Age-related changes in muscle fiber types in the human thyroarytenoid muscle: an immunohistochemical and stereological study using confocal laser scanning microscopy

Neurophysiology of the Superior Laryngeal Nerve in an In Vivo Rat Model

OBJECTIVE

The superior laryngeal nerve (SLN) is fundamental in laryngeal sensation, cough reflex, and pitch control. SLN injury has substantial consequences including altered sensation, aspiration, and dysphonia. To date, in vivo measurement of the SLN remains elusive. The purpose of this study was to assess the feasibility of recording motor and sensory evoked potentials in a rat SLN model.

METHODS

Twenty-two rat hemi-laryngeal preparations (n = 11) were obtained from 4-month-old Sprague-Dawley rats and included in this study. Compound motor action potentials (CMAPs) and motor unit number estimation (MUNE) were calculated by stimulating the SLN at the point of medial extension near the carotid artery and by placing a recording electrode on the cricothyroid muscle. Sensory response was determined through stimulation of the SLN and laryngoscopic visualization of a laryngeal adductor reflex (LAR). SLN and cricothyroid muscle cross-sections were stained and histologic morphometrics were quantified.

RESULTS

Laryngeal evoked potentials were successfully obtained in all trials. Mean CMAP latency and negative durations were 0.99 ± 0.57 ms and 1.49 ± 0.57 ms, respectively. The median MUNE was 2.06 (IQR 1.88, 3.51). LAR was induced with a mean intensity of 0.69 ± 0.20 mV. Mean axon count, myelin thickness, and g-ratio were 681 ± 192.2, 1.72 ± 0.26, and 0.45 ± 0.04, respectively.

CONCLUSIONS

This study demonstrates the feasibility of recording evoked response potentials following SLN stimulation. We hypothesize that this work will provide a tractable animal model to study changes in laryngeal sensation and cricothyroid motor function with aging, neurodegenerative disease, aspiration, or nerve injury.

LEVEL OF EVIDENCE

NA Laryngoscope, 134:1778-1784, 2024.

Treatments for Age-related Vocal Atrophy: A Systematic Review

OBJECTIVE

Age-related vocal atrophy (ARVA) can dramatically affect voice, communication, and quality of life. The objectives of this systematic review were to (1) determine whether treatments for ARVA were superior to controls (2) compare the relative efficacy of procedural and behavioral treatments (3) review the various types of outcome measures, and (4) evaluate the quality of studies.

REVIEW METHODS

The literature was searched using strategies designed by a medical librarian (2/18/21, updated 3/9/22). Studies investigating treatments for bilateral vocal atrophy were included. Studies involving unilateral atrophy, presbyphonia (without endoscopic findings), or an absent comparator group were excluded. The Preferred Reporting Items for Systematic Reviews and Meta-analyses checklist was used to guide this study.

RESULTS

After applying the inclusion/exclusion criteria, 8 articles remained, including 4 randomized trials and 4 cohort studies, and a narrative synthesis was performed. Surgical and behavioral treatments for ARVA appeared to be superior to control groups, based on specific outcome measures. However, the superiority of these treatments over controls was not uniformly observed across multiple outcome measures. When comparing different treatments, superiority could not be established based on the quality and completeness of the studies included in the systematic review. Outcome measures also varied between individual studies. Finally, the risk of bias was analyzed and scored. Consistent point deductions among reviewed studies were noted.

CONCLUSIONS

When comparing treatments for ARVA. Surgery and voice therapy were both superior to control groups based on specific outcome measures from different domains. Superiority of one treatment could not be established.

LEVEL OF EVIDENCE

N/A Laryngoscope, 133:2846-2855, 2023.

Assessing the Prevalence and Associated Risk Factors for Presbylarynx in the Elderly Laryngology Population

OBJECTIVE

The primary objective of this study was to assess the prevalence of presbylarynx and its associated features in an elderly population representative of patients seen in a tertiary care laryngology practice. The secondary objective of this study was to compare laryngeal electromyography (LEMG) findings, coexisting VF conditions, medical history, surgical history, medication use, and other parameters between patients with and without presbylarynx.

METHODS

Adult voice patients aged 60 years and older who underwent strobovideolaryngoscopy were included in the study. Patients were assigned to one of two groups based on the majority (≥2/3) agreement of three blinded authors' (GA, KL, and HP) graded examinations of strobovideolaryngoscopy (SVL) videos for findings consistent with presbylarynx (atrophic vocal folds [VFA], vocal fold bowing [VFB], vocal process prominence [VPP] and anterior glottic insufficiency [GI]). Patient demographics, medical history, surgical history, medication use, laboratory results, and SVL videos were compiled. Statistical analysis was performed using SPSS 28.0.0.0 (IBM, Armonk, NY). All tests were performed two-tailed, and a P-value of less than 0.05 was considered statistically significant.

RESULTS

One hundred sixty-four patients (84 female/80 male, mean age of 68.397 ± 4.947 years) were included in this study. The prevalence of presbylarynx was 52.4% (n = 86) in the study population. The mean age of patients in the presbylarynx group was significantly higher than the nonpresbylarynx group. Additionally, there were significantly more males than females in the presbylarynx group. The presbylarynx group also was found to have a higher proportion of ACE inhibitor (ACEi) use. Further, laboratory results revealed a significantly higher proportion of patients with elevated thyroid stimulating hormone (TSH) levels in the presbylarynx group. Conversely, patients in the nonpresbylarynx group were found to have a significantly higher rate of levothyroxine use. On SVL, patients in the nonpresbylarynx cohort were found to have a significantly higher proportion of benign vocal fold lesions and vocal fold paresis. However, LEMG testing revealed no statistically significant differences in muscle recruitment between groups. Men with presbylarynx were found to have a significantly higher proportion of VFB and VPP compared to women with presbylarynx.

CONCLUSION

This retrospective study investigated the prevalence and risk factors associated with presbylarynx in patients representative of those treated by laryngologists. Signs consistent with presbylarynx are observable even in the presence of coexisting VF conditions. Older age, elevated TSH, the use of ACEi, and male gender was associated with signs of presbylarynx on SVL. Of those diagnosed with presbylarynx, males were identified as having higher proportions of VFB and VPP compared to females. More education regarding presbylarynx and further studies to improve standardization of the criteria for its diagnosis, as well as its relationship with other VF conditions, are encouraged to improve management of the aging voice.

Effect of Aging on the Vocal Muscle

INTRODUCTION

Sarcopenia is a common and natural condition in the elderly, and leads to loss of muscle mass and function. In the presbylarynx there is atrophy of the vocal folds, however the degree of vocal muscle atrophy is poorly studied and the results are contradictory.

AIMS

The aim of this study was to evaluate the effect of aging on the vocal muscle (thyroarytenoid muscle).

METHODS

Thirteen larynxes removed during necropsy from 13 cadavers were included into two age groups: Control group - G1 (n5), between 25 and 40 years; Elderly Group - GI (n-8), aged 70 years or older. The vocal folds were dissected and prepared for scanning electron microscopy, ensuring a cross-section in the musculature area to allow measurements of muscle fiber parameters. Images were analyzed and photographed at different magnifications. Through the ImageJ software, ten distinct fields of each part were selected. Parameters studied:  area, perimeters and diagonals of the thyroarytenoid muscle bundles of both groups.

