Hypoxic burden as a cause of cardiovascular morbidity in childhood obstructive sleep apnea.

Background: To assess whether hypoxic burden (HB) is associated with cardiac autonomic nervous system dysfunction and increased blood pressure (BP) in otherwise healthy children with moderate to severe obstructive sleep apnea (OSA).

Methods: Among 103 children with moderate-to-severe OSA, twenty pairs, matched for age, sex and obstructive apnea-hypopnea index (OAHI) were selected, with low (first quartile) or high (fourth quartile) HB in each pair: median [25th-75th percentiles]; age: 10.8 years [7.3; 13.2] vs. 11.4 [8.6; 13.5]; sex: 7 and 10 girls; z-score of body mass index: 1.50 [0.11; 2.43] vs. 2.40 [1.92; 2.70] (p = 0.012); OAHI: 8.6/hr [6.4; 13.3] vs. 11.1 [6.6; 17.2] and HB: 0.8%.min/h [0.3; 1.5] vs. 13.8 [10.1; 22.3], respectively.

Results: Non-linear heart rate variability (HRV) indices obtained from polysomnography showed sympathetic overflow (Poincaré plot: decreased SD2) and weaker parasympathetic modulation (decreased SD1) in children with high versus low HB. The high versus low HB group had higher percentiles of office BP: systolic, 75th [61; 81] vs. 57th [47; 69], p = 0.049 and diastolic, 70th [60; 78] vs. 55th [46; 65], p = 0.007, adjusted for obesity and arousal index.

Conclusions: Despite similar levels of OAHI, children with higher HB demonstrate parasympathetic withdrawal and increased daytime blood pressure.

Impact: The hypoxic burden predicts cardiovascular morbidity/mortality in adult obstructive sleep apnea syndrome. Our study shows that in children with moderate to severe obstructive sleep apnea, despite similar levels of obstructive apnea-hypopnea index, those with higher hypoxic burden show cardiac autonomic nervous system dysfunction and increased daytime blood pressure. This study is the first one suggesting that the hypoxic burden is a valuable marker of cardiovascular morbidity in childhood obstructive sleep apnea.