Regulation of mucociliary clearance in health and disease

Airway secretions are cleared by mucociliary clearance (MCC), in addition t o other mechanisms such as cough, peristalsis, two-phase gas-liquid flow an d alveolar clearance. MCC comprises the cephalad movement of mucus caused b y the cilia lining the conducting airways until it can be swallowed or expe ctorated. MCC is a very complex process in which many variables are involve d, all of which may modify the final outcome. The structure, number, moveme nt and co-ordination of the cilia present in the airways as well as the amo unt,composition and rheological properties of the periciliary and mucus lay ers are determinants of MCC. Physiological factors such as age, sex, posture, sleep and exercise are rep orted to influence MCC due to a change in the cilia, the mucus or the peric iliary layer, or a combination of these. Environmental pollution is suspect ed to have a depressant effect on MCC dependent on different factors such a s pollutant concentration and the duration of exposure. Most studies focus on sulphur dioxide, sulphuric acid, nitrogen dioxide and ozone. Tobacco smo ke and hairspray have been noted to have a negative influence on MCC. Some diseases are known to affect MCC, mostly negatively. The underlying mechani sm differs from one illness to another. Immotile cilia syndrome, asthma, br onchiectasis, chronic bronchitis, cystic fibrosis and some acute respirator y tract infections are among the most frequently reported. The present paper reviews normal mucociliary clearance and the effects of d iseases on this process.