Correlation between mood and heart rate variability indices during daily life

We investigated the correlation between mood and heart rate variability (HRV) indices during daily life. The RR-interval and body acceleration of 40 normal male subjects were recorded using ambulatory device for 48 to 72 hours. Every hour that the subjects were awake they registered their current mood on a Visual Analogue Scale questionnaire. The questionnaire scales eight of the subjects’ current moods. Those are happiness, tension, fatigue, worry, depression, anger, vigor, and confusion. The following four HRV indices were calculated. Those are heart rate, root mean square of successive differences of RR-interval sequence, the normalized high-frequency (0.15 0.4 Hz) power of RR-interval variability, and mean frequency in the high-frequency band of RR-interval variability. The calculated HRV indices data and the mood data were normalized individually, the data with body acceleration exceeding 30 mG were excluded from the analysis to reduce the effect of exercise, and the differences from the first day (∆mood and ∆HRV-index) were taken to reduce the effect of circadian rhythm. The most three highly correlated combinations were ∆vigor and ∆HFnu (R = –0.24, p < 0.0001), ∆vigor and ∆RMSSD (R = –0.24, p < 0.0001), and ∆vigor and ∆HR (R = 0.22, p < 0.001). Vigor exhibited the most significant correlations with HRV indices of eight moods.