Active standing in healthy subjects elicited sporadic transient R-R interval increases associated with simultaneous increases in high- and low-frequency powers.
Observational
What are the temporal relationships among transient changes in the RRI and LF/HF powers during active standing in healthy subjects?
Ultra-short-term spectral analysis demonstrates that simultaneous increases in LF and HF powers during active standing may reflect enhanced cardiac vagal activity generating transient bradycardia.
Spectral analysis of heart rate variability (HRV) is widely used as a non-invasive method to assess the cardiovascular autonomic function. Of the two main frequency components of HRV, namely low-frequency (LF, 0.04-0.15 Hz) and high-frequency (HF, 0.15-0.4 Hz) components, it is generally accepted that the HF power reflects modulation of heart rate which is mediated by cardiac parasympathetic (vagal) nerve activity. In contrast, the origin and functional correlates of the LF component are still controversial. Although several lines of evidence have indicated a close correlation between LF power and the baroreflex modulation of autonomic outflows, the detailed mechanisms underlying the genesis of the LF component remain unclarified. In this study, we conducted an ultra-short-term (UST) spectral analysis of R-R interval (RRI) time series using Fast Fourier Transform (FFT) with 5- and 25-s windows to clarify the temporal relationships among transient changes in the RRI and, LF and HF powers in healthy subjects. We found that during active standing, transient RRI increases occurred sporadically. The UST spectral analysis revealed that this RRI increase was associated with a simultaneous increase in HF power which was closely linked to the prominent LF power increase. These results indicate that during active standing, increases in LF and HF powers occur simultaneously, and they may reflect enhanced cardiac vagal activity which generates transient bradycardia.
Yokobori et al. (Sun,) conducted a observational in Healthy subjects. Active standing was evaluated on Temporal relationships among transient changes in the RRI, LF, and HF powers. Active standing in healthy subjects elicited sporadic transient R-R interval increases associated with simultaneous increases in high- and low-frequency powers.