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.     

A new electromyographic definition of laryngeal synkinesis

Laryngeal synkinesis involves the misdirected reinnervation of an injured recurrent laryngeal nerve to vocal fold abductor and adductor musculature. The resultant laryngeal dyscoordination can cause vocal fold immobility and airway compromise. Although this entity is sometimes considered in the differential diagnosis, it is only demonstrable with laryngeal electromyography (EMG). We propose a new EMG definition of synkinesis to assist in its identification during workup of vocal fold immobility. A retrospective chart review from 1992 to 1997 in the Voice Disorders Clinic identified 10 patients with laryngeal synkinesis. Five patients had bilateral immobility, and 5 had unilateral immobility. Monopolar EMG was performed on all patients. Fine-wire EMG was performed when monopolar EMG did not elucidate the cause of the immobility. The EMG studies revealed synkinetic reinnervation in all subjects. On the basis of the EMG results, 7 of the 10 patients were treated with botulinum toxin to weaken the undesired reinnervation. Three of the 7 patients had benefit from this therapy. Laryngeal synkinesis should be considered as part of the differential diagnosis of vocal fold immobility. Awake laryngeal EMG is the only method to demonstrate synkinesis of the larynx. The diagnosis of synkinesis is clinically significant in cases of immobility to identify patients who might benefit from botulinum toxin therapy. Additionally, the presence of synkinesis in cases of unilateral immobility may be a contraindication to laryngeal reinnervation procedures. The benefit of botulinum toxin therapy is likely greater in the treatment of bilateral as opposed to unilateral immobility.     

Aberrant recurrent laryngeal nerve reinnervation as a cause of stridor and laryngospasm

Unilateral vocal fold paralysis rarely presents with symptoms of stridor, laryngospasm, and dyspnea. Abnormal reinnervation of abductor nerve branches into adductor fibers may be one cause. Four patients have been positively identified by laryngeal electromyography. Two patients presented after thyroid surgery for thyroid neoplasm. One presented after cervical disk surgery. One patient presented after herpes simplex infection with multiple cranial nerve involvement. All patients had new onset of dyspnea with exertion many months after the recurrent nerve injury. Fiberoptic laryngoscopy showed the affected vocal fold to be immobile. However, with hyperventilation and deep inspiration, there was paradoxical adductor motion of the paretic vocal fold. Laryngeal electromyography showed evidence of reduced but intact voluntary motor units in the thyroarytenoid muscle. These motor units fired on inspiration and not on phonation. This pattern was not seen on the normal side. These findings are consistent with paradoxical innervation and/or synkinesis. Each patient was managed by Botox injection into the adductor muscle. Periodic reinjections may be necessary to manage the condition.     

The effect of patient age on the success of laryngeal reinnervation

The objective of the study was to investigate the influence of patient age on the efficacy of laryngeal reinnervation with ansa cervicalis in unilateral vocal fold paralysis (UVFP) patients. We retrospectively reviewed 349 consecutive UVFP cases of laryngeal reinnervation with ansa cervicalis to the recurrent laryngeal nerve anastomosis. Preoperative and postoperative videostroboscopy, perceptual evaluation, acoustic analysis, maximum phonation time (MPT) and laryngeal electromyography (EMG) data were collected. Gender, age, preoperative EMG status [preoperative voluntary motor unit recruitment (VMUR)] and denervation duration were analyzed in previous multivariable logistic regression analysis. Stratification analysis was performed on patient age in the present study. All patients were divided into four groups according to their age: Group A included patients with an age less than 30 years; Group B, 30–44 years; Group C, 45–59 years; Group D, ≥60 years. Stratification analysis on patient age showed significant differences between Group A and D, Group B and D, Group C and D (P < 0.05), but no significant difference between Group A and B, Group A and C, Group B and C (P > 0.05), respectively, with regard to parameters including glottal closure, overall grade, shimmer, noise-to-harmonics ratio; but there are no significant differences among the four groups with regard to jitter. However, for MPT and postoperative VMUR, there are significant differences among the four groups expect between Group A and B. In addition, glottal closure, perceptual and acoustic parameters, MPT values and VMUR data, were significantly improved postoperatively in each age group (P < 0.01). The data from this study indicate that patient age is an influential factor of the surgical outcome of laryngeal reinnervation for UVFP patients. Laryngeal reinnervation is less effective when patient age is more than 60 years.     

