Cough is a common and nonspecific symptom that may bring patients to the emergency department, particularly if the cough interferes with activity or sleep. Pathophysiology

Cough is a protective reflex that acts to clear secretions and foreign debris from the tracheobronchial tree. 11 Coughing is initiated by stimulation of irritant receptors located largely in the larynx, trachea, and major bronchi. These receptors are stimulated by inhaled irritants (e.g., dust), allergens (e.g., ragweed pollen), toxic substances (e.g., gastric acid), hypo- or hyperosmotic liquids, inflammation (e.g., asthma), cold air, instrumentation, and excess pulmonary secretions. 12 Minor cough receptors located in the upper respiratory tract (sinuses and pharynx) and chest (pleura, pericardium, and diaphragm) may stimulate coughing. Signals from these receptors travel via the vagus, phrenic, and other nerves to the cough center in the medulla.

Once stimulated, the cough center initiates the stereotypical cough pattern: a deep inspiration followed by attempted expiration against a closed glottis that suddenly opens, providing for a forceful exhalation of gas, secretions, and foreign debris from the tracheobronchial tree. Extremely high peak airway velocities have been measured with coughing. The coughing sound is generated at the larynx and resonates in the nasal cavity and the lungs. 11

Coughing patterns vary widely according to the underlying pathologic condition of the lung, the presence or absence of secretions, and whether the cough is voluntary or involuntary. Thus, it is not surprising that the frequency, duration, and quality of coughing vary among patients.

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