Reflection of autonomic regulation behaviour using short-term cross-spectral analysis on RR and QT intervals

The balance of autonomic nervous system (ANS) is of great significance for regulating normal physiological functions of heart and avoiding risk of cardiac diseases. This project is aimed to reveal the regulation state of ANS by analyzing the linear relationship between RR interval (RRI) and QT interval (QTI). The data for this analysis were provided by the Telemetric and Holter ECG Warehouse (THEW), among which database Normal was selected as normal controls (n=189) and database ESRD as typical subjects of ANS dysfunction with high risk for cardiac arrhythmias and sudden cardiac death(n=43). A causal cross-spectral approach based on the autoregressive model was applied to distinguish the directional effect from RRI to QTI. And the causal cross-spectral analysis used here was focused on 2-minute-length series. Firstly, the validity of the short-term indices was verified. Then the relevant indices, such as cross-spectral energy in both low frequency (LF) and high frequency (HF) bands, as well as transfer function G, were calculated. Inner-comparison for the same index between day and night and inter-comparison between Normal and ESRD were made. Results showed that: 1) For Normal, there were significant differences between daytime and nigh-time results of GLF, GHF and LF/HF. However, no significant diurnal variation of the corresponding indices existed in ESRD; 2) GL
F
-
d
/G
LF
-
n
and (LF/HF)
d
/(LF/HF)
n
were significantly smaller in ESRD than that in Normal. The above results suggest the loss of circadian rhythm in ESRD. Furthermore, there is no statistic difference of GHF-d/GHF-n between Normal and ESRD. Since HF band mainly reflect the influence of vagal tone, it was revealed that loss of circadian rhythm in ESRD was primarily caused by the overactivity of sympathetic branch. Our study confirmed the feasibility of very short series based analysis and provided an approach for investigating ANS activity.