Poincaré Plot Width, Morning Urine Norepinephrine Levels, and Autonomic Imbalance in Children With Obstructive Sleep Apnea

Abstract Background Obstructive sleep apnea (OSA) in childhood is accompanied by sympathetic overflow unopposed by the parasympathetic tone. Complex methods like power spectral analysis of heart rate variability have been applied to study this imbalance. In this report, width of Poincare scattergram of the R-R interval (parasympathetic tone) and morning urine norepinephrine concentration (sympathetic activity) were used to assess autonomic imbalance. Methods Poincare plot was obtained from the electrocardiographic channel of nocturnal polysomnography and its width was measured, and norepinephrine-to-creatinine concentration ratio was calculated in morning urine specimen. Results Twenty children with obstructive sleep apnea and moderate-to-severe nocturnal hypoxemia (oxygen saturation of hemoglobin [SpO 2 ] nadir 2 nadir ≥90%), and 11 control subjects were recruited. Children with obstructive sleep apnea and moderate-to-severe hypoxemia had significantly narrower Poincare plot width (318.7 ± 139.3 ms) and higher ln-transformed urine norepinephrine-to-creatinine ratio (4.5 ± 0.6) than control subjects (484.2 ± 104.4 ms and 3.8 ± 0.4, respectively; P P  = 0.02). Conclusions Subjects with obstructive sleep apnea and moderate-to-severe nocturnal hypoxemia have enhanced sympathetic activity and reduced parasympathetic drive. Poincare plot width and urine norepinephrine levels are simple measures of autonomic imbalance in pediatric obstructive sleep apnea.