RESULTS

The cross-sectional areas, perimeters and diagonals of the muscle fibers of the thyroarytenoid muscle of the elderly group were significantly smaller than those of the control group.

CONCLUSION

We demonstrated that the vocal muscle is affected in the presbylarynx, with a reduction of its muscle fibers, corresponding to muscle atrophy. However, these findings may not be directly related to vocal symptoms because the patient may develop muscle compensatory mechanisms capable of reducing glottic insufficiency.

Effects of Vocal Training on Thyroarytenoid Muscle Neuromuscular Junctions and Myofibers in Young and Older Rats

The purpose of this investigation was to determine the effects of vocal training on neuromuscular junction (NMJ) morphology and muscle fiber size and composition in the thyroarytenoid muscle, the primary muscle in the vocal fold, in younger (9-month) and older (24-month) Fischer 344 × Brown Norway male rats. Over 4 or 8 weeks of vocal training, rats of both ages progressively increased their daily number of ultrasonic vocalizations (USVs) through operant conditioning and were then compared to an untrained control group. Neuromuscular junction morphology and myofiber size and composition were measured from the thyroarytenoid muscle. Acoustic analysis of USVs before and after training quantified the functional effect of training. Both 4- and 8-week training resulted in less NMJ motor endplate dispersion in the lateral portion of the thyroarytenoid muscle in rats of both ages. Vocal training and age had no significant effects on laryngeal myofiber size or type. Vocal training resulted in a greater number of USVs with longer duration and increased intensity. This study demonstrated that vocal training induces laryngeal NMJ morphology and acoustic changes. The lack of significant effects of vocal training on muscle fiber type and size suggests vocal training significantly improves neuromuscular efficiency but does not significantly influence muscle strength changes.

Satellite cell capacity for functional adaptation of masseter muscle in Class II and Class III patients after orthognathic surgery-a pilot study

AIM

The aim of the prospective pilot study was to analyze the biomarkers CD34, Pax7, Myf5, and MyoD for stimulation of satellite cells (SCs), which are responsible for functional adaptation.

SUBJECTS AND METHODS

Forty-five Caucasian patients were consecutively recruited from the Maxillo-Facial-Surgery at TU Dresden. Eleven orthognathic Class III patients, 24 Class II patients, and 10 controls with Class I were involved in the study. Tissue samples from masseter muscle were taken from the patients pre-surgically (T1) and 7 months later (T2). Samples from controls were taken during the extraction of third molars in the mandible. Polymerase chain reaction (PCR) for relative quantification of gene expression was calculated with the delta delta cycle threshold (ΔΔCT) method.

RESULTS

The results show significant differences for the marker of SC stimulation between the controls, the patient groups, males, and females. The gene expression of CD34 was post-surgically upregulated for Class III (0.35-0.77, standard deviation [SD] = 0.39, P < 0.05) in comparison with controls. For Pax7, there was a significant difference shown between the retrognathic and the prognathic group because of downregulation in Class II patients (1.64-0.76, SD = 0.55, P < 0.05). In Class III patients, there was a significant upregulation for Myf5 (0.56-1.05, SD = 0.52, P < 0.05) after surgery too.

CONCLUSIONS

The significant decline of Pax7 in Class II patients indicates a deficiency of stimulated SC post-surgically. The expression of CD34 and Myf5 in Class II stayed unchanged. In contrast, there was an upregulation for all Class III patients, mainly in females, shown post-surgically. This may be one reason for weak functional adaptation and relapse in Class II patients.

Notch expression profile and satellite cell stimulation in masseter muscle before and after orthognathic surgery

The aim of this prospective study was to compare the expression of the Notch receptor family with the biomarker for stimulation of satellite cells (SC), which are responsible for functional adaptation. Tissue samples from the masseter muscle were taken presurgically and 7 months later. Samples from controls came from the extraction of third molars. The expression of Notch 1 to 4 and the satellite cell markers CD34, Pax7, and MyoD1 were investigated. PCR was used for relative quantification of gene expression, which was calculated with the ΔΔC_T method. The study involved 38 white patients - 10 prognathic, 18 retrognathic, and 10 orthognathic controls. The median value for Notch 1 was significantly reduced presurgically for prognathic (0.46, SD 0.45) and retrognathic (0.57, SD 0.35) patients compared with the controls. Postsurgically, Notch 2 was significantly upregulated in the prognathic group (0.55, SD 0.28/1.37, SD 0.85). Similarly, there was upregulation of Notch 3 in the prognathic group (0.33, SD 0.42/0.59, SD 1.37) and downregulation in retrognathic patients (0.59, SD 0.79/0.52, SD 0.97). Upregulations for the satellite cell markers CD34 and Pax7 were also found in prognathic patients. The significant upregulation of Notch 1-3 and CD34 in prognathics, but unchanged MyoD expression, signals high stimulation for SC and maintenance of the regeneration cell pool. A lower expression of Notch and SC in retrognathic patients could be responsible for weak functional adaptation.

Voice and Respiratory Characteristics of Men and Women Seeking Treatment for Presbyphonia

BACKGROUND AND OBJECTIVES

Impaired respiratory function could potentially explain why some older speakers experience voice-related handicap whereas others do not, despite presenting with similar age-related laryngeal characteristics. The objectives of this study were therefore to (1) describe voice and respiratory function across men and women in a sample of treatment-seeking patients with presbyphonia; (2) assess how respiratory function differed from the general elderly population, based on normative data; and 3) discuss how respiratory function may play a role in the development of voice symptoms across men and women.

METHODS

Twenty one participants with presbyphonia underwent respiratory assessments (spirometry and respiratory muscle strength testing) in addition to standard of care voice assessments. Respiratory variables included forced vital capacity (FVC), forced expiratory volume in one second (FEV₁), FEV₁/FVC, maximum inspiratory pressure (MIP), and maximum expiratory pressure (MEP).

RESULTS

Voice features were consistent with the diagnosis of presbyphonia and values did not different significantly between males and females, although some trends were noted. Regarding respiratory variables, one-third of the participants (n = 7) presented with FVC and FEV₁ less than 80% of predicted, and 57% (n = 12) were <90% of predicted. Nine percent of the males (n = 1) and none of the females had a MIP below the lower limit of normal (LLN) expected for their age, sex, and weight. Eighteen percent of the males (n = 2) and 20% of the females (n = 2) fell below the LLN for MEP.

CONCLUSION

Our sample of participants with presbyphonia included a non-negligible proportion of patients with decreased percent predicted values of FVC and FEV₁, and with respiratory muscle strength (MEP) below the LLN. Standardized values of pulmonary function were not different across sexes, indicative of a similar respiratory health. However, a lower raw pulmonary function and respiratory muscle strength in women may compound laryngeal changes and have an impact on perceived voice-related handicap. Together, findings warrant further studies to explore the impact of decreased respiratory function on voice and, ultimately, on the response to voice therapy in patients with presbyphonia.

Respiratory Muscle Strength Training to Improve Vocal Function in Patients with Presbyphonia

BACKGROUND AND OBJECTIVE

The effects of presbyphonia are compounded by the decline in respiratory function that occurs with age. Commonly recommended exercises to optimize the use of respiratory muscles during speech, such as diaphragmatic breathing, are unlikely to be intensive enough to induce respiratory changes and impact vocal function. The objective of this study was to assess the effect of adding a targeted intervention, respiratory muscle strength training, to voice exercises in a sample of patients with presbyphonia.

