Comparison of ventilation and voice outcomes between unilateral laryngeal pacing and unilateral cordotomy for the treatment of bilateral vocal fold paralysis.

BACKGROUND/AIMS: Rehabilitation of the bilaterally paralyzed human larynx remains a complex clinical problem. Conventional treatment generally involves surgical enlargement of the compromised airway, but often with resultant dysphonia and risk of aspiration. In this retrospective study, we compared one such treatment, posterior cordotomy, with unilateral laryngeal pacing: reanimation of vocal fold opening by functional electrical stimulation of the posterior cricoarytenoid muscle. METHODS: Postoperative peak inspiratory flow (PIF) values and overall voice grade ratings were compared between the two surgical groups, and pre- and postoperative PIF were compared within the pacing group. RESULTS: There were 5 patients in the unilateral pacing group and 12 patients in the unilateral cordotomy group. Within the pacing group, postoperative PIF values were significantly improved from preoperative PIF values (p = 0.04) without a significant effect on voice (grade; p = 0.62). Within the pacing group, the mean postoperative PIF value was significantly higher than that in the cordotomy group (p = 0.05). Also, the mean postoperative overall voice grade values in the pacing group were significantly lower (better) than those of the cordotomy group (p = 0.03). CONCLUSION: Unilateral pacing appears to be an effective treatment superior to posterior cordotomy with respect to postoperative ventilation and voice outcome measures.

Botulinum toxin injections for new onset bilateral vocal fold motion impairment in adults.

OBJECTIVES/HYPOTHESIS: Review of clinical experience and results using botulinum toxin type A (BTX) for the management of adult patients with respiratory compromise due to new onset bilateral vocal fold motion impairment (BVFMI). STUDY DESIGN: Retrospective case series. METHODS: The records of 11 patients from two institutions with respiratory compromise due to bilateral vocal fold motion impairment were reviewed. Age, sex, etiology of motion impairment, subjective response to BTX injections, changes in pulmonary function studies pre- and postinjection when available, the dosage of botulinum toxin required to achieve response, the number of injections per patient, and complications were reported. RESULTS: All patients were over 18 years old. There were three male and eight female subjects. The etiology of BVFMI was due to previous anterior cervical surgery in nine patients and prolonged intubation in two. Ten patients reported symptomatic improvement and returned for an average of nine injections over the 10-year period of study. The most common interval between injections was 3 months. In all patients the dose required to achieve symptomatic improvement was at least 2.5 mouse units injected into each vocal fold. One patient without relief of symptoms had bilateral cricoarytenoid joint fixation. Complications were limited to moderate dysphagia in one patient and breathy dysphonia in all patients. CONCLUSIONS: BTX injection into the vocal folds provides temporary relief of symptoms in airway obstruction in adult patients with BVFMI. Patients require an average of 2.5 units of botulinum injection into each vocal fold and have an average length of response of 3 months. BTX injection may be used as a form of temporary relief of airway obstruction in patients wishing to avoid ablative surgery or tracheotomy.

Evaluation of a deep brain stimulation electrode for laryngeal pacing.

OBJECTIVES: The purpose of the present study was to evaluate the suitability of a deep brain stimulation electrode for laryngeal pacing. Of interest was whether the smaller and more closely spaced channels could provide sufficient channel redundancy, controlled current distribution, and discrete activation of the posterior cricoarytenoid (PCA) muscle. METHODS: A study was conducted in dogs under differing states of PCA muscle innervation representing complete denervation to complete synkinetic reinnervation. In 3 animals, stimulated glottal opening was assessed in the innervated state and after chemical denervation by pancuronium bromide. In 3 additional dogs, the left side of the larynx was surgically denervated and compared to the innervated, right side to study an anatomic model of clinical paralysis. RESULTS: The thresholds were lower and the maximum level of abduction was greater for the innervated state. The stimulated glottal opening equaled that of a spontaneously breathing animal. Abductory responses were obtained across all channels in the array, demonstrating its anatomic and physiological compatibility for this application. In the denervated state, responses were only 20% of that of the innervated state with a pulse duration of 0.5 ms. The response could be enhanced to 40% and 60% by increasing the pulse duration to 1 and 2 ms. CONCLUSIONS: A deep brain stimulation electrode could effectively reanimate the PCA muscle to a normal level in a case of synkinetic reinnervation and to as much as 60% of the normal level in a case of complete denervation.

Evoked electromyographic technique for quantitative assessment of the innervation status of laryngeal muscles.

