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Heart Rate Variability Analysis for Evaluating Biological Effects of Electric Field Treatment
Abstract and Figures
The purpose of this study was to advance our understanding on the autonomic effects of electric fields, and to investigate the usage of electric fields for self-care by identifying the conditions under which electric field treatment causes changes in heart rate variability. The results have indicated that heart rate variability, related to both sympathetic and parasympathetic activities, increases after a 60Hz 9,000V electric field treatment of 15-minute. These findings suggest that heart rate variability can be used as a biomarker for monitoring the biological effects.
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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.
Simple Summary
With an increasing demand for electricity and electrical equipment, humans are routinely and unintentionally exposed to electric fields (EFs); no significant adverse effects have been identified from exposure to EFs, but slight physiological effects are known to occur. There are, however, methods and devices that expose subjects to EFs for medical purposes. The effects of such methods are not strong and primarily involve the physical properties of EFs, which are invisible and easily disturbed, yet the mechanisms of the biological effects of such EFs have not been identified. We have developed a simple experimental system that allows us to reproducibly observe the inhibitory properties of EFs on the glucocorticoid response to added stress. Using this system, we have revealed the biological effects of EFs. This study has shown that human body posture may affect action of the EF and that it is important to adjust the degree of immobilization in order to capture the effect of the EF. The results of this study provide useful information not only for medical applications of EFs but also for the assessment of risks to health.
Abstract
Various studies on immobilized BALB/c mice to evaluate changes in hormone levels associated with stress responses have advanced the characterization of multiple aspects of the biological actions of extremely low-frequency (ELF) electric fields (EFs). In this study, we aimed to investigate the effect of mouse posture on its stress responses and evaluate the importance of adjusting the stress degree in the model. Mice were immobilized inside centrifuge tubes and exposed to an ELF EF generated between parallel plate electrodes. Blood was collected under anesthesia immediately after EF exposure, and plasma glucocorticoids were assayed. The inhibitory effects of EFs on glucocorticoid elevation by immobilization were reproduced regardless whether mice were in the abdominal or lateral recumbent position, for the EF vector delivered to mice through the sagittal or frontal plane. The effect of ELF EF was reproduced in moderately and mildly stressed mice but not in severely immobilized mice. Hence, adjusting the stress degree is critical to the reproducibility of the results for this model. We characterized the effects of ELF EF on homeostasis, including the stress response, and provided valuable information for the scientific evaluation of the biological risks and medical applications of ELF EF.
Simple Summary
With the increasing demand for electricity and electrical equipment, humans are routinely and unintentionally exposed to electric fields (EFs). Although no considerable adverse effects of EF exposure have been observed, slight physiological effects are known to occur. Additionally, there are methods and devices that expose subjects to EF for medical purposes. The mechanism of the biological effects of EF has not been identified, because the effects are not strong and may involve the physical properties of EFs, which are invisible and easily disturbed by obstacles. In a simple and short experiment using mice, we found that EF has an inhibitory effect on glucocorticoid (GC) responses. The experiment’s reproducibility was almost 100%. We tried to improve the understanding of the biological effects of EF by structuring our observations of the stress-reducing effects under different conditions in the system. We found that the inhibitory effect on the GC response was attenuated by EF shielding. We compared the effects of EF shielding between the head and abdomen, and found that the effects of EF were attenuated in both conditions, but might be more attenuated when the head was shielded. Thus, it appears that the area where the EF is distributed and the body part are important for the biological effects of EF. Two experiments with different conditions were performed. These results will help advance the current understanding of the effects of EF on stress systems.
Abstract
In BALB/c mice, immobilization-increased plasma glucocorticoid (GC) levels are suppressed by extremely low frequency (ELF) electric fields (EF). The aim of this study was to advance our understanding of the biological effects of ELF-EF, using its suppressive effect on the GC response. Mice were exposed to a 50 Hz EF of 10 kV/m via a parallel plate electrode and immobilized as needed. We examined the suppressive effect of ELF-EF on GC level change after repeated immobilizations, electrode polarization, and EF shielding of different portions of the mouse body parts. Additionally, bodyweight changes owing to stress and EF were examined. Immobilization-induced reduction in the plasma GC levels was reproduced in mice with stress and EF exposure, regardless of the stress episode numbers and electrode polarization. Furthermore, when the head of mice was shielded from the EF, the suppressive effect was possibly relatively lower than that when the abdomen was shielded. The bodyweight of the mice decreased for 3 days after immobilization before recovering; ELF-EF did not affect the bodyweight. Thus, to elicit the biological effects of the EF, not only the size of the area where the EF is distributed but also the area where the field is distributed should be important. The results also confirmed the stableness of the present experimental system, at least in terms of the stress-reducing effect. In addition, the restriction in this study caused weight loss, but ELF-EF was not considered to affect it. The results improve the understanding of the biological effect and medical applications of ELF-EF.
