Relationship between Fatigue Severity and Heart Rate Variability in Middle-Aged Male Workers

Song, Sang Wook; Shin, Jin Hee; Findley, Thomas

Abstract

OBJECTIVES
This study investigated the relationship between the severity of fatigue and the cardiac autonomic function by analyzing the heart rate variability on middle-aged male workers.
METHODS
The severity of fatigue and heart rate variability were assessed with the control measures of age, body mass index, blood pressure, alcohol consumption, smoking history, regular exercise on 82 healthy middle-aged male workers in an annual health checkup. The severity of fatigue was evaluated by the Fatigue Severity Scale (FSS), which was developed by Krupp. The 5-minute electrocardiographic recordings were analyzed as a function of the time and the frequency domain methods of the heart rate variability (HRV). Standard Deviation of the NN intervals (SDNN), Root-Mean-Square of Successive Differences (rMSSD), Total Power (TP), Low Frequency (LF: 0.04~0.15 Hz) power, High Frequency (HF: 0.15-0.4 Hz) power, LF/HF ratio were used as the indices of the HRV. For a comparison of autonomic nervous functions and other variables, the subjects were divided into three fatigue groups based on the FSS score as follows: low (N=31), moderate (N=33), high (N=18) fatigue groups.
RESULTS
There were no significant differences in age, blood pressure, heart rate, body mass index, alcohol consumption, or regular exercise except for the smoking history among the groups. In addition, there were no significant differences in the time domain analysis (SDNN, rMSSD) of HRV among the groups. Spectral analysis of the HRV showed that the mean amplitudes of the HF and LF component were lower in the high fatigue group, whereas there was no significant difference in the LF/HF ratio among the fatigue groups. There were no significant differences in the HRV indices between the smoking and non-smoking groups. No significant interacting effects between the severity of fatigue and smoking on the HRV were observed.
CONCLUSIONS
The association between severe fatigue and the reduced high and low frequency components of the HRV in middle-aged male workers reflects a dysregulation of the cardiac autonomous control. Although the pathophysiological mechanism of this association remains unclear, these results might explain their increased risk for cardiovascular disease. However, these effects need to be confirmed through a well-designed prospective study.