Short-Term Linear & Nonlinear Heart Rate Variability During Spontaneous Breathing In Typically-Developing Children & Adolescents

Heart rate variability (HRV) is a measure of the fluctuations in the R-R interbeat intervals in an electrocardiogram (ECG) time series and a biomarker of neurocardiac function. Impairment in HRV is a risk factor for cardiometabolic morbidity and mortality in aging and chronic diseases. Studies on HRV are largely confined to the linear domain; however, the heart rate signal demonstrates nonlinear fractal variability, suggesting complexity in the cardiovascular system. While HRV in aging and disease is well-studied, understanding neurocardiac maturation—especially nonlinear HRV changes during development—is essential for characterizing typical development and comparing pediatric patient groups. PURPOSE: To characterize HRV using short-term linear and nonlinear HRV in (1) typically developing children (ages 7-12 yrs. old, n = 25) and adolescents (ages 13-17 yrs. old, n = 22), and (2) explore the potential role of sex during pubertal development. METHODS: Supine HRV during spontaneous breathing at rest was assessed using 3-lead ECG for 5-minutes. HRV was analyzed using linear (time and frequency domain) and nonlinear (Poincáre analysis [SD1, SD2], approximate entropy [ApEn], and detrended fluctuation analysis [DFA1 & DFA2]) metrics. Analysis of variance was used to determine main effects of age (child vs. adolescent) and sex, and interaction effects. RESULTS: No effect of age in linear HRV was detected, however an effect of sex revealed lower HRV for several linear metrics in females (p < 0.05). An interaction was observed for ApEn, which was lower in adolescents (p < 0.001), driven by increased regularity in adolescent males (p < 0.001). DFA1 was not different by age, but higher in females (p = 0.024), and DFA2 decreased in adolescents (p = 0.023). Poincáre analysis revealed no age effects, however, males had a higher SD1 (p = 0.005), and adolescent males a higher SD2 (p < 0.001). CONCLUSION: Preliminary results suggest unique age- and sex-specific nonlinear changes in short-term nonlinear control of HRV during development. Females had lower linear HRV, but greater nonlinear complexity and fractal variability. Nonlinear HRV appeared to decrease with age in both sexes. Future work into the biobehavioral mechanisms driving nonlinear HRV during development and in pediatric patient populations is warranted. Supported by: Supported by NIH 1R01HLI55764 & NIH P20GM113125 (MW)