Selective resection of the phrenic nerve roots in rabbits. Part II: Respiratory effects

A New Animal Model of Laryngeal Transplantation

Only three laryngeal transplants have been described in the literature to date, and none of the techniques has enabled a completely satisfactory functional result to be obtained. This article presents a new model of laryngeal transplantation, with quality of revascularisation of the transplant being the principal objective and optimisation of the various steps of the procedure, with the integration of a new reinnervation technique as a secondary objective. We present a preclinical animal study. Three pig larynges removed in vivo underwent allotransplantation according to the same protocol. The quality of the revascularisation was examined immediately after the surgery as well as by endoscopy for one animal on the fourth day after the operation. The mean time of cold ischaemia was 3 h 15 min. The anaesthetic tolerance of the pigs was excellent. Revascularisation was achieved and judged to be excellent for the three transplants immediately after the operation and the endoscopy performed for one pig on the fourth day after the operation confirmed this result. The anatomical similarities also enabled the application and integration of an innovative technique of laryngeal reinnervation into the various phases of the operation. We describe a reliable and reproducible animal model for laryngeal transplantation. Its application in humans can be envisaged.

Dual innervation may occur in a partially denervated muscle

INTRODUCTION

With a view to simplifying surgical techniques for selective laryngeal reinnervation, we addressed the question of whether it is feasible to receive additional innervation by a partially denervated muscle using an infrahyoid muscle model.

METHODS

In 90 rats (6 groups of 15), phrenic nerve transfer was used to reinnervate the sternothyroid muscle. In some cases, residual innervation by the original nerve was present. Three months later we performed electromyographic studies, contraction strength measurements, histologic assessment, and retrograde labeling.

RESULTS

Muscles reinnervated by the phrenic nerve had a greater "dual-response" rate (in terms of nerve latency, contraction strength, and retrograde labeling) than muscles in the control groups.

DISCUSSION

The phrenic nerve can impart its inspiratory properties to an initially denervated strap muscle-even when residual innervation is present. The preservation of contractile potential confirmed the feasibility of dual innervation in a previously injured muscle. Muscle Nerve 59:108-115, 2019.

Electromyographic permutation entropy quantifies diaphragmatic denervation and reinnervation

Spontaneous reinnervation after diaphragmatic paralysis due to trauma, surgery, tumors and spinal cord injuries is frequently observed. A possible explanation could be collateral reinnervation, since the diaphragm is commonly double-innervated by the (accessory) phrenic nerve. Permutation entropy (PeEn), a complexity measure for time series, may reflect a functional state of neuromuscular transmission by quantifying the complexity of interactions across neural and muscular networks. In an established rat model, electromyographic signals of the diaphragm after phrenicotomy were analyzed using PeEn quantifying denervation and reinnervation. Thirty-three anesthetized rats were unilaterally phrenicotomized. After 1, 3, 9, 27 and 81 days, diaphragmatic electromyographic PeEn was analyzed in vivo from sternal, mid-costal and crural areas of both hemidiaphragms. After euthanasia of the animals, both hemidiaphragms were dissected for fiber type evaluation. The electromyographic incidence of an accessory phrenic nerve was 76%. At day 1 after phrenicotomy, PeEn (normalized values) was significantly diminished in the sternal (median: 0.69; interquartile range: 0.66-0.75) and mid-costal area (0.68; 0.66-0.72) compared to the non-denervated side (0.84; 0.78-0.90) at threshold p<0.05. In the crural area, innervated by the accessory phrenic nerve, PeEn remained unchanged (0.79; 0.72-0.86). During reinnervation over 81 days, PeEn normalized in the mid-costal area (0.84; 0.77-0.86), whereas it remained reduced in the sternal area (0.77; 0.70-0.81). Fiber type grouping, a histological sign for reinnervation, was found in the mid-costal area in 20% after 27 days and in 80% after 81 days. Collateral reinnervation can restore diaphragm activity after phrenicotomy. Electromyographic PeEn represents a new, distinctive assessment characterizing intramuscular function following denervation and reinnervation.

Laryngeal reinnervation for bilateral vocal fold paralysis

PURPOSE OF REVIEW

Laryngeal reinnervation for bilateral vocal fold paralysis (BVFP) patients is a promising technique to achieve good airway, although preserving a good quality of voice. On the other hand, the procedure is not simple. This review explores the recent literature on surgical technique and factors that may contribute to the success.

