When people get too hot, veins and capillaries expand and hearts beat fast, sending hot blood to outer layers of skin where it can cool off. If that doesn’t work, sweat glands release sweat.
It’s a good system for the most part, but in the heat of Tucson summers — especially when people exert themselves — it sometimes fails.
The risk of overheating doesn’t mean Southern Arizonans should draw their curtains, crank up their air-conditioners and stay sequestered in their homes until winter.
It does mean, though, that desert dwellers must respect their harsh environment and use precaution when gearing up for a bike ride or taking off on a mountain hike.
An important part of avoiding injury from heat is being able to recognize signs that your body is overheated, said Laura Crockett, an exercise physiologist who works at Northwest Medical Center.
Heat exhaustion is characterized by dizziness, lightheadedness, nausea, fatigue, shortness of breath and a body temperature usually between 102 and 105, Crockett said.
Inside the body, it looks like this: Blood flows quickly to the body surface to cool off, so less of it is available to carry oxygen to muscles, the brain and other internal organs, thus the dizziness and fatigue. Sweating causes a loss of water, which also contributes to fatigue because it makes blood thicker and harder to pump.
Heat exhaustion can usually be stopped with a simple rest in the shade and hydration, Crockett said. If the condition progresses to heat stroke, though, it is a medical emergency.
During heat stroke, the body begins losing the ability to control its temperature. Sweating may cease, and a person may hyperventilate, complain of a rapid heart rate, and experience neurological symptoms including seizures, loss of consciousness, hallucination and difficulty speaking or understanding others.
“If you see someone who is delirious or has lost consciousness, that is a sign to call 911,” Crockett said.
Onlookers should use tools at their disposal to help heat stroke victims cool down as they wait for emergency help to arrive. Hoses and fans work well, as do damp sponges. In low humidity, it helps to wrap a heat stroke victim in a cool wet sheet and fan vigorously.
Of course, a better way to handle heat injury is to avoid it entirely by going out into the severe desert elements properly equipped.
Crockett suggests drinking a cup of water for each 20 minutes of outdoor heat and wearing loose-fitting clothing that exposes the body to air and allows sweat to evaporate. Also, people should know when they are taking medications that make it harder for the body to cool itself.
Medication for Parkinson’s disease falls in this category, because it can inhibit perspiration. So do diuretic medications that affect the balance of fluid in a body. Vasoconstrictors and beta blockers can profoundly affect the body’s ability to regulate heat by decreasing its ability to shunt blood away from the body’s core.
“Check with your pharmacist,” Crockett said.
It also helps to know your target heart rate and stay within it, she added. To find out how high your heart rate should ideally get during exercise, subtract your age from 220 and multiply that number by 85 percent. A person’s heart rate should never rise above the number you get when you subtract your age from 220, Crockett said.
“Sometimes when you get to the upper end of the range, it can feel like your head is being thrust into an oven and your trunk can feel like it’s getting chilled,” she said.
That’s probably a pretty good reason to stop for a cold drink.