Coughing is a normal physiological response of the body’s defense and ventilation systems, controlled by voluntary (i.e. conscious control) or involuntary (i.e. reflex) means.

It is associated with a variety of different diseases or ailments; therefore, it is crucial to obtain a close examination of the patient’s medical history, cough duration and other related symptoms to understand the cause.

These factors can differentiate between a short-term cough which could simply be a case of an obstructed airway (i.e. choking) or the presence of a long-term chronic cough that is more likely associated with an underlying disease.

Epidemiology

Coughing is one of the most common symptoms observed by doctors and has critical implications in health and disease management. They account for more than 30 million visits to the physician a year. A systematic review in 2015 uncovered that the global prevalence of a chronic cough was 9.6% with the greatest affected areas in Oceania and Europe ^[1].

Physiology

A cough is a 3-part response triggered by the activation of airway mechanosensory receptors called slowly adapting receptors (SARS) and rapidly adapting receptors (RARS).

• Detection/Sensing: For a cough to be triggered, it must first activate afferent sensory pathways where the RARS acts as a sensor leading to a specific output (like a switch). RARS are the major contributors in triggering a cough which detects mechanical and/or chemical irritation like foreign particles, smoke, etc. The output in this case is the cough.

Once triggered, the action of a cough can be split into three main components: inspiration, compression and expiration.

1. Inspiration: The main muscles of normal inspiration (diaphragm and external intercostal muscles) activate and expand the volume of the thoracic cavity. Accessory muscles including the sternocleidomastoid and scalene muscles draw additional air into the lung to increase air volume within the chest. This subsequently increases the effectiveness of the later stages of the cough.
2. Compression: The glottis, a valve between the vocal folds in the larynx, closes tightly. This seals in the air that was inhaled during inspiration. The expiration muscles begin to contract via the passive recoil of the lungs’ elastic properties and accessory expiration muscles (abdominal and internal intercostal muscles). By decreasing the chest volume, there is a short-lasting build-up of high-pressure air in the lungs that’s ready to be expired.
3. Expiration: In the last stage, the glottis opens which allows the build-up of air to escape quickly and rapidly. Further activation of accessory expiratory muscles forcefully expels the remaining air out. This rapid movement of air exiting the lungs and through the mouth helps dislodge mucous or irritants trapped within the lining of the respiratory tract. Through multiple cycles of these 3 stages, the body can clear out any foreign material or irritants located in the respiratory tract.

A cough can be classified depending on its duration. Those lasting less than 3 weeks would be considered acute, coughs lasting 3-8 weeks are considered subacute and coughs lasting more than 8 weeks are considered chronic.

• Acute cough (<3 weeks)
• Subacute (3-8 weeks)
• Chronic (>8 weeks)

Examples of an Acute Cough

• Acute Pneumonia: An infection within the respiratory system where the lungs could fill with liquid resulting in consolidation during imaging. RARs will detect inflammatory markers and excess fluid in the airway thereby triggering a cough.
  • Why?: The lungs and the body are attempting to remove pathogens and congestion from the clogged respiratory tract.
• Foreign Body Aspiration (Choking): When an object becomes lodged within the respiratory tract (especially the trachea or main bronchi)and triggers mechanosensory RARs inducing a cough.
  • Why?: Pressure build up in the respiratory tract triggers the body to have a rapid emergency response to remove the object as quick as possible.

Examples of a Chronic Cough

• Asthma: A chronic inflammatory obstruction of the airways due to bronchial hypersensitivity which could be triggered by environmental or genetic causes.
  • Why?: Coughing is a natural response due to the inflamed/narrowed airway, allergen/environmental triggers or response to excess mucous secreted
• COPD: A progressive disease with characteristics of both chronic bronchitis and emphysema.
  • Why?: A persistent cough is present due to inflammatory markers, narrowed airways, mucous and failure of efficient expiration (i.e. wheezing) triggering RARs and a subsequent cough.

Management Principles

• Understanding the underlying source of a cough is key in providing an effective treatment.
• A detailed medical history will help determine if the cough is acute (short-term) or chronic (long-term). History taking can reveal any symptoms which may have presented itself when the cough began. Uncovering the systems impacted (immune, gastrointestinal etc.) will give a better picture of the disease.
  • For example, a cough accompanied with a fever and productive cough often indicates an infection.
  • A cough accompanied by a sour taste/heart burn can indicate GERD.
  • Shortness of breath and other specific breathing patterns (i.e. shallow rapid breaths) could indicate COPD.
• A clinical examination should be performed by examining the nose (i.e. obstruction), oropharynx (i.e. swelling, strep throat), and chest (i.e. chest x-ray).
• Pneumonia caused by a bacteria would be managed with antibiotics whereas, a cough triggered by a lodged foreign object would require the removal of the object.
  • An interesting case in 2017 investigated a man who presented to the doctor with a chronic cough. To the doctor’s surprise after a chest x-ray, they discover the patient swallowed a small traffic cone toy 40 years prior, has stayed undetected and lodged! ^[2]
• Cough medications, also known as antitussives, can be given to patients to help suppress a cough which interferes with the patients’ quality of life during work, sleep or exercise. Mucolytics are another option which can be given to help break down mucous and aid in producing a productive cough. The origins and details of an acute or chronic cough helps health care teams understand and create treatment plans tailored to each individual patient for better outcomes.

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