Maximal Airway Response in Adolescents With Long-term Asthma Remission and Persisting Airway Hypersensitivity: Dyspnea
At the time of diagnosis, all had PC20 levels < 18 mg/mL. Atopy was defined by at least one positive skin-prick test result to a panel of 12 common aeroallergens in the presence of positive and negative controls. Most subjects showed a positive skin reaction to house dust mites. Long-term clinical remission was assumed if the subjects reported a complete absence of wheezing and dyspnea at rest and on exertion, and they had not received any medication in order to control asthmatic symptoms for at least 24 months before the study. These subjects underwent spirometry and a methacholine inhalation test. Eligibility criteria for the study also included a FEV1 of at least 70% of the predicted value and a PC20 level < 18 mg/mL.
A second group of adolescents with current atopic asthma was also recruited. These patients had a history of mild symptoms (episodic wheezing or dyspnea) within the previous year, which had been controlled by an as-needed bronchodilator, and a positive skin test result. Those subjects with a history of major exacerbations requiring systemic corticosteroids or near-fatal asthma were excluded. None of the patients had used inhaled or oral corticosteroids, long-acting P2-agonists, leukotriene antagonists, sodium cromoglycate, or nedocromil sodium in the year prior to entry into the study. Candidates were selected, from the results of methacholine inhalation test at the initial diagnostic workup, by matching according to PC20 levels with the subjects with asthma remission.
In the first phase of study, these two subject groups underwent a high-dose methacholine inhalation test, and a maximal airway response as well as the PC20 was measured. None of the subjects had exhibited any symptoms of upper respiratory infection or asthma exacerbation in the month preceding the study. Given that most of the subjects were sensitized predominantly to house dust mites, it was decided to perform the test during the winter season (December to February), when the levels of house dust mites have been found to be the lowest and most constant in our country.