Mucus hypersecretion is a common physiological response to inhalation exposures to pollutants or infectious agents. In most cases, it is short-lived and doesn't cause significant problems to lung function. However, chronic stress/exposure conditions can cause airway remodeling and chronic mucus hypersecretion, leading to respiratory diseases such as chronic obstructive pulmonary disease (COPD) and bronchiectasis.

COPD is a chronic inflammatory lung disease that causes obstructed airflow from the lungs. Mucus hypersecretion is a major feature in all COPD patients, including those without cough and sputum production. Chronic mucus hypersecretion in COPD patients is associated with increased exacerbations, negatively impacting their health status and driving disease progression. Recent estimates show that chronic mucus hypersecretion in the global population ranges from 3.5 to 27%.

Exacerbations of COPD are acute worsening of respiratory symptoms associated with physiological deterioration, which can be triggered by infections, air pollution, or other factors. The strongest predictor of future exacerbations is the number of exacerbations in the prior year. Patients with COPD exacerbations have a higher risk of death, with 23% of hospitalized patients dying within one year. Furthermore, 1 in 5 patients hospitalized with an exacerbation will need re-hospitalization within 30 days.

Given the significant impact of chronic mucus hypersecretion on COPD patients, it should be a therapeutic target in all COPD subjects. Current treatments for chronic mucus hypersecretion in COPD include bronchodilators, mucolytics, anti-inflammatory agents and airway clearance using chest physiotherapy. Newer treatments, such as long-acting muscarinic antagonists (LAMAs) and long-acting beta-agonists (LABAs), have shown promising results in reducing exacerbations and improving lung function.

Bronchiectasis is another respiratory disease characterized by irreversible expansion of the bronchial lumen, which compromises mucus clearance and allows bacteria to colonize the airway. Patients with bronchiectasis show reduced mucociliary activities in the airway and reduced expectoration ability. The rheoligical properties of their mucus are also altered, making it more viscous and difficult to clear.

The release of toxins secreted by bacteria in bronchiectasis causes the activation of pathogen-associated molecular patterns and danger-associated molecular patterns to increase inflammation, which in turn stimulates goblet cell hyperplasia and metaplasia, leading to airway mucus hypersecretion. Treatment for bronchiectasis focuses on managing infections and mucus hypersecretion, with antibiotics and mucolytics being the mainstay of therapy. Airway clearance techniques, such as chest physiotherapy, can also help improve mucus clearance and reduce exacerbations.

In conclusion, chronic mucus hypersecretion is a significant problem in respiratory diseases such as COPD and bronchiectasis, negatively impacting patient health status and driving disease progression. Early diagnosis and management of chronic mucus hypersecretion are crucial to improving patient outcomes and reducing the burden of these diseases on the healthcare system.