Laryngeal pacing in minipigs: in vivo test of a new minimal invasive transcricoidal electrode insertion method for functional electrical stimulation of the PCA

Impact of functional electrical stimulation on nerve-damaged muscles by quantifying fat infiltration using deep learning

Quantitative imaging in life sciences has evolved into a powerful approach combining advanced microscopy acquisition and automated analysis of image data. The focus of the present study is on the imaging-based evaluation of the posterior cricoarytenoid muscle (PCA) influenced by long-term functional electrical stimulation (FES), which may assist the inspiration of patients with bilateral vocal fold paresis. To this end, muscle cross-sections of the PCA of sheep were examined by quantitative image analysis. Previous investigations of the muscle fibers and the collagen amount have not revealed signs of atrophy and fibrosis due to FES by a laryngeal pacemaker. It was therefore hypothesized that regardless of the stimulation parameters the fat in the muscle cross-sections would not be significantly altered. We here extending our previous investigations using quantitative imaging of intramuscular fat in cross-sections. In order to perform this analysis both reliably and faster than a qualitative evaluation and time-consuming manual annotation, the selection of the automated method was of crucial importance. To this end, our recently established deep neural network IMFSegNet, which provides more accurate results compared to standard machine learning approaches, was applied to more than 300 H&E stained muscle cross-sections from 22 sheep. It was found that there were no significant differences in the amount of intramuscular fat between the PCA with and without long-term FES, nor were any significant differences found between the low and high duty cycle stimulated groups. This study on a human-like animal model not only confirms the hypothesis that FES with the selected parameters has no negative impact on the PCA, but also demonstrates that objective and automated deep learning-based quantitative imaging is a powerful tool for such a challenging analysis.

Long-term stimulation by implanted pacemaker enables non-atrophic treatment of bilateral vocal fold paresis in a human-like animal model

A wide variety of treatments have been developed to improve respiratory function and quality of life in patients with bilateral vocal fold paresis (BVFP). One experimental method is the electrical activation of the posterior cricoarytenoid (PCA) muscle with a laryngeal pacemaker (LP) to open the vocal folds. We used an ovine (sheep) model of unilateral VFP to study the long-term effects of functional electrical stimulation on the PCA muscles. The left recurrent laryngeal nerve was cryo-damaged in all animals and an LP was implanted except for the controls. After a reinnervation phase of six months, animals were pooled into groups that received either no treatment, implantation of an LP only, or implantation of an LP and six months of stimulation with different duty cycles. Automated image analysis of fluorescently stained PCA cross-sections was performed to assess relevant muscle characteristics. We observed a fast-to-slow fibre type shift in response to nerve damage and stimulation, but no complete conversion to a slow-twitch-muscle. Fibre size, proportion of hybrid fibres, and intramuscular collagen content were not substantially altered by the stimulation. These results demonstrate that 30 Hz burst stimulation with duty cycles of 40% and 70% did not induce PCA atrophy or fibrosis. Thus, long-term stimulation with an LP is a promising approach for treating BVFP in humans without compromising muscle conditions.

Development of the hyolaryngeal architecture in horseshoe bats: insights into the evolution of the pulse generation for laryngeal echolocation

BACKGROUND

The hyolaryngeal apparatus generates biosonar pulses in the laryngeally echolocating bats. The cartilage and muscles comprising the hyolarynx of laryngeally echolocating bats are morphologically modified compared to those of non-bat mammals, as represented by the hypertrophied intrinsic laryngeal muscle. Despite its crucial contribution to laryngeal echolocation, how the development of the hyolarynx in bats differs from that of other mammals is poorly documented. The genus Rhinolophus is one of the most sophisticated laryngeal echolocators, with the highest pulse frequency in bats. The present study provides the first detailed description of the three-dimensional anatomy and development of the skeleton, cartilage, muscle, and innervation patterns of the hyolaryngeal apparatus in two species of rhinolophid bats using micro-computed tomography images and serial tissue sections and compares them with those of laboratory mice. Furthermore, we measured the peak frequency of the echolocation pulse in active juvenile and adult individuals to correspond to echolocation pulses with hyolaryngeal morphology at each postnatal stage.

RESULTS

We found that the sagittal crests of the cricoid cartilage separated the dorsal cricoarytenoid muscle in horseshoe bats, indicating that this unique morphology may be required to reinforce the repeated closure movement of the glottis during biosonar pulse emission. We also found that the cricothyroid muscle is ventrally hypertrophied throughout ontogeny, and that the cranial laryngeal nerve has a novel branch supplying the hypertrophied region of this muscle. Our bioacoustic analyses revealed that the peak frequency shows negative allometry against skull growth, and that the volumetric growth of all laryngeal cartilages is correlated with the pulse peak frequency.

