Vocal Fold Tension Research Articles

Biomechanics of Arytenoid Adduction Surgery in an Ex Vivo Canine Model

The biomechanics of arytenoid adduction surgery are not well understood. An excised canine larynx model was used to study the effects of variable suture tension on glottal configuration and on vocal fold tension (at the midfold and the vocal process). Arytenoid adduction both medializes the vocal fold and closes a posterior glottal chink. Vocal fold tension at the midfold did not vary significantly with suture tension. As suture tension increased to approximately 100 g, vocal fold tension at the vocal process also increased. Beyond 100 g of suture tension, vocal fold tension at the vocal process did not increase. We conclude that the effects of suture tension on the resistance to lateral movement are different at the midfold compared to the vocal process. Procedures for surgical rehabilitation of vocal fold paralysis should address the biomechanical subunits of the larynx individually in order to achieve optimum results.

Correction of dysphonia using laryngeal framework surgical techniques

Many dysphonias caused by incomplete glottis closure or inadequate vocal fold tension are eligible for phonosurgical correction. Most phonosurgeons presently advocate laryngeal framework surgery as the first treatment of choice.For correction of incomplete glottis closure usually thyroplasty type 1 and arytenoid adduction techniques are used. For correction of vocal fold tension crico-thyroid approximatidn and thyroplasty type 3 can be used. Often combinations of different techniques are required to achieve the best result. It is therefore essential to perform these procedures under local anaesthesia, so that the voice can be monitored during the surgery and so that the surgery can be tailored to the patient's voice.89 patients underwent laryngeal framework surgery, 85 of them for correction of incomplete glottis closure, which in 75 patients was due to unilateral vocal fold immobility. The results in this group were good also in long term follow-up. Complications were few and insignificant.

Endoscopic imaging of vocal cord vibrations. Digital high speed recording with various systems

Vocal fold vibration patterns during phonation are presented with different digital imaging systems. With newly developed technical equipment color images up to 1000 digital images/s were obtained without light intensifying enhancement techniques via rigid and flexible endoscopy. With this color high-speed system, morphologic structures, such as small blood vessels, were visualized in high-resolution quality as a result of additional color information. In another system, zooming of endoscopic pictures via pixel interpolation algorithms provided full-monitor presentation of vocal fold vibratory patterns. This system allows PC-based synchronization with microphone and electroglottographic signals in a frame-by-frame technique. Although only processing gray scale images, analyses of dynamic changes in modes of vibration were facilitated by the higher frame rate recording of up to 2000 frames/s and, in addition, they display corresponding analog signals. Both methods provide clinically important information. Furthermore, we demonstrated irregular vocal fold vibration patterns in a healthy adult volunteer. In this experiment, the irregular vibratory modes were induced by voluntarily applying asymmetric vocal fold tension. The asymmetric vocal fold vibration pattern resulted in (functionally induced) roughness of the voice as predicted by computer models of asymmetric vocal fold vibration. Digital high-speed cinematography proved to be a highly promising technique in the analysis of dysphonia and provided physiological examples that could be compared with models of coupled nonlinear oscillators.

Diagnosis and treatment of unilateral cricothyroid muscle paralysis with a modified Isshiki type 4 thyroplasty.

Cricothyroid adduction increases tension to the vocal folds, thus increasing fundamental frequency and upper pitch range. We treated 10 patients with cricothyroid muscle dysfunction using this technique. Preoperative electromyographic, acoustic, and perceptual analysis was performed. Intraoperatively the effect of increasing tension on the fundamental, falsetto, and basal frequencies was measured by using a strain gauge to the adducting suture at several tensions and a cervical microphone connected to a pitch meter. Postoperative acoustic and perceptual analysis was then performed up to 18 months later. Analysis of pitch vs. tension curves indicates a near-linear relationship until very high tensions are applied. Statistically significant improvement was achieved in both acoustic and perceptual analysis, although some deterioration was noted between early and late results. Cricothyroid adduction is indicated for a large range of vocal fold tension problems.

