The Relation of Emergency Duties to Cardiac Death Among US Firefighters.

Sudden cardiac death accounted for 42% of all firefighter duty-related fatalities over the last decade. This retrospective study analyzed available medical examiner records for duty-related firefighter fatalities among male firefighters 18 to 65 years of age that occurred between 1999 and 2014 and reported the pathoanatomic substrate for cardiac-related fatalities. Odds of duty-related cardiac death during specific duties compared with fire station duties were calculated by pathoanatomic substrate. There were 285 cardiac fatalities. Of fatalities, 80% had evidence at autopsy of coronary heart disease (CHD) and increased heart size (cardiomegaly and/or left ventricular hypertrophy). CHD alone, cardiomegaly or left ventricular hypertrophy, and causes other than CHD or increased heart size were identified in 7.7%, 6.0%, and 6.7% of fatalities, respectively. The largest proportion of deaths occurred during fire suppression (33%), although only 1% of annual occupational time was estimated to be spent performing this duty. For deaths attributed to CHD and increased heart size, fire suppression, alarm response, and physical training were associated with approximately a 112-fold, eightfold, and sevenfold increased risk of cardiac death, respectively, compared with station duties. In conclusion, the majority of firefighters who suffered a duty-related cardiac death had CHD and increased heart size, which was associated with a markedly increased risk of death during fire suppression compared with station duties. Targeted occupational medical screening for CHD and increased heart size may reduce duty-related cardiac deaths among firefighters.

Pathoanatomic Findings Associated With Duty-Related Cardiac Death in US Firefighters: A Case-Control Study.

Background Sudden cardiac death accounts for the greatest proportion of duty-related deaths among US firefighters. Increased understanding of the pathoanatomic causes of sudden cardiac death and the risk associated with underlying cardiac pathologies is needed to develop evidence-based screening recommendations. Methods and Results Using autopsy data for duty-related firefighter fatalities occurring between 1999 and 2014, this retrospective case-control study compared cardiac findings of male firefighters aged 18 to 65 years who died on duty of cardiac-related causes with those who died of noncardiac trauma-related causes. Data from 276 cardiac cases and 351 noncardiac trauma controls were analyzed. Among cardiac cases, the most prevalent (82%) underlying pathoanatomic substrate was comorbid coronary heart disease and cardiomegaly/left ventricular hypertrophy. Cardiac cases had a higher prevalence of cardiomegaly (heart weight >450 g), left ventricular hypertrophy (left ventricular wall thickness ≥1.2 cm), and severe coronary artery stenosis (≥75%) than trauma controls (all P<0.001). In multivariate analyses, heart weight >450 g, coronary artery stenosis ≥75%, and evidence of a prior myocardial infarction were strong independent predictors of cardiac death, with odds ratios of 6.1 (95% confidence interval, 3.6-10.4), 9.3 (95% confidence interval, 5.3-16.1), and 6.2 (95% confidence interval, 3.4-11.3), respectively. Conclusions The majority of cardiac fatalities had evidence of both coronary heart disease and increased heart mass, and each condition was independently associated with a markedly elevated risk of cardiac death. Targeted screening for coronary heart disease, increased heart mass, and evidence of prior myocardial infarction should be considered to reduce duty-related cardiac deaths among firefighters.

Medical Monitoring During Firefighter Incident Scene Rehabilitation.

OBJECTIVE: The objective of this study was to retrospectively investigate aspects of medical monitoring, including medical complaints, vital signs at entry, and vital sign recovery, in firefighters during rehabilitation following operational firefighting duties. RESULTS: Incident scene rehabilitation logs obtained over a 5-year span that included 53 incidents, approximately 40 fire departments, and more than 530 firefighters were reviewed. Only 13 of 694 cases involved a firefighter reporting a medical complaint. In most cases, vital signs were similar between firefighters who registered a complaint and those who did not. On average, heart rate was 104 ± 23 beats·min(-1), systolic blood pressure was 132 ± 17 mmHg, diastolic blood pressure was 81 ± 12 mmHg, and respiratory rate was 19 ± 3 breaths·min(-1) upon entry into rehabilitation. At least two measurements of heart rate, systolic blood pressure, diastolic blood pressure, and respiratory rate were obtained for 365, 383, 376, and 160 cases, respectively. Heart rate, systolic and diastolic blood pressures, and respiratory rate decreased significantly (p < 0.001) during rehabilitation. Initial vital signs and changes in vital signs during recovery were highly variable. CONCLUSIONS: Data from this study indicated that most firefighters recovered from the physiological stress of firefighting without any medical complaint or symptoms. Furthermore, vital signs were within fire service suggested guidelines for release within 10 or 20 minutes of rehabilitation. The data suggested that vital signs of firefighters with medical symptoms were not significantly different from vital signs of firefighters who had an unremarkable recovery.

