A muscle controlled finite-element model of laryngeal abduction and adduction

A three-dimensional finite-element model was developed to simulate the complex movement of the laryngeal cartilages during vocal fold abduction and adduction. The model consists of cricoid and arytenoid cartilages, as well as the intralaryngeal muscles and vocal folds. The active and passive properties of the muscles were idealised by one-dimensional elements based on the Hill theory. Its controlling input value is a time dependent stimulation rate. Optimisation loops have been carried out for the arrangement of the individual stimulation rates. Since in vivo measurements are not feasible, the developed biomechanical model shall be used to analyse the force distribution within the laryngeal muscles during phonatory manoeuvres. Simulations of abduction and adduction in different pitches of voice lead to realistic tensions of the vocal folds. The model is a first step to analyse motional vocal fold diseases and to predict the consequences of phonosurgical interventions.     

Predicting Achievable Fundamental Frequency Ranges in Vocalization Across Species

Vocal folds are used as sound sources in various species, but it is unknown how vocal fold morphologies are optimized for different acoustic objectives. Here we identify two main variables affecting range of vocal fold vibration frequency, namely vocal fold elongation and tissue fiber stress. A simple vibrating string model is used to predict fundamental frequency ranges across species of different vocal fold sizes. While average fundamental frequency is predominantly determined by vocal fold length (larynx size), range of fundamental frequency is facilitated by (1) laryngeal muscles that control elongation and by (2) nonlinearity in tissue fiber tension. One adaptation that would increase fundamental frequency range is greater freedom in joint rotation or gliding of two cartilages (thyroid and cricoid), so that vocal fold length change is maximized. Alternatively, tissue layers can develop to bear a disproportionate fiber tension (i.e., a ligament with high density collagen fibers), increasing the fundamental frequency range and thereby vocal versatility. The range of fundamental frequency across species is thus not simply one-dimensional, but can be conceptualized as the dependent variable in a multi-dimensional morphospace. In humans, this could allow for variations that could be clinically important for voice therapy and vocal fold repair. Alternative solutions could also have importance in vocal training for singing and other highly-skilled vocalizations.     

Ventrolateral medullary respiratory network participation in the expiration reflex in the cat.

The expiration reflex is a distinct airway defensive response characterized by a brief, intense expiratory effort and coordinated adduction and abduction of the laryngeal folds. This study addressed the hypothesis that the ventrolateral medullary respiratory network participates in the reflex. Extracellular neuron activity was recorded with microelectrode arrays in decerebrated, neuromuscular-blocked, ventilated cats. In 32 recordings (17 cats), 232 neurons were monitored in the rostral (including B?tzinger and pre-B?tzinger complexes) and caudal ventral respiratory group. Neurons were classified by firing pattern, evaluated for spinal projections, functional associations with recurrent laryngeal and lumbar nerves, and firing rate changes during brief, large increases in lumbar motor nerve discharge (fictive expiration reflex, FER) elicited during mechanical stimulation of the vocal folds. Two hundred eight neurons were respiratory modulated, and 24 were nonrespiratory; 104 of the respiratory and 6 of the nonrespiratory-modulated neurons had altered peak firing rates during the FER. Increased firing rates of bulbospinal neurons and expiratory laryngeal premotor and motoneurons during the expiratory burst of FER were accompanied by changes in the firing patterns of putative propriobulbar neurons proposed to participate in the eupneic respiratory network. The results support the hypothesis that elements of the rostral and caudal ventral respiratory groups participate in generating and shaping the motor output of the FER. A model is proposed for the participation of the respiratory network in the expiration reflex.     

Reinnervation of Bilateral Posterior Cricoarytenoid Muscles Using the Left Phrenic Nerve in Patients with Bilateral Vocal Fold Paralysis

Objective

To evaluate the feasibility, effectiveness, and safety of reinnervation of the bilateral posterior cricoarytenoid (PCA) muscles using the left phrenic nerve in patients with bilateral vocal fold paralysis.

