Differences in Endotypic Traits Between Obstructive Sleep Apnoea Patients With and Without Excessive Daytime Sleepiness

BACKGROUND AND OBJECTIVE: Obstructive sleep apnoea (OSA) is a heterogeneous disorder. Although excessive daytime sleepiness (EDS) is a hallmark symptom of OSA, many patients remain asymptomatic, and a subset continues to experience EDS despite optimal therapy. The endotypic traits underlying EDS in OSA remain poorly defined. METHODS: We conducted a cross-sectional study of 694 adults at a Beijing sleep center, including 542 participants with AHI ≥ 5 events/h. EDS was defined as an Epworth Sleepiness Scale score > 10. Four endotypic traits were derived from full-night polysomnography using the "Phenotyping Using Polysomnography" method. Associations with EDS were assessed by multivariable logistic regression, and relationships with OSA severity by generalized linear regression. RESULTS: Compared with OSA without EDS, OSA with EDS exhibited significantly higher loop gain (LG), arousal threshold (ArTH), and upper airway collapsibility, and lower upper airway muscle compensation (Vcomp) (all p < 0.05). Multivariable logistic regression identified ArTH as an independent correlate of comorbid EDS, with an odds ratio of 3.12 (95% CI: 1.24-8.02; p = 0.016) for the highest quartile of ArTH. In the fully adjusted linear regression model, collapsibility, LG, and ArTH were significant determinants of OSA severity in both subgroups, whereas Vcomp was predictive predominantly among patients with EDS. CONCLUSIONS: This study suggests that elevated ArTH is an over-expressed trait in OSA patients with EDS, potentially amplifying the link between respiratory pathophysiology and daytime sleepiness. While LG and collapsibility remain key determinants of OSA severity, these findings highlight the value of ArTH-targeted strategies and endotype-informed stratification for personalized management.