Acute Cardiovascular Effects of Transcutaneous Auricular Vagus Nerve Stimulation

Summary

Introduction

Cardiovascular disease (CVD) remains the leading cause of mortality worldwide, with arterial hypertension representing the most significant modifiable risk factor (Lim et al., 2012; Mills et al., 2020). While clinical manifestations of arterial hypertension typically emerge in later life, the underlying pathophysiological mechanisms, particularly autonomic dysfunction, begin decades earlier.

Autonomic imbalance, characterised by sympathetic overactivity and diminished parasympathetic tone, not only precedes sustained arterial hypertension but also independently predicts future cardiovascular risk, even in normotensive individuals (He et al., 2023; Thayer et al., 2010). Reduced heart rate variability (HRV), a non-invasive marker of parasympathetic activity, has been consistently associated with increased cardiovascular morbidity across diverse populations (Task Force, 1996).

Critically, young apparently healthy adults with suboptimal lifestyle factors, including physical inactivity, poor dietary habits, and chronic stress, frequently exhibit reduced HRV and altered sympathovagal balance (Liao et al., 1998). These subclinical autonomic changes represent an early, potentially reversible stage in the cardiovascular disease continuum, suggesting that interventions targeting autonomic balance may prevent or delay progression to overt disease (Goldstein et al., 2011).

The vagus nerve, the main parasympathetic pathway, exerts multiple cardioprotective effects, including heart rate deceleration, baroreflex enhancement, reduced vascular tone, and anti-inflammatory activity (Thayer \& Sternberg, 2006). Transcutaneous auricular vagus nerve stimulation (taVNS) has emerged as a non-invasive method to enhance vagal activity by delivering electrical stimulation to the auricular branch of the vagus nerve via surface electrodes placed on the tragus or cymba conchae (Badran et al., 2018). Neuroimaging studies confirm that taVNS activates central vagal projections, including the nucleus tractus solitarius, the primary relay station for cardiovascular autonomic control (Frangos et al., 2015).

Preliminary research demonstrates that acute taVNS sessions increase HRV, enhance baroreflex sensitivity, and reduce sympathetic vascular tone in healthy adults (Clancy et al., 2014; De Couck et al., 2017), while emerging evidence suggests clinically meaningful reductions in blood pressure (BP) in hypertensive patients (Mbikyo et al., 2024).

Despite these promising findings, significant knowledge gaps remain. Most studies have examined clinical populations with pre-existing autonomic abnormalities, making it difficult to isolate primary taVNS mechanisms from disease-related compensatory responses. Additionally, chronic intervention protocols preclude detailed characterisation of immediate autonomic and hemodynamic changes. Conducting mechanistic studies in healthy populations offers critical advantages: absence of confounding medications and disease adaptations enables clearer identification of taVNS-induced autonomic and hemodynamic changes, while establishing baseline response patterns provides an essential reference framework for interpreting clinical population responses and informing preventive interventions. Investigation of acute responses permits precise temporal mapping of physiological changes, distinguishing primary mechanisms from downstream consequences, enables efficient optimisation of stimulation parameters, and provides biological plausibility for chronic effects while identifying potential responders to therapy.

Therefore, this study proposes a randomised, sham-controlled crossover study to systematically characterise acute cardiovascular and autonomic responses to a single 60-minute taVNS session in healthy young adults. Using continuous non-invasive BP monitoring and detailed HRV analysis, this study will establish whether taVNS produces acute, measurable changes in BP, heart rate, and autonomic balance in individuals with normal baseline function. We will elucidate the temporal dynamics of taVNS-induced effects, characterise the mechanistic pathways distinguishing cardiac, hemodynamic, and autonomic contributions, and evaluate the specificity of active stimulation versus sham conditions. By establishing baseline physiological response patterns and elucidating acute mechanisms in a well-controlled population, our findings will lay the groundwork for subsequent investigations in at-risk and hypertensive individuals, ultimately contributing to evidence-based, personalised autonomic modulation therapy for cardiovascular disease prevention and management.

Conditions

• Vagus Nerve Stimulations

Interventions

DEVICE

Active taVNS condition

For the active taVNS condition, the Parasym taVNS system (Parasym Health, London, United Kingdom) will be used. This device delivers transcutaneous electrical stimulation to the auricular branch of the vagus nerve via a surface electrode placed on the left tragus. The stimulation consists of a proprietary waveform comprising micro-pulses with a pulse width of 200 microseconds delivered at a frequency of 20 Hertz. Before commencing the intervention, each participant will personalise the stimulation intensity based on their individual sensitivity threshold, following the same procedure experienced during the familiarisation session. The participant will gradually increase the current intensity from zero until they perceive a constant, clear tingling sensation at the electrode site. The intensity will then be reduced by one milliampere below their reported discomfort threshold. We anticipated a mean stimulation intensity across participants from 13 to 20 milliampers.

DEVICE

Sham-sound condition

For the sham-sound condition, participants will be asked to adjust the device settings to mimic the intensity range used during the active protocol (Levels 13 to 20), ensuring that the setup procedure and user actions feel identical across sessions. However, in this mode, the device does not deliver any therapeutic electrical stimulation. Instead, a sham electrode, identical in appearance to the active electrode, produces only a mechanical sound that mimics the subtle acoustic feedback associated with active stimulation, without generating electrical current or eliciting any physiological effect. This condition replicates the sensory and procedural aspects of the active session while ensuring no meaningful vagal stimulation is provided, thereby controlling for placebo effects, participant expectations, and non-specific attention effects associated with the intervention procedure.

DEVICE

Sham Mode

For the sub-threshold sham condition, the Parasym device will be switched into its sham mode and set to Level 5, which delivers stimulation intentionally kept below the sensory threshold. Participants will be informed at the beginning of this session: "In this session, the stimulation will be delivered below the sensory threshold, meaning the intensity is very low and you should not feel any sensation. Please confirm that you do not feel anything." Once the device is activated, it will deliver minimal stimulation for a brief period, then automatically ramp down and switch off within approximately 15 seconds. For the remainder of the 60-minute session, no electrical stimulation is delivered, although the device display will appear active to maintain blinding. This condition controls for expectation effects while explicitly informing participants that they should not perceive sensation, thereby maintaining credibility without requiring deception about the absence of sensation

Sponsors & Collaborators

• Northumbria University

  lead OTHER

Principal Investigators

• Gabriel Cucato, PhD · Northumbria University

Study Design

Allocation

RANDOMIZED

Purpose

OTHER

Masking

DOUBLE

Model

CROSSOVER

Eligibility

Min Age

18 Years

Max Age

45 Years

Sex

ALL

Healthy Volunteers

Yes

Timeline & Regulatory

Start

2026-03-01

Primary Completion

2027-12-01

Completion

2027-12-01

Countries

• United Kingdom

Study Locations