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.     

一侧膈神经上根选择性神经再支配环杓后肌的实验研究

目的 探讨一侧膈神经上根选择性神经再支配环杓后肌的可行性和有效性.方法 8只健康雄性青年Beagle犬作为实验动物,全麻下切断Beagle犬左侧膈神经上根与左侧喉返神经,两断端通过游离神经桥接的方式吻合,并将同侧喉返神经内收肌支切断并植入同侧环杓后肌中;右侧不做任何处理,作为正常对照侧.于手术前、神经修复术后即刻、术后6个月分别行电子喉镜和喉肌电图检查,在最后一次检查后处死动物,取双侧环杓后肌和喉内段喉返神经行组织学检查并与对侧比较.结果 术前8只犬的双侧声带运动正常,术后即刻左侧声带固定,术后6个月均恢复了吸气性外展运动.术前8只犬双侧环杓后肌均能记录到自发肌电位,并引出诱发电位;术后即刻左侧环杓后肌呈电静息,未记录到诱发电位;术后6个月均能记录到自发肌电位,并引出诱发电位,而且两种电位幅度分别与术前比较差异均无统计学意义(均为P>0.05).环杓后肌Masson染色示两侧肌肉纤维相对截面积、胶原纤维相对截面积、肌肉/胶原纤维截面积比差异均无统计学意义(均为P>0.05).喉内段喉返神经甲苯胺蓝染色后示神经纤维分布较均匀密集,且左右两侧喉返神经有髓神经纤维数量差异无统计学意义(P>0.05).结论 左侧膈神经上根选择性神经再支配环杓后肌能有效避免神经错向再生,恢复声带的生理性外展运动.     

Spontaneous laryngeal reinnervation after recurrent laryngeal or vagus nerve injury

OBJECTIVES: The status of innervation in patients with laryngeal paralysis is somewhat controversial. Electromyographic activity has been frequently documented in the laryngeal muscles of patients with laryngeal paralysis, and animal experiments report a strong propensity for reinnervation after laryngeal nerve injury. However, a study of intraoperative electromyography performed in patients during reinnervation surgery failed to document activity with stimulation of the recurrent laryngeal nerve (RLN). Noting the long-observed differences in the symptoms of patients with vagus nerve injury and those with RLN injury, I hypothesized that reinnervation is influenced by the site of nerve injury. METHODS: Cats were sacrificed at various intervals after resection of 1 cm of either the RLN or the vagus nerve, without any attempt to repair the nerve. RESULTS: Four months after RLN resection, distal nerve biopsy revealed unmyelinated axons scattered through fibrous tissue. By 6 months, myelinated axons were organized, and electromyographic and histologic examination showed preferential reinnervation of the thyroarytenoid muscle. After vagotomy, the RLN was fibrotic and no axons were present. Both the thyroarytenoid and posterior cricoarytenoid muscles were fibrotic and had no electromyographic activity. CONCLUSIONS: The results confirm the strong propensity for laryngeal reinnervation after RLN injury, but not after vagus nerve injury. Preferential reinnervation of adductor muscles may account for a medial position of the paralyzed vocal fold.     

Photoelectric measurement of laryngeal paralyses correlated with videostroboscopy

Photoglottography and electroglottography are relatively noninvasive techniques that provide detailed information about vocal fold vibration. However, few significant clinical applications have been made by correlating photoelectric waveforms to specific pathologic changes in laryngeal vibration. Videostroboscopy has recently been used to document vibratory patterns of laryngeal paralyses in a canine model of phonation. A study of PGG and EGG waveforms correlated with videostroboscopy in an in-vivo canine model of phonation with simulated unilateral recurrent or superior laryngeal nerve paralysis is presented. The shift quotient--a new glottographic parameter which identifies flaccid laryngeal paralyses--is presented.     

