Recovery of laryngeal sensation after superior laryngeal nerve anastomosis.

OBJECTIVES/HYPOTHESIS: Reliable motor reinnervation has been show in multiple laryngeal transplant studies; however, sensory reinnervation of the larynx after nerve anastomosis has yet to be demonstrated. The role of sensory nerve anastomosis in the transplanted larynx in unknown, but is thought to be necessary to provide airway protection. A canine model was developed to examine the possibility of reformation of sensory pathways in the larynx after nerve section and anastomosis. STUDY DESIGN: Randomized controlled experiment. METHODS: Ten canines were randomly assigned to two groups. Hydrochloric acid-induced laryngospasm was demonstrated in every dog. All dogs then had their necks explored, and the internal branch of the superior laryngeal nerve was identified and transected bilaterally. Following nerve section all dogs were retested for an acid-induced laryngospasm reflex. The control group had their wounds closed and were then awakened from anesthesia. The study group underwent microscopic anastomosis of their sensory nerves. Following a 6-month period the two groups of dogs were compared for the presence of the laryngospasm reflex. RESULTS: No dog in the control group had a response to the acid. All dogs in the study group had some response to the acid, although none of them had return of true laryngospasm. CONCLUSION: We concluded that sensory reinnervation does occur after nerve anastomosis, but the recovery of sensation may be incomplete or altered.     

Vocal shadowing under conditions of normal and altered laryngeal sensation

Five adult male subjects vocally matched the pitches of tones in a steady-state tone matching task (SSTMT) and vocally shadowed frequency changes in a frequency modulated tone matching task (FMTMT). Matching was done in both a normal condition and a condition of topical anesthesia of the laryngeal mucosa. Pitch matching accuracy was not seriously altered in the anethesia condition, but anesthetized subjects required more time and had slower velocities in effecting transitions between tones on the FMTMT, as compared to normal. In both conditions there was a direct proportionality between interval size and each of the time and velocity variables examined, while frequency lowering was generally faster than frequency raising. Analysis of subject response strategies on the FMTMT revealed recurring patterns, described here as Overshoot, Undershoot, Oscillate and Hit. Fewer Hit, and more Oscillate, patterns were observed for the anesthesia condition as compared to normal. It was concluded that the FMTMT, as compared to the SSTMT, required finer and more rapid laryngeal control to coordinate respiratory driving pressures and glottal resistance, and hence was more susceptible to impairment of the laryngeal mucosal reflexogenic system. Implications of the data for modeling certain mechanical and physiological aspects of laryngeal control are discussed.     

Altered laryngeal sensation: a potential cause of apnea of infancy

Delayed maturation of respiratory control of breathing and the laryngeal adductor reflex (LAR) are commonly implicated in infant apnea. A swallow response occurs to remove the stimulus from the pharynx to prevent aspiration once the glottis reopens. Induction of apnea by poorly cleared endogenous upper airway secretions has been postulated to be a potential cause of infant apnea. Our purpose was to determine whether alteration in the LAR, an indicator of laryngeal sensation, and the presence of secretions influenced the responsiveness of the LAR in infants with apnea. The LAR was induced in 20 infants with apnea (median gestational age, 36.5 weeks) by application of air pulses of controlled duration (50 ms) and intensity (2.5 to 10 mm Hg) to the aryepiglottic fold. Twenty infants evaluated for upper respiratory tract anomalies were used as a comparison group (median gestational age, 39 weeks). The infants with apnea required higher-intensity stimuli (p < .001) to induce the LAR (6.2 +/- 1.6 mm Hg) than did the comparison group (4.3 +/- 1.0 mm Hg) and demonstrated poorer clearance of secretions (p < .001). These findings were significant even when we adjusted for postconceptional age at the time of the test (p = .007). The findings of this study suggest that decreased laryngeal sensitivity results in poor endogenous secretion clearance and that it may induce a prolonged glottic closure event to prevent aspiration. This closure may play a role in infant apnea.     

Sensory testing in the assessment of laryngeal sensation in patients with amyotrophic lateral sclerosis

OBJECTIVES: Amyotrophic lateral sclerosis (ALS) is a progressive motor neuron disease of unknown cause. Mortality in the population is frequently due to aspiration pneumonia. Although typically considered to be a disorder limited to motor neuron involvement, some investigators have indicated that decreased sensory function in ALS patients additionally contributes to the disease process. The objective of this study was to evaluate laryngopharyngeal sensation in the ALS population in order to quantify the range of sensory deficits and correlate any abnormalities with demographic data to determine which patients are at risk of having sensory deficits. METHODS: We examined the sensation of the larynx in 22 patients with ALS to determine whether a sensory deficit was present. After completion of a dysphagia questionnaire and medical history, patients underwent flexible endoscopic evaluation of swallowing with sensory testing (FEESST) to evaluate sensory function. Threshold values were determined and recorded for initiation of the adductor reflex. RESULTS: The results of the sensory and swallowing function assessments performed on 22 patients demonstrate abnormal sensation in 54.5% of the tested population. Asymmetric findings were noted in 75% of these patients. There was no correlation noted between the presence of sensory deficits and the severity or duration of the disease. CONCLUSIONS: Progressive dysphagia in the ALS population has typically been attributed to muscle weakness. This study points to the presence of sensory deficits in the larynx, which can further affect proper swallowing function.     

