This unicentric, controlled clinical trial aims to evaluate the effects of vagus nerve neurodynamics and 6 bpm guided breathing, combined with manual therapy, on heart rate variability (HRV) in patients suffering from chronic stress. A total of 62 participants will be randomly assigned into two groups: one receiving guided breathing and neurodynamics with manual therapy, and the other receiving only guided breathing with manual therapy. HRV will be monitored using Polar® H10 sensors. The primary outcome is the change in HRV, measured pre- and post-intervention. The study is ethically approved by the Hospital Clínico San Carlos.

This unicentric, controlled clinical trial investigates the impact of vagus nerve neurodynamics and guided breathing at a rate of 6 breaths per minute (bpm), in conjunction with manual therapy, on heart rate variability (HRV) in patients with chronic stress.

The study involves 62 participants who will be randomly allocated into two groups. Group 1 will receive a protocol of guided breathing combined with neurodynamics and manual therapy, while Group 2 will follow a protocol of guided breathing with manual therapy only.

Each participant will undergo a 15-minute intervention session where HRV will be continuously monitored using Polar® H10 sensors. The intervention will include guided diaphragmatic breathing at 6 bpm to standardize the respiratory rate across participants, ensuring that HRV measurements reflect the effects of neurodynamics rather than respiratory variations.

The neurodynamics technique involves passive movements in the cervical region to enhance the functionality of the vagus nerve, potentially influencing HRV. This technique will be applied during the intervention period, with specific movements synchronized with the participants' respiratory cycle.

Prior to the intervention, baseline HRV will be recorded during a 7-minute rest period. Post-intervention HRV measurements will also be taken for 7 minutes while participants remain in a supine position. Data analysis will focus on comparing the HRV changes between the two groups, providing insights into the effectiveness of combining neurodynamics with guided breathing and manual therapy.

The study adheres to ethical guidelines and has received approval from the Medical Research Ethics Committee of Hospital Clínico San Carlos

Inclusion Criteria:

• Individuals aged 18 years or older.
• Self-perceived chronic stress for at least six months.
• Willingness to provide informed consent and comply with the study procedures

Exclusion Criteria:

• Consumption of tea, caffeine, energy drinks, alcohol, or tobacco within two hours prior to the study.
• Significant neck pain or headache.
• Carotid sinus syndrome.
• Pregnancy.
• Recent cervical or cardiac surgery.
• Recent significant trauma.
• Cancer.
• Neurological disorders affecting muscle tone.
• Underlying conditions such as diabetes mellitus or arterial hypertension.
• Use of beta-blockers.
• Arrhythmias or other cardiac diseases

The study will employ simple blinding. Participants will be blinded to the intervention group to which they belong. Outcome assessors will also be blinded to group assignment to ensure that heart rate variability (HRV) measurements are not influenced by participants' knowledge of the intervention received. Staff delivering interventions will not be blinded due to the nature of neurodynamic and guided breathing techniques, which require knowledge of the specific protocol applied.