Stress-induced changes of heart rate variability in police officers during operational training for demanding tactical tasks

The autonomic nervous system (ANS) is the part of nervous system that controls visceral functions, including the heart rate. Mental and emotional states directly affect the ANS. Many researches have examined the influence of emotions on the ANS utilizing the analysis of heart rate variability (HRV), which is due to the synergistic action of parasympathetic tone, which slow heart rate, and the sympathetic tone, which accelerate it. The HRV can be measured both in the time-domain (pNN50%, SDNN, SDANN, r-MSSD), on a total duration of monitoring, and in the frequency-domain [power spectrum density (PSD) analysis] on short periods of 5 minutes. PSD reduces the HRV signal into its constituent frequency components and quantifies the relative power of these components: very low frequency (VLF, due to sympathetic activity); low frequency (LF, due to mixture of sympathetic and parasympathetic activity), high frequency (HF) primarily due to parasympathetic activity. At the end, the LF/HF ratio can be calculated, that indicate the ANS balance. Therefore, the study of HRV is a powerful, objective and non-invasive tool to explore the dynamic interactions between physiological, mental, emotional and behavioral processes that might be useful to evaluate the level of stress during police officers’ education and training.