Changes in laryngeal sensation evaluated with a new method before and after radiotherapy

Radiotherapy of the laryngopharynx sometimes leads to functional disabilities including swallowing dysfunction. One of the reasons for these disabilities is a deterioration of laryngeal sensation. Laryngeal sensation is an important factor in swallowing, but quantitative evaluation of laryngeal sensation has been difficult. In this study, we evaluated changes in laryngeal sensation before and after radiotherapy for laryngeal and hypopharyngeal cancer, using a flexible laryngoscope and probes. This study was conducted in 12 patients, 8 with laryngeal cancer and 4 with hypopharyngeal cancer, who received radiotherapy alone or chemoradiotherapy at our medical centre. Measurements were performed using a 3.3-mm-diameter flexible laryngoscope with a probe port and four types of probes with 0.06-, 0.13-, 0.20-, and 0.30-mm nylon filaments attached to a wire tip. Sensation was evaluated at the tip of the epiglottis and the arytenoid region. Measurements were performed before radiotherapy, 1, 3 months, and 1 year after completion of radiotherapy. Sensation of the epiglottis and arytenoid deteriorated significantly 1 and 3 months after radiotherapy compared with before radiotherapy. Laryngeal sensation recovered in most cases within 1 year after radiotherapy. The present study clearly demonstrates the deterioration of laryngeal sensation with radiotherapy.     

喉返神经损伤后喉肌病理生理研究

目的：通过对犬喉返神经损伤及再生过程中喉肌电生理及其病理变化进行研究,探讨喉返神经不同损伤形式的病理生理改变及转归特点。方法：实验用犬20只（40侧）分为喉返神经完全损伤组（全切法）、不完全损伤组（结扎法、挫灭法、半切法）及对照组,造模成功后的即刻、1、3、6和12个月观察甲杓肌和环杓后肌肌电特征及组织病理学改变。结果：造模后即刻全切法及结扎法肌电为电静息,挫灭法和半切法存在部分正常单个运动单位（MUP）及振幅减小的MUP混合肌电。神经损伤后1～3个月可出现纤颤电位,不完全损伤组3～6个月出现再生电位。全切法诱发电位基本无法引出,结扎法和半切法早期无诱发电位,后期可以引出振幅减小的诱发电位,结扎法小于半切法;而挫灭法始终都可以引出诱发电位,振幅与对照组无显著性差异,诱发电位潜伏期呈现先延长后缩短的趋势。随着全切、结扎、半切、挫灭损伤程度不同,肌纤维平均直径及肌束直径逐渐增大,单位面积细胞核数逐渐减少。结论：不同损伤,肌电特征及声带运动状态呈动态变化,喉返神经的损伤程度依次为完全损伤、不完全损伤（结扎法、半切法、挫灭法）,喉肌电图检查是声带麻痹诊断和评估的重要方法。     

Effects of denervation on cell cycle control in laryngeal muscle

Denervation of skeletal muscle is thought to lead to an accelerated proliferation of myogenic stem cells known as satellite cells. The transition of these cells from a quiescent to a proliferative state is thought to require satellite cells to enter the cell cycle and replicate. Little is known about the expression of genes associated with cell cycle control, and so the objective of this study was to examine the effects of denervation and reinnervation of the posterior cricoarytenoid (PCA) muscle on key cell cycle genes. Female Sprague-Dawley rats were assigned to control, denervated, or reinnervated groups. Animals were killed at 7, 14, and 30 days after ligation of the recurrent laryngeal nerve. The PCA muscle was then analyzed for changes in the messenger RNA levels of key genes associated with cell cycle control, differentiation, and proliferation. Cyclin D1 is a key gene responsible for initiating progression of the cell cycle from G1 to S phase. Interestingly, neither denervation nor reinnervation affected the expression of this gene. In contrast, we found large increases in key cell cycle inhibitors (p21 and the growth arrest and DNA destruction 45 [GADD45] gene) in both the denervated and reinnervated groups. We interpret the increases in these cell cycle inhibitors to reflect (1) an inhibition of satellite cell proliferation and/or (2) a special form of apoptosis that results in the loss of myonuclei known to occur under atrophic conditions. To our knowledge, this is the first study to examine the effects of denervation on cell cycle regulation.     

Electrical stimulation of laryngeal muscle.

