Unilateral and Bilateral Laryngeal Pacing for Bilateral Vocal Fold Paralysis.

PURPOSE OF REVIEW: Present the state-of-the-art overview of laryngeal pacing for treatment of bilateral vocal fold paralysis. A minimally invasive unilateral pacing system and a fully implantable bilateral pacing system are currently in clinical trials. The relative advantages and disadvantages of each are discussed. RECENT FINDINGS: Research in functional electrical stimulation for the reanimation of the posterior cricoarytenoid muscle has successfully translated from animal models to human clinical trials for unilateral pacing and bilateral pacing. Current findings suggest unilateral pacing in humans significantly improves ventilation but only marginally better than cordotomy. Bilateral pacing in canines increases glottal opening greater than 2-fold over unilateral pacing and restores exercise tolerance to normal. SUMMARY: Unilateral pacing can be considered a breathing assist device and may not be appropriate for active individuals. Bilateral pacing may be preferable for patients who wish to engage in strenuous exercise. Minimally invasive systems may be ideal for patients who prefer less invasive implantation and are not concerned with cosmesis. Fully implantable pacing systems offer greater electrode redundancy and stability, resulting in a system that is robust against electrode migration or damage.

Stimulation of denervated muscle promotes selective reinnervation, prevents synkinesis, and restores function.

OBJECTIVES/HYPOTHESIS: Previously, electrical stimulation of denervated canine laryngeal muscle was shown to promote reinnervation by native over foreign motoneurons. The goal of this study was to assess the effect of different stimulus paradigms on reinnervation quality and functional recovery. STUDY DESIGN: A prospective study of six canines over 8 to 20 months. METHODS: A clinical model of laryngeal paralysis was used, where recurrent laryngeal nerves of the animals were sectioned and ventilation compromised. The abductor, posterior cricoarytenoid (PCA) muscles were implanted bilaterally with electrodes from an implantable pulse generator. Animals were randomly assigned to three groups to assess the effect of different stimulus paradigms: 1) 40 pulses per second (pps) train, 2) 10 pps train, 3) no stimulation. Spontaneous vocal fold movement was measured endoscopically during hypercapnia. Exercise tolerance was measured on a treadmill using pulse oximetry. In the terminal session, electromyography (EMG) potentials were recorded during superior laryngeal nerve stimulation to index foreign reinnervation of the PCA by reflex glottic closure (RGC) motoneurons. RESULTS: After reinnervation started, nonstimulated and stimulated 40 pps animals displayed paradoxical closure of the glottis during hypercapnia and severely decreased exercise tolerance due to faulty reinnervation. In contrast, stimulated 10 pps animals displayed minimal paradoxical closure and normal exercise tolerance (12 minutes up to 8 mph). EMG findings in this group demonstrated significantly less PCA reinnervation by foreign RGC motoneurons. CONCLUSION: PCA stimulation with low frequency reduced synkinetic reinnervation by foreign RGC motoneurons. Paradoxical closure of the glottis with inspiration was reduced and exercise tolerance restored to normal.

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.

Tongue muscle plasticity following hypoglossal nerve stimulation in aged rats.

INTRODUCTION: Age-related decreases in tongue muscle mass and strength have been reported. It may be possible to prevent age-related tongue muscle changes using neuromuscular electrical stimulation (NMES). Our hypothesis was that alterations in muscle contractile properties and myosin heavy chain composition would be found after NMES. METHODS: Fifty-four young, middle-aged, and old 344/Brown Norway rats were included in this study. Twenty-four rats underwent bilateral electrical stimulation of the hypoglossal nerves for 8 weeks and were compared with control or sham rats. Muscle contractile properties and myosin heavy chain (MHC) in the genioglossus (GG), styloglossus (SG), and hyoglossus (HG) muscles were examined. RESULTS: Compared with unstimulated control rats, we found reduced muscle fatigue, increased contraction and half-decay times, and increased twitch and tetanic tension. Increased type I MHC was found, except for in GG in old and middle-aged rats. CONCLUSION: Transitions in tongue muscle contractile properties and phenotype were found after NMES.

Bilateral motion restored to the paralyzed canine larynx with implantable stimulator.

