For a study, the effectiveness of the mandibular advancement device (MAD) in treating obstructive sleep apnea patients varies. The study was to use obstructive sleep apnea phenotypic traits calculated from baseline clinical polysomnography to explain underlying individual differences in efficacy: collapsibility (airflow at normal ventilatory drive), loop gain (drive response to reduced airflow), arousal threshold (drive preceding arousal), compensation (increase in airflow as drive increases), and ventilatory response to arousal (increase in drive explained by arousal). Based on past research, researchers expected that MAD therapy responders had a lower loop gain and milder collapsibility.
About 36 patients (median apnea-hypopnea index [AHI], 23.5 [interquartile range (IQR), 19.7–29.8] events/h) had full polysomnography at baseline and three months later, with a MAD set at 75% of maximal protrusion. According to Sands and colleagues, baseline polysomnography was used to evaluate traits. A response was defined as a 50% reduction in AHI. AHI was significantly lowered by MAD treatment (49.7% baseline [23.9–63.6], median [IQR]). At baseline, responders had lower loop gain than nonresponders (mean [95% CI], 0.53 [0.48–0.58] vs. 0.65 [0.57–0.73]; P=0.020), a difference that remained after adjusting for baseline AHI and body mass index. After adjusting for collapsibility, elevated loop gain remained linked with nonresponse (odds ratio, 3.03 [1.16–7.88] per 1–standard deviation (SD) increase in loop gain [SD, 0.15]; P=0.023). Nonresponders to MAD have more ventilatory instability, as measured by increased loop gain. This determining the degree of ventilatory instability at the outset may help with patient selection for MAD treatment.