Background Lung clearance index (LCI 2.5 ), measured by nitrogen-multiple breath washout (N 2 -MBW), is a sensitive measure of ventilatory inhomogeneity that can be performed awake/unsedated from aged 3 years. However, concerns have been raised about the feasibility of LCI 2.5 measurement by N 2 -MBW in adults with cystic fibrosis (CF), especially those with advanced lung disease, due to prolonged test durations. We assessed the feasibility, technical acceptability and patient perception of N 2 -MBW in adults and children/adolescents with CF within the exercise as an airway clearance technique-CF feasibility trial. Methods N 2 -MBW (Exhalyzer-D, EcoMedics, Switzerland) was performed on two separate occasions, by multidisciplinary trial staff. Data were centrally over-read (European Cystic Fibrosis Society LCI Core Facility). Outcomes included the proportion of technically acceptable tests, numbers of trials per test, times per trial and total time to perform N 2 -MBW. Comparisons were made according to age group and forced expiratory volume in 1 s (FEV 1 ) category ( > 70% vs <70% predicted). Participants also completed a questionnaire assessing acceptability and willingness to repeat testing. Results 49 participants (21 female; age: 10–55 years, FEV 1 : 38%–113% predicted) completed N 2 -MBW. Median (IQR) test durations were similar for adults (42 (27–55) min) and children (37 (26–44) min) with CF. Technically acceptable LCI 2.5 results were obtained for 90/94 (95.8%) tests. Most participants rated the test easy to perform (87%) and comfortable (93%), with none reporting unwillingness to repeat N 2 -MBW testing. Conclusions N 2 -MBW testing is feasible, technically acceptable and well-tolerated in people with CF across a wide age and disease severity spectrum. With appropriate standardised training and over-reading, LCI 2.5 represents a robust outcome measure for consideration in CF clinical trials. Trial registration number NCT05482048 .
Urquhart et al. (Wed,) studied this question.