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

Cross-Cultural Adaptation and Validation of the Vocal Fatigue Index (VFI) to Danish

OBJECTIVES

The aim was to cross-culturally adapt and validate the Vocal Fatigue Index (VFI) to Danish (DK-VFI).

STUDY DESIGN

Cross-sectional design.

METHODS

The original American English VFI was cross-culturally adapted to Danish using a forward-backward translation procedure combined with focus group interviews. The DK-VFI was distributed to 26 patients with vocal fatigue (VF) and 103 vocally healthy controls. A matched subsample based on age and sex of the control group was included. Internal consistency was determined using Cronbach's alpha and test-retest reliability was determined using Spearman's Rho as well as Wilcoxon signed-rank tests. Validity was confirmed using the Wilcoxon rank-sum test. Sensitivity and specificity were assessed using the Receiver Operating Characteristics test and the discriminative ability was determined using the Area Under the Curve (AUC) test. The original VFI consists of three factors, and cutoff values were calculated for each separate factor in the DK-VFI.

RESULTS

Minor changes were made in the phrasing of specific questions in order to appropriate the VFI to the Danish language. The internal consistency for the DK-VFI was high, with a Cronbach's alpha of α = 0.95. The results showed statistically significant differences (P < 0.05) in mean scores of the DK-VFI between patients and controls. The cutoff values between patients and controls for each separate factor were ≥11.5 for factor 1, ≥2.5 for factor 2, and ≤5.5 for factor 3. The results of the AUC analysis showed that the DK-VFI has discriminative abilities of 0.94 for factor 1, 0.92 for factor 2, and 0.82 for factor 3. Analysis of test-retest reliability showed strong reliability for the patient group and acceptable reliability for the control group.

CONCLUSION

The DK-VFI is a valid and reliable tool for identifying symptoms of VF and can sensitively discriminate people with VF from vocally healthy controls.

Effect of Diabetes Mellitus Type 2 on Voice: A Systematic Review and Meta-Analysis

INTRODUCTION

Diabetes mellitus type 2 is a growing health concern that affects several systems in the body, among which is the phonatory apparatus. Voice may be affected in view of the high prevalence of myopathy and neuropathy in diseased subjects. The authors aimed to answer the following question: does type 2 diabetes have an effect on voice?

METHODS

The systematic review included search terms such as "speech, voice, larynx, glucose, diabetes, and hyperglycemia." The search strategy yielded 221 articles, only five of which satisfied the inclusion criteria. Articles were considered for inclusion using the PRISMA method. Analysis included 321 patients with type 2 diabetes mellitus and 171 controls. All studies included were case-control studies except for one study which was an observational cohort. Six parameters were chosen as endpoints for the systematic review and meta-analysis: the presence/absence of voice complaints, fundamental frequency, jitter, shimmer, noise-to-harmonic ratio, and maximum phonation time.

RESULTS

There was no significant difference in the prevalence of voice complaints (i.e., hoarseness) between diabetic patients and control groups. There was also no significant difference in any of the acoustic and aerodynamic measures between patients with type 2 diabetes and controls. These findings can be ascribed to the high resilience of the laryngeal muscles to the adverse effect of systemic diseases.

CONCLUSION

There is no consensus in the literature that the prevalence of voice symptoms in diabetic patients is significantly higher than that reported in healthy subjects.

A review of the peripheral proprioceptive apparatus in the larynx

The larynx is an organ of the upper airway that participates in breathing, glutition, voice production, and airway protection. These complex functions depend on vocal fold (VF) movement, facilitated in turn by the action of the intrinsic laryngeal muscles (ILM). The necessary precise and near-instantaneous modulation of each ILM contraction relies on proprioceptive innervation of the larynx. Dysfunctional laryngeal proprioception likely contributes to disorders such as laryngeal dystonia, dysphagia, vocal fold paresis, and paralysis. While the proprioceptive system in skeletal muscle derived from somites is well described, the proprioceptive circuitry that governs head and neck structures such as VF has not been so well characterized. For over two centuries, researchers have investigated the question of whether canonical proprioceptive organs, muscle spindles, and Golgi tendon organs, exist in the ILM, with variable findings. The present work is a state-of-the-art review of the peripheral component of laryngeal proprioception, including current knowledge of canonical and possible alternative proprioceptive circuitry elements in the larynx.

