Like all warm-blooded mammals, we humans need to get rid of the heat we generate with every chemical reaction in our bodies. Most animals, like dogs, get rid of heat by panting. Panting is actually a fairly bad way to get rid of heat because you cannot run and pant at the same time. So a dog can only run around for a short period of time before it overheats and has to stop to pant. Dogs make for bad endurance athletes.
But we humans are very good endurance athletes. We don’t pant. We sweat. We can run and sweat at the same time. Most four legged creatures can run faster than us for short periods of time. But we can run for longer and we can outlast them. It is suggested that early humans hunted, not so much by attacking their prey directly, but by persistently chasing them down and not giving them a chance to rest and pant. Eventually, not having enough time to cool down between sprints, the animals would collapse from heat exhaustion. Sweat helped early humans survive and compete in a hot African climate.
Admittedly sweat is not the only method by which we lose heat. The human body can lose some heat via the physical processes of radiation (direct loss of heat into the environment), convention (transfer of heat to air currents, this is why fans cool you down) or conduction (transfer of heat to a cooler object). The problem with these methods is that they require the surrounding environment to be colder than your internal body temperature. So, once the temperature exceeds 36 degrees Celcius, these no longer work.
When it gets hot, we need to sweat. But if it gets hot and humid we are in trouble. Humidity, a measure of water vapour in the air, must be low for sweat to evaporate and cause heat loss. Anything higher than 75% humidity and it stops working. A “dry heat,” yes there is such a thing, is more tolerable than a humid day because humidity blocks our best way to get rid of heat. When humidity goes up, it feels hotter, because we lose less heat from sweating.
The excess heat by itself has a direct impact on the human body. As body temperature rises, oxygen consumption and metabolic rate go up which puts greater demand on the heart to deliver oxygenated blood to the body tissues. To make matters worse, in order to maximize sweating and heat loss the body preferentially shunts blood to the skin away from the internal organs. While this helps in the short term, it further deprives key organs of blood and oxygen. Finally, if body temperature rises above 42 degree Celcius certain key enzymes stop working. Neurologic tissue seems particularly susceptible to the rise in temperature and patients suffering form hyperthermia can be confused, slur their speech, have trouble maintain their balance, and ultimately can lapse into a coma if it remains untreated. The dehydration that goes with excess sweating can cause a drop in blood pressure which negatively impacts both heart and kidneys. Eventually all organs can be affected.
For obvious reasons, patients with pre-existing medical conditions are more vulnerable to heat waves because their bodies are less able to adapt and compensate for the added strain. In particular older patients are at greater risk. As we age, we sweat less; so older patients are particularly vulnerable. Older patients also tend to lose their thirst reflex and so are more likely to become dehydrated without realizing it. They also may be taking diuretics for pre-existing cardiac conditions, which makes the situation worse.
The best thing you can do is pray for winter. The next best thing you can do is invest in an air-conditioner because avoiding the extreme heat on days like this is the best solution. If you don’t have an air-conditioner and can’t get one, at lest go somewhere that is air-conditioned even if for just a short time because it will allow you to cool down. At the very least get a fan to help you stay cool. Take cold showers, drink plenty of water to avoid dehydration, and most importantly try not to be alone. People living alone are at greatest risk for complications from the heat because the symptoms can sneak up on you. So check-up on your neighbours, because that should still count for something. Finally don’t be upset if somebody next to you these days is sweating a lot. It’s saving their life.