Novel approaches to the study of laryngeal muscle in functional voice disorders

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PROJECT SUMMARY / ABSTRACT Vocal muscle hyperfunction, tension, and fatigue are considered ubiquitous to functional voice disorders. Alt- hough these voice disorders make up a large portion of cases on clinical caseloads in outpatient voice settings, diagnostic methods and appraisal of treatment approaches lack. This gap has led to a heavy emphasis on ex- clusionary diagnostics and clinical management steeped in trial and error. The long-term goal of this work is to address these methodological gaps and improve diagnostic specificity, therapeutic management, and treatment outcomes in functional voice disorders. As such, the overarching objectives of this proposal are twofold: The first goal (Aim 1) is to validate a novel method—ultrasound shear wave musculoskeletal elastography (SWE)—for the study of laryngeal muscle structure and function in patients with functional voice impairments and compare differences in the laryngeal muscles of individuals without vocal impairments pre- and post-vocal load. SWE uses acoustic radiation force impulse technology, where the acoustic beam generated by the ultrasound trans- ducer compresses the underlying tissue and induces a local shear wave; the higher the propagation velocity of the shear wave, the greater the muscle tension. Quantitative analysis using SWE has been shown to be objec- tive, reproducible, and can capture heterogeneity within motor units of skeletal muscle in the limbs. The second goal (Aim 2) is to identify clusters of laryngeal-respiratory clinical profiles in patients with functional voice disor- ders. This aim will be accomplished using cluster analytic methods of shear wave elastography and laryngo- scopic ratings of laryngeal muscle structure and function as well as aerodynamic measures of subglottal pres- sures and transglottal airflow. A total of 120 participants with (n = 60) and without (n = 60) functional voice impairments—will be enrolled in the study over the course of 3 years. Shear wave velocities of the hyolaryngeal extrinsic muscles—anterior digastric and sternohyoid—in patients with and without functional voice impairments will be conducted twice: the first time before a 1-hour vocally fatiguing task and the second time after vocal load. Shear wave velocities, hyolaryngeal muscle asymmetries, and intrinsic laryngeal muscle stability (% perturbations) will be calculated and used as outcome measures. Additionally, aerodynamic measures of subglottal pressures and transglottal airflow and VALDI ratings of supraglottic compression will be acquired for Aim 2. Anticipated results are improved methodological tools to study the impact of the laryngeal muscles in voice disorders and a better theoretical understanding of relationships between the laryngeal muscles and respiratory system. Outcomes of this proposal will provide a springboard into future investigations to improve mechanisti- cally-driven diagnostic paradigms and increased precision in therapeutic targets in individuals with functional voice disorders, thus reducing burdens of illness and disability.