cough /kôf/ [AS, cohhetan] , a sudden audible expulsion of air from the lungs. Coughing is preceded by inspiration, the glottis is partially closed, and the accessory muscles of expiration contract to expel the air forcibly from the respiratory passages. Coughing is an essential protective response that serves to clear the lungs, bronchi, and trachea of irritants and secretions or to prevent aspiration of foreign material into the lungs. It is a common symptom of diseases of the chest and larynx. Chronic coughing may be indicative of tuberculosis, lung cancer, bronchiectasis, asthma, or bronchitis. Otitis media, allergies, subdiaphragmatic irritation, congestive heart failure, and mitral valve disease may be associated with episodes of severe chronic coughing. Coughing is a reflex action that may be induced voluntarily and, to some extent, voluntarily inhibited. The cough-reflex center is located in the medulla of the brain. It responds to stimulation transmitted by the glossopharyngeal (CN9) or vagus (CN10) nerve. The reflex is initiated by chemical or mechanical irritation of the pharynx, larynx, or tracheobronchial tree. Because the function of coughing is to clear the respiratory tract of secretions, it is important that the cough expel accumulated debris. If it does not because of, for example, weakness or inhibition by pain, instruction in effective coughing and deep-breathing exercises is helpful. Persons with chronic coughs may obtain symptomatic relief through environmental controls that reduce irritants in and humidify air. Medication may help dilate the bronchi, liquefy secretions, and increase expectoration. Antitussive medications are sometimes prescribed even in the absence of mucus or congestion. When congestion is present and the patient is unable to cough up the mucus, an expectorant may be prescribed.
