• Change in FEF75 levels
  
• Change in RV/TLC ratio
  
• Loss of bronchodilator responsiveness (measured at the end of the one month treatment period and follow-up evaluation when participant is 5 years of age)
  

• Change in asthma symptom scores (measured at the end of the one month treatment period and follow-up evaluation when participant is 5 years of age)
  

Asthma prevalence has steadily increased in the United States since the early 1980s, with infants and young children showing the largest increase. Some young children experience wheezing, but it is not known if this is related specifically to asthma. Wheezing may be caused by a respiratory syncytial virus, maternal smoking, a family history of asthma, or allergies. In addition, some infants who experience wheezing may have small or dysfunctional airways and may not respond well to commonly prescribed anti-inflammatory medications. Because of the many causes of wheezing, in order to prescribe the most effective treatment, it is necessary to thoroughly assess lung function, allergic sensitization, and airway inflammation. The purpose of this study is to examine the causes of moderate to severe wheezing in infants and assess the infants' response to inhaled corticosteroid therapy. The study will also assess new and safer ways to measure lung function and airway inflammation.

This study will enroll infants with moderate to severe persistent wheezing. At study entry, participants will undergo lung function testing, which will include a spirometry test, measures of lung volumes, and assessment of bronchodilator responsiveness. Exhaled breath condensate and blood will be collected, and skin-prick testing will be performed to test for allergies. Participants will then be randomly assigned to receive either fluticasone, an inhaled steroid, or placebo for one month. At the end of the month, lung function testing will be performed and exhaled breath and serum measures will be collected to assess airway inflammation. Participants will attend a follow-up evaluation at age 5 years. During the evaluation, lung function, exhaled breath condensate, and serum markers of inflammation will be measured again, and skin-prick testing will also be performed again.