Positional changes of oropharyngeal structures due to gravity in the upright and supine positions

Objectives: To compare the responses of oropharyngeal structures to gravity while sitting upright or lying down in a supine position. Methods: Seven subjects were evaluated by cone beam CT (CBCT) while in the upright position and by a four-row multidetector helical CT (MDCT) while in the supine position. All of the voxel sizes were adjusted to be 0.3 x 0.3 x 0.3 mm3 in the x-y-z axis. The posterior nasal spine, basion and fourth cervical bone were used as references to measure positional changes in the oropharyngeal structures between the upright and supine positions. The smallest areas in the oropharynx were also evaluated. Results: The soft palate, epiglottis and entrance of the oesophagus moved caudally with the positional change from supine to sitting upright, and moved posteriorly when the position changed from an upright to a supine position. The hyoid bone moved caudally but not posteriorly in response to the same positional changes. The width and length of the smallest area present in the oropharynx was larger in the upright position than in the supine position. Conclusions: Gravity can produce movements in oropharyngeal structures in response to postural changes between sitting upright and lying in the supine position.