Abstract

Heart rate variability (HRV) is an essential indicator of a healthy regulatory system, and it reflects the dynamic interplay between the sympathetic and parasympathetic branches of the autonomic nervous system (ANS). The neurovisceral integration model posits that higher HRV reflects better emotion and cognitive regulation. This model is supported by numerous studies, including those demonstrating the effectiveness of HRV biofeedback (HRVBF) training in enhancing emotion and attentional regulation. HRVBF is particularly beneficial for high-stress professions such as law enforcement, as it improves decision-making, stress response, recovery, and self-regulation. Given the relevance of HRVBF for police officers, it is essential to examine further its effectiveness in enhancing their mental resilience and cognitive performance. The overall aim of this thesis is to examine 1) the association between HRV and positive affect (PA) as a trait, hypothesizing that individuals with high PA as a trait and more adaptive emotion regulation will have higher HRV, reinforcing the role of HRV as an indicator for emotion regulation and 2) the influence of a five-week HRVBF resonance frequency training program on the mental resilience of Icelandic police officers, hypothesizing improvement in their mental resilience; and 3) the influence of a five-week HRVBF on cognitive performance of Icelandic police officers, hypothesizing that it will improve their cognitive performance. 

The first paper includes a study with 54 participants who performed various cognitive tasks, the Trier Social Stress Task, and a fatigue-inducing 20-minute Stroop task to assess the first aim. Their vital signs were monitored, and trait PA was measured with The Positive and Negative Affect Schedule (PANAS). Results indicated that participants with higher levels of trait PA had higher HRV, as measured by the root mean square of successive differences (RMSSD), indicating increased parasympathetic nervous system (PSNS) activity compared to individuals with low trait PA, especially towards the end of task performance during fatigue induction. These findings suggest that high trait-PA individuals have a more adaptive response and better emotion regulation in complex, prolonged task settings, supporting previous research, and highlighting the role of HRV as an indicator of emotion regulation.

For the second and third aims, 27 police officers were randomly assigned to an intervention or waitlist control group. The intervention group underwent a five-week HRVBF training, starting with a workshop and individual training, followed by 20-minute resonance breathing exercises twice daily. Both groups participated in physiological, cognitive, and subjective measures before, in the middle, and after the five-week program. The second paper revealed that the intervention group increased significantly in HRV and mental resilience compared to the control group following the HRVBF intervention. Finally, the third paper demonstrated significant improvements in cognitive performance, such as the Psychomotor Vigilance Task (PVT), when comparing results before and after HRVBF. Additionally, significant improvements in HRV were observed when comparing physiological activity pre- and post-intervention as well as during the PVT. These results highlight the role of HRVBF in improving mental resilience, autonomic regulation, and cognitive performance, particularly in high-stress professions such as law enforcement. They also support the potential for proactive use of HRVBF to ensure that professionals in high-stress environments are mentally and physiologically equipped to perform optimally, thereby ensuring public safety and the well-being of the officers.