Progression of lung function with age. A) Changes assessed by repeated measurements of plethysmographic functional residual capacity (FRCpleth), functional residual capacity obtained by the multibreath nitrogen washout (FRCMBNW), and volume of trapped gas (VTG). VTG was calculated as the difference between FRCpleth and FRCMBNW. B) Changes of lung clearance index (LCI) as a measure of ventilation inhomogeneities and effective specific airway resistance (sReff), as measure of airway narrowing. C) Changes of forced vital capacity (FVC), forced expired volume in one second (FEV1) and maximal expired flow at 50% FVC (FEF50) in relation to age. All parameters expressed as z-scores.