Real-time imaging of stress-induced cardiac autonomic adaptation during realistic force-on-force police scenario

Operational stress is a complex matter, which requires a better understanding to improve police officer’s training, survival and prevention of post-traumatic stress disorders. Since objective methods to quantify tactical stress (TSt) are still lacking, this study aimed to evaluate the reliability of heart rate variability analysis (HRVa) to assess autonomic adaptation induced by TSt and to differentiate the contribution of overlapping physical stress (PhS), during realistic scenarios. Methods: Real-time imaging of tactical stress was attempted with Time-Variant (TV) spectral HRVa. Moreoever HRV parameters were evaluated with linear [time-domain (TD) and frequency-domain (FD)] and nonlinear methods, from short-term (5-minutes), very-short-term (60-seconds) and ultra-short-term (30-seconds) intervals, during daily routine, physical stress (PhS) and TSt. Overall 40 healthy volunteers (mean age 35,8±9 years) were studied. The study was approved by local Institutional Review Board. Results: TVspectral HRVa provided dynamic imaging of transient cardiac autonomic adaptation induced by TSt and/or PhS. Quantitative estimation of the majority of TD and FD HRV parameters was not significantly affected by shortening the length of the explored time-segments from 300 to 30 seconds, as demonstrated by the correlation coefficient (R2>0.9). Conclusions: HRVa might allow dynamic imaging and quantification of transient stress-induced autonomic adaptation, but differentiation between respective contribution of TSt and PhS is still difficult.