Why is heat stress so dangerous?
When we are active in hot conditions, our bodies work to maintain body temperatures within a narrow range, generally around 37 degrees Celsius. This can be achieved through behavioural changes such as seeking shade, drinking water, or through the body's natural physiological processes.
We mostly dissipate heat from our bodies via sweating which then evaporates, taking heat with it. Some heat is also lost through conduction when you touch cool objects, and some is lost through radiation into cooler air or water.
In healthy individuals, this process generally works well in a range of environments.
However, for vulnerable populations, particularly the very old and the very young, thermoregulation may be difficult.
Other people at risk are firefighters and some athletes. Both groups – American footballers especially – wear heavy, impermeable clothing, which limits their ability to dissipate heat through sweating and evaporation. As a result, when they perform intense physical activity in hot conditions, there is greatly increased risk of fatal complications.
When the hypothalamus, the body's "thermostat" located in the brain, senses increasing skin temperatures, it triggers a range of physiological processes to achieve cooling.
Primarily, the body aims to shunt blood from the core of the body to the skin where it can be cooled, and then return the cooler blood to the vital organs.
This process, referred to as vasodilation, greatly increases the heart rate.
As temperatures rise during exercise, the heart rate must increase in order to move more blood in an effort to halt rising temperatures while delivering oxygen to working muscles. This raises the risk of heart attacks in vulnerable populations.
When temperatures reach critical levels, individuals will also begin to show symptoms of central and peripheral nervous system dysfunction, which if unchecked can result in heat stroke, a potentially fatal condition. Critical body temperatures are generally above 40 degrees Celsius, although this may be lower or higher.
Heat stress can become a life threatening situation, so you must act early. Symptoms include high body temperature; red, hot, dry skin (sweating has stopped); a rapid pulse; headaches, dizziness, and nausea.
Response by: Dr Anthony Walker, Thermal Physiologist, University of Canberra Research Institute for Sport and Exercise
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