Effects of phonation time and magnitude dose on vocal fold epithelial genes, barrier integrity, and function

Abstract

Objective To investigate the effects of increasing time and magnitude doses of vibration exposure on transcription of the vocal fold's junctional proteins, structural alterations, and functional tissue outcomes. Study Design Animal study. Methods 100 New Zealand White breeder rabbits were studied. Dependent variables were measured in response to increasing time doses (30, 60, or 120 minutes) and magnitude doses (control, modal intensity, and raised intensity) of vibration exposure. Messenger RNA expression of occludin, zonula occluden-1 (ZO-1), E-cadherin, β-catenin, interleukin 1β (IL-1β), cyclooxygenase-2 (COX-2), transforming growth factor β-1 (TGFβ1), and fibronectin were measured. Tissue structural alterations were assessed using transmission electron microscopy (TEM). Transepithelial resistance was used to measure functional tissue outcomes. Results Occludin gene expression was downregulated in vocal folds exposed to 120 minute time doses of raised intensity phonation, relative to control, and modal intensity phonation. ZO-1 gene expression was upregulated following a 120 minute time dose of modal intensity phonation, compared to control, and downregulated after a 120 minute time dose of raised intensity phonation, compared to modal intensity phonation. E-cadherin gene expression was downregulated after a120 minute time dose of raised intensity phonation, compared to control and modal intensity phonation. TEM revealed extensive desquamation of the stratified squamous epithelial cells with increasing time and magnitude doses of vibration exposure. A general observation of lower transepithelial resistance measures was made in tissues exposed to raised intensity phonation, compared to all other groups. Conclusions This study provides evidence of vocal fold tissue responses to varying time and magnitude doses of vibration exposure. Level of Evidence N/A

Acute exposure to vibration is an apoptosis‐inducing stimulus in the vocal fold epithelium

“…The maximum time-dose of 120 minutes was based on work by Solomon, Glaze, Arnold, and van Mersbergen (24) that revealed decreased vocal function after 120 minutes of loud speaking in humans. Subsequent work in our laboratory confirmed that 30- and 60-minute time-doses led to observations of structural and functional vocal fold tissue changes (20, 21). Modal intensity phonation was elicited with mean electrical stimulation of 1.56 mA ( SD = 0.63) and constant airflow rate of 85.03 mL/s ( SD = 0.00).…”

Evaluation of Dying Vocal Fold Epithelial Cells by Ultrastructural Features and TUNEL Method

“…The current study simulated a condition of vibration that best represents the physiologic function of vocal fold vibration. This vibratory condition was selected based on previously reported morphological features of intact paracellular spaces and basement membrane, and a lack of functional tissue changes as measured by transepithelial resistance [Kojima et al, 2014a]. In contrast, raised intensity phonation was not studied due to evidence of pathologic damage, primarily epithelial tissue obligation, which could lead to less viable tissue for analysis [Kojima et al, 2014a].…”

“…This vibratory condition was selected based on previously reported morphological features of intact paracellular spaces and basement membrane, and a lack of functional tissue changes as measured by transepithelial resistance [Kojima et al, 2014a]. In contrast, raised intensity phonation was not studied due to evidence of pathologic damage, primarily epithelial tissue obligation, which could lead to less viable tissue for analysis [Kojima et al, 2014a]. During normal cycles of vibration, we hypothesize that biomechanically-induced stresses signal vocal fold epithelial cells to undergo apoptosis to regularly renew the tissue and maintain homeostasis, as has been reported in the intestinal epithelium [Marchiando et al, 2011].…”

“…Next, a separate condition included approximated vocal folds at midline with no supplied airflow for 120 minutes ( n = 5) to examine the effect of laryngeal movement via vocal fold adduction and abduction. To induce this condition, an in vivo surgical procedure was performed as previously described [Ge et al, 2009; Rousseau et al, 2011; Kojima et al, 2014a; Kojima et al, 2014b]. In brief, the larynx and trachea were exposed by creating a midline incision from the hyoid bone to sternal notch.…”

“…This vibratory condition was selected based on our laboratory’s previous findings which suggest that modal intensity phonation may best represent physiologic vibration. Modal intensity phonation, even up to 120 minutes, revealed no significant structural disruption to the basement membrane zone and no functional changes in transepithelial resistance [Kojima et al, 2014a]. To evoke phonation, the aforementioned surgical procedures were performed in addition to inserting a cuffed, inflated endotracheal tube into the trachea approximately 2 cm below the opening of the glottis.…”