Potential utility of the N2 VC SBW test in cystic fibrosis (CF)

Introduction: Cystic fibrosis (CF) lung disease is characterized by uneven ventilation distribution, which can be measured by the N 2 multiple breath washout (MBW) and the vital capacity single breath washout (VC SBW) test. A MBW test is more time consuming than a VC SBW test. Aims: To determine the prevalence of abnormal MBW and SBW test results in teenagers and adults with CF. Methods: Spirometry and triplicates of N 2 MBW and N 2 VC SBW were performed in 31 subjects (9 females) with CF, aged 13-45 yrs (median 23 yrs) using the Exhalyzer D washout device. Washout results were related to 400 healthy control subjects for N 2 MBW and 224 for N 2 VC SBW. Results: FEV 1 was abnormal in 7/31 (23%) subjects, VC SBW phase III slope (S III ) was abnormal in 20/31 (65%), LCI 29/31 (94%), S cond 30/31 (97%), S acin 24/31 (77%) and fast-to-slow regions specific ventilation ratio in 30/31 (97%). Among the 11 subjects with normal VC SBW S III , 10 (91%) showed abnormal MBW results. Consclusions: Abnormal N 2 VC SBW S III was seen in the majority of teenagers and adult CF subjects with normal FEV 1 , suggesting additional value of this method, but normal S III does not exclude pathological MBW outcomes.