The objective of this clinical, longitudinal, prospective, randomised (randomised) unmasked study is to analyse whether electrical and manual vagal stimulation produces changes in heart rate variability in a healthy population and it have a beneficial clinical effect in reducing dysautonomic symptoms.
The main questions it seeks to answer are:
* Will non-invasive (manual and electrical) stimulation of the vagus nerve produce a significant change in heart rate variability, generating effects on the regulation of the autonomic nervous system, increasing the activation of the parasympathetic nervous system and decreasing the activation of the sympathetic nervous system? * Will non-invasive (manual and electrical) stimulation of the vagus nerve have a beneficial clinical effect in reducing dysautonomic symptoms such as fatigue and improving sleep quality? * Will noninvasive (manual and electrical) vagus nerve stimulation improve quality of life? * Are there differences in the level of satisfaction with the treatment after the intervention program received?
Two groups of participants will be formed:
* Transcutaneous auricular vagus nerve stimulation consists of applying electrical stimulation to the auricular branch of the vagus nerve using a 2-pole stimulation electrode. Stimulation is performed for 1 hour per day for 10 days (5 days per week). * Manual vagus nerve intervention consists of applying a protocol of manual therapy techniques to the vagus nerve and along its path, during 4 sessions lasting 30 minutes, 2 interventions per week.
Healthy volunteers between 40 and 70 years of age.
No known neurological pathology.
Willingness to participate voluntarily in the study.
Cognitive impairment objectively assessed by a neurologist and considered relevant.
Contraindications for the application of transcutaneous auricular stimulation (implanted cardiac pacemaker or deep brain stimulation treatment).
Consumption of tea, caffeine, energy drinks, alcohol or tobacco in the two hours prior to the intervention.
Parallel
Electrical stimulation of the vagus nerve
DeviceThe intervention consists of applying transcutaneous electrical stimulation to the auricular branch of the vagus nerve using a bipolar stimulation electrode. A commercially available transcutaneous electrical stimulation device approved for human use will be used (tVNS R (Hook), from tVNS® Technologies GmbH, Erlangen, Germany). The electrode will be placed on the left ear in contact with the cimba turbinate, an area innervated by the auricular branch of the left vagus nerve. Stimulation protocol: Stimulation will be administered in 60-minute/day cycles for 10 days (5 days a week). Stimulation parameters are: Pulse width: 500 μs, Frequency: 25 Hz, Alternating duty cycle: 60 seconds ON followed by 10 seconds OFF, Total time: 60 minutes per day. Current intensity: 200% of the perception threshold, as long as it is tolerated and does not cause pain.
Manual stimulation of vagus nerve
Procedure/SurgeryThe intervention consists of applying a protocol of manual therapy techniques to the vagus nerve and its pathway, during four 30-minute sessions, two interventions per week for two consecutive weeks. The therapeutic protocol is structured around a total of nine specific maneuvers. The intervention will begin with the application of three techniques targeting the cervical region, followed by two maneuvers focused on the anterior region of the neck. Two techniques will then be performed on the thorax, and finally, two mobilizations targeting the abdominal region.
Heart rate variability
Heart rate variability (HRV) analysis is proposed as a non-invasive and reliable measure to indirectly assess autonomic nervous system dysfunction. Two HRV parameters/domains are assessed: frequency and time. Frequency parameters: the high-frequency (HF) measurement is an indicator of parasympathetic nervous system activity, the low-frequency (LF) measurement is an indicator of sympathetic nervous system activity and finally the relationship between both parameters LH/HF indicates the balance between both systems. Time parameters: a significant decrease in the Standard deviation of the normal-to-normal interval and the Root mean square successive difference and pNN50 indicators would indicate a decrease in parasympathetic nervous system activity. A Polar® H10 chest strap connected to a mobile phone will be used to collect HRV data and the data will be analyzed with Elite software.
Questions about the quality of the sleep: Pittsburgh Sleep Quality Index. (PSQI)
The Pittsburgh Sleep Quality Index is a self-administered questionnaire that assesses sleep quality over the past month. It consists of 19 items grouped into seven components: subjective quality, latency, duration, sleep efficiency, disturbances, use of hypnotic medication, and daytime dysfunction. Each component is scored from 0 to 3, adding up to an overall score between 0 and 21, where scores above 5 indicate poor sleep quality. It is a validated tool, widely used in clinical research for its sensitivity and specificity in detecting sleep problems in various populations.
Quality of life: Eqol5 Questionnaire
The EQ-5D questionnaire is a generic, self-administered instrument designed to measure health-related quality of life. It assesses five dimensions (mobility, self-care, usual activities, pain/discomfort, anxiety/depression), each with five levels of severity. It also incorporates a visual analog scale (0-100) for self-assessment of current health status. The data can be transformed into a synthetic utility index, used in health economic evaluation and QALY estimates, and is one of the most widely used and internationally validated tools for measuring health outcomes.
Fatigue: FACIT Fatigue Scale
The FACIT-Fatigue Scale is a self-administered scale consisting of 13 items designed to measure the intensity and impact of fatigue in patients with chronic illnesses. Each item is rated from 0 (never) to 4 (always), with a total score range of 0 to 52, where lower values indicate greater fatigue. It is a brief tool, validated in various clinical contexts and languages, with high internal consistency and widely used in clinical research and daily medical practice.
Degree of satisfaction regarding the treatment: Treatment Satisfaction Scale (CRES-4)
Treatment Satisfaction Scale (CRES-4): The Treatment Satisfaction Scale (CRES-4) is a self-administered scale consisting of four items, designed to assess patient satisfaction with the treatment received, the perception of resolution of the main problem, and the emotional change experienced before and after the intervention. Each section is scored from 0 to 5 and transformed to a scale from 0 to 100, finally adding up to an overall range from 0 to 300. Higher scores reflect greater satisfaction and perception of effectiveness. It is a brief, validated tool that is ideal for studies of satisfaction and perceived effectiveness in the clinical context.
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