Ventilation: Collateral

When an airway in the lung becomes obstructed, there exists the possibility for that obstructed region to get limited ventilation through pathways that are commonly called collateral channels. Ventilation that results from such pathways is called collateral ventilation. Collateral ventilation may have functional roles in both normal and pathologic situations. Several different channels have been suggested as the site of such ventilation, with the alveolar pores of Kohn being most commonly cited. However, when considering the anatomy and physiology of such potential pathways, it is highly unlikely that these alveolar pores could provide sufficiently low resistance to account for the measured magnitude of collateral flow. Rather, the interbronchial channels of Martin, which exist at the level of the terminal bronchiole, are far more likely to be the primary site of collateral ventilation. These collateral channels exist in nearly all mammalian species. In humans, the collateral channels have been shown to be altered in lung pathology, particularly in both emphysema and asthma. Measurement of the collateral resistance may provide the only means of directly measuring the dimensions of most peripheral airways in the lung in living subjects.