Methods

Forty-four patients with bilateral vocal fold paralysis who underwent reinnervation of the bilateral PCA muscles using the left phrenic nerve were enrolled in this study. Videostroboscopy, perceptual evaluation, acoustic analysis, maximum phonation time, pulmonary function testing, and laryngeal electromyography were performed preoperatively and postoperatively. Patients were followed-up for at least 1 year after surgery.

Results

Videostroboscopy showed that within 1 year after reinnervation, abductive movement could be observed in the left vocal folds of 87% of patients and the right vocal folds of 72% of patients. Abductive excursion on the left side was significantly larger than that on the right side (P < 0.05); most of the vocal function parameters were improved postoperatively compared with the preoperative parameters, albeit without a significant difference (P > 0.05). No patients developed immediate dyspnea after surgery, and the pulmonary function parameters recovered to normal reference value levels within 1 year. Postoperative laryngeal electromyography confirmed successful reinnervation of the bilateral PCA muscles. Eighty-seven percent of patients in this series were decannulated and did not show obvious dyspnea after physical activity. Those who were decannulated after subsequent arytenoidectomy were not included in calculating the success rate of decannulation.

Conclusions

Reinnervation of the bilateral PCA muscles using the left phrenic nerve can restore inspiratory vocal fold abduction to a physiologically satisfactory extent while preserving phonatory function at the preoperative level without evident morbidity.     

Functional electrical stimulation of intrinsic laryngeal muscles under varying loads in exercising horses

Bilateral vocal fold paralysis (BVCP) is a life threatening condition and appears to be a good candidate for therapy using functional electrical stimulation (FES). Developing a working FES system has been technically difficult due to the inaccessible location and small size of the sole arytenoid abductor, the posterior cricoarytenoid (PCA) muscle. A naturally-occurring disease in horses shares many functional and etiological features with BVCP. In this study, the feasibility of FES for equine vocal fold paralysis was explored by testing arytenoid abduction evoked by electrical stimulation of the PCA muscle. Rheobase and chronaxie were determined for innervated PCA muscle. We then tested the hypothesis that direct muscle stimulation can maintain airway patency during strenuous exercise in horses with induced transient conduction block of the laryngeal motor nerve. Six adult horses were instrumented with a single bipolar intra-muscular electrode in the left PCA muscle. Rheobase and chronaxie were within the normal range for innervated muscle at 0.55±0.38 v and 0.38±0.19 ms respectively. Intramuscular stimulation of the PCA muscle significantly improved arytenoid abduction at all levels of exercise intensity and there was no significant difference between the level of abduction achieved with stimulation and control values under moderate loads. The equine larynx may provide a useful model for the study of bilateral fold paralysis.     

Elasticity and stress relaxation of a very small vocal fold

Across mammals many vocal sounds are produced by airflow induced vocal fold oscillation. We tested the hypothesis that stress-strain and stress-relaxation behavior of rat vocal folds can be used to predict the fundamental frequency range of the species' vocal repertoire. In a first approximation vocal fold oscillation has been modeled by the string model but it is not known whether this concept equally applies to large and small species. The shorter the vocal fold, the more the ideal string law may underestimate normal mode frequencies. To accommodate the very small size of the tissue specimen, a custom-built miniaturized tensile test apparatus was developed. Tissue properties of 6 male rat vocal folds were measured. Rat vocal folds demonstrated the typical linear stress-strain behavior in the low strain region and an exponential stress response at strains larger than about 40%. Approximating the rat's vocal fold oscillation with the string model suggests that fundamental frequencies up to about 6 kHz can be produced, which agrees with frequencies reported for audible rat vocalization. Individual differences and time-dependent changes in the tissue properties parallel findings in other species, and are interpreted as universal features of the laryngeal sound source.     

