Three-dimensional Morphological Analyses of Positional Dependence in Patients with Obstructive Sleep Apnea Syndrome

Background: It is generally considered that patients with obstructive sleep apnea syndrome (OSAS) at increased perioperative risk should be placed in nonsupine positions throughout the recovery process; however, not all patients with OSAS show positional dependence. The authors hypothesized that morphological differences exist In three-dimensional (3D) soft tissue and craniofacial structures of the pharyngeal airway between positional and nonpositional OSAS. Methods: The subjects of the study were body mass index-matched, age-matched, and apnea hypopnea index-matched positional (n = 10) and nonpositional (n = 10) Japanese OSAS patients and body mass index-matched Japanese control subjects (n = 10). Pharyngeal magnetic resonance imaging and cephalometric radiography were performed during wakefulness. Results: The patients with positional OSAS had a smaller volume of die pharyngeal lateral wall soft tissues, larger maxilla-nasion-mandible angle, and smaller lower facial height than the nonpositional OSAS and the control subjects. The patients with positional OSAS showed a significantly steeper sella-nasion-mandible angle and smaller craniofacial volume than the control subjects. There were no significant differences In tongue volume and 3D pharyngeal anatomical balance between positional and nonpositional OSAS. Multivariate stepwise regression for positional dependence showed that the dominant determinant was the volume of the lateral pharyngeal wall, followed by lower facial height and maxilla-nasion-mandible angle. Conclusions: Patients with positional OSAS have wider airways In the lateral parts, lower facial height, and more backward position of the lower jaw, which may explain differences in the maintenance of pharyngeal airway patency in the lateral sleep position.