Thyroarytenoid muscle activity and infraglottic aspect of canine vocal fold vibration

OBJECTIVES: To investigate the effect of contraction of the thyroarytenoid (TA) muscle on the location of the mucosal upheaval (MU) and to estimate the location of the MU in relation to the histologic structure of the vocal fold. BACKGROUND: The MU is a small mucosal ridge arising on the lower surface of the vocal fold during phonation and is thought to be the lower border of the vibrating structure. METHODS: Vibrations were elicited under three conditions: during bilateral TA muscle contraction, without TA muscle stimulation, and during vocal fold lengthening. The vibrations were recorded from the tracheal side by high-speed cinematography or videotape recording combined with stroboscopic illumination. The larynx was prepared for histologic observation in the frontal plane. Tattooed marks on the lower surface of the vocal fold were used to locate macroscopically observed landmarks with reference to microscopic structures. RESULTS: The MU shifted laterally toward the tracheal side during TA muscle contraction. When the vocal fold was lengthened, the MU shifted medially toward the free edge. Histologic examination showed that the MU in the absence of TA muscle contraction arose slightly above the area where the muscular layer approached the epithelial layer. CONCLUSION: When the TA muscle contracts, the vibrating area expands toward the tracheal side, and a more dynamic mucosal wave occurs in the vertical direction. We believe that a part of the body and the cover are probably involved in the vibratory movement of the vocal fold.     

Localization of laminin, fibronectin, E-cadherin, and integrins in endometrium and endometriosis

Stiffness of the vocal fold is a significant factor in determining mucosal wave propagation and in the control of the fundamental frequency of phonation. We measured pliability of the vocal fold mucosa in an in vivo canine model as an index of stiffness while the histological layer-by-layer structure of the vocal fold was not disrupted. The point 1 mm below the free edge showed a maximal pliability that gradually diminished toward the tracheal side and reached a minimum. When the thyroarytenoid (TA) muscle contracted, pliability of the mucosa was significantly increased (P < 0.001). Mucosal pliability of the excised larynx was significantly increased compared with that in vivo (P < 0.001). The point of minimal pliability in the absence of TA muscle contraction did not shift after excision of the larynx, while TA muscle contraction caused a downward shift of the point of minimal pliability. Mucosal pliability can thus be used to quantitatively assess the effects of TA muscle contraction on stiffness of the vocal fold mucosa.     

Lubrication mechanism of the larynx during phonation: an experiment in excised canine larynges

To evaluate how the viscosity of the laryngeal mucus influences vocal fold vibration, two fluids of differing viscosity were applied separately to excised canine larynges and experimental phonation was induced. Vibration of the vocal folds was measured by use of a laryngostroboscope and an X-ray stroboscope. With the high viscosity fluid, the amplitude of vibration of the free edge and the peak glottal area was decreased while the open quotient was increased. Because the viscosity of this fluid affected the wave motion of the vocal fold mucosa, changes in viscosity of the mucus may be involved in causing such disorders as hoarseness, in the absence of apparent changes in the vocal folds themselves.     

Fixity of vocal cords and laryngocele in acromegaly

Acromegalic patients have a reduced life expectancy mainly due to cardio-, cerebrovascular and respiratory disorders and increased prevalence of neoplasias. Particularly, the pathogenesis of respiratory disorders in acromegalics is debated. Laryngeal abnormalities are not yet well clarified even if they are frequently involved in the occurrence of respiratory insufficiency. In this study, we report on a 65 year-old acromegalic male suffering from frequent and severe dyspnea attacks and clinical findings of respiratory upperway obstruction, besides the common acromegalic features. At the external examination of the larynx, a bilateral painless and soft mass, located in the laterocervical region under the hyoid bone, was detected. Fiberoptic laryngoscopy, showed bilateral swelling between the aryepiglottic fold and the false vocal cords, whose size increased during the expiration and the phonation, fixity of the vocal cords in paramedian position, with a marked reduction of the respiratory space and increase in arytenoid cartilage size and mucosal edema. Neck and mediastinum CT scan showed the presence of an air containing bilateral swelling, crossing the thyrohyoid membrane. Bilateral cricoarytenoidal joint chondrocalcification, associated to a mixed-type bilateral laryngocele, was diagnosed. Laryngoceles were both surgically removed and a left monolateral arytenoidectomy was performed, using fiberoptic microlaryngoscopy with CO2 laser. The clinical evaluation, one month later, confirmed the complete disappearance of dyspnea and a partial improvement of phonation. Three months later, laryngoscopy showed the bilateral restoration of vocal cords motility and a significant improvement of phonation. This case presents an uncommon and severe respiratory problem in acromegaly such as the fixity of vocal cords associated to laryngocele. Circulating GH and IGF-I hypersecretion caused edema and laxity of laryngeal mucosa as well as bilateral ankylosis of cricoarytenoidal joints. The use of CO2 laser technique via micro-laryngoscopy successfully resolved laryngeal abnormalities.     

