Recovery of inspiratory abduction of the paralyzed vocal cords after bilateral reinnervation of the cricoarytenoid muscles by one single branch of the phrenic nerve

The aim of this study was to provide the bilateral reinnervation of the posterior cricoarytenoid (PCA) muscles by the superior root of the right phrenic nerve. In six adult cats, the right phrenic root was anastomosed to the distal stump of the transected recurrent laryngeal nerve (RLN) on the same side. The RLN adductor branch was then cut and anastomosed to a nerve graft whose end was carried contralaterally and sutured to the left RLN or to the left PCA muscle. The phrenic fibers regrowing along the RLN abductor branch reinnervated the right PCA muscle and restored the inspiratory abduction of the right vocal cord in all the animals. In five of the six cats, the fibers regenerated through the RLN adductor branch and the graft reached the left PCA muscle and also restored the inspiratory opening of the larynx on the left side. Histological nerve examination revealed a fairly symmetrical distribution of the regenerated phrenic axons to the right and left PCA muscles.     

Lack of evoked laryngeal electromyography response in patients with a clinical diagnosis of vocal cord paralysis

There has been recent debate about whether patients with vocal cord immobility have a neurologic paralysis or whether synkinesis, the misdirection of axons to competing laryngeal muscles, is responsible for the lack of voluntary vocal cord motion. This issue was studied in 15 patients with vocal cord paralysis who underwent laryngeal reinnervation. Evoked electromyography was performed with a surface electrode endotracheal tube. The recurrent laryngeal nerve (RLN) was identified and stimulated with constant current. Of the 15 patients, only 1 produced a compound muscle action potential upon nerve stimulation. The remaining 14 patients had no evoked response during RLN stimulation. A control group of 8 patients with normal vocal cord mobility was studied, and each had a normal evoked electromyography response after RLN stimulation. These results support the assertion that patients who require treatment for vocal cord paralysis do not have synkinesis produced by RLN reinnervation.     

Functional remobilization evaluation of the paralyzed vocal cord by end-to-side neurorrhaphy in rats

OBJECTIVE: To investigate the value of end-to-side neurorrhaphy to treat vocal cord paralysis. STUDY DESIGN: A prospective study evaluating the effects of end-to-side neurorrhaphy to treat vocal cord paralysis by means of fiberoptic laryngoscopy and nerve electromyography. METHODS: Thirty Sprague-Dawley rats were divided into experimental group 1, experimental group 2, and a control group randomly. Right recurrent laryngeal nerve (RLN) was incised, and the distal end of the RLN was anastomosed to the right phrenic nerve by end-to-side neurorrhaphy in experimental group 1 or by end-to-end nerve anastomosis in experimental group 2, respectively. The adductor nerve branch of the right RLN was incised and anastomosed to the proximal end of the right ansa cervicalis nerve by end-to-end nerve anastomosis. Fiberoptic laryngoscopy and nerve electromyography were used to examine the vocal cord movement and nerve regeneration. RESULTS: Three months after operation, this effect of end-to-side neurorrhaphy created a significant difference compared with the end-to-end nerve anastomosis (P < .05). The end-to-side neurorrhaphy did not lead to vocal cord movement compared with end-to-end nerve anastomosis. CONCLUSION: Vocal cord paralysis cannot be treated by this microsurgical technique.     

Restoring abduction of paralyzed vocal cords in the cat using selective laryngeal reinnervation by phrenic motoneurons

The aim of this work was to reestablish the respiratory function of the paralyzed larynx through reinnervation of the posterior cricoarytenoid (PCA) muscle by phrenic motoneurons. In nine adult cats the adductor branch of the recurrent laryngeal nerve (RLN) of one side was cut and ligated, while the abductor branch was left intact. The whole RLN was then transected lower in the neck and its distal stump anastomosed to the upper branch of the phrenic nerve. Periodical laryngoscopies under ketamine anesthesia assessed that the inspiratory abduction of the paralyzed vocal cord recovered within 45 days to 60 days in all cats. Abduction was caused by reinnervation of the PCA muscle from phrenic motoneurons, as demonstrated by electrophysiological and anatomical (retrograde transport of horseradish peroxidase) testings.     

