Benign glottic lesions are generally believed to result from mechanical trauma to the vocal folds, and affect million of working Americans. However, the extent of trauma and loading conditions that lead to structural damage, inflammation, and ultimately lesions such as nodules, polyps or cysts, is not well defined. In order to better understand the loading conditions and vocal behaviors that can lead to damage, greater understanding of material properties, stress distributions, and the resulting fiber damage is necessary. Vocal fold tissues experience a type of loading that is unique among soft tissues of the body. They undergo vibration and are loaded in the axial and transverse directions in tension, compression and shear, while most soft tissues are loaded either in tension or compression in a single direction. Because of this difference in load bearing, the structure (extracellular matrix fiber arrangement) and material property trends of the vocal folds differs from other softer tissues, making study of the vocal fold tissue properties critical for understanding the mechanism of structural damage leading to lesions. The overall goal of this proposal is to evaluate the material properties of the vocal folds, the stress experienced during phonation under varying hydration, elongation and subglottal pressure conditions, and the resulting structural damage to the tissue. The results will potentially describe the forces of vibration that result in tissue damage- either fatigue damage or fiber rupture. Methods of material property estimation and structural damage evaluation are novel and will contribute to knowledge about vocal fold tissue properties. 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 characterizing vocal fod material properties. It will employ acousto-elastography, which is a novel measure of the tissue acoustic properties that is linearly related to strain and nonlinearly related to tissue stress. Th results of these methods will be useful for establishing the effects of dehydration on tissue stiffness and informing computer model parameters.
The second aim will focus on finite element modeling of vocal fold vibration and the resulting interstitial fluid dynamics and stress distributions. Elongation, subglottal pressure, hydration and stiffness will be varied and resultin stresses evaluated.
The third aim will focus on excised studies and evaluation of tissue damage under varying subglottal pressure, hydration and elongation phonation challenges. The potential long term implications of this work are (1) better characterizing the vocal behaviors that might lead to lesions to inform therapeutic recommendations and (2) a better understanding of the mechanism of lesion formation to inform interventions.
Mechanical damage to vocal fold tissue has been identified as an important factor in the development of benign vocal fold lesions. Trauma to vocal fold tissue may lead to changes in the extracellular matrix that result in the formation of benign lesions. However, the exact mechanism is not well characterized or understood. By evaluating the tissue properties and structure of vocal folds, estimating the vibratory stress and modeling vocal fold fatigue damage in an excised larynx, we have the potential to quantify the mechanical damage cause by vibration and identify conditions that might result in lesions. This research could lead to clinical recommendations for voice care, and to general knowledge of the structure and organization of vocal fold tissue and role that vocal mechanics play in the formation of benign lesions, such as polyps and nodules.
| Devine, Erin E; Hoffman, Matthew R; McCulloch, Timothy M et al. (2017) Evaluation of type II thyroplasty on phonatory physiology in an excised canine larynx model. Laryngoscope 127:396-404 |