Further studies of phonation threshold pressure in a physical model of the vocal fold mucosa

This paper reports results of further experimentation on a previously developed physical model of the vocal-fold mucosa [Titze et al., J. Acoust. Soc. Am. 97, 3080-3084 (1995)]. The effects of vocal-fold thickness, epithelial membrane thickness, and prephonatory glottal geometry on phonation threshold pressure were studied. Phonation threshold pressures in the range of 0.13 to 0.34 kPa were observed for an 11-mm-thick vocal fold with a 70-micron-thick "epithelial" membrane for different "mucosal" fluid viscosities. Higher threshold pressure was always obtained for thinner vocal folds and thicker membranes. In another set of experiments, lowest offset threshold pressure was obtained for a rectangular or a near-rectangular prephonatory glottis (with a glottal convergence angle within about +/- 3 degrees). It ranged from 0.07 to 0.23 kPa for different glottal half-widths between 2.0 and 6.0 mm. The threshold for more convergent or divergent glottal geometries was consistently higher. This finding only partially agrees with previous analytical work which predicts a lowest threshold for a divergent glottis. The discrepancy between theory and data is likely to be associated with flow separation from a divergent glottis.     

Reticular fibers in the vocal fold mucosa

Light and electron microscopic investigations of the reticular fibers (RFs) in the vocal fold mucosa were carried out on excised human adult larynges. The results are summarized as follows. Reticular fibers were found in the superficial and intermediate layers of the lamina propria of the vocal fold mucosa. They were most abundantly discovered around the vocal fold edge, and they decreased toward the superior and inferior portions of the vocal folds. The RFs were composed of slender fibrils, about 40 nm in diameter, and having cross-bands with a periodicity of about 67 nm. They were found in close association with the basal lamina of the epithelium and blood vessels. The slender fibrils of the RFs did not form any bundles, but branched and anastomosed. The RFs formed delicate 3-dimensional networks, and the spaces among the fibers were relatively large. Glycoprotein and glycosaminoglycan (proteoglycan) were situated around the RFs and in the spaces among the fibers. Elastic fibers were located in the spaces among the RFs. The 3-dimensional structure of the RFs in the vocal fold mucosa, first demonstrated in this study, appears to be one of the key components of the structural maintenance and viscoelasticity of the vibrating vocal fold tissue.     