Firefighter Incident Rehabilitation: Interpreting Heart Rate Responses.

UNLABELLED: The primary objective of this observational study was to document the heart rate (HR) responses of firefighters during incident rehabilitation following firefighting activity in a high-rise building with a simulated fire on the 10th floor. Additionally, the study investigated potential factors, including firefighting workload, ambient temperature, firefighter movement, and individual characteristics, that may have affected HR during recovery. Firefighters (n = 198) were assigned to perform a simulation of fire suppression, search and rescue, or material support during one of six firefighting trials that involved different crew sizes and ascent modes, and were performed in different environmental conditions. After completing the simulated firefighting activity, firefighters reported to a rehabilitation area on the 8th floor. The rehabilitation area was staffed by firefighter/paramedics. HR was monitored continuously during simulated firefighting activity and a 15-minute rehabilitation period. Average HR during rehabilitation (HRmean) was calculated and compared across trials. Simulated firefighting activity was performed in the summer in Virginia, USA, and ambient conditions varied among trials (mean ± SD: 31 ± 4°C; 46 ± 15% relative humidity; 32 ± 4°C heat index). Duration of simulated firefighting activity ranged from 12.0 to 20.3 minutes among trials (mean: 15.4 ± 5.2 minutes). Over all trials, mean peak HR during simulations was 173 ± 18 beats·min(-1). Mean HR over all trials at entry into rehabilitation was 149 ± 24 beats·min(-1). Following 15 minutes of recovery, mean HR over all trials was 126 ± 23 beats·min(-1). Exploratory analyses revealed that higher workload during firefighting (stair trials), higher ambient temperature (≥30°C), greater movement during rehabilitation (≥0.1 g-force), higher age (≥45 years), and higher BMI (≥30.0 kg·m(-2)) were associated with higher HR responses during rehabilitation. During complex emergency operations, emergency medical service personnel will likely encounter considerable variability in HR responses upon initial evaluation and throughout rehabilitation. Following one bout of firefighting activity during a simulated fire scenario, HR decreased but remained elevated well above resting values following 15 minutes of rehabilitation. Based on current fire service recommendations, the majority of firefighters (88%) would not have been released from rehabilitation and eligible for reassignment after a 15-minute rehabilitation period following a brief bout of simulated firefighting activity. KEY WORDS: medical monitoring, cardiac strain, firefighting.

Cardiac strain associated with high-rise firefighting.

Although numerous studies have reported the physiological strain associated with firefighting, cardiac responses during a large-scale fire operation have not been reported and cardiac responses have not been compared based on crew assignment. The aims of this study were (1) to characterize cardiac strain during simulated high-rise firefighting, and (2) to compare the cardiac strain associated with different work assignments (fire suppression vs. search and rescue) and different modes of vertical ascent (stairs vs. elevator). Firefighters (N = 42) completed one assignment (fire suppression, search and rescue, or material support) during one of two trials that differed by ascent mode. Assignments were divided into three phases: Ascent (ascend lobby to 8th floor), Staging (remain in holding area on 8th floor), and Work (perform primary responsibilities). When comparing assignments within the same ascent mode, mean heart rate (HRmean) was higher (p = 0.031) for fire suppression than for search and rescue during Work in the stair trial (170 ± 14 vs. 155 ± 11 beats/min). Search and rescue crews experienced greater cumulative cardiac strain (HRmean × duration) during Work than did fire suppression crews (stairs: 1978 ± 366 vs. 1502 ± 190 beats; elevator: 1755 ± 514 vs. 856 ± 232 beats; p<0.05). When comparing ascent mode, HRmean and peak heart rate (HRpeak) were higher (35-57 beats/min; p≤0.001) for both fire suppression and search and rescue during Ascent and Staging phases in the stairs vs. the elevator trial. During Work, HRmean was higher (p = 0.046) for search and rescue in the stairs vs. the elevator trial (155 ± 11 vs. 138 ± 19 beats/min). HRmean and HRpeak were 47 and 34 beats/min higher (p < 0.01), respectively, when materials were transported to the staging area using the stairs compared with the elevator. Study findings suggest that high-rise firefighting results in considerable cardiac strain and that search and rescue and material support crews experienced more cardiac strain than fire suppression crews due primarily to differences in assignment duration. Furthermore, using stairs to transport firefighters and equipment to upper floors results in significantly greater cardiac strain than using the elevator.

Evaluation of a wearable physiological status monitor during simulated fire fighting activities.

