Pathophysiology of Cough

What is a cough?

Protective mechanism that ensures the removal of mucus, noxious substances and infectious organisms from the larynx, trachea and large bronchi.

Where are cough receptors located?

Nose, sinuses, auditory canals, nasopharynx, larynx, trachea, bronchi, plurae, diaphragm and possibly the pericardium and GI tract.

Describe what occurs once a cough receptor is stimulated.

Vagus and glossopharyngeal nerves transmit the impulse to the cough centre in the medulla. The impulse is then transmitted to the larynx and intercostal and abdominal muscle. Deep inspiration is followed by closure of the glottis, relaxation of the diaphragm, and contraction of the abdominal and intercostal muscles. This results in increased pressure in the lungs, and the glottis opens to release the cough.

Name the 3 types of cough receptor.

Rapidly adapting receptors, slowly adapting receptors and nociceptors on C-fibres.

What type of stimuli do RARs respond to?

Mechanical stimuli, cigarette smoke, ammonia, acidic and alkaline solutions, hypotonic and hypertonic saline, pulmonary congestion, atelectasis and bronchoconstriction.

What type of stimuli do nociceptors on C-fibres respond to?

Chemical stimuli, inflammatory and immunological mediators (histamine, bradykinin, prostaglandins, substance P, capsaicin, acidic pH).

Name the causes of a dry cough.

Laryngitis, dry pleurisy, smoking cough, the beginning of certain diseases, lung abscess, lung cancer.

Name the causes of a wet cough.

Acute viral diseases, bronchitis, pneumonia, tuberculosis, bronchiectacic disease.

Common causes of acute cough?

Upper respiratory infection (common cold, acute bacterial sinusitis, pertussis), pneumonia, pulmonary embolus, CHD.

Causes of sub-acute cough? (3-8 weeks)

Post infectious resulting from persistent airway inflammation or post nasal drip following viral infection.

Causes of chronic cough?

Asthma, COPD, lung cancer, esophageal disease, post nasal drip, ACEi.

Name 6 drug classes used in the treatment of cough.

Antitussives, expectorants, mucolytics, antihistamines, bronchodilators, pharyngeal demulcents.

How do antitussives work in the treatment of cough?

They depress the cough centre in the medulla oblongata or the cough receptors in the throat, trachea or lungs.

Name types of antitussives.

Centrally acting antitussives-narcotics (codeine, hydrocodone) non-narcotics-(dextromethorphan).

Peripherally acting (lidocaine, antihistamines.

Locally acting agents (throat lozenges, cough drops).

How do expectorants work in the treatment of cough?

They increase the leaking of fluid out of lung tissue and into the airways. This thins the thick mucous in the airways so it can be removed more easily, therefore decreasing cough.

What is the most commonly used expectorant?

Guaifenesin (research does not support its effectiveness and not recommended by NICE).

How do mucolytics work in the treatment of cough?

They liquefy mucus in the respiratory tract.

Name the only agents that are recommended as mucolytics.

Sodium chloride solution and acetylcysteine.