When temperatures and humidity outside rise rapidly, a few degrees Celsius can lead to a struggle for life and death in the human body.
The critical outdoor hazard for illness and death from relentless heat is several degrees lower than experts once thought, say researchers who put people in hot boxes to see what happens to them.
With a large part of the United States, Mexico, India and that middle East Suffering from scorching heat waves, exacerbated by human-induced climate changeSeveral doctors, physiologists and other experts explained to the Associated Press what happens to the human body in such heat.
Important body temperature
The core body temperature at rest is normally around 37 degrees Celsius.
That puts it just 7 degrees (4 Celsius) away from heat stroke, said Ollie Jay, professor of heat and health at the University of Sydney in Australia, where he heads the Thermoergonomics Laboratory.
Dr. Neil Gandhi, Head of Emergency Medicine at Houston Methodist The hospital said that during a heat wave, anyone admitted with a body temperature of 39 degrees Celsius or more and without a clear source of infection will be diagnosed with heat exhaustion or more severe heat stroke.
“During some heat waves, we regularly see core body temperatures above 40 to 41 degrees,” Gandhi said. Another one or three degrees and such a patient is at high risk of death, he said.
How heat kills
Heat can cause death in three ways, Jay said. The usual first suspect is heat stroke – a critical increase in body temperature that leads to organ failure.
When body temperature gets too high, the body diverts blood flow to the skin to cool down, Jay said. But this diverts blood and oxygen from the stomach and intestines, and toxins that normally stay in the intestinal area can enter the bloodstream.
“It sets off a cascade of effects,” Jay said. “Blood clots throughout the body, multiple organ failure, and ultimately death.”
But the bigger cause of death in heat is strain on the heart, especially in people with cardiovascular disease, Jay says.
Again, blood starts rushing to the skin to dissipate body heat. This causes blood pressure to drop. The heart responds by trying to pump more blood to prevent you from passing out.
“They’re asking the heart to do a lot more than it normally has to,” Jay said. For someone with heart disease, “it’s like running behind a bus with a broken hamstring. Something’s going to give out.”
The third main cause is dangerous dehydration. People lose so much fluid through sweating that it can put a lot of strain on the kidneys, says Jay.
Many people may not be aware of the danger they are in, said Gandhi from Houston.
Dehydration can lead to shock and cause organ failure due to lack of blood, oxygen and nutrients, which can lead to seizures and death, said Dr. Renee Salas, a professor of public health at Harvard University and an emergency physician at Massachusetts General Hospital.
“Dehydration can be very dangerous for anyone and even fatal if it gets bad enough – but it is especially dangerous for people with underlying health conditions and if they are taking certain medications,” Salas said.
Dehydration also reduces blood flow and worsens heart problems, Jay said.
Attack on the brain
Heat also affects the brain. Several doctors said it can cause a person to become confused or have difficulty thinking.
“One of the first signs that you’re having problems with the heat is if you’re confused,” says Kris Ebi, a professor of public health and climate at the University of Washington. As a symptom, however, that’s not very helpful because the person suffering from the heat probably doesn’t recognize it, she says. And as people get older, it becomes a bigger problem.
One of the classic definitions of heat stroke is a core body temperature of 104 degrees Fahrenheit “coupled with cognitive impairment,” said W. Larry Kenney, a professor of physiology at Pennsylvania State University.
Humidity is what matters
Some scientists use a complicated method of measuring outside temperature called wet-bulb globe temperature, which takes into account humidity, sunlight and wind. It was previously thought that a wet-bulb reading of 95 degrees Fahrenheit was the point at which the body began to have problems, says Kenney, who also runs a hot-box lab and has conducted nearly 600 tests on volunteers.
His tests show the wet bulb temperature is closer to 87 degrees Celsius (30.5 degrees F), which is already common in the Middle East, he said.
And that only applies to young, healthy people. For older people, the danger limit 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 performed up to 52 degrees Celsius, while the older ones had to stop at 43 degrees Celsius. In high or moderate humidity, people did not perform at such a high temperature, he said.
“Humidity affects the evaporation power of sweat,” said Jay.
In a hurry to cool the patients
Heat stroke is an emergency, and medical personnel try to cool the victim within 30 minutes, Salas said.
The best method: immersing them in cold water. Essentially, “you’re throwing them in a bucket of water,” Salas said.
But they aren’t always there. That’s why emergency rooms pump cold fluids into patients intravenously, spray them with nebulizers, put ice packs in their armpits and groin, and lay them on a cooling mat with cold water running into it.
Sometimes it doesn’t work.
“We call it the silent killer because it’s not such a visually dramatic event,” Jay said. “It’s insidious. It’s hidden.”