Effects of nasal emission and microphone placement on nasalance score during /s/

Abstract

Velopharyngeal evaluation is aided by direct and indirect assessment techniques, including nasometry. Nasometers are designed to measure the nasalance resonance, but are unable to distinguish the relevant acoustic energy from the irrelevant aerodynamic energy associated with nasal emission. This can lead to elevation of the nasalance score, lowering the efficacy of nasometry in the presence of nasal emissions. The present study seeks to investigate the extent of this skewing. In order to quantify the influence of nasal emissions on the nasalance score, airflow with no voiced component was passed through [s]-postured airway models based on a subject-specific geometry but with varying velopharyngeal sizes: small, medium, and large. Nasometer microphones measured pressure fluctuations exterior to the nose and mouth, from which the nasalance score was calculated. Flow velocity, size of the velopharyngeal opening, and microphone position (medial or lateral) were varied in a factorial experiment. It was found that in the presence of nasal emissions, placing the nasometer microphones laterally decreases the nasalance score. Furthermore, the nasalance score generally increases with increased velopharyngeal opening size. These results indicate that aerodynamic pressure from nasal emissions can increase the nasalance score and that this influence could be mitigated via microphone placement.