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 supi ne position. Eleven male and nine female healthy adults participated in thi s study. Supine cephalograms were taken at end-expiration during wakefulnes s and in stage 1-2 non-rapid-eye-movement (NREM) sleep judged from the elec troencephalogram and respiratory monitoring. A paired t-test was used to co mpare differences between the values measured during wakefulness and sleep. A significant increase in the amount of jaw opening was observed during sl eep. The anteroposterior width of the upper airway was significantly decrea sed during sleep. The distances between the hyoid bone and the mandibular s ymphysis and between the cervical vertebra and the hyoid bone were signific antly decreased during sleep. Consequently, the distance between the cervic al 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.