Hypoxemia burden and atherogenic indices in OSAS: changes after CPAP therapy

To evaluate the association between nocturnal hypoxemia burden-expressed as the percentage of total sleep time spent below 90% oxygen saturation (%T90/TST)-and atherogenic indices, including the atherogenic index of plasma (AIP), Castelli risk index I (CRI-I), and Castelli risk index II (CRI-II), in obstructive sleep apnea syndrome (OSAS); and to assess pre-post changes after adherent continuous positive airway pressure (CPAP) therapy.

Single-centre retrospective-prospective cohort of adults with moderate-severe OSAS. Hypoxemia burden was quantified as the percentage of total sleep time with peripheral oxygen saturation (SpO₂) < 90% (%T90/TST) and grouped as Low (≤5%), Mild (>5-≤10%), Moderate (>10-≤25%), and Severe (>25%). The lipid panel-total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), triglycerides (TG)-and atherogenic indices (AIP, CRI-I, CRI-II) were compared across %T90 groups and within patients before and after ≥3 months of adherent CPAP (device-verified ≥4 h/night on ≥70% of nights).

One hundred and four patients were included. Higher %T90 was associated with a progressively more atherogenic profile: LDL-C (p = 0.027), TC (p < 0.001), TG (p < 0.001) and CRI-I (p < 0.001), CRI-II (p = 0.006), AIP (p < 0.001) were significantly higher in the >25% group versus ≤5%. The lowest nocturnal SpO₂ (peripheral oxygen saturation) did not correlate significantly with lipids/indices. After adherent CPAP, LDL-C (118.0 → 102.5 mg/dL), TC (199.0 → 182.0 mg/dL), TG (152.5 → 129.0 mg/dL) and CRI-I (4.37 → 3.94), CRI-II (2.58 → 2.24), AIP (0.55 → 0.46) decreased significantly (all p < 0.001), while HDL-C did not change (p = 0.570). Primary endpoints (CRI-I/II, AIP) remained significant after Bonferroni correction.

In OSAS, greater hypoxemia burden (%T90/TST) is linked to a more atherogenic lipid profile, and adherent CPAP is associated with a meaningful reduction in atherogenic load (AIP, CRI-I/II). These findings indicate that nocturnal hypoxaemia, captured using index-based measurements (AIP, Castelli I/II) as well as traditional lipids, is associated with a general reduction in atherogenic risk.