Ainara Aranberri-Ruiz, Unai Liberal Graña
The vagus nerve is a major neurophysiological pathway linking the brain and body, and schools provide a practical setting for delivering stress-regulation programs. This uncontrolled pilot study assessed the feasibility, safety, acceptability, and preliminary outcomes of a school-based intervention combining paced-breathing heart rate variability (HRV) biofeedback with transcutaneous auricular vagus nerve stimulation (taVNS). Seventeen vocational education and training students aged 15-17 years enrolled in six weekly individual sessions of up to 30 min using emWave® biofeedback and Parasym™ taVNS. Feasibility was assessed through recruitment, six-session completion, acceptability, and adverse events. Exploratory outcomes included STAI-State anxiety, hair cortisol concentration (HCC), breathing self-regulation, and acute HRV indices. Recruitment was 50.0% (17/34), and 14 participants completed all sessions (82.4%). Among the 14 participants who completed all six sessions, 13 completed the written satisfaction item: 12 rated the program 5/5 and one rated it 4/5 (M = 4.92, SD = 0.28). One mild, transient stimulation-related adverse event occurred and resolved after pausing and resuming at a lower intensity. STAI-State scores decreased from pre- to post-intervention, whereas HCC increased. In nine participants with paired HRV data from Sessions 1 and/or 2, SDNN, RMSSD, lnHF, and lnLF were lower during combined paced breathing + taVNS than during spontaneous-breathing rest. Because the study was small, nonrandomized, uncontrolled, and the active components were always delivered together, these changes cannot be attributed to the intervention or to either component independently. The findings support cautious conclusions about deliverability and tolerability and provide information for a controlled trial, rather than evidence of efficacy.