Study on Normal Laryngeal Electromyography of Thyroarytenoid Muscle, Cricothyroid Muscle, and Posterior Cricoarytenoid Muscle

OBJECTIVE

The aim of this study was to investigate the physiological activity of intrinsic laryngeal muscle under different functional states of larynx by measuring the normal laryngeal electromyography parameters.

METHODS

Laryngeal electromyography (EMG) was performed in 112 patients with unilateral vocal cord movement disorder. The duration and amplitude of the motor unit potential (MUP) of the thyroarytenoid muscle (TA), posterior cricoarytenoid muscle (PCA), and cricothyroid muscle (CT) were measured when patients were asked to make a deep inspiration and phonate /i/. The normal side of the patients' vocal chords was used as the research object.

RESULTS

(1) The motor unit potential of TA, CT, and PCA were measured when inspiration and phonating /i/. Waveforms were normal. (2) There were significant differences in duration of TA between inspiration and phonating /i/ in comfortable tone. (3) When comparing the duration and amplitude of any 2 of TA, CT, and PCA during inspiration and phonating /i/, there were significant differences in duration between CT and PCA when phonating /i/ only. There were no significant differences in any other comparisons.

CONCLUSIONS

Under either deep inspiration or pronunciation, the TA, CT, and PCA muscles were activated. The TA may play a major role in phonating. The PCA may play a major role in the action of deep inspiration.

Absence of developmental and unconventional myosin heavy chain in human suprahyoid muscles

INTRODUCTION

Contradictory reports of the myosin heavy chain (MHC) composition of adult human suprahyoid muscles leave unresolved the extent to which these muscles express developmental and unconventional MHC.

METHODS

By immunohistochemistry, separation sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE)-Coomassie, separation SDS-PAGE-Western blot, and mRNA PCR, we tested for conventional MHCI, MHCIIA, MHCIIX, developmental MHC embryonic and MHC neonatal, and unconventional MHC alpha-cardiac, MHC extraocular, and MHC slow tonic in adult human anterior digastric (AD), geniohyoid (GH), and mylohyoid (MH) muscles.

RESULTS

By separation SDS-PAGE-Coomassie and Western blot, only conventional MHC are present. By immunohistochemistry all muscle fibers are positive for MHCI, MHCIIA, or MHCIIX, and fewer than 4 fibers/mm(2) are positive for developmental or unconventional MHC. By PCR, mRNA of MHCI and MHCIIA dominate, with sporadically detectable MHC alpha-cardiac and without detectable mRNA of other developmental and unconventional MHC.

CONCLUSIONS

We conclude that human suprahyoid muscles AD, GH, and MH are composed almost exclusively of conventional MHC isoforms.

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.

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.

Neurotrophin expression of laryngeal muscles in response to recurrent laryngeal nerve transection

OBJECTIVE/HYPOTHESIS

The recurrent laryngeal nerve (RLN) commonly regenerates after injury; however, functional motion is rarely recovered. Animal experiments have documented aberrant reinnervation after nerve transection, with motor axons reaching inappropriate muscles. More recently, experimental results suggest that lack of vocal fold motion after RLN injury is due to preferential reinnervation of adductor muscles, with inadequate reinnervation of the posterior cricoarytenoid muscle (PCA), the only abductor muscle of the larynx. Information on factors that could influence the receptiveness of these muscles to reinnervation could be useful in developing new therapeutic strategies. It is hypothesized that the thyroarytenoid muscle (TA) and the PCA differ in expression of neurotrophins in response to denervation.

STUDY DESIGN

Laboratory experiment.