A physiological status monitor (PSM) has been embedded in a fire-resistant shirt. The purpose of this research study was to examine the ability of the PSM-shirt to accurately detect heart rate (HR) and respiratory rate (RR) when worn under structural fire fighting personal protective equipment (PPE) during the performance of various activities relevant to fire fighting. Eleven healthy, college-aged men completed three activities (walking, searching/crawling, and ascending/descending stairs) that are routinely performed during fire fighting operations while wearing the PSM-shirt under structural fire fighting PPE. Heart rate and RR recorded by the PSM-shirt were compared to criterion values measured concurrently with an ECG and portable metabolic measurement system, respectively. For all activities combined (overall) and for each activity, small differences were found between the PSM-shirt and ECG (mean difference [95% CI]: overall: -0.4 beats/min [-0.8, -0.1]; treadmill: -0.4 beats/min [-0.7, -0.1]; search: -1.7 beats/min [-3.1, -.04]; stairs: 0.4 beats/min [0.04, 0.7]). Standard error of the estimate was 3.5 beats/min for all tasks combined and 1.9, 5.9, and 1.9 beats/min for the treadmill walk, search, and stair ascent/descent, respectively. Correlations between the PSM-shirt and criterion heart rates were high (r = 0.95 to r = 0.99). The mean difference between RR recorded by the PSM-shirt and criterion overall was 1.1 breaths/min (95% CI: -1.9 to -0.4). The standard error of the estimate for RR ranged from 4.2 breaths/min (treadmill) to 8.2 breaths/min (search), with an overall value of 6.2 breaths/min. These findings suggest that the PSM-shirt provides valid measures of HR and useful approximations of RR when worn during fire fighting duties.

Effect of base layer materials on physiological and perceptual responses to exercise in personal protective equipment.

Ten men (non-firefighters) completed a 110 min walking/recovery protocol (three 20-min exercise bouts, with recovery periods of 10, 20, and 20 min following successive bouts) in a thermoneutral laboratory while wearing firefighting personal protective equipment over one of four base layers: cotton, modacrylic, wool, and phase change material. There were no significant differences in changes in heart rate, core temperature, rating of perceived exertion, thermal discomfort, and thermal strain among base layers. Sticking to skin, coolness/hotness, and clothing humidity sensation were more favorable (p < 0.05) for wool compared with cotton; no significant differences were identified for the other 7 clothing sensations assessed. Separate materials performance testing of the individual base layers and firefighting ensembles (base layer + turnout gear) indicated differences in thermal protective performance and total heat loss among the base layers and among ensembles; however, differences in heat dissipation did not correspond with physiological responses during exercise or recovery.

Use of the HR index to predict maximal oxygen uptake during different exercise protocols.

This study examined the ability of the HRindex model to accurately predict maximal oxygen uptake ([Formula: see text]O2max) across a variety of incremental exercise protocols. Ten men completed five incremental protocols to volitional exhaustion. Protocols included three treadmill (Bruce, UCLA running, Wellness Fitness Initiative [WFI]), one cycle, and one field (shuttle) test. The HRindex prediction equation (METs = 6 × HRindex - 5, where HRindex = HRmax/HRrest) was used to generate estimates of energy expenditure, which were converted to body mass-specific estimates of [Formula: see text]O2max. Estimated [Formula: see text]O2max was compared with measured [Formula: see text]O2max. Across all protocols, the HRindex model significantly underestimated [Formula: see text]O2max by 5.1 mL·kg(-1)·min(-1) (95% CI: -7.4, -2.7) and the standard error of the estimate (SEE) was 6.7 mL·kg(-1)·min(-1). Accuracy of the model was protocol-dependent, with [Formula: see text]O2max significantly underestimated for the Bruce and WFI protocols but not the UCLA, Cycle, or Shuttle protocols. Although no significant differences in [Formula: see text]O2max estimates were identified for these three protocols, predictive accuracy among them was not high, with root mean squared errors and SEEs ranging from 7.6 to 10.3 mL·kg(-1)·min(-1) and from 4.5 to 8.0 mL·kg(-1)·min(-1), respectively. Correlations between measured and predicted [Formula: see text]O2max were between 0.27 and 0.53. Individual prediction errors indicated that prediction accuracy varied considerably within protocols and among participants. In conclusion, across various protocols the HRindex model significantly underestimated [Formula: see text]O2max in a group of aerobically fit young men. Estimates generated using the model did not differ from measured [Formula: see text]O2max for three of the five protocols studied; nevertheless, some individual prediction errors were large. The lack of precision among estimates may limit the utility of the HRindex model; however, further investigation to establish the model's predictive accuracy is warranted.

The effect of precooling on cardiovascular and metabolic strain during incremental exercise.

