Determination of superior surface strains and stresses, and vocal fold contact pressure in a synthetic larynx model using digital image correlation

Abstract

Stresses and strains within the vocal fold tissue may play a critical role in voice fatigue, in tissue damage and resulting voice disorders, and in tissue healing. In this study, experiments were performed to determine mechanical fields on the superior surface of a self-oscillating physical model of the human vocal folds using a three-dimensional digital image correlation method. Digital images obtained using a high-speed camera together with a mirror system were used to measure displacement fields, from which strains, strain rates, and stresses on the superior surface of the model vocal folds were computed. The dependence of these variables on flow rate was established. A Hertzian impact model was used to estimate the contact pressure on the medial surface from superior surface strains. A tensile stress dominated state was observed on the superior surface, including during collision between the model folds. Collision between the model vocal folds limits the medial-lateral stress levels on the superior surface, in conjunction with compressive stress or contact pressure on the medial surface.

Verification of two minimally invasive methods for the estimation of the contact pressure in human vocal folds during phonation

“…where a is the equivalent radius of the contact area, P c is the contact pressure, and E Ã is the effective modulus (Spencer et al, 2008). The effective modulus, E Ã , is defined as…”

“…The displacement field is obtained by tracking the deformation of the speckle pattern. More details about the underlying principles can be found in previous studies (Sutton et al, 1986;Spencer et al, 2008). Images of the superior surface motion of the vocal fold replica were obtained using two cameras with a frame rate of 15 frames/s.…”

“…The total penetration depth was obtained through the extrapolation of the peak strain values measured for increasing flow rates, assuming that the medial-lateral strain can develop freely without the presence of the rigid wall (Spencer et al, 2008). The penetration depth was obtained using…”

“…The equivalent subglottal tract length was 41 cm. The DIC method was used to measure the displacement field over the vocal fold model superior surface (Spencer et al, 2008). Digital images are represented mathematically by matrices.…”

“…Contact pressure data obtained from the probe microphone served as reference data. The approach proposed by Spencer et al (2008) was modified to estimate contact pressures based on superior surface deformation data obtained using DIC. The analysis procedure proposed by Gunter (2003) was used to estimate the contact pressure using a tuned FEM model of the same physical replica (Chen, 2009).…”