Expiratory nitric oxide will collected bed side with a bag collection system (Siemens) and analysed within 72 h at the Department of Clinical Physiology, Turku University Central Hospital, Turku, Finland (20). Oscillometric studies will be performed at the Department of Paediatric Turku University Central Hospital, Turku, Finland. Nasal cytokine (IL-8 and RANTES) measurements will be performed in the Children’s Hospital, University of Texas Medical Branch, Galveston, Texas, USA. Other laboratory tests will be performed in the Central Laboratory, Turku University Central Hospital, Turku, Finland.