METHODS

Rats were sacrificed at 3 days, 6 weeks, or 4 months after unilateral RLN injury measure expression of brain-derived nerve growth factor (BDNF), nerve growth factor (NGF), and neurotrophin 4 (NT-4) in the TA and PCA muscles, using immunohistochemistry. We also assessed nerve regeneration.

RESULTS

NGF was significantly diminished in the denervated TA muscle at 3 days after injury and increased at 6 weeks. BDNF expression was unchanged in the TA, but was diminished in both PCA muscles at 3 days and 6 weeks, returning to near-normal levels at 4 months after injury. Robust nerve regeneration of distal RLN was present at 4 months.

CONCLUSIONS

Results suggest that the TA and PCA muscles respond differently to denervation.

Myosin heavy-chain composition of the human hyoglossus muscle

The human tongue muscle hyoglossus (HG) is active in oromotor behaviors encompassing a wide range of tongue movement speeds. Here we test the hypothesis that the human HG is composed of "uncommon" myosin heavy-chain (MHC) isoforms MHCembryonic, MHCneonatal, and MHCslow tonic as has been reported for other head and neck muscles active during kinematically diverse behaviors. Following reaction of human HG with antibodies specific for MHCI, MHCIIA, MHCII, MHCembryonic, MHCextraocular, MHCneonatal, and MHCslow tonic, only antibodies to MHCI, MHCIIA, and MHCII label more than occasional muscle fibers. These antibodies describe five phenotypes with prevalence MHCIIA > MHCI > MHCI-IIX > MHCI-IIA > MHCIIX. In MHC composition, the human HG is thus similar to human appendicular muscles and many human head and neck muscles but different from human masseter and extraocular muscles which contain five or more MHC isoforms.

Neuroanatomy of the equine dorsal cricoarytenoid muscle: surgical implications

REASON FOR PERFORMING STUDY

Studies are required to define more accurately and completely the neuroanatomy of the equine dorsal cricoarytenoid muscle as a prerequisite for developing a neuroprosthesis for recurrent laryngeal neuropathy.

OBJECTIVES

To describe the anatomy, innervation, fibre types and function of the equine dorsal cricoarytenoid muscle.

METHODS

Thirty-one larynges were collected at necropsy from horses with no history of upper airway disease and 25 subjected to gross dissection. Thereafter, the following preparations were made on a subset of larynges: histochemical staining (n = 5), Sihler's and acetylcholinesterase staining for motor endplates (n = 2). An additional 6 larynges were collected and used for a muscle stimulation study.

RESULTS

Two neuromuscular compartments (NMC), each innervated by a primary nerve branch of the recurrent laryngeal nerve, were identified in all larynges. Stimulation of the lateral NMC produced more lateral displacement of the arytenoid cartilage than the medial NMC (P<0.05). The medial NMC tended to rotate the arytenoid cartilage dorsally. Motor endplates were identified at the junction of the middle and caudal thirds of each NMC. If fibre type grouping was present it was always present in both NMCs.

CONCLUSIONS

The equine dorsal cricoarytenoid muscle has 2 distinct muscle NMCs with discrete innervation and lines of action. The lateral NMC appears to have a larger role in increasing cross-sectional area of the rima glottidis.

POTENTIAL RELEVANCE

This information should assist in planning surgical reinnervation procedures and development of a neuroprosthesis for recurrent laryngeal neuropathy.

Quantification of myosin heavy chain RNA in human laryngeal muscles: differential expression in the vertical and horizontal posterior cricoarytenoid and thyroarytenoid

BACKGROUND

Human laryngeal muscles are composed of fibers that express type I, IIA, and IIX myosin heavy chains (MyHC), but the presence and quantity of atypical myosins such as perinatal, extraocular, IIB, and alpha (cardiac) remain in question. These characteristics have been determined by biochemical or immunohistologic tissue sampling but with no complementary evidence of gene expression at the molecular level. The distribution of myosin, the main motor protein, in relation to structure-function relationships in this specialized muscle group will be important for understanding laryngeal function in both health and disease.

