Physiological adaptation during heart rate variability biofeedback in young adults: A survival analysis in high-stress academic environments.

Medical education is a high-demand environment where stress may disrupt autonomic and HPA-axis regulation. We examined symptom trajectories and adaptation during heart rate variability biofeedback (HRV-BF) in an academic setting. Forty-seven students were followed for ~3 months. The intervention group completed HRV-BF twice weekly (~30 min/session). Psychological outcomes (PSS, SAS, BAI, BDI) were assessed at baseline and follow-up, with clinically meaningful improvement defined as a ≥ 20% reduction. HRV/coherence indices were analyzed with mixed-effects models, and cortisol and secretory IgA were measured around Maastricht Acute Stress Test before and after training. Within the HRV-BF group, perceived stress, anxiety, and depression declined by May (all p < 0.001; d≈1.28-1.86), although between-group differences converged. Meaningful improvement was more frequent in HRV-BF group across scales. Acute sessions increased coherence and inter-beat interval and reduced heart rate (p ≤ 0.015), while RMSSD and inter-beat interval gains plateaued after ~14 sessions. Cortisol responses to stress differed after training, whereas sIgA showed no between-group effects. In this nonrandomized study, HRV-BF was associated with clinically meaningful improvement by follow-up and autonomic adaptation; however, because the group was not matched on baseline distress severity and no sham comparator was used, reductions in anxiety and depression cannot be attributed definitively to the intervention.