Length-tension relationship of the feline thyroarytenoid muscle

Impact of Instructed Laryngeal Manipulation on Acoustic Measures of Voice-Preliminary Results

BACKGROUND

Control of laryngeal muscles is required to manipulate pitch, volume, and voice quality. False vocal fold activity (FVFA) refers to the constriction and release of constriction of the false vocal folds. True vocal fold mass (TVFM) represents the cross-sectional thickness of the vocal folds. Larynx height (LH) refers to the vertical position of the larynx in the neck. To date, studies of voice control have examined the effects of these parameters separately. No study has investigated the impact of instructed systematic manipulation of these parameters on acoustic voice measures in vocally healthy trained subjects.

AIMS

This study examined the effects of systematically manipulating FVFA, TVFM, and LH on several acoustic voice measures.

METHOD

Twelve vocally trained speakers were instructed to use specific techniques to achieve experimental conditions of constriction and release of constriction of FVFA, thicker and thinner TVFM, and normal and low LH. Each condition was implemented in combination with manipulating the other parameters. Voice recordings of sustained vowel /a/ and Rainbow Passage were obtained for all laryngeal manipulation conditions and underwent acoustic analyses for fundamental frequency (F0), signal typing, harmonics-to-noise ratio (HNR), cepstral peak prominence (CPP), and vocal relative intensity.

RESULTS

Constricted FVFA caused more aperiodicity in the signals, lower CPP, and lower vocal relative intensity than release of constriction. Thicker TVFM resulted in significantly higher CPP and vocal relative intensity than thinner TVFM. Modifying TVFM did not affect F0 and HNR. Low LH had significantly lower F0 but did not impact on HNR, CPP, and intensity.

CONCLUSIONS

The effects of systematic manipulation of each laryngeal parameter resulted in independent acoustic effects without measurable interaction. Release of constriction of FVFA, thicker TVFM, and low LH were configurations that resulted in more optimal acoustic signals.

Microstimulation in Different Parts of the Periaqueductal Gray Generates Different Types of Vocalizations in the Cat

In the cat four different types of vocalization, mews, howls, cries, and hisses were generated by microstimulation in different parts of the periaqueductal gray (PAG). While mews imply positive vocal expressions, howls, hisses, and cries represent negative vocal expressions. In the intermediate PAG, mews were generated in the lateral column, howls, and hisses in the ventrolateral column. Cries were generated in two other regions, the lateral column of the rostral PAG and the ventrolateral column of the caudal PAG. In order to define the specific motor patterns of the mews, howls, and cries, the following muscles were recorded during these vocalizations; larynx (cricothyroid, thyroarytenoid, and posterior cricoarytenoid), tongue (genioglossus), jaw (digastric), and respiration muscles (diaphragm, internal intercostal, external, and internal abdominal oblique). During these mews, howls, and cries we analyzed the frequency, intensity, activation cascades power density, turns, and amplitude analysis of the electromyograms (EMGs). It appeared that each type of vocalization consists of a specific circumscribed motor coordination. The nucleus retroambiguus (NRA) in the caudal medulla is known to serve as the final premotor interneuronal output system for vocalization. Although neurochemical microstimulation in the NRA itself also generated vocalizations, they only consisted of guttural sounds, the EMGs of which involved only small parts of the EMGs of the mews, howls, and cries generated by neurochemical stimulation in the PAG. These results demonstrate that positive and negative vocalizations are generated in different parts of the PAG. These parts have access to different groups of premotoneurons in the NRA, that, in turn, have access to different groups of motoneurons in the brainstem and spinal cord, resulting in different vocalizations. The findings would serve a valuable model for diagnostic assessment of voice disorders in humans.

Changes in Vocal Fold Morphology During Singing Over Two Octaves

OBJECTIVE

Vocal folds are widely assumed to only elongate to raise vocal pitch. However, the mechanisms seem to be more complex and involve both elongation and tensioning of the vocal folds in series. The aim of the present study was to show that changes in vocal fold morphology depend on vocal fold elongation and tensioning during singing.

STUDY DESIGN

This was a prospective study.

METHODS

Forty-nine professional female singers (25 sopranos, 24 altos) were recruited and three-dimensional laryngeal images analyzed in a coronal view derived from high-resolution computed tomography scans obtained at the mean speaking fundamental frequency (ƒ₀) and one (2ƒ₀) and two octaves (4ƒ₀) above ƒ₀.

RESULTS

The vocal fold angle, defined by a tangent above and below the vocal folds, was 58° at ƒ₀, 47° at 2ƒ₀, and 59° at 4ƒ₀.

CONCLUSION

The decreased caudomedial angle of the vocal fold from ƒ₀ to 2ƒ₀ (change in muscle belly from ";fat" to "thin") and increased angle from 2ƒ₀ to 4ƒ₀ (from "thin" to "fat") strongly supports the hypothesis that the vocal folds elongate and then tension when singing from ƒ₀ to 4ƒ₀. This is the first study to show this relationship in vivo.

