There are multiple mechanisms underlying obstructive sleep apnea (OSA) development. However, how classic OSA risk factors such as body mass index (BMI) and sex portend to OSA development have not been fully described. Thus, we sought to evaluate how obesity leads to OSA, and assess how these mechanisms differ between men and women. Methods The San Diego Multi-Outcome OSA Endophenotype (SNOOzzzE) cohort includes 3,319 consecutive adults who underwent a clinical in-laboratory polysomnography at the UCSD sleep clinic between 1/2017-12/2019. Using routine polysomnography signals, we determined OSA endotypes. We then performed mediation analyses stratified by sex to determine how BMI influenced apnea hypopnea index (AHI) using OSA endotypic traits as mediators. Results We included 2,146 patients of whom 919 (43%) were women and 1,227 (57%) were obese. BMI was significantly associated with AHI in both women and men. In men, the effect of BMI on AHI was partially mediated by a reduction in upper airway stiffness (31% of total effect, TE), by a reduction in circulatory delay (16%TE), and by an increase in arousal threshold (7%TE). In women, the effect of BMI on AHI was partially mediated by a reduction in circulatory delay (22%TE). Discussion BMI-related OSA pathogenesis differs by sex. An increase in upper airway collapsibility (in men) is consistent with prior studies. A reduction in circulatory delay may lead to shorter and thus more events per hour (i.e., higher AHI), while the association between a higher arousal threshold and higher AHI may reflect reverse causation.
Keywords: endotypes; gender; mediation analysis; obesity; sleep apnea.