The superficial surface of the tracheobronchial epithelium is covered by a blanket of mucus, a heterogeneous mixture of water, inorganic salts, glycoproteins, proteoglycans, lipids and other proteins, and peptides [5,6]. Airway mucus humidifies inspired air and traps inhaled matter, such as particulates, bacteria, viruses, irritant gases, and aerosols . This latter action of mucus in concert with coordinated ciliary beating (which transports the mucus toward the mouth) or coughing serves an important defensive mechanism in the normal airways for removal of foreign particulates.
The rate of removal of mucus from the airways is determined by such factors as mucus viscosity, the amount of mucus produced, and the degree of ciliary activity. These processes may be influenced by a variety of diseases, including asthma, cystic fibrosis, and chronic bronchitis [82,83]. In patients suffering from cystic fibrosis or chronic bronchitis, mucus hypersecretion is evident and mucociliary function is impaired. The failure to clear mucus from the airways leads to airway obstruction and to chronic colonization of the airways with bacterial organisms (which leads to lung infections and airway inflammation and damage). In asthmatic subjects, airway mucus is more viscous and ciliary transport mechanisms are inhibited [82,83]. In these diseases, the therapeutic objective is to improve mucus clearance from the airways. For example, aerosols of water or saline (especially hypertonic saline) promote clearance of mucus by liquefying secretions [84,85]. Acetylcysteine is a compound that reduces disulfide bonds in mucoproteins and mucopolysaccharides and thereby diminishes mucus viscosity by reducing the size of constituent molecules . Administered as an aerosol, acetylcysteine may irritate the airways and induce bronchospasm in hyperreactive individuals, necessitating the concomitant administration of a b2-adrenoceptor agonist. A more efficacious mucolytic agent for the treatment of cystic fibrosis is human DNase (dornase), a recombinant human protein. Delivered to the airways as an aerosol, this agent reduces mucus viscosity by degrading extracellular DNA released from neutrophils infiltrating the mucus .
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If you suffer with asthma, you will no doubt be familiar with the uncomfortable sensations as your bronchial tubes begin to narrow and your muscles around them start to tighten. A sticky mucus known as phlegm begins to produce and increase within your bronchial tubes and you begin to wheeze, cough and struggle to breathe.