0642 Neuromuscular Adaptive Therapeutic Effects of Hypoglossal Nerve Stimulation (HNS) for Obstructive Sleep Apnea (OSA)

Abstract Introduction Hypoglossal nerve stimulation (HNS) is an effective yet still evolving treatment for obstructive sleep apnea (OSA). During titration polysomnography (PSG), some nightly HNS users show lower apnea–hypopnea index (AHI) before stimulation, suggesting a possible adaptive response of upper-airway muscles. This study aimed to characterize this pattern and identify related clinical factors. Methods We retrospectively analyzed 113 adults who received HNS at the hospital based sleep laboratory. All participants completed a baseline sleep study, followed by a titration PSG approximately three months after activation. The primary outcome was the change AHI across three conditions: baseline, the device-OFF, and the device-ON period during the titration PSG. Paired AHI values were compared using Wilcoxon signed-rank tests. Factors associated with the percentage reduction in AHI from baseline to the device-OFF period were examined using linear regression. Results Total AHI decreased markedly from baseline (34.8 23.3–47.6) to the OFF period (4.7 0.0–27.3, p 0.001) and to the ON period (13.1 6.0–26.2, p 0.001). AHI increased from OFF to ON (p = 0.04). In NREM subset (n = 45), baseline NREM AHI (30.2 19.4–46.6) decreased to 4.4 2.0–20.0 during OFF (p 0.001) and to 9.5 4.9–21.6 during ON (p 0.001), with no significant difference between OFF and ON (p = 0.50). Higher BMI was the only variable associated with smaller OFF-period improvement (β = –3.9, p = 0.04), and this association remained significant in multivariable models (β = –4.0, p = 0.03). Benzodiazepine use and male sex showed borderline associations. These factors were associated with less neuromuscular adaptation. Conclusion Participants demonstrated marked AHI improvement three months after HNS initiation, with this improvement evident even during the device-OFF period. This pattern supports the possibility that HNS elicits a neuromuscular adaptive effect beyond immediate stimulation. Higher BMI was associated with a smaller adaptive change, suggesting that participant characteristics may influence the extent to which this carryover effect emerges. These findings indicate that long-term HNS therapy may warrant protocol adjustments or individualized titration as the aforementioned adaptive effects may develop. Support (if any)