Mechanical stress during phonation in a self-oscillating finite-element vocal fold model

The stress information during phonation in the vocal folds is helpful in understanding the etiologies of vocal trauma and its related vocal diseases, such as nodules. In this paper, a self-oscillating finite-element model, which combines aerodynamic properties, tissue mechanics, airflow-tissue interactions, and vocal fold collisions, was used to simulate the vocal fold vibration during phonation. The spatial and temporal characteristics of mechanical stress in the vocal folds were predicted by this model. Temporally, it was found that mechanical stress periodically undulates with vibration of the vocal folds and that vocal fold impact causes a jump in the normal stress value. Spatially, the normal stress is significantly higher on the vocal fold surface than inside of the vocal folds. At the midpoint of the medial surface, the peak-to-peak amplitude of the normal stress reaches its maximum value. Using different lung pressures (0-1.5kPa) to drive the self-oscillating model, we found that lower lung pressure can effectively decrease the mechanical stress in the vocal folds. This study supports the fatigue damage hypothesis of vocal trauma. With this hypothesis and the numerical simulation in this study, the clinical observations of vocal fold trauma risk can be explained. This implies the mechanical stress predicted by this self-oscillating model could be valuable for predicting, preventing, and treating vocal fold injury.     

Correspondence between laryngeal vocal fold movement and muscle activity during speech and nonspeech gestures.

To better understand the role of each of the laryngeal muscles in producing vocal fold movement, activation of these muscles was correlated with laryngeal movement during different tasks such as sniff, cough or throat clear, and speech syllable production. Four muscles [the posterior cricoarytenoid, lateral cricoarytenoid, cricothyroid (CT), and thyroarytenoid (TA)] were recorded with bipolar hooked wire electrodes placed bilaterally in four normal subjects. A nasoendoscope was used to record vocal fold movement while simultaneously recording muscle activity. Muscle activation level was correlated with ipsilateral vocal fold angle for vocal fold opening and closing. Pearson correlation coefficients and their statistical significance were computed for each trial. Significant effects of muscle (P < or = 0.0005) and task (P = 0.034) were found on the r (transformed to Fisher's Z') values. All of the posterior cricoarytenoid recordings related significantly with vocal opening, whereas CT activity was significantly correlated with opening only during sniff. The TA and lateral cricoarytenoid activities were significantly correlated with vocal fold closing during cough. During speech, the CT and TA activity correlated with both opening and closing. Laryngeal muscle patterning to produce vocal fold movement differed across tasks; reciprocal muscle activity only occurred on cough, whereas speech and sniff often involved simultaneous contraction of muscle antagonists. In conclusion, different combinations of muscle activation are used for biomechanical control of vocal fold opening and closing movements during respiratory, airway protection, and speech tasks.     

Mechanism of initiation of oscillatory motion in human glottis

Phonatory onsets of 17 normal subjects under usual speech conditions were investigated by measuring the cross-sectional area of the glottic aperture, using a photoelectric device. During a normal soft or breathy onset of phonation, the vocal fold vibration begins with an open glottis; the pattern of the optical signal is a sine wave of increasing amplitude with one to eight cycles before steady state oscillation is achieved. The first deflection of the base-line is either towards adduction or towards abduction. The classically assumed--since van den Berg et al. (1957)--retro-aspiration phenomenon, consisting in a narrowing of the glottic chink due to the accelerated air flow, according to Bernoulli's law, is incompatible with these observations. An aerodynamic study, with accurate calibration of the photoelectric transducer in one trained subject, as well as flux and subglottic pressure measurements, suggests that the gas flux (air as well as a helium-oxygen mixture) reaches the condition of turbulence at the level of the glottic nozzle, just before vocal folds are set into oscillatory motion. The setting in motion of the free edge of the vocal folds in normal soft or breathy onset of phonation can be explained by a sudden modification of flow conditions within the expiratory gas : the flow is laminar in the trachea and suddenly becomes turbulent at the level of the glottic nozzle. On the other hand, approximately normal atmospheric pressure values are attained due to a Bernoulli-effect at that level, allowing the vocal folds to oscillate sinusoidally about their vibration axes, corresponding to their virtual resting position, like a forced oscillator.     

Laryngeal muscle responses to mechanical displacement of the thyroid cartilage in humans.

