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Persistence of Airway Obstruction and Hyperresponsiveness in Subjects With Asthma Remission: Statistical Analysis

Published in Asthma

Persistence of Airway Obstruction and Hyperresponsiveness in Subjects With Asthma Remission: Statistical AnalysisStudy Design
The subjects came to the laboratory on three different occasions. On the first visit, one of the investigators administered a questionnaire on the characteristics of their former asthma (duration, severity, medication requirements, potential initiating factors, time of asthma diagnosis and of remission, including last 2 years’ respiratory symptoms, and family history of asthma). Lung volumes, expiratory flows, and bronchodilator response were measured. Skin prick tests with 26 common airborne allergens completed this first visit.
Measurements
The subjects were asked to measure their peak expiratory flow rates (PEFRs) with a peak flow meter (mini-Wright) twice daily for a 2-week period. They recorded on a diary card the results of three reproducible PEFR measurements in the morning and in the evening. Pulmonary function tests included three reproducible measurements of FEVi and forced vital capacity (FVC) before and after inhalation of albuterol (200 fig). Measurements were obtained with a spirometer (Vitalograph PTF II). Pulmonary volumes were measured by body plethysmography according to the method of Dubois et al. canadian neightbor pharmacy

Airway responsiveness to methacholine was determined according to the method described by Juniper et al on two occasions on separate days, to assess repeatability. Before each FEVi measurement, during the methacholine challenge, estimated reduction of FEVi and perception of breathlessness were evaluated according to a modified Borg scale (0 to 10).  Results were expressed as mean±SEM. Pulmonary function tests in asthmatics “in remission” and their matched controls were compared by paired Student’s t tests. The PC20 was measured from individual dose-response curves and geometric mean values were calculated for each subject (two tests) and then for the groups. Paired t tests were done on the natural logarithms of PC20 values. For FEVi, FVC, forced expiratory flow between 25 and 75 percent of FVC (FEF25-75%), and the ratio FEVi/FVC, which are related variables, a p value <0.0125 (0.05/4) was considered as statistically significant. For A FEVi and A FEF25-75% and for the mean and maximal APEFR, the target p value was p <0.025. Natural logarithm of PC20 and duration of asthma (years), duration of remission (years), or age at diagnosis of asthma were compared by linear correlation tests and p value <0.05 was considered as statistically significant. A PC20 value of >128 mg/ml was considered as equal to 128 mg/ml for calculations and correlation tests. Two sets of comparisons of exasthmatics were made, first with the 30 initially enrolled “control” subjects and second with 30 normoresponsive subjects (the 5 hyperresponsive subjects being replaced by 5 normoresponsive subjects for this last analysis).