- Exposure to extreme heat and physical exertion during firefighting brings about changes in physiological measures of cardiovascular function.
- This exposure to heat causes fluctuations in blood pressure, body temperature and hemoglobin levels.
- Blood clotting also occurs as an exaggerated normal physiological reaction to both these stressors.
Cardiovascular events are the leading cause of death among firefighters and are responsible for roughly 45% of on-duty firefighter fatalities annually in the United States.
"These harsh conditions can cause injury to the heart muscle in healthy firefighters and may explain the link between fire suppression and risk of heart attacks," said Nicholas Mills, M.D., Ph.D., lead researcher and chair of cardiology and consultant cardiologist at the University of Edinburgh in Scotland.
For the study, 19 nonsmoking, healthy firefighters were randomly selected from the Scottish Fire and Rescue Service.
Seventeen participated in two fire simulation exercises, each a week apart.
They had to retrieve a 'victim' (weighing roughly 176 pounds) from a two-story structure and the exercise exposed participants to temperatures reaching upward of 400 degrees Celsius (752°F).
Their heart rate and blood pressure were monitored for 30 minutes before the exercises and for 24 hours following it.
"The firefighters wore heart monitors that continuously assessed their heart rate, heart rhythm and the strength and timing of electrical impulses passing through each part of the heart. We analyzed these to look for evidence of heart strain that might signify a lack of blood being delivered to the heart muscle," Mills said.
The findings showed:
- a drop in blood pressure due to dehydration or diversion of blood to skin to help cool the body
- increase in core body temperature
- increase in hemoglobin level due to loss of water from blood
"Lower blood pressure immediately following fire suppression is likely due to dehydration and an increase in blood being diverted to the skin to help the body cool down. We discovered the core body temperature increased, on average, nearly 2 degrees Fahrenheit over 20 minutes. And increases in hemoglobin occur as the body loses water and the blood gets more concentrated," Mills said.
The results highlight the unique stress to the cardiovascular system faced by firefighters.
The findings also suggest that people working in extremely high temperatures should stay well hydrated and allow time to cool down afterward.
"This new study should encourage practitioners to aggressively evaluate and treat firefighters for cardiovascular disease risk factors, and when indicated, perform additional studies - such as exercise stress testing, coronary artery calcium scans or echocardiography-- to detect atherosclerosis or cardiac enlargement," said Stefanos N. Kales M.D., M.P.H., associate professor, Harvard Medical School & Harvard School of Public Health, The Cambridge Health Alliance - Occupational Medicine in Cambridge, Massachusetts.
The findings are published in the American Heart Association's journal Circulation.
- Nicholas Mills et al. Fire Simulation and Cardiovascular Health in Firefighters. Circulation; (2017) doi.org/10.1161/CIRCULATIONAHA.116.025711