Vocal Folds

Objectives. To examine the current state of the science regarding the role of systemic hydration in vocal
function and health.
Study Design. Literature review.
Methods. Literature search spanning multiple disciplines, including speech-language pathology, nutrition and dietetics,
medicine, sports and exercise science, physiology, and biomechanics.
Results. The relationship between hydration and physical function is an area of common interest among multiple professions.
Each discipline provides valuable insight into the connection between performance and water balance, as well
as complimentary methods of investigation. Existing voice literature suggests a relationship between hydration and
voice production; however, the underlying mechanisms are not yet defined and a treatment effect for systemic hydration
remains to be demonstrated. Literature from other disciplines sheds light on methodological shortcomings and, in some
cases, offers an alternative explanation for observed phenomena.
Conclusions. A growing body of literature in the field of voice science is documenting a relationship between hydration
and vocal function; however, greater understanding is required to guide best practice in the maintenance of vocal
health and management of voice disorders. Integration of knowledge and technical expertise from multiple disciplines
facilitates analysis of existing literature and provides guidance as to future research.

Abstract: Characterisation of the bio-mechanical properties of the human vocal fold is an essential aid to understanding vocal fold oscillation, as an aid to diagnosis, and to support surgical as well as tissue engineering therapies. The authors will present preliminary results of an extensive study that has examined 20 excised human larynxes, and obtained data from 8 volunteer patients in-vivo during surgery under general anaesthesia.

Dehydration may alter vocal fold viscoelastic properties, thereby hampering phonation. The effects of water loss induced by an osmotic pressure potential on vocal fold tissue viscoelastic properties were investigated. Porcine vocal folds were dehydrated by immersion in a hypertonic solution, and quasi-static and low-frequency dynamic traction tests were performed for elongations of up to 50%. Digital image correlation was used to determine local strains from surface deformations. The elastic modulus and the loss factor were then determined for normal and dehydrated tissues. An eight-chain hyperelastic model was used to describe the observed nonlinear stress-stretch behavior. Contrary to the expectations, the mass history indicated that the tissue absorbed water during cyclic extension when submerged in a hypertonic solution. During loading history, the elastic modulus was increased for dehydrated tissues as a function of strain. The response of dehydrated tissues was much less affected when the load was released. This observation suggests that hydration should be considered in micromechanical models of the vocal folds. The internal hysteresis, which is often linked to phonation effort, increased significantly with water loss. The effects of dehydration on the viscoelastic properties of vocal fold tissue were quantified in a systematic way. A better understanding of the role of hydration on the mechanical properties of vocal fold tissue may help to establish objective dehydration and phonotrauma criteria.

The purpose of this study was to measure the relationship between the shear elastic properties of vocal fold with respect to the direction of applied stress. There is extensive published material that quantifies the shear viscoelastic properties of the vocal fold, but as much of these data were obtained using rotating parallel plate rheometers, which are unable to resolve out difference of the shear elastic behaviour with respect to direction, there is very little data that indicates anisotropic behaviour. To overcome this gap in knowledge, the team devised an apparatus that is capable of applying a shear stress in a known direction. A series of measurements were taken at the mid-membranous position, in the transverse and longitudinal directions. Point-specific measurements were performed using fourteen human cadaver excised larynges, which were hemi-sectioned to expose the vocal fold. An extremely low sinusoidal shear force of 1 g was applied tangentially to the membrane surface in both the longitudinal and transverse direction, and the resultant shear strain was measured. With the probe applied to the intact vocal fold, the average ratio of the elasticity in the transverse with respect to the longitudinal direction was 0.55. Further investigation using histological staining of collagens in the lamina propria indicates that there is a visible difference in the general alignment of collagen fibres when comparing the coronal and the sagittal sections. Our conclusion is that there is a quantifiable difference between the shear elastic response of the lamina propria in the longitudinal and transverse directions, and that this could be explained by the difference in alignment of collagen fibres within the lamina propria.

