Heart Rate Variability as an Early Objective Indicator of Subjective Feeling of Depression in Daily Life

Objectives: Changes in the autonomic nervous system have been observed in patients with depressive disorders by measuring their heart rate variability (HRV). However, whether HRV associates with depressive events in healthy people remains unknown. Methods: Four healthy people participated in the present study. Their HRVs were measured routinely for 6 to 13 months. During this time, two participants reported experiencing two and three bouts of depression, respectively. This approach allowed us to examine changes in the participants' HRVs by comparing their HRVs from before and after the unexpected depressive events. Changes in HRV were compared against those of two participants who did not report any depressive event. Results: Participants' low frequency/high frequency (LF/HF) ratios of HRV were lower after the event of depression than before. Their LF/HF ratios increased after recovery from the depressive events. In contrast, two participants who did not report any depressive event showed relatively smaller changes in their LF/HF ratios across measurements. Conclusions: These results suggest that the LF/IIF ratio may provide an objective measure of subjective experiences of depression and help identify potential cases of clinical depression.