The effect of temperature on basal tension and thyroarytenoid muscle contraction in an isolated rat glottis model

The pitch of voice is closely related to the vocal fold tension, which is the end result of coordinated movement of the intralaryngeal muscles, and especially the thyroarytenoid muscle. It is known that vocal quality may be affected by surrounding temperature; however, the effect of temperature on vocal fold tension is mostly unknown. Thus, the aim of this study was to evaluate the effect of temperature on isolated rat glottis and thyroarytenoid muscle contraction induced by electrical field stimulation. In vitro isometric tension of the glottis ring from 30 Sprague-Dawley rats was continuously recorded by the tissue bath method. Electrical field stimulation was applied to the glottis ring with two wire electrodes placed parallel to the glottis and connected to a direct-current stimulator. The tension changes of the rat glottis rings that were either untreated or treated with electrical field stimulation were recorded continuously at temperatures from 37 to 7 °C or from 7 to 37 °C. Warming from 7 to 37 °C increased the basal tension of the glottis rings and decreased the electrical field stimulation-induced glottis ring contraction, which was chiefly due to thyroarytenoid muscle contraction. In comparison, cooling from 37 to 7 °C decreased the basal tension and enhanced glottis ring contraction by electrical field stimulation. We concluded that warming increased the basal tension of the glottis in vitro and decreased the amplitude of electrical field stimulation-induced thyroarytenoid muscle contraction. Thus, vocal pitch and the fine tuning of vocal fold tension might be affected by temperature in vivo.

Phonatory characteristics of the excised human larynx in comparison to other species

OBJECTIVE

The purpose of this study was to determine the conditions needed to elicit phonation from excised human larynges and the resultant range of phonations produced; compare that with similar information previously obtained from canine, pig, sheep, and cow; and relate those findings to previously reported information about viscoelastic properties of the vocal fold tissue (ie, stress-strain curves and Young's modulus).

METHODS

Six human larynges of the geriatric group (age range, 70-89) were mounted on the bench without supraglottic structures, and phonation was achieved with the flow of heated and humidified air through the tracheal tube. Using various sutures to mimic the function of the laryngeal muscles, the larynges were put through a series of sustained oscillations with adduction as a control parameter.

RESULTS

The human larynges oscillated with an average frequency that was close to the canine larynges, but the oscillation behavior and wide frequency range were similar to those of pig larynges. The similarity of the wide vibration frequency ranges of human and pig larynges may be because of the nonlinear behavior of their elasticity, which is related to the high collagen content of the vocal folds. On the contrary, other species with limited frequency ranges showed almost linear stress-strain curves because of the higher elastin and lower collagen contents.

CONCLUSIONS

The physiological differences in the linearity and ranges of oscillation of excised larynges reported in this study and previous studies are reflective of the tissue composition and mechanics.

Comparison of muscle force after immediate and delayed reinnervation using nerve-muscle-endplate band grafting

BACKGROUND

Because of poor functional outcomes of currently used reinnervation methods, we developed novel treatment strategy for the restoration of paralyzed muscles-the nerve-muscle-endplate band grafting (NMEG) technique. The graft was obtained from the sternohyoid muscle (donor) and implanted into the ipsilateral paralyzed sternomastoid (SM) muscle (recipient).

METHODS

Rats were subjected to immediate or delayed (1 or 3 mo) reinnervation of the experimentally paralyzed SM muscles using the NMEG technique or the conventionally used nerve end-to-end anastomosis. The SM muscle at the opposite side served as a normal control.

RESULTS

NMEG produced better recovery of muscle force as compared with end-to-end anastomosis. A larger force produced by NMEG was most evident for small stimulation currents.

CONCLUSIONS

The NMEG technique holds great potential for successful muscle reinnervation. We hypothesize that even better muscle reinnervation and functional recovery could be achieved with further improvement of the environment that favors axon-end plate connections and accelerates axonal growth and sprouting.

Force recovery and axonal regeneration of the sternomastoid muscle reinnervated with the end-to-end nerve anastomosis

BACKGROUND

End-to-end nerve anastomosis (EEA) is a commonly used nerve repair technique. However, this method generally results in poor functional recovery. This study was designed to determine the correlation of functional recovery to the extent of axonal reinnervation after EEA procedure in a rat model.

MATERIALS AND METHODS

Seven adult rats were subjected to the immediate reinnervation of an experimentally paralyzed sternomastoid (SM) muscle. The SM nerve was transected and immediately repaired with EEA. The SM muscle at the opposite side, without nerve transection, served as a control. Three months after EEA nerve repair, the muscle force of the SM muscle was measured and the regenerated axons in the muscle were detected using neurofilament immunohistochemistry.