Objective. This study mapped the variation in tissue elasticity of the subglottic mucosa, applied these data to provide initial models of the likely deformation of the mucosa during the myoelastic cycle, and hypothesized as to the impact on the process of phonation. Study Design. Six donor human larynges were dissected along the sagittal plane to expose the vocal folds and sub-glottic mucosa. A linear skin rheometer was used to apply a controlled shear force, and the resultant displacement was measured. These data provided a measure of the stress/strain characteristics of the tissue at each anatomic point. A series of measurements were taken at 2-mm interval inferior of the vocal folds, and the change in elasticity was determined. Results. It was found that the elasticity of the mucosa in the subglottic region increased linearly with distance from the vocal folds in all 12 samples. A simple deformation model indicated that under low pressure conditions the sub-glottic mucosa will deform to form a cone, which could result in a higher velocity, thus amplifying the low pressure effect resulting from the Venturi principle, and could assist in maintaining laminar flow. Conclusions. This study indicated that the deformation of the subglottic mucosa could play a significant role in the delivery of a low pressure airflow over the vocal folds. A large scale study will now be undertaken to secure more data to evaluate this hypothesis, and using computational fluid dynamics based on actual three-dimensional structure obtained from computed tomography scans the aerodynamics of this region will be investigated.

Currently, surgeons have no objective means to evaluate and optimize results of phonosurgery intraoperatively. Instead, they usually judge the vocal folds subjectively by visual inspection or by listening to the voice. This paper describes a new device that measures Young's (elastic) modulus values for the human vocal fold intraoperatively. Physiologically, the modulus of the vocal fold may be important in determining the nature of vocal fold vibration in normal and pathologic states. This study also reports the effect of recurrent laryngeal nerve stimulation on Young's modulus of the human vocal folds, measured by means of transcutaneous nerve stimulation techniques. Young's modulus increased with increases in current stimulation to the recurrent laryngeal nerve. Ultimately, Young's modulus values may assist surgeons in optimizing the results of various phonosurgeries.

Summary: The aim of this study was to measure the shear modulus of the vocal fold in a human hemilarynx, such that the data can be related to direction of applied stress and anatomical context. Dynamic spring rate data were collected using a modified linear skin rheometer using human hemilarynges, and converted to estimated shear modulus via application of a simple shear model. The measurement probe was attached to the epithelial layer of the vocal fold cover using suction. A sinusoidal force of 3 g was applied to the epithelium, and the resultant displacement logged at a rate of 1 kHz. Force measurement accuracy was 20 mg and position measurement accuracy was 4 mm. The force was applied in a transverse direction at the midmembranous point between the vocal process and the anterior commissure. The shear modulus of the three female vocal folds ranged from 814 to 1232 Pa. The shear modulus of the three male vocal folds ranged from 1021 to 1796 Pa. These data demonstrate that it is pos...

Objectives: To perform preliminary measurements of the shear modulus of the vocal fold cover layer during intrinsic laryngeal muscle contraction. Study Design: Shear modulus was measured in an in vivo canine larynx and an ex vivo human larynx. Methods: Shear stress was applied to the transverse axis of the vocal fold using a modified linear skin rheometer (LSR) via an attached suction probe. The probe displacement in response to the applied force was measured at various levels of laryngeal muscle contraction. The force- ...

The ability to measure the biomechanical properties of the vocal fold in vivo is both an aid to diagnosis and enhances our knowledge of how the vocal folds operate. This paper details a new instrument that is capable of taking readings of the spring rate of the vocal fold in a repeatable manner. We also present three sets of readings taken from two volunteer patients. Patient 1 was suffering from polyp growth, and the data presented are taken from both the damaged vocal fold and the healthy vocal fold. The third set of readings was ...

DMU has a track record securing research funding, and managing successful research programmes. We have a specialised administrative structure to support research, and to develop links with external bodies, both industrial and academic. The SERC Centre, at the heart of the City Campus, houses our major research groups. In the recent RAE announcements my department was one of 11rated 4, with two other departments being rated 5.