Comperative Effects of Transcutaneous Auricular and Cervical Vagus Nerve Stimulation in Subacute Stroke Patients

Stroke is characterized as a neurological deficit resulting from a sudden focal injury to central nervous system due to vascular issue by blockage and rupture of artery that leads to hypoxic injury and ultimately cell death. Stroke is primarily categories into two types: ischemic stroke that accounts for 85 % of cases and haemorrhagic stroke which make up 15%. Stroke leads to physical, cognitive, speech, perceptual and psychological Impairments. Post stroke impairments of the upper limb and lower limb leads to activity limitations in self-care and mobility and restricted participation in caring family and employment.

Multidisciplinary approach is used in stroke rehabilitation to create a rehabilitation program that aim to improve the function and improve the quality of life. Physical medicine and rehabilitation is focused on promoting recovery, improving or restoring functional abilities, anticipating potential long-term complications, and enhancing the quality of life for individuals with physical impairments or disabilities. Now a days there are many contemporary approaches used in rehabilitation like non-invasive brain simulation, robotics, gamification, virtual reality, CIMT, mirror therapy and many others, aimed to enhance the recovery after stroke.

Transcutaneous vagus nerve stimulation tVNS was developed two decades ago as a non-invasive, cost effective and easily applicable treatment option as compared to invasive vagus nerve stimulation for the treatment of epilepsy, cognitive impairments and stroke rehabilitation. Cutaneous innervation of vagus nerve is by two branches, one through auricular branch at external acoustic meatus, inner tragus, and the periauricular skin surrounding the cymba conchae and the other through cervical branch at anterior to sternocleidomastoid at the mid of neck. Several devices are used for stimulating the vagus nerve transcutaneously, as NEMOS that stimulates at the concha of outer ear, CE (European Conformity) and a hand held device Gammacore. On the other hand TENS-200 or Digitimer DS7A often require custom-made electrodes, also used in stimulation. In 2018 a systematic review was conducted on the safety of tVNS that results in transcutaneous vagus nerve stimulation (tVNS) is generally well tolerated in humans at the tested doses and is considered safe.

In parasympathetic nervous system vagus nerve is a major component that emerges from the medullae oblongata, passes through the jugular foramen to leave the cranial activity and travel downward between the neurovascular bundle situated between internal jugular vein and common carotid artery. It extends to thoracic and abdominal cavities and supply multiple organs and regulate autonomic nervous system. VNS play its role by stimulating the afferent and efferent fibers of the VN that primarily comprises the unmyelinated sensory afferent fibers, accounting for 80-90% of the nerve fiber, with the remaining 10-20% being myelinated efferent fibers. These fibers project upward to the brainstem nucleus and relay circuit, influencing the nucleus tractus solitarius (NTS) and locus coeruleus (LC). NTS projects different brain areas as amygdala, hippocampus, locus coeruleus and prefrontal cortex. The effects of direct VNS on enhancement of memory, motor learning and neuroplasticity also suggest a role for treatment of cognitive disorders, stroke, and other conditions. The cholinergic activity of the efferent branch of the vagus nerve has an immune inflammatory regulatory effect, which is referred to as the cholinergic anti-inflammatory pathway (CAP).

Upper limb impairment is a frequent outcome of stroke, greatly affecting a patient's quality of life. Recent research has shown that vagus nerve stimulation (VNS) combined with rehabilitation significantly enhances forelimb strength and movement speed in rat models of ischemic stroke. VNS is thought to amplify the advantages of rehabilitation by fostering neuroplasticity.

While the efficacy of taVNS in enhancing motor recovery post-stroke is well-documented, there is a paucity of comparative studies investigating the distinct effects of auricular and cervical tVNS on upper limb function, cognitive outcomes, and quality of life in subacute stroke patients. This gap necessitates further research to determine optimal stimulation modalities and their broader neurorehabilitation benefits

Inclusion criteria

• First ever ischemic stroke
• Subacute phase of stroke 3-6 months post onset
• Fugl-Meyer Assessment-Upper Extremity (FMA-UE) scores ranged from 20 - 50

Exclusion criteria

• Previous injury or surgical intervention of vagus nerve
• Patients with cardiac arrest and arrythmias
• Uncontrolled hypertension
• Apraxia
• Other neurologic or musculoskeletal diseases
• Presence of implanted electronic devices