A rat excised larynx model of vocal fold scar.

PURPOSE: To develop and evaluate a rat excised larynx model for the measurement of acoustic, aerodynamic, and vocal fold vibratory changes resulting from vocal fold scar. METHOD: Twenty-four 4-month-old male Sprague-Dawley rats were assigned to 1 of 4 experimental groups: chronic vocal fold scar, chronic vocal fold scar treated with 100-ng basic fibroblast growth factor (bFGF), chronic vocal fold scar treated with saline (sham treatment), and unscarred untreated control. Following tissue harvest, histological and immunohistochemical data were collected to confirm extracellular matrix alteration in the chronic scar group; acoustic, aerodynamic, and high-speed digital imaging data were collected using an excised larynx setup in all groups. Phonation threshold pressure (P(th)), glottal resistance (R(g)), glottal efficiency (E(g)), vibratory amplitude, and vibratory area were used as dependent variables. RESULTS: Chronically scarred vocal folds were characterized by elevated collagen Types I and III and reduced hyaluronic acid abundance. Phonation was achieved, and data were collected from all control and bFGF-treated larynges; however, phonation was not achieved with 3 of 6 chronically scarred and 1 of 6 saline-treated larynges. Compared with control, the chronic scar group was characterized by elevated P(th), reduced E(g), and intralarynx vibratory amplitude and area asymmetry. The bFGF group was characterized by P(th) below control-group levels, E(g) comparable with control, and vocal fold vibratory amplitude and area symmetry comparable with control. The sham group was characterized by P(th) comparable with control, E(g) superior to control, and vocal fold vibratory amplitude and area symmetry comparable with control. CONCLUSIONS: The excised larynx model reported here demonstrated robust deterioration across phonatory indices under the scar condition and sensitivity to treatment-induced change under the bFGF condition. The improvement observed under the sham condition may reflect unanticipated therapeutic benefit or artifact. This model holds promise as a tool for the functional characterization of biomechanical tissue changes resulting from vocal fold scar and the evaluation of experimental therapies.

Aerodynamic, acoustic, and vibratory comparison of arytenoid adduction and adduction arytenopexy.

HYPOTHESIS: Adduction arytenopexy (AP) with thyroplasty provides improved physiologic placement of the vocal fold and therefore provides improved acoustic, aerodynamic, and vibratory function as compared with arytenoid adduction (AA) with thyroplasty. METHODS: Five cadaveric human larynges were prepared by removing supraglottic tissues and fixing the nontest vocal fold medially on the cricoid facet with a needle in a physiologic phonating position. Each test vocal fold was then sequentially tested using an excised larynx phonation system, first with AA with silastic medialization and then converted to AP without changing the contralateral fold position or silastic wedge. The excised larynx setup allowed for simultaneous collection of data, specifically subglottic pressure (including measurement of phonation threshold pressure [PTP]), mean airflow, acoustic output, and full-frame high-speed digital video. RESULTS: Aerodynamic evaluation was similar for each group with similar subglottic pressure versus output curves. Conditions involving AP typically had PTP values that were 80% of that for comparable AA conditions. Acoustic evaluation revealed differences between the two groups. Each AA was found to be vibrating with two dominant frequencies with their associated harmonics. Each AP vibrated at a single dominant frequency with its harmonics. CONCLUSION: AP provides improved vocal outcomes by decreasing system noise and decreasing PTP, which may lead to a stronger glottal signal with decreased vocal effort.

The influence of epilarynx area on vocal fold dynamics.

OBJECTIVE: This study investigated the influence of epilarynx area on an excised human vocal fold during phonation. STUDY DESIGN: A hemilarynx set-up using an excised human larynx was used. An artificial vocal tract with an epilarynx tube of variable cross-sectional area was attached. High-speed imaging was performed and standard phonatory variables were measured. RESULTS: Glottal airflow, fundamental frequency, and sound level increased as a function of subglottal pressure. A decrease in epilarynx area decreased phonation threshold pressure, glottal airflow, and vocal fold displacements and velocities. CONCLUSIONS: Preliminary experimental results confirm that narrowing the epilarynx area facilitates phonation by decreasing phonation threshold pressure, presumably through impedance matching of the glottal source and vocal tract. SIGNIFICANCE: As this phenomenon associated with epilarynx narrowing is further quantified and generalized, eventually new surgical alterations of the epilaryngeal structure may be suggested to facilitate phonation, in addition to standard phonosurgical procedures.