Speakers may use laryngeal sensory feedback to adjust vocal fold tension and length before initiating voice. The mechanism for accurately initiating voice at an intended pitch is unknown, given the absence of laryngeal muscle spindles in animals and conflicting findings regarding their existence in humans. Previous reports of rapid changes in voice fundamental frequency following thyroid cartilage displacement suggest that changes in vocal fold length modulate laryngeal muscle contraction in humans. We tested the hypothesis that voice changes resulting from mechanical perturbation are due to rapid responses in the intrinsic laryngeal muscles. Hooked wire electrodes were used to record from the thyroarytenoid, cricothyroid, and sternothyroid muscles along with surface electrodes on the skin overlying the thyroid cartilage in 10 normal adults. Servomotor displacements produced consistent changes in the subjects' vocal fundamental frequency at 70-80 ms, demonstrating changes in vocal fold length and tension. No simultaneous electromyographic responses occurred in the thyroarytenoid or cricothyroid muscles in any subjects. Instead, short-latency responses at 25-40 ms following stimulus onset occurred in the sternothyroid muscles, simultaneous with responses in the surface recordings. The sternothyroid responses may modulate long-latency changes in voice fundamental frequency (approximately 150 ms). The absence of intrinsic laryngeal muscle responses is consistent with a lack of spindles in these muscles. Our results suggest that other sensory receptors, such as mucosal mechanoreceptors, provide feedback for voice control.     

Vocal fold composition and early glottic carcinoma infiltration

ABSTRACT: BACKGROUND: Current imaging techniques provide only limited information pertaining to the extent of infiltration of laryngeal carcinomas into vocal fold tissue layers. Therefore, it is needed to seek the contribute to the body of knowledge surrounding examination and characterization in laryngeal carcinoma infiltration. METHODS: Excised larynges were collected from 30 male laryngectomy patients with an average age of 43.5 years (ranging 36 to 55 years) and history of smoking ([GREATER-THAN OR EQUAL TO]10 years) exhibiting T1, T2, or subglottal (normal vocal fold) carcinomas. Vocal folds were preserved via freezing or immersion in paraffin. The depth of the mucosa, submucosa, and muscular layers in both normal vocal folds and tumor tissues of afflicted vocal folds was measured. RESULTS: The average depths of the mucosa, submucosa, and muscular layers in normal vocal folds were 0.15 [PLUS-MINUS SIGN] 0.06 mm, 2.30 [PLUS-MINUS SIGN] 0.59 mm, and 2.87 [PLUS-MINUS SIGN] 0.88 mm, respectively. Infiltration measurements of T1 tumors showed a depth of 1.62 [PLUS-MINUS SIGN] 0.51 mm and 1.32 [PLUS-MINUS SIGN] 0.49 mm in frozen sections and paraffin-embedded samples, respectively. Similarly, T2 tumors showed a depth of 2.87 [PLUS-MINUS SIGN] 0.68 mm and 2.58 [PLUS-MINUS SIGN] 0.67 mm in frozen sections and paraffin-embedded samples, respectively. T1 and T2 tumors occupied 24.8 [PLUS-MINUS SIGN] 10 and 48.5 [PLUS-MINUS SIGN] 15 percent of the normal vocal fold depth, respectively. CONCLUSION: This data provides a baseline for estimating infiltration of laryngeal carcinomas in vocal fold tissue layers, of particular interest to surgeons. This information may be used to assess typical depths of infiltration, thus allowing for more appropriate selection of surgical procedures based on individual patient assessment.     

Perinatal development of laryngeal function

The resistance of the upper airway is strongly influenced by the action of opposing sets of laryngeal muscles. Expiratory airflow may be retarded by active adduction of the arytenoid cartilages or by a reduction in the activity of abductor muscles. In developing sheep the adductor muscles appear to represent the principal means by which lung recoil is opposed. This mechanism, which is most pronounced during non-rapid-eye-movement sleep, is regulated by afferent traffic from the lungs. In fetal sheep the laryngeal muscles are also influenced by breathing movements and sleep states. The adductor muscles are normally tonically active during non-rapid-eye-movement sleep when rhythmical breathing movements are absent. It is possible that this activity is at least partially responsible for elevated tracheal pressures and depressed flow of tracheal fluid during fetal apnea. This hypothesis has been tested by observing the effects of fetal paralysis and recurrent laryngeal nerve section. These experiments suggest that in the fetus near term the larynx makes a major contribution to upper airway resistance and hence to the maintenance of pulmonary expansion which has been shown to influence lung development.     

