Quantification of acute vocal fold epithelial surface damage with increasing time and magnitude doses of vibration exposure.

Because the vocal folds undergo repeated trauma during continuous cycles of vibration, the epithelium is routinely susceptible to damage during phonation. Excessive and prolonged vibration exposure is considered a significant predisposing factor in the development of vocal fold pathology. The purpose of the present study was to quantify the extent of epithelial surface damage following increased time and magnitude doses of vibration exposure using an in vivo rabbit phonation model. Forty-five New Zealand white breeder rabbits were randomized to nine groups and received varying phonation time-doses (30, 60, or 120 minutes) and magnitude-doses (control, modal intensity phonation, or raised intensity phonation) of vibration exposure. Scanning electron microscopy and transmission electron microscopy was used to quantify the degree of epithelial surface damage. Results revealed a significant reduction in microprojection density, microprojection height, and depth of the epithelial surface with increasing time and phonation magnitudes doses, signifying increased epithelial surface damage risk with excessive and prolonged vibration exposure. Destruction to the epithelial cell surface may provide significant insight into the disruption of cell function following prolonged vibration exposure. One important goal achieved in the present study was the quantification of epithelial surface damage using objective imaging criteria. These data provide an important foundation for future studies of long-term tissue recovery from excessive and prolonged vibration exposure

Damage severity descriptions used for visual evaluation of microprojections.

<p>All images were categorized into four groups according to the degree of surface damage. (1) extensive – the cell surface was destroyed and cytoskeleton was exposed; (2) moderate – all microprojections were damaged and appeared flat or normal; (3) minimal – microprojections were slightly damaged; and (4) normal – microprojections showed no damage.</p

Figure 6

<p>A. Measurement of depth of the remaining viable cell surface. Objective measurement of the depth (Dp) of the remaining viable cell surface layer in the control (C), modal intensity phonation (M), and raised intensity phonation (R) conditions after 30, 60, and 120 minutes of phonation. Measurement bar represents 4 µm. B. Objective examination of depth of the remaining viable cell surface using TEM. Average depth (µm) of the remaining viable cell surface in the control (C), modal intensity phonation (M), and raised intensity phonation (R) conditions for 30, 60, and 120 minutes. * Denotes a significant difference between groups (p<0.0167).</p

Figure 5

<p>A. Measurement of epithelial surface microprojection density and height. Objective measurement of the density (Dn) and height (H) of vocal fold epithelial surface microprojections in the control (C), modal intensity phonation (M), and raised intensity phonation (R) conditions after 30, 60, and 120 minutes of phonation. Measurement bar represents 1 µm. B. Objective examination of epithelial surface microprojection density using TEM. The number of microprojections per 10 µm field in the control (C), modal intensity phonation (M), and raised intensity phonation (R) conditions after 30, 60, and 120 minutes. * Denotes a significant difference between groups (p<0.0167). C. Objective examination of epithelial surface microprojection height using TEM. Average height (µm) of microprojections in the control (C), modal intensity phonation (M), and raised intensity phonation (R) conditions after 30, 60, and 120 minutes. * Denotes a significant difference between groups (p<0.0167).</p

Figure 4

<p>A. SEM representative images for control, modal intensity, and raised intensity phonation. Representative 2×2 µm SEM images for the control, modal intensity, and raised intensity phonation conditions after 30, 60, and 120 minutes of phonation. Measurement bar represents 0.5 µm. B. Visual examination of epithelial surface microprojections. Classification of images by damage severity using routine visual examination of epithelial surface microprojections. Four categories of damage severity: extensive (black fill), moderate (dark gray fill), minimal (light gray fill), and normal (white fill) in the control (C), modal intensity phonation (M), and raised intensity phonation (R) conditions after 30, 60, and 120 minutes of phonation. C. Objective examination of epithelial surface microprojection density using SEM. The percentage of vocal fold surface covered by microprojections in the control (C), modal intensity phonation (M), and raised intensity phonation (R) conditions after 30, 60, and 120 minutes of phonation. * Denotes a significant difference between groups (p<0.01).</p

SEM image of a rabbit vocal fold.

<p>Scanning electron microscopy image of a rabbit vocal fold. Large box represents the central portion of the middle one-third region of the vocal fold. Small box represents a 2×2 µm image used for SEM analysis.</p