Critical review of phonosurgical methods in the treatment of sulcus vocalis

INTRODUCTION: Sulcus vocalis is an epithelial invagination along the free edge of the membranous vocal fold. It interferes with the glottic closure and vibration pattern. Sulcus vocalis provokes voice fatigue, hoarseness and breathiness, and it usually appears in association with hyperkinetic phonatory pattern. Hyperkinesis develops secondarily, due to the compensatory effort to overcome the deficiency in glottic closure. The treatment of sulcus vocalis is very difficult. Phonosurgery is used, and is followed by postoperative voice therapy. PHONOSURGICAL OPERATIONS: Various surgical techniques are used in the therapy of sulcus vocalis. Over a 10-year period we have operated on 1550 patients with benign lesion of the vocal folds, of whom only 11 had sulcus vocalis (0.7%). We carried out various surgical techniques. a) Excision of sulcus A longitudinal incision of mucosa is performed along the upper surface of the vocal fold, distant of the free edge. Mucosa is undermined caudally, and sulcus is detached from its base. Sulcus is then removed by surgical scissors. With this technique we could not provide physiological phonation and vibration pattern, in spite of an apparent improvement in the voice. b) "Slicing mucosa" technique This procedure was suggested by Pontes, and it also begins with a longitudinal incision followed by creation of inferiorly based slices of mucosa. c) Excision plus rhyroplasty Excision of sulcus is combined with thyroplasty type I in order to achieve medialization of the vocal fold. It can be used in cases with severe glottal gap in order to improve the results of excision. d) Implants Various materials were used in order to enlarge the mass of the vocal fold. In our patients, the results of this procedure were inferior as related to excision surgery. DISCUSSION: The surgical procedure which is safe and accepted by the majority of surgeons has not yet been at our disposal. The treatment of sulcus vocalis should start with voice therapy, which lasts as long as the patient shows a progress. Only then the surgical procedure can be discussed. We obtained the best results with the combination of excision and voice therapy. However, the surgeon and the patient must be aware that the treatment is demanding and long-lasting.     

Functional differences between the two bellies of the cricothyroid muscle

The contraction of the cricothyroid (CT) muscle, which results in a decrease in the distance between the thyroid and cricoid cartilages, is considered to be the main factor in lengthening the vocal folds. This is achieved by rotation of the CT joint. The CT muscle is composed of two distinct bellies, the pars recta and the pars obliqua. The function of each subunit is not clearly understood, although it is believed that they act differently because their fibers run in different directions. To clarify the function of the two bellies in phonation, the fundamental frequency (F0), vocal intensity, subglottic pressure, vocal fold length, and CT distance were measured using an in vivo canine laryngeal model. On the basis of these measurements, we demonstrated that the two bellies are varied in their effect on raising the pitch, rotation, and forward translation of the CT joint. The stimulation of the pars recta nerve resulted in a greater increase in the F0 value compared with that of pars obliqua. The combined activity of the pars recta and pars obliqua is important in adjustment of the vocal fold length. The CT approximations directed parallel to the pars recta and pars obliqua simultaneously were more effective in elevation of the pitch than the approximation placed parallel to the pars recta only. This finding may be clinically significant with regard to CT approximation thyroplasty in human trails.     

Pleiotropic functions of neurotrophins in development

Laryngeal framework surgery can change the position and tension of the vocal folds safely without direct surgical intervention in the vocal fold proper. Some 23 years of experience with phonosurgery have proved its usefulness in treating dysphonia related to unilateral vocal fold paralysis, vocal fold atrophy, and pitch-related dysphonias . Meanwhile, much information about the mechanism of voice production has been obtained through intraoperative findings of voice and fiberscopic examination of the larynx . Based on such knowledge together with information obtained through model experiments, the human vocal organ was reconsidered mainly from the mechanical view point, and the roles of voice therapy and singing pedagogy were discussed in relation to phonosurgery. The vocal organ may not be an ideal musical organ and is rather vulnerable, but its potential is enormous.     

A precricoid swelling in a patient treated with Teflon injection in the vocal fold after idiopathic left vocal fold palsy

Vocal fold palsy is a cause of dysphonia. Due to incomplete glottic closure during phonation, patients with a unilateral vocal fold palsy present with a weak and breathy voice and recurrent aspiration. To lessen the clinical manifestations of unilateral vocal fold palsy, polytetrafluoroethylene (Teflon) paste is one agent which has been injected into the paraglottic region, thus causing the vocal fold to move more medially. One of the complications associated with Teflon paste injection is migration of the paste into the surrounding tissues. We present a patient with idiopathic left vocal fold palsy who underwent Teflon injection to the vocal fold and subsequently developed a precricoid nodule, mimicking a cartilaginous swelling.     

