How heat causes illness and death

[New Sancai Compilation and First Release] As outside temperatures and humidity soar, what happens inside the human body can become a life-or-death battle, just a few degrees apart.

Researchers who put people in heat boxes to see what happens to them say the critical danger point for illness and death from extreme heat outdoors is several degrees cooler than experts once thought.

As much of the U.S., Mexico, India and the Middle East suffers from sweltering heat waves made worse by human-caused climate change, several doctors, physiologists and other experts explained to The Associated Press what the human body does in such hot weather. what happened.

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

Ollie Jay, professor of heat and health at the University of Sydney in Australia, who runs the Thermal Ergonomics Laboratory, said we are only 7 degrees Fahrenheit (4 degrees Celsius) away from catastrophic heatstroke.

Dr. Neil Gandhi, chief of emergency medicine at Houston Methodist Hospital, said that during the heat wave, anyone with a fever of 102 degrees Fahrenheit (39 degrees Celsius) or higher and no clear source of infection will be tested. Suffering from heat exhaustion or more seriously, heat stroke.

"During certain periods of high temperatures, we typically see core temperatures exceeding 104 to 105 degrees," Gandhi said. Anywhere from one to three degrees above that, he said, such patients are at high risk of death.

Jay said there are three main ways in which high temperatures can cause death. Often the first symptom is heatstroke - a sudden rise in body temperature that leads to organ failure.

When the internal temperature gets too hot, the body sends blood toward the skin to cool it down, Jay said. But this diverts blood and oxygen away from the stomach and intestines and can cause toxins normally confined to the intestinal area to leak into the circulatory system.

"This triggers a cascade of effects," Jay said. "Blood clots appear around the body, leading to multiple organ failure and ultimately death."

But Jay says the bigger killer of the heat is the stress on the heart, especially for people with cardiovascular disease. Again, blood rushes to the skin, helping to dissipate core heat. This causes blood pressure to drop. The heart responds by trying to pump more blood to prevent you from passing out.

"You're asking your heart to do more work than usual," Jay said. This is dangerous for people with heart disease.

The third major pathway is dangerous dehydration. When people sweat, they lose fluid to a point that puts severe stress on the kidneys, Jay said. Gandhi, of Houston, said many people may not realize their dangers.

Dehydration can develop into shock, causing organs to shut down due to a lack of blood, oxygen and nutrients, said Dr. Renee Salas, a professor of public health at Harvard University and an emergency room physician at Massachusetts General Hospital. Causes seizures and death.

"Dehydration, if severe, can be very dangerous and even fatal for everyone, but it is especially dangerous for those with existing health problems and those taking certain medications," said Jay. , dehydration can also reduce blood flow and worsen heart problems.

Heat also affects the brain. Several doctors say it can cause a person to become confused or have trouble thinking.

“One of your first symptoms of heat is confusion,” said Kris Ebi, a professor of public health and climate at the University of Washington. “That’s not helpful as a symptom because people suffering from heat are unlikely to Detect their confusion. She said this becomes a bigger problem as people age.

One of the classic definitions of heat stroke is a core body temperature of 104 degrees Fahrenheit (40 degrees Celsius), "along with cognitive impairment," said W. Larry Kenney, a professor of physiology at Penn State University.

Some scientists use a sophisticated measure of outside temperature called wet-bulb temperature, which takes humidity, solar radiation and wind into account. In the past, it was believed that health problems began when wet-bulb temperatures reached 95 degrees Fahrenheit (35 degrees Celsius).

Kenny's tests show the wet-bulb danger point is close to 87 degrees Fahrenheit (30.5 degrees Celsius). He said that number is already starting to appear in the Middle East. This only applies to healthy young people. The danger point for older adults is a wet-bulb temperature of 82 degrees Fahrenheit (28 degrees Celsius), he said. "Wet heat waves kill many more people than dry heat waves," Kenney said.

When Kenney tested young and old in dry heat conditions, young volunteers could function at 125.6 degrees Fahrenheit (52 degrees Celsius), while older volunteers had to stop at 109.4 degrees Fahrenheit (43 degrees Celsius). He said people wouldn't be able to function at such high temperatures in high or moderate temperatures.

"Humidity affects the ability of sweat to evaporate," Jay says. Salas said heat stroke is an emergency and medical staff will try to cool the victim within 30 minutes. The best method: cold water soaking. Basically, "you throw them in a bucket," Salas said.

But these are not always present. So the emergency room will give patients cold fluids intravenously, spray them with a spray, put ice packs in their armpits and groin, and then place them on a cooling pad with cold water running through it. Sometimes it doesn't work though. "We call it the Silent Killer because it's not a visually dramatic event," Jay said. "It's insidious. It's hidden."

(Compiled by: Wang Jimin)
(Editor: Jiang Qiming)
(Source of the article: Compiled and published by New Sancai)