Diagnosis and treatment of unilateral cricothyroid muscle paralysis with a modified Isshiki type 4 thyroplasty

Cricothyroid adduction increases tension to the vocal folds, thus increasing fundamental frequency and upper pitch range. We treated 10 patients with cricothyroid muscle dysfunction using this technique. Preoperative electromyographic, acoustic, and perceptual analysis was performed. Intraoperatively the effect of increasing tension on the fundamental, falsetto, and basal frequencies was measured by using a strain gauge to the adducting suture at several tensions and a cervical microphone connected to a pitch meter. Postoperative acoustic and perceptual analysis was then performed up to 18 months later. Analysis of pitch vs. tension curves indicates a near-linear relationship until very high tensions are applied. Statistically significant improvement was achieved in both acoustic and perceptual analysis, although some deterioration was noted between early and late results. Cricothyroid adduction is indicated for a large range of vocal fold tension problems. (OTOLARYNGOL HEAD NECK SURG 1995;113:679-88.)

Open slope quotient: A new glottographic parameter

This study introduces a new objective measurement of the vibratory pattern termed the open slope quotient (OSQ). This parameter is based on the maximum slope of the photoglottographic waveform during glottal opening. Using an excised canine larynx model, the electroglottographic and photoglottographic waveforms, sound intensity, and subglottic pressure were recorded as vocal fold tension; glottic width and airflow rate were systematically varied. Multiple regression analysis of the data from nine larynges revealed OSQ to be inversely related to glottic width (p < 0.001) and vocal fold tension (p < 0.001) and directly related to glottic resistance (p < 0.001) and subglottic pressure (p < 0.001). The OSQ was better correlated with glottic width, subglottic pressure, and glottic resistance than speed quotient. OSQ is related to the velocity of vocal fold opening and laryngeal resistance. OSQ may also be related to vocal fold stiffness.

Neurophysiology, biomechanics, and modeling of normal voice production

This paper reviews recent progress in the development of models of the larynx and its control by the central nervous system (CNS). Biomechanical studies provide the data from which laryngeal models are built. These models, in turn, address questions such as the self-oscillatory behavior of the vocal folds, laryngeal mechanisms controlling vocal fold tension and fundamental frequency aerodynamics in the vocal tract, and the mechanisms controlling voice loudness. CNS studies, especially those studies measuring neural activity during vocal behavior, provide data that might prove useful in developing models of CNS vocal control mechanisms. Only very preliminary, limited models of such function are currently feasible. Despite the limitations of current neurolaryngologic data and models, relationships with clinical issues are becoming apparent.

Pliability of vocal fold mucosa in relation to the location of subglottic mucosal upheaval during phonation

Mucosal pliability was measured in 23 excised larynges, 19 canine and four human, at the three portions of the vocal fold, namely the midline, the anterior 1/4 and the posterior 1/4. The pliability at the midline showed a greater value than those at the other two portions. The free edge of the vocal fold showed a maximum pliability which gradually diminished toward the tracheal side and reached a minimum 3mm from the free edge of the fold. An increase in vocal fold tension resulted in lowering of mucosal pliability at all measured points and the point of minimal pliability shifted toward the oral side. The point of minimal pliability moved toward the tracheal side with direct electrical stimulation of the thyroarytenoid muscle (TA). Both pliability measurement and observation of mucosal vibration from the tracheal side using high speed cinematography or stroboscopy were performed on eleven of the excised canine larynges. The mucosal upheaval occurred at the point around which pliability was minimal. An increase in vocal fold tension resulted in an upward shift of the mucosal upheaval which occurred slightly below the point of minimal pliability. Electric stimulation of the TA resulted in a downward shift of the mucosal upheaval which occurred in accordance with the point of minimal pliability. Histological examination of the canine larynges revealed that the lamina propria became increasingly thin toward the point around which pliability was minimal and at which the mucosal upheaval occurred. At this point, the muscle layer approximated the epithelial layer with disappearance of the deep layer of the lamina propria. The point shifted to the oral side following an increment in vocal fold tension, while the point moved toward the tracheal side following contraction of the TA. Pliability of the vocal fold is minimal at the point around which the deep layer of the lamina propria disappears and the mucosal upheaval occurs.

Tracheal view of vocal fold vibration in excised canine larynxes.

