Before we hit the button on a fan, turn on the air conditioner, or fan ourselves with air to cool off, our bodies are already ready to escape the dangers that threaten us with these increasingly frequent heatwaves.
Our body’s ability to maintain constant levels of various parameters is called homeostasis, and within this, thermoregulation (our normal body temperature ranges from 36.5-37⁰C) is most disturbed during episodes of extreme heat above 40⁰C. Thus, our body is forced to work harder to avoid a rise in temperature that compromises vital functions.
What is happening in our body?
Faced with stress caused by excessive heat, the human body must cool down. It attempts to do this through two mechanisms:
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First, it redistributes blood flow, increasing it in the skin by dilating blood vessels, which improves heat transfer from the muscles to the skin and from the skin to the outside.
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You then sweat because the evaporating sweat removes the internal heat.
These physiological responses are necessary to limit the increase in core temperature, but they can affect people differently depending on age. Even worse, they are aggravated by the presence of other diseases or by taking certain drugs with subsequent negative effects on the body.
Ebi, K.L. et al. k. (2021). Adapted and translated by M. Jimenez.
oh my heart
The redistribution and increased blood flow to the skin due to vasodilation increases cardiac demand and reduces the filling pressure of the heart.
This means that our heart has to work harder and faster, which requires more oxygen in the coronary tissue. In people with pre-existing heart disease, this extra need can lead to cardiac ischemia (impaired blood supply), heart attack, and ultimately cardiovascular collapse.
Various studies have shown that cardiovascular disease is the leading cause of death during heat waves. And with almost half a billion people affected worldwide, any densely populated area hit by extreme heat will be at risk of increased mortality from a combination of both.
We must drink when we sweat
Evaporation of sweat leads to cooling of our body. But it also means that when water is lost, blood volume decreases, putting the cardiovascular system at risk. In addition, there is a risk of kidney damage and even acute renal failure.
That is why it is so necessary to fill the deficit of water in our body and avoid the consequences of dehydration.
heatstroke
If our ability to thermoregulate fails, overheating can lead to heat stroke, which will have long-term consequences due to damage to the central nervous system. It can even be fatal if not treated on time.
Early symptoms of dizziness, confusion, and seizures indicate dysfunction, which may be associated with a possible combination of cerebral edema, cerebral ischemia, and metabolic disorders.
If a lack of blood supply or ischemia persists after redistribution of blood, damage to cells, tissues, or organs may occur. In particular, the brain, heart, kidneys, intestines, liver and lungs are most at risk.
Heat damage to the lungs is exacerbated by even more pressure on the lungs due to hyperventilation, which is directly related to the increase in temperature. If we add in the increase in air pollution during heat waves, we find ourselves in second place in mortality and morbidity during these periods.
What about our defense system?
It turns out that the heat also affects the functioning of the immune system. It must be borne in mind that the innate immune system is activated by signs of tissue damage, that is, the possible consequences of infection with a pathogen that we do not remember.
In addition, our immune system prioritizes, and its response to a threat (what it considers so dangerous that it could end our lives in a short time) makes it forget about any other threat that it considers a non-priority, such as a cold, flu, or even cancer. All these reactions are stopped during the struggle with the impending danger.
Much of the research into how the immune system responds to extreme heat has come from animal experiments – anyone looking for human volunteers to expose them to prolonged extreme heat! But they can be extrapolated to humans.
Fever protects us by raising our body temperature
The first concept that comes to mind when talking about fever and immunity is fever.
Fever is an increase in body temperature, but not as a result of the opposition of our immune system to the pathogen, but as a tool in this fight.
That is, an increase in body temperature is produced by changing the point of internal temperature, which is considered optimal. This is caused by immune cells that secrete substances such as interleukins, interferon, and tumor necrosis factor. Under these conditions, the immune system acquires optimal functionality to fight a pathogen that potentially threatens us with death.
As we saw earlier, fever is very different from heat stroke, where the body temperature rises due to external factors, but the internal temperature, marked as optimal, does not change.
Signaling Molecules: Literally Another Stomach Pain
Before the outside temperature rises, proteins are released into the bloodstream that we share with yeast and flies, called “heat stroke proteins” (Heat shock proteins or HSP). Its function is to protect other more sensitive proteins from possible conformational changes due to temperature rise that could affect their functionality. But, in addition, they have pro-inflammatory activity: they act like sirens warning the immune system of danger.
We have seen that, as a mechanism for reducing body temperature, blood moves to the outer capillaries to lower the temperature and does not reach the rest of the body sufficiently.
Changes in the intestinal mucosa occur in the abdominal cavity organs and, as a result, its porosity increases, bacterial residues that activate TLR receptors are released into the blood.Paid receptorsin English) in immune cells.
Ahmad, R. et al. (2022). Adapted and translated by M. Canelles.
At this point, our body acts just as if we had an acute infection: everything is focused on fighting the supposed (non-existent) pathogen. Intestinal tissue regeneration is suppressed and what was wrong worsens: lymphocytes react and multiply as if we had a bacterial infection in the blood (sepsis).
Give me warmth, but not much
Given this scenario, we’d better avoid extreme heat by taking measures that are in our hands. But not only the air conditioning control, fan button and fan: it is important to avoid prolonged exposure to high temperatures.
We must avoid working and exercising outdoors during the hottest hours and stop the global temperature increase that is troubling us, causing more and more frequent episodes that put our health at risk.
