High-intensity, occupation-specific training in a series of firefighters during phase II cardiac rehabilitation

Abstract

Six male firefighters who were referred to phase II cardiac rehabilitation after coronary revascularization participated in a specialized regimen of high-intensity, occupation-specific training (HIOST) that simulated firefighting tasks. During each session, the electrocardiogram, heart rate, and blood pressure were monitored, and the patients were observed for adverse symptoms. No patient had to discontinue HIOST because of adverse arrhythmias or symptoms. For physicians who must make decisions about return to work, the information collected over multiple HIOST sessions might be more thorough and conclusive than the information gained during a single treadmill exercise stress test (the recommended evaluation method).

Firefighting is arduous and has one of the highest occupational fatality rates in the United States (1). Surprisingly, coronary heart disease (CHD), not injury, is the number one cause of on-duty deaths among firefighters (2). However, the vast majority of these firefighters were not previously diagnosed with CHD and had uncontrolled risk factors (3). Current recommendations state that firefighters with CHD should be restricted from performing strenuous emergency duties (4). To our knowledge, there are no data regarding firefighters’ exercise tolerance following successful revascularization of their CHD and hence no assessment of whether they are then able to perform simulated firefighting tasks.

The National Fire Protection Agency, which promotes codes and standards for fire safety worldwide, has proposed guidelines for veteran firefighters who may want to return to work in the presence of CHD. These guidelines include seven criteria, four of which are clinical observations that can be obtained from a patient history: 1) no angina, 2) no major coronary artery stenosis (>70% of lumen), 3) normal left ventricular ejection fraction, and 4) no persistent modifiable risk factor for plaque rupture (i.e., tobacco use, hypertension, total cholesterol >180 mg/dL, low-density lipoprotein cholesterol >100 mg/dL, or glycated hemoglobin >7%). The other three criteria involve observations made during an exercise stress test: 5) exercise tolerance >12 metabolic equivalents (METs), 6) no exercise-induced angina, and 7) no ischemia or ventricular arrhythmia during exercise (with imaging) (5). However, treadmill exercise stress tests are not always reliable predictors of performance in activities that require both strength and endurance (6), such as firefighting. Deciding whether a firefighter should return to work on the basis of the results from a single treadmill exercise stress test might be inadequate considering the unique specificity and intensity of the job.

In a prior study of the exercise tolerance of firefighters, we collected metabolic data on healthy subjects as they performed simulated firefighting tasks on an obstacle course (7). We then translated the study's tasks, which required a mean level of 12 METs, into a telemetry-monitored program of high-intensity, occupation-specific training (HIOST) within the cardiac rehabilitation (CR) program at our institution. Our goal was to evaluate the firefighter-patient's tolerance for performing strenuous occupational tasks in repeated sessions, with the resulting information assisting the physician's decision about the patient's physical potential for returning to work. Here, we report data from the first six patients with CHD to undergo this training.

PATIENT TRAINING

From June 2008 through May 2012, six male firefighters were referred to outpatient phase II CR in Dallas, Texas, following revascularization of CHD, and they consented to participate in CR 3 days per week. CR staff gave them the option of participating in HIOST or conventional CR; all selected the HIOST option. The hospital's institutional review board approved the reporting of their data.

The patients’ demographic and clinical information is summarized in the Table. At enrollment, all six patients were on an antiplatelet regimen and were taking lipid-lowering drugs and beta-blockers. In addition, one was taking a nitrate and diuretic; another was taking ranolazine for angina.

The patients were monitored by telemetry during exercise training. Resting heart rate and blood pressure measurements were taken before and after each session, and the patients performed warm-up and cool-down routines. A physician was in the room and approved the exercise regimen. The patients participated in supervised endurance training (treadmill walking) during several early sessions (the number varied per individual) until their vital signs were found to respond appropriately to exercise. At that juncture, the patients began the subsequent HIOST sessions, which were specifically designed to mirror the occupational tasks included in our prior study of healthy firefighters (7).

During HIOST, no calculated target heart rate range was used to restrict exercise intensity. Training was symptom-limited; patients were monitored for hypertension (blood pressure >240/110 mm Hg), hypotension (systolic blood pressure decrease of ≥10 mm Hg), elevated rate-pressure product (≥36,000), ventricular arrhythmias, ST depression, angina, dizziness, pain, shortness of breath, and perceived exertion.

The HIOST workouts were customized by incrementally increasing cardiovascular intensity and weight loads over the course of the CR program exercise sessions. The patients wore weighted vests (10 to 55 pounds) as they completed the following occupation-specific tasks (Figure):

• Carrying a weighted box ranging from 11.5 to 50 pounds (simulates carrying equipment)

• Climbing stairs carrying a 15- or 30-pound hose (simulates carrying a high-rise hose pack to an upper-story location)

• Dragging a 50-, 95-, or 165-pound dummy (simulates removing a victim from a fire scene)

• Using a stair-climbing machine (simulates walking up stairs)

• Pulling a 30- or 60-pound fire hose (simulates advancing a hose)

• Raising a pike pole weighing 5.5 to 15.4 pounds (simulates removing debris from a ceiling)

• Hitting a tire for 20 to 60 seconds with a 9-pound sledgehammer (simulates forcible entry)

Figure.