神经端侧吻合术治疗声带麻痹的实验研究

目的 :研究神经端侧吻合术治疗声带麻痹的效果及临床应用价值。方法 :6 0只SD大鼠被分为 3组 ,实验组为神经端侧吻合组 ,切断右侧喉返神经 ,将其远断端与右侧膈神经行神经端侧吻合 ,然后切断喉返神经内收支 ,将颈袢的胸骨舌骨肌支与内收支行神经端端吻合 ;对照组为神经端端吻合组 ,切断右侧喉返神经后将其远断端与右侧切断的膈神经近断端行神经端端吻合 ,其他同实验组 ;以上两组均将右侧的喉上神经切断 ,并结扎断端 ,排除环甲肌对声带活动的影响。正常组仅暴露上述神经后不作任何处理。术后 1、3个月利用纤维喉镜及神经肌电图观察声带活动及神经再生情况。结果 :术后 1个月实验组与对照组手术效果差异有显著性意义 (P<0 .0 5 ) ;术后 3个月差异无显著性意义 (P >0 .0 5 )。结论 :神经端侧吻合术手术效果与神经端端吻合术相似 ,并且避免了膈神经的损伤 ,保护了膈肌功能 ,为喉返神经修复术提供了一种新的手术方法。     

正常喉诱发电位特点的研究

目的 分析正常喉肌诱发电位特点,得出其参数正常参考值范围,以利于喉神经功能的评估.方法 检测36例健康受试者72侧喉诱发电位反应,刺激相应喉返神经、喉上神经内、外支及迷走神经,检测诱发肌电反应潜伏期、时程、波幅(电位).结果 甲杓肌喉返神经诱发肌电潜伏期正常参考值(-x±2s,以下同)为(1.13～2.25)ms,迷走神经诱发肌电潜伏期(2.57～5.85)ms,迷走神经与喉返神经潜伏期相比差异有统计学意义(P＜0.01);其中右侧迷走神经诱发肌电潜伏期(2.01～4.53)ms,左侧迷走神经(3.70～6.98)ms,双侧比较差异有统计学意义(P＜0.01),左侧明显较右侧长.诱发肌电时程和波幅各神经亦略有差异,时程差异较小,波幅值变化较大.刺激喉上神经(外支)在环甲肌可直接引出诱发电位,其波形和潜伏期与喉返神经诱发电位大致相同,刺激喉上神经(内支)在甲杓肌、环杓侧肌和环杓后肌可引出反射性感觉诱发电位前波R1和迟发波R2.结论 喉各支配神经诱发电位特点各不相同;神经诱发电位的潜伏期相对时程和波幅来说,是更重要的评估参数.     

甲状腺手术中解剖喉返神经的意义

目的:探讨甲状腺手术中解剖喉返神经的意义及预防喉返神经损伤的方法.方法:回顾性分析230例行甲状腺手术患者的资料,所有患者均在全身麻醉下进行,行单侧腺叶切除术109例,单侧腺叶加峡部切除术59例,甲状腺次全切除术44例,甲状腺全切除术18例.术中常规解剖显露喉返神经;根据术中病变情况决定手术切除范围,手术前后分别进行喉镜观察声带活动情况.结果:解剖暴露喉返神经共292条(右侧156条,左侧136条);位于气管食管沟内走行者134条,偏离者158条;神经位于下动脉深面通过197例(67.5%),神经位于动脉浅面通过60例(20.5%).神经在动脉分支之间通过24例(8.2%),神经分支与动脉分支交叉穿过者11例(3.8%).喉返神经入喉前分支者185条(63.4%),未分支直接入喉者107条(36.6%).术后8例出现声音嘶哑,经过治疗7例恢复,1例经6个月后对侧声带超越代偿嘶哑改善,无永久性声音嘶哑和呼吸困难.结论:甲状腺手术中解剖喉返神经是防止术后喉返神经损伤的有效方法.     

