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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. © 2024 The Author(s). IEEJ Transactions on Electrical and Electronic Engineering published by Institute of Electrical Engineers of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Featured Application: A low-intensity extremely low-frequency electric field treatment can be applied for stress management in healthcare by reducing sympathetic activity and promoting relaxation. (1) Background: Our previous studies indicated that low-intensity extremely low-frequency electric field (ELF-EF) treatment alters autonomic activities, as revealed through heart rate variability (HRV) analysis. However, the high-frequency (HF) component of HRV that reflects parasympathetic activity showed no changes either during or after the end of the treatment, suggesting the involvement of sympathetic nerves. (2) Methods: To examine this issue in the present study, the effect of ELF-EF on skin conductance (SC), which is controlled solely by sympathetic nerves, was analyzed. Twelve healthy subjects underwent a 20 min ELF-EF treatment (applied voltage: 9 kV, induced current density: below 6 mA/m2) and a sham treatment in a random order with an interval of more than 2 weeks. SC and HRV were recorded under the eyes-open condition during a 2 min period both before and after the treatment. (3) Results: The number of spontaneous fluctuations in skin conductance (SC-SFs) significantly decreased after the ELF-EF treatment, suggesting psychological changes, including relaxation. The skin conductance level, heart rate, and HRV indices did not change after the ELF-EF treatment. (4) Conclusion: The results support the idea that low-intensity ELF-EF affects autonomic nerves by reducing sympathetic activity, as reflected by SC-SFs. [ABSTRACT FROM AUTHOR]

Our previous study examined the neural effects of extremely low frequency electric field (ELF‐EF) using electroencephalogram (EEG) and heart rate variability (HRV) measurement and revealed that the theta power of EEG increases during 1‐min EF treatment (30 kV and 50 Hz). In the present study, the effects of a longer treatment duration were assessed. EF was applied between two electrodes, one above the head and the other under the feet, for 20 min to 10 healthy men sitting on a chair. Occipital EEG and HRV were measured in the eyes‐open condition. Power spectrum analysis showed that during the EF treatment, the power of alpha and theta rhythms as well as the low frequency component of HRV increased, and the heart rate decreased. These effects did not persist after the end of EF treatment. It is suggested that ELF‐EF treatment alters not only the brain activity but also the autonomic activity reflected in HRV. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]