Heart rate and ventricular repolarization variabilities interactions modification by microgravity simulation during head-down bed rest test

Features extracted from heart rate variability (HRV) have allowed to classify several cardiac disorders. In this work, the linear relationship between HRV and ventricular repolarization variability is studied as a possible feature for stratifying risk of cardiac arrhythmias under weightlessness conditions. Three VR beat-to-beat indexes extracted from ECG signals as QT, QT_p (QRS onset to T wave peak) and T_pe (peak to end of T wave) were measured. ARARX modeling was used to estimate the VR variability fraction driven by HRV. Head down bed rest as microgravity Earth-based test increased the linear dependency of VR variability driven by HRV. Furthermore, in a pairwise comparison between PRE and POST conditions showed significant differences (p-values <; 0.05) for T_pe variability contents. These results evidence a reduced recovery capacity for the T_pe re-polarization variability to restore its linear dependency values to HR in the first moments at the end of BR.