Heat stroke: a risk during the summer to be taken seriously

The sharp rise in temperatures in 2003 and the phenomenon of heatstroke that followed caused 70,000 deaths in Europe. This year again, the summer heat will be significant. It is better to fully understand the mechanism of heat stroke and protect yourself well, especially for the elderly.

The body reacts very quickly to any increase in temperature: an increase of only 10°C in blood temperature is detected by specific receptors which activate the thermoregulation center located in the hypothalamus of the brain and generate two main phenomena:

– vasodilation of the blood vessels to convey a greater quantity of warm blood to the surface of the body, up to 8 liters per minute, so as to favor the dissipation of heat towards the external environment.

– activation of the sweating process which allows heat to be dissipated by evaporation of sweat. If the air surrounding the surface of the body is dry, sweat is vaporized and can dissipate up to 600 kcal of heat per hour.

When the air is laden with humidity, on the other hand, the heat gradient is disturbed and evaporation is not as efficient, which is why we feel the heat more intensely in humid weather.

2003 heatstroke: 70,000 deaths in Europe

Heat stroke is clinically defined as a body temperature above 40°C, accompanied by dry, hot skin and central nervous system abnormalities, such as delirium, seizures or coma. These heat strokes can be caused by exposure to a very high temperature or even following a very high intensity effort; in both cases, the high heat exceeds the body’s ability to maintain its normal temperature (37°C) through the process of thermoregulation. These heat strokes are extremely dangerous, as evidenced by the 70,000 deaths that occurred during the heat wave that affected Europe in 2003, and the 10,000 deaths caused by the one that affected Russia in 2010.

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Heat Stroke: A Five-Step Process

A recent synthesis of the knowledge acquired on the mechanisms responsible for heat stroke provides a better understanding of the mechanisms involved in this increase in mortality associated with extreme heat waves. By analyzing all the available data, the authors identified 5 main mechanisms that disrupt the functioning of 7 main organs and which, collectively, are responsible for the mortality associated with heatstroke:

– Ischemia: the massive redistribution of blood to the surface of the body means that the internal organs are not sufficiently irrigated (what is called ischemia) and see their function disturbed by a lack of oxygen.

– Heat shock toxicity: the high temperature causes the production of several stress proteins and free radicals that damage the cells. In addition to disrupting the function of the affected organs, the breakdown of cells increases the permeability of organs to pathogens and toxins.

– Inflammation: In the intestine, the erosion of the mucosa caused by heat shock and ischemia promotes the infiltration of pathogens into the blood and the development of a systemic inflammatory response that damages the organs (sepsis) .

– Coagulation: Another damage of this systemic inflammation is the exaggerated activation of the coagulation system, which causes the formation of clots that can block the arrival of blood to the organs.

– Rhabdomyolysis: Ischemia and thermal shock can also lead to the disintegration of muscle fibers, releasing myoglobin which is very toxic to the kidneys.

In all, there are therefore 27 patho-physiological phenomena which are responsible, alone or in combination, for the enormous damage caused by heatstroke on the human body.

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Older people: those most at risk

Older people are particularly at risk of heatstroke due to poorer physiological adaptation to high temperatures. For example, while cardiac output increases considerably in young adults exposed to intense heat (to promote surface heat diffusion), this increase is half as low in the elderly. They also secrete 20-30% less sweat than younger people, which makes adaptation to high heat more difficult. This decrease in the amount of sweat also means that electric fans, which cool by increasing the evaporation of sweat, are less effective in the elderly.

Public health organizations generally recommend that these people, as well as those who are ill, avoid unnecessary exposure to the sun on very hot days and, above all, stay well hydrated: in very hot weather, the loss of water through sweating can reach up to 2 liters or more per hour and must absolutely be compensated by adequate hydration


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