METHODS/DESIGN

In this prospective, randomized-controlled trial, 12 participants received either (1) vocal function exercises (VFE), (2) VFE combined with inspiratory muscle strength training (IMST), or (3) VFE combined with expiratory muscle strength training (EMST). Data collected prior to and following 4 weekly intervention sessions included respiratory measures (pulmonary function and respiratory muscle strength) and voice measures (videostroboscopy, acoustic, auditory-perceptual, aerodynamic, and self-assessment measures).

RESULTS

Participants who received IMST improved their voice quality during connected speech (smoothed cepstral peak prominence and ratings of overall voice quality) and their scores on the three self-assessment questionnaires with large to very large within-group effect sizes (|d| = 0.82-1.61). In addition, participants in the IMST group reduced their subglottal pressure with a large effect size (d = -0.92). Participants who received EMST improved their maximum expiratory strength and smoothed cepstral peak prominence with large effect sizes (d = 0.80 and 0.99, respectively) but had limited improvements in other outcomes. Participants who received only VFE decreased their amount of vocal fold bowing, improved their voice quality on a sustained vowel (amplitude perturbation quotient), and improved their Glottal Function Index score with large effect sizes (|d| = 0.74-1.00).

CONCLUSION

Preliminary data indicate that adding IMST to voice exercises may lead to the greatest benefits in patients with presbyphonia by promoting improved subglottal pressure control as well as increasing air available for phonation, resulting in improved self-assessment outcomes.

The Impact of Respiratory Function on Voice in Patients with Presbyphonia

BACKGROUND AND OBJECTIVE

Presbyphonia is an age-related voice disorder characterized by vocal fold atrophy and incomplete glottal closure during phonation. The extent to which the effects of presbyphonia may be compounded by age-related declines in the respiratory system and further impact communication and quality of life remains unknown. Therefore, the objective of this study was to determine how variations in respiratory function impacts voice measures in a sample of participants with presbyphonia.

METHODS

In this pilot study, 21 participants with presbyphonia underwent respiratory assessments (spirometry and respiratory muscle strength testing) and voice assessments (videostroboscopy, acoustic analysis, auditory-perceptual ratings, aerodynamic assessment, and self-assessments). Factor and cluster analyses were conducted to extract voice and respiratory constructs and to identify groups of participants with similar profiles. Correlations and regression analyses were conducted to better describe the relationships between voice and respiratory function.

RESULTS

Respiratory function was found to impact voice via two main pathways: through its physiological effect on voice and through its impact on general health and impairment. A lower respiratory function was associated with a lower vocal fold pliability and regularity of vibration and with an elevated aerodynamic resistance accompanied by laryngeal hyperfunction. Standardized measures of respiratory function were associated with perceived voice-related handicap. Respiratory function did not associate with voice quality, which was mostly influenced by the severity of vocal fold atrophy.

CONCLUSION

Poor respiratory health exacerbates the burden of vocal fold atrophy and, therefore, implementation of respiratory screening prior to starting voice therapy may significantly affect the treatment plan and consequently the outcomes of voice therapy in this patient population.

Volumetric Analysis of the Vocal Folds Using Computed Tomography: Effects of Age, Height, and Gender

OBJECTIVE

The goal of this study was to use computed tomography (CT) volumetric analysis to assess the effect of age, gender, height, body mass index (BMI), and ethnicity on vocal fold volume in patients with normal larynges.

STUDY DESIGN

Retrospective cross-sectional study.

METHODS

Vocal fold length, width, and height were measured in a total of 105 patients without a history of laryngeal or thyroid pathology on thin-section soft-tissue neck CTs. The product of the three dimensions was used to calculate vocal fold volume. Simple and multiple linear regression analyses were used to assess for an association between vocal fold volume and age, gender, height, BMI, and ethnicity. Intraclass correlation coefficients (ICCs) were estimated to evaluate the degree interobserver and intraobserver agreement.

RESULTS

Vocal fold volume was not associated with age, BMI, or ethnicity. Gender-adjusted height (P = .002) and height-adjusted gender (P = .016) were significantly associated with volume. Height remained significantly associated with volume after stratifying by gender (P < 0.001). There was moderate-to-good correlation in both interobserver (ICC = 0.690 to 0.761) and intraobserver (ICC = 0.733 to 0.873) agreement.

CONCLUSION

Age was not associated with vocal fold volume, which is in accordance with several prior negative studies. Age-related vocal fold atrophy may not substantially contribute to presbyphonia symptoms, but other processes such as changes in the extracellular matrix may play a larger role. However, both gender and height were independently associated with vocal fold volume.

LEVEL OF EVIDENCE

4 Laryngoscope, 131:E240-E247, 2021.

A Tutorial of the Effects of Sex Hormones on Laryngeal Senescence and Neuromuscular Response to Exercise

Purpose The purpose of this tutorial is to summarize how sex hormones affect both laryngeal senescence and neuromuscular response to exercise, highlighting the importance of considering sex differences in developing treatment for the senescent voice. Conclusion Men and women's voices are sexually dimorphic throughout the life span, including during the laryngeal adaptations observed during senescence. Therefore, presbyphonia (age-related dysphonia) likely clinically manifests differently for men and women due to differences in how the male and the female larynx change in response to aging. Because sexual dimorphism is evident in both laryngeal aging and response to exercise, voice therapy programs aimed at treating the typical and disordered aged voice should consider sex differences in their design.

Characterization of aged rat vocal fold fibroblasts

OBJECTIVES/HYPOTHESIS

To elucidate the aging physiology of the vocal folds, we examined the characters of aged vocal fold fibroblasts (VFFs) in various conditions.

STUDY DESIGN

In vitro study.

METHODS

VFFs from young (12-week-old) and aged (19-month-old) Sprague-Dawley rats were compared. Proliferative capacity, ratio of myofibroblast to fibroblast, myofibroblast function, and extracellular matrix production were examined in the following conditions: naïve, basic fibroblast growth factor (bFGF) supplemented, and hepatocyte growth factor (HGF) supplemented.

RESULTS

Aged VFFs demonstrated reduced proliferation by cell counting, though the ratio of Ki-67-positive cells showed no difference. Aged VFFs exhibited an increased expression of α-smooth muscle actin (α-SMA); however, they demonstrated no enhanced contractile ability in a gel contraction assay. Type I collagen protein was increased age dependently, accompanied with decreased Mmp1 and unchanged Col1a1 transcription. Type I collagen protein and α-SMA represented quite similar reduction patterns to bFGF or HGF administration.

CONCLUSIONS

The following possible characteristics of aged VFFs were implied: long duration of mitosis, increased myofibroblast population size with certain dysfunctions, reduced type I collagen turnover, and correlation between α-SMA expression and type I collagen metabolism. Further investigations of these features will help to clarify presbyphonia's pathology and establish treatment strategies.

LEVEL OF EVIDENCE

NA Laryngoscope, 129:E94-E101, 2019.

