COPD treatment: about collateral channels and collapsing airways.

Collateral channels inside the human lungs? This phenomenon, first described by KOHN [1] in 1893, is the subject of recent investigations in the field of endoscopic lung volume reduction (ELVR) for the treatment of severe chronic obstructive pulmonary disease (COPD). ELVR with valves is a new and promising therapeutic option for irreversibly damaged emphysematous lungs. The aim of the therapy is the complete occlusion of a lobe, with endobronchial one-way valves delivered through a bronchoscope to intentionally induce a targeted atelectasis of the most damaged lobe. Many studies have described improvements in lung function, quality of life and exercise capacity in a subset of severe COPD patients, where interlobar collateral ventilation was an exclusion criterion for valve treatment [2–8]. Interlobar collateral ventilation is defined as the ventilation of alveolar structures through passages or channels that bypass the normal airways, and includes the interalveolar pores of Kohn, the bronchiole–alveolar communications of Lambert and the interbronchiolar pathways of Martin [9–14]. Collateral ventilation is present not only in COPD lungs, but also in healthy lungs [15]. The physiological function of the collateral channels is still unknown; in COPD patients they might provide channels of low resistance to better ventilate less emphysematous lung segments. The importance of collateral ventilation was ignored for over a century, but now, with their role in ELVR and the development of new bronchoscopic techniques, the study of these little channels has gained enormously in importance.