Four of the occupation-specific activities performed by firefighters while wearing a weighted vest: (a) after climbing stairs with a hose pack, (b) dragging a dummy, (c) using a stair-climbing machine, and (d) hitting a tire with a sledgehammer.

The six patients participated in a total of 153 sessions; 36 consisted of supervised endurance training and 117 were HIOST. During each session, the peak exercise heart rate was determined from the electrocardiogram. Peak blood pressure was recorded a total of 73 times during HIOST, and the resulting rate-pressure product values were calculated (see the Table).

None of the patients had to stop training because of adverse arrhythmias or symptoms. Peak heart rates were likely blunted by beta-blocker therapy, but all six patients were able to perform firefighting tasks that mirrored the 12-MET activities from the prior study. During exercise, their peak blood pressures remained well below 240/110 mm Hg, the limit recommended by established guidelines (8), and their rate-pressure product values were below the 36,000 threshold (9).

DISCUSSION

The American College of Sports Medicine endorses using specificity of training for cardiac patients who desire to return to manual labor occupations (10). To our knowledge, this is the first report of firefighters’ ability to perform occupation-specific tasks following successful coronary revascularization.

The HIOST program has limitations. Because the CR setting lacks the danger and stress of actual fire suppression activities, the patients’ physiological responses during training may not reflect their responses on the job at a fire scene. In addition, the program cannot simulate many of the hazardous work conditions that firefighters must face, including exposure to smoke, carbon monoxide, fumes, and other chemicals (11); heat stress (12); and high noise levels (13).

Despite these limitations, HIOST allows patients to perform simulated firefighting tasks while their electrocardiogram, blood pressure, and heart rate are monitored in a clinical setting, providing information about exercise-induced angina, ischemia, and arrhythmias over multiple sessions. For physicians who must make decisions about return to work, these findings might be more thorough and conclusive than the information gained during a single treadmill exercise stress test.

Acknowledgments

Grant support was provided by the Harry S. Moss Heart Trust and the Baylor Health Care System Foundation, Dallas, Texas, through the Cardiovascular Research Review Committee and in cooperation with the Baylor Heart and Vascular Institute. The authors thank the committee for their continued support of cardiovascular rehabilitation research projects. Beverly Peters, MA, ELS, a freelance medical editor, assisted with manuscript development and preparation.

Table.

Clinical characteristics of six male firefighters and the data from their high-intensity, occupation-specific training (HIOST) sessions after coronary revascularization

								Peak values during HIOST (mean ± SD)†
						No. of sessions
Pt. no. (age, y)	EF (%)	BMI (kg/m)	Additional cardiac risk factors∗	MI	Type of revasc.	Total	HIOST	HR (bpm)	SBP (mm Hg)	DBP (mm Hg)	RPP‡
1 (61)	65	32.4	DM, FHx, PI, STR	−	PCI	24	21	140 ± 13	174 ±17	84 ± 9	23,432 ± 3515
2 (54)	50	35.1	PI, SM, STR	−	CABG	34	26	147 ± 5	143 ± 12	68 ± 10	21,220 ± 1844
3 (48)	50	28.2	−	+	PCI	28	20	142 ± 13	168 ± 28	83 ± 14	24,160 ± 4879
4 (58)	55	26.3	FHx, PI, STR	+	PCI, CABG	24	20	141 ± 9	163 ± 31	69 ± 8	22,767 ± 4793
5 (51)	50	25.3	FHx	−	PCI, CABG	25	15	139 ± 8	167 ± 24	85 ± 8	23,494 ± 4368
6 (52)	NA	31.1	−	−	PCI	18	15	149 ± 9	202 ± 12	88 ± 10	29,958 ± 2744

^∗Other than hypertension and hyperlipidemia (present in all six patients) and obesity (see BMI).

^†Peak heart rate recorded every session; peak blood pressure recorded a total of 73 times.

^‡Calculated for sessions during which peak heart rate and blood pressure were recorded.

BMI indicates body mass index; CABG, coronary artery bypass graft surgery; DBP, diastolic blood pressure; DM, diabetes mellitus; EF, ejection fraction; FHx, family history; HR, heart rate; MI, myocardial infarction; NA, not available (pending follow-up); PCI, percutaneous coronary intervention; PI, physical inactivity; RPP, rate-pressure product (heart rate × systolic blood pressure); SBP, systolic blood pressure; SM, smoking; STR, stress.