Non-Invasive Auricular Vagus Nerve Stimulation Decreases Heart Rate Variability Independent of Caloric Load

Area of Science:

• Neuroscience
• Cardiovascular Physiology
• Autonomic Nervous System Research

Background:

• The vagus nerve plays a key role in regulating cardiovascular functions.
• Transcutaneous auricular vagus nerve stimulation (taVNS) is explored for modulating autonomic activity, but its effects on heart rate (HR) and heart rate variability (HRV) are inconsistent, with limited data on right-sided stimulation.
• Existing research often assumes taVNS increases cardiovagal activity, reflected by increased HRV.

Purpose of the Study:

• To investigate the effects of taVNS on HR and HRV.
• To compare the impact of left versus right ear stimulation on cardiovascular indices.
• To assess if taVNS effects interact with physiological state, such as postprandial changes.

Main Methods:

• A randomized crossover study involving 36 healthy participants.
• Electrocardiograms were recorded during four sessions per participant, including baseline, taVNS (left or right ear) or sham stimulation, and post-consumption phases.
• HRV was analyzed using SDRR, RMSSD, HF-HRV, and LF/HF ratio.

Main Results:

• Moderate evidence suggests taVNS does not significantly affect HR.
• taVNS demonstrated a significant decrease in overall HRV, with strong evidence for reductions in RMSSD and HF-HRV, irrespective of stimulation side or physiological state.
• Stimulation effects were comparable between left and right taVNS and stronger than sham stimulation.

Conclusions:

• taVNS reduces HRV (RMSSD, HF-HRV, SDRR) without altering HR, challenging the notion that it inherently increases cardiovagal tone.
• The findings suggest taVNS-induced HRV changes may reflect arousal mediated by vagal afferent activation rather than direct cardiovagal enhancement.
• Bilateral taVNS is safe for modulating the cardiovascular system in healthy individuals, presenting potential therapeutic avenues without risks like bradycardia.