The interaction between vocal fold hydration and vibratory biomechanics

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Project Summary/Abstract Voice disorders affect millions of people worldwide. Patients have reported many negative social econmic impacts of dysphonia. Proper fluid homeostasis is critical to normal vocal fold function. Maintenance of normal fluid levels in vocal fold tissue ensures normal biomechanical and vibratory parameters. Potential disturbances to this homeostasis include overuse, misuse, systemic or surface dehydration, trauma, and inflammation. The results of these disturbances can lead to changes in stress distribution, mechanical damage, and inflammation. Further damage to the tissue might result in the formation of edema or a benign lesion. The overall goal of this proposal is to evaluate the contributions of vocal fold fluid homeostasis, tissue properties, and vibratory biomechanics to tissue damage and ultimately edema. The results will explain changes in vibration mechanics over extended periods of phonation. Methods of quantifying fluid content in excised and in vivo models developed in this proposal will provide necessary information on fluid content and further our knowledge and understanding of the role of fluid in vocal fold vibration. Knowledge gained from this research is essential for a more complete understanding of clinical management of voice disorders. The approach to this research will involve three specific aims. The first aim will focus on methods of quantifying fluid content and tissue properties. We will employ four technologies novel to laryngology: (1) tissue dielectric properties (TDP), a measure of tissue water content; (2) Optical Coherence Tomography (OCT) as a method to quantify fluid volume in tissues; (3) laser Doppler flowmetry, a measure of blood flow through a tissue; and (4) acoustoelastography, a measure of the acoustic properties of the tissue that is linearly related to strain and nonlinearly related to tissue stress. The results of these methods will be useful for establishing standards in interstitial fluid levels and tissue properties. The second aim will focus on evaluating the effects of vibration on fluid content and dynamics in the vocal folds. First, finite element modeling will be used to study the effects of vibration on fluid content and dynamics while varying elongation, subglottal pressure, capillary permeability and stiffness. Physiological validation of the model trends will be carried out on excised animal models. Finally, an animal model of inflammation due to prolonged vibration will be used to observe how edema might occur in vocal overuse. The third aim will focus on the effects of fluid content on vocal fold vibration. We will determine hydration levels at which the vocal folds are pathologically changed. In other words, when there is a significant change to phonation parameters such as phonation threshold pressure. Excised models will be used in this aim to study the biomechanical effects of dehydration and overhydration. In addition, acoustoelastography will be employed to study the change in stress distribution of the tissue with changes in fluid content.