, and the two remaining dogs served as denervated controls. Four months later all dogs underwent videolaryngoscopy, electromyography, and electrical stimulation of the SCT. The PCA muscles were excised, sectioned, and stained for glycogen and ATPase. All four experimental PCA muscles demonstrated electrically evoked abduction and tonic electromyographic activity. In two of the specimens, staining (ATPase and PAS) revealed areas of reinnervation with fiber type grouping and glycogen depletion. These results are consistent with the successful reinnervation of the PCA muscle. Further refinement of this technique could be of benefit to patients with bilateral vocal cord paralysis.

The evolution of the assessment and treatment of paralytic dysphonia

Vocal fold paralysis has been an omnipresent disorder throughout the annals of laryngologic history since the origin of the specialty in 1858. The attendant complexity of laryngoscopic presentation, physiologic dysfunction, and surgical rehabilitation have led to a rich heritage of scientific investigations that can be traced through the past 140 years. The following historical summary provides the reader with a working knowledge of past experiences that connect to current initiatives and portend future progress.

Sir Charles Ballance: pioneer British neurological surgeon

Sir Charles A. Ballance (1856-1936) began his medical career at St. Thomas's Hospital the University College, London, England, in 1875, receiving honors in every subject and a gold medal in surgery. Victor Horsley (1857-1916) and Ballance were classmates at the University and in the later 1880s began work together at the Brown Institute and the National Hospital, Queen Square. In addition to important studies on vascular surgery, Ballance was involved in primate work on cerebral localization with lifelong friends Charles Beevor, Charles Sherrington, David Ferrier, and others. In June of 1887, Ballance assisted Horsley at Queen Square in the successful removal of an extramedullary spinal cord tumor. Horsley was about to abandon the operation, but his friend urged the removal of one lamina higher and the tumor was discovered. Ballance, a demonstrator in anatomy, realized the spinal cord segments lay higher in relation to the vertebral bodies than was generally appreciated. Ballance popularized the operation of radical mastoidectomy for advanced middle ear infection (1890), standardized an approach to drain or excise temporal brain abscesses, and was the first to clearly understand the neurological signs of cerebellar abscess (1894). Ballance also devised cranial base approaches to attack infectious thrombophlebitis of the lateral, petrosal, and cavernous sinuses. He was the first to completely remove an acoustic tumor (1894); 18 years later, the patient remained well. Ballance also drained a posterior fossa subdural hematoma (1906) and successfully sectioned the auditory nerve for Meniere's syndrome (1908). Ballance's operative experience with both supra- and infratentorial brain lesions included approximately 400 cases, which are detailed in his 1907 book, Some Points in the Surgery of the Brain and Its Membranes. His two-volume set, Essays on the Surgery of the Temporal Bone (1919), remains a brilliantly written and illustrated classic. Ballance was an expert on nerve regeneration and nerve grafting, and after many years of devoted research, he devised successful operations for facial nerve paralysis. For this and early vascular work, he is often credited as the first English surgeon to reintroduce classical Hunterian methods of experiment into surgery. He was honored as the founder and President of The Society of British Neurological Surgeons in 1926. Perhaps best known as a general and aural surgeon, Ballance was second only to Horsley in reputation as a pioneer British neurological surgeon. Described as a painstakingly slow but delicate and meticulous operator, Ballance made a contribution to neurosurgery and temporal bone surgery that was immense.

Objective measures of laryngeal function after reinnervation of the anterior and posterior recurrent laryngeal nerve branches

Previous research indicates that separate reinnervation of the anterior and posterior branches of the recurrent laryngeal nerve (RLN) can provide purposeful motion of the larynx, even after transplantation. This canine study was undertaken to better determine the results of RLN reinnervation after nerve transection distal to its bifurcation. This approximates ideal conditions for transplantation, because potential rejection and nerve branch mismatch are eliminated. Eight months after nerve repair, video, electromyographic, mechanical, and histologic data were collected on four canines. Results show return of appropriate motion without synkinesis, including purposeful abduction on endotracheal tube occlusion. Abductory function was weaker on the reinnervated side, but adduction was equal or stronger on the reinnervated vocal cord. These results indicate that this method of RLN reinnervation produces consistent, strong physiologic motion in the denervated larynx.

The three bellies of the canine posterior cricoarytenoid muscle: implications for understanding laryngeal function

The posterior cricoarytenoid (PCA) muscle is known to be active during phonation and respiration. The presence of muscle compartments (bellies) that might subserve these functions was investigated in the canine PCA by anatomical dissection and muscle fiber histochemistry. Five PCA muscles were microdissected and the origins and insertions of all muscle bundles were recorded. An additional six PCA muscles were frozen, sectioned, and stained for adenosine triphosphatase (ATPase) activity. The total number of fast- and slow-twitch fibers were counted and their proportion was determined for each region of the muscle. The PCA muscle was found to contain three distinct neuromuscular compartments. The vertical compartment is oriented at 24 degrees from true vertical, inserts on the lateral aspect of the muscular process of the arytenoid, and is composed of 65% type 2 (fast) muscle fibers. The oblique is oriented at 44 degrees from vertical, inserts on the top of the muscular process of the arytenoid, and is composed of 77% type 2 muscle fibers. The horizontal is oriented at 63 degrees from vertical, inserts on the medial aspect of the muscular process of the arytenoid, and is composed of 59% type 2 muscle fibers. The cricoarytenoid joint is capable of three arcs of motion and the physical arrangement of each compartment appears to correspond to each of these motions. Moreover, the histochemical profiles show that the activity of the three bellies is quite different. These results suggest that the different compartments of the PCA perform distinctive motions during phonation and inspiration.

