All Obstructive Sleep Apnea Events Are Not Created Equal: The Relationship between Event-related Hypoxemia and Physiologic Response

Rationale: Obstructive sleep apnea (OSA) severity is typically assessed by the apnea-hypopnea index (AHI), a frequency-based metric that allocates equal weight to all respiratory events. However, more severe events may have a greater physiologic impact. Objective: The purpose of this study was to determine whether the degree of event-related hypoxemia would be associated with the post-event physiologic response. Methods: OSA patients (AHI>5/h) from the multi-center Canadian Sleep and Circadian Network cohort were studied. Using mixed-effect linear regression, we examined associations between event-related hypoxic burden (HBev) assessed by the area under the event-related oxygen saturation recording with heart rate changes (ΔHRev), vasoconstriction (vasoconstriction burden (VCBev) assessed with photoplethysmography), and electroencephalographic responses (power ratio before and after events). Results: Polysomnography recordings from 658 patients (Median [IQR] age= 55.00 [45.00, 64.00] years, AHI= 27.15 [14.90, 64.05] event/h, 42% female) were included in the analyses. HBev was associated with an increase in all physiologic responses after controlling for age, sex, body mass index (BMI), sleep stage, total sleep time, and study centers; for example, one standard deviation (SD) increase in HBev was associated with a 0.21 [95% CI: 0.2, 0.22], 0.08 [0.08, 0.09] and 0.22 [0.21, 0.23] SD increase in ΔHRev, VCBev and Beta power ratio respectively). Conclusion: Increased event-related hypoxic burden was associated with greater responses across a broad range of physiologic signals. Future metrics that incorporate information about the variability of these physiologic responses may have promise in providing a more nuanced assessment of OSA severity.