Real-time Imaging of Stress-induced Cardiac Autonomic Adaptation During Realistic Force-on-force Police Scenarios

Operational stress is a complex matter. It requires a better understanding based on scientific knowledge of the psychophysiology of stress to improve training methods for officer’s survival and prevention of post-traumatic stress disorders. This study aimed to assess the reliability and sensitivity of heart rate and of heart rate variability (HRV) as possible objective methods to quantify police operational stress (OS) in the real world and to differentiate the contribution of overlapping physical stress (PhS) during realistic training scenarios. 12-lead ECG of 113 police officers (POs) were continuously monitored during rest, daily activity (control state), and during 172 realistic tactical training scenarios requiring the use of force and/or of shooting firearms (OS, with or without associated PhS). Baseline physiological and psychological measurements were collected on the days of the training session. POs behavior and tactical outcome were rated by police instructors and documented with multiple video cameras. Real-time imaging of tactical stress was tempted with time-varying (TV) spectral HRV analysis (HRVa). Quantitative estimates of time-domain (TD), frequency-domain (FD), and nonlinear HRV parameters were computed from standard (300 and 120 seconds) and very short-term (60 and 30 seconds) intervals. The study was approved by a local Institutional Review Board. TV spectral HRVa provided dynamic imaging of transient cardiac autonomic adaptation induced by OS and/or PhS. Quantitative estimation of the majority of TD and FD HRV parameters were not significantly affected by shortening the length of the explored time-segments from 300 to 30 seconds, as demonstrated by the intraclass correlation coefficient analysis (> 0.70). Discrimination analysis of HRV parameters allowed a differentiation between rest and stress conditions and between mental and physical stress. HRVa provides dynamic imaging and quantification of transient stress-induced autonomic adaptation in police officers during realistic tactical training scenarios.