Selective stimulation of human intrinsic laryngeal muscles: Analysis in a mathematical three-dimensional space.

OBJECTIVES/HYPOTHESIS: Standard stimulating methods using square waves do not appropriately restore physiological control of individual intrinsic laryngeal muscles (ILMs). To further explore our earlier study of evoked orderly recruitment by quasitrapezoidal (QT) currents, we integrated the contribution of the cricothyroideus (CT) with attention to mutual activation in an additional patient, based on recent studies of appropriate responses via strict recurrent laryngeal nerve (RLN) stimulation. STUDY DESIGN: Basic science study. METHODS: The patient received functional electrical stimulation (FES) with QT pulses at 5 Hz, 60 to 2,000 µAmp, 100 to 500 µs pulse width, 0 to 500 µs decay. Ipsilateral electromyography (EMG) responses were calculated using the average maximum amplitude, area under the curve, and the root mean square of the rectified amplitude waveforms. The thyroarytenoideus (TA), posterior cricoarytenoideus (PCA), lateral cricothyroideus (LCA), and the CT were each interrogated via two monopolar electrodes, values were recorded in MATLAB, exported to Excel, and analyzed. Individual and mutual recruitment configurations and activation delays with stimulation were explored using multiple regression and exploration factor analyses. RESULTS: A total of 868 EMG data points based on 18 trials and up to 11 subtrials were captured from each of the four ILMs. Various combinations of pulse amplitude, pulse width, and exponential decay were found to produce significant (P ≤ .001) individual ILM responses. CT mirrored the LCA, whereas the TA and PCA exhibited separate interactions along shared trajectories in a three-dimensional space. CONCLUSIONS: FES calibrated to individual and coupled ILMs offers promise for restoring normal and pathological contraction patterns via strict RLN stimulation. LEVEL OF EVIDENCE: 5 Laryngoscope, 130:967-973, 2020.

Selective intraoperative stimulation of the human larynx.

OBJECTIVES/HYPOTHESIS: Laryngeal contraction normally entails activation of mutually cooperative intrinsic laryngeal muscles (ILMs). Unfortunately, standard stimulating methods do not completely mimic the normal ongoing synchrony between the muscles. We submit that this problem can be addressed by modifying the stimulating waveform. STUDY DESIGN: This study extends prior canine research to the human using quasitrapezoidal (QT) currents instead of standard square waves, which while valuable incompletely express normal ILM interactions. METHODS: In two patients undergoing laryngectomy for cancer, the recurrent laryngeal nerve on the uninvolved side received QT pulses (4 Hz, 60-2,000 µA, 100-500 µs width, 0-500-µs decay) via a bipolar cuff electrode. Pairs of needle electrodes placed into the posterior cricoarytenoideus (PCA), lateral cricoarytenoideus (LCA), and thyroarytenoideus (TA) were used to record electromyography amplitudes, and waveforms were analyzed by a specially designed computer program. RESULTS: With activity from square waves serving as control, we observed statistically significant (P < .05) shifts in mutual relationships among PCA, LCA, and TA for an array of specific QT configurations. CONCLUSIONS: Our preliminary data on selective ILM manipulation offer promise for improved dynamic control of faulty laryngeal contraction patterns.

Subcutaneous emphysema after otologic surgery: a case report.

Subcutaneous emphysema of the head and neck after otologic surgery is exceedingly rare. The mechanism relates to the intimate relationship of the temporomandibular joint to the external auditory canal. We present a rare case of subcutaneous emphysema after otologic surgery for ear disease. An astute clinical index of suspicion coupled with prompt treatment can help minimize morbidity and improve patient outcomes.

Paced glottic closure for controlling aspiration pneumonia in patients with neurologic deficits of various causes.

OBJECTIVES: We undertook to determine whether paced vocal fold adduction can check aspiration in patients with various neurologic conditions. METHODS: Five patients with fluoroscopically documented aspiration and repeated pneumonias were enrolled. Two previously reported patients with hemispheric stroke were compared to 3 additional subjects with brain stem-basal ganglia and cerebellar stroke, cerebral palsy, and multiple sclerosis. A modified Vocare stimulator was implanted subcutaneously and linked to the ipsilateral recurrent laryngeal nerve via perineural electrodes. Vocal fold adduction and glottic closure were effected with pulse trains (42 Hz; 1.2 mA; 188 to 560 micros) and recorded with Enhanced Image J. Fluoroscopy results with and without stimulation were assessed by 2 independent blinded reviewers. Pneumonia rates were compared before, during, and after the 6- to 12-month enrollment periods. RESULTS: There was statistically significant vocal fold adduction (p < 0.05) for all patients, further verified with bolus arrest (p < 0.05 for thin liquids, thick liquids, and puree depending on the speech-language pathologist). Pneumonia was prevented in 4 of the 5 patients during enrollment. In the fifth patient, who had brain stem-basal ganglia and cerebellar stroke, we were unable to completely seal the glottis and open the cricopharyngeus enough to handle his secretions. CONCLUSIONS: Vocal fold pacing for aspiration pneumonia from a variety of neurologic insults appears to be appropriate as long as the glottis can be sealed. It is not sufficient when the cricopharyngeus must be independently opened.

