Heart rate variability, ECG minor changes, and HRV–ECG coupling associated with an adjunctive structured breathing–meditation protocol in combat-exposed military personnel

Introduction: Combat-related stress is associated with autonomic nervous system (ANS) dysregulation-sympathetic predominance, reduced vagal tone, and decreased heart rate variability (HRV)-linked to increased cardiovascular risk. Non-pharmacological interventions targeting autonomic regulation show promise, but controlled studies in combat-exposed populations remain limited. We assessed whether adding a structured breathing-meditation protocol, the Technique of Mental Relaxation (TMR), to standard rehabilitation is associated with changes in HRV and electrocardiogram (ECG)-derived indices of autonomic regulation in Ukrainian servicemen. Methods: A controlled, non-randomized study screened 84 male servicemen; 77 were allocated to a TMR group (n = 37; TMR plus standard treatment) or a control group (n = 40; standard treatment alone). Paired baseline and post-treatment 5-min supine recordings, obtained over a 14-day rehabilitation period, were available for 74 participants (TMR n = 35, control n = 39); a civilian reference group (n = 89) provided baseline comparison. Primary HRV outcomes were SDNN, RMSSD, the Baevsky Stress Index, and heart rate; ECG analysis added repolarization intervals, with Hedges' g. Results: At baseline, both military groups showed impaired autonomic regulation versus civilians (all p < 0.0001). After intervention, the TMR group improved (SDNN 23→30 ms, p < 0.001; RMSSD 12→19 ms, p < 0.001; Stress Index 422→253, p < 0.001), whereas controls deteriorated; post-treatment between-group differences were significant for all primary outcomes (p ≤ 0.008). Conclusion: Heart-rate-adjusted analyses attenuated part of this difference, the Stress Index remaining most robust. Given the non-randomized design, these findings warrant caution and support randomized trials, with HRV as an objective monitoring tool.