Respiratory System >
“Chronic reversible airway obstruction characterised by reversible airflow limitation, airway hyper-responsiveness to stimuli and bronchial inflammation“
- Exposure to occupational triggers
- Exercise (exercise-induced asthma)
- Allergy (atopic triad = asthma, allergic rhinitis, and eczema)
- Exposure to atmospheric pollutants
- Exposure to irritant dust/fumes
- Cold air
- Low childhood allergen exposure (hygiene hypothesis)
- Airway hyperresponsiveness
- Maternal smoking
- Drugs (e.g. NSAIDs/ beta-blockers)
- Genetic component
- 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.
- Asthma causes acute episodes of symptoms including:
- Chest tightness
- Shortness of Breath
- 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
- Chest X-Ray – can show hyperinflated chest during an acute attack
- 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.
- Reliever therapies (bronchodilators):
- SABA (salbutamol)
- LABA (salmeterol)
- LAMA (tiotropium)
- Preventer therapies:
- Biologics (omalizumab)
- Acute severe asthma (can be fatal)
- Inability to exercise