An illustration shows the 27 different ways extreme heat can lead to death. Photo by UHM
Nov. 9 (UPI) -- As global temperatures continue to rise and heatwaves become more common, scientists are working to better understand the impacts on human health.
According to a study published this week, the threats posed by heatwaves are surprisingly diverse. In fact, heatwaves can kill humans 27 different ways. Researchers detailed the different fatal mechanisms in the journal Circulation: Cardiovascular Quality and Outcomes.
"We know of many case examples when people have died as a result of heatwaves," lead author Camilo Mora, researcher the University of Hawaii at Manoa, said in a news release. "However, why people died is a question whose answer is scattered."
Mora and his colleagues identified five physiological mechanisms affected by extreme heat. They determined those five mechanisms can damage seven different organs. The researchers then surveyed the medical literature for evidence the 35 possible mechanism-organ combinations. The literature suggests 27 of the combinations can prove fatal.
"Dying during a heatwave is like a terror movie with 27 bad endings to choose from," Mora said. "It is remarkable that humanity overall is taking such a complacency on the threats that ongoing climate change is posing."
During instances of extreme heat, the body's hypothalamus redirects blood to the skin for cooling purposes. This can leave vital organs without sufficient blood supply. The mechanism, called ischemia, can produce toxic chemical compounds. Another mechanism, cytotoxity, describes direct cell damage caused by heat.
Both mechanisms can damage the brain, heart, kidneys, liver or digestive tract. The mechanisms can kill a person on their own, or lead to variety of other deadly complications. For example, ischemia and cytotoxity can lead to the breakdown and failure of the intestinal wall, allowing a person's guts to spill into the bloodstream, triggering what's known as systemic inflammatory response syndrome, or SIRS.
The inflammatory response recruits white blood cells to battle the infection, but the mechanism can worsen the breakdown of the intestines. This physiological train wreck can trigger another mechanism, called disseminated intravascular coagulation, during which a cascade of overactive proteins cause blood to begin clotting throughout the body, shutting off blood supply to the brain and other vital organs, and leading to fatal hemorrhaging.
The final mechanism is triggered when ischemia and cytotoxity are exacerbated by strenuous activity, leading to the breakdown of muscle tissue and the release of myoglobin, which is toxic to the liver, lungs and kidneys.
Though the elderly and people with compromised immune systems are most at risk, the latest research is reminder that heatwaves can harm anyone and everyone. Researchers say such risks demand policy makers do what's necessary to prevent further warming.