John Beale, Post-Gazette Duane Primac of Ford City takes a drink while working on a repaving project along Route 268 in East Franklin, Armstrong County, He said with the heat he drinks as much as a gallon a day. Click photo for larger image.

Pinch your nose closed and breathe through a straw for one full minute.

By the time the minute is up, you'll be ready for a big gulp of fresh air.

Carol Ann Kuczma, director of programs and services at the American Respiratory Alliance of Western Pennsylvania, said it demonstrates what some asthma sufferers and people with respiratory ailments experience when temperatures climb into the 90s with a dew point at 72 percent, as happened yesterday.

For people with asthma, heat and humidity can make the act of getting enough air into one's lungs a sizable undertaking. The hot, humid spell that continued yesterday turned southwestern Pennsylvania into a danger zone for breathing.

Consider that heat increases ozone, nitrogen oxide and other pollutants. It also boosts the amount of mold in the air, all of which can trigger asthma attacks, said Dr. Andrej Petrov, assistance professor of medicine in the Division of Pulmonary, Allergy and Critical Care Medicine at the University of Pittsburgh Medical Center.

The mold count listed yesterday on the American Academy of Allergy, Asthma and Immunology's Web site, he noted, was 23,121 per cubic meter, which he described as "very high."

Although good research is lacking on the effect of heat and humidity on asthma sufferers, Dr. Petrov said it's clear to him why they can trigger asthma attacks.

Heat increases metabolism and body temperature, which makes the body use more energy and require more oxygen. For anyone with respiratory problems, the need for more oxygen poses problems, he said.

Humidity, meanwhile, makes it more difficult to lower one's core body temperature, which keeps the body working longer and harder, again increasing the need for oxygen.

"That's what happens for moderate or severe asthmatics who are not adequately controlled," Dr. Petrov said. "But asthmatics in good therapy, like Jerome Bettis, can play a football game in hot weather."

Asthma is a chronic inflammatory pulmonary disorder that prompts obstruction of the airways. But its effects can be treated with medication and lifestyle changes.

Dr. Petrov said he's still awaiting a definitive study that proves that heat and humidity can trigger asthma attacks.

"It's a great question," he said. "We're all looking for the answer."

Dr. David Nash, assistant professor of asthma, allergy and immunology at Children's Hospital, said he's open to new research on the topic, but has seen no solid evidence that heat and humidity are triggers.

"As a general rule, temperature extremes are hard on asthmatics, but the exact mechanism is not well known," he said. "No one talks about high temperatures and humidity as triggers."

True in the academic arena, but don't tell that to asthmatics.

Dr. Ritu Pabby, allergist at Allegheny General Hospital, said her patients identify heat and humidity as common triggers for asthma, just as cold, dry air is a documented trigger.

There's other evidence that heat and humidity put an added burden on people with asthma.

Yesterday, the Allegheny General Hospital emergency room reported three asthma emergencies, which was deemed to be an unusually high number for one day, said Heather Holtschlag, hospital spokeswoman.

Mercy Hospital's emergency room had no such episodes.

Ms. Kuczma said people with asthma tend to monitor the dew point.

The National Weather Service at Pittsburgh International Airport defines dew point as the amount of water vapor in the air. When dew point and temperature are the same, it means 100 percent humidity.

The highest dew point for the region, the National Weather Service said, is about 75. But Ms. Kuczma said a dew point of 60 and above can pose problems for those with asthma.

"We've had some calls," she said. "Most people who come to us have been educated enough to know about weather and to know their limitations. On days when it's not as blatant as today, they'll call and say, 'Boy, it's a heavy-air day.' "

This week, she said, has been full of heavy-air days.

Doctors and respiratory specialists suggest that people with respiratory problems remain indoors with the air conditioner and humidifier working. They should also drink plenty of fluids and make sure to take all prescribed medications.

But Ms. Kuczma said not only asthma sufferers are feeling the effects of the heat and humidity. Everyone has felt the effects of recent heavy-air days.

"When you are in air conditioning, you get immune to the heat," she said. "Then you go outside into the convection oven and you say, 'Put a fork in me. I'm done.' "