The Changes in Heart Rate Variability between Morning and Afternoon

Choi, Chang Jin; Choi, Whan Seok; Kim, Kyung Soo

Abstract

BACKGROUND: Short-term measurement of heart rate variability is known to be a non-invasive technique to examine autonomic nerve system. Heart rate variability exhibits circadian rhythm according to work/sleep cycle and biological clock. In primary practice, short-term measurement of heart rate variability is usually used during the day. Therefore the aims of this study were to investigate the possibility of differences in heart rate variability between morning and afternoon and also to examine the relationship among associated factors.
METHODS
Sixty-eight healthy volunteers underwent short- term measurement of heart rate variability on two occasions: in the morning (08:30~11:00) and in the afternoon (13:30~16:00). A structured questionnaire was used to access general characteristics, emotion, fatigue and sleeping hours.
RESULTS
The mean heart rate was significantly increased and SDNN, RMSSD, TP, HF and VLF were significantly decreased in the afternoon compared to the morning. LF and LF/HF were not changed. The anxiety group, the depression group and the fatigue group showed significantly greater reduction in TP and RMDDS than the control group.
CONCLUSION
In the afternoon, parasympathetic activity and total power were decreased significantly compared to the morning. Short-term heart rate variability should be measured in the same time zone and need to consider food intake effect. Those who complained of anxiety, depression or fatigue were related to much decrease in TP and RMSSD in the afternoon.