OBJECTIVES

We determined the quantity of MyHC genes expressed in human posterior cricoarytenoid (PCA) and thyroarytenoid (TA) muscle using real-time quantitative reverse-transcriptase polymerase chain reaction in a large number of samples taken from laryngectomy subjects. The PCA muscle was divided into vertical (V) and horizontal (H) portions for analysis.

RESULTS AND CONCLUSIONS

No extraocular or IIB myosin gene message is present in PCA or TA, but IIB is expressed in human extraocular muscle. Low but detectable amounts of perinatal and alpha gene message are present in both of the intrinsic laryngeal muscles. In H- and V-PCA, MyHC gene amounts were beta greater than IIA greater than IIX, but amounts of fast myosin RNA were greater in V-PCA. In TA, the order was beta greater than IIX greater than IIA. The profiles of RNA determined here indicate that, in humans, neither PCA nor TA intrinsic laryngeal muscles express unique very fast-contracting MyHCs but instead may rely on differential synthesis and use of beta, IIA, and IIX isoforms to perform their specialized contractile functions.

Vocal fatigue and its relation to vocal hyperfunction †

This article reviews current literature on vocal fatigue and considers its potential relationship to vocal hyperfunction. Vocal fatigue is defined by its symptoms. Specifically, the voice user perceives an increase in phonatory effort over time that may be accompanied by decreased phonatory function. Vocal fatigue can present as a pure condition, such that no specific aetiology is apparent, or as a component of other voice disorders. The underlying bases of vocal fatigue appear to include the neurophysiological and biomechanical effects of extended periods of phonation. It can also be a function of strategies used to adapt to extended periods of phonation, such as the use of excessive muscular tension and suboptimal vocal fold posturing. Studies that have attempted to identify observable responses that are reliably associated with vocal fatigue have met with limited success, but recent advances in research methodology are promising. This review addresses current approaches to the study of vocal fatigue, especially regarding subject selection, design variables, and measurement variables. Future studies should address the relationship between vocal fatigue and other voice disorders, differences in individual responses to vocal-loading tasks, and differential evaluation and management of the neuromuscular, biomechanical, and central processes involved in vocal fatigue.

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.

Refinements in modeling the passive properties of laryngeal soft tissue

The nonlinear viscoelastic passive properties of three canine intrinsic laryngeal muscles, the lateral cricoarytenoid (LCA), the posterior cricoarytenoid (PCA), and the interarytenoid (IA), were fit to the parameters of a modified Kelvin model. These properties were compared with those of the thyroarytenoid (TA) and cricothyroid (CT) muscles, as well as previously unpublished viscoelastic characteristics of the human vocal ligament. Passive parameters of the modified Kelvin model were summarized for the vocal ligament, mucosa, and all five laryngeal muscles. Results suggest that the LCA, PCA, and IA muscles are functionally different from the TA and CT muscles in their load-bearing capacity. Furthermore, the LCA, PCA, and IA have a much larger stress-strain hysteresis effect than has been previously reported for the TA and CT or the vocal ligament. The variation in this effect suggests that the connective tissue within the TA and CT muscles is somehow similar to the vocal ligament but different from the LCA, PCA, or IA muscles. Further demonstrating the potential significance of grouping tissues in the laryngeal system by functional groups in the laryngeal system was the unique finding that, over their working elongation range, the LCA and PCA were nearly as exponentially stiff as the vocal ligament. This paper was written in conjunction with an online technical report (http://www.ncvs.org/ncvs/library/tech) in which comprehensive muscle data and sensitivity analysis, as well as downloadable data files and computer scripts, are made available.

