![]() However, it is known that the mucin, MUC5AC, which is the principal gel-forming mucin is upregulated in the airway inflammation that is characteristic of this condition. The pathology of mucus hypersecretion is also complex in asthma. ![]() ![]() Neutrophil activity leads to hypersecretion and associated accumulation of excess mucus, resulting in an increased risk for patients to acquire opportunistic infections from inhaled pathogens. Bronchiectasis is a lung condition in which the airways become abnormally and permanently widened. In COPD, mucus viscosity is also increased, often by the action of agents in smoke inhalation associated with cigarette use as a cause of this deleterious change. The causes of excessive mucus production are more complex than in CF and have been attributed to increased secretion, decreased mucociliary clearance and/or reduced mucin degradation within the airways. Mucus hypersecretion is also an important aspect of chronic obstructive pulmonary disease (COPD), resulting in effective airway narrowing leading to eventual blockage, an outcome that ultimately impairs lung function in association with episodes of severe acute exacerbations of disease. The accumulation of over-abundant and highly viscous mucus that cannot be easily cleared via the mucociliary escalator results in plug formation, blocking gas exchange via the alveolar sacs served by that airway. In cystic fibrosis (CF), the viscosity increase is brought about by dysregulation of the epithelial sodium channel, resulting in dehydration of airway surfaces. Several acute and chronic respiratory diseases result in a large increase in mucus viscosity and/or rate of mucus production (hypersecretion). Effective mucus clearance is therefore essential for maintaining respiratory health. This process ultimately transfers the mucus to the oropharynx via the carina, whereupon it is either swallowed or expectorated by coughing. The viscoelastic properties of the overlying mucus layer facilitate the transfer of energy from the cohesive beating cilia to mobilize the mucus layer. ![]() The projecting microscopic hair-like cilia (6–7 μm long and 0.2–0.3 μm in diameter ), move mucus and incorporated debris up the respiratory escalator. Under ordinary conditions, mucus is produced continuously from goblet cells lining the epithelium of the conducting airways. The other components include 2–3% glycoproteins (from goblet cells and submucosal glands), proteoglycans (0.1–0.5%), lipids (0.3–0.5%), proteins, and deoxyribonucleic acid (DNA). Normal mucus is a low-viscosity fluid primarily comprised of approximately 95% water. A further function of mucus is to provide moisture to the epithelial lining. The presence of a thin mucus lining also defends the airways of lungs from pathogens seeking to target the cells lining the airways or using the lungs as a portal of entry to organs distal to the lungs via either the lymphatic and/or bloodstream routes. Mucus secretion is a natural process that protects the delicate alveolar gas-exchange region of the lungs from inhaled insoluble particle accumulation by capture and removal via the mucociliary escalator. Advice is provided as to the features that appear to be the most effective at mucus mobilization. Particular attention is given to the evolving application of oscillating positive expiratory pressure (OPEP) therapy via a variety of devices. This narrative review article focuses on the use of non-pharmacological airway clearance therapies (ACTs) that promote mechanical movement from the obstructed airway. These processes severely impair the delivery of inhaled medications to obstructed regions of the lungs, resulting in poorly controlled disease with associated increased morbidity and mortality. Diseases such as cystic fibrosis (CF) and associated bronchiectasis, as well as chronic obstructive pulmonary disease (COPD), result in mucus layer thickening, associated with high viscosity in CF, which can eventually lead to complete airway obstruction. Mucus secretion in the lungs is a natural process that protects the airways from inhaled insoluble particle accumulation by capture and removal via the mucociliary escalator.
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