Sexual Dimorphism of the Larynx of the Mongolian Gazelle (Procapra gutturosa Pallas, 1777) (Mammalia, Artiodactyla, Bovidae)

The larynges (except for the epiglottis) of two adult Mongolian gazelles, one male and one female, were dissected. This species is characterized by a pronounced sexual dimorphism of the larynx. Dimorphism with regard to the size of the entire larynx and of the thyroid cartilage is about 2:1 whereas the difference of mean body mass is about 1.3:1 between males and females. Unexpectedly, and in contrast to other bovids, the larynx of the male Mongolian gazelle has a paired lateral laryngeal ventricle. However, in contrast to horse, dog, pig and many primate species also possessing such a paired ventricle, its rostral opening in the Mongolian gazelle is situated lateral to the corniculate process of the arytenoid cartilage. The neck of the laryngeal ventricle is embraced by the bifurcated cuneiform process of the epiglottis. Despite the enlarged laryngeal cartilages, the vocal process of the male arytenoid cartilage is relatively shorter than that of the female. The male thyroarytenoid muscle is clearly separated into a rostral ventricular muscle and a caudal vocal muscle whereas the female's, as in other bovids, is almost uniform. The lateral sac of the two-chambered laryngeal ventricle in the male projects laterally between the ventricular and the vocal muscle. As in the domestic bovids and in many other artiodactyls the larynx of the male Mongolian gazelle is lacking any rostrally directed membraneous portion of the vocal fold. Instead, the thick and tough bow-like vocal fold projects caudally into the infraglottic cavity and is supported by a peculiar pan-like fibroelastic pad. This resilient element, situated medial to the bipartite thyroarytenoid muscle, might be a homologue of the vocal ligament, eventually including lateral portions of the elastic cone. A fibroelastic pad is absent in the female. The resilient floor of the laryngeal vestibulum, ventral to the fibroelastic pad, is rostrally and caudally subducted by tube-like spaces. Evolutionary enlargement of the male larynx, including the vocal folds, and of the caudal portions of the vocal tract may have shifted the fundamental and formant frequencies to a lower register. The paired lateral laryngeal ventricle might produce an amplitude increase of the vocalizations assisted by differential action of the bipartite thyroarytenoid muscle. In addition, the peculiar shape, size and tough consistency of the male vocal folds may, as in roaring felids, assist in producing high amplitude and low frequency vocalizations. Perhaps the biological role of the enlarged male larynx of Procapra gutturosa has evolved in relation to its mating system. In the rutting season, dominant males establish individual territories and maintain harems. During prolonged courtship prior to mating, these males perform an acoustic display uttering loud and guttural bellows. In addition, the bulging ventral neck region of males may serve as an optical attractant for the females. Thus, the evolution of the enlarged larynx of the male Mongolian gazelle may have been favoured by sexual selection.     

Physical simulation of laryngeal disorders using a multiple-mass vocal fold model

This paper reports on the use of a high-dimensional discrete vocal fold model for the simulation of voice production under the presence of laryngeal disorders. Specifically, the effect of increases in mass and stiffness, both unilateral and bilateral, has been analysed independently for both magnitudes. The glottal flow waveform and the mass displacement have been studied and the obtained results are coherent with clinical observations that relate mass increments with lowered fundamental frequencies and mass and stiffness increments with reduced vibratory amplitudes of vocal folds. The reported results also indicate that asymmetries in the physical properties of vocal folds result in asymmetries in their vibratory patterns, including phase, amplitude and behaviour on collision. These are also correlated with voice perturbation measures such as jitter, shimmer and normalised noise energy.     

Optical measurements of vocal fold tensile properties: implications for phonatory mechanics

In voice research, in vitro tensile stretch experiments of vocal fold tissues are commonly employed to determine the tissue biomechanical properties. In the standard stretch-release protocol, tissue deformation is computed from displacements applied to sutures inserted through the thyroid and arytenoid cartilages, with the cartilages assumed to be rigid. Here, a non-contact optical method was employed to determine the actual tissue deformation of vocal fold lamina propria specimens from three excised human larynges in uniaxial tensile tests. Specimen deformation was found to consist not only of deformation of the tissue itself, but also deformation of the cartilages, as well as suture alignment and tightening. Stress-stretch curves of a representative load cycle were characterized by an incompressible Ogden model. The initial longitudinal elastic modulus was found to be considerably higher if determined based on optical displacement measurements than typical values reported in the literature. The present findings could change the understanding of the mechanics underlying vocal fold vibration. Given the high longitudinal elastic modulus the lamina propria appeared to demonstrate a substantial level of anisotropy. Consequently, transverse shear could play a significant role in vocal fold vibration, and fundamental frequencies of phonation should be predicted by beam theories accounting for such effects.     

