As temperatures and humidity soar outside, what happens inside the human body can become a life-or-death battle with the outcome decided by just a few degrees.
The critical danger point outdoors for illness and death from relentless heat is several degrees lower than experts previously thought, according to researchers who put people in hot boxes to see what happened to them.
As much of the United States, Mexico, India and the Middle East experience sweltering heat waves, made worse by human-caused climate change, several doctors, physiologists and other experts have explained to the Associated Press what happens to the human body in such heat.
The resting core body temperature is usually around 37 degrees Celsius.
According to Ollie Jay, professor of heat and health at the University of Sydney, Australia, where he directs the Thermoergonomics Lab, that temperature is only 4 degrees Celsius away from disaster in the form of a blow heat.
Dr. Neil Gandhi, director of emergency medicine at Houston Methodist Hospital, explained that during heat waves, anyone presenting with a fever of 39 Celsius or higher and no obvious source of infection will be screened. for heat exhaustion or more severe heat stroke.
“We regularly see core temperatures above 40 degrees during some heat events,” Gandhi said. One or three degrees higher and the patient is at high risk of death, he added.
Heat kills in three main ways, Jay says. The usual first suspect is heat stroke, which is the critical increase in body temperature that leads to organ failure.
When the body’s internal temperature becomes too high, the body redirects blood flow to the skin to cool itself, Jay said. But this diverts blood and oxygen from the stomach and intestines, and can allow toxins normally confined to the intestinal area to leak into the circulation.
“It sets off a cascade of effects,” Mr. Jay continued. Clotting in the body, multiple organ failure, and ultimately death. »
But the biggest killer in heat is the strain on the heart, especially in people with cardiovascular disease, Jay said.
Again, blood rushes to the skin to help carry heat away from the body. This leads to a drop in blood pressure. The heart responds by trying to pump more blood to keep you from passing out.
“You’re asking the heart to do a lot more effort than it usually does,” Mr. Jay said. For someone with a heart condition, “it’s like running to catch a bus with bad hamstrings. Something’s going to give.”
The third main cause is dangerous dehydration. When people sweat, they lose fluid to such an extent that the kidneys can be strained, Jay said.
Many people do not realize the danger they are in, said Dr. Gandhi of Houston.
Dehydration can progress to shock, causing organs to shut down from lack of blood, oxygen and nutrients, leading to seizures and death, said Dr. Renee Salas, a professor of public health at the university. Harvard and emergency physician at Massachusetts General Hospital.
“Dehydration can be very dangerous, even fatal, for anyone if it is severe enough, but it is particularly dangerous for people who have a medical condition or are taking certain medications,” Dr. Salas said.
Dehydration also reduces blood circulation and amplifies heart problems.
Heat also affects the brain. It can lead to confusion or thought disorders, according to several doctors.
“One of the first symptoms of a heat-related problem is confusion,” said Kris Ebi, who is a professor of public health and climatology at the University of Washington. It’s not a very helpful symptom because the person suffering from the heat is unlikely to notice it, she added. And the problem gets worse with age.
According to W. Larry Kenney, a professor of physiology at Pennsylvania State University, one of the classic definitions of heat stroke is a body temperature of 40 degrees “associated with cognitive dysfunction.”
Some scientists use a complex measure of outdoor temperature, called wet globe temperature, which takes into account humidity, solar radiation and wind. In the past, it was thought that a wet-bulb temperature of 35 Celsius was the point where the body started to have problems, said Mr. Kenney, who also runs a hot box laboratory and has performed nearly 600 tests with it. volunteers.
His tests show that the danger point for wet bulb temperature is closer to 30.5 degrees Celsius, a number that has started to appear in the Middle East, he said.
And this only concerns healthy young people. For older people, the danger point is a temperature of 28 degrees Celsius.
“Moist heat waves kill many more people than dry heat waves,” Kenney said.
When Kenney tested young and old people in dry heat, young volunteers could run up to 52 degrees Celsius, while older people had to stop at 43 degrees Celsius.
“Humidity impacts the ability of sweat to evaporate,” Jay said.
Heatstroke is an emergency, and medical workers try to cool a victim within 30 minutes, Dr. Salas said.
The best way is immersion in cold water. Basically, “you drop them in a bucket of water,” she explained.
But there isn’t always one. That’s why emergency departments give patients cool fluids intravenously, spray them with mist sprays, put ice packs under their armpits and groins, and place them on a cooling mat with ice flowing inside. cold water.
Sometimes it doesn’t work.
“We call it the silent killer because it’s not a visually spectacular event,” Jay said. “He’s insidious. He’s sneaky. »
