Principal Connection Between Typical Heart-Rate-Variability Parameters as Revealed by a Comparative Analysis of Their Heart-Rate- and Age-Dependence

Heart rate (HR) is strongly affected by the autonomic nervous system (ANS), while its spontaneous fluctuations, called heart-rate variability (HRV), are reporting about the dynamics of the complex, vegetative regulation of the heart rhythm.Hence, HRV is widely considered an important marker of the ANS-effects on the cardiac system, and as such, a crucial diagnostic tool in cardiology. In order to get nontrivial results from HRV-analysis, it would be desirable to establish exact, universal interrelations between the typical HRV parameters and HR itself that, however, has not been fully accomplished, yet. Hence, our aim was to perform a comparative statistical analysis of ECG-recordings from a public database, with a focus on the HR-dependence of typical HRV parameters. We revealed their fundamental connections, which were substantiated by basic mathematical considerations, and were experimentally demonstrated via the analysis of 24-hours ECG-recordings of more than 200 healthy individuals. The large database allowed us to perform unique age-cohort analyses, too. We confirmed the HR-dependence of typical time-domain parameters as RMSSD and SDNN, frequency-domain parameters as the VLF-, LF- and HF-components, and nonlinear indices as sample entropy and DFA-exponent. In addition to shedding light on their relationship, we are the first to our knowledgeidentified a new, diffuse structure in the VHF regime, as an important indicator of the SNS activity. In addition, the demonstrated age-dependence of the HRV parameters gives important new insight into the long-term changes of the ANS-regulation of the cardiac system. As a possible molecular physiological mechanism underlying our new findings, we suggest that they are associated to Piezo2 channel functionand its age-related degradation. We expect our results to be utilized in HRV analysis related to both medical research and practice.