Physiological and psychological impacts of nighttime call response in firefighters from volunteer and paid-on-call fire departments




Service, Thomas W.

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An oft overlooked population in research, firefighters of volunteer and paid-on-call fire departments respond to nighttime calls as a supplement to their normal working hours, making the duties taxing on the autonomic system leading to cardiovascular and endocrine disruptions. These duties also come with a tax burden on the volume and distribution of sleep. The current study was executed in order to gain valuable insight into the impact of nighttime call response in this population and the magnitude and duration of any perturbations. Eight firefighters from Greater Victoria Volunteer and Paid-on-call departments were recruited to wear Equivital EQ02 heart monitors and FitBit Charge 2 devices to record autonomic cardiovascular responses and track sleep between 1900 and 0700. HR MAX was found to significantly increase with a large effect size (p<0.0005) from 97 +/- 20 to 157 +/- 18 beats per minute in the 15 minutes preceding versus following a call within the time period. LF/HF ratios increased during the first 15-minutes following a call to 4.055 +/- 1.316 from 1.911 +/- 0.599 pre-call. HF power, RMSSD, and pNN50 all decreased significantly compared to pre-call values (796.176 +/- 414.296 ms2 vs 244.119 +/- 153.880 ms2, 51.940 +/- 7.119 ms vs 35.072 +/- 2.624 ms, 25.017 +/- 7.034% vs 7.403 +/- 2.411%). Further, all HRV measures with the exception of normalized LF and HF were found to be significantly different when waking for and attending a call versus waking on a normal day despite there being no significant differences among any variables when going to bed on nights with and without a call. Total and REM sleep were the most significantly impacted measurables of sleep. Total sleep fell to 261.11 +/- 61.11 minutes from 417.13 +/- 52.04 minutes while REM absolute and percentage of total sleep dropped from 109.88 +/- 28.47 minutes to 51.44 +/- 17.92 minutes, and 22.25 +/- 3.73% to 16.33 +/- 3.17% respectively. In response to a call, mean salivary cortisol levels increased from pre-call values by 0.426 +/- 0.202 ug/dL (p<.001). Salivary c-reactive protein levels also showed significant increases with a small effect size, though due to secretion kinetics, call response is not the likely cause. The results of this study demonstrate the presence of a significant shift in autonomic control from parasympathetic (PSNS) dominance to sympathetic control and PSNS withdrawal which evokes a cortisol-mediated stress response of comparable magnitude to literature standards for normal waking fluxes. Sleep volume, and arguably the most critical stage of sleep, rapid eye movement, are significantly impacted and the links between cognitive performance and both total and overall REM sleep indicate that call response does not just impact the cardiovascular system but may in fact be reducing mental acuity of firefighters. This is important as it has the potential to impact both self and team health and safety, not only during night time call response, but at the firefighters’ day jobs which they regularly proceed to the very same morning following a call, evidently with significant deprivation in sleep.



firefighter, physiology, occupational physiology, stress response, cardiovascular response to stress, sleep deprivation