M-mode obstruction index (MIO): an ultrasound method to evaluate presence and severity of airway obstruction in COPD patient

Abstract

Introduction: MIO is an ultrasound index obtained from the ratio between the diaphragmatic excursion during the first second of a forced expiration (FEDE1, cm) and the total expiratory excursion (EDEmax, cm). Zanforlin et al showed that a MIO below 77% may discriminate patients with airway obstruction from healthy subjects.

Aims and objectives: To confirm the validity of MIO in detecting airway obstruction and to assess its sensitivity in identifying the severity of the obstruction.

Methods: Spirometry and M-MODE diaphragmatic ultrasound were performed in 21 subjects with normal spirometry (group A) and in 38 COPD patients (group B), 18 GOLD 1-2 (group B1) and 20 GOLD 3-4 (group B2). FEDE1, EDEmax and their percent ratio (MIO) were calculated during a maximal forced open-mouth expiration. The median value of 3 repeated measurements was used for the analysis.

Results: ANOVA showed that MIO was higher (p<0.05) in group A (88±6.9%) than in group B (59±12%) and in group B1 (69±4%) than in B2 (50±10%). In all subjects MIO was related to FEV1 %pred (r=0,79,p<0.001). ROC analysis showed that the optimal MIO cut-off to discriminate airway obstruction (FEV1/VC<70%) was 73.5% (AUC 0.98,p<0.01,sensitivity 94,7%,specificity 95%) while the cut-off to discriminate B2 (FEV1<50%) from B1 group was 60.9% (AUC 0,93,p<0.01,sensitivity 95%,specificity 94,4%).

Conclusions: MIO is a good index to detect airway obstruction and it’s closely related to FEV1. We identified a MIO cut-off value for airway obstruction of 73.5% (similar to the 77% previously proposed) and we found that a MIO of 60.9% can discriminate patients with severe from those with mild-moderate airway obstruction.