Recurrent laryngeal nerve monitoring during cricotracheal resection

Cricotracheal resection has been advocated in the management of severe subglottic stenosis. One of the possible complications of this procedure is injury to the recurrent laryngeal nerve (RLN). We describe a new technique in which electrodes are placed directly through the thyroid cartilage to monitor the RLN intraoperatively. Nine cats' left vocal cords were monitored, and 3 cats had unilateral vocal cord injury postoperatively: 1 right cord and 2 left cords. Even though this technique was efficacious, our ability to monitor the RLNs was difficult secondary to difficulty interpreting the nerve monitor's wave morphologies. The future use of RLN nerve monitoring during cricotracheal resection will depend upon the ability to distinguish true stimulation from artifact. Monitoring of the RLN could be beneficial in patients with previous operations for subglottic stenosis.     

Experimental study on simultaneous selective reinnervation of the adductors and the abductor muscle for the treatment of the laryngeal paralysis

OBJECTIVE: The aim of this study is to estimate the value of a new surgical procedure in the treatment of the chronic unilateral laryngeal paralysis. METHODS: The recurrent laryngeal nerve of the left side of the dog was totally cut and served as a model of unilateral laryngeal paralysis at the first step of the research. The adductor and abductor branches of the recurrent laryngeal nerve were then, selected and cut. Afterwards, they were micro-sutured respectively with one branch of ansa cervicalis and phrenic nerve immediately (group 1) and 4 months later (group 2). Six months after this reinnervation, the laryngeal physiologic function of the lateral crico-arytenoid muscle (LCA) and the posterior crico-arytenoid muscle (PCA) have been checked by the methods of electromyography (EMG) and direct laryngoscopy. All the data have been analysed by the statistic methods. RESULTS: Among all the data of EMG, only the wave amplitude of action potential of the LCA muscle of the group 2 was diminished (p < 0.05). Under the direct laryngoscopy, the adductor movement of the left vocal cord of the group 2 was also lightly reduced. But the adductor and abductor movements of the left vocal cord were synchronous with the mouvements of the right vocal cord. CONCLUSION: Though the result of nervous reinnervation of a four month's laryngeal paralysis was not so good by comparison with that of an immediate reinnervation, this surgical procedure can however on the clinical point of view, reach a satisfactory level. The duration maximum of the reinnervation operation after laryngeal paralysis, is, at the present, not clear. It is necessary for us to make further studies.     

Transtracheal/transesophageal stimulation of the recurrent laryngeal nerve

A new technique is described which allows stimulation of the recurrent laryngeal nerve (RLN) through intact tracheal and esophageal mucosa. In ten anesthetized dogs, the posterior-lateral tracheal wall and the anterior-lateral esophageal wall were stimulated by a 1 to 2 mA current with a probe placed just distal to the edge of the cricoid cartilage. The tracheal mucosa was approached through a tracheostomy stoma and the esophageal mucosa through the mouth. The resultant vocal cord motion was frequency dependent, with graded abduction occurring below 30 Hz and adduction above 40 Hz. By stimulating the posterior laryngeal mucosa proximal to the cricoid edge, the RLN branch to the posterior cricoarytenoid muscle was activated, causing ipsilateral vocal cord abduction independent of frequency. Monitoring of cardiopulmonary parameters demonstrated no alterations at these amperages. There were no mucosal abrasions noted. The transtracheal and transesophageal approaches to RLN stimulation appear promising as diagnostic techniques for evaluating vocal cord function during laryngoscopy and, possibly, as methods of glottic airway control.     

Afferent activity in the external branch of the superior laryngeal and recurrent laryngeal nerves.

We investigated the presence of respiratory-modulated receptors in the recurrent laryngeal nerve (RLN) and the external branch of the superior laryngeal nerve (ExtSLN) in anesthetized, spontaneously breathing dogs. Of 39 receptors recorded from the ExtSLN, the vast majority responded with a slowly adapting discharge to compression of the cricothyroid muscle, and only 1 responded to probing of the laryngeal mucosa. Ten receptors showed a respiratory modulation. All 30 receptors recorded from the RLN responded to probing of the laryngeal lumen, most of them (60%) with a rapidly adapting response. Seven of the slowly adapting receptors exhibited a respiratory modulation; 38% of the receptors tested were stimulated by water, and only 15% by smoke. No receptors stimulated by laryngeal cooling were identified in either nerve. Our study indicates that in the RLN and the ExtSLN there are relatively few afferents responding to changes in transmural pressure and mechanical irritation, as compared to the internal branch of the SLN. The relative scarcity of receptors responding to transmural pressure and irritant stimuli is consistent with previous observations in dogs that indicate a preponderant role for afferents in the internal branch of the SLN in the reflex responses to laryngeal stimulation.     

