Heart Rate Variability, Risk-Taking Behavior and Resilience in Firefighters During a Simulated Extinguish-Fire Task

Abstract

Firefighters face a high-risk potential, thus their psychological ability to cope with critical or traumatic events is a crucial characteristic. This study examines correlations between cardiac autonomic modulation, risk-taking behavior, and resilience in professional firefighters. Twenty male professional firefighters underwent a 20 min beat-to-beat heart rate (HR) monitoring at baseline in the morning upon awakening, then before, during and after a realistic deployment in a container, systematically set on fire. Risk-taking behavior, resilience, and subjective stress were assessed by specific validated tools after deployment: the Risk-taking Scale (R-1), the Resilience Scale (RS-13), and the multi-dimensional NASA-Task Load Index. The cardiac autonomic modulation at rest and in response to stress was assessed by classic indexes of heart rate variability (HRV) as RMSSD and LF/HF ratio. Results showed that: (i) risk-taking behavior correlated with a withdrawal in vagal indices, shifted the baseline sympathovagal balance toward sympathetic predominance (LF/HF ratio r(8) = 0.522, p = 0.01), and increased mean HR both in baseline and during physical exercise (r(8) = 0.526, p = 0.01 and r(8) = 0.445, p = 0.05, respectively); (ii) resilience was associated with higher vagal indices (RMSSD r(18) = 0.288, p = 0.04), and with a baseline sympathovagal balance shifted toward parasympathetic predominance (LF/HF ratio r(18) = -0.289, p = 0.04). Associations of risk-taking behavior and resilience with cardiac autonomic modulation could be demonstrated, showing that HRV may be a valuable monitoring tool in this specific population; however further studies are warranted for validation.

Keywords: autonomic modulation; autonomic nervous system; cardiac stress; firefighters; heart rate variability; resilience; risk-taking behavior; workload.

FIGURE 1

Experimental protocol overview. HRV, heart rate recoding for heart rate variability assessment; PSY. SCALES, psychometric scales conduction.

FIGURE 2

Self-built rower ergometer. A cuff was attached so that the handle could not be pulled further than 60 cm. The wooden pallet identifies the standardized seating position.

FIGURE 3

Floor plan of the container. The doors are closed during the exercise. 1. location of the rowing machine, in front of it two stacked seats. 2. location of the experimenter. 3. waiting area for participants.

FIGURE 4

Time course of HRmean and HRV indices. Blue circles indicate the no-exercise group (NoEx) and red triangles indicates the exercise group (Ex). Time of measurements: base, 2 ± 1 days before deployment exercise (baseline); pre, before entering the container; dur, during deployment in the container; post, immediately after deployment. (A) HRmean (bpm); (B) DFA1 detrended fluctuation alpha 1, index of sympathovagal balance in non-linear domain; (C) log LF (ms²) low-frequency power, index of sympathetic and parasympathetic drive; (D) log HF (ms²) high-frequency power, index of vagal tone. Black asterisks: significance between the groups for each timepoint. Red asterisks: significance between the groups for the respective timepoint. **p < 0.01, *p < 0.05.

FIGURE 5

Regression of resilience and HRV indices at baseline. Panel (A) RMSSD (ms): root mean square of successive differences between NNs (index of vagal tone) and RS-13 score: short version of Resilience Scale with a score ranging between 13 and 91 (13–66 score: low expression of resilience; 67–72 score: moderate expression of resilience; 73–91 score: high expression of resilience). Panel (B) logLF/HF, index of sympathovagal balance in frequency domain and RS-13 score.

FIGURE 6

Regression of resilience and logLF/HF at pre. Regression of logLF/HF, index of sympathovagal balance and resilience as RS-13 score (short version of Resilience Scale with a score ranging between 13 and 91 (13–66 score: low expression of resilience; 67–72 score: moderate expression of resilience; 73–91 score: high expression of resilience), before entering the container.