SBW and FOT in healthy and asthmatics pre and post bronchial challenge

Abstract

BACKGROUND: Nitrogen (N2) single breath washout (SBW) and Forced Oscillation Technique (FOT) are sensitive to airway closures and choke points by different physical mechanisms. AIM: to characterize SBW and FOT in healthy and asthmatics pre and post methacholine challenge (Mch) and to compare the information provided by the two approaches. METHODS: Lung function was evaluated in 13 healthy subjects (9F/4M, 46±13years) and 12 stable asthmatics (7F/3M, 37±13years) by SBW and within-breath FOT at 5, 11 and 19Hz. Closing volume (CV N2 ) and the slope of phaseIII (SIII) from SBW were identified by a blinded expert. Resistance (R 5 ), reactance (X 5 ) and frequency dependence of resistance (R 5 -R 19 ) were measured during quiet breathing and during a slow vital capacity maneuver (SVC). CV FOT was defined as the volume corresponding to X 5 =-7 cmH2O*s/l during SVC. Asthmatics were studied also post Mch at 20% fall in FEV 1 . RESULTS: No differences in FOT and SBW parameters were found between healthy and asthmatics pre-Mch. However, all of them changed significantly in asthmatics after Mch, with CV FOT showing the biggest change for all the patients (minimal change=103% vs -3% in CV N2 ; 8% in SIII; 22% in R 5 ; 48% in X 5 and 75% in R 5 -R 19 ). pIII N2 correlates with all FOT parameters while CV N2 showed only a weak correlation with CV FOT (Spearman, p=0.04). CONCLUSION: CV FOT might be useful to assess in a more accurate and sensitive way the response to bronchial challenge.