[Pathophysiology, diagnostics and therapy of chronic cough: neuronal reflexes and antitussiva]

Cough is the number one symptom for patients to visit a physician worldwide. It is an important neuronal reflex which serves to protect the airways from inhaled exogenous microorganisms, thermal and chemical irritants. Moreover, it prevents the airways from mucus retention.The cough reflex is initiated by activation of different cough receptors. These cough receptors can be divided into three groups according to their electrophysiological properties: into the two Aδ-fiber types "rapid-adapting mechanoreceptor" (RAR) and "slow-adapting mechanoreceptor" (SAR), and the C-fiber receptor.The stimulus is detected by cough receptors which conduct the signal to the cerebral cough centre via vagal-sensory neurons. The cough itself is mediated by efferent motoneurons. Hence the cough reflex consists of 5 functionally sequential parts 1: the cough receptors 2, the primary afferent fibres of the N. vagus 345, N. trigeminus and N. glossopharyngeus 1, the cough centre in the medulla oblongata (N. tractus solitarius) 678, the afferent fibres of the N. phrenicus, spinal nerve and N. laryngeus recurrens, as well as the diaphragm and the abdominal, intercostal and laryngeal muscles. The cough receptors are mainly located in the larynx, trachea and main bronchi 2.The event of coughing can be divided into four subsequent parts: After the first phase of fast inspiration with an opened glottis, there is compression with a closed glottis and increasing tracheal pressure, acceleration and ultimately maximum expiration with an opened glottis 9. According to its characteristics, cough can be split into two distinct types, "aspiration cough", which is loud and involuntary, and "urge-to-cough sensation", which describes an irritant, scratchy, and controlled cough of slowly increasing intensity 10.Acute cough mostly develops because of infection of the respiratory system 111213 and ends spontaneously after 4 weeks. In contrast to this, bacterial infection with pathogens like Adenovirus, Bordetella pertussis and Mycoplasms can last up to 8 weeks 121314. In additional to the division of cough according to its cause, it can also be differentiated according to its manner: dry and mucus-producing cough.With this review we want to give an overview of neuronal processes and mechanisms, as well as diagnostics of and therapy for chronic cough. Thereby the focus is also placed on the efficiency of already established and potential future antitussive agents.