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As temperatures and humidity rise outside, what happens inside the human body can become a life-or-death battle decided by just a few degrees. Researchers say the outside threat for disease and death from persistent heat is many degrees lower than experts previously thought Researchers put people in heat boxes and watched what happens to them. As much of the United States, Mexico, India and the Middle East are suffering from extreme heat waves made worse by human-caused climate change, several doctors, physiologists and other experts told The Associated Press about what happens to the human body in such heat.
Core Body Temperature
The body’s resting core temperature is typically around 98.6 degrees Fahrenheit (37 degrees Celsius). That’s just 7 degrees (4 Celsius) away from something as catastrophic as heatstroke, said Ollie Jay, a professor of nutrition and health at the University of Sydney in Australia, where he runs the Thermoergonomics Laboratory.
Dr. Neil Gandhi, director of emergency medicine at Houston Methodist Hospital, said anyone who comes in with a fever of 102 or higher during heat waves and no obvious source of infection should be seen for heat exhaustion or the more severe heatstroke. “We routinely see temperatures over 104, 105 degrees during some of the heat episodes,” Gandhi said. Another degree or three higher and such a patient is at higher risk of death, he said.
How does heat kill?
Heat kills in three main ways, Jay said. The most common first suspect is heatstroke — a severe rise in body temperature that causes organs to fail. When the body’s internal temperature gets too high, the body redirects blood flow toward the skin to cool down, Jay said. But this diverts blood and oxygen away from the stomach and intestines, and can allow toxins normally confined to the gut area to leak into the circulation.
“This starts a cascade of effects,” Jay said. “Clot formation around the body and multiple organ failure and eventually death.” But the biggest harm from the heat is the strain on the heart, especially for people with heart disease, Jay said. This again starts with blood flowing toward the skin to help expel core heat. This lowers blood pressure. The heart responds by trying to pump more blood to keep you from fainting.
“You’re making the heart work a lot more than it normally does,” Jay said. For a person with heart disease, “it’s like running for a bus with a torn hamstring. Something’s going to happen.” The third main way is dangerous dehydration. Jay said when people sweat, they lose fluids to the point that it can put too much strain on the kidneys. Many people may not realize their risk, Houston’s Gandhi said.
Dehydration can progress to shock, whereby a lack of blood, oxygen and nutrients causes organs to shut down, 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.
“If dehydration becomes severe, it can be very dangerous and even life-threatening for everyone — but it’s especially dangerous for people who have underlying medical conditions and are taking certain medications,” Salas said. Dehydration also reduces blood flow and increases the risk of cardiovascular problems, Jay said.
Attack on the brain
Many doctors say that heat also affects the brain. This can cause confusion or trouble in thinking in a person.
“If you get confused, heat exhaustion is the first symptom,” said Chris Eby, a public health and climate professor at the University of Washington. He added that it’s hardly helpful as a symptom because a person suffering from heat exhaustion is unlikely to recognize it. And it becomes a bigger problem as you age.
A classic definition of heat stroke is a core body temperature of 104 degrees “associated with cognitive dysfunction,” said W. Larry Kenney, a physiology professor at Pennsylvania State University.
Humidity matters
Some scientists use a more complex outdoor temperature measurement called wet bulb globe temperature, which takes into account humidity, solar radiation and wind. In the past, it was believed that a wet-bulb reading of 95 Fahrenheit (35 Celsius) was the point when the body begins to experience trouble, said Kenney, who also runs a hot box lab and has conducted about 600 tests with volunteers.
His tests show the wet-bulb danger point is closer to 87 (30.5 Celsius). That’s a figure he said is starting to show up in the Middle East. And that’s just for young healthy people. For older people, he said, the danger point is a wet-bulb temperature of 82 (28 degrees Celsius). “Humid heat waves kill a lot more people than dry heat waves,” Kenney said.
When Kenny tested young and old people in dry heat, the young volunteers could work up to 125.6 degrees (52 degrees Celsius), while the elderly had to stop at 109.4 (43 degrees Celsius). He said that with high or moderate humidity, people could not work at nearly as high temperatures. “Humidity affects the ability of sweat to evaporate,” Jay said.
rushed to cool the patients
Heatstroke is an emergency, and medical personnel try to cool the victim within 30 minutes, Salas said. The best way: immersion in cold water. Basically, “you put them in a bucket of water,” Salas said. But that’s not always around. So emergency rooms give patients cold fluids intravenously, spray them with mist, put ice packs in the armpits and groin and lay them on a cold mat filled with cold water. 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.”
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