Improvement of respiratory compromise through abductor reinnervation and pacing in a patient with bilateral vocal fold impairment.

OBJECTIVES/HYPOTHESIS: To determine whether respiratory compromise from bilateral vocal fold impairment (paralysis) can be objectively alleviated by reinnervation and pacing. METHODS: A patient with paramedian vocal folds and synkinesis had a tracheotomy for stridor after bilateral laryngeal nerve injury and Miller Fisher syndrome. One posterior cricoarytenoideus (PCA) received a nerve-muscle pedicle fitted with a perineural electrode for pacemaker stimulation. The airway was evaluated endoscopically and by spirometry for up to 1 year. RESULTS: Bilateral vocal fold patency during quiet breathing was reversed to active vocal fold adduction during tracheal occlusion. Peak inspiratory flows (PIFs) were significantly higher (P < .001) after reinnervation. PIFs and glottic apertures increased further under stimulation (42 Hz, 1-4 mA, 42-400 microsec). although the differences were not significant. CONCLUSIONS: Based on our preliminary data, PCA reinnervation and pacing offer promise for amelioration of respiratory compromise after paradoxical adduction in bilateral vocal fold impairment.

Tissue-engineered trachea for airway reconstruction.

OBJECTIVES/HYPOTHESIS: Scaffold-free cartilage has been used to engineer biocompatible and mechanically stable neotracheas in vivo. The purpose of this animal study was to determine if neotracheal constructs, implanted paratracheally, could successfully be used for segmental tracheal reconstruction. STUDY DESIGN: Animal study. METHODS: Culture-expanded auricular rabbit chondrocytes were used to engineer scaffold-free cartilage sheets. Cartilage and a strap muscle flap were wrapped around a tube and implanted paratracheally. At 12 to 14 weeks postimplantation neotracheas were used to reconstruct 20 mm tracheal defects. Surgical technique was modified several times in an attempt to decrease the amount of neotracheal obstruction and fibrosis. In one of the six rabbits, neotrachea with its intact strap muscle flap was dropped into the defect followed by an end-to-end anastomosis; in two animals the muscle flap was partially, and in one rabbit completely removed. In two animals the muscle flap was partially removed, the tube reinserted, and the construct reimplanted for 5 weeks to allow formation of a fibrous lining over the exposed cartilage followed by tracheal reconstruction. RESULTS: All implants developed into vascularized and mechanically sound neotracheas. Following reconstruction, none of the animals showed immediate signs of respiratory distress; however, one died after 24 hours due to extensive endotracheal muscle flap edema, whereas rabbits who had undergone partial or complete muscle flap removal survived up to 39 days before developing cicatricial stenosis. CONCLUSIONS: Tissue-engineered neotracheas proved to have excellent biocompatibility and stability to function under physiologic conditions, but lacked adequate endotracheal lining resulting in neotracheal stenosis.

An unusual presentation of Teflon granuloma: case report and discussion.

For more than 25 years, Teflon was the most commonly used material for injection laryngoplasty. However, the incidence of Teflon granuloma and the consequent deterioration of glottic function ultimately led to the development of other injectable materials, and as a result, Teflon granulomas are no longer frequently encountered. We present a case of Teflon granuloma that was unusual in that (1) a long period of time had elapsed between the injection and the granuloma formation and (2) there was no change in the patient's glottic function.

Fabrication of a neotrachea using engineered cartilage.