Volumetric analysis of vocal fold atrophy via magnetic resonance imaging

Objective

To quantitatively test the hypothesis that older patients have increased thyroarytenoid muscle atrophy by comparing thyroarytenoid muscle volumes across different age groups.

Methods

A retrospective chart review was conducted. The study included 111 patients with no history of laryngeal pathology. Two investigators reviewed magnetic resonance imaging studies of these patients and manually traced the thyroarytenoid muscles on multiple slices bilaterally. Thyroarytenoid muscle volumes were then computed using imaging analysis software. Patients were stratified into three age groups (18–50 years, 51–64 years, and 65 years or older) for comparison.

Results

Intra- and inter-rater reliabilities were excellent for all measurements (intraclass correlation co-efficient > 0.90). There was no statistically significant difference in the mean volumes of left and right thyroarytenoid muscles in all age and gender groups.

Conclusion

Given the lack of statistically significant difference in thyroarytenoid muscle volume between age groups on magnetic resonance imaging, the prevailing assumption that age-related thyroarytenoid muscle atrophy contributes to presbyphonia should be re-examined.

Treatment Receipt and Outcomes of Self-Reported Voice Problems in the US Population Aged ≥65 Years

Objectives

(1) Characterize the US population aged ≥65 years with self-reported voice problems, (2) describe voice treatment characteristics in this group, and (3) identify factors associated with self-reported voice improvement.

Study Design

Retrospective cohort study.

Setting

Population-based cross-sectional US national survey sample.

Subjects and Methods

We identified a cohort of adults aged ≥65 years from the 2012 National Health Interview Survey, a population-based US national survey. Descriptive and multivariable regression analyses were performed.

Results

The prevalence of self-reported voice problems in this cohort was 10%. Of those, 44% reported voice problems for >1 month. The strongest predictor of reporting voice improvement was receipt of voice treatment (odds ratio, 3.50; 95% confidence interval, 1.36-9.00), after adjusting for sex, age, race, education, and health status. Eleven percent reported voice treatment, which included 20% of those with moderate or worse voice problem severity. Female sex and worse health status were associated with reporting voice treatment. Among those with voice treatment, 38% reported “better,” 33% “same,” and 29% “worse” voice symptoms over the past year, compared to 17%, 67%, and 16%, respectively, among those without treatment. Health status influenced likelihood of reporting voice improvement but not universally.

Conclusions

We observed a significant self-reported burden of voice problems in the US population aged ≥65 years. Most are untreated and thus not well represented in the current literature. Vocal improvement was strongly associated with treatment. Further investigation is needed to clarify patient and treatment characteristics most associated with vocal improvement.

Neonatal Satellite Cells Form Small Myotubes In Vitro

Although palatal muscle reconstruction in patients with cleft palate takes place during early childhood, normal speech development is often not achieved. We hypothesized that the intrinsic properties of head satellite cells (SCs) and the young age of these patients contribute to the poor muscle regeneration after surgery. First, we studied the fiber type distribution and the expression of SC markers in ex vivo muscle tissue from head (branchiomeric) and limb (somite-derived) muscles from neonatal (2-wk-old) and young (9-wk-old) rats. Next, we cultured SCs isolated from these muscles for 5, 7, and 9 d, and investigated the in vitro expression of SC markers, as well as changes in proliferation, early differentiation, and fusion index (myotube formation) in these cells. In our ex vivo samples, we found that virtually all myofibers in both the masseter (Mass) and the levator veli palatini (LVP) muscles contained fast myosin heavy chain (MyHC), and a small percentage of digastric (Dig) and extensor digitorum longus myofibers also contained slow MyHC. This was independent of age. More SCs were found in muscles from neonatal rats as compared with young rats [17.6 (3.8%) v. 2.3 (1.6%); P < 0.0001]. In vitro, young branchiomeric head muscle (BrHM) SCs proliferated longer and differentiated later than limb muscle SCs. No differences were found between SC cultures from the different BrHMs. SC cultures from neonatal muscles showed a much higher proliferation index than those from young animals at 5 d (0.8 v. 0.2; P < 0.001). In contrast, the fusion index in neonate SCs was about twice as low as that in SCs from young muscles at 9 d [27.6 (1.4) v. 62.8 (10.2), P < 0.0001]. In conclusion, SCs from BrHM differ from limb muscles especially in their delayed differentiation. SCs from neonatal muscles form myotubes less efficiently than those from young muscles. These age-dependent differences in stem cell properties urge careful consideration for future clinical applications in patients with cleft palate.

Independent exercise for glottal incompetence to improve vocal problems and prevent aspiration pneumonia in the elderly: a randomized controlled trial

Objectives:

To evaluate the effect of a self-controlled vocal exercise in elderly people with glottal closure insufficiency.

Design:

Parallel-arm, individual randomized controlled trial.

Methods:

Patients who visited one of 10 medical centers under the National Hospital Organization group in Japan for the first time, aged 60 years or older, complaining of aspiration or hoarseness, and endoscopically confirmed to have glottal closure insufficiency owing to vocal cord atrophy, were enrolled in this study. They were randomly assigned to an intervention or a control group. The patients of the intervention group were given guidance and a DVD about a self-controlled vocal exercise. The maximum phonation time which is a measure of glottal closure was evaluated, and the number of patients who developed pneumonia during the six months was compared between the two groups.

Results:

Of the 543 patients enrolled in this trial, 259 were allocated into the intervention group and 284 into the control; 60 of the intervention group and 75 of the control were not able to continue the trial. A total of 199 patients (age 73.9 ±7.25 years) in the intervention group and 209 (73.3 ±6.68 years) in the control completed the six-month trial. Intervention of the self-controlled vocal exercise extended the maximum phonation time significantly (p < 0.001). There were two hospitalizations for pneumonia in the intervention group and 18 in the control group, representing a significant difference (p < 0.001).

Conclusion:

The self-controlled vocal exercise allowed patients to achieve vocal cord adduction and improve glottal closure insufficiency, which reduced the rate of hospitalization for pneumonia significantly.

ClinicalTrial.govIdentifier-UMIN000015567

Effect of age on human-computer-interface control via neck electromyography

The purpose of this study was to determine the effect of age on visuomotor tracking using submental and anterior neck surface electromyography (sEMG) to assess feasibility of computer control via neck musculature, which allows people with little remaining motor function to interact with computers. Thirty-two healthy adults participated: sixteen younger adults aged 18 - 29 years and sixteen older adults aged 69 - 85 years. Participants modulated sEMG to achieve targets presented at different amplitudes using real-time visual feedback. Root-mean-squared (RMS) error was used to quantify tracking performance. RMS error was increased for older adults relative to younger adults. Older adults demonstrated more RMS error than younger adults as a function of increasing target amplitude. The differential effects of age found on static tracking performance in anterior neck musculature suggest more difficult translation of human-computer-interfaces controlled using anterior neck musculature for static tasks to older populations.

