Lung clearance index: should we really go back to nitrogen washout?

We (Innovision ApS, Odense, Denmark) are the manufacturer of the AMIS 2000 medical mass spectrometer system that, using user-specific software and hardware, was adapted to perform MBW. The AMIS 2000-based devices are now considered the ‘‘gold standard’’ device for SF6 LCI measurements in cystic fibrosis patients by opinion leaders in the field [2]. This device has been used in the vast majority of studies demonstrating the clinical value of SF6 LCI in cystic fibrosis patients, with one recent notable exception: the demonstration of the change in LCI caused by Ivacaftor in cystic fibrosis patients with normal forced expiratory volume in 1 s, where a prototype version of our other system, Innocor, adapted for open-circuit SF6 LCI, was used [3].