Anatomy and fiber type composition of human interarytenoid muscle

Intrinsic laryngeal muscle investigations, especially those of the interarytenoid (IA) muscle, have been primarily teleologically based. We determined IA muscle anatomy and histochemical and immunohistochemical classification of extrafusal and intrafusal (muscle spindle) fibers in 5 patients. Extrafusal fibers were oxidative type I and glycolytic types IIA and IIX. Intrafusal fibers of muscle spindles were identified by the presence of tonic and neonatal myosin. The results demonstrate that the IA muscle has a phenotype similar to that of limb skeletal muscle. Myosin coexpression, the absence of intrafusal fibers, and fiber type grouping were unusual features found previously in the thyroarytenoid and posterior cricoarytenoid muscles, but they were not present in the IA muscle. These findings lead to the conclusion that the IA muscle has functional significance beyond its assumed importance in maintaining vocal fold position during phonation. The presence of spindles demonstrates differences in motor control as compared to the thyroarytenoid and posterior cricoarytenoid muscles. Further, extrafusal fiber characteristics implicate IA muscle involvement in muscle tension dysphonia and adductor spasmodic dysphonia. Given the unique physiologic characteristics of the human IA muscle, further research into the role of the IA muscle in voice disorders is warranted.

Staining of human thyroarytenoid muscle with myosin antibodies reveals some unique extrafusal fibers, but no muscle spindles

This study describes the myosin composition of extrafusal and intrafusal muscle fibers found in the human thyroarytenoid (TA) and sternohyoid (control) muscles. We sought to determine the presence of muscle spindles in the TA muscle, and to identify unusual extrafusal fiber types, using the commonly accepted approach of tissue staining with myosin isoform specific antibodies. Extrafusal fibers are organized into motor units, which subsequently produce muscle movement, whereas intrafusal fibers compose muscle spindles, the primary stretch receptor that provides afferent (feed back) information to the nervous system for regulation of motor unit length and tonicity. Immunohistochemical identification of muscle spindles was confirmed in sternohyoid, but not in TA samples; however, some extrafusal fibers contained tonic myosin. These results indicate that human TA muscle functions similar to some mammalian extraocular muscle, performing unloaded (non-weight bearing) contractions without afferent information from native muscle spindles.

Specialized cranial muscles: how different are they from limb and abdominal muscles?

Mammalian skeletal muscle fibers can be classified into functional types by the heavy chain (MyHC) and light chain (MyLC) isoforms of myosin (the primary motor protein) that they contain. Most human skeletal muscle contains fiber types and myosin isoforms I, IIA and IIX. Some highly specialized muscle fibers in human extraocular and jaw-closing muscles express either novel myosins or unusual combinations of isoforms of unknown functional significance. Extrinsic laryngeal muscles may express the extraocular MyHC isoform for rapid contraction and a tonic MyHC isoform for slow tonic contractions. In jaw-closing muscles, fiber phenotypes and myosin expression have been characterized as highly unusual. The jaw-closing muscles of most carnivores and primates have tissue-specific expression of the type IIM or 'type II masticatory' MyHC. Human jaw-closing muscles, however, do not contain IIM myosin. Rather, they express myosins typical of developing or cardiac muscle in addition to type I, IIA and IIX myosins, and many of their fibers are hybrids, expressing two or more isoforms. Fiber morphology is also unusual in that the type II fibers are mostly of smaller diameter than type I. By combining physiological and biochemical techniques it is possible to determine the maximum velocity of unloaded shortening (V(o)) of an individual skeletal muscle fiber and subsequently determine the type and amount of myosin isoform. When analyzed, some laryngeal fibers shorten at much faster rates than type II fibers from limb and abdominal muscle. Yet some type I fibers in masseter show an opposite trend towards speeds 10-fold slower than type I fibers of limb muscle. These unusual shortening velocities are most probably regulated by MyHC isoforms in laryngeal fibers and by MyLC isoforms in masseter. For the jaw-closing muscles, this finding represents the first case in human muscle of physiological regulation of kinetics by light chains. Together, these results demonstrate that, compared to other skeletal muscles, cranial muscles have a wider repertoire of contractile protein expression and function. Molecular techniques for reverse transcription of mRNA and amplification by polymerase chain reaction have been applied to typing of single fibers isolated from limb muscles, successfully identifying pure type I, IIA and IIX and hybrid type I/IIA and IIA/IIX fibers. This demonstrates the potential for future studies of the regulation of gene expression in jaw-closing and laryngeal muscles, which have such a variety of complex fiber types fitting them for their roles in vivo.