In their recent review, Shah et al 1 made an excellent presentation of the latest perspectives of lung volume reduction with endobronchial valves, emphasising the importance of collateral ventilation (CV) and fissure analysis on selecting proper candidates, as shown in the VENT studies.2 ,3 The authors described representative cases of patients with positive and negative CV using the Chartis system4 and recommended that persistence of flow after 5 min of balloon inflation, particularly where more than a litre of air has been expelled, suggests the presence of significant CV.

Our centre has extensive experience in evaluating CV with Chartis. We agree with Dr Shah and colleagues on their clear definition of positive CV. We feel, however, that the accurate assessment of negative CV is not always …