Firefighting Affects Cardiac System
|Tuesday, 06 September 2011|
Source: University of Illinois
Firefighting causes stiff arteries and “cardiac fatigue,” conditions also found in weightlifters and endurance athletes, according to two recent studies by researchers at the Illinois Fire Service Institute (IFSI), located at the University of Illinois.
The researchers found that three hours of firefighting activity caused acute increases in arterial stiffness and impaired cardiac functioning in young, apparently healthy male firefighters. The study, which was published recently in the journal Vascular Medicine, is believed to be the first study to examine arterial stiffness and blood flow after fire-suppression activities.
“These changes appear to be similar to what is observed after maximal aerobic and/or heavy resistance exercise and are likely due to a combination of thermal, metabolic, and psychological stresses that occur during fire-suppression activities,” wrote study authors Gavin Horn, the director of research at IFSI, and Bo Fernhall, a professor in the department of kinesiology and community health in the University of Illinois College of Applied Health Sciences.
The 69 firefighters who participated in the study were in active service and had been medically cleared by their home departments to participate in live-fire activities, although many were overweight, as assessed by body mass index. The participants, all male, ranged in age from 19-48, with an average age of 29.
“It was a representative cross-section of the firefighters who would be in the line doing the firefighting activities, although relatively young,” Horn said.
Wearing full firefighting gear, the participants engaged in typical fire suppression activities – advancing hose, forcing doors open, extinguishing a fire – at IFSI’s training facility. They engaged in four or five activity periods, which lasted 15-25 minutes each, with several 10-15 minute rest periods in between to hydrate and cool themselves.
Shortly before and afterward, researchers measured various cardiovascular functions, including heart rate; brachial, carotid, and aortic blood pressures; blood flow in their forearms; and arterial stiffness and thickness. Firefighters’ body temperatures were measured using a monitor and a small disposable sensor capsule that they ingested the night before the test.
About one hour before the pre-firefighting data collection, the participants consumed a standardized meal and a 2-gram Vitamin C capsule or a placebo so researchers could investigate whether the supplement improved arterial function, mitigating the risk of cardiovascular events, as prior studies suggested. The Vitamin C supplements did not appear to affect any of the outcomes, however.
“We found that their arteries changed with firefighting, becoming stiff afterward,” Fernhall said. “Usually a stiff artery is associated with an increase in inflammation and blood pressure, but we didn’t find any increase in either of those.”
Surprisingly, participants’ endothelial function – blood flow as controlled by the inner lining of blood vessels – improved after the firefighting exercise. Similar effects – improved endothelial function and arterial stiffness – are often seen in athletes after heavy weight training or resistance exercise.
“Firefighters do a lot of resistance-type exercise when they’re fighting a fire – handling heavy equipment, doing forcible entry, and other tasks that increase blood flow in their arms, which is where we measured endothelial functioning,” Fernhall said. “However, the arterial stiffening is not a response that we would expect. Whether the results increase the risk of a firefighter having a heart attack or stroke, we don’t know.”
In a related study, using ultrasound and Tissue Doppler Imaging, the researchers found that heart function – its stroke volume, or the amount of blood pumped with each beat; and its diastolic function, its ability to relax between beats – deteriorated after firefighting, a condition called “cardiac fatigue,” which has been documented in athletes who participate in marathons and other endurance sports.
“There’s no question that heart function did deteriorate, according to the measures,” but it is difficult to draw any conclusions because participants’ cardiac loading conditions could not be standardized, Fernhall said.
Almost 75 percent of U.S. firefighters are volunteers, not career firefighters. And, like the average American, many exhibit several of the risk factors for cardiovascular disease, including being overweight and having elevated blood pressure and/or cholesterol. Multiple stressors are inflicted on the body simultaneously during firefighting – heat stress exacerbated by heavy gear that doesn’t allow the body to cool, acute periods of aerobic and resistance exercise, and activation of the “fight or flight” response of the sympathetic nervous system, Horn said.
“If you have a person with a vulnerable heart, that could potentially (cause a problem),” Fernhall said.
While endurance athletes train for months before races, volunteer firefighters may not be in peak condition and physically prepared for the strain of fighting a fire.
About 45 firefighters die each year in the U.S. from heart attacks or strokes while on duty. (That represents about half the on-duty firefighter fatalities nationwide annually.) The triggers of these sudden deaths are unknown, and they are often attributed to overexertion. The potential mechanisms must continue to be studied so that interventions can be developed, Horn said.
The Department of Homeland Security Assistance to Firefighters Grant provided funding for the research.
Fernhall also is affiliated with the Exercise and Cardiovascular Research Laboratory.