Endotypic traits of supine position and supine-predominant obstructive sleep apnea in Asian patients

Background Over half of all cases of obstructive sleep apnea (OSA) are classified as supine-related OSA, however, the pathological endotype during supine position is not fully understood. This study aims to investigate the endotypic traits of supine predominant OSA (spOSA) and explore the variations in endotypic traits between the supine and lateral positions. Methods We prospectively recruited 689 adult patients with OSA from a single sleep center between April 2020 and December 2022. Endotypic traits, namely arousal threshold, collapsibility, loop gain, and upper airway muscle compensation, were retrieved from polysomnographic signals. We identified spOSA by a ratio of AHI supine to AHI non−supine greater than 2 as spOSA. We cross-sectionally compared demographic and endotypic traits between spOSA and non-positional OSA (npOSA) and examined the associations between spOSA and endotypic traits. Additionally, we compared the changes in endotypic traits between supine and lateral positions in patients with spOSA and npOSA. Results In our study sample, 75.8% of patients were identified as having spOSA. Compared to npOSA, spOSA was associated with low collapsibility (β=−3.46, 95% confidence interveal [CI]=−5.93 to −1.00) and reduced compensation (β=−6.79, 95% CI=−10.60 to −2.99). When transitioning from the lateral to supine position, patients with spOSA had a substantial decrease in compensation compared to those with npOSA (−11.98 versus −6.28%eupnea ventilation). Conclusions spOSA is a prevalent phenotype of OSA in Asian patients. Inadequate upper airway compensation appears to be a crucial underlying pathology in patients with spOSA.