Most functional electrical stimulation (FES) research has focused on the spinal cord-injured patient whose muscles are paralyzed but still maintain their innervation. This article details the investigation of FES of the laryngeal muscles. In time, FES may become a useful treatment for bilateral vocal cord paralysis (BVCP) and for some laryngeal movement disorders.     

Effect of thyroplasty on laryngeal airflow

Thyroplasty has virtually replaced Teflon injection as the procedure of choice for treatment of the unilateral paralyzed vocal cord. Previous studies have shown that Teflon injection, by stiffening the vocal cord, decreases the extrathoracic airway obstruction occasionally measured by pulmonary function testing in patients with unilateral vocal cord paralysis. We became interested in the effect of thyroplasty on extrathoracic airflow. In this prospective study, patients underwent prethyroplasty and postthyroplasty pulmonary function testing. Flow volume loops combined with traditional spirometry were used. Postoperative pulmonary function tests were performed at least 2 months after surgery to allow resolution of surgical edema. Our study results support the previous finding that vocal cord paralysis alone causes some degree of extrathoracic obstruction. However, in contrast to Teflon injection, thyroplasty decreased extrathoracic airflow in all but 1 patient, and by criteria based on the ratio of the midexpiratory flow to the midinspiratory flow, caused new postoperative extrathoracic obstruction in 27% of patients. Symptomatic evidence of this obstruction may be more evident in those active patients with more ventilatory demand.     

Morphologic and histochemical characteristics of laryngeal muscle

Laryngeal muscle (LM) is highly specialized for phonation and sphincter activity. We queried whether this specialization is reflected in the structure of LM. We examined, using histochemical techniques, the structure of five LM from three men who died suddenly and who had no evidence of laryngeal disease. Compared with nonlaryngeal skeletal muscle, our specimens demonstrated moderate fibrosis, rounding of fibers, basophilia, and ragged red fibers that were shown to be mitochondria. In general, LM fibers are smaller, have more variability in size, and contain a greater percentage of histochemically type 1 fibers than limb skeletal muscles. These differences suggest that theories of motor control derived from studies of limb skeletal muscles may not apply to LM.     

The effects of chronic electrical stimulation on laryngeal muscle reinnervation

The present study examined the effects of functional neuromuscular stimulation (FNS) on reinnervation of the posterior cricoarytenoid (PCA) muscle. In 4 canines, the recurrent laryngeal nerve (RLN) was sectioned and anastomosed and a patch electrode array implanted for stimulation and recording at multiple PCA sites. Following implantation, FNS was applied to 2 canines for a period of 6 weeks. Two additional animals served as nonstimulated controls. In each animal, histomorphometric analysis of the RLN was used to assess the quality of nerve regeneration and the potential for muscle reconnection. The magnitude of reinnervation was monitored by electromyographic (EMG) potentials evoked by RLN stimulation. The appropriateness of reconnection was determined by the pattern of spontaneous EMG activity and recovery of vocal fold abduction. Results of this preliminary study indicated that FNS caused an overall repression of reinnervation. However, the repression preferentially inhibited reconnection by foreign nerve fibers, promoting selective reinnervation and preventing synkinesis.     

Effect of gabapentin on the sensation and impact of tinnitus

OBJECTIVES/HYPOTHESIS: This study evaluated the effectiveness of gabapentin in treating chronic tinnitus in two populations: participants with tinnitus with associated acoustic trauma and participants with tinnitus without associated acoustic trauma. The hypothesis was that gabapentin would decrease both subjective and objective features of tinnitus in the trauma group but would be less effective in the nontrauma group. STUDY DESIGN: Prospective, placebo-controlled, single-blind clinical trial. METHODS: Pure-tone audiograms and personal histories were used to categorize tinnitus etiology as either secondary to acoustic trauma or not associated with acoustic trauma. Participants were restricted to those with moderate to severe tinnitus for at least 1 year. All participants received gabapentin in a graduated ascending-descending dose series extending over 20 weeks (peak dose of 2,400 mg/d). RESULTS: There was a significant improvement in tinnitus annoyance for the trauma group (P = .05). Other subjective aspects of tinnitus were not significantly affected in either group. Between-subject variability of therapeutic response was considerable. Nevertheless, in consideration of subjective loudness ratings, 4 of 19 nontrauma participants and 6 of 20 trauma participants showed an improvement of 20% or better. In consideration of psychoacoustic loudness estimates, 3 of 19 nontrauma and 6 of 20 trauma participants showed an improvement of 20 dB HL or greater. Evenly dividing each group into high and low responders revealed significant improvement in loudness at 1,800 and 2,400 mg/day for the trauma high-response subgroup (P = .007). No significant improvement was obtained for other subgroups. CONCLUSION: Gabapentin is effective in reducing subjective and objective aspects of tinnitus in some individuals, with the best therapeutic response obtained in individuals with associated acoustic trauma.     

