Use of flow-volume curves to predict oral appliance treatment outcome in obstructive sleep apnea

Background: It has been recognized that mandibular advancement splint (MAS) treatment is effective in some, but not all, patients with obstructive sleep apnea (OSA). Hence there is a need for a simple and reliable clinical tool to assist in the differentiation of treatment responses. We hypothesized that abnormalities of flow-volume curves, together with other clinical variables, may have clinical utility in the prediction of MAS treatment outcome. Methods: Fifty-four patients with known OSA underwent MAS treatment. Expiratory and inspiratory flow-volume curves were measured in the erect and supine positions to derive midinspiratory flow (MIF₅₀) and the ratio of expiratory to inspiratory flow at 50% of vital capacity (MEF₅₀:MIF₅₀). Multivariable logistic regression was performed to identify additional significant clinical variables in the prediction of treatment outcome. Results: The mean (± SD) apnea-hypopnea index (AHI) in 35 responders was significantly reduced from 28.9 ± 13.7 to 6.7 ± 5.8/hour (p < 0.001). In 19 nonresponders there was no significant change in AHI. MIF ₅₀ was lower (6.04 ± 1.80 vs. 6.88 ± 1.08 L/second; p = 0.035) and the MEF₅₀:MIF₅₀ ratio was higher (0.82 ± 0.23 vs. 0.61 ± 0.15; p = 0.001) in responders than nonresponders. Logistic regression analysis revealed that the MEF ₅₀:MIF₅₀ ratio was the most important predictive factor for MAS treatment outcome, but that body mass index, age, and baseline AHI were also contributory. Conclusions: These data suggest that flow-volume curves, in combinationwith other factors such as body mass index, age, and baseline AHI, may have a useful clinical role in the prediction of treatment outcome with MAS.