Correlation between obesity and obstructive sleep apnea has been documented in both adults and children. This investigation evaluated importance of body mass index (BMI) in relation to age as predictor of severity of obstructive sleep-disordered breathing (SDB). Children with habitual snoring referred for polysomnography were recruited. BMI Z score (> or =1.036 vs <1.036, i.e. at risk for overweight or overweight vs normal) was assessed as predictor of severity of SDB (apnea-hypopnea index [AHI] >five vs < or =five episodes per hour) at different ages (< or =6 vs >6 years). Two hundered eighty-four participants were recruited: 75 young children (4.6 +/- 1 years) with high BMI (1.9 +/- 0.7); 95 young subjects (4.5 +/- 1.1 years) with low BMI (-0.2 +/- 1.3); 55 older children (9.2 +/- 1.8 years) with high BMI (1.8 +/- 0.5); and 59 older participants (9.7 +/- 2.2 years) with low BMI (-0.2 +/- 1.1). Odds ratios for AHI >5 in young/high BMI children, young/low BMI subjects, and older/high BMI subjects relative to older/low BMI participants were: 6.5 (95% confidence interval 2.1-19.9), 7.3 (2.4-22) and 2 (0.6-7.3), respectively. Large tonsil size was associated with young age (odds ratio 1.97; 1.2-3.3). Among children with habitual snoring, adiposity does not predict severity of obstructive SDB in early childhood probably due to the prominent role of adenotonsillar hypertrophy. However, it may have a more important contribution to severity of SDB in older children.

Summary. Introduction: Adults with obstructive sleep apnea have increased sympathetic activity. It was hypothesized that in children with symptoms of obstructive sleep-disordered breathing (SDB), morning urine levels of catecholamines correlate with severity of nocturnal hypoxemia. Methods: Children with snoring referred for polysomnography and controls without snoring were recruited. Morning urine norepinephrine, epinephrine, normetanephrine, and metanephrine levels were measured (ng/mg urine creatinine). Results: Twelve children (age 5.2 AE 2.3 years) with severe hypoxemia (oxygen saturation of hemoglobin-SpO 2 nadir 86%), 20 subjects (age 6.1 AE 2.1 years) with moderate hypoxemia (SpO 2 nadir 90% and >86%), 22 children (age 6.6 AE 1.5 years) with mild nocturnal hypoxemia (SpO 2 nadir >90%), and 10 controls (age 7.1 AE 2.8 years) were studied. Children with severe hypoxemia had significantly higher log-transformed norepinephrine levels (1.63 AE 0.29) compared to those with moderate hypoxemia (1.43 AE 0.22; P < 0.05) or compared to controls (1.39 AE 0.31; P < 0.05). In subjects with SDB, log-transformed oxygen desaturation of hemoglobin index or SpO 2 nadir predicted log-transformed norepinephrine levels after adjustment by age, gender and body mass index (r 2 ¼ 0.24; and r 2 ¼ 0.24, respectively; P < 0.01). Conclusions: Severity of nocturnal hypoxemia in children with intermittent upper airway obstruction during sleep correlates with morning urine levels of norepinephrine suggesting increased sympathetic tone.

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