Changes in Rat 50-kHz Ultrasonic Vocalizations During Dopamine Denervation and Aging: Relevance to Neurodegeneration

Vocal communication is negatively affected by neurodegenerative diseases, such as Parkinson disease, and by aging. The neurological and sensorimotor mechanisms underlying voice deficits in Parkinson disease and aging are not well-understood. Rat ultrasonic vocalizations provide a unique behavioral model for studying communication deficits and the mechanisms underlying these deficits in these conditions. The purpose of this review was to examine the existing literature for methods using rat ultrasonic vocalization with regard to the primary disease pathology of Parkinson disease, dopamine denervation, and aging. Although only a small amount of papers were found for each of these topics, results suggest that both shared and unique acoustic deficits in ultrasonic vocalizations exist across conditions and that these acoustic deficits are due to changes in either dopamine signaling or denervation and in aging models changes to the nucleus ambiguus, at the level of the neuromuscular junction, and the composition of the vocal folds in the larynx. We conclude that ultrasonic vocalizations are a useful tool for studying biologic mechanisms underlying vocal communication deficits in neurodegenerative diseases and aging.

Effects of aging on thyroarytenoid muscle regeneration

OBJECTIVES/HYPOTHESIS

Regenerative properties of age-associated changes in the intrinsic laryngeal muscles following injury are unclear. The purpose of this study was to investigate the regenerative properties of the thyroarytenoid (TA) muscle in an aging rat model. The hypothesis was that following myotoxic injury, old animals would exhibit a decrease in mitotic activities of muscle satellite cells when compared with younger rats, suggesting reduced regenerative potential in the aging rat TA muscle.

STUDY DESIGN

Animal group comparison.

METHODS

Regeneration responses following injury to the TA muscle were examined in 18 young adult, middle-aged, and old Fischer 344/Brown Norway rats. TA muscle fiber cross-sectional area (CSA), satellite cell mitosis (number/fiber), and regeneration index (CSA injured side/CSA noninjured side) were measured and compared across age groups.

RESULTS

Young adult animals had a significantly higher regeneration index than the middle-aged and old groups. Within the lateral region of the TA muscle (LTA), the regeneration index was significantly higher in the young adult animals than in the middle-aged and old animals. The regeneration index of the medial TA was significantly higher than the LTA across all age groups.

CONCLUSIONS

The regenerative capacity of the TA muscle is impaired with increasing age.

Cytochrome c oxidase deficiency in human posterior cricoarytenoid muscle

BACKGROUND

Mitochondrial alterations occur in skeletal muscle fibers throughout the normal aging process, resulting from increased accumulation of reactive oxide species (ROS). These result in respiratory chain abnormalities, which decrease the oxidative capacity of muscle fibers, leading to decreased contractile force, sarcopenia, or fiber necrosis. Intrinsic laryngeal muscles are a cranial muscle group that possesses some distinctive genotypic, phenotypic, and physiologic properties. Their susceptibility to mitochondrial alterations resulting from biological processes that increase levels of oxidative stress may be one of these distinctive characteristics.

OBJECTIVES

The incidence of cytochrome c oxidase (COX) deficiency (COX(-)) was determined in human posterior cricoarytenoid (PCA) muscle when compared with the human thyrohyoid (TH) muscle, an extrinsic laryngeal muscle that served as "control" muscle. Ten PCA and 10 TH muscles were harvested postlaryngectomy from 10 subjects ranging in age from 55 to 86 years. Differences in COX(-) were compared within and between muscle types using tissue section staining and standard morphometric analysis.

RESULTS AND CONCLUSIONS

COX(-) fibers were identified in both the PCA and TH muscles. The PCA muscle had 10 times as may affected fibers as the TH muscle, with significant differences in COX(-) found between muscle type and fiber type (P=0.003). Almost all of this effect was the result of elevated levels of COX(-) in type I fibers from the PCA muscle (P=0.002) that showed a strong positive correlation with increased age. These results suggest that increased mitochondrial alterations may occur in the PCA muscle during normal aging.

Challenges and opportunities in the management of the aging voice

Presbyphonia, or age-related dysphonia, is a diagnosis of exclusion, and other comorbidities must be considered in a complete evaluation of elderly patients with dysphonia. The aging voice can have a significant effect on the quality of life of the patient. In addition to the molecular effects of aging on the laryngeal tissues, the etiology of presbyphonia is often multifactorial because of comorbidities in the other organ systems involved in phonation. After a comprehensive evaluation, presbyphonia may be treated conservatively with voice therapy or with a range of interventions. Research into tissue engineering and electrical reanimation offers future options for treatment of presbyphonia. Currently, a multidisciplinary approach offers the most complete improvement in the vocal quality of life in this patient population.

Posterior cricoarytenoid bellies: relationship between their function and histology

OBJECTIVES/HYPOTHESIS

Complete physiological information about human posterior cricoarytenoid muscle (PCA) is essential and is not only of basic science interest but also could lead directly to understanding phonation and many clinical issues in neurolaryngology. The purpose of the study was to investigate and compare the histochemical and morphological properties to know contractile muscle fiber characteristics of two bellies of the PCA.

STUDY DESIGN

Cross-sectional experimental study.

METHODS

The PCAs were harvested from the total laryngectomy simples. Serial transverse sections of the two PCA bellies were performed and studied by immunohistochemical analysis.

RESULTS

Two separate muscle bellies were always identified within 15 PCA. The following muscle fiber types were observed: I, I-IIA, and IIA. Comparisons of the vertical and horizontal bellies of the PCA reveled differences in the fiber-type composition.

CONCLUSION

In our experience, the PCA should be considered as a combination of two functional subunits, which significantly differ in their muscle fiber-type composition.

A senescence accelerated mouse model to study aging in the larynx

Objective: Age-related changes in the larynx lead to significant voice impairment and reduced quality of life. There is a need for aged animal models that have practical generation times to study the fundamental changes and new therapeutics for the aging voice. The senescence accelerated prone mouse strain (SAMP) animals experience rapid aging without any experimental manipulation. The main objective of this study was to demonstrate the use of senescence accelerated mice to study aging in the larynx.

Study Design: Murine model.

Setting: Department of Animal Resources, Emory University.

Subjects and Methods: Larynges from five senescence accelerated prone mice, five normal aging senescence resistant mice, and five C57BL/6 mice were harvested and processed for paraffin sections. Histomorphometry was performed for assessment of collagen and hyaluronic acid distribution. In addition, frozen laryngeal tissue was harvested for transcriptional and translational assessment of collagen-1, using real-time polymerase chain reaction with specific primers and Western blots. Myofibroblast assessment was performed by immunostaining for the presence of α-smooth muscle actin.

Results: The deposition of collagen increased at six months of age in the SAMP vocal fold, and the level of collagen-1 mRNA increased with age. The myofibroblast protein α-smooth muscle actin was also found at a higher concentration in the SAMP vocal tissue. In contrast, the levels of hyaluronic acid in the vocal folds of SAMP mice decreased with age when compared to age-matched C57BL/6 mice.

Conclusion: SAMP mice show accelerated, age-related changes in the vocal fold that were evident at as early as six months of age. The use of senescence accelerated mice offers promise as a model to study age-related laryngeal changes.

