Study of heart-rate variability in a video task using Holo-Hilbert spectral analysis

In this study, we applied the Holo-Hilbert spectral analysis (HHSA) method to analyze HRV in electrocardiography (ECG) signals. The HHSA intends to interpret the measured interbeat-interval (IBI) signal as the multiplication of an oscillatory signal (carrier wave) with a modulatory signal (envelope wave). Instantaneous frequency analysis (IFA) was adopted to calculate the frequency modulation (FM) and amplitude modulation (AM) frequencies at each time point. The probability of FM-AM distribution across the whole measured IBI signal was accumulated and displayed on a Holo-Hilbert spectrum (HHS). Twenty healthy subjects were recruited in our ECG study. Each subject was requested to view two video clips, including one relaxing video clip and one horror video clip. We observed the very high-frequency (VHF) band was modulated by a ∼0.05 Hz AM frequency on the calculated HHS. The value of VHF power was significantly decreased (p < 0.01, Wilcoxon signed rank test) in viewing the horror video clip, compared to the condition in viewing the relaxing video clip. We also found both the power in VHF and high-frequency (HF) bands decreased in viewing the horror video clip. The HHSA provides a new perspective to analyze HRV which might provide insightful information in future studies.