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 Heart attacks are the most common cause of death among on-duty
firefighters, and they are much more likely to occur during or
shortly after work to subdue a fire, said senior study author
Nicholas Mills of the British Heart Foundation Center for
Cardiovascular Sciences and the University of Edinburgh.
“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 said by email.
Heart attacks occur when an artery leading to the heart becomes
blocked, stopping the flow of blood to the muscle and damaging it.
To assess the heart attack risk tied to intense heat and exertion,
researchers randomly selected 19 non-smoking, healthy firefighters
from the Scottish Fire and Rescue Service to participate in two fire
simulation exercises two weeks apart.
During these exercises, participants attempted to rescue a dummy
victim weighing 176 pounds from a two-story structure as
temperatures reached upwards of 400 degrees Celsius (752 degrees
Fahrenheit).
Each time, participants wore heart rate and blood pressure monitors
starting 30 minutes before the exercises and for 24 hours afterwards
to see what changes might happen in the body to make a heart attack
more likely.
The monitors continuously assessed heart rate, heart rhythm and the
strength and timing of electrical impulses passing through each part
of the heart.
Firefighters’ core body temperatures increased about 2 degrees
Fahrenheit on average during the simulation exercises and remained
high for three to four hours afterwards, researchers report in
Circulation.
Participants had lower blood pressure immediately following the
exercises, which researchers suspect is due to dehydration and
increased blood flow to the skin to help the body cool down.
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In addition, the blood became stickier and more likely to form
clots, the experiment found. This probably happened due to a
combination of fluid loss from sweating and an inflammatory response
to heat that made the blood become more concentrated and more likely
to clot, the researchers conclude.
Blood vessels also didn’t relax properly even when the firefighters
took medication.
Beyond its small size, other limitations of the study include the
possibility that firefighters might encounter other stressors on the
heart in real life that weren’t present in the simulations, such as
smoke or psychological stress, the authors note. All of the
firefighters in the experiment had previously done training
exercises at the same simulation center, which might also cut down
on stress during the experiment.
Even so, the findings confirmed previous research on the heart
attack risk faced by firefighters and offered fresh evidence of how
this work might lead to heart muscle damage even in otherwise
healthy firefighters, said Dr. Stefanos Kales a researcher at
Harvard Medical School and author of an accompanying editorial.
“It is very rare and unusual for a healthy person without heart
disease to have a heart attack even under such extreme conditions,”
Kales said by email. “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.”
SOURCE: http://bit.ly/2oEWRr6 and http://bit.ly/2nFY802 Circulation,
online April 3, 2017.
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