The purpose of this study was to investigate the effect of precooling on the chronotropic index defined as the slope of the heart rate (HR) and oxygen uptake during incremental exercise. Ten men performed incremental exercise following 2 conditions: control (rest in a thermoneutral laboratory, 21.5 ± 0.7 °C; performed first) and precooling (cold-water immersion, 23.1 ± 0.2 °C). Prior to exercise, core temperature was significantly lower for precooling (36.6 ± 0.3 °C) compared with control (37.1 ± 0.4 °C; p < 0.001) and remained lower throughout exercise (p < 0.05). Time to volitional fatigue during the incremental exercise test was significantly longer in the control (914 ± 97 s) compared with precooling (889 ± 97 s; p = 0.015). Precooling reduced HR by 8-10 beats·min(-1) compared with control throughout exercise (peak HR: precooling, 178 ± 9 beats·min(-1); control, 188 ± 6 beats·min(-1); p = 0.001). Oxygen uptake did not differ between conditions (p > 0.05). The chronotropic index did not differ between conditions (p = 0.301); however, the y intercept was significantly lower (p = 0.009) for precooling (53.6 ± 11.0) compared with control (67.3 ± 11.0). Thus, the benefit of precooling was a lower HR that was maintained throughout exercise rather than a reduced rate of rise in HR. These results suggest the potential use of precooling to mitigate cardiovascular strain in individuals working at elevated metabolic rates. However, the reduced exercise time warrants consideration.

Effect of clothing layers in combination with fire fighting personal protective clothing on physiological and perceptual responses to intermittent work and on materials performance test results.

Personal protective clothing (PPC) shields firefighters from thermal and other occupational hazards; however, it also contributes to physiological and perceptual strain. This study examined the effect of clothing layers worn under structural fire fighting turnout gear (TOG) on physiological and perceptual responses during alternating work/recovery cycles and assessed the clothing ensembles' (PPC + base layer) material performance. Values are reported as mean ± standard error of the mean. Ten men (age, 21 ± 0.3 yr; height, 1.74 ± 0.02 m; weight, 74.3 ± 2.3 kg; VO2max, 58.9 ± 2.0 mL/kg/min) completed a 110-min alternating work/recovery walking protocol (three 20-min exercise bouts/10-, 20-, and 20-min recovery sessions) in a thermo-neutral (21.0°C, 58.7% RH) laboratory while wearing a cotton t-shirt (COT) or COT and a station uniform (SU) shirt under fire fighting TOG (COT+TOG and COT+SU+TOG, respectively). Changes in heart rate (HR), core temperature (Tco), skin temperature (Tsk), rating of perceived exertion (RPE), and thermal sensations (TS) were compared across exercise and recovery periods. During exercise sessions, HR, Tco, Tsk, and RPE reached similar levels for COT+TOG and COT+SU+TOG. During Recoveries 1, 2, and 3, mean chest Tsk decreased by 3.96, 6.64, and 6.49°C, respectively, for COT+TOG compared with 2.24, 3.78, and 4.09°C for COT+SU+TOG (p < 0.05 for each period). Change in TS differed during Exercise 1; however, mean peak TS corresponded to "hot" for both ensembles. This study demonstrates that the additional layer of clothing in the COT+SU+TOG ensemble imposed no greater level of physiological or perceptual strain during moderate-intensity work bouts compared with the COT+TOG ensemble. However, some modest benefits were experienced during the recovery sessions for the COT+TOG ensemble as evidenced by a lower chest Tsk. In addition, materials performance testing revealed COT+SU+TOG provided greater thermal protection (64.8 ± 1.9 vs. 56.4 ± 0.3 cal/cm(2); p < 0.05) and equivalent heat dissipation compared with COT+TOG. These findings could guide departmental decisions about the use of station shirts.

The prevalence of cardiovascular disease risk factors and obesity in firefighters.

Obesity is associated with increased risk of cardiovascular disease (CVD) mortality. CVD is the leading cause of duty-related death among firefighters, and the prevalence of obesity is a growing concern in the Fire Service. Methods. Traditional CVD risk factors, novel measures of cardiovascular health and a measurement of CVD were described and compared between nonobese and obese career firefighters who volunteered to participate in this cross-sectional study. Results. In the group of 116 men (mean age 43 ± 8 yrs), the prevalence of obesity was 51.7%. There were no differences among traditional CVD risk factors or the coronary artery calcium (CAC) score (criterion measure) between obese and nonobese men. However, significant differences in novel markers, including CRP, subendocardial viability ratio, and the ejection duration index, were detected. Conclusions. No differences in the prevalence of traditional CVD risk factors between obese and nonobese men were found. Additionally, CAC was similar between groups. However, there were differences in several novel risk factors, which warrant further investigation. Improved CVD risk identification among firefighters has important implications for both individual health and public safety.