Experimental Study on Reinnervation of Vocal Cord Adductors With the Ansa Cervicalis

The purpose of this study was to reestablish the adduction of the paralyzed vocal cord through reinnervation of the adductor muscles for unilateral vocal cord paralysis. In nine dogs, the adductor branch of the recurrent laryngeal nerve was anastomosed to the main branch of the ansa cervicalis. Six months later, various techniques of observation showed that seven of nine cases had excellent to good adduction during whining. Adduction was caused by reinnervation of the adductor muscles from the ansa cervicalis as demonstrated by laryngeal spontaneous and evoked electromyography, contraction tension, and various histologic findings. Therefore, the new technique could be a good treatment of unilateral vocal cord paralysis.     

Update: Laryngeal Reinnervation for Unilateral Vocal Cord Paralysis With the Ansa Cervicalis

Eight patients underwent ansa cervicalis anastomosis to the adductor branch of the recurrent laryngeal nerve for unilateral vocal cord paralysis. They were followed long enough (at least 1 year) to determine if the procedure was successful. All cases have been subjected to preoperative and postoperative voice recording, acoustic analysis, and videolaryngoscopy. Some of them have been subjected to stroboscopy and electromyography (EMG). Data from these cases indicate that satisfactory phonatory quality may be achieved after the procedure. The reinnervated vocal cord neither abducted nor adducted, but it presented itself in midline for precise apposition with the normal cord. Synchronous mucosal waves in both vocal cords could be observed. EMG showed that the procedure produced satisfactory reinnervation of the adductory muscles. Therefore, the authors believe that the procedure could be proposed as an alternative to Teflon injection or thyroplasty in selected cases.     

Thyroarytenoid muscle maintains normal contractile force in chronic vocal fold immobility.

BACKGROUND: Denervation of skeletal muscle typically results in irreversible denervation atrophy over time. This finding has generated controversy as to the efficacy of reinnervation procedures for chronic vocal fold immobility related to recurrent laryngeal nerve injury. OBJECTIVE: To test the hypothesis that chronic vocal fold immobility after recurrent laryngeal nerve injury does not result in diminished maximal isometric force generation in the thyroarytenoid muscle. STUDY DESIGN: Adult random-bred cats underwent either unilateral laryngeal denervation (n = 6) or sham surgery (n = 6). After 6 months, videolaryngoscopy was performed followed by in vitro measurement of maximal isometric tetanic force produced by the thyroarytenoid muscle. RESULTS: All animals in the denervation group showed right vocal fold paralysis after the initial denervation operation; none of these animals had return of appropriately phased movement with respiration. Four had intermittent disorganized twitching movements. One had these movements plus an occasional weak adduction, and one had no movement. Normal vocal fold mobility was observed in 6 of 6 animals undergoing sham surgery. The maximal isometric tetanic force measured from the thyroarytenoid muscle in the sham group was 438 mN (+/-92 mN standard deviation [SD]). The maximal isometric tetanic force measured from the thyroarytenoid muscle in the chronically immobile group was 405 mN (+/-107 mN SD). Differences were not statistically significant. CONCLUSION: Maximal isometric force in the thyroarytenoid muscle is not diminished in chronic vocal fold immobility after recurrent laryngeal nerve injury. We conclude that the possibility for restoration of contractile force to the chronically immobile thyroarytenoid muscle exists. This finding supports the pursuit of reinnervation procedures in the treatment of chronic vocal fold immobility.     

Combined arytenoid adduction and laryngeal reinnervation in the treatment of vocal fold paralysis

