Reference values for lung clearance index (LCI) derived from sulphur hexafluoride multiple breath washout testing

Abstract

Background: Ventilation heterogeneity is frequent in obstructive lung disease and linked to small airway dysfunction. It can be potentially revealed using multiple breath washout (MBW) testing while being missed by commonly used tests. Lung clearance index (LCI) is the most commonly used MBW outcome parameter but normative data is scarce. We therefore set out to provide LCI reference values in pulmonary healthy adults. Methods: We prospectively evaluated 104 pulmonary healthy non-smokers and smokers (mean age 51±20, range 20-88 years). LCI was derived from triplicate MBW measurements based on Sulphur hexafluoride (SF6). We used the 2.5% (LCI2.5) and 5% (LCI5) stopping points and defined upper limit of normal (ULN) as the 95th percentile. Results: LCI2.5 increases from a mean 6.3 to 8.8 in subjects between 20 and 90 years. Upper limits of normal were calculated as of 7.4 to 9.9 (Figure). LCI5 correspondingly yielded lower mean values between 4.9 and 6.9 with ULN of 5.7 and 7.7, respectively. Age was the only meaningful parameter influencing LCI explaining 47% of its variance. Conclusions: LCI showed an age-dependent increase from early adulthood to senectitude. No influence of height, weight and gender was seen. Reference values can now be provided over the whole age range and for two different stopping points.