Chapter 034. Cough and Hemoptysis (Part 1)

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Harrison's Internal Medicine Chapter 34. Cough and Hemoptysis Cough Cough is an explosive expiration that provides a normal protective mechanism for clearing the tracheobronchial tree of secretions and foreign material. When excessive or bothersome, it is also one of the most common symptoms for which patients seek medical attention. Reasons for this include discomfort from the cough itself, interference with normal lifestyle, and concern for the cause of the cough, especially fear of cancer. Mechanism Coughing may be initiated either voluntarily or reflexively. As a defensive reflex it has both afferent and efferent pathways. ...

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Chapter 034. Cough and Hemoptysis (Part 1) Harrison's Internal Medicine > Chapter 34. Cough and Hemoptysis Cough Cough is an explosive expiration that provides a normal protective mechanism for clearing the tracheobronchial tree of secretions and foreign material. When excessive or bothersome, it is also one of the most common symptoms for which patients seek medical attention. Reasons for this include discomfort from the cough itself, interference with normal lifestyle, and concern for the cause of the cough, especially fear of cancer. Mechanism
Coughing may be initiated either voluntarily or reflexively. As a defensive reflex it has both afferent and efferent pathways. The afferent limb includes receptors within the sensory distribution of the trigeminal, glossopharyngeal, superior laryngeal, and vagus nerves. The efferent limb includes the recurrent laryngeal nerve and the spinal nerves. The cough starts with a deep inspiration followed by glottic closure, relaxation of the diaphragm, and muscle contraction against a closed glottis. The resulting markedly positive intrathoracic pressure causes narrowing of the trachea. Once the glottis opens, the large pressure differential between the airways and the atmosphere coupled with tracheal narrowing produces rapid flow rates through the trachea. The shearing forces that develop aid in the elimination of mucus and foreign materials. Etiology Cough can be initiated by a variety of irritant triggers either from an exogenous source (smoke, dust, fumes, foreign bodies) or from an endogenous origin (upper airway secretions, gastric contents). These stimuli may affect receptors in the upper airway (especially the pharynx and larynx) or in the lower respiratory tract, following access to the tracheobronchial tree by inhalation or aspiration. When cough is triggered by upper airway secretions (as with postnasal drip) or gastric contents (as with gastroesophageal reflux), the initiating factor can go unrecognized and the cough may persist. Additionally, prolonged exposure to such irritants may initiate airway inflammation, which can itself precipitate cough
and sensitize the airway to other irritants. Cough associated with gastroesophageal reflux is due only in part to irritation of upper airway receptors or to aspiration of gastric contents, as a vagally mediated reflex mechanism secondary to acid in the distal esophagus may also contribute. Any disorder resulting in inflammation, constriction, infiltration, or compression of airways can be associated with cough. Inflammation commonly results from airway infections, ranging from viral or bacterial bronchitis to bronchiectasis. In viral bronchitis, airway inflammation sometimes persists long after resolution of the typical acute symptoms, thereby producing a prolonged cough that may last for weeks. Pertussis infection is also a possible cause of persistent cough in adults; however, diagnosis is generally made on clinical grounds (Chap. 142). Asthma is a common cause of cough. Although the clinical setting commonly suggests when a cough is secondary to asthma, some patients present with cough in the absence of wheezing or dyspnea, thus making the diagnosis more subtle ("cough variant asthma"). A neoplasm infiltrating the airway wall, such as bronchogenic carcinoma or a carcinoid tumor, is commonly associated with cough. Airway infiltration with granulomas may also trigger a cough, as seen with endobronchial sarcoidosis or tuberculosis. Compression of airways results from extrinsic masses such as lymph nodes or mediastinal tumors, or rarely from an aortic aneurysm.
Examples of parenchymal lung disease potentially producing cough include interstitial lung disease, pneumonia, and lung abscess. Congestive heart failure may be associated with cough, probably as a consequence of interstitial as well as peribronchial edema. A nonproductive cough complicates the use of angiotensin- converting enzyme (ACE) inhibitors in 5–20% of patients taking these agents. Onset is usually within 1 week of starting the drug but can be delayed up to 6 months. Although the mechanism is not known with certainty, it may relate to accumulation of bradykinin or substance P, both of which are degraded by ACE. In contrast, angiotensin II receptor antagonists do not seem to increase cough, likely because these drugs do not significantly increase bradykinin levels. The most common causes of cough can be categorized according to the duration of the cough. Acute cough (8 weeks) in a smoker raises the possibilities of chronic obstructive lung disease or bronchogenic carcinoma. In a nonsmoker who
has a normal chest radiograph and is not taking an ACE inhibitor, the most common causes of chronic cough are postnasal drip (sometimes termed the upper airway cough syndrome), asthma, and gastroesophageal reflux. Eosinophilic bronchitis in the absence of asthma has also been recognized as a potential cause of chronic cough.