Effects of velopharyngeal openings on flow characteristics of nasal emission
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ORIGINAL PAPER
Effects of velopharyngeal openings on flow characteristics of nasal emission Elias Sundström1 · Suzanne Boyce2 · Liran Oren1 Received: 26 June 2019 / Accepted: 17 December 2019 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Nasal emission is a speech disorder where undesired airflow enters the nasal cavity during speech due to inadequate closure of the velopharyngeal valve. Nasal emission is typically inaudible with large velopharyngeal openings and very distorting with small openings. This study aims to understand how flow characteristics in the nasal cavity change as a function of velopharyngeal opening using computational fluid dynamics. The model is based on a subject who was diagnosed with distorting nasal emission and a small velopharyngeal opening. The baseline geometry was delineated from CT scans that were taken, while the subject was sustaining a sibilant sound. Modifications to the model were done by systematically widening or narrowing the velopharyngeal opening while keeping the geometry constant elsewhere. Results show that if the flow resistance across the velopharyngeal valve is smaller than resistance across the oral constriction, flow characteristics such as velocity and turbulence are inversely proportional to the size of the opening. If flow resistance is higher across the velopharyngeal valve than the oral constriction, turbulence in the nasal cavity will be reduced at a higher rate. These findings can be used to generalize that the area ratio of the velopharyngeal opening to the oral constriction is a factor that determines airflow characteristics and subsequently its sound during production of sibilant sound. It implies that the highest level of turbulence in the nasal cavity, and subsequently the sound that will likely be perceived as the most severe nasal emission is produced when the size of openings is equal. Keywords Nasal emission · Velopharyngeal valve opening · Turbulence · Computational fluid dynamics
1 Introduction The velopharyngeal (VP) valve regulates the coupling between the oral and nasal cavities during speech. The VP valve can be fully open for nasal sounds (e.g., /m/, /n/, and /ŋ/), partially open (e.g., nasalized vowels), and fully closed (e.g., high-pressure sounds such as /s/ or word initial /p/). The opening/closing of the VP valve determines how airflow and sound are channeled from the pharynx into the nasal and oral cavities.
* Elias Sundström [email protected] 1
Department of Otolaryngology‑Head and Neck Surgery, University of Cincinnati, 231 Albert Sabin Way, Cincinnati, OH 45267, USA
Department of Communication Sciences and Disorders, University of Cincinnati, 3202 Eden Avenue, Cincinnati, OH 45267, USA
2
Inadequate closure of the VP valve during speech will generate a speech disorder because of undesired airflow and/ or resonance in the nasal cavity. The underlying mechanism for incomplete closure can be obligatory (due to abnormal structure, known as velopharyngeal insufficiency [VPI]) or compensatory (due to
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