P045 Comparative analysis of rapid eye movement sleep oxygen saturation and clinical characteristics in overlap syndrome vs chronic obstructive pulmonary disease alone

Abstract Background Co-existing chronic obstructive pulmonary disease (COPD) and obstructive sleep apnoea (OSA), known as overlap syndrome (OVS), is associated with worse outcomes than either condition alone. This may be due to more severe nocturnal hypoxemia during REM (rapid eye movement) sleep, when respiratory function is markedly compromised. We hypothesise that there will be significantly greater REM-related desaturation in OVS compared to COPD-only controls, indicating an additive hypoxic burden from concomitant OSA. Methods Retrospective case–control study of adults who underwent in-laboratory diagnostic polysomnography and spirometry at a tertiary centre between April 2020 and April 2025. Three groups will be analysed: OVS (AHI >15 & spirometry-confirmed COPD), OSA-only (AHI >15) and COPD-only (AHI ≤15 & spirometry-confirmed COPD). The primary outcome is mean REM SpO₂ in OVS vs COPD-only participants matched by lung function. Secondary outcomes will include analysis of other metrics of oxygenation in REM between the three groups. Data will be compared using linear regression methods. Progress to Date Currently under human research ethics committee review. Data collection to be completed in August 2025. Intended outcome and impact These results will add insight into the effects of COPD and OSA on oxygenation during sleep in overlap syndrome. This information will improve the current understanding of sleep disordered breathing in OVS, and the reasons why OVS is associated with worse outcomes than either condition alone.