Vocal fold bowing in elderly male monozygotic twins: a case study

This case study examined case histories, diagnostic features, and treatment response in two 79-year-old male monozygotic (identical) twins with vocal fold bowing, exploring both genetic and environmental factors. DNA concordance was examined via cheek swab. Case histories, videostroboscopy, auditory- and visual-perceptual assessment, electromyography, acoustic measures, and Voice Handicap ratings were undertaken. Both twins underwent surgical intervention and subsequent voice therapy. Monozygosity was confirmed for DNA polymorphisms, with 10 of 10 concordance for STR DNA markers. For both twins, auditory- and visual-perceptual assessments indicated severe bowing, hoarseness, and breathiness, although Twin 1 was judged to be extremely severe. Differences in reference to root-mean-square amplitudes were observed for thyroarytenoid and lateral cricoarytenoid muscles, with smaller relative amplitudes observed for the Twin 1 versus Twin 2. No consistent voice improvement was observed after surgical intervention(s), despite improved mid-membranous vocal fold closure. Marked reductions in Voice Handicap Index total scores were observed after behavioral voice therapy, coinciding with increased mid-membranous and posterior laryngeal (interarytenoid) glottal closure. No substantive differences in acoustic measures were observed. Vocal fold bowing was more severe for Twin 1 versus Twin 2 despite identical heritability factors. Overall voice improvement with treatment was greater for Twin 2 than Twin 1. Environmental factors might partially account for the differences observed between the twins, including variability in their responsiveness to behavioral voice therapy. Voice therapy was useful in improving mid-membranous and posterior laryngeal closure, although dysphonia remained severe in both cases.

Age-related blood flow changes in the rat intrinsic laryngeal muscles

CONCLUSIONS

These results indicate that a deceased laryngeal blood flow (BF) could be one contributing factor to age-related phonatory and airway dysfunction.

OBJECTIVE

Studies of non-laryngeal muscles suggest that decreased BF may contribute to an age-related decline in muscle performance. We hypothesized that there is an age-related BF decrease to the intrinsic laryngeal muscles.

MATERIALS AND METHODS

Intrinsic laryngeal muscle BF was measured in young (3-6 months old; n=11) and old (28-30 months old; n=21) male Fischer 344 rats during quiet respiration using the radiolabeled microsphere technique.

RESULTS

BF to the posterior cricoarytenoid (PCA) was very high even during this submaximal recruitment, consistent with its specialization for oxidative metabolism and fatigue resistance. The results demonstrated significant (p<0.05) age-related BF decreases in the thyroarytenoid (young, 163; old, 64 ml/min/100 g), cricothyroid (young, 104; old, 52 ml/min/100 g), and PCA (young, 404; old, 235 ml/min/100 g).

Palliative treatment of dysphonia and dysarthria

The focus of this article is the palliative treatment of a variety of dysphonic conditions. Symptomatic relief of hoarseness can be achieved by voice therapy, augmentative alternative communication modalities, and surgery. The causes of dysphonia addressed herein include amyotrophic lateral sclerosis, Parkinson's disease, multiple sclerosis, stroke, head and neck cancers requiring glossectomy or laryngectomy, unilateral vocal fold paralysis, and presbyphonia. Palliative treatment of dysphonia and voice disorders provides symptomatic relief but not a cure of the underlying disease state. For these patients there are a number of palliative interventions that can greatly improve their quality of life.

Dysphagia in the elderly

The capacity to swallow or eat is a basic human need and can be a great pleasure. Older adults look forward to sharing mealtimes and participating in social interactions. The loss of capacity to swallow and dine can have far-reaching implications. With age, the ability to swallow undergoes changes that increase the risk for disordered swallowing, with devastating health implications for older adults. With the growth in the aging population, dysphagia is becoming a national health care burden and concern. Upward of 40% of people in institutionalized settings are dysphagic. There is a need to address dysphagia in ambulatory, acute care, and long-term care settings.

Análise quantitativa das fibras mielínicas dos nervos laríngeos em humanos de acordo com a idade

INTRODUÇÃO E OBJETIVO: Realizar análise morfométrica das fibras mielínicas dos nervos laríngeos com a finalidade de verificar modificações quantitativas decorrentes do processo de envelhecimento. FORMA DE ESTUDO: Clínico e experimental. Material e Método: Foi coletado fragmento de 1cm dos nervos laríngeos superiores e nervos laríngeos recorrentes de 12 cadáveres do sexo masculino. A amostra foi dividida em dois grupos: idade inferior a 60 anos (Adulto) e idade igual ou superior a 60 anos (Idoso). O material foi avaliado em microscópio de luz acoplado a sistema analisador de imagem. RESULTADOS: O número total de fibras mielínicas do nervo laríngeo superior foi semelhante nos dois grupos etários, mas com tendência para o maior número de fibras de 1µm no grupo adulto (p=0,0744). O grupo adulto apresentou maior número total de fibras mielínicas no nervo laríngeo recorrente (p=0,0006), e esta diferença ocorreu nas fibras com diâmetros de 1-3µm (p<0,007). O grupo adulto apresentou maior número total de fibras mielínicas nos nervos laríngeos (soma das fibras dos nervos laríngeos superiores e dos nervos laríngeos recorrentes) que o grupo idoso (p<0,0091). CONCLUSÃO: O número total de fibras mielínicas dos nervos laríngeos é maior no grupo com idade inferior a 60 anos.

Quantitative analysis of myelinic fibers in human laryngeal nerves according to age

Introduction and aim

To carry out a morphometric analysis of myelinic fibers in laryngeal nerves aiming to identify quantitative changes as a result of aging. Study design: Clinical and experimental.

Material and Method

A 1cm fragment was collected from the superior laryngeal nerves and recurrent laryngeal nerves taken from twelve male cadavers. The sample was divided into two groups: those aged below 60 years (Adult) and those aged 60 years or more (Elderly). The material was evaluated under light microscopy coupled with an image analysis system.

Results

The total number of myelinic fibers from the superior laryngeal nerve was similar in both age groups; there was, however, a trend for a higher number of 1μm fibers in the adult group (p=0.0744). The adult group had a higher total number of myelinic fibers in the recurrent laryngeal nerve (p=0.0006), and this difference was seen in fibers with diameters betwee 1–3μm (p<0.007). The adult group had a higher total number of myelinic fibers in the laryngeal nerves (sum of superior laryngeal nerves and recurrent laryngeal nerves fibers) compared to the elderly group (p<0.0091).

Conclusion

The total number of myelinic fibers in laryngeal nerves is higher for the group aged below 60 years.

Stereological estimates indicate that aging does not alter the capillary length density in the human posterior cricoarytenoid muscle

Studies of some human skeletal muscles demonstrate an age-related capillarity decrease. An age-related decrease in blood flow to the posterior cricoarytenoid muscle (PCA) in rats has been reported, as well as a decreased ability to abduct the vocal folds. We, therefore, hypothesized that decreased muscle capillarity may contribute to PCA dysfunction in the elderly. Using immunological and stereological techniques, human PCAs (ages 18-98 yr; 28 men, 23 women) were examined for age-related changes in muscle fiber-type-specific and/or total capillary length density. While analysis shows no age-related changes in total muscle or fiber-type-specific capillary length densities (L(V cap)), there are significant age-related increases in L(V cap) within the interstitial tissue (P = 0.001) and in the ratio of the type I L(V cap) to type I surface (P = 0.002), with a strong trend for type II L(V cap) (P = 0.055). There is also an age-related decrease in the muscle fiber surface density for both type I and II fibers (P < 0.001 and 0.04, respectively). Data also show that women have a significantly higher type II L(V cap) (P = 0.039), regardless of age. In addition, with the exception of female type I L(V cap), all measured variables are significantly higher for type I fibers (P < 0.001), independent of age or sex. While data indicate there are age-related changes of capillary-muscle fiber relationships within the PCA, they do not support the hypothesis of an age-related loss of capillarity.

