Mandible Positions and Upper Airway Volume in Awake Supine Position

Objectives: Obstructive sleep apnea (OSA) is occurred due to recurrent occlusion, both partially or completely, of the upper airway during sleep. It has been shown that by protruding the mandible, the upper airway morphology can be changed not only antero-posteriorly, but also medio-laterally. However, such dimensional changes seem not to be constant for different subjects. The aim of this study was thus to analyze the upper airway volume (UAV) changes affected by mandible positions instead. Materials and methods: 10 non-obese (BMI<25) severe OSA (AHI>30) male patients and 10 gender, BMI and age matched control (AHI<5) were recruited for this study. Upper airway of each subject was imaged by using static and dynamic MRI at 9 different combinations of antero-posterior and vertical separations of the jaws in supine posture but awake. The UAV at each mandible position was then reconstructed by using Matlab to quantify its changes. Results: Till submission of this abstract, only part of the measurements are finished. The preliminary results have indicated that, the UAV in severe OSA patients seems to be smaller than that in the normal control. The UAV is changed at different mandible positions for both severe OSA and control groups. The volume changes seem to be affected more important by antero-posterior separation than the vertical separation of the jaws. Surprisingly, the UAV is not always increased but reduced while the mandible is protruded and mouth opened in some subjects. By simply mouth opening without mandible protrusion, UAV is reduced in comparison with the UAV while biting on intercuspal position in all subjects. Such volume reduction can be as high as 35%. Conclusion: Mouth opening seems to result in compromise of the upper airway volume in supine position during awake.