Influence of Heart Rate, Age, and Gender on Heart Rate Variability in Adolescents and Young Adults.

Key autonomic functions are in continuous development during adolescence which can be assessed using the heart rate variability (HRV). However, the influence of different demographic and physiological factors on HRV indices has not been fully explored in adolescents. In this study we aimed to assess the effect of age, gender, and heart rate on HRV indices in two age groups of healthy adolescents (age ranges, 13-16 and 17-20 years) and two groups of healthy young adults (21-24 and 25-30 years). We addressed the issue using 5-min ECG recordings performed in the sitting position in 255 male and female participants. Time, frequency, and informational domains of HRV were calculated. Changes in HRV indices were assessed using a multiple linear regression model to adjust for the effects of heart rate, age, and gender. We found that heart rate produced more significant effects on HRV indices than age or gender. There was a progressive reduction in HRV with increasing age. Sympathetic influence increased with age and parasympathetic influence progressively decreased with age. The influence of gender was manifest only in younger adolescents and young adults. In conclusion, age, gender, and particularly heart rate have a substantial influence on HRV indices, which ought to be considered to avoid biases in the study of the autonomic nervous system development. The lack of the gender-related effects on HRV indices in late adolescence could be related to non-completely achieved maturity of the autonomic mechanisms, which deserves further exploration.

Very High Frequency Oscillations of Heart Rate Variability in Healthy Humans and in Patients with Cardiovascular Autonomic Neuropathy.

Literature reports on the very high frequency (VHF) range of 0.4-0.9 Hz in heart rate variability (HRV) are scanty. The VHF presence in cardiac transplant patients and other conditions associated with reduced vagal influence on the heart encouraged us to explore this spectral band in healthy subjects and in patients diagnosed with cardiac autonomic neuropathy (CAN), and to assess the potential clinical value of some VHF indices. The study included 80 healthy controls and 48 patients with spinocerebellar ataxia type 2 (SCA2) with CAN. The electrocardiographic recordings of short 5-min duration were submitted to three different spectral analysis methods, including the most generally accepted procedure, and the two novel methods using the Hilbert-Huang transform. We demonstrated the presence of VHF activity in both groups of subjects. However, VHF power spectral density, expressed in relative normalized units, was significantly greater in the SCA2 patients than that in healthy subjects, amounting to 36.1 ± 17.4% vs. 22.9 ± 14.1%, respectively, as also was the instantaneous VHF spectral frequency, 0.58 ± 0.05 vs. 0.64 ± 0.07 Hz, respectively. These findings were related to the severity of CAN. We conclude that VHF activity of HRV is integral to the cardiovascular autonomic control.