Laryngeal reinnervation for unilateral traumatic recurrent laryngeal nerve injuries]

OBJECTIVE: To investigate 5 procedures of laryngeal reinnervation for unilateral vocal cord paralysis induced by traumatic recurrent laryngeal nerve injury. METHODS: 35 cases were selected for our study, all patients had unilateral recurrent laryngeal nerve injury, including 8 for nerve decompression, 6 for end to end anastomosis of recurrent laryngeal nerve, 16 for main branch of ansa cervicalis anastomosis to recurrent laryngeal nerve, 3 for nerve muscular pedicle and 2 for nerve implantation. All cases have been subjected to preoperative and postoperative voice recording, acoustic analysis, videolaryngoscopy, strobscopy and electromyography. RESULTS: It is found the adductory and abductory motion of the vocal cord restored in 5 cases with less than 4 months course who received nerve decompression. Although functional motion of vocal cord was not seen in two patients who received nerve decompression with a course longer than 4 months and one less than 4 months, and in all cases who received ansa cervicalis anastomosis and end to end anastomosis of recurrent laryngeal nerve, these procedures resulted in medialization of vocal cord and the mass and tension of the reinnervated vocal cord may become much the same as the contralateral normal vocal cord, thus resuming symmetric vibration of the vocal cords and physiological phonation. Nerve muscular pedicle technique and nerve implantation enabled adductory muscles to be reinnervated, thus improving severe hoarseness, but they didn't restore normal voice. CONCLUSIONS: (1) Nerve decompression seems to be the best procedure in laryngeal reinnervation; (2) Main branch of ansa cervicalis technique raises satisfactory reinnervation of adductor muscles; (3) Selection of the laryngeal reinnervation protocols should depend on the course, severity and type of nerve injury.     

Laryngeal mask anesthesia with intraoperative laryngoscopy for identification of the recurrent laryngeal nerve during thyroidectomy

OBJECTIVES/HYPOTHESIS: A critical step in thyroidectomy involves definitive identification of the recurrent laryngeal nerve (RLN). Using the laryngeal mask airway, identification of the RLN can be facilitated by stimulation of the nerve while monitoring vocal cord movement with a fiberoptic laryngoscope. We present this technique as an effective and safe means to identify the RLN during thyroid surgery, with significant advantages over existing techniques in appropriately selected patients. STUDY DESIGN: Retrospective case series. METHODS: We performed thyroidectomy on 8 patients (13 RLN identifications) in which laryngeal mask airway anesthesia with fiberoptic laryngoscopy was used to identify the RLN. Results are reviewed with regard to postoperative vocal cord function, as well as intraoperative and postoperative courses with laryngeal mask airway anesthesia. RESULTS: In all 13 cases in which the RLN was sought, it was definitively identified by witnessing brisk vocal cord movement on a video screen with stimulation of the RLN. No patient had postoperative vocal cord paresis or paralysis. Overall recovery from laryngeal mask airway anesthesia was uneventful and had advantages when compared with general anesthesia with endotracheal intubation. CONCLUSIONS: Laryngeal mask airway anesthesia with intraoperative fiberoptic laryngoscopy to identify the RLN is effective and safe in carefully selected patients. Advantages include decreased postoperative throat discomfort, absence of coughing during emergence from anesthesia, and elimination of the possibility of vocal cord mobility impairment secondary to RLN ischemia from the endotracheal tube balloon. In addition, this technique is applicable in operations besides thyroid surgery, in which definitive identification of the RLN is indicated.     