Phonosurgery of chronic vocal cord edema

INTRODUCTION: Chronic (Reinke's) oedema of the vocal folds is a frequent and declicate objective of phonosurgery. It is characterized by a marked bilateral subepithelial oedema, which develops by degrees, as a non-specific reaction of the vocal folds to various irritative noxious agents (especially smoking), in patients with some predisposition. It is found, by the light and electron microscopes and immunohistochemistry, that oedema is characterized by subepithelial fissure-like spaces, which accumulate a protein-rich fluid, and develops like neobursae. Therefore, mechanical factors and functional influences may also contribute to the development of Reinke's oedema. The voice is low pitched and with various degrees of hoarseness. Reinke's oedema alters the mechanical properties of the cover, which becomes very pliable and with reduced stiffness, incapacitating the vocal fold for production of high tones. Hoarseness is induced in subject with associated laryngitis, or disbalance in mechanical properties of the vocal folds. Hyperkinetic pattern of voice production can often be seen in patients with Reinke's oedema, which is a compensatory results of reduced functional capability of the vocal folds. Stroboscopy reveals a prolonged closed phase of the vibratory cycles and strikingly marked mucosal waves. MATERIAL AND METHOD: A series of 371 patients with Reinke's oedema was operated by direct microlaryngoscopy, under the general anaesthesia. The "excessive" mucosa was removed by bimanual micro-procedure, while the care was not taken to severe layers deeper than a superficial part of the intermediate layer of the vocal fold (Reinke's space). In this procedure we used the micro-forceps and scissors, to detach oedema parallel to the free edge of the vocal fold, at its upper and lower demarcation lines, beginning from the posterior part of oedema. Another 27 patients were operated by indirect procedures. Microstroboscopy (IMS) was used in subjects, while videostroboscopy (IVS) was carried out in another 18 patients. These procedures were used when general anaesthesia was contraindicated, and in patients with Reinke's oedema of the first degree (initial oedema). In these patients only a mucosal strip was removed from the upper surface of the vocal fold, apart from the free edge. Oedema was removed bilaterally, while the formation of the postoperative web was prevented by regular examinations of the patient. In several cases of adherence between the two folds in their anterior commissure, the problem was solved indirectly by the use of a curved forceps and under the topical anaesthesia. Postoperative voice rest and administration of steroids were mandatory. Surgical and functional results were followed-up by stroboscopy over the period of at least three years after surgery. The majority of patients were additionally treated by the voice therapy, while the decision about its use was made three weeks after surgery. RESULTS: Functional results of our therapeutic strategy were satisfactory in our series of 398 subjects with Reinke's oedema. In comparison with other benign lesions of the vocal folds, it was more time-consuming and required a more frequent use of the postoperative voice therapy (Table 1). Thus, we have not encountered recurrences. DISCUSSION: During the last 10 years we operated on 1550 patients with various benign lesions of the vocal folds, including 398 subjects with Reinke's oedema (25.7%). Excision of the "excessive" mucosa may appear today as a procedure which is too radical if compared with many techniques which have been offered during the last decades: conservative excision and suction, squeezing technique, laser. Nevertheless, the histological structure of Reinke's oedema, with subepithelial fissure-like spaces indicated that the latter procedures can hardly be expected to prevent recurrences. It was found that the use of laser was not favourable in this area for its deteriorative local effect.     

Functional damage of the larynx

INTRODUCTION: The basic mechanism of the development of functional voice disorders is an excessive collision pressure between the vocal folds during phonation, which occurs between the membranous folds, and/or the vocal processes. Functional-traumatic lesions of the vocal folds appear mainly at the junction between the anterior and the middle thirds of the vocal folds, slightly below the free edge. This is the "predilection site" of the vocal folds, which is the most active part of the vocal folds during phonation, and is therefore mostly exposed to functional-traumatic changes. This study is aimed at establishing the most frequent benign lesions of the vocal folds, which appear at the predilection sites of the vocal folds, and discussing their functional-traumatic aetiology. MATERIAL AND METHODS: During the past 10 years 1550 patients underwent various microsurgical procedures for benign lesions of the vocal folds. They were studied for the precise localization of the lesions by the use of indirect videostroboscopy or microstroboscopy, and direct microlaryngoscopy related to the technique which has been used in each particular patient. In this way an overall number of lesions was established, which were located at the predilection sites of the vocal folds, indicating their functional-traumatic aetiology. RESULTS: It has been established that 1068 lesions (68.6%) were located at the predilection site of the vocal folds (Table 1). Namely, these were nodular lesions, polyps, cysts, and haematoma. Contact hyperplasia appeared at the posterior third of the vocal folds due to a special mechanism of its development. DISCUSSION: Functional-traumatic lesions are mucous stranding, nodular lesions, polyps, cysts, contact hyperplasia and haematoma. All these lesions are either of functional origin or functional voice disorders which contribute, to some degree, to their development.     

