Comparison of acceleration and impact stress as possible loading factors in phonation: a computer modeling study.

Impact stress (the impact force divided by the contact area of the vocal folds) has been suspected to be the main traumatizing mechanism in voice production, and the main cause of vocal fold nodules. However, there are also other factors, such as the repetitive acceleration and deceleration, which may traumatize the vocal fold tissues. Using an aeroelastic model of voice production, the present study quantifies the acceleration and impact stress values in relation to lung pressure, fundamental frequency (F0) and prephonatory glottal half-width. Both impact stress and acceleration were found to increase with lung pressure. Compared to impact stress, acceleration was less dependent on prephonatory glottal width and, thus, on voice production type. Maximum acceleration values were about 5-10 times greater for high F0 (approx. 400 Hz) compared to low F0 (approx. 100 Hz), whereas maximum impact stress remained nearly unchanged. This suggests that acceleration, i.e. the inertia forces, may present at high F0 a greater load for the vocal folds, and in addition to the collision forces may contribute to the fact that females develop vocal fold nodules and other vocal fold traumas more frequently than males.