The mucosal upheaval where the mucosal wave starts and propagates upward appears on the lower surface of the vocal fold during vibration. We investigated the location of the mucosal upheaval in response to variations in vocal fold tension and mean air flow rate. Twelve excised canine larynxes were used in the experiment. The lower surfaces of the vocal folds were marked with india ink. After cinematography was performed, a small cut wound was made at the mark. This wound served to relate cinematographic findings with the histologically observed position of the mark. The larynx was then fixed, sectioned in the frontal plane, and stained for histologic examination. Horizontal movements of the free edge, mucosal wave, mucosal upheaval, and marks were analyzed. Under a fixed vocal fold tension, the mucosal upheaval appeared more laterally to a limited extent as mean air flow rate increased, but its location on the vocal fold mucosa did not change from its position before the increase of mean air flow rate. The mucosal upheaval appeared more medially when vocal fold tension increased. The position of the mucosal upheaval actually changed medially compared with its original position before the tension increase. Histologic examination indicated that the mucosal upheaval arose on the lower surface of the vocal fold between the free edge and the area where the muscular layer comes in close proximity to the epithelial layer.

声帯振動の解析

The mucosal upheaval (MU) where the mucosal wave starts and propagates upward appears on the lower surface of the vocal fold during vibration. We investigated the location of the MU in response to variations in vocal fold tension and to contraction of the thyroarytenoid muscle (TA). Fresh excised larynxes (seven canine and four human) were used in the experiment. The lower surface of the vocal fold was tattooed with india ink as a reference point. Vocal fold vibration was observed either by high-speed filming or by videostroboscopy. Vocal fold tension was increased by cricothyroid approximation and TA contraction was obtained by its direct electrical stimulation. When vocal fold tension increased, the MU appeared medially or upward compared to its original position. With TA contraction, the lower surface of the vocal fold bulged medially and thus horizontal amplitude of the vibration became smaller. When TA contracted, the MU appeared less prominent and was located more downward compared to its position without TA contraction. These were basically common findings to both canine and human excised larynxes. Moreover, vocal fold vibration was stroboscopically observed through a tracheostoma in twelve patients. The MU occurred on the lower surface of the vocal fold as seen in the excised larynx and the mucosal wave was elicited upward from the MU.

Acoustic and aerodynamic effects of interarticulator timing in voiceless consonants.

Interarticulator timing is a mechanism for producing linguistic contrasts that is widely used in different languages. This paper explores acoustic and aerodynamic effects of variations in laryngeal-oral coordination in voiceless consonants. Measurements of voice onset time and interarticulator phasing for individual tokens of stop consonants show weak correlations, indicating that interarticulator timing is only one factor determining voice onset time. Other factors most likely involved are glottal opening, transglottal pressure and air flow, and vocal fold tension. Taken together, these observations suggest that speakers may only have limited control of voice onset time. This could explain why languages do not seem to make fine-grain use of VOT for linguistic contrasts. Measurements of peak and minimum air flow during individual source pulses, obtained by inverse-filtering oral flow, show a pattern of decrease and increase in vowels following voiceless consonants. Subtle differences in the time course of these patterns occur following different consonants, suggesting that interarticulator phasing may be partly responsible for them. Closer examination reveals consistent correlations with interarticulator phasing for one speaker but inconsistent results for another. The results are discussed in terms of speech motor control and controlled variables in speech.

Influence of consonantal environment on voice source aerodynamics

Studies of the voice source during speech have been concerned mostly with variations in fundamental frequency and overall amplitude. However, the source variations also include spectral characteristics and the harmonics-to-noise ratio which reflect changes in glottal abduction and vocal fold tension. The present study reports detailed measurements of voice source aerodynamics during transitions between consonants and vowels and between vowels and consonants. Air flow, oral air pressure and glottal opening were recorded from two subjects producing reiterant speech with the vowel /α/ and different voiced and voiceless consonants. The flow signal was inverse-filtered to obtain an estimate of the glottal pulse. The results show considerable influences on the source from the consonant both before the end of the preceding vowel and after the onset of the following vowel. These influences are most marked for voiceless consonants, where the source is breathy at both vowel offset and onset. The observed source variations can be rationalized with reference to aerodynamic and myodynamic factors during vowel offset and onset.

Effect of Superior Laryngeal Nerve on Vocal Fold Function: An in Vivo Canine Model

