Spinal Cord Injury, Chronic
Conditions
Keywords
Transcutaneous auricular vagus nerve stimulation, Heart rate variability, Autonomic nervous system, Neuromodulation, Spinal cord injury, Exercise physiology, Nonlinear dynamics
Brief summary
This study investigates the effects of transcutaneous auricular vagus nerve stimulation (taVNS) on autonomic cardiovascular regulation during exercise and recovery in individuals with chronic spinal cord injury (SCI). Participants undergo two experimental conditions (active taVNS and sham stimulation) in a randomized crossover design while performing a standardized exercise protocol. Heart rate variability (HRV) is used as a non-invasive biomarker to assess autonomic nervous system dynamics across different phases (baseline, exercise, and recovery). The aim is to characterize physiological responses to neuromodulation and explore whether taVNS modulates autonomic adaptability in this population. This is a mechanistic physiological study designed to improve the understanding of autonomic regulation in SCI and to explore potential biomarkers of response to neuromodulation.
Detailed description
Spinal cord injury (SCI) is associated with significant impairments in autonomic nervous system function, particularly affecting cardiovascular regulation. These alterations reduce physiological adaptability to internal and external stressors and may contribute to increased cardiovascular risk. Transcutaneous auricular vagus nerve stimulation (taVNS) is a non-invasive neuromodulation technique that has been proposed as a potential tool to influence autonomic function. However, its effects on dynamic autonomic regulation during physiological stress, such as exercise, remain insufficiently characterized in individuals with SCI. The present study is a randomized, controlled, crossover experimental protocol designed to investigate the acute effects of taVNS on autonomic cardiovascular dynamics during a structured exercise and recovery paradigm. Participants with chronic SCI are exposed to two conditions: active taVNS and sham stimulation, applied in a randomized order. Each experimental session includes three phases: baseline (rest), exercise (submaximal effort), and recovery. Continuous electrocardiographic recordings are obtained to derive heart rate variability (HRV) metrics. Both linear (time and frequency domain) and non-linear analyses are performed to characterize autonomic regulation and system dynamics. The primary objective is to evaluate whether taVNS modulates autonomic responsiveness and adaptability across different physiological states. Secondary objectives include the exploration of HRV-derived biomarkers that may reflect autonomic complexity and the identification of response patterns to neuromodulation. This study is not designed to evaluate clinical efficacy or therapeutic outcomes but to provide mechanistic insight into autonomic regulation and neuromodulation effects in SCI. The results may contribute to the development of personalized approaches in neurorehabilitation and autonomic monitoring.
Interventions
DEVICETranscutaneous Auricular Vagus Nerve Stimulation
Non-invasive electrical stimulation applied to the auricular branch of the vagus nerve using transcutaneous electrodes during the experimental protocol.
DEVICESham Stimulation
Sham stimulation delivered with identical device setup but without effective activation of the vagus nerve.
Sponsors
University of the Balearic Islands
Health Research Institute of the Balearic Islands (IdISBa, Spain)
University of the Balearic Islands - Institute for Health Sciences Research (UNICS)
Study design
Allocation
RANDOMIZED
Intervention model
CROSSOVER
Primary purpose
BASIC_SCIENCE
Masking
SINGLE (Subject)
Masking description
Participants are blinded to the stimulation condition (active taVNS vs sham), while investigators are aware of the assigned condition.
Intervention model description
Randomized, controlled, crossover experimental study with two conditions (active taVNS and sham). Each participant undergoes both conditions during standardized exercise and recovery phases.
Eligibility
Sex/Gender
ALL
Age
18 Years to 70 Years
Healthy volunteers
No
Inclusion criteria
* Adults (≥18 years) with chronic spinal cord injury * Medically stable condition * Ability to perform the exercise protocol * Ability to provide informed consent
Exclusion criteria
* Acute spinal cord injury * Severe cardiovascular or respiratory instability * Use of medications significantly affecting autonomic function * Skin lesions or contraindications to transcutaneous stimulation * Cognitive impairment preventing protocol compliance
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| DFA α2 | Baseline (last 5 minutes of rest), 10, 15, 20, 25, 30, 35, and 40 minutes. | Detrended fluctuation analysis (α2) derived from RR intervals to assess long-term fractal scaling properties of heart rate variability. RR intervals are recorded continuously and analyzed offline. Data are processed using 5-minute overlapping windows. The value reported at each specific time point represents the calculation for the preceding 5-minute window to characterize autonomic regulation across the session. |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| RMSSD (ms) | Baseline (last 5 minutes of rest), 10, 15, 20, 25, 30, 35, and 40 minutes. | Root mean square of successive differences (RMSSD) of RR intervals to assess short-term heart rate variability and parasympathetic activity. RR intervals are recorded continuously and analyzed offline. Data are processed using 5-minute overlapping windows. The value reported at each time point represents the calculation for the preceding 5-minute window.. |
| HF power (ms²) | Baseline (last 5 minutes of rest), 10, 15, 20, 25, 30, 35, and 40 minutes. | High-frequency (HF) power (0.15-0.40 Hz) derived from RR intervals to assess parasympathetic modulation. Spectral analysis is performed using standard frequency-domain methods. Data are processed using 5-minute overlapping windows. Each reported value corresponds to the preceding 5-minute window at the specified time point. |
| LF power (ms²) | Baseline (last 5 minutes of rest), 10, 15, 20, 25, 30, 35, and 40 minutes. | Low-frequency (LF) power (0.04-0.15 Hz) derived from RR intervals to assess combined autonomic modulation. Frequency-domain analysis is performed after preprocessing of RR interval data. Data are processed using 5-minute overlapping windows. Each reported value corresponds to the preceding 5-minute window at the specified time point. |
| SD1 (ms) | Baseline (last 5 minutes of rest), 10, 15, 20, 25, 30, 35, and 40 minutes. | SD1 derived from the Poincaré plot of RR intervals, representing short-term beat-to-beat variability. RR intervals are recorded continuously and analyzed offline. Data are processed using 5-minute overlapping windows. Each reported value corresponds to the preceding 5-minute window at the specified time point. |
Countries
Spain
Outcome results
None listed