Protective glottic closure: biomechanical effects of selective laryngeal denervation

Glottic closure constitutes the primary mechanism for prevention of intradeglutitive and postdeglutitive aspiration. Laryngeal paralysis therefore exerts a considerable impact on deglutition, yet little is understood regarding the biomechanical effects of selective denervation on the laryngeal protective function. We measured the glottic closing force (GCF) in each of 6 male, 40-kg Yorkshire pigs 1) after selective unilateral superior laryngeal nerve (SLN) section; 2) after selective unilateral recurrent laryngeal nerve (RLN) section; and/or 3) after combined SLN-RLN section as both right and left SLNs were simultaneously stimulated to evoke the glottic closure response. Stimulation was provided through an oscilloscope with bipolar platinum-iridium electrodes, and the GCF was measured with a pressure transducer positioned between the vocal cords. Six repetitive measures of GCF were obtained before nerve section, and 6 after nerve section, in each subject. Unilateral SLN section reduced the GCF to 54.14% of control, RLN section reduced the GCF to 23.39% of control, and combined SLN-RLN section reduced the GCF to 22.67% of control. These findings underscore the profound differential effects exerted by isolated lesions on the glottic closure function.     

Surgical anatomy of the recurrent laryngeal nerve: implications for laryngeal reinnervation

Functional laryngeal reinnervation depends upon the precise reinnervation of the laryngeal abductor and adductor muscle groups. While simple end-to-end anastomosis of the recurrent laryngeal nerve (RLN) main trunk results in synkinesis, functional reinnervation can be achieved by selective anastomosis of the abductor and adductor RLN divisions. Few previous studies have examined the intralaryngeal anatomy of the RLN to ascertain the characteristics that may lend themselves to laryngeal reinnervation. Ten human larynges without known laryngeal disorders were obtained from human cadavers for RLN microdissection. The bilateral intralaryngeal RLN branching patterns were determined, and the diameters and lengths of the abductor and adductor divisions were measured. The mean diameters of the abductor and adductor divisions were 0.8 and 0.7 mm, while their mean lengths were 5.7 and 6.1 mm, respectively. The abductor division usually consisted of one branch to the posterior cricoarytenoid muscle; however, in cases in which multiple branches were seen, at least one dominant branch could usually be identified. We conclude that the abductor and adductor divisions of the human RLN can be readily identified by an extralaryngeal approach. Several key landmarks aid in the identification of the branches to individual muscles. These data also indicate the feasibility of selective laryngeal reinnervation in patients who might be candidates for laryngeal transplantation after total laryngectomy.     

Laryngeal reinnervation

In the past, numerous experiments have been performed to attempt reinnervation of the paralyzed larynx. None have been consistently successful. Two experiments were performed in this study, one to restore abduction of a paralyzed vocal cord and one to restore adduction. To paralyze the vocal cord, the recurrent laryngeal nerve was sectioned in all dogs in both experiments. The first experiment was to restore abduction and was performed as follows. An intralaryngeal dissection was performed to separately identify the abductor and adductor branches of the recurrent laryngeal nerve. The adductor branch was sectioned and ligated. Next the phrenic nerve was identified and sectioned. In the dog, the phrenic nerve will not reach the abductor branch of the recurrent laryngeal nerve, so it was sutured to the main trunk of the recurrent laryngeal nerve. Since the adductor branch was severed, regenerating fibers from the phrenic nerve could only grow into the abductor branch and thus to the posterior cricoarytenoid muscle. This experiment produced excellent return of abduction synchronous with inspiration. The second experiment was to restore adduction and was performed as follows. Intralaryngeal dissection was again done to identify the abductor and adductor branches of the recurrent laryngeal nerve. In addition, the motor branch of the superior laryngeal nerve was identified and transected as it entered the cricothyroid muscle. This branch was then anastomosed to the adductor branch of the recurrent laryngeal nerve. The results of this experiment led to chronic adduction of the vocal cord throughout the respiratory cycle. Suggestions for future research include anastomosis of the ansa cervicalis to the abductor branch of the recurrent laryngeal nerve and anastomosis of the main trunk of the vagus nerve to either the abductor or adductor branches of the recurrent laryngeal nerve.     

