Results of Sleep-Disordered Breathing and Uric Acid in Overweight and Obese Children and Adolescents

Severity of SDBPatient and Polysomnographic Characteristics

A total of 94 children and adolescents were initially included in the study; afterward, 1 subject was excluded because of an abnormal serum creatinine value of 1.5 mg/dL. Of those subjects, 44% were boys, 58% were prepubertal (mean age, 11.1 ± 2.5 years; age range, 6.3 to 16.3 years). The mean BMI z-score was 2.31 ± 0.50 (range, 1.32 to 3.83); and 25 subjects (27%) were classified as overweight, and 68 subjects (73%) as obese. All subjects were nondiabetic.

All children had a normal UA excretion rate (mean rate, 0.33 ± 0.06 mg/dL; range, 0.20 to 0.47 mg/dL); and the mean urinary UA/creatinine ratio was 0.58 ± 0.13 (range, 0.31 to 0.85). There were 15 subjects (16%) with a total urinary creatinine concentration of < 500 mg/d, possibly suggesting an unreliable 24-h urinary collection. Excluding these 15 subjects did not result in significant changes in any of the subsequent analyses. A fasting measurement of serum UA was available for 62 patients (67%). Mean serum UA was 4.8 ± 1.4 (range, 1.5 to 8.8). The polysomnographic data of the subjects with or without SDB are presented in Table 1. There was no difference in age, sex, pubertal stage distribution, and anthropometric variables between these three groups.

Relation Between the Severity of SDB and UA Metabolism

RDI, oxygen desaturation index, and percentage of total sleep time with Sa02 s 89% correlated significantly with serum UA levels. None of the SDB variables were correlated with UA excretion or with urinary UA/creatinine ratio (Table 2). RDI and oxygen desaturation index were almost perfectly correlated (r = 0.99; p < 0.001); therefore, oxygen desaturation index was not used in the regression analysis. RDI and the percentage of total sleep time with Sa02 s 89% remained significant in their respective multiple regression models for serum UA, controlling for sex, puberty, and waist circumference (Tables 3, 4).

Table 1—Polysomnographic Characteristics of Subjects With and Without SDB

Variables RDI < 2 (n = 53) RDI a 2 and < 5 (n = 32) RDI a 5(n = 8) p Value
Total sleep time, min 455.0 ± 49.1 465.4 ± 41.0 460.2 ± 40.8 0.6t
RDI 0.8 ± 0.5 3.0 ± 0.9 13.1 ± 8.9 < 0.0001J
Sao2, % 97.0 ± 0.7 96.7 ± 0.6 96.1 ± 1.1 0.005|
Sao2 nadir, % 91.7 ± 3.0 87.2 ± 3.8 83.9 ± 4.7 < 0.0001J
Total sleep time, % Sao2 a 95% 98.7 ± 2.2 97.1 ± 2.8 82.2 ± 23.7 < 0.0001J
Sao2 > 89 to < 95% 1.3 ± 2.2 2.8 ±2.7 17.1 ± 23.0 < 0.0001J
Sao2 s 89% 0.0 ± 0.1 0.1 ± 0.1 0.6 ± 0.8 < 0.0001J
Oxygen desaturation index 0.6 ± 0.5 2.4 ± 1.1 12.4 ± 8.3 < 0.0001J

Table 2—Correlation Analysis Between the Severity of SDB and UA Metabolism

Variables RDI Oxygen Desaturation Index Mean Sao2 Sao2 Nadir Percentage of Total Sleep Time With Sao2 s 89%
Serum UA 0.26* 0.29* -0.07 -0.18 0.39t
UA excretion -0.06 -0.03 -0.03 0.06 -0.16
Urinary UA/creatinine ratio -0.04 – 0.03 0.01 0.10 -0.14

Table 3—Multiple Linear Regression Analysis With Serum UA as Outcome Variable (Adjusted R2 = 0.40) and RDI as Predictor Variable, Controlling for Sex, Puberty, and Waist Circumference

Variables э ± SE PartialCorrelation
Coefficient
p Value
Intercept 0.46 ± 1.18 0.7
Sex 0.32 ± 0.29 0.14 0.3
Puberty 0.87 ± 0.34 0.32 0.01
Waist circumference 0.04 ± 0.01 0.36 0.005
RDI 0.09 ± 0.03 0.32 0.01

Table 4—Multiple Linear Regression Analysis With Serum UA as Outcome Variable (Adjusted R2 = 0.39) and % of Total Sleep Time With SaO2 < 89% as Predictor Variable, Controlling for Sex, Puberty, and Waist Circumference

Variables ±S
И
PartialCorrelation
Coefficient
p Value
Intercept 1.05 ± 1.27 0.4
Sex 0.22 ± 0.30 0.10 0.5
Puberty 0.83 ± 0.35 0.30 0.02
Waist circumference 0.04 ± 0.02 0.31 0.02
Percentage of total sleep time with Sa02 ^ 89% 0.94 ± 0.45 0.28 0.04
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