Asthma Definition

• Asthma - definition:

  • A chronic inflammatory disorder of the airways associated with recurrent episodes of wheezing, breathlessness and cough, variable airflow obstruction and bronchial hyper-responsiveness
• Asthma - epidemiology:

  • Occurs in 5 % of the population
  • Most common in childhood
  • decreases at puberty
  • increases with age
  • Can occur at any age
  • increasing in frequency in patients with multiple medical problems
• • Asthma falls under COPD umbrella along with chronic bronchitis and emphysema
  • these 3 often co-exist with each other

  
• Inflammatory Response:

  1. Macrophages in airway
  2. present antigen to T helper cells
  3. T helper cells activate & secrete cytokines
  4. IgE production & eosinophil recruitment (via cascade response)
  5. IgE binds high affinity receptor on mast cell
  6. Degranulation of mast cell
  7. Release histamine & proteases (allergic response) & Pro-inflammatory cytokines attract neutrophils & eosinophils (prolong allergic response)
• Pathophysiology:

  • Inflammatory response
  • affecting mucosa & sub mucosa which leads to
  • mucosal oedema
  • Bronchospasm - when the muscles that line your bronchi tighten
  • Sputum production
  • Chronic inflammation and remodelling
• Chronic Inflammation:

  • Hypertrophy of smooth muscle
  • Hyperplasia of mucous glands
  • Thickening of basement membrane
  • Continuing cellular infiltration -> Airway remodelling
• Relevance of Clinical Features:

  • Mucosal oedema
  • Bronchoconstriction
  • Sputum production
  • Airway remodelling
  • All of the above lead to:
  • Airway obstruction → Increased airway resistance → Increased work of breathing
• Consequences of Airway Obstruction:

  1. Airflow obstruction occurs due to mucosal oedema, bronchoconstriction, sputum production and later airway remodelling
  2. Air trapping
  3. Hyperinflation
  4. V/Q mismatch
  5. Decrease in compliance
  6. Increased work of breath
• Clinical Features:

  • shortness of breath increases work of breath
  • Wheeze – Diurnal variation
  • Chest tightness
  • Hyperinflation
  • Cough
  • Mucus production
  • Hypoventilation
  • Exercise tolerance