Treating Asthma: Underlying Mechanisms

25.10.05

What is asthma?
• Reversible airways obstruction.
• Characterised by
-wheeze
-expiration greater than inspiration
-younger patient
-small to medium airways
-triggers.

Causes:
• Genes (runs in families).
• Triggers
-infection
-animal dander
-house dust
-coldβ
-exercise
-pollen
-food, drugs etc.
• Inflammation
-mast cell
-lymphocyte
-eosinophil.
• Bronchospasm.
-Sympathetic response [fight of flight - stress-related] = dilate airways - β2 receptors opposite.
-Parasympathetic response [relaxed] = constrict airway - cholinergic receptors.

Clinical features:
• Breathlessness.
• Expiratory wheeze.
• Cough (dry or productive).
• Early morning waking.
• Hyper-expanded chest.
• Low peak flow.

Treatment:
• Acute asthmatic attack.
• Long-term.

Severity of acute asthmatic attack:
• Peak flow.
• Clinical symptoms.
• Chest signs ('silent' chest).
• Arterial blood gases.
NOTE: A 'normal' of high pCO2 may be a danger sign.

Treatment of acute asthma:
• Remove/avoid triggers.
• Treat infection.
• Reverse bronchospasm.
• Reduce inflammation.

Reverse bronchospasm - relievers:
• Immediate relief.
• Treats symptoms.
• Does not prevent attack.

Reduce inflammation - preventers:
• No immediate benefit.
• Treats underlying disease.
• Prevents attacks.

Long-term management
• May not need treatment.
• May need only β2 agonist.
• May need regular inhaled steroid + as-required β2 agonist.
• May need home nebulisers.
• May need long-term oral steroids.
• May need immunosuppressants.