Both hot and cold environments trigger a stress response in the human body and can lead to cardiovascular problems. Physiologist Justin Lawley from the Department of Sport Sciences at the University of Innsbruck and colleagues recently investigated both factors in scientific studies. Results published in journals Scientific Reports and Experimental PhysiologyIt is particularly interesting in light of the current multiple global crises.
The climate and energy crises are one of the greatest challenges of our time and have a direct physical impact on people’s health. The climate crisis, for example, is causing more frequent, longer and more intense heatwaves, causing more deaths than natural disasters. Moreover, the energy crisis is causing energy costs to rise, forcing many households to heat their homes less or not at all.
Physiological responses to a simulated heat wave and cold ambient temperatures have now been investigated by Justin Lawley in two studies with his research group, the Laboratory of Exercise and Environmental Physiology and international scientists – the focus was the cardiovascular system. “In both studies, we replicated the real-world environmental temperatures the body could be exposed to and were able to demonstrate physiological responses that could help explain the known seasonal variations in cardiovascular deaths,” Lawley explains.
As part of the Horizon 2020 Heat Shield project, Lawley’s group collaborated with colleagues from Slovenia to examine how heat waves affect the health of industrial workers. Seven male participants spent nine consecutive regular workdays in a controlled laboratory environment.
In the first and last three days, normal summer temperatures for Central European conditions ranged from 25.1 to 25.7 degrees during work and between 21.8 and 22.8 degrees during rest periods. The fourth to sixth days represented the heatwave; During this time, the researchers established ambient temperatures between 35.2 and 35.8 degrees Celsius during study periods and between 25.5 and 27.1 degrees Celsius during rest periods, including nighttime sleep. Throughout the entire study, participants completed daily tasks to simulate typical industrial jobs.
“In this study, we used a protocol simulating current heat wave conditions along with orthostatic stress, which implies a change in posture, to determine cardiovascular and thermoregulatory stress in industrial workers,” explains Lawley. The results show that even relatively mild heat waves cause an increase in core and skin temperatures and an increase in skin blood flow. While these physiological reactions prevent the body from overheating at rest, while standing, the body now has to both maintain core temperature and maintain blood pressure to prevent fainting, which puts extra strain on the cardiovascular system.
Interestingly, many of these reactions continued after the heatwave ended, suggesting that the heatwave had a residual effect. “These responses reflect the stress on the cardiovascular system that industry workers face during heat waves, which can lead to heat sickness, fainting, and even potentially death from accidents or serious medical complications in people with underlying cardiovascular disease,” Lawley said.
In another study, Lawley, together with a team of eleven researchers, examined the effect of mild cold exposure on the cardiovascular system, with a particular focus on which mechanisms are responsible for the increase in blood pressure. In addition to researchers from Innsbruck, scientists from Great Britain and Canada were also involved.
It was aimed to investigate whether the increase in vascular resistance (i.e. vasoconstriction) was due to a change in blood flow in skeletal muscles or just the skin, since it is important to prevent the rise of blood pressure in cold. In a lab at the University of Innsbruck’s Department of Sport Sciences, researchers cooled 34 subjects’ skin temperatures from the normal 32 to 34 degrees Celsius to about 27 degrees Celsius by ten degrees of cold air—once the entire body was cooled, and in the other, only the face was cooled.
“We observed that when the entire surface of the body is cooled, blood pressure increases mainly due to the increase in the vascular resistance of the skin, but there is also a slight reflex increase in the resistance of the blood vessels in the skeletal muscle. We’ve seen a similar increase,” explains Lawley.
Thus, the team were able to show that the mechanism(s) responsible for the increase in blood pressure during cold exposure depended on which parts of the body were cold. These data are important for educating the public about preventing the potential negative consequences of cold exposure because contrary to the perception of many, cold is more dangerous for the body than heat.
“As you might think, sub-zero temperatures don’t have to cause serious reactions in the body, which will become commonplace for many people who cannot heat their homes during an energy crisis. People often know how to dress thickly. With clothes that protect their body, arms and legs, face even in a mild ambient temperature of ten degrees. we were able to show that protection is equally important,” Lawley continues.
Both studies show that climatic conditions can have extreme effects on our cardiovascular system. Although the negative health dimensions triggered by heat waves will increase due to the climate crisis, it is particularly surprising that even cold temperatures of around 10 degrees can have significant negative effects on our cardiovascular system, even in the young people who participate in these studies. Future studies that extend these findings to our aging population and those with pre-existing medical conditions will certainly help reduce the risk of these new environmental challenges.