Cough

Cough

A young boy coughing due to pertussis.
ICD-10	R05.
ICD-9	786.2
MedlinePlus	003072
eMedicine	ENT/1048560

In medicine, a cough (pronunciation Latin: tussis) is a sudden and often repetitively occurring defence reflex which helps to clear the large breathing passages from excess secretions, irritants, foreign particles and microbes. The cough reflex consists of three phases: an inhalation, a forced exhalation against a closed glottis (the complex of the vocal folds), and a violent release of air from the lungs following opening of the glottis, usually accompanied by a distinctive sound.^[1] Coughing can happen voluntarily as well as involuntarily.

Frequent or severe coughing usually indicates the presence of a disease. Many viruses and bacteria benefit by causing their host to cough, which helps to spread the disease to new hosts. Coughing is classified as acute (of sudden onset) if it is present less than three weeks, subacute if it is present between three and eight weeks, and chronic when lasting longer than eight weeks. A cough can be dry or productive, depending on whether sputum is coughed up. Most of the times, coughing is acute and caused by a respiratory tract infection. Coughing can be triggered by food entering the windpipe rather than the esophagus due to a failure of the epiglottis in patients who have difficulties swallowing. Smoking and air pollution are common causes of coughing.^[1] Provided the patient is a non-smoker and has a normal chest X-ray, the three most common causes of chronic cough are asthma, gastroesophageal reflux disease and post-nasal drip. Other causes of chronic cough include chronic bronchitis, heart failure and medications such as ACE inhibitors.

Since cough is a natural protective reflex, suppressing the cough reflex might have deleterious effects, especially if the cough is productive.^[2] Nonetheless, coughing might be severe enough (in terms of psychological, physical and social distress) to warrant treatment. This should be targeted towards the cause as much as possible, for example by smoking cessation and discontinuing ACE inhibitors. Some patients may only be worried about serious illnesses, and reassurance may suffice. Cough suppressants (or antitussives) such as codeine or dextromethorphan are frequently prescribed although scientific evidence supporting their use is often of poor quality. Other treatment options may target airway inflammation or may promote mucus expectoration.

Physiology

A cough is a protective, primitive reflex in healthy individuals. The cough reflex is initiated by stimulation of two different classes of afferent nerves, namely the myelinated rapidly adapting receptors, and nonmyelinated C-fibers with endings in the lungs. However it is not certain that the stimulation of nonmyelinated C-fibers leads to cough with a reflex as it's meant in physiology (with its own five components): this stimulation may cause mast cells degranulation (through an asso-assonic reflex) and edema which may work as a stimulus for rapidly adapting receptors.

Causes

Cough can be a sign of respiratory tract infections such as tracheobronchitis, pneumonia, pertussis and tuberculosis. In patients with a normal chest X-ray, tuberculosis is a rare finding. Pertussis is increasingly being recognised as a cause of troublesome coughing in adults. Cough can also worsen in an acute exacerbation of chronic obstructive pulmonary disease.

The common causes of chronic dry coughing include post-nasal drip, gastroesophageal reflux disease, asthma, post viral cough and ACE inhibitors. When coughing is the only complaint of a person who meets the criteria for asthma (bronchial hyperresponsiveness and reversibility), this is termed cough-variant asthma. Two related conditions are atopic cough and eosinophilic bronchitis. Atopic cough occurs in individuals with a family history of atopy, abundant eosinophils in the sputum, but with normal airway function and responsiveness. Eosinophilic bronchitis is also characterized by eosinophilia in the sputum, without airway hyperresponsiveness or an atopic background. This condition responds to treatment with corticosteroids.

Individuals who smoke often have a smoker's cough, a loud, hacking cough which often results in the expiration of phlegm. Coughing has also been linked to air pollution.

A foreign body can sometimes be suspected, for example if the cough started suddenly when the patient was eating. Rarely, sutures left behind inside the airway branches can cause coughing. A cough can be triggered by dryness from mouth breathing or recurrent aspiration of food intro the windpipe in people with swallowing difficulties.

