 - use of ICS within 8 weeks prior to the first visit, a cumulative life-time systemic prednisolone use more than 3 days at a dose of 2 mgkg, an equipotent dose of another systemic corticosteroid or ICS use more than 4 weeks, respiratory infection in the 14 days preceding lung function measurement and obvious tracheobronchomalacia or other structural defect. 