RECENT FINDINGS

Research and literature in this area are limited due to variability and complexity of the nerve supply. The posterior cricoarytenoid (PCA) muscle also receives nerve supply from the interarytenoid branch. Transection of this nerve at the point between interarytenoid and PCA branch may prevent aberrant reinnervation of adductor nerve axons to the PCA muscle. A varying degree of regeneration of injured recurrent laryngeal nerves (RLN) in humans of more than 6 months confirms subclinical reinnervation, which may prevent denervation-induced atrophy.

SUMMARY

Several promising surgical techniques have been developed for bilateral selective reinnervation for BVFP patients. This involves reinnervation of the abductor and adductor laryngeal muscles. The surgical technique aims at reinnervating the PCA muscle to trigger abduction during the respiratory cycle and preservation of good voice by strengthening the adductor muscles as well as prevention of laryngeal synkinesis.

Schwannoma of the accessory phrenic nerve

Otolaryngologists are frequently confronted with the management of cervical tumors. Neurogenic tumors concern, especially, the cranial, sympathetic, or peripheral nerve sheathes. These tumors are benign and grow slowly. The involvement of the cervical part of the phrenic nerve is exceptional, and only 2 cases are reported in the literature. We describe the first case of a cervical schwannoma involving the accessory phrenic nerve. The anatomy and function of the accessory phrenic nerve are reviewed.

Diaphragmatic effects of selective resection of the upper phrenic nerve root in dogs

The aim of this study was to evaluate the effects on the diaphragm of upper phrenic nerve root resections in dogs. During laryngeal reinnervation, selective resections of the upper phrenic nerve root (C5) were performed unilaterally (right side, n=7; Group A) and bilaterally (n=6; Group B) and compared to non denervated animals (n=5). After 8 months, a diaphragmatic evaluation was performed: X-ray, EMG, transdiaphragmatic pressure (Pdi) after ipsi- and bilateral tetanic stimulation of the phrenic nerves and a bilateral histological study of five hemidiaphragmatic regions. EMG alterations were significantly more severe in Group B than in Group A, for the left (p<0.05) and right hemidiaphragms (p<0.01). No differences in the X-rays were noted between the three groups. The Pdi of the three groups after occlusion and phrenic nerve stimulations (unilateral and bilateral) were not statistically different. Histological data demonstrated that there were no differences in fibre irregularity, predominant fibre type or fibrosis between the three groups. Macroscopic and microscopic atrophy, which was mainly present on the anterior regions of the hemidiaphragms, was significantly higher in Group B than in Group A and undenervated dogs (p<0.05). In conclusion, resection of the upper phrenic nerve root of one phrenic nerve (right side) have limited effect on the diaphragm in dogs. However, resection of the upper phrenic nerve root on both sides resulted in a significant effect on the EMGs and histology of the entire diaphragm without any significant consequences on transdiaphragmatic pressure.

Spontaneous recovery of diaphragmatic strength in unilateral diaphragmatic paralysis

The aim of the present study was to evaluate diaphragmatic strength in patients with unilateral diaphragmatic paralysis and to determine whether patients with recent diaphragm paralysis develop lower inspiratory pressure than patients with longstanding diaphragmatic paralysis. Twenty patients (16 men and 4 women, 62+/-12 years) and six control subjects were included (4 men and 2 women, 53+/-15 years) in the study. Esophageal pressure during sharp sniff (Pes,sniff), bilateral cervical phrenic nerve magnetic stimulation (Pes,cms) and unilateral phrenic nerve stimulation (Pes,ums) (in nine patients) were measured. Sixteen patients presented right diaphragmatic paralysis and four, left diaphragmatic paralysis. Pes,sniff was higher in control subjects than in patients with diaphragmatic paralysis (respectively 110+/-22 cmH2O and 82+/-24 cmH2O, P<0.05). There was no difference in Pes,cms between patients with diaphragmatic paralysis and control subjects (14+/-7 cmH2O vs. 16+/-4 cmH2O; ns). Pes,ums after stimulation of the affected phrenic nerve was less than 4 cmH2O, was 8+/-2 cmH2O after stimulation of the intact phrenic nerve and was correlated to Pes,cms (R=0.87, P<0.01). There was a positive correlation between Pes,cms, Pes,ums of the intact hemidiaphragm, Pes,sniff and the time from the onset of symptoms and the diaphragmatic explorations (respectively R=0.86, P<0.0001; R=0.72, P<0.05; R=0.48, P<0.05). In conclusion, diaphragmatic strength after unilateral diaphragmatic paralysis seems to improve with time.

Restoration of diaphragmatic function after diaphragm reinnervation by inferior laryngeal nerve; experimental study in rabbits

OBJECTIVES

To assess the possibilities of reinnervation in a paralyzed hemidiaphragm via an anastomosis between phrenic nerve and inferior laryngeal nerve in rabbits. Reinnervation of a paralyzed diaphragm could be an alternative to treat patients with ventilatory insufficiency due to upper cervical spine injuries.