CONCLUSIONS

The unique patterns of muscle and innervation revealed in this study appear to have been obtained concomitantly with the acquisition of tracheal chambers in rhinolophids and hipposiderids, improving sound intensity during laryngeal echolocation. In addition, significant protrusion of the sagittal crest of the cricoid cartilage and the separated dorsal cricoarytenoid muscle may contribute to the sophisticated biosonar in this laryngeally echolocating lineage. Furthermore, our bioacoustic data suggested that the mineralization of these cartilages underpins the ontogeny of echolocation pulse generation. The results of the present study provide crucial insights into how the anatomy and development of the hyolaryngeal apparatus shape the acoustic diversity in bats.

Bilateral Functional Electrical Stimulation for the Treatment of Presbyphonia in a Sheep Model

OBJECTIVES

The aim of the study was to increase muscle volume and improve phonation characteristics of the aged ovine larynx by functional electrical stimulation (FES) using a minimally invasive surgical procedure.

METHODS

Stimulation electrodes were placed bilaterally near the terminal adduction branch of the recurrent laryngeal nerves (RLN). The electrodes were connected to battery powered pulse generators implanted subcutaneously at the neck region. Training patterns were programmed by an external programmer using a bidirectional radio frequency link. Training sessions were repeated automatically by the implant every other day for 1 week followed by every day for 8 weeks in the awake animal. Another group of animals were used as sham, with electrodes positioned but not connected to an implant. Outcome parameters included gene expression analysis, histological assessment of muscle fiber size, functional analysis, and volumetric measurements based on three-dimensional reconstructions of the entire thyroarytenoid muscle (TAM).

RESULTS

Increase in minimal muscle fiber diameter and an improvement in vocal efficiency were observed following FES, compared with sham animals.

CONCLUSION

This is the first study to demonstrate beneficial effects in the TAM of FES at molecular, histological, and functional levels. FES of the terminal branches of the RLN reversed the effects of age-related changes and improved vocal efficiency.

LEVEL OF EVIDENCE

NA Laryngoscope, 134:848-854, 2024.

Electrical Stimulation of Vocal Fold Adduction Triggered by Laryngeal Electromyography Using a Custom Implant

PURPOSE

Medialization procedures for unilateral vocal fold (VF) paralysis generally improve voice but do not fully replace dynamic VF adduction. Paralyzed VFs typically experience synkinetic reinnervation, which makes it feasible to elicit movement through electrical stimulation. We tested a novel laryngeal pacing implant capable of providing closed-loop (automatic) stimulation of a VF triggered by electromyography (EMG) potentials from the contralateral VF.

METHOD

A custom, battery-powered, microprocessor-based stimulator was tested in eight dogs with bipolar electrodes implanted for recording EMG from the left VF and stimulating adduction of the right VF. A cuff electrode on the left recurrent laryngeal nerve (RLN) stimulated unilateral VF adduction, modeling voluntary control in anesthetized animals. Closed-loop stimulation was tested in both acute and chronic experiments. Synkinetic reinnervation was created in two animals by right RLN transection and suture repair to model unilateral VF paralysis.

RESULTS

In all animals, left VF activation through RLN stimulation generated a robust EMG response that rapidly triggered stimulation of contralateral thyroarytenoid and lateral cricoarytenoid muscles, causing nearly simultaneous bilateral adduction. Optimal triggering of VF stimulation from elicited EMG was achieved using independent onset and offset thresholds. Real-time artifact blanking allowed closed-loop stimulation without self-perpetuating feedback, despite the proximity of recording and stimulation electrodes.

CONCLUSIONS

Using a custom implant system, we demonstrated real-time closed-loop stimulation of one VF triggered by the activation of the contralateral VF. This approach could potentially restore dynamic glottic closure for reflexive behaviors or phonation in cases of unilateral VF paralysis with synkinetic reinnervation.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.24492133.

An Endoscopic Cap Electrode for Posterior Cricoarythenoid Muscle Stimulation in a Porcine Model

OBJECTIVE

Laryngeal pacing (LP) is a highly anticipated therapeutic option for patients suffering from bilateral vocal fold paralysis with synkinesis. Identification of candidate patients requires confirmation of a stimulable posterior cricoidarythenoid muscle (PCA) by neuromuscular electrical stimulation (NMES). A silicone endoscopic cap electrode (ECE50) was designed to be operated as an endoscopic extension tip for selective PCA stimulation and confirmation of a glottic opening movement in a setting comparable to a gastroscopy procedure.

