0514 Non-Supine Respiratory Events Improve Significantly After Hypoglossal Nerve Stimulation in Non-Positional Obstructive Sleep Apnea

Abstract Introduction Studies examining long-term outcomes of hypoglossal nerve stimulation (HNS) by positional phenotype remain limited. This study evaluated 1-year HNS outcomes in patients with positional obstructive sleep apnea (POSA) and non-POSA, and additionally assessing post-treatment changes in positional phenotype. Methods We retrospectively reviewed adults who underwent HNS at a tertiary sleep center between December 2020 and January 2024. To ensure reliable positional indices, only patients who slept ≥15 minutes in both supine and non-supine positions were analyzed. POSA defined as a supine AHI more than twice the non-supine AHI. Thirty-eight patients (POSA=20, non-POSA=18) who completed baseline and 1-year follow-up sleep apnea testing were analyzed. Outcomes included total AHI, supine AHI, non-supine AHI, minimum oxygen saturation (MinSpO₂), and Epworth Sleepiness Scale (ESS) scores. Results In the overall cohort, median total AHI improved from 32.6 to 11.1/h (p 0.001). Supine AHI decreased from 43.3 to 17.1 (p 0.001) and non-supine AHI from 16.7 to 7.0 (p=0.001). ESS scores improved from 8.0 to 6.0 (p=0.003). When comparing phenotypes, total and supine AHI reductions were similar between POSA and non-POSA. However, non-supine AHI improved markedly in non-POSA compared to POSA (30.3 vs 0.9; p 0.001), with a greater percent reduction (73.0% vs 27.9%; p=0.025). Within non-POSA group, non-supine AHI reduction was also greater than supine AHI reduction (30.3 vs 18.4, p 0.001). Regarding phenotype stability, 65% of baseline POSA and 50% of baseline non-POSA maintained the same position-dependency after 1 year. Patients who remained non-positional (n=9) showed no significant total AHI improvement (p=0.086) and had persistently elevated AHI (30.6/h). In contrast, baseline POSA improved significantly regardless of position-dependency change, and non-POSA patients who became position-dependent also exhibited significant reductions in total AHI. Conclusion Long-term HNS significantly improved respiratory and clinical outcomes in both phenotypes. While total and supine AHI responses were comparable, non-supine AHI improved predominantly in non-POSA patients than POSA. In non-POSA, respiratory events in non-supine position improved more than in supine position. Persistent non-position dependency after treatment was associated with suboptimal outcomes, suggesting that such patients may benefit from earlier adjunctive or combination therapies. Support (if any)