Magnetic resonance imaging of the upper airway in obstructive sleep apnea before and after oral appliance therapy.

OBJECTIVE: To determine the mechanism by which an oral appliance may be used to treat obstructive sleep apnea syndrome (OSAS). METHODS: Eleven OSAS patients (8 males and 3 females) were involved in the study. Mean age was 52.2 +/- 10.6 years; height was 166.6 +/- 7.2 cm, and weight was 75.6 +/- 9.3 kg; body mass index (BMI) was 27.2 +/- 2.9 kg/m2. Each patient underwent magnetic resonance imaging (MRI) and polysomnography before and after oral appliance therapy. Pharyngeal changes were measured and compared with the variation in sleep parameters. Also, Pearson's correlation and multiple linear regression were performed to investigate the relationship of sleep parameters and MRI items. RESULTS: Through oral appliance therapy, the sleep disorder decreased. Apnea/hypopnea index (AHI) decreased from 44.6 +/- 21.5 to 9.6 +/- 6.3 per hour of sleep. Lowest oxygen desaturation rose from 71.4 +/- 15.0% to 82.0 +/- 7.7%. Meanwhile, the upper airway increased at most levels, and especially at oropharynx. As measured by the correlation and regression analysis, the AHI changes had a negative association with tongue volume (R = -0.5730) and a positive association with the area alternation of high oropharynx (R = 0.5823); the change of the lowest oxygen desaturation (SaO2%) was positively associated with whole airway volume (R = 0.6554). CONCLUSION: The oral appliance works by enlarging the upper airway morphology and keeping the airway open, mainly at the back of soft palate. The effect of the oral appliance is associated with the degree of enlargement of the high oropharynx. Those who have a small tongue and a large pharynx may expect to have good results with the use of the oral appliance.