Cough may also be caused by conditions affecting the lung tissue such as bronchiectasis, cystic fibrosis, interstitial lung diseases and sarcoidosis. Coughing can also be triggered by benign or malignant lung tumors or mediastinal masses. Through irritation of the nerve, diseases of the external auditory canal (wax, for example) can also cause cough. Cardiovascular diseases associated with cough are heart failure, pulmonary infarction and aortic aneurysm.

Coughing may also be used for social reasons, such as the coughing before giving a speech. Cough may also be psychogenic, which is different from habit coughing and tic coughing.^[3] Coughing may occur in tic disorders such as Tourette's syndrome, although it should be distinguished from throat-clearing in this disorder.

Given its irritant nature to mammal tissues, capsaicin is widely used to determine the cough threshold and as a tussive stimulant in clinical research of cough suppressants. Capsaicin is what makes chilli peppers spicy, and might explain why workers in factories with these vegetables can develop a cough.

Complications

The complications of coughing can be classified as either acute or chronic. Acute complications include cough syncope (fainting spells due to decreased blood flow to the brain when coughs are prolonged and forceful), insomnia, cough-induced vomiting, rupture of blebs causing spontaneous pneumothorax (although this still remains to be proven), subconjunctival hemorrhage or "red eye," coughing defecation and in women with a prolapsed uterus, cough urination. Chronic complications are common and include abdominal or pelvic hernias, fatigue fractures of lower ribs and costochondritis.

Treatment

Coughs can be treated with cough medicines. Dry coughs are treated with cough suppressants (antitussives) that suppress the body's urge to cough, while productive coughs (coughs that produce phlegm) are treated with expectorants that loosen mucus from the respiratory tract.

Cough suppressants act to reduce the urge to cough. Centrally acting cough suppressants, such as codeine and dextromethorphan, work by depolarization, or a dulling, of the vagus nerve, the nerve leading from the brain stem and serving the chest area. Benzonatate, sold under the brand names Tessalon Perles or Tessalon Capsules, works by anesthetizing stretch receptors in the lungs.

Research has demonstrated that gargling with a mixture of warm water and salt washes away the layer of mucus on the throat containing bacteria and proteins that cause inflammation, according to the American Academy of Otolaryngology.^[4]

During injections

Coughing during an injection can lessen the pain of the needle stick caused by a sudden, temporary rise in pressure in the chest and spinal canal, inhibiting the pain-conducting structures of the spinal cord.^[5]

Psychological causes of Cough

Sometimes a cough can be found to have no apparent physical or medical cause. In these instances emotional and psychological problems are likely causes and the cough is often called a "psychogenic cough" (also known as a "habit cough" or "tic cough"). However, other illnesses have to be ruled out before a firm diagnosis of psychogenic cough is made. Psychogenic cough is thought to be more common in children than in adults. A possible scenario: psychogenic cough develops in a child who has a chronically ill brother or sister.

Social aspects of coughing

Coughing is not always involuntary, and can be used in social situations. Coughing can be used to attract attention, release internal psychological tension, or become a maladaptive displacement behavior. It is believed that the frequency of such coughing increases in environments vulnerable to psychological tension and social conflict. In such environments, coughing may become one of many displacement behaviors and/or defense mechanisms.

See also

• Croup
• Pertussis
• Kennel cough

References

• McCool F (2006). "Global physiology and pathophysiology of cough: ACCP evidence-based clinical practice guidelines.". Chest 129 (1 Suppl): 48S–53S. doi:10.1378/chest.129.1_suppl.48S. PMID 16428691. Full text
• Irwin, RS, Glomb, WB, Chang, AB (2006). "Habit Cough, Tic Cough, and Psychogenic Cough in Adult and Pediatric Populations.". Chest 129 (1 Suppl): 174S–179S. doi:10.1378/chest.129.1_suppl.174S. PMID 16428707. [1]

^ Arella, A. (nd), Coughing as an Indicator of Displacement Behaviour, <http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ33337.pdf> (Unpublished thesis)