Study of heart rate variability in healthy humans as a function of age: considerations on the contribution of the autonomic nervous system and the role of the sinoatrial node

Isabel María Irurzun^1*David A Jorge Tasé^1,2Leopoldo Garavaglia³Magdalena María Defeo⁴

• ¹Centro de Simulación Computacional para Aplicaciones Tecnológicas (CSC-CONICET), Ciudad autónoma de Buenos Aires, Argentina
• ²Laboratorio de Procesamieno de Señales y Comunicación. Departamento de Electronica, Facultad de Ingenieria, Universidad de Buenos Aires, Buenos Aires, Buenos Aires, Argentina
• ³Centro de Investigaciones Opticas (CONICET-UNLP), La Plata, Buenos Aires, Argentina
• ⁴General Interzonal Hospital of Acute Rodolfo Rossi, La Plata, Buenos Aires, Argentina

Introduction: We studied the behavior of the heart rate variability (HRV) in healthy humans as a function of age from conception, including fetal data. We calculated statistical quantities such as the mean value of RR intervals (), the standard deviation of these intervals (SD), the power of the very low frequency (VLF), low frequency (LF) and high frequency (HF) bands, and the large-scale properties of HRV. We rationalized our findings discussing previous results that identify the signatures of the sinoatrial node (SAN) and the autonomic nervous system (ANS) in the HRV. This work provides further insights into the contribution of the SAN and the ANS to the cardiac rhythm in humans. Methods: We analyzed 205 HRV time series; 195 correspond to born individuals aged between 1 month and 74 years, 50% females. The remaining ten time series correspond to healthy fetuses. The age was expressed in weeks, including gestational age to avoid finite size effects due to rounding errors. We included results previously reported in the literature. Results and discussion: followed a power law with age from gestation and throughout life. The scale factor was 0.15±0.01. SD evolved during pregnancy and underwent a sudden change at birth. From birth to puberty SD followed a scale behavior with age and the scale factor was 0.37±0.04. We calculated the VLF, LF and HF bands. The HF/VLF ratio followed a power law with age, and the scale factor was −0.55±0.06. We analyzed the effect of age on the scale behavior. Both the scale factor and the frequency range in which it was determined depended on age. Scale behavior began at low frequencies and evolved from 1/f2-like behavior to 1/f-like behavior during pregnancy. After birth, 1/f behavior extended to occupy the entire frequency range in the puberty. With aging, the frequency range regressed again towards lower frequencies. The results demonstrated that the complex structure of HRV primarily reflects the structural complexity of the SAN. There is a white noise component in HRV that can be attributed to the ANS.