VARIABILITY OF HEART RATE PARAMETERS AND THEIR RELATIONSHIPS IN YOUNG ADULTS

Abstract

Aim. This paper aims to identify relationships between RR interval duration and spectral and pNNx parameters. Materials and methods. A young adult sample was analyzed (aged 18–23 years; n = 54). In the supine position, the following parameters were determined: total power (TP, 0.003–0.40 Hz), high-frequency (HF, 0.15–0.4 Hz), low-frequency (LF, 0.04–0.15 Hz), very-low-frequency (VLF, 0.003–0.04 Hz), and pNNx% (across the pNN10–100 ms ranges). Statistical processing was performed using Statistica 10.0, with group differences assessed via the Mann – Whitney U Test and clustering performed using k-means cluster analysis. Results. Cluster analysis revealed two groups: Group 1 – individuals with irregular physical activity (n = 36), Group 2 – athletes who regularly train in cyclic sports (n = 18). The defining feature of Group 2 is a marked predominance of frequency-domain HRV characteristics, longer pNN intervals, and progressively increasing differences across the ascending pNN10-100 series. Interval duration modulates heart rate variability depending on the level of physical activity. Conclusion. The effect of increasing cardiac interval duration on pNNx was as follows: in Group 1, it leads both to an increase in the intensity of
the direct correlation with pNN and to an expansion of the range of significant x values; in Group 2, it results in stable moderate (0.42–0.45) and clearly localized (pNN40–60) correlation values, indicating a reduced influence of cardiac interval duration. The effect of increasing cardiac interval duration on spectral para­meters in Group 1 was as follows: at minimal cardiac interval duration, there is no heart response to autonomic influences; with increasing cardiac interval duration, only minimal correlations with TP, HF, and LF are observed. At maximal cardiac interval duration, there is an increase in autonomic regulation – specifically, in TP and HF. In Group 2, spectral redistribution occurs under constant TP: from a complete disregard of VLF modulation to a faster autonomic component, and then to the fastest HF.