Variations in velopharyngeal structures between upright and supine positions using upright magnetic resonance imaging.

OBJECTIVE: No studies have used MRI to compare the dimensional changes of the velopharyngeal musculature between upright and supine positions. The purpose of this study is to provide a comparison between structures of the velopharyngeal mechanism while in the supine and upright positions during rest and sustained speech productions of four female subjects.
METHODS: Four healthy white female subjects between 30 and 36 years of age (mean, 32.5 ± 1.75 years) were imaged using a 0.6-tesla open-type multi-position MRI scanner. Subjects produced two speech tasks (/i/ and /s/) in the two body positions.
RESULTS: Velar measures (length, thickness, and height), pharyngeal measures (retrovelar and retrolingual), and levator muscle measures (length and angles of origin) demonstrated a small variation between upright and supine positions. Differences in velar height during production of /i/ between the two positions was significant for all subjects. In most cases, the velar thickness remained nearly the same (group mean difference was between -0.2 and 1.2 mm). Group means demonstrated an average levator muscle shortening from upright to supine of 2.8 mm at rest, 2.0 mm during /i/ production, and 2.3 mm during /s/ production. Percentage of levator shortening were 17% for /i/ production and 21% for /s/ production, which were independent of body position.
CONCLUSIONS: Overall, gravity had a minimal effect on velar thickness, velar length, velar height, levator muscle length, angles of origin, and pharyngeal dimensions. Differences between the two body positions (upright and supine) were not significant during rest or during production of /i/ and /s/, with the exception of velar height during /i/ production.