An Investigation of Cricoarytenoid Joint Mechanics Using Simulated Muscle Forces

[[abstract]]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 major influence on all aspects of vocal fold vibration, including fundamental frequency, voice quality, voice register, and phonation threshold pressure

Vocal power and pressure–flow relationships in excised tiger larynges

Despite the functional importance of loud, low-pitched vocalizations in big cats of the genus Panthera, little is known about the physics and physiology of the mechanisms producing such calls. We investigated laryngeal sound production in the laboratory using an excised-larynx setup combined with sound-level measurements and pressure–flow instrumentation. The larynges of five tigers (three Siberian or Amur, one generic non-pedigreed tiger with Bengal ancestry and one Sumatran), which had died of natural causes, were provided by Omaha's Henry Doorly Zoo over a five-year period. Anatomical investigation indicated the presence of both a rigid cartilaginous plate in the arytenoid portion of the glottis, and a vocal fold fused with a ventricular fold. Both of these features have been confusingly termed ‘vocal pads’ in the previous literature. We successfully induced phonation in all of these larynges. Our results showed that aerodynamic power in the glottis was of the order of 1.0 W for all specimens, acoustic power radiated (without a vocal tract) was of the order of 0.1 mW, and fundamental frequency ranged between 20 and 100 Hz when a lung pressure in the range of 0–2.0 kPa was applied. The mean glottal airflow increased to the order of 1.0 l s–1 per 1.0 kPa of pressure, which is predictable from scaling human and canine larynges by glottal length and vibrational amplitude. Phonation threshold pressure was remarkably low, on the order of 0.3 kPa, which is lower than for human and canine larynges phonated without a vocal tract. Our results indicate that a vocal fold length approximately three times greater than that of humans is predictive of the low fundamental frequency, and the extraordinarily flat and broad medial surface of the vocal folds is predictive of the low phonation threshold pressure

Prevention of vocal fold scarring by topical injection of hepatocyte growth factor in a rabbit model

[[abstract]]Objectives/Hypothesis Vocal fold scarring disrupts the layer structure of the vocal fold lamina propria that is essential for optimal mucosal vibration. Prevention of vocal fold scarring remains challenging. Hepatocyte growth factor (HGF) has strong antifibrotic activity. The authors' previous studies have found that HGF stimulates hyaluronic acid production and suppresses collagen production from vocal fold fibroblasts, suggesting that HGF has therapeutic potential in prevention of vocal fold scarring. The present study aimed to demonstrate the effects of HGF on vocal fold scarring in an in vivo rabbit model. Study Design Animal experiment. Methods The vocal fold mucosa was stripped unilaterally in 20 rabbits, then HGF or saline (sham‐treated group) was immediately injected into the injured site. At 6 months after the procedure, histological, rheological, and physiological examinations of vibratory behavior were completed. Results Histological examination revealed excessive collagen deposition and disorganized elastin in the sham‐treated group, whereas the HGF‐treated group presented with better wound healing exhibiting less collagen deposition. Contraction of the injured vocal folds observed in the sham‐treated group did not occur in the HGF‐treated group. Rheological data indicated that the HGF‐treated vocal folds were less stiff and viscous compared with the sham‐treated group. Mucosal vibration of HGF‐treated vocal folds appeared much better than the sham‐treated group in terms of phonation threshold pressure, vocal efficiency, mucosal wave amplitude, and glottal closure. Conclusion Hepatocyte growth factor proved to be useful in preventing vocal fold scarring and maintaining viscoelastic shear properties of the vocal fold