This article contains a summary of the findings of a research study that was conducted by a group of independent researchers. For information about the group of researchers and the full study manuscript, see the information at the bottom of this article.
Snapshot of Findings
- Noninvasively stimulating the vagus nerve (nVNS) using electrical impulses applied to the ear immediately reduces heart rate in young, healthy individuals, but not significantly when compared to sham stimulation.
- Noninvasive vagus nerve stimulation using electricity applied to vagal afferents around the ear is safe
- Noninvasive vagus nerve stimulation using electricity applied to vagal afferents around the ear lessens the severity of the physical side effects of increased sympathetic output (stress and anxiety).
- Elevated heart rate returned to baseline significantly faster in participants who received vagus nerve stimulation than those who did not.
Title of Research
"Short trains of transcutaneous auricular vagus nerve stimulation (taVNS) have parameter specific effects on heart rate."
Technology Used
Noninvasive Vagus Nerve Stimulation applied to vagal afferents around the ear area.
Measured Variable
The variable being measured was parasympathetic activity as indicated by acute changes in heart rate.
Various stimulation parameters were used and therefore safety of each stimulation parameter was measured.
Adverse effects were monitored and included variables like heart rate, respiration difficulty, cardiac arrest, skin discomfort, irritation, headache, facial pain, and dizziness.
Patient Population
15 healthy individuals were recruited for the study, 7 of whom were female.
The mean age of the participants was 26.5 years of age.
Vagal Nerve Stimulation Parameters
Location of Stimulation:
- For the active group, vagal afferents between the ear canal and tragus on left ear only were stimulated.
- For the sham group, the earlobe was used since there are little or no vagus nerve branches in that location.
Electrode Design:
- Desktop waveform generator from Digitimer.
- Custom built electrodes with a surface diameter of 1cm. These were ear clip electrodes that pinch against the skin of the ear and must be soaked in a gel or paste before treatment.
- Alcohol swabs were used to prepare the skin before electrode placement.
Waveform Frequency:
- Three different frequencies and pulse widths were tested for a total of 9 possible stimulation paradigms.
- The frequencies used were 1 pulse per second (1Hz), 10 pulses per second (10 Hz), and 25 pulses per second (25 Hz)
- The pulse widths used were 100 microseconds, 200microseconds, and 500 microseconds.
Intensity:
- Stimulation intensity was delivered at 200% of the individuals perception threshold, meaning twice as high as the minimum required current for the individual patient to feel the stimulation.
Duration of Stimulation:
- The stimulation session consisted of 60 seconds of stimulation followed by 3 minutes of no stimulation, and this pattern continued until all 9 stimulation paradigms were used.
- Total of 9 minutes of active stimulation and 27minutes of active rest. 36 total minutes.
Frequency of Stimulation:
- The study consisted of one single lab visit with each patient receiving one full vagal nerve or sham stimulation session.
Results
For all stimulation settings, including the sham stimulation settings, heart rate was immediately decreased when the stimulation was turned on. This decrease in heart rate was sustained during the 60 seconds of treatment for all active and sham stimulation sessions.
For all active stimulation groups, the average decrease in heart rate immediately following active stimulation was 1.43 BPM. For all control groups combined, the average decrease in heart rate was 1 BPM. Both groups experienced a decrease in heart rate, but the decrease in the active group was not significant when compared to a sham.
When the stimulation was turned off, there was an immediate spike in heart rate and a slow regression back to mean resting heart rate that took about 30 seconds. This occurred in both active and sham stimulation groups.
The maximum spike in HR in the active group was 8 BPM and the maximum spike in HR in the control group was 11.3 BPM. The sham group had a larger increase in HR immediately following stimulation compared to the active group. This difference was found to be statistically significant.
Conclusions
The authors concluded that the lower spike in HR immediately following termination of stimulation in the active group suggests the stimulation lessens the effects of increased sympathetic activity on the body. This is likely due to increased vagal tone from the active vagal nerve stimulation. Increasing vagal tone has the effect of lessening the severity of the effects from increased sympathetic activity or from experiencing a stressful situation or event. This conclusion was drawn by observing the smaller rise in heart rate immediately following stimulation.
The control group would be considered to have a lower vagal tone since the vagus nerve was not stimulated. This group experienced a larger Jump in heart rate immediately following stimulation, which suggests people with a lower vagal tone will experience more severe physiological effects from increased sympathetic activity or from experiencing daily stressors.
These results suggest that daily stimulation to improve vagal tone is a great way to help your body keep the physical side effects of stress to a minimum, and that vagal nerve stimulation is a great way to immediately suppress the effects of stress, anxiousness, or any type of increased sympathetic activity.
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Hoolest Performance Technologies (Hoolest) is a neurotechnology development company that develops personal vagal activation products to improve mental health and human performance. Their first product VeRelief is a powerful yet simple vagal nerve stimulation device and is now available for anyone looking to add the benefits of vagal activation to their daily lives.
They have several vagal nerve stimulation products in development to solve very specific mental and physical health challenges. If you are interested in learning more about Hoolest, their product development efforts and research opportunities, you may contact them at any time.
About The Research
Authors and Affiliations
Bashar W. Badranet et al.
- Department of Neuroscience, Medical University of South Carolina, Charleston SC 29425, United States
Link
Abstract
Background:
Optimal parameters of transcutaneous auricular vagus nerve stimulation (taVNS) are still undetermined. Given the vagus nerve’s role in regulating heart rate (HR), it is important to determine safety and HR effects of various taVNS parameters.
Objective:
We conducted two sequential trials to systematically test the effects of various taVNS parameters on HR.
Methods:
15 healthy individuals participated in the initial two-visit, crossover exploratory trial, receiving either tragus (active) or earlobe (control) stimulation each visit. Nine stimulation blocks of varying parameters (pulse width: 100 μs, 200 μs, 500 μs; frequency: 1 Hz, 10 Hz, 25 Hz)were administered each visit. HR was recorded and analyzed for stimulation-induced changes. Using similar methods and the two best parameters from trial 1 (500μs 10 Hz and 500μs 25 Hz), 20 healthy individuals then participated in a follow-up confirmatory study.
Results:
Trial 1- There was no overall effect of the nine conditions on HR during stimulation. However multivariate analysis revealed two parameters that significantly decreased HR during active stimulation compared to control (500μs 10 Hz and 500μs 25 Hz; p < 0.01). Additionally, active taVNS significantly attenuated overall sympathetic HR rebound(post-stimulation) compared to control (p < 0.001). Trial 2- For these two conditions, active taVNS significantly decreased HR compared to control (p = 0.02), with the strongest effects at 500μs 10 Hz (p = 0.032).
Conclusion:
These studies suggest that 60s blocks of tragus stimulation are safe, and some specific parameters modulate HR. Of the nine parameters studied, 500μs 10 Hz induced the greatest HR effects.
Citation
Badran, B. W., Mithoefer, O. J., Summer, C. E., LaBate, N. T., Glusman, C. E., Badran, A. W., DeVries, W. H., Summers, P. M., Austelle, C. W., McTeague, L. M., Borckardt, J. J., & George, M. S. (2018). Short trains of transcutaneous auricular vagus nerve stimulation (taVNS) have parameter-specific effects on heart rate. Brain stimulation, 11(4), 699–708. https://doi.org/10.1016/j.brs.2018.04.004.