A cough can arise for a variety of reasons, for which the cause must first be determined. Physiologically speaking, the cough is a necessary body function. It is the body’s mechanism of action for clearing material from the airway. For example, if some fluid or small food particle is aspirated upon ingestion, cough acts as a protective mechanism.
The cough mechanism is thought to be the result of cough receptors found in the nose, sinuses, auditory canals, nasopharynx, larynx, trachea, bronchi, pleurae, diaphragm , and probably, the pericardium and GI tract. (1) If one or more of the receptors is stimulated, the resultant cascade travels through the vagus and glossopharyngeal nerves to the medulla, which is located in the brainstem. This is known as the cough center.
Upon the stimulation of a given receptor, the cough center is activated. This causes a reflexive action of laryngeal, intercostal, and abdominal muscles; combined with closure of the glottis and deep inspiration. The processes increase lung pressure and causes the glottis to forcefully open forcefully. This is the event we term cough. This cascade can also be externally stimulated from either applied force, or by forced expiration.
Cough is categorized into productive and nonproductive types, which refers to whether sputum or blood is being expelled. A chronic cough is defined as a cough that persists beyond one month, as coughs may occur as a single or paroxysmal episode.
Troubled breathing (dyspnea), chest or throat pain, hoarseness, or weight loss are vital to understanding the cause of a chronic cough. The most common cause of chronic cough is cigarette smoking. Smokers cough is referred to as a productive cough. This production is due to the expelling of a mucus-like sputum that appears clear to yellow, or even brown.
The physical characteristics of sputum can help inform the care provider as to the nature of the disorder. For example, if there is gritty material, it may be a condition known as broncholithiasis. Another important aspect to consider is the onset, duration, and chronology of the cough. A well educated provider will ask to examine all attributes of the patient’s history, and will perform a full physical examination to determine the nature of the chronic cough. Laboratory tests and diagnostic imaging will likely be performed to rule out conditions such as bronchogenic carcinoma (a type of lung cancer) or tuberculosis.
Other causes of chronic cough include;
- COPD (chronic obstructive pulmonary disease)
- hypersensitivity pneumonitis
- interstitial lung disease
- aryngeal tumor
- pulmonary edema
- chronic lung abcess
- allergic rhinitis
As mentioned, the cause of the chronic cough must first be determined before initiating any treatment plan. Any patient with a chronic cough must be seen by a primary care provider to identify and treat the underlying cause. If the cough is productive, it usually should not be suppressed because the sputum must be expelled.
Again, cigarette smoking is the most common cause of productive cough. Smoking damages the mucociliary tract in the bronchial pathways by causing metaplasia (change in cell type) of the cells in this area. These cells will revert back to a state of normality over time, once a person quits smoking. Therefore the only treatment for chronic cough caused by cigarette smoking is smoking cessation.
Treatments directed specifically for a cough can be categorized into antitussives, expectorants, demulcents, local anesthetics, mucolytics, antihistamines, and bronchodilators (2).
- Antitussives inhibit or suppress the cough reflex by either acting centrally or peripherally. The most commonly prescribed medications in this class are dextromethorphan and codeine.
- Local anesthetics include; lidocaine, benzocaine, and tetracaine. These drugs suppress the cough reflex and are used before a medical procedure such as bronchoscopy.
- Expectorants release bronchial secretions by decreasing the viscosity (thickness) of this material, and by increasing the amount of fluid which facilitates the expulsion of sputum. Due to lack of objective evidence, there is controversy about whether this class of treatment has any beneficial effect upon chronic cough. Expectorants include; syrup of ipecac, guaifenesin, iodides, creosote, ammonium chloride, and terpin hydrate.
- Demulcents provide a protective coat over pharyngeal mucosa and, thus, are only useful for coughs originating above the larynx. They include natural remedies such as honey, licorice, and wild cherry, administered in the form of syrups or lozenges.
- Mucolytics reduce the viscosity of mucus, and include nebulized acetylcysteine and isoproterenol. These medicines are generally used for chronic bronchitis or cystic fibrois.
- Antihistamines may be used if the chronic cough is due to allergic rhinitis. Otherwise, they are considered ineffective and possibly harmful for use aginst other causes of cough.
- Bronchodilators such as ephedrine and theophylline can be used if there is associated bronchospasm.
Glutathione Glutathione, a tripeptide composed of three amino acids (cysteine, glutamic acid and glycine), acts as a mucolytic. Nebulized (aerosolized) glutathione has been observed to improve breathing and overall well being in patients with COPD. (3)
N-Acetylcysteine N-Acetylcysteine is a precursor to glutathione and also acts as a mucolytic. It has been shown to reduce the recurrence rate of bronchitis. (4)
Allium Sativum (Garlic) Garlic, and other plants found in the garlic and mustard family, decrease the viscosity of mucus by altering the structure of its mucopolysaccharide constituents; which assists with expectoration. There may also be a reflexive irritation to the pharynx and increased blood flow to the respiratory mucosa, all of which encourage expectoration (5).
Syrup of ipecac Syrup of ipecac induces vomiting which generally produces noticeable expectoration as a reflex. This type of action is termed stimulating or reflexive expectoration. Ipecac is thought to act on peripheral and central 5-HT3 receptors (6).
Althea Officianalis (Marshmallow) Marshmallow has a demulcent action on respiratory mucosa. Extracts from marshmallow have been shown to have pronounced antitussive activity with oral doses of 1000 mg/kg body weight. 50mg/kg of isolated polysaccharides have also been shown to be equally effective in the treatment of cough. (7)
Glycyrrhiza Glabra (Licorice) One of the key constituents of licorice is glycyrrhetinic acid (GA). When given orally, GA has a similar antitussive effect as codeine. (8)
Inula Helenium (Elecampagne) Elecampagne may provide antitussive action in those suffering from chronic cough. Volatile oils in this herb have been shown to be useful for inhibiting tracheal smooth muscle spasm. (9) The herbs primary constituents, inulin & mucilage, are thought to be responsible for this herb’s purported antitussive effect. (10)
Prunun Serotina (Wild Cherry) (PS) The bark of wild cherry contains compounds known as cyanogenic glycosides. These glycosides, once broken down in the body, act by quelling spasms in the smooth muscles lining bronchioles, which relieves coughs (11).
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4. Grandjean EM et al. Efficacay of long-term N-acetylcysteine in chronic bronchopulmonary disease: a meta-analysis of published double-blind, placebo controlled clinical trials. Clin Ther 2000;22:209-221.
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6. Minton NA. Volunteer models for predicting antiemetic activity of 5-HT3 receptor antagonists. British Journal of Clinical Pharmacology 1994; 37(6):525-530.
7. Nosalova G, Strapkova A, Kardosova A et al. Antitussive action of extracts and polysaccharides of marsh mallow (Althea officinalis L., var. robusta). Pharmazie 1992;47(3):224-226.
8. Anderson DM, Smith WG. J Pharm Pharmacol 1961; 13:396-404.
9. Mills S, Bone K. Principles & Practice of Phytotherapy. Churchhill Livingstone, NY, NY, 2000:29.
10. Lininger et al. Healthnotes: Clinical Essentials, Herb Monographs. Prima Publishing, Rocklin, CA, 2001.
11. Lininger et al: Healthnotes: Clinical Essentials, Herb Monographs. Prima Publishing, Rocklin, CA. 2001