Ear your heart: transcutaneous auricular vagus nerve stimulation on heart rate variability in healthy young participants

A framework for the interpretation of heart rate variability applied to transcutaneous auricular vagus nerve stimulation and osteopathic manipulation

Reports on autonomic responses to transcutaneous auricular vagus nerve stimulation (taVNS) and osteopathic manipulative techniques have been equivocal, partly due to inconsistent interpretation of heart rate variability (HRV). We developed a mechanistic framework for the interpretation of HRV based on a model of sinus node automaticity that considers autonomic effects on Phase 3 repolarization and Phase 4 depolarization of the sinoatrial action potential. The model was applied to HRV parameters calculated from ECG recordings (healthy adult humans, both genders) before (30 min), during (15 min), and after (30 min) a time control intervention (rest, n = 23), taVNS (10 Hz, 300 μs, 1-2 mA, cymba concha, left ear, n = 12), or occipitoatlantal decompression (OA-D, n = 14). The experimental protocol was repeated on 3 consecutive days. The model simulation revealed that low frequency (LF) HRV best predicts sympathetic tone when calculated from heart rate time series, while high frequency (HF) HRV best predicts parasympathetic tone when calculated from heart period time series. Applying our model to the HRV responses to taVNS and OA-D, revealed that taVNS increases cardiac parasympathetic tone, while OA-D elicits a mild decrease in cardiac sympathetic tone.

Modulation of vagal activity may help reduce neurodevelopmental damage in the offspring of mothers with pre-eclampsia

Maternal Immune Activation (MIA) has been linked to the pathogenesis of pre-eclampsia and adverse neurodevelopmental outcomes in the offspring, such as cognitive deficits, behavioral abnormalities, and mental disorders. Pre-eclampsia is associated with an activation of the immune system characterized by persistently elevated levels of proinflammatory cytokines, as well as a decrease in immunoregulatory factors. The Cholinergic Anti-inflammatory Pathway (CAP) may play a relevant role in regulating the maternal inflammatory response during pre-eclampsia and protecting the developing fetus from inflammation-induced damage. Dysregulation in the CAP has been associated with the clinical evolution of pre-eclampsia. Some studies suggest that therapeutic stimulation of this pathway may improve maternal and fetal outcomes in preclinical models of pre-eclampsia. Modulation of vagal activity influences the CAP, improving maternal hemodynamics, limiting the inflammatory response, and promoting the growth of new neurons, which enhances synaptic plasticity and improves fetal neurodevelopment. Therefore, we postulate that modulation of vagal activity may improve maternal and fetal outcomes in pre-eclampsia by targeting underlying immune dysregulation and promoting better fetal neurodevelopment. In this perspective, we explore the clinical and experimental evidence of electrical, pharmacological, physical, and biological stimulation mechanisms capable of inducing therapeutical CAP, which may be applied in pre-eclampsia to improve the mother's and offspring's quality of life.

Modifying functional brain networks in focal epilepsy by manual visceral-osteopathic stimulation of the vagus nerve at the abdomen

Non-invasive transcutaneous vagus nerve stimulation elicits similar therapeutic effects as invasive vagus nerve stimulation, offering a potential treatment alternative for a wide range of diseases, including epilepsy. Here, we present a novel, non-invasive stimulation of the vagus nerve, which is performed manually viscero-osteopathically on the abdomen (voVNS). We explore the impact of short-term voVNS on various local and global characteristics of EEG-derived, large-scale evolving functional brain networks from a group of 20 subjects with and without epilepsy. We observe differential voVNS-mediated alterations of these characteristics that can be interpreted as a reconfiguration and modification of networks and their stability and robustness properties. Clearly, future studies are necessary to assess the impact of such a non-pharmaceutical intervention on clinical decision-making in the treatment of epilepsy. However, our findings may add to the current discussion on the importance of the gut-brain axis in health and disease. Clinical Trial Registration: https://drks.de/search/en/trial/DRKS00029914, identifier DRKS00029914.

