Collateral ventilation

[5] In normal respiratory conditions, airflow is through the pathway of least resistance offered by the bronchial tree, to the alveoli and back to the bronchi and trachea.

[2] In this normal state the pathways of collateral ventilation offer a greater resistance to airflow and are thus redundant or insignificant.

[2][1] The interalveolar pores of Kohn are epithelial-lined openings between adjacent alveoli, with a diameter of between three and thirteen micrometres (μm).

[6] It has been suggested that the pores of Kohn are too small to offer a pathway of decreased resistance, and that the larger interbronchiolar channels of Martin are the primary site of collateral ventilation.

[1] The presence of interlobar collateral ventilation will affect the choice of lung volume reduction procedure that may be offered in severe cases of emphysema.

Ageing can alter the size of the pores of Kohn, further reducing the normal resistance of the collateral ventilation pathways.

[3][8] In lung volume reduction procedures interlobular collateral ventilation is a major factor that can affect a successful outcome.

In chronic bronchitis where the airways are more affected than the lung parenchyma, collateral ventilation does not come into play and the blood is less oxygenated giving the bluish colour of the blue bloaters.