METHODS

A porcine animal model (n = 6) was applied to develop and test endoscopic cap prototypes in general anesthesia and sedation at a biomedical research center. Two ENT endoscopy experts evaluated and refined the cap design and performance in regard to procedure safety, endoscope handling, accessibility of the PCA by the transoral approach and selective muscle stimulation.

RESULTS

Vocal fold opening movements could be evoked by the investigators in 9 of 12 PCA muscles to stimulate with similar electric parameters. The endoscopic approach using the ECE50 proved to be atraumatic and sufficiently controlled under sedation to locate the required hotspot for NMES of the PCA.

CONCLUSION

The functionality of the novel endoscopic cap concept has been proven in a porcine model. It can be expected to be transferable to human application and to be of diagnostic importance in the screening and identification of LP candidate patients in future.

LEVEL OF EVIDENCE

NA Laryngoscope, 133:2279-2284, 2023.

Active and Passive Bioimplants for Vocal Fold Paralysis

Vocal fold paralysis is one of the diseases that particularly affect quality of life. While unilateral paralysis leads to glottis closure insufficiency and hoarseness, bilateral paralysis compromises respiration and limits the exercise tolerance. Bioimplants have been used to treat persistent paralysis for over 100 years. The spectrum ranges from autologous tissue transfer and resorbable or permanent injection materials to composite thyroplasty implants and active electrical implants for neurostimulation of the larynx. If bioimplants are used in accordance with the recommendations, the quality of life of affected patients can be significantly improved today.

Development of a constant pressure perfused ex vivo model of the equine larynx

Distal axonopathy is seen in a broad range of species including equine patients. In horses, this degenerative disorder of the recurrent laryngeal nerve is described as recurrent laryngeal neuropathy (RLN). The dysfunctional innervation of the cricoarytenoideus dorsalis muscle (CAD) leads to a loss of performance in affected horses. In general, ex vivo models of the larynx are rare and for equine patients, just one short report is available. To allow for testing new therapy approaches in an isolated organ model, we examined equine larynges in a constant pressure perfused setup. In order to check the vitality and functionality of the isolated larynx, the vessels´ reaction to norepinephrine (NE) and sodium nitroprusside (NP) as vasoactive agents was tested. Additionally, the contractility of the CAD was checked via electrical stimulation. To determine the extent of hypoxic alterations, lactate dehydrogenase (LDH) and lactate were measured and an immunofluorescent analysis of hypoxia-inducible factor (HIF-1α), a key transcription factor in hypoxia, was performed. For this, a hypoxia-induced cell culture for HIF-1α was developed. The application of NE led to an expected vasoconstriction while NP caused the expected vasodilation. During a perfusion period of 352 ±20.78 min, LDH values were in the reference range and lactate values slightly exceeded the reference range at the end of the perfusion. HIF-1α nuclear translocation could reliably be detected in the hypoxia-induced cell cultures, but not in sections of the perfused CAD. With the approach presented here, a solid basis for perfusing equine larynges was established and may serve as a tool for further investigations of equine larynx disorders as well as a transferrable model for other species.

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.

Laryngeal pacing for bilateral vocal fold paralysis: Voice and respiratory aspects

OBJECTIVE

To evaluate the effects of neurostimulation with the laryngeal pacemaker (LP) system in patients with bilateral vocal fold paralysis (BVFP) in terms of voice quality and respiratory function.

STUDY DESIGN

Feasibility study, first-in-human, single-arm, open-label, prospective, multicenter study with group-sequential design and 6-month follow-up period, as described in details in our previous publication.

METHODS

Nine symptomatic BVFP subjects were unilaterally implanted with the LP system at three study sites in Germany and Austria. Subjective and objective voice function, spirometric parameters other than peak expiratory/inspiratory flow (PEF/PIF), and PEF-meter self-assessment were evaluated pre- and 6 months postimplantation.

RESULTS

In general, the LP system did not considerably change the voice quality of the implanted patients. Only the sound pressure level range improved significantly 6 months postimplantation (P = 0.018). The LP system implantation did not affect the glottal closure configuration, the duration of the closed phase, and the mucosal wave of the implanted side. The evaluated spirometric parameters were not significantly affected by laryngeal pacing, whereas PEF meter self-assessment showed a stable and significant (P = 0.028) improvement of the PEF within a week upon activation of the LP system.

CONCLUSION

Neurostimulation with the LP system results in an immediate and stable PEF improvement, without negative effects on the voice quality. The PEF meter self-assessment confirmed the spirometry results of the PEF. The stimulated abduction did not affect the glottal closure during phonation. These results should be confirmed in larger and more homogenous patient cohorts.

