Characteristics of unilateral main bronchus obstruction and differentiation from chronic obstructive pulmonary disease by spirometry

BACKGROUND: Pattern of flow-volume (F-V) loop in unilateral main bronchus obstruction (UMBO) is under-represented and sometimes misinterpreted as chronic obstructive pulmonary disease (COPD). METHODS: A cross-sectional study was performed among patients with UMBO and COPD confirmed by bronchoscopy, radiographic imaging and spirometry from 2006 to 2019. Data were extracted from electronic medical records. Spirometry data and flow-volume curves (F-V curves) were analyzed. Expiratory F-V curve was classified as monophasic or biphasic according to the absence or presence of breakpoint separating two distinct slopes. Propensity score method was used to reduce the selection bias, and logistic analysis in combination with decision tree approach was performed to explore the differences among groups. RESULTS: Fifty-six patients with UMBO, 121 individuals with COPD and 68 healthy subjects were included. Typical biphasic expiratory F-V curve was observed in 57.1% in UMBO group, especially of grade II (stenosis was 51–90%), and in 46.3% in COPD group, while biphasic inspiratory curve presented in 7.1% of UMBO, and none in COPD. In UMBO, breakpoints tended to appear gradually and smoothly between MEF(75) and MEF50, whereas in COPD they often occurred abruptly and rigidly, ahead of MEF(75). CONCLUSIONS: The characteristics of F-V curve, apart from biphasic pattern, the location and configuration of breakpoint in expiratory curve, seemed to be important features of UMBO, which might help to differentiate them from COPD. More data is needed to validate these findings.