[1] Univ Groningen, Univ Med Ctr Groningen, Dept Pulm Dis & Home Mech Ventilat, AA62,Postbox 30001, NL-9700 RB Groningen, Netherlands
[2] Univ Groningen, Univ Med Ctr Groningen, Groningen Res Inst Asthma & COPD GRIAC, Groningen, Netherlands
[3] Tampere Univ, Dept Resp Med, Tampere, Finland
[4] Tampere Univ, Fac Med & Hlth Technol, Tampere, Finland