COUGH REFLEX: MECHANISM, HOW TO STIMULATE IT, DEPRESSION, SYNDROME - MEDICINE - 2025

The cough reflex, or cough reflex, is a complex automatic neurological response that triggers the sudden outflow of air through the mouth. It is commonly known as a cough and is usually associated with a respiratory illness.

Coughing is an important defense mechanism that serves to clear the airway of secretions, microorganisms, and particles; it also prevents the aspiration of foreign bodies. It is the most common symptom that patients describe in the consultation (approximately 40% of people have consulted a specialist for this condition).

Woman coughing during a conference. By GabboT - https://www.flickr.com/photos/tonyshek/15058305422, CC BY-SA 2.0, commons.wikimedia.org

Cough occurs due to the aspiration of microscopic material, pathogens and infection by microorganisms; also due to the accumulation of secretions and postnasal drip (when associated with rhinitis).

Cough is considered unproductive when, far from helping to keep the patient healthy, it persists over time, becoming a condition that irritates and inflames the mucosa, triggering an inflammatory response that can be difficult to manage.

Physiology

The cough reflex begins when there is irritation of a cough receptor, which are special neurological centers found in the trachea and main bronchi.

There are cough receptors in the external auditory canal, eardrums, stomach, heart, pharynx, and paranasal sinuses. However, the upper airway receptors are much more sensitive than the rest.

Irritation can be caused by mechanical or chemical stimuli. Chemicals include acidic, hot, and pungent. For their part, the mechanics are tactile stimuli. The impulse travels through sensory neurological fibers of the vagus nerve, mainly, reaching the cough center. This connection is known as the afferent pathway.

The cough center is an area of ​​the central nervous system that is responsible for processing stimuli and sending the signals that generate the cough.

The signal from the cough center travels through the vagus and phrenic nerves that carry it to the lungs, larynx, trachea, bronchi, intercostal muscles, diaphragm, and abdominal muscles. This route is known as the efferent pathway.

Final answer

The final answer is the sudden outflow of air through the mouth known as a cough, which occurs in 3 phases:

- Inspiratory: includes a deep air intake.

- Compression: at this time the larynx closes and the intercostal muscles, the diaphragm and the abdominal wall contract, which causes an increase in intrathoracic pressure.

- Expiratory: the larynx opens, letting a quantity of air escape abruptly accompanied by the characteristic sound of coughing. In this phase there is also a contraction of the components of the airway, which mobilizes the mucous secretions that may have lodged there.

Inspiration and expiration process. By Ivaabca - Own work, CC BY-SA 3.0, commons.wikimedia.org

Stimulation of the cough reflex

Stimulation of the cough reflex is performed to study the physiology of cough and to make it more effective in some patients who cannot adequately mobilize secretions.

The simplest stimulus is done by pressing on the trachea, above the sternal notch. The doctor stands behind the patient, who will have the neck stretched at all times, and locates the site where the sternum has a depression, sternal notch.

The patient is asked to take a deep inspiration and the trachea is pressed for 2 to 4 seconds, blocking the airway. With this maneuver, the patient is able to keep the air inside the lungs long enough to increase the intra-thoracic pressure and thus achieve the sudden exit of air that is sought.

Medical maneuver to cause the air to escape. By Unknown / CDC - This media comes from the Centers for Disease Control and Prevention's Public Health Image Library (PHIL), with identification number # 6378. Note: Not all PHIL images are public domain; be sure to check copyright status and credit authors and content providers., Public Domain, commons.wikimedia.org

Stimulation of the eardrum and soft palate are often helpful in evaluating the reflex in highly sensitive patients.

In some research studies, nebulization with citric acid or capsaicin is used, being very effective in triggering the cough response.

Cough reflex depression

In patients with degenerative diseases and in the elderly, the cough reflex can be altered.

People with these characteristics can present aspiration pneumonia, being a very frequent pathology. It consists of a lung infection caused by the aspiration of particles that in normal conditions would be cleaned by the mechanism of coughing.

From James Heilman, MD - Own work, CC BY-SA 3.0, commons.wikimedia.org

The triggers of this pathology can be simple activities, such as eating or swallowing saliva, causing very serious infections.

Those patients who present diseases that include musculoskeletal and neurological degeneration, also have problems when coughing since they breathe ineffectively.

Thus, the diaphragm and intercostal muscles fail to make sufficient contractions to mobilize secretions and clear the airway. Recurrent pneumonia and other pulmonary complications such as atelectasis are common in these patients.

When the cough reflex is depressed, evaluation and treatment by a respiratory physiotherapy service is important. These professionals specialize in teaching patients exercises that they can practice when coughing.

In cases where the person has no muscle control, the cough can be mechanically assisted through ventilators.

Cough syndrome

Cough syndrome refers to a persistent cough, lasting more than 8 weeks, as the only symptom in a patient. It occurs due to the existence of a continuous stimulus of the airway that triggers the cough.

Allergic rhinitis with postnasal drip is the main cause of cough syndrome. In these cases, the secretion produced in the nose and paranasal sinuses drips into the larynx, stimulating the sensory receptors in that area.

Other common causes of cough syndrome are bronchial asthma and gastroesophageal reflux disease (GERD).

Whooping cough is an infectious disease caused by the bacteria Bordetella pertussis. It is characterized by violent fits of coughing that lead the patient to vomit. It is very contagious and can cause a chronic cough.

References

1. Polverino, M; Polverino, F; Fasolino, M; Andò, F; Alfieri, A; De Blasio, F. (2012). Anatomy and neuro-pathophysiology of the cough reflex arc. Multidisciplinary respiratory medicine. Taken from: ncbi.nlm.nih.gov
2. Widdicombe, JG (1995). Neurophysiology of the cough reflex. European Respiratory Journal. Taken from: erj.ersjournals.com
3. Benich, J. J; Carek, PJ (2011) Evaluation of the patient with chronic cough. Am Fam Physician. Taken from: aafp.org
4. Yamanda, S; Ebihara, S; Ebihara, T. (2008) Impaired urge-to-cough in elderly patients with aspiration pneumonia. Cough. Taken from: coughjournal.biomedcentral.com
5. Barría, T; Chuang, A; Ortega, Andrés. (2018). Persistent cough and laryngeal neuropathy. Journal of otorhinolaryngology and head and neck surgery. Taken from: scielo.conicyt.cl
6. Torres-Castro, R; Monge, G; Vera, R; Puppo, H; Céspedes, J; Vilaró, Jordi. (2014). Therapeutic strategies to increase the efficacy of cough in patients with neuromuscular diseases. Medical Journal of Chile. Taken from: scielo.conicyt.cl
7. Widdicombe, J; Fontana, G. (2006). Cough: what's in a name? European Respiratory Journal. Taken from: erj.ersjournals.com