Although extremely low-frequency electric fields (ELF-EF) have been utilised for therapeutic purposes, the biological effect and the underlying mechanism of ELF-EF have not been elucidated. Here, we developed a mouse model of immobilisation-induced increase in glucocorticoid (GC) to evaluate the effect of ELF-EF. Mice were exposed to 50-Hz 10 kV/m EF via a parallel plate electrode and immobilised as needed. The ELF-EF suppressed the immobilisation-induced increase in blood GC level. Here, the results of 32 tests using the model were pooled and analysed. The suppressive effect of ELF-EF on immobilisation-induced increase in GC was reproduced, and the GC level was slightly higher in the ELF-EF-treated mice than in the sham-controlled mice, a novel observation. The immobilisation-induced increase in lactate dehydrogenase, glutamic oxaloacetic transaminase, and glutamic pyruvic transaminase, markers of tissue damage, was suppressed by co-treatment with EF in the biochemical tests using the same plasma sample. In the metabolome analysis, the changes in corticosterones, leukotrienes, and hydroxyeicosatetraenoic acids, markers of inflammation, showed a pattern similar to that of the plasma GC level. Thus, ELF-EF suppresses the stress response that causes an increase in the GC level and slightly promotes GC production in the absence of stress. Moreover, the suppressive effect of ELF-EF on induced stress response might be involved in stress-induced tissue damage or inflammation in immobilised mice. Overall, the model and the data help explore the biological effect of ELF-EF and explain the stress-relieving effect of EF. They would be useful in determining the medical applications of EF in humans and animals.
Background:
Possible modulatory effects of non-invasive brain stimulation have gained interest recently. In our study, the effect of low frequency electric fields (LF-EF) on stress-induced electrophysiological, behavioral changes and the possible involvement of serotonergic 5-HT2C receptors were investigated.
Materials and methods:
A total of 8 groups including the control groups were formed by applying LF-EF with or without a 5-HT2C receptor agonist to naïve or acute stress exposed rats to demonstrate the effects of LF-EF. LF-EF administration at 10 kV/m was started 30 minutes before acute stress application and lasted for 1 hour in total. Anxiety levels and social interaction were evaluated using the elevated plus maze test and social interaction test, respectively. Auditory evoked potentials (AEP) were recorded by using ascending loudness paradigms. Loudness dependence AEP (LDAEP) was calculated by using amplitude values to analyze serotonergic transmission. Serotonin and glucocorticoid levels were measured in the frontal cortex and hippocampus.
Results:
It was observed that the applied LF-EF reduced the anxiety behavior, and attenuated the LDAEP responses in stress and/or 5-HT2C receptor agonist applied groups. In parallel, an increase in serotonin levels and a decrease in glucocorticoid levels were observed. However, LF-EF exposure was ineffective in impaired social interaction.
Conclusions:
Our findings show that 10 kV/m LF-EF administration may modulate the neural network and physiological responses associated with mild acute stress. 5-HT2C receptor dependent functions are thought to play a role in the anxiolytic effect of LF-EF.
Potential therapy, using a device to create an electric field around a person, is widely used as a home-healthcare apparatus to treat ailments such as headaches, muscle stiffness, or insomnia. However, the mechanisms for its effects remain unknown. In this study, we assumed that this therapy interacted with the autonomic nerve because its effects include remission of insomnia. Although patients report an increase in skin temperature during treatment, it has not been studied whether the body temperature also increases during the treatment. Thus, this study aims to evaluate influence of potential therapy on the autonomic nerve and the axillary temperature. Twenty healthy males participated in the experiment, receiving 60 minutes of potential therapy. Before and after the therapy, electrocardiogram was recorded for five minutes and the axillary temperature was measured. The effect on the autonomic nerve was evaluated using the low frequency/high frequency (LF/HF). A result of t test revealed no significant difference in LF/HF before and after the treatment. On the other hand, the same test indicated a significant increase in the axillary temperature.