Single And Multiple Breath Washout As Compared To The Metacholine Test In Patients With Suspected Asthma

Introduction: The clinical application of washout tests is limited and one of the most used tests to diagnose asthma in patients with normal spirometry remains the bronchoprovocation test with methacholine (MCT). The aim of the study was to compare the diagnostic efficacy of the MTC, nitrogen single (N2 SBW) and multiple (N2 MBW) washout tests in subjects with clinical suspicion of asthma. Methods: In this investigator-initiated, single center study, we enrolled 106 patients between April 2019 and January 2020 with FEV1/FVC≥70% and a clinical suspicion of asthma. All patients performed a N2 SBW and N2 MBW before the MCT, as well as N2 SBW between each MTC dose. Clinical symptoms were assessed with the ACQ and AQLQ questionnaires. Results: The average age was 41±1.4 years with a preponderance of female participants 62% (66/106). 42% were current or past smokers and 83/102 (81%) had a positive prick test result. FeNO≥25 ppb was observed in 27%. 21/95 (22%) and 17/95 (18%) patients had been previously treated with corticosteroids and long-acting beta-agonists. MCT test was positive (fall FEV1 ≥ 20%) in 48% of the cases. There was no significant difference in age (44 vs. 39, p=0.092), FeNO (20 vs. 22, p=0.25), ACQ score (0.8 vs. 1.1, p=0.13), AQLQ total score (p=0.16), LCI (p=0.57), Scond (p=0.68) or Sacin (p=0.53) between patients positive or negative MTC test. Conversely, SIII at baseline (1.5 vs. 2.0; p=0.002) and after each methacholine provocation (p<0.0001) differed significantly between the two groups. Conclusions: SIII seems to be associated with airway ventilation heterogeneity in patients with asthma as assessed by methacholin test.