OBJECTIVES: The purpose of this study was to develop a minimally invasive, noninjurious evoked electromyographic technique that could accurately quantitate the level of innervation of laryngeal muscles with recurrent laryngeal nerve stimulation. METHODS: A four-phase study was conducted in 24 canines, including 1) identification of the best stimulation-recording configuration, 2) statistical analysis of sensitivity and accuracy, 3) evaluation of safety, and 4) identification of the laryngeal muscle(s) that contribute to the evoked response. RESULTS: The results demonstrated that an entirely noninvasive technique is not feasible. The stimulating cathode must be invasive to ensure discrete activation of the recurrent laryngeal nerve, whereas both recording electrodes should remain on the surface with one overlying the thyroid ala. This configuration proved to be highly accurate, with an error rate of only 6% to 7%, and with sensitivity sufficient to detect a signal in a nerve with fewer than 1% of the axons intact. There was no evidence of nerve injury in any animal over the course of 350 stimulus needle penetrations. By use of neuromuscular blockade to identify those muscles generating the surface response, the thyroarytenoid muscle was found to be the primary contributor, whereas the posterior cricoarytenoid muscle was uninvolved. CONCLUSIONS: This evoked electromyographic technique could provide quantitative information regarding the extent of muscle innervation during denervation and regeneration in case of laryngeal paralysis.

Neurophysiology of vocal fold paralysis.

Although a tremendous volume of energy and literature has been devoted to laryngeal paralysis in the past decade, there are still substantial gaps in our understanding of fundamental issues. Oddly enough, controversy remains regarding the actual innervation pathways of the larynx and whether the paralyzed larynx is truly denervated or dysfunctionally reinnervated. An appreciation of these basic issues is prerequisite to making prudent decisions regarding the most appropriate type of intervention. The purpose of this article is to provide a brief overview of basic laryngeal anatomy and neurophysiology to prepare the reader for a subsequent discussion of futuristic research for treatment of laryngeal paralysis.A novel approach is described, which can induce selective reinnervation of individual laryngeal muscles by their original motor fibers within the recurrent laryngeal nerve.

Reanimation of the paralyzed human larynx with an implantable electrical stimulation device.

OBJECTIVES/HYPOTHESIS: Electrical stimulation of the posterior cricoarytenoid muscle, when paced with inspiration, offers a physiological approach to restore ventilation in bilateral laryngeal paralysis without any of the disadvantages associated with conventional treatment. STUDY DESIGN: A prospective study of six patients. METHODS: The patients were successfully implanted with an Itrel II stimulator (Medtronic, Inc). In postoperative sessions, stimulated vocal fold abduction, patient ventilation, and voice were assessed and compared with preoperative values. RESULTS: The optimum stimulus paradigm was a 1- to 2-second train of 1-millisecond pulses delivered at a frequency of 30 to 40 Hz and amplitude of 2 to 7 V. Posterior cricoarytenoid stimulation produced a large dynamic abduction (3.5-7 mm) in three patients and moderate abduction (3 mm) in a fourth patient. The fifth patient showed a large but delayed response of 4 mm to stimulation with some lateralization of the vocal fold. In the sixth patient, stimulated abduction was noted on device implantation but was lost postoperatively. All five patients with stimulated abduction postoperatively met the ventilatory criteria for decannulation, and three patients subsequently had decannulation. Long-term stimulation of the posterior cricoarytenoid muscle had no appreciable effect on voice quality. CONCLUSIONS: Electrical stimulation of the posterior cricoarytenoid muscle shows potential as an improved therapy for bilateral vocal fold paralysis.

Voice outcome following thyroplasty in patients with longstanding vocal fold immobility.

OBJECTIVE: Length of time elapsed between recurrent laryngeal nerve (RLN) injury and surgery may affect voice result. The purpose of this study was to compare voice outcome after thyroplasty in patients with short- and long-term vocal fold immobility. METHODS: Thirty-five patients with longstanding vocal fold immobility (8.3 years) and 35 patients more acutely denervated (10 months) underwent type I thyroplasty. Trained listeners before and after surgery rated perceptual judgments of voice. Acoustic and aerodynamic data were analyzed. RESULTS: Voice outcome did not differentiate the two groups with respect to objective measures. Perceptual ratings of post-operative voice quality favored the short-term patients, with the long-term group having a mildly 'constricted' quality. CONCLUSION: Thyroplasty yields a functional voice result even when substantial time has elapsed. Patients with chronic immobility may be unable to release longstanding hyperfunctional voicing behaviors even after surgery has afforded them an improved mechanism. In five of 35 long-term patients, therapy enhanced voice quality.

Comparison of neuromuscular blockade and recovery with botulinum toxins A and F.

Intramuscular injection of botulinum toxin A is used to treat focal dystonias. Because immunoresistance has been documented in some patients, other molecular forms of the toxin have been evaluated clinically. The present investigation compared the time course and extent of neuromuscular blockade and recovery of botulinum toxin types A and F using an electromyographic monitoring system implanted in the rat hindlimb. For a given dose, the degree and duration of blockade was more complete with type A toxin. Delayed onset of recovery in animals that received high doses of type A toxin allowed time for denervative changes to prevent a full return to baseline, as confirmed histologically. Conversely, animals receiving type F toxin fully recovered within 30 days at all dose levels. The rapid recovery with type F toxin suggested that neuromuscular transmission was restored via the original terminals rather than through functional collateral sprouting. The reversible nature of blockade with this molecular species puts in question its future clinical utility.