Modulation of myosin heavy chains in rat laryngeal muscle

OBJECTIVES: To test the hypothesis that myosin heavy chain (MHC) composition is a biological marker indicative of appropriate and functional reinnervation. STUDY DESIGN: Age-matched adult rats were randomized for prospective study under three experimental conditions. METHODS: In adult rats, three experimental conditions were surgically created, including transient recurrent laryngeal nerve (RLN) crush injury, RLN transection and repair, and cricoarytenoid joint fixation with intact RLN. Animals were survived for 30, 90, and 180 days. At each interval, vocal fold mobility was assessed by rigid microlaryngoscopy. Laryngeal electromyography (EMG) was performed before euthanasia. The thyroarytenoid and posterior cricoarytenoid muscles were then excised, each muscle was processed for sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and MHC composition was determined. RESULTS: Thirty days after nerve crush injury, three of six animals regained vocal fold mobility and normal MHC composition. Impaired vocal fold motion in three of six animals was associated with MHC composition characteristic of denervation. At 90 and 180 days, normal vocal fold motion and normal MHC composition were observed in all animals. Following nerve transection and repair, impaired vocal fold motion and MHC composition characteristic of denervation were observed in all animals, despite evidence of reinnervation on EMG. Following joint fixation, alteration in MHC composition consistent with denervation was observed only at 30 days, as was evident in the nerve crush model. CONCLUSION: Temporary injury and vocal fold immobilization result in transient shifts in MHC composition. Nerve transection and repair result in persistent alteration of MHC composition and vocal fold dysfunction. The expression of normal MHC composition is dependent on the condition of appropriate neural contact and functional reinnervation.     

去细胞喉支架的制备及喉肌细胞再生的可行性研究

Objective To prepare a deeelhilarized whole laryngeal scaffold by utilizing a perfusion-decellularized technique, reseed cells on it, and construct recellularized laryngeal muscles. Methods Perfusion decelluarized larynxes were obtained by common carotid arterious perfusion with detergents. Then they were performed by macroscopic view, histological examination, scanning electron microscopy (SEM) and cartilage viability. Decellularized laryngeal scaffold were then reseeded with inducted mesenchymal stem cells (MSCs). Composites were transferred into greater omentums of rabbits after one day' s adherence and harvested after eight weeks. Macroscopic view, histological examination and immunohistochemistry were performed. Results Perfusion larynxes became transparent after two hours. Histology and SEM indicated that perfnsion method shewed better deculluarized effect. More ventages and collagen fibers but no intact cell or anclei were retained in the decellularized martrix. Porosity measured by Image pro plus 6. 0 was 80. 4% ± 3.2% (x ± s). Chondrocyte vitality assay indicated chondrocyte vitality rate in the perfusion group was 86. 9% ± 1.5% . After eight weeks, vascularization formed and integrated cartilage frameworks still remained. Histological examination could clearly show the presence of muscle bundles and vessels. Immunohistoehemical examination indicated that sarcomeric-α actin expressed positively in corresponding areas. Conclusions It is feasible to reseed MSCs into the decellularized laryngeal muscle matrix for constructing tissue-engineered laryngeal muscles. This in vivo maturation into the omentum could be the first step before in situ implantation of the construct.     

去细胞喉支架的制备及喉肌细胞再生的可行性研究

Objective To prepare a deeelhilarized whole laryngeal scaffold by utilizing a perfusion-decellularized technique, reseed cells on it, and construct recellularized laryngeal muscles. Methods Perfusion decelluarized larynxes were obtained by common carotid arterious perfusion with detergents. Then they were performed by macroscopic view, histological examination, scanning electron microscopy (SEM) and cartilage viability. Decellularized laryngeal scaffold were then reseeded with inducted mesenchymal stem cells (MSCs). Composites were transferred into greater omentums of rabbits after one day' s adherence and harvested after eight weeks. Macroscopic view, histological examination and immunohistochemistry were performed. Results Perfusion larynxes became transparent after two hours. Histology and SEM indicated that perfnsion method shewed better deculluarized effect. More ventages and collagen fibers but no intact cell or anclei were retained in the decellularized martrix. Porosity measured by Image pro plus 6. 0 was 80. 4% ± 3.2% (x ± s). Chondrocyte vitality assay indicated chondrocyte vitality rate in the perfusion group was 86. 9% ± 1.5% . After eight weeks, vascularization formed and integrated cartilage frameworks still remained. Histological examination could clearly show the presence of muscle bundles and vessels. Immunohistoehemical examination indicated that sarcomeric-α actin expressed positively in corresponding areas. Conclusions It is feasible to reseed MSCs into the decellularized laryngeal muscle matrix for constructing tissue-engineered laryngeal muscles. This in vivo maturation into the omentum could be the first step before in situ implantation of the construct.