“Chronic reversible airway obstruction characterised by reversible airflow limitation, airway hyper-responsiveness to stimuli and bronchial inflammation

Risk Factors
  • Modifiable:
    • Obesity
    • Smoking
    • Exposure to occupational triggers
    • Exercise (exercise-induced asthma)
  • Non-Modifiable:
    • Allergy (atopic triad = asthma, allergic rhinitis, and eczema)
    • Exposure to atmospheric pollutants
    • Exposure to irritant dust/fumes
    • Cold air
Aetiology
  • Low childhood allergen exposure (hygiene hypothesis)
  • Airway hyperresponsiveness
  • Maternal smoking
  • Drugs (e.g. NSAIDs/ beta-blockers)
  • Smoking
  • Genetic component
Pathophysiology
  • Airflow limitation:
    • The airway lumen is reduced due to airway inflammation and smooth muscle hypertrophy due to chronic bronchoconstriction.
    • Airway inflammation is primarily mediated by eosinophils, mast cells and T lymphocytes.
  • Bronchial hyper-responsiveness:
    • Excess goblet cells and eosinophils in the respiratory epithelium → mucus hypersecretion.
    • Increased numbers of mast cells in the lamina propria → mast cell degranulation → mass histamine release (causes hypersensitivity).
  • Airway inflammation:
    • Inflammatory processes also result in oedema and plasma exudate, which further reduce airflow.
    • In chronic asthma, airway remodelling can result in some element of irreversible airway obstruction.
Clinical Presentation
  • Asthma causes acute episodes of symptoms including:
    • Wheezing
    • Chest tightness
    • Shortness of Breath
    • Tachypnoea.
  • Individuals can have a frequent cough (productive in some).
  • Symptoms are often worse at night (patient may report waking up breathless at night) and can occur after exposure to a known trigger or exercise
Investigations
  • Imaging:
    • Chest X-Ray – can show hyperinflated chest during an acute attack
  • Special:
    • Peak flow (↓ PEFR) twice a day – should show a pattern of diurnal variation.
    • Spirometry – ↓FEV1:FVC ratio that increases >15% after administering a bronchodilator (reversibility here distinguishes from COPD
    • Corticosteroid trial –  30mg prednisolone given for 2 weeks; LFTs before and immediately after the course.
Management
  • Reliever therapies (bronchodilators):
    • SABA (salbutamol)
    • LABA (salmeterol)
    • LAMA (tiotropium)
    • Theophylline
  • Preventer therapies:
    • ICS
    • Cromones
    • LTRAs
    • Biologics (omalizumab)
Complications
  • Acute severe asthma (can be fatal)
  • Anxiety
  • Inability to exercise

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