Estimating phonation threshold pressure

Phonation threshold pressure (PTP) is the minimum subglottal pressure required to initiate vocal fold oscillation. Although potentially useful clinically, PTP is difficult to estimate noninvasively because of limitations to vocal motor control near the threshold of soft phonation. Previous investigators observed, for example, that trained subjects were unable to produce flat, consistent oral pressure peaks during/pae/syllable strings when they attempted to phonate as softly as possible (Verdolini-Marston, Titze, & Druker, 1990). The present study aimed to determine if nasal airflow or vowel context affected phonation threshold pressure as estimated from oral pressure (Smitheran & Hixon, 1981) in 5 untrained female speakers with normal velopharyngeal and voice function. Nasal airflow during /p/occlusion was observed for 3 of 5 participants when they attempted to phonate near threshold pressure. When the nose was occluded, nasal airflow was reduced or eliminated during /p/;however, individuals then evidenced compensatory changes in glottal adduction and/or respiratory effort that may be expected to alter PTP estimates. Results demonstrate the importance of monitoring nasal flow (or the flow zero point in undivided masks) when obtaining PTP measurements noninvasively. Results also highlight the need to pursue improved methods for noninvasive estimation of PTP.     

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.     

Fine three-dimensional structure of pericytes in the vocal fold mucosa

An investigation was carried out to determine the fine three-dimensional structure of pericytes in excised human vocal fold mucosa, by means of scanning and transmission electron microscopic observation. The results are summarized as follows. 1) There were many pericytes around the true capillaries, arterial capillaries, and venous capillaries in the vocal fold mucosa. 2) Newborns had pericytes around the capillaries in the vocal fold mucosa. 3) The pericytes had bulged fusiform or polygonal cell bodies and branching processes. The branching processes consisted of long and relatively thick longitudinal ones and short circumferential ones. 4) The cell body and processes of the pericytes encircled the capillaries, and the tips of the processes formed intercellular tight junctions with endothelial cells and made a firm connection with them. 5) The pericytes had many cytoplasmic filaments. 6) The pericytes in the vocal fold mucosa appeared to support and protect capillary walls in the vibrating tissue.     

Reversibility of medialization laryngoplasty. An experimental study

Medialization laryngoplasty has become a routine procedure for cases of unilateral vocal fold paralysis. In certain clinical situations, it may become desirable to reverse the procedure and remove the implant. This process was studied experimentally in eight dogs in a chronic model of induced canine phonation. A silicone polymer implant was inserted to medialize one normal vocal fold for a period of 1 month, after which it was removed. Motion of the cricoarytenoid (CA) joint and induced phonation were studied weekly while the implant was in place, and for another month following implant removal. Significant abnormalities were found even with this relatively short period of implantation. With the implant in place, impairment of CA joint mobility was found in seven of the eight dogs, precluding phonation. A dense fibrous capsule rapidly developed around the implant, making its removal technically difficult. Following implant removal, a gradual return to normal function was found in only three of the eight dogs. One of the animals had evidence of neural injury, while four had intact neural function but impaired mobility or fixation of the CA joint. Medialization laryngoplasty should not be considered a reversible procedure. The clinical implications of these findings are discussed.     