Aging thyroarytenoid and limb skeletal muscle: lessons in contrast

Voice production is vital throughout life because it allows for the communication of basic needs as well as the pursuit and enjoyment of social encounters. Unfortunately, for many older individuals the ability to produce voice is altered. Structural and functional declines in the neuromuscular system occur with aging and likely contribute to the modification of voice. One specific target of the aging process is the thyroarytenoid (TA) muscle, the primary muscle of voice production. The objectives of this overview article are to (1) share current findings related to the aging of limb skeletal muscle, (2) identify age-related morphological and physiological features of TA muscle, (3) compare and contrast age-related changes in TA with those in limb skeletal muscle, and (4) describe therapies for reversing sarcopenia in limb muscle and consider the applicability of these therapies for addressing vocal fold atrophy and age-related voice changes. The article shares current knowledge from the basic sciences related to skeletal muscle aging and compares/contrasts typical muscle aging to TA aging. Current evidence suggests that (1) the TA muscle undergoes notable remodeling with age, (2) aging of the TA is multifactorial, resulting from a myriad of neurologic, metabolic, and hormonal changes, many of which are distinct from the age-related processes of typical limb skeletal muscle, (3) investigation of the aging of the TA and its role in the aging of voice is in its infancy, and (4) potential behavioral and nonbehavioral therapies for reversing aging of the TA must be further examined.

Morphometric aspects of the human hypoglossal nerve in adults and the elderly

AIM

Perform a morphometric analysis of the myelinic fibers of the right hypoglossal nerve, in two age groups; to verify quantitative changes as a result of the aging process.

STUDY DESIGN

Anatomic.

MATERIAL AND METHOD

A 1 cm fragment of the right hypoglossal nerve was collected from 12 male corpses without any medical history of diseases such as: diabetes, alcoholism, and malignant neoplasia. The sample was divided in two groups: group with six corpses under sixty years old (adult), and another group with six corpses sixty years old or above (elderly). The material was fixed at 2.5% glutaldehyde and 2% paraformaldehyde solution; post-fixed at 2% osmium tetroxide; dehydrated with increasing ethanol concentrations, and included in epoxy resin. Semi-thin sections of 0.3 microm were obtaining, colored in 1% toluidine blue, and evaluated with light microscope combined with image analyzing system. The following morphometric data were quantified: intraperineural transversal section area, number, and diameter of the myelinic fibers.

RESULTS

The intraperineural area of the hypoglossal nerve was similar in both age groups (p=0.8691). The average area in the adult group was 1.697 mm2 and in the elderly group it was 1.649 mm2. The total number of myelinic fibers of the hypoglossal nerve was similar in both age groups (p=0.9018). The adult group presented an average of 10,286 +/- 2,308 myelinic fibers, and the elderly group presented an average of 10,141 +/- 1,590 myelinic fibers. A bimodal distribution of the myelinic fibers was observed, with a significant peak on the 9 microm fibers, and another smaller peak on the 2 microm fibers.

CONCLUSION

The intraperineural area and the total number of myelinic fibers of the right hypoglossal nerve are similar in both age groups.

Treatment of adductor-type spasmodic dysphonia by surgical myectomy: a preliminary report

OBJECTIVES

Despite the belief that it represents a central neurologic dysfunctional process, adductor-type spasmodic dysphonia without tremor is usually effectively treated by injection of botulinum toxin A; however, in most cases such injections must be repeated every few months. A promising new surgical procedure is herein reported.

METHODS

Under local anesthesia with intravenous sedation, a large laryngoplasty window is created, and under direct vision with intraoperative voice monitoring, fibers from the thyroarytenoid and lateral cricoarytenoid muscles are removed until breathiness occurs. The two sides are staged; that is, one side is done at a time, with surgery on the second side being performed 3 to 6 months after that on the first side, if needed.

RESULTS

This was a retrospective, unblinded study of 5 patients who underwent myectomy of the thyroarytenoid and lateral cricoarytenoid muscles. The preliminary results show improved voice fluency in all patients at 5 to 19 months of follow-up. There was no period of prolonged breathiness or dysphagia in any of the patients, and there were no surgical complications.

CONCLUSIONS

Myectomy of the thyroarytenoid and lateral cricoarytenoid muscles is a promising new surgical treatment for adductor-type spasmodic dysphonia that may effectively mimic "permanent" botulinum toxin injections.

Contractile dysfunction and altered metabolic profile of the aging rat thyroarytenoid muscle

The larynx and its muscles are important for ventilation, coughing, sneezing, swallowing, Valsalva's maneuver, and phonation. Because of their functional demands, the intrinsic laryngeal muscles have a unique phenotype: very small and fast fibers with high mitochondrial content. How aging affects their function is largely unknown. In this study, we tested the hypothesis that an intrinsic laryngeal muscle (thyroarytenoid muscle, a vocal fold adductor) would become weaker, slower, and fatigable with age. Muscles from Fischer 344 x Brown Norway F1 hybrid rats (6, 18, and 30 mo of age) were used for in vitro contractile function and histology. Thyroarytenoid muscles generated significantly lower twitch and tetanic forces at 30 mo vs. 6 and 18 mo. Maximal shortening velocity decreased by 20% at 30 mo (vs. 6 mo), and velocity of unloaded shortening was slower at 18 and 30 mo by 19 and 27% vs. 6 mo. There was no histochemical evidence of altered myosin ATPase activity at 18 or 30 mo of age. Fatigue resistance was significantly decreased at 18 and 30 mo. We also found abundant mitochondrial clusters and ragged red fibers in the muscles of 30-mo-old rats, and there was an age-related increase in glycogen-positive fibers. We conclude that rat thyroarytenoid muscles become weaker, slower, and more fatigable with age. These functional changes are not due to alterations in myosin ATPase activity, but a switch in the expression of myosin isoforms remains a possibility. Finally, the alterations in mitochondrial and glycogen content indicate a shift in the metabolic characteristics of these muscles with age.

Muscle fiber type composition and effects of vocal fold immobilization on the two compartments of the human posterior cricoarytenoid: a case study of four patients

The human posterior cricoarytenoid (PCA) muscle is divided into two compartments, the vertical and horizontal bellies, which contain differences in their myosin heavy chain (MyHC) composition. Using immunohistochemical techniques on whole PCA samples, this study provides a more thorough description of the fiber type composition of entire bellies of the PCA. Four patients provided complete PCA samples containing both compartments of their right and left sides; two with unilaterally immobilized vocal folds. The horizontal belly had 80% slow (type I) fibers and 20% fast (type II) fibers. The vertical belly contained equal amounts of slow and fast fibers (approximately 55%:45%); clearly distinguishing between two compartments. Atrophy of muscle fibers and fiber type grouping were also present in both normal and affected subjects; providing no clear confirmation of the clinical findings of vocal fold immobilization. Further study of the PCA muscle from patients with unilaterally immobilized vocal folds is needed.

