A cat and its dander can trouble people who A harr. asthma long after the animal has left the room according to a new study.

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

"Cat allergens can be smaller particles than normal allergens, such as pollen or flowers, and [they can] reach deeper into the airway of the lungs," Allen explains.

The Study

Allen started this study after noticing that asthmatics often complain of symptoms even days after exposure to the triggers-such as cats or hair-that had spurred the 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 that is 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 that is trapped, the more symptoms you will have."

His team performed a test called high-resolution computed tomography (HRCT) 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 people who had known allergies to cats, and then performed a HRCT. The next day, they exposed these individuals to cats, and took another scan six hours later. The researchers performed 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 people 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 for up to 22 hours," Allen says. 'And the patient's airways could be hypersensitive to additional challenges."

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

The findings may help explain why some people who have 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 that [Allen] used these newer techniques, and you can see a positive result [for airway problems] when you have no other objective evidence of a patient's complaint," Mendelson says.

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