Increased sympathetic activity in children with obstructive sleep apnea: cardiovascular implications

Background: Obstructive sleep apnea (OSA) is associated with increased sympathetic activity and hypertension in adults. We tested the hypothesis that children with OSA also have increased sympathetic activity as measured by overnight urinary catecholamines, and that this increase is related to the severity of OSA and to blood pressure (BP).

Methods: Seventy snoring children referred for assessment of sleep disordered breathing and 26 healthy non-snoring control children (age range: 3-12 years, 59 M/37 F) were studied. Overnight polysomnography was performed coincident with a 12h overnight urine collection. Urinary catecholamine levels were determined using high performance liquid chromatography (noradrenaline, adrenaline and dopamine, with levels adjusted for creatinine excretion). Simple linear and stepwise multiple linear regressions were used to determine the independent associations between catecholamine levels and age, gender, BMI z-score, systolic BP z-score, diastolic BP z-score, and apnea hypopnea index (AHI).

Results: Simple linear regressions revealed significant associations between noradrenaline and AHI (r = 0.32) and age (r = -0.20, p < 0.05 for both). Significant associations were also found between adrenaline and AHI (r = 0.27) and age (r = -0.25, p < 0.05 for both). Systolic BP z-score and diastolic z-score were both significantly associated with adrenaline (r = 0.22 and r = 0.20 respectively, p < 0.05 for both). Multivariate analysis revealed that only AHI was a significant independent predictor of noradrenaline (model R(2) = 0.10, p = 0.001). Similarly, only AHI and age were significant independent predictors of adrenaline (model R(2) = 0.12, p < 0.05).

Conclusions: This study demonstrates that levels of overnight urinary noradrenaline and adrenaline are related to the severity of OSA in children. These data indicate that children with OSA have increased sympathetic tone that may contribute to the cardiovascular consequences of the condition.