Clinical background
Oral appliances are an alternative treatment for obstructive sleep apnea. The idea is to enlarge the upper airway volume by advancing the mandibula through a mouthpiece which is worn intra orally during the night. The aim of the enlargement is to prevent or reduce the number of upper airway collapses. A typical success rate for this type of therapy is around 50%.
Principle of upper airway volume enlargement through mandibular repositioning
Question
Can functional imaging be used to assess the mode of action of a mandibular repositioning appliance (MRA) and can it be used to identify responders and non-responders?
Imaging and CFD
In this study a total of 10 mild to moderate patients suffering from obstructive sleep apnea were enrolled. All patients underwent a split-night polysomnography with and without MRA to determine the number of upper airway collapses at baseline and while using the device. The polysomnography was followed by a low dose CT scan of the upper airway region with and without MRA.
Segmentation of maxilla, mandibula and upper airway with and without MRA in a patient treated with and without success
The CT images were used to segment the upper airway, the maxilla and the mandibula. From these images the changes in airway volume could be measured and the respective positions of the bone fragments could be determined. From the volumetric 3D models a computational grid could be constructed which can be used for flow simulations. These flow simulations provide the total pressure drop over the models and hence the upper airway resistance.
Contours of velocity in the upper airway determined by CFD
A significant correlation was found between the change in upper airway volume and the severity of sleep apnea; the more the airway could be enlarged by the MRA the more the number of airway collapse could be reduced. An even more significant correlation was found between the changes in CFD-based airway resistance and the change in disease severity. This indicates that the CFD-based resistance calculation is a sensitive outcome parameter to detect clinically relevant changes in airway models. This was also a finding in our other airway studies such as the bronchodilator study. The combination of both functional imaging parameters could be used in this study to distinguish the responders from the non-responders.
Conclusions
Imaging and CFD can be used to describe the mode of action of a mandibular repositioning appliance. The technique can distinguish possible responders from non-responders.
Publication
Oral devices for the treatment of obstructive sleep apnea
Bailey, D
Chest net
Functional imaging using computational fluid dynamics to predict treatment success of mandibular advancement devices in sleep-disordered breathing.
De Backer JW, Vanderveken OM, Vos WG, Devolder A, Verhulst SL, Verbraecken JA, Parizel PM, Braem MJ, Van de Heyning PH, De Backer WA.
J Biomech. 2007;40(16):3708-14