P151 Short-term mandibular advancement splint therapy for Obstructive Sleep Apnoea improves parasympathetic modulation

INTRODUCTION: Altered autonomic function (specifically, sympathoexcitation and vagal withdrawal) contributes to cardiovascular risk. Obstructive sleep apnoea (OSA) is associated with altered autonomic function. Heart rate variability (HRV) is a non-invasive measure of autonomic function. We aimed to assess whether short-term OSA treatment with mandibular advancement splints (MAS) improves autonomic function measured by HRV. METHODS: A retrospective analysis of participants in MAS treatment studies (N=105, 56% male, age, 56±1 years; BMI, 30±5 kg/m2) was undertaken. Nocturnal HRV was assessed using electrocardiograms from pre and post-treatment polysomnograms. HRV was calculated across 2-minute epochs over the entire electrocardiogram and divided into each sleep stage (wake, non-rapid eye movement (NREM), and rapid eye movement (REM)). HRV measures reflecting sympathetic (normalised low frequency (LFnu)), parasympathetic (pNN50%, RMSSD (ms), normalised high frequency (HFnu)), total HRV (SDNN (ms) and HTI) and R-R interval were calculated. Changes in HRV measures following treatment were assessed (paired t-test) and compared to AHI change (linear regression, with adjustment for age, sex, BMI). RESULTS: Following MAS treatment, HTI increased (14.78±39.99, p=0.008), and LFnu reduced during wake (-0.43±38.18, p=0.03). Linear regression, showed AHI reduction related to increased R-R interval during wake (-0.002, 0.001), p=0.009) [unstandardised β/SE] and REM (-0.002, 0.001) [unstandardised β/SE], p=0.008), and increased pNN50% during wake (-0.24, 0.08), p=0.005) [unstandardised β/SE] suggesting MAS efficacy relates to these improvements. CONCLUSION: We found evidence of reduced sympathetic and increased parasympathetic modulation, following short-term MAS therapy. This suggests MAS therapy has potential to improve cardiac autonomic function and hence reduce cardiovascular risk.