LEVEL OF EVIDENCE

2b Laryngoscope, 127:1838-1844, 2017.

Reversing Age Related Changes of the Laryngeal Muscles by Chronic Electrostimulation of the Recurrent Laryngeal Nerve

Age related atrophy of the laryngeal muscles -mainly the thyroarytenoid muscle (TAM)- leads to a glottal gap and consequently to a hoarse and dysphonic voice that significantly affects quality of life. The aim of our study was to reverse this atrophy by inducing muscular hypertrophy by unilateral functional electrical stimulation (FES) of the recurrent laryngeal nerve (RLN) in a large animal model using aged sheep (n = 5). Suitable stimulation parameters were determined by fatiguing experiments of the thyroarytenoid muscle in an acute trial. For the chronic trial an electrode was placed around the right RLN and stimulation was delivered once daily for 29 days. We chose a very conservative stimulation pattern, total stimulation time was two minutes per day, or 0.14% of total time. Overall, the mean muscle fiber diameter of the stimulated right TAM was significantly larger than the non-stimulated left TAM (30μm±1.1μm vs. 28μm±1.1 μm, p<0.001). There was no significant shift in fiber type distribution as judged by immunohistochemistry. The changes of fiber diameter could not be observed in the posterior cricoarytenoid muscle (PCAM). FES is a possible new treatment option for reversing the effects of age related laryngeal muscle atrophy.

Laryngeal pacing via an implantable stimulator for the rehabilitation of subjects suffering from bilateral vocal fold paralysis: A prospective first-in-human study

OBJECTIVES/HYPOTHESIS

To evaluate the performance and safety of the newly developed Laryngeal Pacemaker System (LP System) for the treatment of bilateral vocal fold paralysis (BVFP).

STUDY DESIGN

Feasibility, first-in-human, single-arm, open-label, prospective, multicenter study with a group sequential design and a 6-month follow-up period.

METHODS

Nine symptomatic BVFP subjects were implanted unilaterally with the LP System. Pre- and 6-month postimplantation evaluations consisted of the 6-Minute Walk Test (6MWT), the Peak Expiratory and Inspiratory Flow (PEF and PIF) evaluation, the PEF meter analysis, the 36-Item Short Form Health Survey (SF-36), the Glasgow Benefit Inventory (GBI), the 12-Item Voice Handicap Index (VHI-12), and the Fiberoptic Endoscopic Evaluation of Swallowing. The safety profile of the LP System was continuously monitored.

RESULTS

The LP System implantation was achieved in 8/9 cases. Seven of the nine subjects completed the study. Absolute PEF and PIF values improved significantly 6 months postimplantation (P < .05). 6MWT results showed a non-statistically significant improvement (P = .09). The mental component of the SF-36 showed a significant improvement (P = .043), whereas the other SF-36 components, the GBI, and the VHI-12 results did not changed significantly. The LP System did not affect the voice and swallowing quality and maintained a reliable safety profile for the duration of the study.

CONCLUSIONS

This feasibility study showed that the LP System has the potential to become an effective and safe treatment for BVFP subjects without compromising the patients' voice.

LEVEL OF EVIDENCE

2b Laryngoscope, 126:1810-1816, 2016.

Functional Electrical Stimulation of the Feline Larynx With a Flexible Ribbon Electrode Array

OBJECTIVES

Success of laryngeal reanimation through neurorrhaphy has been limited by synkinesis and preoperative muscle atrophy. The objective of this study was to investigate the use of epimysial electrode arrays as a means of delivering electrical stimulation to the posterior cricoarytenoid muscles in order to control laryngeal abduction.

METHODS

Ribbon electrode arrays with 4 or 8 electrode contacts were used. Four cats underwent implantation of electrode arrays along the surface of the posterior cricoarytenoid muscles. The glottis was visualized with a 0° telescope while electrodes were stimulated at different amplitudes and pulse-width durations. Recordings of stimulated vocal folds were analyzed, and the degree of vocal fold abduction was measured in order to create recruitment curves for the left and right posterior cricoarytenoid. Recruitment curves from electrode channels within the array were compared.

RESULTS

Electrodes oriented along the medial aspect of the posterior cricoarytenoid stimulated graded physiologic degrees of abduction depending on the amplitude of stimulation. Electrodes oriented laterally along the posterior cricoarytenoid stimulated greater degrees of simultaneous adduction with abduction.

CONCLUSION

Acute studies of ribbon surface electrode arrays placed onto the posterior cricoarytenoid reproduce graded degrees of abduction necessary for the precise function of respiration and speech.

