Non-invasive Auricular Vagus Nerve Stimulation (taVNS) on Postural Control and Autonomic Responses in Stroke

Effects of Non-invasive Auricular Vagus Nerve Stimulation (taVNS) on Postural Control and Autonomic Responses in Stroke Patients

This randomized controlled trial is conducted to determine the effects of transcutaneous auricular Vagus nerve stimulation (taVNS) on postural control in stroke patients (e.g., improvements in balance, mobility, and functional stability) and to evaluate the effects of taVNS on autonomic nervous system responses in stroke patients (e.g., changes in heart rate variability, blood pressure variability, skin conductance, and temperature).

Stroke remains one of the leading causes of long-term disability worldwide, impacting millions of individuals each year. Beyond motor and cognitive deficits, stroke survivors often experience significant impairments in postural control and autonomic nervous system (ANS) regulation, both of which are essential for functional independence and overall quality of life. Impaired balance increases the risk of falls, while autonomic dysfunction-manifesting as irregular heart rate variability (HRV), blood pressure variability (BPV), and abnormal skin conductance and temperature-can lead to complications affecting cardiovascular stability and daily functioning.

Traditional rehabilitation approaches primarily focus on physical therapy to improve movement and strength; however, interventions that target neuromodulation and autonomic regulation are still underutilized in post-stroke care. This gap opens the door for novel, non-invasive techniques that can enhance neural recovery and improve both motor control and autonomic function.

Transcutaneous auricular vagus nerve stimulation (taVNS) is a non-invasive method that stimulates the auricular branch of the vagus nerve through external electrodes placed on parts of the ear, typically the tragus or cymba conchae. The vagus nerve is a critical component of the parasympathetic nervous system and plays a key role in maintaining autonomic balance, inflammatory regulation, and neuroplasticity. By stimulating the vagus nerve, taVNS is believed to influence brain regions associated with motor control, cardiovascular regulation, and arousal-including the nucleus tractus solitarius (NTS), locus coeruleus, thalamus, and insula.

Recent studies have shown that taVNS may enhance post-stroke recovery by promoting cortical reorganization, reducing neuroinflammation, and improving neural connectivity. It has also been found to modulate HRV and BPV, reflecting improvements in autonomic nervous system activity, and may contribute to better cardiovascular health and stress resilience. This randomized controlled trial aims to explore the therapeutic potential of taVNS in improving postural control and autonomic responses in patients recovering from stroke. Participants will receive taVNS using clinically standardized stimulation parameters (e.g., 25 Hz frequency, 250 μs pulse width, up to 6 mA intensity) administered for 30 minutes daily over 4 weeks. Postural outcomes will be evaluated using validated tools such as the Berg Balance Scale (BBS), Postural Assessment Scale for Stroke Patients (PASS), and Fugl-Meyer Assessment for Lower Extremities (FMA-LE). Autonomic responses will be assessed through heart rate variability, blood pressure variability, skin conductance, and skin temperature monitoring.

This study is significant because it addresses an important gap in stroke rehabilitation: the lack of non-invasive, targeted interventions that simultaneously improve both balance and autonomic function. By evaluating the dual impact of taVNS on these domains, this research has the potential to inform future stroke rehabilitation protocols, contributing to more holistic, patient-centered care. If effective, taVNS may offer a low-cost, portable, and easily integrated adjunct to conventional therapy, especially in low-resource settings or for patients with limited access to specialized care. In summary, this study investigates whether taVNS can serve as an effective tool to support postural stability and autonomic regulation in stroke survivors ultimately aiming to enhance recovery outcomes, reduce fall risk, and improve quality of life.

Inclusion Criteria:

• Age between 18 to 70years who are diagnosed with ischemic brain injury, intracerebral hemorrhage shown by magnetic resonance imaging, or computed tomography.
• First occurrence of stroke characterized by a unilateral lesion, with an onset time (acute/ subacute) < 6 months
• With balance impairment (BBS Score = 21-44);
• no or mild spasticity on the lower-limb assessed by Modified Ashworth Scale (MAS ≤ 2);
• sufficient cognition to follow the instructions provided by the therapists and the computer.

Exclusion Criteria:

• Individuals exhibiting unstable vital signs, consciousness disorders, or an inability to cooperate with examination and treatment procedures
• Those with a heart rate below 60 beats per minute, or with implantable devices such as pacemakers or cochlear implants.
• Other medical or psychological conditions affecting participation