The human body has been tested in recent weeks in a heat wave that has killed more than 100 people in California, many of them elderly or homeless. The human body has complex strategies for beating the heat -- but when the system is overwhelmed, it can fail on many fronts.
-- Mary Beckman
The body keeps tabs on its internal temperature via a thermoregulator in a part of the brain called the hypothalamus. If it senses the body is overheated, the brain cranks up the sweat glands as well as the cardiovascular system. "The brain shunts more blood to the skin," says physiologist Yuval Heled of the Uniformed Services University of the Health Sciences in Bethesda, Md. "The blood carries the heat from the internal parts of the body to the surface."
A system of proteins within cells also helps stave off damage from heat. Called heat shock proteins, these special molecules stabilize important enzymes and other proteins from denaturing -- which protects internal organs from damage.
The human body is always generating heat, which it has to slough off to maintain a constant temperature. "Your body wants to dissipate the heat, and it goes by the laws of physics: Heat goes from the hot to the cool environment," Heled says.
In cooler conditions, our hot bodies radiate the heat to the air. But if the outside temperature exceeds the human body temperature of approximately 98.6 degrees, the environment is radiating its heat toward us -- because we're the cooler entity.
That's when the sweating starts. As the sweat evaporates, it uses heat from our skin, cooling us down.
Evaporation doesn't work so well if it's humid, explains Dr. Larry Baraff, who works in emergency medicine at UCLA. When evaporation fails, it's time to jump into a cold shower or use wet washcloths to allow the toastiness to dissipate quickly through a process called conduction. The heat is transferred to the water -- in other words, it's literally washed away.
In heat waves, experts say, the people most at risk are the elderly, those who are sick and athletes who insist on exercising in high heat, which makes the body hotter. Young children are also at risk, mostly because babies and toddlers are at the mercy of others who might keep them wrapped up too much or leave them in hot cars.
When people get overheated, the first problem they encounter is dehydration from sweating and not drinking enough liquids. Blood thickens, and blood vessels lose their tone. Blood pools in the lower part of the body, causing people to faint if they stand up too fast.
The combination of the heart pumping faster to get blood to the skin and pumping harder due to pliant vessels puts people with heart disease -- whether diagnosed or not -- at heightened risk of heart attacks.
Age mixes especially badly with hot weather. "Cooling methods are inadequate at extremes of age, when the body doesn't work as efficiently as it should," Baraff says. For example, older people can't sweat as easily. Thus, in heat, their skin becomes warm to the touch but not moist. They are also more likely to suffer internal damage because they don't make heat shock proteins as efficiently.
If the body can't cool down, heatstroke is a risk. One of the first signs of this is mental fuzziness because the brain is a very sensitive organ. People might have trouble remembering their names or lose consciousness.
But it's the internal organs -- such as the kidneys, liver and heart -- that give out when a body reaches 105 degrees.
If heat shock proteins in organs can't keep up with the heat, the stomach becomes leaky, and bits of the bacteria that normally reside there ooze out. "This induces a massive inflammatory reaction and is probably what kills people," says Dr. Paul Wischmeyer, associate professor of anesthesiology at the University of Colorado Health Sciences Center in Denver.
Most healthy people tolerate heat fine if they remain hydrated and do not exercise in the heat, experts say. "They need to rest at the hottest parts of the day," Heled says.
Friends, neighbors and relatives should keep an eye on the elderly too. Seniors should get into air conditioning if possible and drink lots of liquids. Baraff points out that even gardening is exercise. "For every hour of work," he says, "you should get 15 minutes of rest."
In March, Wischmeyer reported in the journal Shock that giving rats glutamine -- a common nutritional supplement used by athletes -- improved their ability to survive severe heat.
Because glutamine also helps in the survival of human trauma victims, Wischmeyer suggests giving the elderly some glutamine in milk (unless they're on dialysis). "It tastes a little like sugar," he says. What a sweet way to weather the heat.