Abstract
Mucoobstructive lung diseases have highlighted the importance of a proper description of the normal mucus clearance system. A useful description of the normal mucus clearance apparatus requires the presence of two gels on the airway surface (i.e., a mucus layer gel and a periciliary gel). Importantly, most mucoobstructive lung diseases are distributed heterogeneously in the lung, and exacerbations may reflect spread of the disease to previously normal areas. The spread may reflect disturbances in the balance of water between the two gel layers, producing heterogeneous mucus adhesion and infection within the lung. Ultimately, spread can produce losses of lung function that may be associated with acute exacerbation frequency.