Circulation of the airway mucosa.

The major part of tracheobronchial blood flow is distributed to the mucosa. Its microvasculature comprises 10-20% of the subepithelial tissue volume, with blood flow ranging from 30 to 95 ml.min-1.100 g wet tissue-1 in different animal species. Mucosal blood flow is influenced by vascular and airway pressures, inspired air conditions, and autonomic neurotransmitters. Several inflammatory mediators and neuropeptides are capable of enhancing the permeability for macromolecules in postcapillary venules and of augmenting tissue water volume, often with a concomitant increase in perfusion. These microvascular responses of the lower airway mucosa have an important role under various conditions of physiological stress and in airway inflammation.