Acute Treatment of 60‐Hz Electric Field Increases Parasympathetic Activity in Depressed Subjects: A Pilot Study Using Heart Rate Variability Analysis

Research indicated that extremely low‐frequency (ELF) electric field (EF) treatment modifies autonomic activity in healthy subjects; however, the effects do not persist after the treatment. This study examined whether persistence of the effects is dependent on the baseline autonomic conditions. The depressed subjects are known to frequently exhibit autonomic dysregulation, and were enrolled in the present study to test this hypothesis. Autonomic activity was evaluated using heart rate variability (HRV) analysis. Heart rate (HR) was measured using R‐R intervals of the electrocardiogram in the resting state before and after the 20‐min ELF‐EF treatment (30 kV, 60 Hz) in the patients with major depressive disorder and in the control subjects, and HRV was analyzed using frequency‐domain power spectrum analysis of R‐R interval trend. Sham treatment was conducted in the control subjects but not in the patients due the ethical restriction. In the patients with depression, high‐frequency variation (HF) related to breathing‐dependent parasympathetic activity was low before the 60‐Hz EF treatment and increased to the control level after treatment. No effects of EF were found for low‐frequency variation (LF), LF/HF, and HR. The results indicated that acute 60‐Hz EF treatment increased parasympathetic activity in the depressed subjects, who showed a reduction in baseline parasympathetic activity. This study suggests that the effects of ELF‐EF treatment on autonomic activity are dependent on the baseline autonomic conditions. Future studies with larger sample sizes, incorporating sham treatment in the patients with depression, are needed to confirm these observations.