Cough

Basics

Description

  • A reflexive or voluntary expulsion of air to clear airways, triggered by irritants, inflammation, or disease, usually accompanied by a distinctive sound
  • Phases of the cough reflex:
    • Inspiratory phase: Deep inspiration
    • Compression phase: Glottis closes; expiratory muscles contract increasing intrapulmonary pressure
    • Expulsion phase: Glottis opens, releasing high-pressure air
    • Clears secretions foreign material
  • Control mechanisms:
    • Involuntary: Regulated by vagal afferent nerves via the brainstem cough center
    • Voluntary: Under cortical control, allowing suppression or initiation:
      • Because of cortical control, placebos can have a profound effect on coughing
  • Reflex pathways and stimuli:
    • Activation of afferent neurons to the central cough center followed by efferent output to the respiratory muscles
    • Afferent sensory activation:
      • Mechanical receptors (larynx, trachea, carina) detect touch/displacement
      • Chemical receptors (larynx, bronchi) respond to gases, fumes, irritants
      • Common Triggers: Mucus, edema, pus, thermal stimuli
    • Efferent response: Central cough center triggers expiratory muscle contraction
  • Classification of cough:
    • Acute (<3 wk): Usually self-limited, often viral
    • Subacute (3–8 wk): Follows infection, may resolve spontaneously
    • Chronic (>8 wk): Requires further evaluation for underlying cause
    • Wet (productive): Produces mucus, helps clear airways
    • Dry (non-productive): No mucus, often irritative
    • Reflex: Protective response to airway threats
    • Inflammatory: Due to airway or lung irritation
    • Neurogenic: Triggered by hypersensitive cough pathways
  • Complications of severe coughing:
    • Epistaxis
    • Subconjunctival hemorrhage
    • Syncope
    • Pneumothorax
    • Pneumomediastinum
    • Emesis
    • Hernia
    • Rectal prolapse
    • Incontinence
    • Intracranial hemorrhage
    • Spinal epidural hemorrhage

Etiology

  • Acute:
    • Pneumonia
    • Acute bronchitis
    • Sinusitis
    • Pertussis
    • Tuberculosis
    • Upper respiratory tract infection
    • Cough variant asthma
    • COPD exacerbation
    • Bronchiectasis
    • Pulmonary embolism
    • Left ventricular failure
    • Airway obstruction (food, pills)
    • Gastroesophageal reflux disease (GERD)
    • Allergies
    • Bronchospasm
    • Hypersensitivity pneumonitis
  • Subacute:
    • Postinfectious cough
    • Pertussis
    • Bronchitis
    • Bacterial sinusitis
    • Asthma
    • GERD
    • Postnasal drip (upper airway cough syndrome)
    • Pulmonary embolism
  • Chronic:
    • Upper airway cough syndrome
    • Asthma
    • GERD
    • Chronic bronchitis
    • Tuberculosis
    • Bronchiectasis
    • Eosinophilic bronchitis
    • ACE inhibitor use
    • Bronchogenic carcinoma
    • Malignancy (primary or metastatic lung cancer, lymphangitic carcinomatosis)
    • Sarcoidosis
    • Interstitial lung diseases
    • Left ventricular failure
    • Aspiration syndrome
    • Somatic cough syndrome
    • Tic cough

Pediatric Considerations

  • Most frequent causes:
    • Asthma
    • Viral illness
    • Acute bronchitis
    • Pneumonia
    • Sinusitis
    • GERD
  • Less common causes:
    • Tracheobronchomalacia
    • Mediastinal tumor
    • Acyanotic congenital heart disease
    • Ventricular septal defect
    • Patent ductus arteriosus
    • Pulmonary stenosis
    • Tetralogy of Fallot
    • Lodged foreign body
    • Chronic aspiration of milk
    • Environmental exposure
  • Consider:
    • Neonatal history
    • Feeding history
    • Growth and developmental history
    • Allergies
    • Eczema
    • Sleep disorders

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