(The New York Times News Service) -- A cat and its dander can trouble people with asthma long after the animal has left the room, a new study shows.

Cat allergens, in fact, can hamper the lung function of those who have asthma and are allergic to cats for up to 22 hours after exposure, says Jared W. Allen, a postdoctoral researcher at the David Geffen School of Medicine at the University of California, Los Angeles.

That's because "cat allergens can be smaller particles than normal allergens, such as pollen or flowers, and reach deeper into the airway of the lungs," Allen explains. He presented his findings Tuesday at the Radiological Society of North America annual meeting in Chicago.

Asthma, a chronic lung disease, affects more than 17 million Americans, according to the American Academy of Allergy, Asthma and Immunology. It is marked by an inflammation of the airways that makes it difficult for air to move in and out of the lungs.

Asthmatics often experience cough, shortness of breath and difficulty breathing during an attack.

Allen says he started the study after noticing that asthmatics often complain of symptoms even days after exposure to triggers such as cats or cat hair that spur an asthma attack. Conventional lung-function tests may come up normal, he says, so his team decided to do more sophisticated testing that can measure the amount of air trapped deep in the lung.

"The amount of air trapped in the lung correlates with airway reactivity -- how sensitive your airways are," he says. "The more air is trapped, the more symptoms you will have."

His team performed a test called high-resolution computed tomography, using it to examine the functioning of the small airways deep in the lungs to detect the extent of impairment caused by exposure to the allergen.

Allen's team first induced an asthma attack in 10 persons with asthma and known allergies to cats, then took a high-resolution computed tomography. The next day, they exposed these individuals to cats, then took another scan six hours later. They took yet another scan 22 hours after that cat exposure, during another induced asthma attack.

Even after the outward symptoms such as difficulty breathing abated, all 10 persons continued to experience a decrease in lung function, the testing showed.

"Our conclusions are (that) there is a significant response in the small airways of the lung that can persist up to 22 hours," Allen says. "And not only may there be increased air trapping, but the patient's airways could be hypersensitive to additional challenges."

So if exposure to cat allergens has left an allergic person with symptoms, and then he or she is exposed again, they may be even more sensitive the second time around, Allen says. If that second exposure occurs within 22 hours, he says, that could make the second attack worse than the first.

The findings may help explain why some persons with allergies and asthma seem to still have symptoms when traditional tests come out normal, says Dr. David Mendelson, an associate professor of radiology at Mount Sinai Medical Center in New York City.

"To me, the provocative thing is, he used these newer techniques, and he has a result that says (that) you can see a positive result on this (for airway problems) when you have no other objective evidence of a patient's complaint," Mendelson says.

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