Pathophysiology and clinical presentations of cough.

The human cough reflex is still poorly understood, although it is known to occur independently of bronchoconstriction. Sensitization of the cough reflex is a unifying hypothesis for chronic dry cough in several conditions, including gastroesophageal acid reflux, angiotensin-converting enzyme inhibitor cough, and cough-variant asthma. The most common cause of chronic dry cough is a group of related conditions of chronic rhinitis, sinusitis, and postnasal drip. In these cases the cough reflex may be sensitized through an action of inflammatory mediators from the nasal mucosa on the airways or a reflex sensitization of airway sensory nerves. The association of cough with gastroesophageal reflux may occur through a local esophageal-tracheobronchial reflex. Angiotensin-converting enzyme inhibitor cough is a side effect of treatment in about 10% of patients; it probably results from inhibition of the degradation of kinins, particularly bradykinin, in the airway. Why some patients with asthma have cough as the principal feature of their disease is unclear. Tachykinins are probably involved in the mechanism of sensitization of the cough reflex, and the development of neuropeptide antagonists may open new research opportunities. A study that used ambulatory recording of cough in a group of subjects with asthma confirmed the presence of significant cough, the frequency of which did not correlate with lung function or diurnal variation in peak flow. This finding highlights the problem of cough in patients with asthma, a problem that probably has been underestimated in the past.