Multiple breath nitrogen washout test and methacholine challenge test in clinical suspicion of asthma

Abstract

Background: Nitrogen washout tests are more sensitive than spirometry to evidence ventilation inhomogeneity; however, its role in patients with clinical suspicion of bronchial asthma and normal spirometry has not been investigated so far. Aims and Objectives: To assess small airways of patients with clinical suspicion of asthma and normal spirometry with multiple breath nitrogen washout tests (MBNW). Methods: This pilot, cross-sectional study assessed data from 50 adult patients with clinical suspicion of asthma. Subjects were submitted to MBNW, MCT, FeNO and skin prick test. In NMBW the main outcome was lung clearance index (LCI). In MCT we assessed the pulmonary methacholine concentration to either a fall ≥20% of FEV1 (PC20) or an increase ≥ 40% in airway resistance (PC40). Results: Fifty consecutive patients were included with mean age 45 ± 16.3 years, 62% females, 51% never smokers and 58% with a positive skin prick test. Patients had a basis mean FEV1 94%pred (±10), FEV1/FVC 79.9% (±2.9) and FVC 100.9% (±14.05). MCT was positive in 45% of the patients according to resistance increase criteria (mean PC40 0.37mg ± 0.06) and their LCI% was significantly higher than the ones with a negative test (125.04% ± 20.95 vs. 112.23% ± 15.61, p= 0.028). The same tendency was observed in patients with positive MCT according to FEV1 decrease (LCI% 122.04% ± 19.5 vs. 114.36 ± 17.75, p=0.07). There was a significant association between LCI% and PC40 (Beta -0.340 95%CI -2.503-0.063, p=0.04), even after adjustment for smoking status and presence of atopy. Conclusions: Patients with positive MCT had higher LCI, justifying more detailed evaluation of the MBNW method in clinical suspicion of asthma.