Different Vibratory Conditions Elicit Different Structural and Biological Vocal Fold Changes in an In-Vivo Rabbit Model of Phonation

Abstract

Vibration of the vocal folds can disrupt the tissue and induce structural, functional, and molecular changes; the presence or absence of contact between the vocal folds during vibration can affect the type and extent of these changes. The purpose of this study was to characterize vocal fold changes following 2 hours of contact phonation or phonation without vibratory contact. Six New Zealand white breeder rabbits underwent 120 minutes of phonation with or without vibratory contact, and four served as nonphonated controls. The larynx was exposed and current was applied to the cricothyroids bilaterally to achieve vocal fold adduction while humidified airflow was delivered to induce vocal fold vibration. Laryngeal position, airflow, and stimulation levels were adjusted to obtain phonation with or without contact, and phonation was elicited for 120 minutes. Following excision, larynges were stained using Hematoxylin & Eosin, Elastica van Gieson, and Grocott's Methenamine Silver, or labeled with immunofluorescent markers for E-cadherin, CD31, CD11b, and Vimentin. All images were captured using a Nikon 90i microscope and analyzed using ImageJ. Differences between vibratory conditions and control samples were observed. There was more extensive epithelial thinning, reduced epithelial integrity and increased vascularity in the contact phonation group, while both phonatory groups demonstrated a decreased presence of mucous on the luminal surface and a decrease in elastin band thickness and lamina propria depth. Neither condition showed differences in inflammatory cell presence compared to control tissue. By showing that these two vibratory conditions result in structural changes of different types and magnitude, we have provided the first empirical evidence that vocal fold tissue is sensitive to differences in forces, and that changes in vibratory pattern can elicit different downstream biological changes within the tissue. The differences described herein are an important step toward understanding the vocal folds' potential for differential response to phonotraumatic damage following different vibratory behaviors.