Advances in understanding and treatment of cough.

Many different conditions and diseases cause cough. The commonest acute causes are pollution, including cigarette smoke, and upper respiratory tract infection. The commonest chronic causes are postnasal drip, asthma, chronic bronchitis and gastro-oesophageal reflux. Epidemiological studies give widely different patterns of incidence. The different conditions that cause cough have in common the fact that the cough is mediated via the vagus nerves, with sensory receptors in and under the epithelium from the larynx down to the smaller bronchi. These receptors are polymodal, responding to a large variety of stimuli, including mechanical and chemical irritants, inflammatory mediators, intraluminal material and large volume changes of the lungs. With irritation and inflammation, C fibre receptors release neurokinins such as substance P, which in turn stimulate cough receptors. The central nervous pathways for the cough reflex are poorly understood. They can be activated or inhibited voluntarily. Studies on the pharmacology of the central nervous pathways of coughing are opening up new therapeutic possibilities. Other new therapies include drugs acting on the sensory receptors for cough, thereby avoiding adverse central nervous effects.