Distribution of 24-h ambulatory blood pressure in children: normalized reference values and role of body dimensions.

BACKGROUND: Twenty-four-hour ambulatory blood pressure monitoring (ABPM) is an essential tool in the diagnosis and therapeutic monitoring of arterial hypertension in children. The statistical use of pediatric ABPM reference values has been compromised by the non-Gaussian distribution of 24-h blood pressure (BP) in children.
OBJECTIVE: To develop distribution-adjusted pediatric ABPM reference tables.
METHODS: From cross-sectional ABPM data obtained in 949 healthy children and adolescents aged 5-20 years, a set of reference tables was developed for 24-h, daytime and night-time mean values of systolic, diastolic, mean arterial BP and heart rate, utilizing the LMS method to account for the variably skewed distribution of ABPM data. Age- and gender-specific estimates of the distribution median (M), coefficient of variation (S) and degree of skewness (L) were obtained by a maximum-likelihood curve-fitting technique. The estimates of, and can be used to normalize ABPM data to gender and age or height.
RESULTS: Re-application of the established, and values in the reference population confirmed appropriate normalization of ABPM values. Height standard deviation scores (SDS), body mass index (BMI) SDS and heart rate SDS were independent positive predictors of 24-h systolic BP SDS. Diastolic 24-h mean BP SDS showed a weak correlation with BMI SDS only.
CONCLUSIONS: The use of LMS reference tables permits calculation of appropriate SDS values for ABPM in children. Whereas systolic 24-h BP is independently correlated with age, relative height and obesity, diastolic values are almost independent of age and relative height, and weakly associated with relative obesity.