Muscular control of the vocal tract during release signaling in the toad Bufo valliceps

The release vibration and release call of Bufo valliceps have been studied by electromyography of the muscles involved, coupled with pressure and sound recording. The sequences are powered by contraction of the muscles of the body envelope and with the energy transmitted via the compressed pulmonary contents. Each pulse of a call starts as the laryngeal muscles relax and pulmonary pressure forces the arytenoid cartilages apart. Sound emission ceases when the laryngeal dilators pull the arytenoids out of the airstream. Reverse flow of air from buccal cavity to lungs may occur within prolonged release sequences. Inflation of the vocal sac results in marked increase in amplitude of the radiated sound without equivalent increase in amplitude of the myograns. The call is intimately associated with the pulsepumping method of breathing used by frogs.     

Synthetic,Multi-Layer,Self-Oscillating Vocal Fold Model Fabrication

Sound for the human voice is produced via flow-induced vocal fold vibration. The vocal folds consist of several layers of tissue, each with differing material properties ¹. Normal voice production relies on healthy tissue and vocal folds, and occurs as a result of complex coupling between aerodynamic, structural dynamic, and acoustic physical phenomena. Voice disorders affect up to 7.5 million annually in the United States alone ² and often result in significant financial, social, and other quality-of-life difficulties. Understanding the physics of voice production has the potential to significantly benefit voice care, including clinical prevention, diagnosis, and treatment of voice disorders.Existing methods for studying voice production include in vivo experimentation using human and animal subjects, in vitro experimentation using excised larynges and synthetic models, and computational modeling. Owing to hazardous and difficult instrument access, in vivo experiments are severely limited in scope. Excised larynx experiments have the benefit of anatomical and some physiological realism, but parametric studies involving geometric and material property variables are limited. Further, they are typically only able to be vibrated for relatively short periods of time (typically on the order of minutes).Overcoming some of the limitations of excised larynx experiments, synthetic vocal fold models are emerging as a complementary tool for studying voice production. Synthetic models can be fabricated with systematic changes to geometry and material properties, allowing for the study of healthy and unhealthy human phonatory aerodynamics, structural dynamics, and acoustics. For example, they have been used to study left-right vocal fold asymmetry ^3,4, clinical instrument development ⁵, laryngeal aerodynamics ^6-9, vocal fold contact pressure ¹⁰, and subglottal acoustics ¹¹ (a more comprehensive list can be found in Kniesburges et al. ¹²)Existing synthetic vocal fold models, however, have either been homogenous (one-layer models) or have been fabricated using two materials of differing stiffness (two-layer models). This approach does not allow for representation of the actual multi-layer structure of the human vocal folds ¹ that plays a central role in governing vocal fold flow-induced vibratory response. Consequently, one- and two-layer synthetic vocal fold models have exhibited disadvantages ^3,6,8 such as higher onset pressures than what are typical for human phonation (onset pressure is the minimum lung pressure required to initiate vibration), unnaturally large inferior-superior motion, and lack of a "mucosal wave" (a vertically-traveling wave that is characteristic of healthy human vocal fold vibration).In this paper, fabrication of a model with multiple layers of differing material properties is described. The model layers simulate the multi-layer structure of the human vocal folds, including epithelium, superficial lamina propria (SLP), intermediate and deep lamina propria (i.e., ligament; a fiber is included for anterior-posterior stiffness), and muscle (i.e., body) layers ¹. Results are included that show that the model exhibits improved vibratory characteristics over prior one- and two-layer synthetic models, including onset pressure closer to human onset pressure, reduced inferior-superior motion, and evidence of a mucosal wave.     

