Abstract
Background: Heart rate variability (HRV) is primarily heart rate (HR) dependent, and therefore, different HR may exert different impact on HRV. The objectives of the study were to evaluate the effect of HR on HRV in children and to determine whether HRV indices normalized to HR are sex- and age-related.Methods: Short-term ECG recordings were performed in 346 healthy children. Standard time and frequency domain HRV parameters and HR were analyzed in four age subgroups (6–7, 8–9, 10–11, and 12–13 years old). To investigate the HR impact on HRV, standard HRV parameters were normalized to prevailing HR.Results: Standard HRV measures did not differ between age subgroups, however, HR significantly decreased with subjects age and turned out to be the strongest determinant of HRV. The normalization of HRV to prevailing HR allowed to show that sex-related differences in standard HRV resulted from differences in HR between boys and girls. The normalized HRV significantly decreased with age—before the normalization this effect was masked by age-related HR alterations.Conclusions: HR significantly impacts HRV in pediatric population and turns out to be the strongest determinant of all standard HRV indices. The differences in standard HRV between boys and girls result from differences in their HR. The normalized HRV is decreasing with age in healthy children and it is accompanied by the reduction of HR—as a net result, the standard HRV is constant in children at different ages. This may reflect the maturation of the autonomic nervous system.
Highlights
During the past 30 years a large number of studies employing heart rate variability (HRV) analysis to assess cardiac autonomic function in both healthy subjects and patients with various pathological conditions have been published (Billman, 2011; Xhyheri et al, 2012)
In the consecutive age subgroups the standard HRV parameters were not statistically different (Figure 1) and they did not present any relevant correlation with age, i.e., standard deviation of all normal R-R intervals (SDNN), r = −0.06 (p = 0.29); RMSSD, r = −0.03 (p = 0.59); pNN50, r = −0.01 (p = 0.88); LF, r = −0.06 (p = 0.27); HF, r = −0.06 (p = 0.29); and TP, r = − 0.06 (p = 0.31)
All standard HRV indices were negatively correlated with HR (Figure 2) with correlation coefficients ranging between −0.56 to −0.77 (p < 0.001 for all)
Summary
During the past 30 years a large number of studies employing heart rate variability (HRV) analysis to assess cardiac autonomic function in both healthy subjects and patients with various pathological conditions have been published (Billman, 2011; Xhyheri et al, 2012). Most of the studies addressing the HRV normalization for HR have been carried out in adults (Sacha and Grzeszczak, 2001; Sacha and Pluta, 2005a,b, 2008; Grant et al, 2013; Sacha, 2013, 2014a,b,c; Sacha et al, 2013a,b,c, 2014; Carter et al, 2014; Monfredi et al, 2014; Pradhapan et al, 2014; Billman et al, 2015) and, to the best of our knowledge, there is no such a study in pediatric population This is even more important since children usually exhibit higher HR and higher variations of HR than adults and their HR gradually decreases with age (Fleming et al, 2011). The objectives of the study were to evaluate the effect of HR on HRV in children and to determine whether HRV indices normalized to HR are sex- and age-related
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