Evaluation of functional recovery of recurrent laryngeal nerve using transoral laryngeal bipolar electromyography: a rat model

OBJECTIVES: We developed a standardized method of minimally invasive transoral laryngeal (ToL) bipolar electromyography (EMG) for evaluation of recurrent laryngeal nerve (RLN) recovery after a controlled crush injury in a rat model. METHODS: Ten 200- to 250-g Sprague-Dawley rats underwent a controlled crush injury to the left RLN performed with 60 seconds of use of a calibrated aneurysm clamp with a closing force of 0.61 N. Serial ToL bipolar EMG was performed on adductor muscles and the posterior criocoarytenoid muscle during spontaneous vocal fold motion under anesthesia. Each animal underwent ToL EMG immediately after surgery and 1, 3, and 6 weeks after surgery. RESULTS: The EMG signals showed normal motor unit potentials and recruitment patterns 3 weeks after crush injury. Endoscopic evaluation of vocal fold mobility yielded consistently normal findings 6 weeks after crush injury. CONCLUSIONS: We have developed a standardized method of crush injury to the rat RLN model and a minimally invasive transoral bipolar spontaneous EMG technique to serially evaluate and follow nerve injury and recovery in rats. This model is intended to simulate intraoperative RLN injury, to elucidate the electrophysiological events that occur during nerve recovery, and to form the basis for studying agents to enhance such recovery.     

Modulation of myosin heavy chains in rat laryngeal muscle

OBJECTIVES: To test the hypothesis that myosin heavy chain (MHC) composition is a biological marker indicative of appropriate and functional reinnervation. STUDY DESIGN: Age-matched adult rats were randomized for prospective study under three experimental conditions. METHODS: In adult rats, three experimental conditions were surgically created, including transient recurrent laryngeal nerve (RLN) crush injury, RLN transection and repair, and cricoarytenoid joint fixation with intact RLN. Animals were survived for 30, 90, and 180 days. At each interval, vocal fold mobility was assessed by rigid microlaryngoscopy. Laryngeal electromyography (EMG) was performed before euthanasia. The thyroarytenoid and posterior cricoarytenoid muscles were then excised, each muscle was processed for sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and MHC composition was determined. RESULTS: Thirty days after nerve crush injury, three of six animals regained vocal fold mobility and normal MHC composition. Impaired vocal fold motion in three of six animals was associated with MHC composition characteristic of denervation. At 90 and 180 days, normal vocal fold motion and normal MHC composition were observed in all animals. Following nerve transection and repair, impaired vocal fold motion and MHC composition characteristic of denervation were observed in all animals, despite evidence of reinnervation on EMG. Following joint fixation, alteration in MHC composition consistent with denervation was observed only at 30 days, as was evident in the nerve crush model. CONCLUSION: Temporary injury and vocal fold immobilization result in transient shifts in MHC composition. Nerve transection and repair result in persistent alteration of MHC composition and vocal fold dysfunction. The expression of normal MHC composition is dependent on the condition of appropriate neural contact and functional reinnervation.     

Motion-specific laryngeal reinnervation using muscle-nerve-muscle neurotization

There is no current treatment method that can reliably restore physiologic movement to a paralyzed vocal fold. The purposes of this study were to test the hypotheses that 1) muscle-nerve-muscle (M-N-M) neurotization can be induced in feline laryngeal muscles and 2) M-N-M neurotization can restore movement to a paralyzed vocal fold. Muscle-nerve-muscle neurotization can be defined as the reinnervation of a denervated muscle via axons that are induced to sprout from nerves within an innervated muscle and that then traverse a nerve graft interposed between it and the target denervated muscle. A paralyzed laryngeal muscle could be reinnervated by axons from its contralateral paired muscle, thus achieving motion-specific reinnervation. Eighteen adult cats were divided into sham, hemilaryngeal-denervated, and M-N-M-reinnervated thyroarytenoid muscle groups. Five of the 6 reinnervated animals had histologic evidence of axons in the nerve graft, 4 of the 6 had evoked electromyographic evidence of crossed reinnervation, and 1 of the 6 had a return of appropriately phased adduction. This technique has great potential and should be further investigated.