title: Strain modulations as a mechanism to reduce stress relaxation in laryngeal tissues.
abstract: Vocal fold tissues in animal and human species undergo deformation processes at several types of loading rates: a slow strain involved in vocal fold posturing (on the order of 1 Hz or so), cyclic and faster posturing often found in speech tasks or vocal embellishment (1-10 Hz), and shear strain associated with vocal fold vibration during phonation (100 Hz and higher). Relevant to these deformation patterns are the viscous properties of laryngeal tissues, which exhibit non-linear stress relaxation and recovery. In the current study, a large strain time-dependent constitutive model of human vocal fold tissue is used to investigate effects of phonatory posturing cyclic strain in the range of 1 Hz to 10 Hz. Tissue data for two subjects are considered and used to contrast the potential effects of age. Results suggest that modulation frequency and extent (amplitude), as well as the amount of vocal fold overall strain, all affect the change in stress relaxation with modulation added. Generally, the vocal fold cover reduces the rate of relaxation while the opposite is true for the vocal ligament. Further, higher modulation frequencies appear to reduce the rate of relaxation, primarily affecting the ligament. The potential benefits of cyclic strain, often found in vibrato (around 5 Hz modulation) and intonational inflection, are discussed in terms of vocal effort and vocal pitch maintenance. Additionally, elderly tissue appears to not exhibit these benefits to modulation. The exacerbating effect such modulations may have on certain voice disorders, such as muscle tension dysphonia, are explored.
authors.affiliation: Communicative Sciences and Disorders, Michigan State University, East Lansing, Michigan, United States of America; National Center for Voice and Speech, The University of Utah, Salt Lake City, Utah, United States of America.
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Hunter
authors.affiliation: School of Mechanical Engineering, Purdue University, West Lafayette, Indiana, United States of America.
authors.forename: Thomas
authors.initials: T
authors.lastname: Siegmund
authors.affiliation: Otolaryngology-Head and Neck Surgery, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America.
authors.forename: Roger W
authors.initials: RW
authors.lastname: Chan
mesh_terms: D001696:Biomechanical Phenomena; D003198:Computer Simulation; D006801:Humans; D007830:Larynx / Q000502:physiology*; D008297:Male; D008954:Models, Biological; D012212:Rheology; D013314:Stress, Mechanical