RESULTS

Three months after surgery, the reinnervated SM muscle produced limited anatomical and functional recovery (calculated as the percentage of the control). Specifically, the wet weight of the operated SM muscle (a measure of muscle mass recovery) was 78.0% of the control. The maximal tetanic force (a measure of muscle functional recovery) was 56.7% of the control. The area fraction of the neurofilament stained intramuscular axons (a measure of axonal regeneration and muscle reinnervation) was measured to be only 13.4% of the control. A positive correlation was revealed between the extent of muscle reinnervation and maximal muscle force.

CONCLUSIONS

The EEA reinnervated SM muscle in the rat yielded unsatisfactory muscle force recovery as a result of mild to moderate nerve regeneration. Further work is needed to improve the surgical procedure, enhance axonal regeneration, and/or develop novel treatment strategies for better functional recovery.

Differences in neuromuscular junctions of laryngeal and limb muscles in rats

OBJECTIVES/HYPOTHESIS

Laryngeal muscles are specialized for fine control of voice, speech, and swallowing, and may differ from limb muscles in many aspects. Because muscles and their controlling motor neurons communicate via neuromuscular junctions (NMJs), we hypothesized that NMJs in laryngeal muscles have specialized characteristics different from limb muscles.

STUDY DESIGN

In vivo study.

METHODS

Single muscle fibers from 12 Sprague-Dawley rats (six male, six female) were used to analyze the postsynaptic side of NMJs from laryngeal thyroarytenoid (TA), cricothyroid (CT), posterior cricoarytenoid (PCA), limb soleus (SOL), and extensor digitorum longus (EDL) muscles. NMJs were labeled with rhodamine-conjugated α-bungarotoxin. With confocal microscopy, we counted cluster fragments and measured the NMJ area, both absolute and normalized (corrected by muscle fiber diameter), for at least 10 single fibers from each muscle of each animal. Differences between genders were also compared.

RESULTS

Cluster fragments of postsynaptic NMJs were more numerous in PCA and TA compared to CT, SOL, and EDL muscles (P < .01) in both male and female rats. NMJ cluster fragments were more numerous in female than in male rats only in the TA muscle (P < .01). The absolute area covered by the NMJs showed SOL > EDL > PCA > CT > TA (P < .01); however, with normalization the SOL = EDL = PCA > CT = TA.

CONCLUSIONS

Differences found in NMJ surface and organization between laryngeal and limb muscle fibers may relate to specialized laryngeal muscle functions. Differences in NMJs between male and female rats were found only in the TA muscle, suggesting an underlying mechanism for some gender-specific laryngeal disorders related to abnormal TA muscle activity.

Cooperative regulation of vocal fold morphology and stress by the cricothyroid and thyroarytenoid muscles

Voice is produced by vibrations of vocal folds that consist of multiple layers. The portion of the vocal fold tissue that vibrates varies depending primarily on laryngeal muscle activity. The effective depth of tissue vibration should significantly influence the vibrational behavior of the tissue and resulting voice quality. However, thus far, the effect of the activation of individual muscles on the effective depth is not well understood. In this study, a three-dimensional finite element analysis is performed to investigate the effect of the activation of two major laryngeal muscles, the cricothyroid (CT) and thyroarytenoid (TA) muscles, on vocal fold morphology and stress distribution in the tissue. Because structures that bear less stress can easily be deformed and involved in vibration, information on the morphology and stress distribution may provide a useful estimate of the effective depth. The results of the analyses indicate that the two muscles perform distinct roles, which allow cooperative control of the morphology and stress. When the CT muscle is activated, the tip region of the vocal folds becomes thinner and curves upward, resulting in the elevation of the stress magnitude all over the tissue to a certain degree that depends on the stiffness of each layer. On the other hand, the TA muscle acts to suppress the morphological change and controls the stress magnitude in a position-dependent manner. Thus, the present analyses demonstrate quantitative relationships between the two muscles in their cooperative regulation of vocal fold morphology and stress.

Characteristics of tetanic force produced by the sternomastoid muscle of the rat

The sternomastoid (SM) muscle plays an important role in supporting breathing. It also has unique anatomical advantages that allow its wide use in head and neck tissue reconstruction and muscle reinnervation. However, little is known about its contractile properties. The experiments were run on rats and designed to determine in vivo the relationship between muscle force (active muscle contraction to electrical stimulation) with passive tension (passive force changing muscle length) and two parameters (intensity and frequency) of electrical stimulation. The threshold current for initiating noticeable muscle contraction was 0.03 mA. Maximal muscle force (0.94 N) was produced by using moderate muscle length/tension (28 mm/0.08 N), 0.2 mA stimulation current, and 150 Hz stimulation frequency. These data are important not only to better understand the contractile properties of the rat SM muscle, but also to provide normative values which are critical to reliably assess the extent of functional recovery following muscle reinnervation.

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.