Assessment of laryngeal framework surgery requires an awareness of the effect of vocal fold mass, stiffness, and position on voice production. The vibratory pattern of vocal folds during phonation depends on the subglottic pressure as well as the mass and stiffness of the folds. To assess the effect of variations in vocal fold tension with contraction of the cricothyroid muscle on phonation, eight mongrel dog larynges were studied in vivo. Photoglottography, electroglottography, and subglottic pressure were simultaneously recorded as airflow rate and superior laryngeal nerve (SLN) stimulation were varied. Stimulation of the SLN was modified by varying the frequency and voltage of the stimulating electrical signal. Multiple regression analysis of the data revealed a direct relationship between the voltage of SLN stimulation and frequency of vibration (p less than 0.001) at constant subglottic pressure. Increases in the stimulating voltage to the SLN also led to an increase in open quotient (p less than 0.001), but no statistically significant change in speed quotient, subglottic pressure, or sound intensity. Changing the frequency of SLN stimulation had only a modest effect on the frequency of vibration. These results are consistent with the reported findings of an increase in frequency and open quotient with increased tension in an in vitro canine model. The glottographic measurement open quotient appears to be an estimator of cricothyroid contraction and longitudinal vocal fold tension, and may be clinically applicable to the assessment of superior laryngeal nerve injuries and laryngeal framework procedures.

Study of Phonation in the Excised Canine Larynx

Previous studies have demonstrated that the laryngeal muscles responsible for pitch variation and vocal efficiency are the cricothyroid muscles, affecting longitudinal tension of the vocal folds, and the thyroarytenoid muscles, controlling the lateral stiffness of the vocal folds. Longitudinal tension in the vocal fold is easily simulated in the excised canine larynx. The effect of the thyroarytenoid muscle, however, has not been adequately analyzed. To simulate the effect of the thyroarytenoid muscle, small balloons were placed in the paraglottic space at the level of the vocal folds in 10 excised canine larynges. These balloons (Fogarty catheters) could be inflated in increments to simulate the effect of the thyroarytenoid muscle contraction in altering the lateral stiffness of the vocal fold. During phonation subglottic pressure, vocal fold longitudinal tension and balloon size were systematically varied. The photoglottographic and electroglottographic signals, sound intensity, and airflow rate were measured. Multiple regression analysis showed that sound intensity was directly related to subglottic pressure (p less than 0.001) and inversely related to balloon size (p less than 0.001). Vocal efficiency was directly related to subglottic pressure (p less than 0.001). Frequency of vibration was directly related to balloon size (p less than 0.05), vocal fold tension (p less than 0.001), and subglottic pressure (p less than 0.001). Open quotient was directly related to vocal fold tension (p less than 0.01) and inversely related to balloon size (p less than 0.001). Clinical implications of these results will be discussed.

Regulation of Phonatory Efficiency by Vocal Fold Tension and Glottic Width in the Excised Canine Larynx

An excised canine larynx was used to assess the effects of glottic width and vocal fold tension on acoustic power, aerodynamic power, and vocal efficiency. Multiple regression analysis of the data obtained from 10 larynges revealed that with increased vocal fold tension there is a logarithmic decline in radiated acoustic power, while aerodynamic power remains constant (p less than .05). Vocal efficiency has a similar logarithmic decrease with increased tension (p less than .05). With narrowing of the glottis, the acoustic power increases more than the aerodynamic power delivered to the larynx, and the efficiency increases. The inverse relationships glottic width has with acoustic power and vocal efficiency are best described by a reciprocal model (p less than .01). There is a negative linear relationship between glottic width and aerodynamic power. These results suggest that within the larynx the energy conversion is regulated by glottic aperture and longitudinal vocal fold tension. The optimal width for efficiency appears to be the narrowest width that produces phonation within the modal register, whereas increased tension decreases the efficiency of the glottis.

A Model for Neurologic Sources of Aperiodicity in Vocal Fold Vibration

The time course of a force twitch in the thyroarytenoid muscle is modeled, and trains of twitches are summed to simulate force tetani. By incorporating means and standard deviations of motoneuron firing rates, and by applying random phase relationships between simulated motor units, a quantitative model of the ripple of vocal fold tension is obtained. From this ripple, perturbations in fundamental frequency are calculated as a function of the number of motor units in the muscle, the mean and standard deviation of the firing rate of dominant motoneurons, and the variability in the size (twitch amplitude) of the motor units. Predicted perturbations range between 0.2% and 1.2%, depending on the choice of parameters. Perturbation decreases with the number of motor units and with increased mean firing rate, but increases with the variability in motor unit size and with variability in the firing rate. Techniques are discussed by which neurologic jitter might be isolated from other sources of irregularity in vocal fold vibration.

