Research on Transcranial Direct Current Stimulation Over Vagus Nerve for Post-Stroke Dysphagia

Academic Background
Stroke is the second leading cause of death worldwide, and survivors often face a range of complications, among which dysphagia is particularly common, with an incidence rate ranging from 27% to 64%. Dysphagia can lead to serious problems such as pneumonia and malnutrition, affecting patient prognosis and, in severe cases, resulting in death. Traditional rehabilitation methods for swallowing function, such as indirect basic training, direct feeding therapy, acupuncture, and electrical stimulation, have limited effectiveness. With the development of neuroregulation technologies, non-invasive brain stimulation (NIBS) and vagus nerve stimulation (VNS) have gradually been applied in the rehabilitation of stroke patients. Transcranial direct current stimulation (tDCS) is a form of NIBS that has shown potential in treating swallowing dysfunction, but its stimulation targets are mostly focused on the motor or sensory cortex. The vagus nerve plays a key role in regulating metabolic balance and brain function, and recent studies have increasingly shown that VNS can reduce brain inflammation and protect neural cells through various mechanisms. This study aims to explore the efficacy of transcranial direct current stimulation over the vagus nerve (tDCSVN) in improving post-stroke dysphagia.

Source of the Paper
The authors of this study include Xinyue Yan, Xiwei Zhang, Chuan Huang, Yujuan Jiang, and Chunxiao Wan, affiliated with the Department of Rehabilitation Medicine at Tianjin Medical University General Hospital and Cangzhou Central Hospital. The research paper was published in December 2024 in the Journal of Neurophysiology (J Neurophysiol), with DOI 10.1152/jn.00588.2024.

Research Process
1. Study Participants
The study retrospectively collected clinical data and blood samples from post-stroke dysphagia patients treated at Tianjin Medical University General Hospital from January 2020 to June 2023. Using propensity score matching, patients were divided into a control group (conventional treatment) and a tDCSVN group. Ultimately, 57 patients were included in the control group and 56 in the tDCSVN group.

1. Inclusion and Exclusion Criteria
   Inclusion criteria: Stroke occurrence within the last 3 months; stable vital signs; water swallow test (WST) score of 3 to 5; informed consent from patients and their families. Exclusion criteria: Critical illness or unstable vital signs; severe cognitive, visual, or auditory impairments; presence of severe complications such as pulmonary infection or acute myocardial infarction; swallowing dysfunction caused by non-stroke-related conditions.

2. Treatment Protocol

   • Control Group: Patients received conventional treatment according to the Chinese guidelines for the diagnosis and treatment of cerebral hemorrhage and acute ischemic stroke, including swallowing function training, cold stimulation therapy, and feeding training, conducted 5 days a week for 4 weeks.
     
   • tDCSVN Group: In addition to conventional treatment, the IS200 intelligent electrical stimulator was used for tDCSVN treatment, with the anode placed on the left mastoid area and the cathode on the opposite shoulder, at a current intensity of 1 mA for 20 minutes per session, 5 days a week for 4 weeks.

3. Evaluation Metrics

   • Clinical Efficacy: Efficacy was classified into recovery, significant improvement, effective, and ineffective based on WST scores.
     
   • Standard Swallowing Scale (SSA) and Functional Dysphagia Scale (FDS): Used to assess swallowing function, with higher scores indicating worse swallowing function.
     
   • Hemoglobin and Serum Albumin: Used as indicators of nutritional status.
     
   • Serum IL-1β and IL-8 Levels: Measured using ELISA to assess inflammatory response.

Research Results
1. Clinical Efficacy
The recovery rate in the tDCSVN group (19.6%) was significantly higher than in the control group (10.5%), and the rate of significant improvement (32.1%) was also higher than in the control group (14.0%), while the ineffective proportion (17.9%) was lower than in the control group (24.6%).

1. Swallowing Function Assessment
   There were no significant differences in SSA and FDS scores between the two groups before treatment. After treatment, the SSA score (25.77±5.41) and FDS score (42.43±11.81) in the tDCSVN group were significantly lower than in the control group (29.37±5.86 and 50.09±11.48, respectively).

2. Nutritional Indicators
   There were no significant differences in hemoglobin and albumin levels between the two groups before treatment. After treatment, hemoglobin (128.79±16.46 g/L) and albumin (41.86±5.72 g/L) levels in the tDCSVN group were significantly higher than in the control group (120.14±14.23 g/L and 37.87±6.44 g/L, respectively).

3. Inflammatory Factor Levels
   There were no significant differences in IL-1β and IL-8 levels between the two groups before treatment. After treatment, IL-1β (49.63±10.93 pg/mL) and IL-8 (74.85±14.47 pg/mL) levels in the tDCSVN group were significantly lower than in the control group (57.02±12.05 pg/mL and 84.03±15.54 pg/mL, respectively).

Conclusion
tDCSVN treatment significantly improved swallowing function in post-stroke dysphagia patients, as evidenced by significant reductions in SSA and FDS scores, as well as significant increases in hemoglobin and albumin levels. Additionally, tDCSVN treatment was more effective in reducing serum IL-1β and IL-8 levels, indicating an improvement in swallowing function through the inhibition of inflammatory responses.

Research Highlights
1. Innovative Treatment Approach: This study is the first to apply tDCSVN for the treatment of post-stroke dysphagia, providing a new method for swallowing function rehabilitation.
2. Inhibition of Inflammation: The study confirmed that tDCSVN improves swallowing function by reducing levels of inflammatory factors IL-1β and IL-8, offering new evidence for stroke rehabilitation mechanisms.
3. Clinical Application Value: The significant efficacy of tDCSVN treatment provides an important reference for the clinical treatment of post-stroke dysphagia, especially in resource-limited healthcare settings.

Additional Value
This study offers new treatment ideas for the rehabilitation of post-stroke dysphagia. Future research could further explore the long-term efficacy of tDCSVN and its applicability in different patient populations. Additionally, dynamic monitoring of changes in inflammatory factors and nutritional indicators may help to deepen understanding of the mechanisms underlying tDCSVN.