How does heat kill? | fortune well

As temperatures and humidity soar outside, what happens inside the human body can become a life-or-death battle decided by just a few degrees.

The outdoor danger threshold for illness and death from relentless heat is several degrees lower than experts thought, say researchers who put people in hot boxes to see what happens to them.

As much of the United States, Mexico, India and the Middle East suffer from scorching heat waves, made worse by man-made climate change, several doctors, physiologists and other experts explained to The Associated Press what happens to the human body with that heat.

Key body temperature

The body’s resting core temperature is usually about 98.6 degrees Fahrenheit (37 degrees Celsius).

That’s just 7 degrees (4 Celsius) away from a heatstroke catastrophe, said Ollie Jay, a professor of heat and health at the University of Sydney in Australia, where he directs the thermoergonomics lab.

Dr. Neil Gandhi, director of emergency medicine at Houston Methodist Hospital, said that during heat waves, anyone who arrives with a fever of 102 or higher and no clear source of infection will be tested for heat exhaustion. or more severe heat stroke.

“We will routinely see core temperatures above 104, 105 degrees during some of the hot spells,” Gandhi said. One or three degrees higher and that patient is at high risk of death, he said.

How heat kills

Heat kills in three main ways, Jay said. The usual first suspect is heat stroke: critical increases in body temperature that lead to organ failure.

When the body’s internal temperature rises too much, the body redirects blood flow to the skin to cool it, Jay said. But that diverts blood and oxygen from the stomach and intestines, and can allow toxins normally confined to the intestinal area to leak into the circulation.

“That sets off a cascade of effects,” Jay said. “Clotting around the body, multiple organ failure, and ultimately death.”

But the biggest cause of death in the heat is stress on the heart, especially in people with cardiovascular disease, Jay said.

Again it starts with blood rushing to the skin to help remove core heat. That causes blood pressure to drop. The heart responds by trying to pump more blood to prevent you from passing out.

“You’re asking the heart to do a lot more work than it normally has to do,” Jay said. For someone with a heart condition, “it’s like running for a bus with a dodgy hamstring.” “Something is going to give.”

The third main way is dangerous dehydration. As people sweat, they lose fluid to a point that can severely stress the kidneys, Jay said.

Many people may not realize the danger they are in, said Gandhi of Houston.

Dehydration can progress to shock, which causes organs to shut down from lack of blood, oxygen and nutrients, leading to seizures and death, said Dr. Renee Salas, a public health professor at Harvard University. and emergency physician at Massachusetts General Hospital.

“Dehydration can be very dangerous and even fatal for everyone if it gets bad enough, but it is especially dangerous for those who have medical conditions and take certain medications,” Salas said.

Dehydration also reduces blood flow and aggravates heart problems, Jay said.

attacking the brain

Heat also affects the brain. It can cause confusion or trouble thinking in a person, several doctors said.

“One of the first signs that you’re having trouble with the heat is if you get confused,” said Kris Ebi, a professor of climate and public health at the University of Washington. That’s of little help as a symptom because the person suffering from the heat is unlikely to recognize it, he said. And it becomes a bigger problem as people get older.

One of the classic definitions of heat stroke is a core body temperature of 104 degrees “along with cognitive dysfunction,” said Pennsylvania State University physiology professor W. Larry Kenney.

Humidity matters

Some scientists use a complicated outdoor temperature measurement called wet-bulb globe temperature, which takes into account humidity, solar radiation and wind. In the past, a wet-bulb reading of 95 Fahrenheit (35 Celsius) was thought to be the point at which the body began to have problems, said Kenney, who also runs a hot box laboratory and has performed nearly 600 tests with volunteers.

Their tests show that the wet bulb danger point is closer to 87 (30.5 degrees Celsius). That’s a figure that has started to appear in the Middle East, he said.

And that’s only for young, healthy people. For older people, the danger point is a wet-bulb temperature of 82 (28 degrees Celsius), he said.

“Wet heat waves kill many more people than dry heat waves,” Kenney said.

When Kenney tested young and old people in dry heat, the young volunteers could run up to 125.6 degrees (52 degrees Celsius), while the elderly had to stop at 109.4 (43 degrees Celsius). With high or moderate humidity, people would not be able to function at such a high temperature, he said.

“Humidity affects sweat’s ability to evaporate,” Jay said.

Running to calm patients

Heat stroke is an emergency and medical workers try to cool the victim within 30 minutes, Salas said.

The best way: Immersion in cold water. Basically, “you drop them in a bucket of water,” Salas said.

But those are not always present. So emergency rooms pump patients with cold liquids intravenously, spray them with vaporizers, place ice packs in their armpits and groin, and place them on an ice mat with cold water running through them.

Sometimes it doesn’t work.

“We call it the silent killer because it’s not this kind of visually dramatic event,” Jay said. “It’s insidious. He is hidden “.

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