RESEARCH ARTICLE Reproducibility of 24-h heart rate variability in children Bojko Bjelakovic 1,2 • Dragana Ilic 1 • Stevo Lukic 2,3 • Vladislav Vukomanovic 4,5 • Cojbasic Zarko 6 • Zoran Stankovic 7 • Jovic Marko 2 Received: 26 May 2017 / Accepted: 22 June 2017 Ó Springer-Verlag GmbH Germany 2017 Abstract Background Over the last decades, time domain heart rate (HR) variability analysis has been explored in different pediatric clinical settings to obtain information on the cardiac autonomic tone. However, the consistency over time of 24 h time domain HRV measurements in children is not well-known. Methods We investigated the reproducibility of 24 h HRV time-domain indices (1 day apart), from 39 healthy chil- dren (9.5 ± 5.3 years, 56.4% girls). The parameters anal- ysed included: standard deviation of all the adjacent NN intervals, standard deviation of the averages of NN inter- vals (the intervals between normal R-peaks) in all 5-min segments, and square root of the mean of the sum of the squares of the differences between adjacent NN intervals, uncorrected and corrected for HR. Reproducibility between two 24-h ECG recordings was evaluated by intraclass correlation coefficients, standard error of measurement, coefficients of variation and Bland–Altman plots. Results For the analyzed time-domain indices, standard deviation of all the adjacent NN intervals corrected for HR showed best reproducibility with the highest intraclass correlation coefficient (0.987), the lowest coefficients of variation (5.5%) and the best level of agreement between two recordings as assessed by Bland–Altman plots. Conclusions Our results indicate that the standard devia- tion of all the adjacent NN intervals corrected for the HR parameter obtained from 24-h ambulatory recordings in children is consistent and reproducible over time, thus allowing reliable identification of cardiac autonomic tone in this age group. Keywords Heart rate variability Á Children Á Reproducibility Abbreviations HRV Heart rate variability SDNN Standard deviation of all the adjacent NN intervals SDANN Standard deviation of the averages of NN intervals in all 5-min segments RMSSD Square root of the mean of the sum of the squares of the differences between adjacent NN intervals SDNNc SDANN corrected for heart rate SDANNc SDANN corrected for heart rate RMSSDc RMSSD corrected for heart rate ECG Electrocardiogram ICCs Intraclass correlation coefficients SEM Standard error of measurement CV Coefficient of variation Electronic supplementary material The online version of this article (doi:10.1007/s10286-017-0445-3) contains supplementary material, which is available to authorized users. & Bojko Bjelakovic bojko968@gmail.com 1 Clinic of Pediatrics, Clinical Center, Zorana Djindjica 48 Boulevard, Nis 18000, Serbia 2 Medical Faculty, University of Nis, Nis, Serbia 3 Clinic of Neurology-Clinical Center, Nis, Serbia 4 Mother and Child Health Institute, ‘‘Dr Vukan Cupic’’, Belgrade, Serbia 5 Medical Faculty, University of Belgrade, Belgrade, Serbia 6 Mechanical Engineering Faculty, University of Nis, Nis, Serbia 7 Faculty of Electronic Engineering, University of Nis, Nis, Serbia 123 Clin Auton Res DOI 10.1007/s10286-017-0445-3