OBJECTIVES/HYPOTHESIS: Bilateral stimulation of posterior cricoarytenoid (PCA) muscles offers a physiologic approach to restore ventilation to a normal level in case of bilateral laryngeal paralysis. The objective of this study was to evaluate the long-term efficacy and safety of a new generation stimulator in restoring ventilation and exercise tolerance. STUDY DESIGN: A prospective study of four canines over 8-20 months. METHODS: A Genesis XP stimulator and electrodes were implanted and recurrent laryngeal nerves were sectioned and repaired bilaterally. In bimonthly sessions, vocal fold movement resulted from PCA stimulation or induced hypercapnea, was measured endoscopically in the anesthetized animal. Exercise tolerance was measured on a treadmill and swallowing function was examined endoscopically and radiographically. RESULTS: During the denervation phase, there was minimal ventilatory compromise and near-normal exercise tolerance. PCA stimulation produced only nominal abduction. During the reinnervation phase, synkinetic reinnervation became significant, resulting in a narrowed passive airway and paradoxical glottic closure during hypercapnea. Animals were stridorous and could walk for only 1-2 minutes. Bilateral PCA stimulation increased glottal area, equaling that of a normally innervated animal. Exercise tolerance was also normal. The optimal stimulus paradigm for the synkinetically reinnervated larynx was not different from that for the innervated larynx. Stimulation remained efficacious over the study period. Lead integrity could be maintained by prevention of device migration. There was no evidence of aspiration. CONCLUSIONS: This study demonstrates that ventilatory compromise only occurs following faulty reinnervation. Bilateral PCA stimulation can restore ventilation and exercise tolerance completely without aspiration over the long term.

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.

Rehabilitation of bilaterally paralyzed canine larynx with implantable stimulator.

OBJECTIVES/HYPOTHESIS: Bilateral stimulation of the posterior cricoarytenoid (PCA) muscles offers a physiologic approach to rehabilitate ventilation to a normal level in case of bilateral laryngeal paralysis. The objective was to evaluate the safety and efficacy of a new generation stimulator in restoring glottal opening, ventilation, and exercise tolerance. STUDY DESIGN: A prospective study in three canines over 6 to 17 months. METHODS: A Genesis XP stimulator and electrodes were surgically implanted, and the recurrent laryngeal nerves sectioned/repaired bilaterally. In bimonthly sessions, vocal fold movement was measured endoscopically in the anesthetized animal. The movement resulted from PCA stimulation or hypercapnea during spontaneous breathing. Exercise tolerance was measured on a treadmill using pulse oximetry and swallowing function examined by videofluoroscopy. RESULTS: During the denervation phase, there was minimal ventilatory compromise and near normal exercise tolerance with the device off (12 minutes, up to 8 mph). PCA stimulation produced only nominal abduction. During the reinnervation phase, synkinetic reinnervation became significant with narrowed passive airway and paradoxical closure of the glottis during hypercapnea. Animals were stridorous and could walk for only 1 to 2 minutes at 4 mph. With the device activated, bilateral PCA stimulation increased glottal area from 50 mm(2) to 250 mm(2), even during hypercapnea, equaling that of a normally innervated animal. Exercise tolerance was normal. There was no evidence of aspiration during deglutition. CONCLUSIONS: This study demonstrates that severe ventilatory compromise only occurs following faulty reinnervation of laryngeal muscles. Bilateral PCA stimulation can result in complete rehabilitation of ventilation and exercise tolerance without impairment of swallowing.

Characterization of raised phonation in an evoked rabbit phonation model.

OBJECTIVES/HYPOTHESIS: Our laboratory has developed an in vivo rabbit model to investigate the effects of phonation on expression and turnover of the vocal fold extracellular matrix. As a logical outgrowth of this research to include phonotrauma in the present study, we investigated the hypothesis that an increase in airflow rate delivered to the glottis produces a change in glottal configuration and an increase in mean phonation intensity. STUDY DESIGN: Prospective animal study. METHODS: Six New Zealand white breeder rabbits weighing 3 to 5 kg were used in this study. A rigid endoscope and camera were used to document glottal configuration. Acoustic signals of modal and raised phonation were recorded and digitized. Two separate one-way repeated measures analysis of variance (ANOVA) tests were used to investigate within subject differences in phonation intensity and fundamental frequency between modal and raised phonation. RESULTS: Phonation intensity was 54.19 dB SPL (6.21 standard deviations [SD]) during modal phonation, and 60.31 dB SPL (5.68 SD) during raised phonation. Endoscopic images revealed a convergent glottis, with greater separation of the vocal folds during raised phonation. Results of ANOVA revealed a significant within subjects effect for phonation intensity (P = .011). Pairwise comparisons revealed that phonation intensity increased significantly during raised phonation, compared to modal phonation (P = .008). No differences in mean fundamental frequency were observed between phonation conditions. CONCLUSIONS: Improved understanding of factors that control phonation output in the in vivo rabbit model will result in improved capabilities to match phonation dose across animals and provide immediate direction to future biochemical studies.

Model of evoked rabbit phonation.