Functional outcomes of reduced hyaluronan in acute vocal fold scar.

To examine the functional effects of hyaluronan and collagen alterations in acute vocal fold scar, we injured 15 pig larynges by vocal fold mucosa stripping. At 3, 10, and 15 days after operation, we performed excised larynx experiments to measure phonation threshold pressure (PTP) and vocal economy (an acoustic output-cost ratio; OCR), and then performed hyaluronan and collagen assays. Five uninjured larynges were used as excised controls. Hyaluronan was reduced in the scarred vocal folds through 15 days of wound healing. Collagen was increased at day 15. The PTP was increased and OCR was decreased in scarred larynges, indicating decreased vocal efficiency and ease of phonation. Thus, PTP and OCR were sensitive to the biomolecular changes in acute vocal fold scar. Hyaluronan was more susceptible than collagen to acute tissue ultrastructural alterations. These findings may provide a rationale for increasing hyaluronan in acute vocal fold scar to improve postoperative vocal outcomes.

Growth factor therapy for vocal fold scarring in a canine model.

Vocal fold scarring remains a therapeutic challenge. Hepatocyte growth factor (HGF) has strong antifibrotic activity and has proved to have therapeutic potential in restoration of scar tissues such as liver cirrhosis and lung fibrosis. The present study aimed to clarify the effects of HGF injection into scarred vocal folds in a canine model. Canine vocal folds were stripped unilaterally and treated with intracordal injection of saline solution (sham group), HGF (HGF group), or HGF with cultured autologous normal vocal fold fibroblasts (Fb/HGF group) 1 month after injury. The larynges were harvested 6 months after the initial injury and then subjected to vibratory and histologic examination. The results of vibratory examinations in the excised larynx setup revealed that phonation threshold pressure significantly increased and vocal efficiency was significantly reduced in all treated groups as compared to normal data obtained from normal canine larynges. However, the HGF group presented much better results than both the sham and Fb/HGF groups in terms of mucosal wave amplitude and incidence of vocal fold bowing, glottal incompetence, and phase asymmetry. The histologic data indicated a significant increase of collagen in both the sham and Fb/HGF groups, while normal levels of collagen were found in the HGF group. Tissue contraction of the lamina propria was also observed in both the sham and Fb/HGF groups, but was barely detectable in the HGF group. Although the HGF-treated vocal folds appeared to require more driving forces for vibration, HGF might prevent excessive collagen deposition and tissue contraction and thus reduce the effects of scarring on the vibratory properties of the vocal folds. From these data it is concluded that HGF has considerable potential in the treatment of vocal fold scarring.

An investigation of cricoarytenoid joint mechanics using simulated muscle forces.

Rotational and translational stiffnesses were calculated for arytenoid motion about the cricoarytenoid joint. These calculations were obtained from measurements on five excised human larynxes. For each larynx, known forces were applied to the arytenoid cartilage, and three markers were tracked as a function of applied forces. Assuming rigid body motion, arytenoid translations and rotations were computed for each applied force. Translational stiffnesses were obtained by plotting force versus displacement, and rotational stiffnesses were calculated by plotting torque versus angular rotation. A major finding was that the translational stiffness along the anterior-posterior direction was three times as great as the translational stiffnesses in the other two directions. This nonisotropic nature of the stiffnesses may be an important consideration for phonosurgeons who wish to avoid subluxation of the cricoarytenoid joint in patients. The computed rotational and translational stiffnesses currently are being implemented in 2D and 3D models. These stiffness parameters play a vital role in prephonatory glottal shaping, which in turn exerts a majorinfluence on all aspects of vocal fold vibration, including fundamental frequency, voice quality, voice register, and phonation threshold pressure.