Age-related changes in sensory and secretomotor nerve endings in the larynx of F344/N rat

The aim of the present study was to define the age-related changes in sensory and secretomotor nerve endings in the larynx of F344/N rats. For this purpose, laryngeal tissue sections obtained from 12-, 24- and 35-month-old F344/N rats were compared with respect to the density, distribution and morphology of various types of sensory and secretomotor nerve endings immunoreactive for protein gene product 9.5 (PGP 9.5), calcitonin gene-related peptide (CGRP) and substance P (SP). Two distinct forms of PGP 9.5-immunoreactive motor end-plates were noted; the large sized motor end-plates localized in thyroarytenoid and cricoarytenoid muscles were degenerated in aged rats, while the small sized motor end-plates, localized predominantly in vocal muscles, did not show any age-related changes. CGRP- and SP-immunoreactive nerve fibres of the laryngeal glands did not show any age-related changes. Subepithelial laminar nerve endings immunoreactive to PGP 9.5 showed degeneration with ageing. Aggregates of terminal arborisations in the subepithelial region were smaller in aged animals. PGP 9.5-immunostained taste cells and well-developed subgemmal network were abundant in 12- and 24-month-old rats, but only a few were noted in aged rats. The total number of taste buds decreased significantly with ageing. CGRP- and SP-immunostained taste bud-nerve endings were noted in 12- and 24-month-old rats, but only rarely in 35-month-old rats. The laryngeal epithelium contained PGP 9.5-, CGRP- and SP-immunoreactive thin free nerve endings with many varicosities; their number and distribution were similar between 12- and 24-month-old rats, while only a few endings were observed in 35-month-old rats. Our results indicated that ageing is associated with the reduction of laryngeal sensory and secretomotor nerve endings.

Neuromuscular junction changes in aged rat thyroarytenoid muscle

Dynamic remodeling of neuromuscular junction (NMJ) structure is postulated as a cause of age-related muscular atrophy. Direct study of NMJ morphology in laryngeal muscles is important to our understanding of age-related decrements in voice and swallowing. The morphology of NMJs was studied in a rat model to compare young and old specimens of thyroarytenoid muscle--a muscle critical to airway protection and phonation. Fluorescent, triple-label immunohistochemical analysis and confocal microscopic visualization were used to analyze the structure of NMJs. We found that laryngeal NMJs underwent significant changes that were similar to those observed after denervation. Specifically, the axon terminal area was significantly reduced, there were a number of postsynaptic acetylcholine receptor areas unoccupied by nerve terminals, and there was increased variability in end plate architecture in the old muscles. The results of this study increase our understanding of the age-related morphological changes in the larynx, and may serve as a baseline to test the effectiveness of future interventions.

Unloaded shortening velocity and myosin heavy chain variations in human laryngeal muscle fibers

Myosin description in human laryngeal muscles is incomplete, but evidence suggests the presence of type I, IIA, IIX, and tonic myosin heavy chain (MHC) fibers. This study describes the unloaded shortening velocity (V0) of chemically skinned laryngeal muscle fibers measured by the slack test method in relation to MHC content. Skeletal fibers from human laryngeal and limb muscle biopsy specimens were obtained for determination of V0, and subsequently, glycerol-sodium dodecyl sulfate-polyacrylamide gel electrophoresis was used to determine the MHC isoform content. The fibers from human limb muscle had shortening speeds similar to those in previous reports on human skeletal fibers. Type I, IIA, and IIX fibers of laryngeal muscle had shortening speeds similar to those of fibers from limb muscle, but laryngeal fibers with heterogeneous MHC expression had a wide range of shortening speeds, some being nearly twice as fast as limb fibers. In addition, MHC isoform bands from human extraocular muscle comigrated with some bands from laryngeal muscle--a finding suggesting that extraocular myosin may also be expressed.

Muscle fiber and satellite cell apoptosis in the aging human thyroarytenoid muscle: a stereological study with confocal laser scanning microscopy

OBJECTIVE

This study determines the role of changes in numerical densities of apoptotic myonuclei and satellite cells in age-related remodeling of the thyroarytenoid muscle (TA).

DESIGN

Changes in numerical densities of apoptotic myonuclei and satellite cells were estimated for the entire TA by using stereological techniques.

RESULTS

There was an increase in N(V apoptotic myonucleus, fiber type) (P < 0.05) and in the percentage of apoptotic myonuclei (P < 0.05) in type 1 but not in type 2 muscle fibers. There was also an increase in N(V apoptotic satellite cell, fiber type) (P < 0.05) and in the percentage of apoptotic satellite cells (P < 0.05) in type 1 fibers but not in type 2 fibers.

CONCLUSION

Apoptosis may contribute to age-related fiber loss and atrophy in the TA.

SIGNIFICANCE

Therapeutic techniques based on decreasing the frequency of apoptosis may block age-related fiber loss and atrophy in the TA.

Numerical densities of myonuclei and satellite cells in muscle fiber types in the aging human thyroarytenoid muscle: an immunohistochemical and stereological study using confocal laser scanning microscopy

OBJECTIVE

This study determines the role of changes in numerical densities of myonuclei and satellite cells in age-related remodeling of the thyroarytenoid muscle (TA).

DESIGN

Changes in numerical densities (N(V)) and ratios (N(N)) of myonuclei and satellite cells were estimated for the entire TA by use of stereological techniques.

RESULTS

There was no age-related change or difference between fiber types for N(V myonucleus, fiber), but N(V myonucleus, fiber) increased with decreasing fiber diameter. There was a trend toward a decrease in N(V satellite cell, fiber) and a decrease in N(N satellite cell, myonucleus). N(V satellite cell, fiber) was higher for type 1 than for type 2 fibers, and type 1 satellite cells increased disproportionately with increasing total satellite cell numerical density.

CONCLUSION

Decreased satellite cell proliferation may contribute to age-related fiber loss and atrophy in the TA.

SIGNIFICANCE

Therapeutic techniques based on activation of satellite cells may block age-related fiber loss and atrophy in the TA.

Aging effects on motor units in the human thyroarytenoid muscle

OBJECTIVES

To determine whether age differences are present in the human laryngeal thyroarytenoid muscle that would indicate that different normative values would be needed for identifying motor unit abnormalities.

STUDY DESIGN

Twenty-six consecutively recruited healthy subjects between the ages of 21 and 72 years participated in a laryngeal electromyography study.

METHODS

Bipolar needle electrodes were used to record motor unit action potentials from several locations in the right and left thyroarytenoid muscles of each subject. The duration of a motor unit was measured when at least 10 firings of the same motor unit could be identified. On the average, four units were measured per muscle.

RESULTS

In the subjects less than 60 years of age, motor unit duration did not increase significantly with age. However, motor units from subjects greater than 60 years of age had longer durations than those from subjects less than 60 years of age (P < .00005), and 25% of the units measured in subjects greater than 60 years of age had longer durations than any of the units measured in subjects less than 60 years of age. Further, the older subjects differed from each other in their mean unit durations (P < .0001). In subjects less than 60 years of age, significantly longer durations were found for units innervated by the longer, left-side recurrent laryngeal nerve in comparison with the right-side nerve (P = .005).

CONCLUSIONS

Different mean and SD values should be used for patients less than and greater than 60 years of age and for the right and left sides, when evaluating motor units in the thyroarytenoid muscles.