Bronchial Mucus: Basic research and clinical application

Mucoobstructive lung diseases, including chronic obstructive pulmonary disease, asthma, cystic fibrosis, non-cystic bronchiectasis and, primary ciliary dyskinesia, are characterized by intrapulmonary accumulations of hyperconcentrated mucus. Clearance of intrapulmonary mucus by the high-velocity airflow generated by cough is the major rescue clearance mechanism in subjects with mucoobstructive diseases. Ultimately, the mucus accumulation in diseases reflects the failure of said clearance mechanism. Given the multifunctionality of mucus, the various mechanisms of mucus production and exposure to the environment, but also to the systemic circulation, it is not surprising that both its genesis and its operation can be compromised in said pathologies. We proceed to review the biochemical and biophysical properties of mucus relative to airway function, the mucin concentration in health and diseases and the integrated cilia and cough-dependent mucus clearance. Then we proceed to review various diseases that have mucus dysfunction in common, the mechanism that generates this dysfunction and how it impacts the symptoms and the natural evolution of these pathologies. At the end it is discussed how restoration of cough efficacy may be most effectively provided by restoring mucus concentrations to normal ranges with hydrating agents coupled with viscosity-lowering agents.