Viscoelastic measurements of vocal folds using the linear skin rheometer.

As the number of interventions for vocal fold scar grows and with the advancement of mathematical modeling, greater accuracy and precision in the measurement of vocal fold pliability will become essential. Although indirect pliability measures have been used successfully, direct measurement of tissue pliability is essential. Indirect measurement with parallel plate technology has limitations; it requires the tissue to be removed from the surrounding framework, allows no site specificity, and offers no future for in vivo use in animals or humans. We tested the linear skin rheometer (LSR) in the evaluation of vocal fold pliability. We measured site-specific rheology of vocal folds thereby creating "pliability maps" in human, dog, and rat cadaveric larynges under conditions of altered stiffness; the canine vocal folds possessed sulci, the rat vocal fold was stiff secondary to controlled biopsy, and the human vocal fold was injected with trichloroacetic acid. Histology was performed to confirm the site and type of canine sulci. We found that the LSR reliably detected stiffness in the vocal folds of all species and created "pliability maps" consistent with previous data and clinical observations. The LSR should prove useful in the evaluation of vocal fold pliability for ex vivo and ultimately for in vivo applications.