OBJECTIVES: We describe a method for eliciting phonation in an in vivo rabbit preparation using low-frequency, bipolar pulsed stimulation of the cricothyroid muscles with airflow delivered to the glottis. METHODS: Ten New Zealand White breeder rabbits weighing 3 to 5 kg were used in this study. The cricothyroid muscles were isolated bilaterally, and separate pairs of anode-cathode hooked-wire electrodes were inserted into each muscle. A Grass S-88 stimulator and 2 constant-current PSIU6 isolation units were used to deliver bipolar square wave pulses to each cricothyroid muscle, with airflow delivered to the glottis through a cuffed endotracheal tube. RESULTS: Phonation was evoked with a 50-Hz, 4-mA stimulus train of 1-ms pulses delivered to each cricothyroid muscle. The pulse trains were on for 2 seconds and were repeated every 5 seconds over a period of 180 minutes. Airflow was delivered at 143 cm3/s, producing phonation measuring 71 to 85 dB sound pressure level. CONCLUSIONS: Evoked phonation is feasible in rabbits by use of bipolar stimulation of the cricothyroid muscles with airflow delivered to the glottis. The in vivo rabbit preparation described may provide a useful small animal option for studies of evoked phonation. From the level and consistency of the adduction observed, we hypothesize that current spreading to the underlying adductor muscles and nerves resulted in neural pathway involvement beyond discrete activation of the cricothyroid muscle, providing sufficient approximation of the vocal folds for phonation.

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.

Experimentally induced phonation increases matrix metalloproteinase-1 gene expression in normal rabbit vocal fold.

OBJECTIVES: An in vivo rabbit model was used to study the effect of 3 hours of experimentally induced phonation on messenger RNA expression of the normal vocal fold. STUDY DESIGN: Prospective; animal model. SUBJECTS AND METHODS: Ten rabbits received experimental phonation for 3 hours, followed by 1 hour of recovery. A separate group of 5 rabbits served as no-phonation controls. We measured messenger RNA expression of matrix metalloproteinase-1, MMP-9, and interleukin-1beta using real-time reverse-transcribed polymerase chain reaction. Gene expression ratios from phonation and control animals were assessed with the Mann-Whitney U test. RESULTS: Phonation (77 +/- 3 dB; 429 +/- 141 Hz) resulted in increased matrix metalloproteinase-1 gene expression from rabbits receiving experimental phonation compared with controls, and a nonsignificant increase in matrix metalloproteinase-9 and interleukin-1beta gene expression. CONCLUSION: Matrix metalloproteinases play a role in maintaining tissue homeostasis. Investigation of cellular responses to experimental phonation may provide insight into how matrix metalloproteinases and other extracellular matrices contribute to maintenance of the vocal fold and development of pathology.

A sequential double labeling technique for studying changes in motoneuronal projections to muscle following nerve injury and reinnervation.

The purpose of this study was to develop an anatomical technique that could directly demonstrate the motoneuron projections to the muscle both before injury and again following reinnervation. Investigation focused on the identification of a long-term retrograde fluorescent tracer that would label original motoneurons and persist long enough for reinnervating motoneurons to become labeled by a second fluorescent tracer. True Blue (TB) was evaluated as a potential long-term tracer, Fluoro-ruby (FR) and Fluoro-emerald (FE) were tested as potential short-term tracers in 45 adult Sprague-Dawley rats. In the initial phase of the study, TB was injected into the tibialis anterior (TA) muscle in 16 rats and sacrificed 1 week to 6 months later, to study its persistence. During the second stage, a short-term tracer was injected into the TA muscles bilaterally in 15 rats with survival time ranging from 4 to 28 days. Sequential double labeling was subsequently performed using the combination of TB and FR in 14 rats. The number and brightness of TB cells did not change over 6 months time, a period sufficient for complete reinnervation. FR and FE showed maximum labeling of motoneurons at 1 week after tracer application. In the double labeling study, we could easily distinguish double-labeled cells from those labeled only by TB or FR. These results suggest that sequential double labeling of TB and FR is a valuable method for long-term muscle reinnervation studies.

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.

Functional electrical stimulation of laryngeal adductor muscle restores mobility of vocal fold and improves voice sounds in cats with unilateral laryngeal paralysis.

Functional electrical stimulation (FES) has been proposed as a potential treatment for restoring motor functions of denervated motor systems. We investigated whether FES of paralyzed laryngeal adductor muscles could restore adduction to the vocal folds. In addition, we studied the effect of stimulated vocal fold adduction on the intensity and overall quality of voice production. We recorded movement of the vocal fold, electromyographic activity of muscles recruited for vocalization, and sound production in unanesthetized decerebrate cats during FES of the paralyzed thyroarytenoid (TA) muscle. FES of the paralyzed TA muscle induced adduction of the vocal fold. Appropriate stimulus parameters for induction was 1.5-3.0 mA intensity pulses delivered at a frequency of 30-50 pulses per second (pps). FES of the paralyzed TA muscle prolonged phonation time and increased intensity of voice sounds during vocalization induced by electrical stimulation (0.2 ms, 20-50 microA, 50 pps) of the periaqueductal gray (PAG). The quality of voice sounds evaluated by sound spectrography was shown to improve during vocalization with FES. We conclude that FES of the paralyzed laryngeal adductor muscle was effective in restoring adduction of the vocal fold and improving voice sounds impaired by unilateral 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.

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.

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.