Vocal fold vibration of the canine larynx: Observation from an infraglottic view

Summary The authors studied the vibratory action of the canine vocal fold from the tracheal side utilizing high-speed cinematography. Five excised canine larynges were used, and the lower surface of the vocal fold of three of them were marked with India ink as a tracer of a specific point on the vocal fold. A mucosal prominence, called the mucosal upheaval, appeared between the anterior commissure and the vocal process. Vibration was not seen below the mucosal upheaval. The mucosal wave started to move medially from just above the mucosal upheaval. The mucosal wave then became the free edge (lower lip) and collided with that of the other side at the midline. After collision, the lower lip moved upward to become the upper lip. At the same time, a part of the lower lip reflected laterally. The mucosal wave of the next cycle started from just above the mucosal upheaval during an opening phase. The mucosal upheaval vibrated with a low amplitude and with an earlier phase than the other portion of the vocal fold. The increase in tension of the vocal fold did not change the basic vibratory pattern of the mucosal upheaval, the mucosal wave, or the free edge. However, analysis of the mark before and after the increase in tension revealed that the mucosal upheaval occurred more medially or above when the vocal fold tension increased.

Phonatory vocal fold function in the excised canine larynx

The development of valid objective measurements of vocal cord vibration during phonation is a goal of current research in laryngeal physiology. An excised canine larynx was used to study the effects of vocal cord tension, air flow rate, and glottic width on glottographic parameters. The electroglottographic and photoglottographic wave-forms were simultaneously recorded as the vocal cord tension, glottic width, and air flow rate were systematically varied. These glottographic waveforms were analyzed to determine the open quotient and speed quotient. Multiple regression analysis of the data obtained from 10 larynges showed the open quotient to be directly related to vocal fold tension (p less than 0.001), glottic width (p less than 0.01), and fundamental frequency (p less than 0.001). Speed quotient was inversely related to glottic width and and subglottic pressure (p less than 0.05). Regression analysis also showed frequency of vibration to be directly related to tension (p less than 0.001) and inversely related to glottic width (p less than 0.001), with different combinations of glottic tension and width capable of producing the same frequency. The open and speed quotients thus reflect the changes in the vibratory patterns of the vocal folds produced by alterations in tension and width. The clinical implications of these results will be discussed, with emphasis on glottography as an objective assessment of the various laryngeal framework procedures being performed.

Glottographic Analysis of Phonation in the Excised Canine Larynx

An excised canine larynx model of phonation was developed to assess the effect of vocal fold length and tension on glottographic waveforms. The canine larynx in an experimentally produced phonatory model vibrated in a two-mass system comparable to human voice production. The recorded glottographic waveforms for the excised canine larynx were similar to signals recorded in humans in the chest register. Vocal fold length, longitudinal vocal fold tension, glottic width, and airflow rate were varied while simultaneous measurements were made of the subglottic pressure, electroglottographic signal, photoglottographic signal, and acoustic signal. The model used is illustrated and discussed, with emphasis on the method of simulating the actions of all of the intrinsic laryngeal muscles, including the thyroarytenoid muscles. The open quotient and speed quotient, calculated from the glottographic signals, were dependent on vocal fold length and tension and glottic width. These results suggest that glottographic analysis, particularly speed quotient and open quotient, provide valuable information on vocal fold vibration during phonation, and may be important in assessing laryngoplasty procedures.

声帯の物性について

Simple and objective methods were developed to evaluate the mechanical properties of the vocal fold in relation to mobility of the vocal fold mucosa and stiffness of the vocal fold. Mobility of the vocal fold mucosa was measured with a fine suction tube, and stiffness of the vocal fold was evaluated by analyzing stress-strain curves in human and canine excised larynges under various conditions.1) Mobility of the vocal fold mucosa was greatest in the middle of the membranous portion and less around the anterior commissure and the vocal process. Stiffness of the membranous portion of the vocal fold was least at the middle and greater around the anterior commissure and the vocal process. Mobility of the false vocal fold mucosa was much greater, and stiffness of the false vocal fold was much less, than those of the true vocal fold.2) As the vocal fold tension increased, mobility of the vocal fold mucosa decreased and stiffness of the vocal fold increased as the vocal pitch rose. Marked differences of the mechanical properties were observed between the “body” and the “cover” of the vocal fold, especially when tension was applied to the vocal fold.3) When the vocalis muscle contracted, the vocal fold tended to be less stiff and more viscous.4) When the vocal fold mucosa became dry, stiffness of the vocal fold became greater.5) Submucosal injection of saline solution reduced mobility of the vocal fold mucosa and increased stiffness and viscosity of the vocal fold.