Study links heat, exertion to heart attacks in healthy firefighters

A small experiment suggests physical exertion and exposure to extreme heat may put firefighters at an elevated risk for a heart attack, as the elements could trigger the formation of blood clots and prevent blood vessels from relaxing. To reach these conclusions, the study’s authors randomly selected 19 non-smoking, healthy firefighters from the Scottish Fire and rescue Service, Reuters reported.

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According to the study’s senior study author, Nicholas Mills, heart attacks are the most common cause of death among on-duty firefighters, with the potentially fatal cardiac event most likely to occur during or shortly after working to put out a fire.

“We found a direct link between the heat and physical activity levels encountered by firefighters during their duties and changes in blood clotting that would increase their risk of suffering a heart attack,” Mills, of the British Heart Foundation Center for Cardiovascular Sciences and the University of Edinburgh, told Reuters.

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Researchers observed the 19 firefighters attempt to rescue a dummy victim weight 176 pounds from a two-story structure as temperatures soared up to 752 degrees Fahrenheit, Reuters reported. They were outfitted with heart rate and blood pressure monitors for 30 minutes prior to the exercise as for 24 hours afterwards to measure what changes occurred in the body.

According to the Reuters report, firefighters’ core body temperatures increased about two degrees Fahrenheit on average during the simulation exercises, and remained high for three to four hours post rescue. Participants’ blood pressure also dropped immediately following the exercises, which researchers told Reuters was likely due to dehydration and the body’s mechanism to cool down.

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In the report published in Circulation, researchers also noted that participants’ blood became stickier and more likely to form clots, which was due to a combination of fluid loss from sweating and an inflammatory response to heat that made the blood become more likely to clot.

In addition to the study’s small size, authors noted other limitations such as the possibility that firefighters might encounter other stressors not replicated in the exercise like smoke or psychological stress.

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“It is very rare and unusual for a health person without heart disease to have a heart attack even under such extreme conditions,” Dr. Stefanos Kales, a researcher at Harvard Medical School who wrote an accompanying editorial, told Reuters. “However, a person who appears healthy, but who has unrecognized coronary blockages and/or heart enlargement could succumb to an acute cardiac event under these conditions.”

Reuters contributed to this report.