Objective: Oral appliances (OAs) have become a popular treatment option for subjects with obstructive sleep apnea (OSA). However, little information is available on how brain activation induced by respiratory challenge is modulated by treatment using an OA. We hypothesized that the brain activation caused by respiratory stress may be alleviated by treatment with an OA.
Methods: Three OSA patients participated in the study. The effects of OA treatment were objectively evaluated at pre- (pre-OA) and post-treatment (post-OA) using blood-oxygenation-level-dependent (BOLD) functional magnetic resonance imaging (fMRI). Respiratory stress was induced by resistive inspiratory loading to simulate airway obstruction. The anteroposterior position of the mandible was set at either the resting position or 67% of the maximum protrusive position. Breathlessness during inspiratory loading was subjectively evaluated on a five-point scale using a keypad. The fMRI study was designed with a block paradigm and data were compared with the cortical activation patterns in non-OSA controls in an identical experimental setting (Hashimoto et al., 2006).
Results: OA treatment decreased daytime sleepiness and the apnea/hypopnea index in all patients. The score on the five-point scale decreased with mandibular advancement at both pre- and post-OA. A significant reduction (p<0.05) in the BOLD signal in association with mandibular advancement was localized to the bilateral cingulate gyri at pre- and post-OA and to the bilateral middle frontal gyri at post-OA. These regions are known to be involved in respiratory control.
Conclusions: These results suggest that OA treatment may alleviate brain activation caused by respiratory stress.