Hypercapnic Burden in Adults With Obesity Undergoing Diagnostic Polysomnography for Suspected Obstructive Sleep Apnea

Obesity-related sleep hypoventilation represents a continuum ranging from isolated nocturnal hypoventilation to obesity hypoventilation syndrome. Current diagnostic criteria rely mainly on dichotomous thresholds and may not adequately reflect cumulative nocturnal carbon dioxide exposure. Hypercapnic burden, defined as the cumulative area under the transcutaneous carbon dioxide (PtcCO₂) curve above a predefined threshold, has recently emerged as a novel physiological marker integrating both the intensity and duration of nocturnal hypercapnia. This prospective observational cohort study aims to evaluate the association between nocturnal hypercapnic burden and obstructive sleep apnea severity, assessed by the apnea-hypopnea index (AHI), in adults with obesity referred for diagnostic polysomnography. Secondary objectives include evaluating associations between hypercapnic burden and sleep architecture, respiratory events, oxygenation parameters, daytime symptoms, and patient-reported outcomes. In addition, the study will investigate the relationship between nocturnal hypercapnic burden and sleep inertia, assessed using the Sleep Inertia Questionnaire (SIQ), based on the hypothesis that greater nocturnal carbon dioxide exposure immediately before awakening may contribute to impaired alertness upon awakening. Hypothesis: Increased nocturnal hypercapnic burden is associated with greater obstructive sleep apnea severity and reflects an additional physiological dimension of obesity-related sleep hypoventilation beyond conventional polysomnographic indices. Furthermore, higher nocturnal hypercapnic burden is hypothesized to be associated with greater sleep inertia.