The physiology of cough.

Cough is comprised of three phases (inspiratory, compressive and expiratory) and serves as a vital defensive mechanism for lung health. It prevents pulmonary aspiration, promotes ciliary activity and clears airway debris. The importance of an intact cough mechanism is reflected in the occurrence of pulmonary problems when cough is inefficient. Cough efficiency is dependent on physical/mechanical aspects (respiratory muscles, mucus, airway calibre and larynx) and integrity of the neurophysiological pathway of cough. The understanding of the latter has progressed significantly (albeit mostly in animals) with the discovery of vanniloid receptors (and subtypes) and, more recently, by the characterisation of distinct cough receptors. However, the relative contributions of previously described airway afferents/receptors to cough are still disputed. Plasticity of the peripheral and central afferent pathways in cough has recently been shown to be important in pathological states associated with increased cough. To date, little is known of the developmental aspects of cough.