Pacing parameters of the canine posterior cricoarytenoid muscle

The electrical pacing of laryngeal tissue consists of many uncharted parameters. We carried out several acute experiments in the canine model to narrow parametric ranges to serve future research and development in this field. Our findings were as follows. Stimulation intensities greater than 6 V caused tissue damage. Optimum stimulation frequency ranged from 60 to 90 Hz. Optimum pulse duration was 2.0 milliseconds. Biphasic stimulation reduced accumulation of electrical charge at the electrodes.

Functional electrical stimulation for the treatment of bilateral recurrent laryngeal nerve paralysis

We have previously presented the concept of electrophysiologic pacing of bilaterally paralyzed vocal cord abductors as a solution to the difficult problem incurred in this clinical situation. Initially, we demonstrated that it was indeed feasible to electrophysiologically pace abduction of the vocal cords synchronously with respiration, employing the EMG activity of the diaphragm as a trigger stimulus. Further research has led us to evaluate other possible physiologic trigger stimuli to ascertain which of these will prove most suitable in long-term pacing studies. In this article, we will report our preliminary results, employing negative intrathoracic pressure occurring with respiration--as detected by an implanted pressure transducer as a trigger stimulus. This device was interfaced with a muscle stimulator attached to electrodes placed in the cricoarytenoid muscles in five canines whose recurrent laryngeal nerves had been sectioned bilaterally. In all animals, obvious physiologic synchrony of vocal cord abduction and a reduction of negative inspiratory intratracheal pressure was achieved during electrical pacing. This reinforces our initial findings that it is indeed feasible to pace vocal cord abduction in bilateral recurrent laryngeal nerve paralysis with resultant return of physiologic normality to the glottis. Thus, functional electrical stimulation offers an alternative approach to the difficult problems incurred in the patient with bilateral recurrent laryngeal nerve paralysis. It also demonstrates that physiologic negative intrathoracic pressure activity occurring with inspiration can be a trigger source.

Coordinated electrical pacing of vocal cord abductors in recurrent laryngeal nerve paralysis

Electrodes were placed into the posterior cricoarytenoid and diaphragmatic muscles of five tracheostomized dogs. With the use of a sensor that would selectively detect diaphragmatic electromyographic activity, this activity served as a trigger and was amplified and interfaced with a muscle stimulator attached to electrodes placed in the posterior cricoarytenoid muscles. In all animals obvious physiologic synchrony of vocal fold abduction and a reduction of the negative inspiratory intratracheal pressure were observed during electrical pacing. This represents a preliminary step in the development of an alternative approach to the patient with bilateral recurrent laryngeal nerve paralysis.

Electrophysiologic pacing of vocal cord abductors in bilateral recurrent laryngeal nerve paralysis

We have reconfirmed our previous findings that controlled, reproducible, sustained, discrete vocal cord abduction can be achieved synchronously with respiration by electrophysiologic stimulation of the paralyzed posterior cricoarytenoid muscles. Moreover, we have demonstrated that this can be triggered synchronously by employing the normal physiologic chest wall movements that occur on respiration. To our knowledge, this represents the first report of functionally paced vocal fold abduction with respiration employing physiologic chest wall motions using an implantable device, and may represent an important step in the development of a physiologic approach to bilateral recurrent laryngeal nerve paralysis.

Experiments in laryngeal reinnervation

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 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.

Transposition of infrahyoid muscles to replace intrinsic laryngeal muscles: technique and long-time observations on return of function

Insertion of the separate motor branches of the caudal laryngeal nerve of the dog separately and atraumatically into a denervated infrahyoid muscle resulted in reinnervation of that muscle, as indicated by the appearance of electromyographic potentials two months postoperatively. When the nerve branches were used to reinnervate a sufficiently large mass of muscle, which was transposed to replace surgically removed intrinsic laryngeal muscles, nearly normal adduction and abduction of the vocal cord was obtained on the experimental side in some dog if ample time were allowed for maturation of nerve fibers and motor end plates. The minimum time for return of effective function under these circumstances was slightly more than 12 months, and function may improve for up to 36 months. A simplified procedure is described for reconstructing the intrinsic laryngeal muscles following submucosal resection. Electromyography is useful in monitoring the progress of reinnervation of muscle, but it is not a reliable indicator of mechanical function.

Reconstruction of laryngeal function for recurrent laryngeal nerve paralysis: historical view, advancement of latest investigations and a preliminary experiment

Historical investigations of the functional restoration for recurrent laryngeal nerve paralysis are reviewed and some advancement in recent studies are introduced. A preliminary experiment is reported in which the ansa hypoglossi and the sternothyroid muscle pedicle was implanted into the denervated posterior cricoarytenoid muscle in dogs. From these experiments we have concluded that the ansa hypoglossi and sternothyroid muscle pedicle, which has been shown to transmit efferent inspiratory bursts, is capable of restoring function to the paralyzed posterior cricoarytenoid muscle in some dogs.