Non-invasive Vagus Nerve Stimulation in Healthy Humans Reduces Sympathetic Nerve Activity

TLDR: In this paper, the effects of transcutaneous electrical nerve stimulation (tVNS) on autonomic function in 48 healthy participants were investigated using heart rate variability (HRV) and microneurography.

About: This article is published in Brain Stimulation.The article was published on 2014-11-01 and is currently open access. It has received 312 citations till now. The article focuses on the topics: Vagus nerve stimulation & Transcutaneous electrical nerve stimulation.

Figures

Figure 1. The distribution of the auricular branch of the vagus nerve to the external ear (shaded area, extrapolated from Peuker and Filler(11)). C, concha; T, tragus; CyC, cymba concha.

Figure 2 There is a significant decrease in LF/HF ratio during active tVNS (p = 0.026) whereas there is no significant change during sham tVNS.

Table 2 Heart rate variability values for sham and active tVNS groups There was a significant decrease in LF/HF ratio during active tVNS (p = 0.026). There was no significant (n.s.) change in total power, low power or high power during active tVNS. There was no significant change in any HRV values in the sham tVNS group.

Table 1 Baseline characteristics. There was no significant difference in baseline characteristics between active and sham tVNS groups.

Figure 4 Example microneurography recording during baseline (A) and during tVNS (B) indicating electrocardiogram (ECG), blood pressure (BP) and MSNA. MSNA units in more detail (C) and overlaid (D). tVNS significantly reduces MSNA frequency (E; *P = 0.0001) and incidence (F; *P = 0.0002; normalized data; n = 10).

Figure 3. There is a relationship between baseline LF/HF ratio and change in LF/HF ratio during tVNS indicating that higher LF/HF ratios predict a greater decrease in LF/HF during tVNS (R2=0.58; p<0.0005; A). There is a relationship between age and baseline LF/HF ratio (R2=0.19; p=0.013; B).

Frequently asked questions

Q1. What are the contributions in "Non-invasive vagus nerve stimulation in healthy humans reduces sympathetic nerve activity" ?

This is indicated by the licence information on the White Rose Research Online record for the item. 

Q2. What were the participants asked to avoid on the morning of the study?

They were also asked to avoid caffeine and nicotine on the morning of the study and to void their bladder before the study commenced. 

Q3. What is the procedure for implantation of a generator?

VNS requires surgical implantation of a bipolar electrode around the cervical vagus nerve and implantation of a generator subcutaneously in the thoracic wall. 

Q4. What is the recent study of tVNS?

tVNS using surface electrodes has been investigated as a possible analgesic (15, 36) and has also been trialled as an15alternative to invasive cervical VNS in patients with refractory epilepsy (14). 

Q5. What is the somatovisceral reflex of the tragus?

These include the ear-cough reflex (Arnold’s reflex), estimated to be present in approximately 4% of the general population (43), whereby stimulation of the external auditory meatus (e.g. syringing) mimics the cough response mediated by vagal afferent innervation of the trachea. 

Q6. What is the HF component of the heart rate?

The HF component reflects parasympathetic modulation of heart rate (20) and the LF component reflects both sympathetic and parasympathetic modulation of heart rate (21). 

Q7. What frequency was used to calculate the power spectrum of the tachogram?

The resulting tachogram underwent 512 point Fast Fourier Transform with a Hanning window to calculate the power spectrum of HRV with the low frequency (LF) component at 0.04-0.15 

Q8. What is the effect of tVNS on the ear?

Based on the results of this study, the proposed pathway of tVNS autonomic effects could involve activation of the NTS by ABVN afferents. 

Q9. What was the effect of the stimulation parameters on the LF/HF ratio?

There was a significant interaction between stimulation parameters and time (mixed mode repeated measures ANOVA, p = 0.048), indicating that the stimulation parameters contributed to the change in LF/HF ratio. 

Q10. What is the common indication for VNS?

VNS has proven effective in pilot studies for the treatment of heart failure (16), for which a multi-centre trial is on-going (ClinicalTrials.gov Identifier: NCT01303718). 

Q11. What was the effect of tVNS on heart rate?

a significant decrease in MSNA frequency (time effect, p = 0.001) and incidence (time effect, p = 0.002; Figure 4) was detected during tVNS (n=10). 

Q12. What is the effect of tVNS on heart rate?

Higher baseline LF/HF values were also observed with increasing age (R2 = 0.19; p = 0.013; Figure 3B).12tVNS reduces muscle sympathetic nerve activity Applying microneurography to directly record sympathetic vasoconstrictor nerve. 

Q13. What is the first clinical study of tVNS?

The first clinical study of tVNS found that electroacupuncture of both ears was beneficial for patients with coronary artery disease (12, 13). 

Q14. What is the effect of tracing on the ear?

In addition, neuronal tracing from the junction of the concha and external auditory meatus in rats revealed16sensory afferent terminations in the NTS and dorsomedial spinal trigeminal tract (42). 

Q15. What was the effect of electrode configuration on LF/HF?

A mixed mode ANOVA revealed no impact of electrode configuration on LF/HF ratio (main effect for electrode configuration, p > 0.05).