Abstract
The very low-frequency (VLF) band of heart rate variability (HRV) has different characteristics compared with other HRV components. Here we investigated differences in HRV changes after a mental stress task. After the task, the high-frequency (HF) band and ratio of high- to low-frequency bands (LF/HF) immediately returned to baseline. We evaluated the characteristics of VLF band changes after a mental stress task. We hypothesized that the VLF band decreases during the Stroop color word task and there would be a delayed recovery for 2 h after the task (i.e., the VLF change would exhibit a “slow recovery”).Nineteen healthy, young subjects were instructed to rest for 10 min, followed by a Stroop color word task for 20 min. After the task, the subjects were instructed to rest for 120 min. For all subjects, R-R interval data were collected; analysis was performed for VLF, HF, and LF/HF ratio. HRV during the rest time and each 15-min interval of the recovery time were compared. An analysis of the covariance was performed to adjust for the HF band and LF/HF ratio as confounding variables of the VLF component.HF and VLF bands significantly decreased and the LF/HF ratio significantly increased during the task compared with those during rest time. During recovery, the VLF band was significantly decreased compared with the rest time. After the task, the HF band and LF/HF ratio immediately returned to baseline and were not significantly different from the resting values. After adjusting for HF and LF/HF ratio, the VLF band had significantly decreased compared with that during rest.The VLF band is the “slow recovery” component and the HF band and LF/HF ratio are the “quick recovery” components of HRV. This VLF characteristic may clarify the unexplained association of the VLF band in cardiovascular disease prevention.
Highlights
Heart rate variability (HRV) is used to measure autonomic activity
We propose that the HF band and LF/HF ratio are the “quick recovery” components, and the very low-frequency (VLF) band is the “slow recovery” component
The HF band has been used to measure vagal activity, and the LF/HF ratio was used as a measure of sympathetic activity
Summary
Heart rate variability (HRV) is used to measure autonomic activity. In 1996, a task force standardized the methods of HRV measurement [1]. One of the most commonly used methods for HRV analysis is power spectral density (PSD) analysis [2]. The HRV analysis, HF and LF/HF ratio, was widely used for analysis of autonomic nervous activity for cardiovascular diseases [3], stroke [4], and epilepsy [5,6]. The VLF band has a stronger association with cardiovascular disease prognosis [9], metabolic syndromes [3], and all-cause mortality after traumatic brain injury than with the other HRV components [10]. Low VLF power has been associated with increased chronic inflammation [11,12,13], and the nocturnal VLF band may be a predictor of infection after acute stroke [14].
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