Adapted to roar: functional morphology of tiger and lion vocal folds

Vocal production requires active control of the respiratory system, larynx and vocal tract. Vocal sounds in mammals are produced by flow-induced vocal fold oscillation, which requires vocal fold tissue that can sustain the mechanical stress during phonation. Our understanding of the relationship between morphology and vocal function of vocal folds is very limited. Here we tested the hypothesis that vocal fold morphology and viscoelastic properties allow a prediction of fundamental frequency range of sounds that can be produced, and minimal lung pressure necessary to initiate phonation. We tested the hypothesis in lions and tigers who are well-known for producing low frequency and very loud roaring sounds that expose vocal folds to large stresses. In histological sections, we found that the Panthera vocal fold lamina propria consists of a lateral region with adipocytes embedded in a network of collagen and elastin fibers and hyaluronan. There is also a medial region that contains only fibrous proteins and hyaluronan but no fat cells. Young's moduli range between 10 and 2000 kPa for strains up to 60%. Shear moduli ranged between 0.1 and 2 kPa and differed between layers. Biomechanical and morphological data were used to make predictions of fundamental frequency and subglottal pressure ranges. Such predictions agreed well with measurements from natural phonation and phonation of excised larynges, respectively. We assume that fat shapes Panthera vocal folds into an advantageous geometry for phonation and it protects vocal folds. Its primary function is probably not to increase vocal fold mass as suggested previously. The large square-shaped Panthera vocal fold eases phonation onset and thereby extends the dynamic range of the voice.     

Non-invasive in vivo measurement of the shear modulus of human vocal fold tissue

Voice is the essential part of singing and speech communication. Voice disorders significantly affect the quality of life. The viscoelastic mechanical properties of the vocal fold mucosa determine the characteristics of the vocal folds oscillations, and thereby voice quality. In the present study, a non-invasive method was developed to determine the shear modulus of human vocal fold tissue in vivo via measurements of the mucosal wave propagation speed during phonation. Images of four human subjects' vocal folds were captured using high speed digital imaging (HSDI) and magnetic resonance imaging (MRI) for different phonation pitches, specifically fundamental frequencies between 110 and 440 Hz. The MRI images were used to obtain the morphometric dimensions of each subject's vocal folds in order to determine the pixel size in the high-speed images. The mucosal wave propagation speed was determined for each subject and at each pitch value using an automated image processing algorithm. The transverse shear modulus of the vocal fold mucosa was then calculated from a surface (Rayleigh) wave propagation dispersion equation using the measured wave speeds. It was found that the mucosal wave propagation speed and therefore the shear modulus of the vocal fold tissue were generally greater at higher pitches. The results were in good agreement with those from other studies obtained via in vitro measurements, thereby supporting the validity of the proposed measurement method. This method offers the potential for in vivo clinical assessments of vocal folds viscoelasticity from HSDI.     

Morphological aspects of the euphonic voice

The high quality of a euphonic voice is the result of complex interactions between many organs and systems. Vibrating vocal folds play a crucial role in this process. Their physiological motion is conditioned by the presence of the layered structure of laryngeal mucosa. In this study, we assessed the degree of dysphonia according to the Union of European Phoniatrics (UEP) scale. Videoendoscopy (VLS) and videostroboscopic (VLSS) examination of the larynx was used to visualize the vibration of the vocal folds. Morphological assessment of the inter-membranous part of the vocal fold mucosa was carried out using material collected after surgical treatment (60%) or obtained from autopsy (40%). The samples were examined by light microscopy and transmission electron microscopy. In euphonic voices, 1° of dysphonia (UEP) and the physiological endoscopic (VLS) and stroboscopic (VLSS) findings of vocal folds were registered. No morphological or ultramorphological changes were observed in the cells of the multilayered flat epithelium, basal membrane or in the stroma. Unchanged epithelial cells were situated on the basal membrane with folds. Moreover, numerous pericytes, vessels with multiplication of basal membranes, scanty collagenous fibers, plasmatic cells and lymphocytes were seen. Morphological changes with signs of atrophy and polypoid degeneration of the vocal fold mucosa were found in only 3 (15%) patients.