Long-term model of induced canine phonation

Experimental induced phonation in the dog has been used in short-term studies by several investigators and has proved quite useful in laryngeal research. In this study a long-term canine phonation model is described that uses permanently implanted electrodes on the superior and recurrent laryngeal nerves. A serial induced phonation model has not been previously reported and is needed for laryngeal research in which voice results are a primary end point. Inexpensive, reliable, nontoxic electrodes were designed and fabricated. The laryngeal nerves were found to be quite susceptible to injury, necessitating a series of changes in electrode design. Electrode durability and laryngeal nerve viability improved with each design modification; the final design gave a recurrent laryngeal nerve viability rate of 100% at 6 weeks, 83% at 9 weeks, and 73% at 12 weeks. Induced phonation was successfully produced on a repeated basis by stimulating the recurrent laryngeal nerves while passing air through the larynx, in 22 (95.6%) of 23 animals. Stimulation of the superior laryngeal nerves increased vocal fold length and tension but was not required for phonation. Technical aspects of chronic implantation and stimulation of the laryngeal nerves are discussed. The development and successful long-term implantation of electrodes on the laryngeal nerves and their use in repeated induced phonation have not been reported previously.     

Longitudinal evaluation of vocal function following thyroplasty type I for the treatment of unilateral vocal paralysis

Longitudinal changes of vocal efficiency and stability following thyroplasty type I were analysed. Fifty-three patients with unilateral vocal fold paralysis underwent vocal function evaluation preoperatively and 1, 3 and 6 months postoperatively. Vocal function assessment included videostrobolaryngoscopic examination, acoustical and aerodynamic analyses, and perceptual ratings of voice. Parameters including glottic gag size, maximum phonation time, glottic flow rate, jitter, harmonic to noise ratio, breathness, hoarseness, loudness and phrasing showed significant improvement after thyroplasty and remained stable within 1 month with only slight fluctuations over a 6 month period. Postoperative voice outcome was not affected by age, sex, duration of vocal symptoms, etiology of paralysis, or preoperative pulmonary function.     

An animal experiment on short gut lengthening

OBJECTIVE: To investigate the anatomical and histological changes of the lengthened gut by a special intraluminal tubular expander on the basis of the theory of "tension-stress". METHODS: Nineteen New Zealand white rabbits were used. A 5 cm segment of the terminal ileum with a pedicle was put underneath the abdominal wall, with its proximal end closed and its distal end exteriorized as a stoma. One week later, as the wound healed well, an expander made of a small rubber tube was inserted into the short gut loop through the stoma. Three milliliters of water was injected as an initial dose. Then 0.5 ml water as an increment was injected subsequently every 12 hours until the total amount of water reached 15 ml and kept stable for two weeks. RESULTS: Anatomically, the length and the capacity of the intestinal loop were recorded, after 15 ml expanding, as an average of 150% lengthening of the original and an average of 293% expansion. Two weeks after the removal of the expander, partial shrinking was observed. A stable lengthening had 123% of the original length, while the capacity reduced to 200% of the original one. Histologically, there was no remarkable changes of the mucosa or submucosa. But significant hypertrophy of the musculature and serosa layer was observed. The total thickness of the musculatures was 618% of the normal control's. Ultrastructurally, there were enlargement of the smooth muscle cells, increase in number and size of the mitochondria in the cytoplasm and widening of the intercellular space. CONCLUSION: A short gut can be lengthened by a tubular expander following the rule of gradual tension and stress.     

Assessment of vocal function using simultaneous aerodynamic and calibrated videostroboscopic measures

Despite many attempts to model how vocal fold movements relate to the aerodynamic forces acting on them during phonation, there have been few simultaneous measurements of glottal area and transglottal air pressures and flows. A novel system is described that combines endoscopic measurement of glottal area with aerodynamic flow and pressure measures made during phonation. Results from bench top model tests and from one human subject are presented. For both tests, an aerodynamic model of airflow through a constriction was used to predict the area of the constriction (glottis), and these predictions were compared with endoscopic measurements. The results showed good correlation between predicted and observed areas; however, for small constrictions (<0.025 cm2), whether artificial or glottal, the errors in estimating areas with either optical or aerodynamic methods increase significantly. These results suggest that this measurement system has the potential to enhance the assessment of vocal function.