OBJECTIVE/HYPOTHESIS: Glottal closure and symmetrical thyroarytenoid stiffness are two important functional characteristics of normal phonatory posture. In the treatment of unilateral vocal cord paralysis, vocal fold medialization improves closure, facilitating entrainment of both vocal folds for improved phonation, and reinnervation is purported to maintain vocal fold bulk and stiffness. A combination of medialization and reinnervation would be expected to further improve vocal quality over medialization alone. STUDY DESIGN: A retrospective review of preoperative and postoperative voice analysis on all patients who underwent arytenoid adduction alone (adduction group) or combined arytenoid adduction and ansa cervicalis to recurrent laryngeal nerve anastomosis (combined group) between 1989 and 1995 for the treatment of unilateral vocal cord paralysis. Patients without postoperative voice analysis were invited back for its completion. A perceptual analysis was designed and completed. METHODS: Videostroboscopic measures of glottal closure, mucosal wave, and symmetry were rated. Aerodynamic parameters of laryngeal airflow and subglottic pressure were measured. A 2-second segment of sustained vowel was used for perceptual analysis by means of a panel of voice professionals and a rating system. Statistical calculations were performed at a significance level of P = .05. RESULTS: There were 9 patients in the adduction group and 10 patients in the combined group. Closure and mucosal wave improved significantly in both groups. Airflow decreased in both groups, but the decrease reached statistical significance only in the adduction group. Subglottic pressure remained unchanged in both groups. Both groups had significant perceptual improvement of voice quality. In all tested parameters the extent of improvement was similar in both groups. CONCLUSION: The role of laryngeal reinnervation in the treatment of unilateral vocal cord paralysis remains to be established.     

甲状腺手术喉返神经损伤规律及治疗的探讨

目的探讨甲状腺手术喉返神经损伤的规律及中早期神经减压的疗效。方法甲状腺手术喉返神经损伤单侧声带麻痹87例，其中行喉返神经探查65例，非手术治疗22例。探查术中观察喉返神经损伤部位、类型、程度及神经肌肉形态；对缝扎、粘连伤行神经减压治疗14例。治疗前后以喉镜、嗓音声学参数、肌电图检查等评价治疗效果。结果探查发现喉返神经被缝线结扎、瘢痕粘连压迫、断离分别占43％(28／65)、9％(6／65)、48％(31／65)。损伤部位以近环甲关节处多见，占75％(49／65)；甲状腺中下部占25％(16／65)。病程半年以内喉内肌及损伤处远端神经干萎缩并不严重，病程越长萎缩变性越明显。神经切断伤上述改变较缝扎伤及压迫伤更为明显；但病程18个月喉内肌仍可见肌纤维组织结构。病程3个月内神经减压10例中9例声带恢复了不同程度的内收及外展功能；病程3个月以内1例、3—5个月4例神经减压术后声带未恢复运动，但均恢复了正常的肌张力、肌体积，声带振动及黏膜波对称，嗓音亦恢复正常。非手术治疗组声嘶有改善，但嗓音未恢复正常，声带亦未恢复运动。结论通过喉返神经探查初步揭示甲状腺手术喉返神经损伤的规律，中早期喉返神经减压术能恢复声带生理性运动功能。     

New Laryngeal Muscle Weakness in Post-Polio Syndrome

The authors describe the clinical presentations of post-polio laryngeal muscle weakness in three patients with prior polio infection who presented with new complaints including slowly progressive dyspnea, dysphagia, and/or hoarseness. Evaluations by laryngeal videostroboscopy and electromyography revealed vocal cord abductor and/or adductor weakness, recurrent posterior glottic web in one case, and, in the two patients who agreed to electromyography, evidence of prior denervation and reinnervation in laryngeal muscles. Treatment was directed at attempting to maintain an airway and optimize vocal quality. One patient benefitted from tracheostomy, one benefitted from vocal cord medialization, and one benefitted from resection of interarytenoid scarring. The authors conclude that diagnosis of laryngeal post-polio syndrome is facilitated by laryngeal electromyography. Interventions directed at maintaining an appropriate airway and optimizing vocal quality may be helpful.     

Acoustic and perceptual evaluation of laryngeal reinnervation by ansa cervicalis transfer

