Cough is a complex reflex, either involuntary or voluntary, generated by the respiratory system to clear the air passages of irritants, secretions, foreign bodies or obstructions and to protect the lungs from potential damage. Thus, the complex function serves as an essential protective and defensive exercise that ensures effective respiratory health and unobstructed airflow within the tracheobronchial tree. Stimuli for coughing involve various sensory nerves located primarily in the mucosa of the respiratory tract, including the nasopharynx and oropharynx, larynx, trachea, and bronchi. This has contributed to multiple cough receptors that can be activated by the following conditions: mechanical stimuli—dust or food particles in the airway, chemical stimuli—smoke or other environmental pollutants, temperature changes, and monitoring of mucus or inflammation due to infection or allergy.
When cough receptors detect the presence or absence of air, they send signals to the brainstem cough center located within the medulla oblongata. The brainstem coordinates a series of actions needed to initiate a cough, using muscle output to the motor nerves as well as sensory nerve input that controls lung involvement. The cough reflex has three main phases: the inspiratory phase—the deepest breath taken to ensure maximum expansion of the lungs; the compression phase—during which the glottis closes, and contraction of the respiratory muscles, primarily the intercostals and the diaphragm, increases the pressure within the chest cavity; and finally, the expiratory phase—the glottis opens abruptly and the released pressure manifests as a rushing stream of air that propels mucus, particles, or irritating substances away from the respiratory tract at high speed.
Cough is a very specific form of human expression characterized by certain characteristics, duration, and causes. This wide variety forms the basis for the different types of cough, ranging from acute to subacute to chronic. Acute coughs may last less than three weeks, usually associated with coughs caused by infection: colds, flu, and acute bronchitis are likely causes of acute cough. Acute coughs resolve after three to eight weeks but are sometimes called post-infectious coughs. Chronic coughs last eight weeks or longer and involve chronic medical conditions such as asthma, gastroesophageal reflux disease (GERD), chronic obstructive pulmonary disease, or more suspicious issues such as lung cancer or interstitial lung diseases.
The noise and nature of the cough serve as strong diagnostic clues for whether the cough may be dry, failing to bring up mucus, or productive, bringing up mucus or phlegm. Dry coughs are more indicative of irritation or a viral infection, while productive coughs point to bacterial infections, chronic bronchitis, or even other conditions where mucus production will be increased. The timing and frequency of coughing, in addition to other symptoms such as fever, chest pain or wheezing, will be relevant in determining the cause of the cough. For example, when a person coughs at night, it may suggest that he or she has asthma or GERD. A cough that lasts a long time but coughs up in the morning may indicate chronic bronchitis or even lung damage from smoking.
Postnasal drip can also flow outside the respiratory tract, and there are medications such as angiotensin-converting enzyme (ACE) inhibitors that cause dry coughs in many individuals. The other aspect that can bring on a cough is psychological, and this in turn can become a habitual cough, especially for a child. Such children then move into a condition called psychogenic or somatic cough syndrome because couching is observed without any notable physical cause. Environmental factors such as smoking, allergies, or occupational irritants play a large role in developing these chronic coughs.
Coughing forms a natural, harmless reflex that, on rare occasions, can complicate matters, especially with frequent changes in severity or intensity. It can make the person uncomfortable through symptoms such as sore throat and chest and muscle pain. In extreme cases, a severely intense cough has complications such as broken ribs, pneumothorax (collapsed lungs) and hemoptysis (bleeding). It can also keep a person in such a state that he or she may not feel like having a normal sleep, work or life, and can result in anxiety and depression.
Management of cough depends on the cause. In case of dry cough, antitussives or cough suppressants will provide symptomatic relief, while expectorants are for productive cough. Non-medical treatments for dry cough such as fluids, humidifiers and steam soaks will also relieve symptoms. If there is an organism or some specific condition that induces the symptoms, then specific directed treatment such as antibiotics, antivirals or inhalers will be necessary. Lifestyle changes such as quitting smoking as well as avoiding allergens and reducing exposure to environmental irritants are important for the prevention and management of chronic cough.
You know, coughs are much more than just symptoms; they are actually important physiological functions in their own right as they function to maintain the integrity of the respiratory system. They are incredibly coordinated actions between these two sensory modalities – the neurological as well as the muscular systems – that function in relation to each other to protect the airways and lungs from damage. Studying such highly diverse mechanisms and causative agents of cough increases the effectiveness of the diagnosis, treatment and prevention of cough, thereby affecting respiratory health as well as overall well-being.
