What is hyperthermia? It is an abnormally high body temperature. The average body temperature is between 36.5 ˚C and 37.5 ˚C. Under 35 ˚C and you have hypothermia. Between 37.5 ˚C and 38.3 ˚C you have fever. Over 38.3 ˚C, you have hyperthermia.
Our body has various systems to keep us cool. All of these methods are controlled by the hypothalamus, which monitors body temperature. We naturally lose heat from our body to the surrounding air. However, if the air temperature is higher than our body temperature, this won’t be enough to pull heat out and our body has to cool itself. This generally happens through sweating and vasodilation. The central nervous system tells the hypothalamus that the body is too hot. The hypothalamus instructs the body to start sweating. Sweating helps us lose heat in two ways. Firstly, the sweat pulls heat out of our body as it leaves the pores. Secondly, when this heat evaporates on the skin, the heat energy goes up and cooler air rushes in to fill the gap. The cool air that rushes in is able to pick up more heat energy and the process repeats. This is called convection. The hypothalamus also orders the blood vessels near the skin to dilate. This brings more blood close to the skin, allowing the heat in the blood to be pulled out into the air.
We start to have problems when we can’t lose heat fast enough. If the body absorbs more heat than it can get rid of, it can be fatal. It should be noted that hyperthermia is different to fever because a fever is caused by the hypothalamus raising the body’s base temperature to make the body warm itself up and cook any viral or bacterial infections. In hyperthermia, the base body temperature stays the same. Hyperthermia can be caused by excessively humid weather because the body cannot lose heat to the air, or by exertion in hot weather because the body produces a lot of heat.
Hyperthermia has several stages. The first stage is heat stress. The body becomes uncomfortably hot and people can get headaches and nauseous. The person will feel very thirsty. At this stage, the hyperthermia is easily reversed by getting the person out of the heat. If the person cannot get out of the heat then the next stage is heat fatigue, which can bring confusion and dizziness. This is caused because the body dilates the veins to get as much blood close to the skin as possible, lowering blood pressure and reducing the amount of blood that reaches the brain.
Heat cramps, heat oedema, and heat rashes are the next stage of hyperthermia. A heat rash is caused when the sweat pores become blocked by excessive sweat that cannot evaporate off the body. This can be itchy, but it has a worse effect because it prevents the body from being able to sweat, worsening the hyperthermia. Heat oedema and heat cramps are connected. The rising heat causes the blood pressure to fall. The kidneys respond to this by reabsorbing salt into the blood. This does two things. The first is that a lack of salt in the muscles will cause them to cramp, which are heat cramps. The second thing is that it causes fluid to build up in the extremities of the body, which is heat oedema. Everything can still be reversed here, if the person can be cooled down.
The next stage is heat exhaustion. The person has become dehydrated because they have been sweating for so long and their blood pressure is very low. They will have cool and pale skin, and they may start to shiver because the hypothalamus cannot control the body’s response to heat anymore. The person may feel cold. The pulse will be very fast because the blood pressure is low, and the heart is working hard to pump blood to the brain. The person will be dizzy and confused.
The last stage is heat stroke, which requires immediate medical attention. Heat stroke is diagnosed when a person has an internal temperature of over 40 ˚C. The blood pressure is so low at this point that the heart has to work very hard to keep the blood pumping. A person with heat stroke will be breathing very fast to try to oxygenate their blood. They will probably have trouble staying conscious. Survival rates from heat stroke are directly related to how long someone spends at this temperature. A hospital can cool them down quickly and improve survival rates. If the person cannot be cooled down, the situation can become fatal. There are four areas that can cause damage or death. The first is in the organs. The body prioritizes the lungs and brain over other organs, reducing their blood supply and switching them off. This can result in permanent organ damage. The second is in the intestines. When the internal temperature gets too high, the digestive enzymes start to digest the intestines, allowing bacteria out into the body, causing sepsis. The third is in the brain. The blood brain barrier breaks down at this temperature and proteins and ions can build up in the brain, causing inflation and killing brain cells. The fourth place is the heart. It can only pump at high speed for so long before it shuts down.
The faster someone can be cooled down, the more chance they have of survival. And this is what I learned today.
Photo by Jean Frenna: https://www.pexels.com/photo/coconut-trees-on-brown-sand-1045113/
Sources
https://my.clevelandclinic.org/health/diseases/22111-hyperthermia
https://en.wikipedia.org/wiki/Hyperthermia
https://www.cancer.gov/about-cancer/treatment/types/hyperthermia
https://www.energy.gov/energysaver/principles-heating-and-cooling
https://newsinhealth.nih.gov/2013/07/stay-cool
https://www.vinmec.com/en/news/health-news/healthy-lifestyle/how-does-the-body-cool-itself/
https://www.physio-pedia.com/Hyperthermia
https://www.mymed.com/diseases-conditions/hyperthermia/what-are-the-phases-and-signs-of-hyperthermia
https://www.mayoclinic.org/diseases-conditions/heat-rash/symptoms-causes/syc-20373276
https://www.sciencedirect.com/science/article/abs/pii/S0736467919307395