"We studied cat allergen because it's an extra-fine particle that is both airborne and capable of penetrating deep into the small airways of the lungs," said lead author Jared W. Allen, Ph.D., researcher at David Geffen School of Medicine at the University of California, Los Angeles.
Exposure to cat allergen is very common and can contribute significantly to morbidity in the 15 million Americans with asthma. In many cases, the lung changes triggered by allergen exposure do not produce symptoms but contribute to persistent inflammation in the small airways that, if untreated, could lead to subsequent severe asthma attacks.
The prolonged inflammatory lung reaction is both clinically silent and poorly detectable with conventional pulmonary function tests. However, Dr. Allen and colleagues have developed a new high-resolution computed tomography (HRCT) technique that examines the function of small airways deep in the lungs to reveal the extent of impairment.
For the study, Dr. Allen's team used baseline pulmonary function tests and HRCT to measure lung function in 10 people with known allergy to cats. After being exposed to cat allergens, the patients were studied for three days. The results showed all 10 patients exhibited significant and prolonged decrease in lung function, even after outward symptoms had abated.
"Twenty-two hours after exposure, patients appeared to have otherwise recovered from respiratory symptoms according to clinical measures," Dr. Allen said. "However, HRCT still showed significant air trapping, suggesting that constriction and inflammation of the small airways remain long after initial exposure."