Objectives/Hypothesis: To evaluate the acoustic and perceptual results of laryngeal reinnervation with ansa cervicalis to recurrent laryngeal nerve anastomosis. Study Design: Retrospective study of voice samples from 12 patients with unilateral recurrent laryngeal nerve paralysis, treated with ansa cervicalis to recurrent laryngeal nerve anastomosis. Samples were recorded before surgery and at least 8 months after surgery. Methods: The samples were subjected to several acoustic analyses sensitive to paralytic dysphonia, including cepstral peak prominence, noise-to-harmonics ratio, and measures of frequency and amplitude perturbation. The voice samples from the patients were randomized with age- and sexmatched samples from normal subjects and judged by trained listeners for overall dysphonia, roughness, breathiness, asthenia, and strain. The preoperative and postoperative results were compared statistically, and the postoperative results were compared with the matched normal subjects. Results: As a group, the patients showed improvement (P < .05) in cepstral peak prominence, frequency perturbation, and perceptual judgments of overall dysphonia, breathiness, and asthenia. The best results occurred in patients with isolated vocal fold paralysis. The postoperative group as a whole did not improve to the level seen in matched normals. Suboptimal results were seen primarily in patients with untreated laryngeal or extralaryngeal pathology beyond the laryngeal paralysis. Conclusions: These data suggest that laryngeal reinnervation has the potential to bring about a return to normal or near-normal voice in patients with isolated unilateral vocal fold paralysis.     

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.     

甲状腺手术喉返神经损伤规律及治疗的探讨

目的 探讨甲状腺手术喉返神经损伤的规律及中早期神经减压的疗效。方法 甲状腺手术喉返神经损伤单侧声带麻痹87例,其中行喉返神经探查65例,非手术治疗22例。探查术中观察喉返神经损伤部位、类型、程度及神经肌肉形态;对缝扎、粘连伤行神经减压治疗14例。治疗前后以喉镜、嗓音声学参数、肌电图检查等评价治疗效果。结果 探查发现喉返神经被缝线结扎、瘢痕粘连压迫、断离分别占43％(28/65)、9％(6/65)、48％(31/65)。损伤部位以近环甲关节处多见,占75％(49/65);甲状腺中下部占25％(16/65)。病程半年以内者喉内肌及损伤处远端神经干萎缩并不严重,病程越长萎缩变性越明显。神经切断伤上述改变较缝扎伤及压迫伤更为明显;但病程18个月喉内肌仍可见肌纤维组织结构。病程3个月内神经减压10例中9例声带恢复了不同程度的内收及外展功能;病程3个月以内1例、3-5个月4例神经减压术后声带未恢复运动,但均恢复了正常的肌张力、肌体积,声带振动及黏膜波对称,嗓音亦恢复正常。非手术治疗组声嘶有改善,但嗓音未恢复正常,声带亦未恢复运动。结论 通过喉返神经探查初步揭示甲状腺手术喉返神经损伤的规律,中早期喉返神经减压术能恢复声带生理性运动功能。     

A novel modification of the ansa to recurrent laryngeal nerve reinnervation procedure for young children

Vocal ford paralysis is a condition often seen in otolaryngologic adult and pediatric clinics. We report a case we believe to be the youngest child to undergo ansa cervicalis (ansa) to recurrent laryngeal nerve (RLN) reinnervation for unilateral vocal fold paralysis. We have included the preoperative and postoperative videostroboscopic and acoustic findings. The acoustic data shows improvement and is consistent with the patient's improved voice quality. Most notably the patient's voice quality is less raspy and his volume has improved while subjectively requiring less effort.     

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.     

Measurements of oxygen pressure in the vocal fold during laryngeal nerve stimulation

To clarify the mechanisms of ischemic change in the vocal fold on phonation, model experiments were performed under various conditions by recording tissue oxygen pressure (Pto2) values under electrical stimulation of either the recurrent laryngeal nerves or external branches of the superior laryngeal nerves. In addition, autonomic nerve regulation of laryngeal vessels was estimated under administration of succinylcholine chloride. Oxygen pressures of the vocal fold were measured in the lamina propria and vocal muscle at the middle of the membranous portion. The Pto2 in the lamina propria showed a slight increase during lower-frequency stimulation and a slight decrease during higher-frequency stimulation of the recurrent laryngeal nerve. The Pto2 in the vocal muscle showed a decrease during stimulation of the recurrent laryngeal nerve. On the other hand, the Pto2 showed almost no change in the lamina propria or vocal muscle during stimulation of the external branch of the superior laryngeal nerve. It is supposed that an ischemic change in the vocal muscle on phonation results mainly from contraction of the vocal muscle. On the contrary, the ischemic change in the vocal mucosa on phonation does not appear to be directly caused by the contraction of the vocal muscle but by other factors, such as wavelike movement.