Supine cephalometric study on sleep-related changes in upper-airway structures in normal subjects

The purpose of this study was to examine sleep-related changes in the upper airway and surrounding structures including the mandible, hyoid bone, and cervical vertebra in normal subjects using lateral cephalograms in the supine position. Eleven male and nine female healthy adults participated in this study. Supine cephalograms were taken at end-expiration during wakefulness and in stage 1-2 non-rapid-eye-movement (NREM) sleep judged from the electroencephalogram and respiratory monitoring. A paired t-test was used to compare differences between the values measured during wakefulness and sleep. A significant increase in the amount of jaw opening was observed during sleep. The anteroposterior width of the upper airway was significantly decreased during sleep. The distances between the hyoid bone and the mandibular symphysis and between the cervical vertebra and the hyoid bone were significantly decreased during sleep. Consequently, the distance between the cervical vertebra and the mandibular symphysis was significantly decreased. These results suggest that the upper-airway dimension is significantly decreased and relatively small structural changes are induced during sleep in normal subjects.