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Scientists have been testing how heat affects our hearts for years. But here's the thing: the most commonly used method might not provide much insight into what happens to the heart during heat waves.

A new study led by the , with researchers from the �°������ϲʿ���, , , and the , has revealed critical insights into how we test extreme heat’s impact on heart function. 

With rising global temperatures, understanding these effects is crucial for protecting public health, especially during heat waves.

The research, published in , analysed data from over 400 laboratory studies involving more than 6,800 participants. It highlights how different heating methods affect the heart’s performance under heat stress. 

Co-author, Dr Joe Costello from the �°������ϲʿ���’s Extreme Environments Laboratories, said: “It is well established that prolonged heat stress causes various cardiovascular issues in humans. With global temperatures and the incidences of heat waves rising, this poses a great concern; particularly for individuals and locations most vulnerable to heat stress. 

“This extremely large study highlights that there is an urgent need to develop and refine empirical physiological models in both laboratories and natural settings. These models can then be used to facilitate and inform urgently required heat-health action plans and policies.”

, who was a postdoctoral fellow at  and lead author of the study, added: "Our study shows that exposure to encapsulated heating methods, like water-perfused suits or hot water immersion, can lead to significantly increased heart rates, blood pressures, and cardiac strain when compared to natural heat exposures, like those experienced during hot weather.”

When exposed to heat, the body may struggle to function normally, potentially resulting in serious cardiovascular issues. To cool down, the body increases blood flow to the skin, leading to higher heart rates and increased cardiac workloads. The resultant increase in strain on the heart can pose a significant risk for vulnerable groups, including older adults and individuals with pre-existing heart conditions.

The study revealed that the most common heating method, suits that perfuse large volumes of hot water directly over the skin, may result in rapid overheating and exacerbated increases in cardiac strain. 

In contrast, participants exposed to climate-controlled environments simulating hot weather or heat waves exhibited distinct cardiac responses that are more applicable to real-life scenarios. 

The research offers vital data that can be used to design that will more easily translate to the real world to enhance public health strategies.

The scientists behind the study hope their findings will influence how health agencies develop strategies to protect people during extreme heat events. They are now heading back to the drawing board, ready to figure out what really happens when the mercury rises - not in the lab, but in the real world where it matters most.

, a full professor of physiology at and Director of the Human and Environmental Physiology Research Unit, emphasised the importance of these findings: “As temperatures continue to rise, we need to understand how heat affects heart health. This research helps us address the physiological challenges posed by heat and will inform how we protect individuals during extreme weather events."

The �°������ϲʿ���’s Extreme Environments Laboratories (EEL) support areas such as sport, product development, emergency rescue, military training, polar exploration, and film and TV production.

Researchers regularly collaborate with external organisations for research and training, including the Ministry of Defence, the Royal Society for the Prevention of Accidents, the Royal National Lifeboat Institution (RNLI), and Olympic and Paralympic athletes.

Find out more about �°������ϲʿ���’s EEL here.