Self-Oscillating Vocal Fold Model Mechanics Associated with Aging

From infancy to old age, humans depend on their ability to voice speech in order to effectively communicate their needs. Voiced speech is produced when a critical lung pressure is achieved, forcing air through two bands of tissue stretched across the airway, known as the vocal folds (VFs). The aerodynamic forces then impart energy to the tissues of the VFs and induce self-sustained oscillations. Growths on the VF surfaces, such as nodules and polyps, can result from the repeated and prolonged collision between the tissues of opposing VFs, and can be devastating to one’s daily life. Approximately 30% of people will suffer from a voice disorder at some point in their lives with this probability doubling for those who rely heavily on their voice for work, such as teachers and singers. Further, by 2060, there is expected to be 92 million adults over the age of 64. As this large segment of the population grows, the incidence of voice disorders is expected to be between 12-35%. The objective of this research is to study and improve synthetic VF models to replicate physiological VF motion and characteristic parameters of human speech and relate that to aging. This study includes clinical aerodynamic measures from healthy young men as well as healthy aged men to determine whether the various VF models may be differentially valuable for study of non-normative populations. Synthetic, self-oscillating, and geometrically idealized multi-layer VF models are fabricated from Smooth-On EcoFlex silicone to exhibit material properties representative of the different layers of human VFs. Two-layer VF models are fabricated with cover layers of varying moduli of elasticities to mimic loss of muscle tone associated with aging. The VF models are evaluated experimentally in a vocal tract simulator to replicate physiological conditions. The fabricated silicone synthetic VF models possessed modulus of elasticity values within the range of physiological values, and exhibited good repeatability in our experiments. Further, the two-layer pathological VF models exhibited mean speed quotient values within the range of healthy aged voice physiological values, indicating that silicone is an acceptable material for modeling aging VFs. This study integrates speech science with engineering and flow physics and extends the use of synthetic VF models by assessing their ability to replicated behaviors observed in human subject data to advance a means of investigating voice production as well as the vocal changes associated with aging