Palatal adhesion: the treatment of unilateral palatal paralysis after high vagus nerve injury.

BACKGROUND: Resection of skull base tumors commonly necessitates intraoperative sacrifice of lower cranial nerves at the level of the jugular foramen. Sequelae of unilateral vagus nerve loss include ipsilateral laryngeal paralysis, ipsilateral palatal and pharyngeal paralysis, and velopharyngeal incompetence (VPI) marked by hypernasal speech and nasopharyngeal reflux of liquids during swallowing. METHODS: Palatal adhesion (PA), a procedure whereby the unilaterally paralyzed palate is attached to the posterior pharyngeal wall, decreases the size of the velopharyngeal port and minimizes the symptoms. This study assessed the outcome of PA in 31 patients with VPI secondary to proximal vagus nerve injury. RESULTS: PA decreased postoperative nasality in 96% of patients. Nasopharyngeal reflux was significantly improved in 83%. Three patients (11%) had minor wound breakdown postoperatively, all of which healed completely with conservative management. CONCLUSION: PA offers a favorable result with minimal concomitant morbidity and is recommended for patients with VPI secondary to unilateral proximal vagus nerve paralysis.

Electrically stimulated glottal opening combined with adductor muscle botox blockade restores both ventilation and voice in a patient with bilateral laryngeal paralysis.

The purpose of this study was to determine whether paced electrical stimulation of the posterior cricoarytenoid muscle with an implantable device could restore ventilation in a patient with bilateral vocal fold paralysis without disturbing voice. In the first US case of a multi-institutional study, this patient was implanted with an Itrel II stimulator (Medtronic, Inc). In monthly postoperative sessions over an 18-month period, an effective stimulus paradigm was derived, the magnitude of stimulated vocal fold abduction and ventilation was measured, and perceptual judgments of voice quality were made. After identification of optimum parameters, posterior cricoarytenoid muscle stimulation produced a moderately large vocal fold abduction of 4 mm, but only marginal improvement in mouth ventilation, with no change in voice quality. After adductor muscle blockade with botulinum toxin, the patient's voice improved with increased phonatory airflow, but ventilation through the passive airway was still inadequate. However, by combining these two therapeutic strategies, dynamic abduction increased to 7 mm, ventilation through the mouth surpassed that through the tracheotomy (allowing decannulation), and voice quality was restored to normal.

Effect of chronic electrical stimulation of laryngeal muscle on voice.

Conventional surgical therapies for bilateral laryngeal paralysis sacrifice voice to enlarge the airway. Electrical pacing of the posterior cricoarytenoid (PCA) muscle to restore glottal opening and allow ventilation offers a new treatment approach. The purpose of this investigation was to determine whether long-term stimulation of the PCA muscle altered perceptual, acoustic, and aerodynamic parameters of voice. Two patients underwent implantation of a Medtronic Itrel II laryngeal pacemaker. Voice evaluation was performed before surgery and at monthly postoperative sessions with the pacemaker off. Months of PCA stimulation did not change perceptual descriptors of voice quality. Measures of fundamental frequency and intensity, upper and lower limits of the dynamic frequency and intensity range, and phonatory flow rates were largely unaltered. The results indicated that there was no effect of laryngeal pacing on voice.

Electrical stimulation of a denervated muscle promotes selective reinnervation by native over foreign motoneurons.

The effect of electrical stimulation of the denervated posterior cricoarytenoid (PCA) muscle on its subsequent reinnervation was explored in the canine. Eight animals were implanted with a planar array of 36 electrodes for chronic stimulation and recording of spontaneous and evoked electromyographic (EMG) potentials across the entire fan-shaped surface of a muscle pair. Normative EMG data were recorded from each electrode site before unilateral nerve section, and from the innervated partner after nerve section. After randomizing the animals to experimental and control groups, the right recurrent laryngeal nerve innervating the PCA abductor muscle and its adductor antagonists was sectioned and reanastomosed. The PCA muscle in four experimental animals was continuously stimulated during the 11-mo experiment, using a 1-s, 30-pps, biphasic pulse train composed of 1-ms pulses 2-6 mA in amplitude and repeated every 10 s. The remaining four animals served as nonstimulated controls. Appropriate reinnervation by native inspiratory motoneurons was indexed behaviorally by the magnitude of vocal fold opening and electromyographically by the potential across all electrode sites. Inappropriate reinnervation by foreign adductor motoneurons was quantitated by recording EMG potentials evoked reflexly by stimulation of sensory afferents of the laryngeal mucosa. All four experimental animals showed a greater level of correct PCA muscle reinnervation (P < 0.0064) and a lesser level of incorrect reinnervation (P < 0.0084) than the controls. Direct muscle stimulation also appeared to enhance the overall magnitude of reinnervation, but the effect was not as strong (P < 0.113). These findings are consistent with a previous report and suggest that stimulation of a mammalian muscle may profoundly affect its receptivity to reinnervation by a particular motoneuron type.