More Relaxation by Deep Breath on Methacholine- Than on Exercise-Induced Bronchoconstriction During the Routine Testing of Asthmatic Children

Children were referred to the lung function department by their pediatric pulmonologist. Asthma was defined by a complaint of wheezing, cough, dyspnoea or chest tightness at rest or on exercising and a positive response to methacholine or exercise challenge.

The response to exercise was considered positive when Forced Expiratory Volume in 1 s (FEV1) decreased at least 8% from Baseline.

The response to methacholine was considered positive when FEV1 decreased at least 20% or Rrs increased at least 50% from baseline, at or below a cumulated dose of 1,200 μg.

Bronchodilator medications were discontinued at least 12 hours prior to the testing and provocation allowed when the child had been free of respiratory symptoms for at least 2 weeks and baseline FEV1 was larger than 70% pred. Exercise and methacholine groups were matched for age, height, baseline FEV1 z-score, a moderate level of airway response to challenge and DI amplitude ranging 40-60% of the predicted Forced Vital Capacity (FVC). Written informed consent was obtained from the children and their parents for the procedures. Procedures for spirometry, exhaled fraction of NO (FENO), GrsDI (Respiratory conductance response to a deep inhalation) and challenges have been described previously. Acceptable GrsDI's were analyzed at a 10-20% FEV1 decrease from baseline. Statistics were performed using Mann-Whitney, Chi square tests and multiple regression as required. Data are median and interquartile range.