SandBox

Cough

Editor-In-Chief: C. Michael Gibson, M.S., M.D.; Associate Editor(s)-in-Chief:Abiodun Akanmode

Overview

Cough is a physiologic reflex action, it serves to rid the respiratory tract of excessive secretions and other environmental debris such as dust, pollen, and other irritants.

Coughing also referred to as 'tussis' is associated with the rapid release of air from the lung this is associated with the loud and distinctive sound associated with coughing. Cough is the most common cause of visits to primary care doctors and pulmonologist, it accounts for about 40% of outpatient visits.Cough is mostly a symptom of an underlying disease, however, establishing the exact cause of cough can be challenging. While most cough is ussaully acute due to postnasal drip,bronchial asthma and heartburn other more serious causes such as COPD,lung cancer should be considered when a chronic cough is suspected.

Classification

Cough can be classified based on duration i.e

• Acute cough: This type of cough usually presents with a duration of fewer than 3 weeks.
• Sub Acute cough: Last between 3-8weeks.
• Chronic Cough: Chronic cough usually presents for a duration greater than 8weeks.

Cough can also be classified based on sputum production i.e

• Non-productive cough.
• Productive cough.

Pathophysiology

The act of cough is a vital one that occurs through the stimulation of the cough reflex which is a complex relex arc. The cough reflex arc is constituted by 3 main components ie

• The Afferent pathway: This made up of sensory nerve fibers in the ciliated epithelium found in the upper airways. The afferent impulses are transmitted into the medulla.
• The efferent pathway: cough impulse3s that is originated from the cough central travels via the vagus nerve,phrenic nerve and spinal motor nerves to the diaphragm and abdominal wall muscles.
• Central pathway: This is a central area located within the pons and brainstem. It coordinates the cough reflex arc.

The Afferent sensory nerves:There are 3 manjor classes of afferent sensory nerves,this classification is based on there conduction velocity(A-fiber, > 3 m/s; C-fiber, < 2 m/s),origin ,myelination,neurochemistry etc.

• Rapidly adapting receptors (RARs)
• Slowly adapting stretch receptors (SARs)
• C-fibres.

The series of mechanical activities that take place during coughing is divided into 3 phases.

• The inspiratory phase: Here there in inhalation of an appropriate amount of air needed to produce cough.
• The Compression Phase: The contraction of the muscles of the chest wall, abdominal wall, and the diaphragm against a closed larynx brings about a rapid increase in intrathoracic pressure.
• The Expiratory Phase: At this last phase the glottis is open bringing about a large expiratory airflow and the unique sound associated with coughing.

Causes

The common causes of cough are:

• Bronchial asthma.
• GERD.
• Postnasal drip.
• Post viral cough.
• Allergic rhinitis.

Less common causes of cough are:

• Drug use eg: Abacavir, Abatacept, ABVD, ACE inhibitor, Acetylmorphone, Acyclovir, Adalimumab, Adefovir, Albuterol, Alefacept, Alfuzosin, Aliskiren, Amiodarone, Amlodipine and Benazepril, Amphotericin B, Anagrelide, Anastrozole, Artemether/lumefantrine, Atazanavir, Aztreonam, Benazepril, Bepridil, Bevacizumab, Bitolterol, Bortezomib, Brimonidine, Budesonide, Busulfan, Captopril, Carvedilol, Cetuximab, Cevimeline, Chlorambucil, Ciclesonide, Cladribine, Clobutinol, Clofarabine, Clofedanol, Co-trimoxazole, Conjugated estrogens, crofelemer, Cromolyn Sodium, Cytarabine, Dacarbazine, Dactinomycin, Darbepoetin Alfa, Denileukin diftitox, Desmopressin, Diborane,
• Infectious diseases eg.Adenoviridae, Aphthovirus, Ascaris infection, Aspergillosis, Blastomycosis, Bordetella pertussis, Byssinosis, Chickenpox, Chlamydophila pneumonia, Cladosporium, CMV Pneumonitis, Coccidioidomycosis, Community-acquired pneumonia, Cryptococcosis, Fasciolosis, Filariasis, Gnathostomiasis, Histoplasmosis, Human ehrlichiosis, Infectious mononucleosis, Influenza, Lady Windermere syndrome, Lassa fever, Legionellosis, Measles, Melioidosis, Miliary tuberculosis, Mucor.
• Genetic diseases: Cystic fibrosis, Juvenile Myelomonocytic Leukemia (JMML)
• Environmental agents eg: Chronic beryllium disease (CBD), Hay fever, Low humidity, Occupational exposure of irritants Passive smoking, Sick building syndrome, Silicosis, Smoking.
• Malignancies: Cervical mass, Esophageal cancer, Kaposi's sarcoma, Laryngeal cancer, Lymphangitis carcinomatous, Mediastinal tumor, Mesothelioma, Papillomatosis, Thymoma.