OBJECTIVES: Surgical management of long-segment tracheal stenosis is an ongoing problem. Many types of tracheal prostheses have been tried but with limited success because of immune rejection, graft ischemia, or restenosis. Tissue engineered cartilage may offer a solution to this problem, although scaffolds, which are currently often used for support, can lead to biocompatibility problems. This study investigated the feasibility of scaffold-free cartilage to tissue engineer a vascularized neotrachea in rabbits. STUDY DESIGN: Animal study. METHODS: Autologous neotracheal constructs were implanted in the abdomen of six New Zealand white rabbits. Auricular chondrocytes were used to engineer scaffold-free cartilage sheets. A muscle flap raised from the external abdominal oblique muscle and the engineered cartilage were wrapped around a silicone stent to fabricate a vascularized neotrachea in vivo. In two of the six rabbits, a full thickness skin graft was used to create an epithelial lining. The constructs were harvested after either 6 or 10 weeks. RESULTS: All neotracheal constructs were healthy with well-vascularized and integrated layers. The implanted engineered cartilage underwent a remodeling process, forming a solid tracheal framework. Constructs harvested after 10 weeks proved to have significantly better mechanical properties than after 6 weeks and were comparable with the rabbit's native trachea. CONCLUSION: Scaffold-free engineered cartilage can successfully fabricate a well-vascularized, autologous neotrachea with excellent mechanical properties. The results suggest that this approach can be used to reconstruct tracheal defects in rabbits.

Hyaluronan-based scaffolds to tissue-engineer cartilage implants for laryngotracheal reconstruction.

OBJECTIVES: Donor site morbidity, including pneumothorax, can be a considerable problem when harvesting cartilage grafts for laryngotracheal reconstruction (LTR). Tissue-engineered cartilage may offer a solution to this problem. This study investigated the feasibility of using Hyalograft C combined with autologous chondrocytes to tissue engineer cartilage grafts for LTR in rabbits. STUDY DESIGN: Animal study. METHODS: Eighteen New Zealand white rabbits underwent LTR: 12 rabbits received autologous tissue-engineered cartilage grafts and 6 animals, serving as a positive control group, native auricular cartilage. To determine any differences in response to the site of implantation and any potential immune response to the scaffold, a second piece of engineered neocartilage and a non-cell-loaded scaffold were inserted paralaryngeally into a subset of the rabbits. The rabbits were sacrificed 3, 6, 8, 10, and 12 weeks after the LTR and their larynx examined. RESULTS: None of the 18 rabbits showed signs of respiratory distress. A smooth, noninflammatory scar was visible intraluminally. Histologically, the native auricular cartilage implants showed excellent integration without any signs of inflammation or cartilage degradation. In contrast, all tissue-engineered grafts and empty scaffolds revealed marked signs of an unspecific foreign body reaction, leading to a complete degradation of the neocartilage, whether implanted para- or intralaryngeally. CONCLUSION: In contrast to the success with which Hyalograft C has been applied in articular defect repair, our results indicate that, in rabbits, Hyalograft C initiates a foreign body reaction if implanted intra- or paralaryngeally, leading to cartilage degradation and possible graft failure. These findings suggest limitations on the environment in which Hyalograft C can be applied.

Artificial voice modulation in dogs by recurrent laryngeal nerve stimulation: electrophysiological confirmation of anatomic data.

OBJECTIVES: We hypothesized that voice may be artificially manipulated to ameliorate dystonias considered to be a failure in dynamic integration between competing neuromuscular systems. METHODS: Orderly intrinsic laryngeal muscle recruitment by anodal block via the recurrent laryngeal and vagus nerves has allowed us to define specific values based on differential excitabilities, but has precluded voice fluency because of focused breaks during stimulation and the need to treat several neural conduits. Such problems may be obviated by a circuit capable of stimulating some axons while simultaneously blocking others in the recurrent laryngeal nerve, which carries innervation to all intrinsic laryngeal muscles, including the arguably intrinsic cricothyroideus. In 5 dogs, both recurrent laryngeal nerves received 40-Hz quasi-trapezoidal pulses (0 to 2000 microA, 0 to 2000 micros, 0 to 500 micros decay) via tripolar electrodes. Electromyograms were matched with audio intensities and fundamental frequencies recorded under a constant flow of humidified air. Data were digitized and evaluated for potential correlations. RESULTS: Orderly recruitment of the thyroarytenoideus, posterior cricoarytenoideus, and cricothyroideus was correlated with stimulating intensities (p < .001), and posterior cricoarytenoideus opposition to the thyroarytenoideus and cricothyroideus was instrumental in manipulating audio intensities and fundamental frequencies. CONCLUSIONS: Manipulation of canine voice parameters appears feasible via the sole recurrent laryngeal nerve within appropriate stimulation envelopes, and offers promise in human laryngeal dystonias.