Effect of Stimulation Current in Transcutaneous Vagus Nerve Stimulation (tVNS): A Study Using Concurrent Magnetoencephalography (MEG)

Transcutaneous vagus nerve stimulation (tVNS) is a non-invasive method of brain stimulation that has been investigated for its use in the clinical treatment of a number of different conditions. There has been little investigation into the stimulation current that is delivered and the effect on individual variability in response to tVNS.Seventeen participants underwent tVNS, and stimulation current was determined based on individual pain threshold. To investigate individual variability, brain dynamics were measured concurrently using magnetoencephalography (MEG) in response to two different stimulation protocols of tVNS. The first protocol consisted of a sequence of equally spaced short (1ms) stimulation pulses applied 24 times per second (24 Hz), and the second consisted of a sequence of 24 pulses per second spaced according to a 6 Hz pulse frequency modulation (PFM). Both stimulation sequences were delivered to the cymba concha in the left ear.The difference in brain responses to the two sequences was initially calculated using a one-sample t-test at the group level, based on z-scoring of the data at the individual level, and no statistically significant differences were observed. Further investigation of individual variability suggested that participants fell into two groups; one that responded more strongly to 24 Hz and one that responded more strongly to the irregular spacing of pulses in the PFM protocol.We tested whether the stimulation current that the participant received could predict how they would respond to the stimulation, but we did not observe any correlation. This supports the literature that suggests that selecting stimulation current based on individual pain threshold is a suitable procedure for tVNS, and higher stimulation intensities does not correspond to stronger brain response. Further investigation into individual variability in response to different frequencies and pulse spacing of tVNS should also be investigated further and may lead to the development of personalised stimulation protocols.Clinical relevance- The stimulation current at which tVNS is delivered does not appear to influence brain response to stimulation, and the value of stimulation current should be selected based on individual participant comfort.

A systematic review of the effects of transcutaneous auricular vagus nerve stimulation on baroreflex sensitivity and heart rate variability in healthy subjects

PURPOSE

This systematic review aimed to evaluate the effect of transcutaneous auricular vagus nerve stimulation on heart rate variability and baroreflex sensitivity in healthy populations.

METHOD

PubMed, Scopus, the Cochrane Library, Embase, and Web of Science were systematically searched for controlled trials that examined the effects of transcutaneous auricular vagus nerve stimulation on heart rate variability parameters and baroreflex sensitivity in apparently healthy individuals. Two independent researchers screened the search results, extracted the data, and evaluated the quality of the included studies.

RESULTS

From 2458 screened studies, 21 were included. Compared with baseline measures or the comparison group, significant changes in the standard deviation of NN intervals, the root mean square of successive RR intervals, the proportion of consecutive RR intervals that differ by more than 50 ms, high-frequency power, low-frequency to high-frequency ratio, and low-frequency power were found in 86%, 75%, 69%, 47%, 36%, and 25% of the studies evaluating the effects of transcutaneous auricular vagus nerve stimulation on these indices, respectively. Baroreflex sensitivity was evaluated in six studies, of which a significant change was detected in only one. Some studies have shown that the worse the basic autonomic function, the better the response to transcutaneous auricular vagus nerve stimulation.

CONCLUSION

The results were mixed, which may be mainly attributable to the heterogeneity of the study designs and stimulation delivery dosages. Thus, future studies with comparable designs are required to determine the optimal stimulation parameters and clarify the significance of autonomic indices as a reliable marker of neuromodulation responsiveness.

Brief periods of transcutaneous auricular vagus nerve stimulation improve autonomic balance and alter circulating monocytes and endothelial cells in patients with metabolic syndrome: a pilot study

BACKGROUND

There is emerging evidence that the nervous system regulates immune and metabolic alterations mediating Metabolic syndrome (MetS) pathogenesis via the vagus nerve. This study evaluated the effects of transcutaneous auricular vagus nerve stimulation (TAVNS) on key cardiovascular and inflammatory components of MetS.

METHODS

We conducted an open label, randomized (2:1), two-arm, parallel-group controlled trial in MetS patients. Subjects in the treatment group (n = 20) received 30 min of TAVNS with a NEMOS® device placed on the cymba conchae of the left ear, once weekly. Patients in the control group (n = 10) received no stimulation. Hemodynamic, heart rate variability (HRV), biochemical parameters, and monocytes, progenitor endothelial cells, circulating endothelial cells, and endothelial micro particles were evaluated at randomization, after the first TAVNS treatment, and again after 8 weeks of follow-up.

RESULTS

An improvement in sympathovagal balance (HRV analysis) was observed after the first TAVNS session. Only patients treated with TAVNS for 8 weeks had a significant decrease in office BP and HR, a further improvement in sympathovagal balance, with a shift of circulating monocytes towards an anti-inflammatory phenotype and endothelial cells to a reparative vascular profile.

CONCLUSION

These results are of interest for further study of TAVNS as treatment of MetS.