Investigations of mechanical stresses within human vocal folds during phonation

Li-Jen Chen, Purdue University

Abstract

The human vocal folds experience mechanical stresses during phonation. In particular, the contact pressure on the vocal fold medial surface is postulated to be one major source of phonotrauma. A knowledge of mechanical stresses within the vocal folds is required. A physical replica of the human vocal folds was used as a test bed to investigate mechanical stresses within the vocal folds during phonation. The validity of the physical replica was confirmed by comparing phonation onset characteristics obtained using a theoretical model with those from experimental observations through a series of tests. Mechanical stresses within the physical replica were obtained using a tuned FEM model built based on experimental data. The FEM model allowed the extrapolation of deformation data that were not available from the experiment. Detailed stress and strain distributions on model surfaces were obtained. Maximum von Mises stresses were found on the medial and inferior surfaces when no vocal fold collision is involved. The fact that lesions seldom develop on the inferior surface, where von Mises stresses are the largest, suggest that stress states associated with vocal fold collisions play a more important role in lesion development. A probe microphone was developed for direct contact pressure measurements. Indirect estimations including estimation based on a Hertzian impact model and a well-tuned FEM model were performed. These estimations were compared with the direct measurement data. The estimation based on the Hertzian impact model was found to be a good first cut estimate, although the temporal resolution of the contact pressure data is limited to the camera frame rate. The estimation based on the well-tuned FEM model was able to provide detailed information with high temporal and spatial resolution, but for a rather high computational cost. The probe microphone was then used for in-vivo measurements of the contact and subglottal/supraglottal acoustic pressures. Contact pressures for breathy, normal and pressed voices were obtained. The overall contact pressure amplitudes were found to be smaller than those reported in previous studies due to the probe size. The probe microphone was found to be a robust tool for future clinical studies.

Degree

Ph.D.

Advisors

Nauman, Purdue University.

Subject Area

Biomedical engineering|Mechanical engineering

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