The study from researchers at the University of Edinburgh, and published today in the journal Circulation, may explain why cardiovascular events - such as heart attacks - are the leading cause of death amongst on-duty firefighters.
As a result, the researchers are now calling on fire services to help to reduce the number of firefighters suffering from heart attacks by limiting the time each individual spends tackling a blaze, as well as helping them to cool down and rehydrate after exposure.
Nineteen non-smoking, healthy firefighters were randomly selected from the Scottish Fire and Rescue Service to participate in two exercises at least a week apart, including a fire simulation and a control exposure. The fire simulation exposed seventeen of the participants to extremely high temperatures, resulting in an average increase in core body temperature of 1 degree Celsius amongst participants as they attempted a mock rescue from a two-story structure.
The firefighters wore heart monitors that continuously assessed their heart rate and electrocardiogram (ECG). Researchers assessed these for evidence of strain on the heart that might be a sign of a lack of oxygen being delivered to the heart muscle. Blood samples were also taken before and after exposures took place, including measurement of a protein called troponin that is released from the heart muscle when it is damaged.
Core body temperatures remained high for three to four hours following the fire simulation. The researchers used sophisticated techniques to measure blood vessel function and blood clotting and discovered that firefighters’ blood vessels failed to relax in response to medication. Their blood also became stickier and was over 66 percent more likely to form potentially harmful clots after the fire simulation.
The research team believe that this increase in clotting was caused by a combination of fluid losses in sweat and an inflammatory response to the fire simulation, which resulted in the blood becoming more concentrated and thus more likely to clot. The researchers also showed that exposure to fire simulation causes minor injury to the heart muscle in healthy firefighters.
The study’s findings are not directly applicable to the public; however, the combination of heavy physical exertion, high ambient temperatures and air pollution can present an increased risk in everyday life. As such, the researchers recommend that anyone who is exercising in high ambient temperatures should take regular breaks, keep well hydrated and allow time to cool down afterwards.
Professor Nick Mills, BHF Senior Clinical Research Fellow at the University of Edinburgh, who led the research, said: “Studies from the USA have shown that nearly half of all firefighters who die on duty are killed by heart disease.
“Our study has shown a direct link between the heat and physical activity levels encountered by firefighters during the course of their duties and their risk of suffering a heart attack.
“However, we’ve also found that there are simple measures, such as staying well hydrated, that firefighters can take to reduce this risk.”
Dr Mike Knapton, Associate Medical Director at the British Heart Foundation, said: “Firefighters routinely risk their lives to save members of the public. The least we can do is make sure we are protecting their hearts during the course of their duties.
“It’s essential that firefighters are aware of this risk and take simple steps such as taking time to cool down and rehydrate after tackling a blaze. It’s also important for them to be aware of the early warning signs of a heart attack so that, if the worst should happen, they can receive medical attention as soon as possible.
“Most of us will never experience the scorching heat of a blazing inferno, but it’s still good general health advice to drink plenty of fluid and take breaks if you’re working up a sweat in high temperatures.”