Pre-clinical evaluation of a minimally invasive laryngeal pacemaker system in mini-pig

Microlaryngoscopic enlargement techniques have been the standard treatment for bilateral vocal fold paralysis (BVFP) for decades. Laryngeal pacing is a promising alternative treatment based on the electrostimulation of the posterior cricoarytenoid (PCA) muscle. This paper reports on the results of a pre-clinical study aiming to evaluate this method. Eight Göttingen mini-pigs were implanted with a laryngeal pacemaker (LP) implant prototype and with two LP electrodes, one in each PCA muscle. The 6-week follow-up included endoscopic stimulation controls in general anaesthesia and radiographic controls of electrode integrity and position stability. Stimulation parameters for optimal glottal opening were evaluated via videolaryngoscopy. Histopathology was performed upon conclusion of the study. 7/8 (87.5 %) animals were successfully implanted with the LP implant prototype and two LP electrodes. In general, stimulation was effectively delivered and correlated with the expected PCA muscle activation. 2/14 (14.3 %) electrodes dislocated and 1/14 (7.1 %) electrode tip broke. The LP system used in this experiment to induce vocal fold abduction by means of selective functional electrical stimulation of the PCA showed promising results. It may be a valid alternative to the current golden standard for BVFP treatment. Clinical studies are needed to confirm the medical relevance of the LP.

Nerve branches to the posterior cricoarytenoid muscle may complicate the laryngeal reinnervation procedure

OBJECTIVES/HYPOTHESIS

To better understand the reason for the low success rate of posterior cricoarytenoid (PCA) muscle reinnervation, we attempted to identify the communicating branches that may exist between the nerve branch to the PCA muscle and the other laryngeal adductors in addition to the interarytenoid (IA) muscle.

STUDY DESIGN

Quantitative histological assessment.

METHODS

Twenty human hemilarynges from patients with laryngeal or hypopharyngeal cancer were obtained after surgery and stained with Sihler's stain, which rendered the muscle translucent while counterstaining the neuroanatomy of the recurrent laryngeal nerve (RLN) inside the larynges.

RESULTS

The nerve supply to the PCA muscle was separated into two main branches. One upper branch supplied the horizontal compartment, and the lower branch supplied the vertical/oblique compartment. In 14 specimens, two nerve branches to the PCA muscle arose separately from the RLN. In six specimens, one single main branch arose from the RLN and immediately ramified into two secondary branches. In all specimens except one, the nerve branch to the horizontal compartment was connected to the IA muscle. However, no communicating branches were observed between the nerve to the PCA muscle and the other laryngeal adductors. No anastomosis between nerve branches to the horizontal and vertical/oblique compartments or other variations of nerve distribution were observed.

CONCLUSIONS

The communicating branches between the nerve branches to the PCA muscle and the IA muscle may be the only branch, complicating the reinnervation procedure. More investigations are needed to identify variations in the terminal branch distribution from the RLN.

LEVEL OF EVIDENCE

NA.

Airway tissue engineering: an update

INTRODUCTION

Prosthetic materials, autologous tissues, cryopreserved homografts and allogeneic tissues have thus far proven unsuccessful in providing long-term functional solutions to extensive upper airway disease and damage. Research is therefore focusing on the rapidly expanding fields of regenerative medicine and tissue engineering in order to provide stem cell-based constructs for airway reconstruction, substitution and/or regeneration.

AREAS COVERED

Advances in stem cell technology, biomaterials and growth factor interactions have been instrumental in guiding optimization of tissue-engineered airways, leading to several first-in-man studies investigating stem cell-based tissue-engineered tracheal transplants in patients. Here, we summarize current progress, outstanding research questions, as well as future directions within the field.

EXPERT OPINION

The complex immune interaction between the transplant and host in vivo is only beginning to be untangled. Recent progress in our understanding of stem cell biology, decellularization techniques, biomaterials and transplantation immunobiology offers the prospect of transplanting airways without the need for lifelong immunosuppression. In addition, progress in airway revascularization, reinnervation and ever-increasingly sophisticated bioreactor design is opening up new avenues for the construction of a tissue-engineered larynx. Finally, 3D printing is a novel technique with the potential to render microscopic control over how cells are incorporated and grown onto the tissue-engineered airway.

Stem cell-based organ replacements-airway and lung tissue engineering

Tissue engineering requires the use of cells seeded onto scaffolds, often in conjunction with bioactive molecules, to regenerate or replace tissues. Significant advances have been made in recent years within the fields of stem cell biology and biomaterials, leading to some exciting developments in airway tissue engineering, including the first use of stem cell-based tissue-engineered tracheal replacements in humans. In addition, recent advances within the fields of scaffold biology and decellularization offer the potential to transplant patients without the use of immunosuppression.