It is a certainty: the heat wave kills. The 2003 heat wave caused the death of 70,000 people in Europe, and more than 2,000 deaths were recorded in India during the 2010 heat wave when temperatures exceeded 47°C. But what exactly are the physiological mechanisms at work? There would actually exist not one, but 27 ways to die of heat!
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Our body is in principle capable of temporarily adapting to temperature variations thanks to a ” thermostat which triggers physiological defense mechanisms when the internal temperature deviates too much from normal. In humans, it ishypothalamusan area located at the base of the brain, which acts as a thermostat. But if the mechanisms triggered by this gland initially have a beneficial effect, after a while they cause deleterious effects on a good number oforgans. ” When the body temperature exceeds 40°C, the body reaches its self-regulation limits and the risk of losing control of temperature regulation is real “, warns Pieter Vancamp, researcher at the National Museum of Natural History (MNHN).
27 ways to die of hot
A University of Hawaii study identified 27 ways to die of heat, according to five mechanisms affecting seven organs. ” Dying of Hot is akin to a horror movie where you have to choose between 27 terrifying endings “, Reports Camilo Mora, the main author of the study. Because all the defense mechanisms put in place by the body to try to cool the body (sweatredirection of blood flow to peripheral organs to dissipate the heatinflammatory response…) end up racing and turning against ourselves, endangering several organs.
Heart and kidneys put to the test
The cardiovascular system is one of the first to be affected: blood pressure drops and the heart speeds up in an attempt to compensate for the lack of oxygen due to the displacement of blood circulation. This is why people with heart disease are among the first victims during heat waves. The kidneys are also put to the test by the dehydration : the hypothalamus produces a hormone antidiuretic to try to stop water loss, which increases the reabsorption of water and salts, and damages kidney tissue.
“Internal air conditioning” with perverse effects
Another organ put to the test: the brain. ” When overheated, the body increases the frequency of breathing, thereby cooling the blood going to and from the brainexplains Pieter Vancamp. This system, which can be considered as a air conditioner natural, however, has a negative effect: it increases the blood pH, due to the decrease in pressure in CO2which endangers the cellular functions of other organs “. Heat also disrupts communication between nerve cells and affects theintegrity of the’DNA and cell membranes.
When the machine is racing
For their part, theischemia and the cytotoxic attack (see box) lead to the rupture of the mucosa intestine and the release of heat-killed cell debris into the blood stream. This provokes a mechanism called the systemic inflammatory response: panicked, the immune system releases cytokines toxins that sustain theinflammation and accelerate cell destruction. An effect that is all the more deleterious as the walls of the tissues have become permeable to these toxins. The protein who control the coagulation become hyperactive, causing clots that cut off the blood supply to the brain, kidneys, liver and to lungs. At the same time, depletion of clotting factors can lead to fatal bleeding, even in the absence of injury. At this point, any activity physical (hiking, working outside, etc.) may cause the breakage of the skeletal muscles.
Hyperthermia, a vital emergency
To avoid reaching this point, it is necessary at all costs to cool the body when the first symptoms hyperthermia appear (red skin, headaches or stomach aches, pulse too weak or too fast, altered consciousness, etc.). When overheating is already advanced, cooling is no longer sufficient and emergency management is then required to treat each failure: re-oxygenation, dialysis, rebalancing of the debit blood, treatment of infectious complications…
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