MATERIAL AND METHOD

Rabbits were divided into five groups of seven rabbits each. Groups I and II were respectively the healthy and the denervated control groups. The 3 other groups were all reinnervated using three different surgical procedures. In groups III and IV, phrenic nerve was respectively anastomosed with the abductor branch of the inferior laryngeal nerve and with the trunk of the inferior laryngeal nerve. In group V, the fifth and fourth cervical roots were respectively anastomosed with the abductor branch of the inferior laryngeal nerve and with the nerve of the sternothyroid muscle (originating from the hypoglossal nerve). Animals were evaluated 4 months later using electromyography, transdiaphragmatic pressure measurements, sonomicrometry and histological examination.

RESULTS

A poor inspiratory activity was found in quiet breathing in the reinnervated groups, with an increasing pattern of activity during effort. In the reinnervated groups, transdiaphragmatic pressure measurements and sonomicrometry were higher in group III with no significant difference with groups IV and V.

CONCLUSION

Inspiratory contractility of an hemidiaphragm could be restored with immediate anastomosis after phrenic nerve section between phrenic nerve and inferior laryngeal nerve.

Experimental reinnervation of a strap muscle with a few roots of the phrenic nerve in rabbits

In order to compare application of the roots of the phrenic nerve to the ansa hypoglossi for laryngeal muscle neurotization, 1 or more roots from the phrenic nerve were implanted into the right sternothyroid (RST) muscle of rabbits (n = 36). Controls were intact animals (in which RST innervation is provided by the ansa; n = 6) and denervated ones (n = 6). At 66 +/- 2 days (mean +/- SE) after neurotization, during quiet breathing, inspiratory electromyographic activity and isometric contraction force were observed in all reinnervated RST muscles (n = 24). During maximal inspiratory effort, electromyographic activity and force increased. In animals reinnervated by the C4 root alone, forces (46.22 +/- 7.8 g) were significantly higher than in intact animals (10.83 +/- 5.0 g). Retrograde labeling proved the phrenic origin of the neurotization. Electromyography of the diaphragm was recorded. We conclude that in rabbits, neurotization of a strap muscle by 1 or 2 roots of the phrenic nerve allows inspiratory contraction, even during quiet breathing. Such inspiratory activity is not observed in sternothyroid muscles of intact animals innervated by the ansa hypoglossi.

Cervical anatomy of phrenic nerve roots in the rabbit. European Group for Research on the Larynx

The cervical anatomy of the different nerve contributions that constitute the phrenic nerve (phrenic nerve roots and accessory phrenic nerve) were studied in rabbits. In 55 dissections, 6 main root arrangement types were observed. The roots that issued from the fourth and fifth cervical nerves (C4 and C5 roots) were constant. The C4 root was either short or long. The C6 root was at times absent, or sometimes double. An accessory phrenic nerve was present in 43% of the right and 28% of the left dissections. The distribution of the phrenic nerve roots often displayed left-right asymmetry. We conclude that a better knowledge of the cervical anatomy of the phrenic nerve is useful both in physiological studies involving diaphragm denervation and in experimental laryngeal reinnervation.

Selective resection of the phrenic nerve roots in rabbits. Part I: Cartography of the residual innervation

Partial unilateral diaphragmatic paralysis remains poorly understood. This study evaluates the residual innervation of the diaphragm after selective resection of one or several roots of the right phrenic nerve in rabbits. Forty-seven animals were operated on according to five root resection modalities. Seven animals served as control. Eight weeks after surgery, the different regions of each hemidiaphragm were analyzed. Electromyographic activity was measured during quiet inspiration and the following histomorphometric parameters were studied: mean fiber area, fiber area dispersion, and ratio large diameter over small diameter. The results obtained from the two measurements were similar. When the accessory phrenic nerve was spared, the crural diaphragmatic region was preserved; denervation was encountered in anterior and lateral parts of the hemidiaphragm. When the highest root of the right phrenic nerve was resected, denervation denervation was limited to the sternal region. When resection of the two highest roots was performed, partial denervation was observed in each region, with residual innervation in the posterior hemidiaphragm. When resection of both the lowest roots was performed, denervation was maximal in the costal region; sternal region remained intact. No contralateral innervation was observed. We conclude that in rabbits: 1) resection of a single root of the phrenic nerve preserves consistent residual innervation. 2) somatotopy of the diaphragm innvervation follows an anteroposterior distribution.