Perturbations In Heart Rate And Heart Rate Variability Of Volunteer Firefighters Responding To Nighttime Calls

Abstract

Firefighters (FFs) can increase their risk of cardiovascular (CV) events >100-fold during emergency response. FF research has tended to analyze career FFs or a career-volunteer blend, while neglecting to provide specific results for the volunteer population. This leaves a gap in literature that seeks to understand the magnitude and duration of call-related perturbations. Autonomic tone (AT), measured by heart rate variability (HRV) is a non-invasive measure providing insight into CV risk and resiliency, and stress response. PURPOSE: To identify the magnitude and duration of changes in volunteer FFs’ autonomic CV control during night time emergency response. METHODS: Eight male FFs (36.9 ± 12.1 years) wore monitors to track heart rate (HR) and R-R intervals from 1900-0700 on nights with, and without call response for a total of 12 calls. Data filtering preceded HRV analysis in both time and frequency domain. Data was organized into 15-minute epochs, focusing on: 15-0 (PRE) pre-dispatch, 0-15 (PC1) and 75-90 (PC2) post-dispatch, and 0-15 (WAKE) when waking without a call. RESULTS: Compared to PRE, increases in the LF/HF ratio were observed at both PC1 (1.784 ± 1.345, p= .014), and PC2 (1.265 ± 1.238, p= .046) η2=.505 in the call condition. PRE-PC1 comparisons showed increases in HRMEAN (43 ± 13 bpm, p<.0005, η2=.837) and HRMAX (60 ± 22 bpm, p<.0005, η2=.923) at PC1, though only HRMEAN remained elevated from PRE values at PC2 (12 ± 8 bpm, p=.005). RMSSD and HF Power (HFp) decreased at PC1 (RMSSD:16.868 ± 8.100 ms, p=.001, η2=.781; HFp: 552.057 ± 311.930 ms2, p=.002, η2=.758), returning within PRE ranges by PC2. Comparisons of PC1 to normal WAKE revealed decreased HFp (234.726 ± 163.721 ms2, p=.002, η2=.577) and increases in both LF/HF (6.920 ± 5.044, p= .013, η2=.556) and HRMEAN (18 ± 13 bpm, p=.012, η2=.564). CONCLUSION: Results from the current study show sympathetic activation and parasympathetic withdrawal at PC1 and PC2 compared to PRE. This facilitated a rapid spike in HR to 85% of age-adjusted HRMAX. Compared to waking normally, waking for call response evokes a distinctly different response where perturbations in AT tend to persist 90-minutes. This persistent ANS imbalance may indicate physiological perturbations that could explain increased atherosclerosis and CVD risk for FFs.