Normalized phase III slope (Sn ) indices from multiple breath washout (MBW) estimate ventilation inhomogeneity. Alternate (*) protocols for Sn indices exist, however the utility of these outcomes in children with mild-to-moderate cystic fibrosis (CF) is unknown.
METHODS
We measured nitrogen MBW and spirometry in 135 children (43 controls) aged 4-18 years. We assessed validity, practicability, and reliability of Sn protocols. Outcomes included the ability to detect abnormal lung function, test agreement, measurement duration, intra-test repeatability, and quality.
RESULTS
Lung clearance index (LCI) was abnormal in 80 (87%), Scond in 55 (60%), Scond* in 17 (19%), Sacin in 10 (11%), Sacin* in 11 (12%), and FEV in 28 (30%). Alternate protocols reduced measurement duration. Agreement of indices to detect abnormal lung function was poor. The quality of analysis and repeatability deteriorated with the alternate technique compared to standard.
CONCLUSION
In children with mild-to-moderate CF lung disease, alternate protocols seem practical but clinimetric properties of standard Sn protocols are preferable.
