A MARTINEZ, HOST:
Heat waves sweeping across much of the nation have led to more emergency room visits. From New York to Oregon, doctors say the long stretch of scorching temperatures is taking its toll. As NPR's Allison Aubrey reports, heat-related illnesses can sneak up on people faster than they expect, especially if they take certain kinds of medications.
ALLISON AUBREY, BYLINE: If you live in Texas, you're no stranger to the heat. But Roy McFadden, who lives in Katy, a suburb of Houston, says he didn't realize just how hot it was getting last weekend.
ROY MCFADDEN: Sunday morning, I got up and worked out, went for a walk, came back and did some weight resistance training in my garage.
AUBREY: After that, he went to play softball with his daughter. They were out for a few hours as the temperature climbed to 99 degrees and the heat index hit 105. He started to feel very dizzy and lightheaded.
MCFADDEN: I was surprised that when I got to the car and I sat in the AC, I couldn't cool off. My wife and my daughter insisted to take me to the ER. I really didn't want to go, quite frankly, but I was a little disoriented and nonresponsive.
AUBREY: When he arrived at Memorial Hermann Katy Hospital, he was treated by Dr. Wafi Momin, a cardiologist who suspected heat exhaustion.
WAFI MOMIN: He presented with symptoms of chest tightness, shortness of breath. And when EMS arrived, his blood pressures were reported to be very low.
AUBREY: After intense heat exposure, Dr. Momin says, the body is doing all it can to just cool itself down.
MOMIN: A lot of the blood flow circulation is pumped to our skin to try to expel heat in the form of sweat.
AUBREY: And when this happens, blood vessels can dilate or expand, leading to a drop in blood pressure, which for Roy McFadden was too much. Turns out his risk of heat exhaustion was elevated because, like millions of Americans, he takes blood pressure medications.
MOMIN: A lot of these blood pressure medications - the way they work is they relax to smooth the muscles around our blood vessels. And at the same time, your body by itself is trying to dilate these blood vessels because of exposure to the excessive heat. And both of those things can cause lowering of the blood pressure, which can be too much for someone.
AUBREY: Roy McFadden, who's about 50 years old, was given IV fluids and kept overnight in the hospital. He's feeling better now, but he says he has a new appreciation of the dangers of intense heat.
MCFADDEN: Have a bit more respect for the sun (laughter) what I had previously.
AUBREY: The combination of age, intensity of heat exposure and overall health all influence a person's risk of heat-related illness. What the medications can do is add another layer of risk. Scott Hall is a pharmacist at the Mayo Clinic Health System in Wisconsin. He says it's not just blood pressure medications.
SCOTT HALL: There are many medications out there that have the ability to affect the way the human body is able to tolerate or manage high temperatures.
AUBREY: This includes drugs such as beta blockers used to treat certain heart conditions, tricyclic antidepressant medications and over-the-counter allergy medicines, antihistamines, which tend to dry people out.
HALL: Antihistamines, do, you know, help with that runny nose and watery eyes but can also affect the body's ability to make sweat effectively or in enough amounts to help keep the body cool.
AUBREY: Not everyone will respond the same. Some people may not notice any increased sensitivity. Emergency medicine doctor Eric Legome of Mount Sinai in New York says other drugs to be aware of are benzodiazepines, such as Xanax, used for anxiety or sleeping medications.
ERIC LEGOME: Those don't necessarily cause issues with getting rid of heat, but what they may do is impair your ability to realize you're getting hotter.
AUBREY: Which could put you at higher risk of heat-related illness. He says people shouldn't stop medications just because of the heat. But some may want to modify in consultation with their medical providers. What's most important, he says, is to be aware. Allison Aubrey, NPR News.
(SOUNDBITE OF ARMS AND SLEEPERS' "WHEN THE BODY")
NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.