by As the temperature and humidity rise outside, what is happening inside the human body can be a life or death battle decided by just a few degrees.
The critical outdoor danger point for illness and death from unrelenting heat is several degrees lower than experts once 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 blistering heat waves, exacerbated by human-caused climate change, several doctors, physiologists and other experts explained to The Associated Press what happens to the human body in that heat.
key body temperature
The body’s resting core temperature is usually around 98.6 degrees Fahrenheit (37 degrees Celsius).
That’s just 7 degrees (4 Celsius) away from disaster in the form of heat stroke, said Ollie Jay, a heat and health professor at the University of Sydney in Australia, where he runs the thermodynamics lab.
Dr. Neil Gandhi, director of emergency medicine at Houston Methodist Hospital, said during heat waves anyone who comes in with a fever of 102 or higher and no obvious source of infection will be looked for heat exhaustion or a more severe heat rash.
“We will regularly see core temperatures higher than 104, 105 degrees during some of the heat events,” Gandhi said. Another step or three and such a patient is in serious danger 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 cause organ failure.
When the internal body temperature becomes too hot, the body diverts blood flow towards the skin to cool down, Jay said. But that diverts blood and oxygen from the stomach and intestines, and can allow toxins normally confined to the bowel area into circulation.
“That sets off a cascade of effects,” Jay said.
But the biggest killer in the heat is the pressure on the heart, especially for people with cardiovascular disease, said Jay.
It starts again with blood rushing to the skin to help shed heart heat. It causes blood pressure to drop. The heart responds by trying to pump more blood to keep you from dying.
“You’re asking the heart to do a lot more work than it normally has to,” Jay said. For someone with a heart condition “it’s like running on a bus with a hamstring. Something will give.”
The third main way is dangerous dehydration. As people sweat, they lose fluids to a point that puts a lot of stress on the kidneys, Jay said.
Many people may not understand their danger, Gandhi said from 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 professor of public health at Harvard University and an emergency room physician at Massachusetts General Hospital.
“Dehydration can be very dangerous and even fatal for everyone if it gets bad enough — but it’s especially dangerous for those with medical conditions and on certain medications,” Salas said.
Dehydration also reduces blood flow and increases cardiac problems, Jay said.
Attack on the brain
Heat also affects the brain. It could cause confusion or trouble for a person, some doctors said.
“One of the first signs that you’re in trouble with the heat is if you get confused,” said Kris Ebi, a University of Washington professor of public health and climate. to recognize, she said. And it becomes more of a 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.
There are moisture matters
Some scientists use a complex outdoor temperature measurement called the wet-bulb absolute 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 when trouble started at the company, said Kenney, who also runs a hot box lab and has conducted nearly 600 tests with volunteers.
His tests show that the wet bulb’s danger point is closer to 87 (30.5 Celsius). That’s a figure that’s starting to emerge in the Middle East, he said.
And that’s just for healthy young people. For the elderly, the danger point is a wet bulb temperature of 82 (28 degrees Celsius), he said.
“Moist heat waves kill a lot more people than dry heat waves,” Kenney said.
When Kenney tested young and old people in dry heat, young volunteers could perform up to 125.6 degrees (52 degrees Celsius), while the elderly had to stop at 109.4 (43 degrees Celsius). With high or moderate temperatures, the people could not function at nearly as high a temperature, he said.
“Humidity affects the ability of sweat to evaporate,” Jay said.
Rushing to make patients cool
Heatstroke is an emergency, and medical workers try to cool a victim within 30 minutes, Salas said.
The best way: Cold water immersion. Basically, “you drop them in a bucket of water,” Salas said.
But those are not always around. So emergency rooms pump patients with cool intravenous fluids, spray them with mist, put ice packs in armpits and groins and place them on a cooling mat with cold water running through it.
Sometimes it doesn’t work.
“We call it the silent killer because it’s not a dramatic event like this,” Jay said. “It’s insidious. It’s hidden.”
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