A Guide to Asthma - Medicine BM5 RCR1

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  • Asthma
    • Epidemiology
      • 5.4 million people in the UK receive treatment
      • Affects approximately 1 in 10 children suffer
      • Costs the NHS about £1billion p/a
      • The UK has one of the highest prevelances and mortality rates
    • Defined as a disease of the conducting airways associated with widespread airway narrowing
    • Clinical Presentation
      • Breathlessness
      • Wheeze
      • Cough
      • Chest tightness
      • Rhinitis
      • Exacerbating factors
        • Cold weather
        • Exercise
        • Pollution
        • Working environment
        • Common allergens (house dust mite, grass pollen, cats & dogs)
      • Diurnal variation
      • Risk factors
        • Smoking
        • FH of asthma
        • Eczema
        • Premature birth
        • Low birth rate
        • Maternal smoking
    • Asthma can be classed as allergic and non-allergic
      • Allergic asthma tends to have childhood onsent, test positive to IgE allergy tests and respond well to treatment
      • Non-allergic asthma tends to have adult onset, react negatively to allergy tests and responds less well to treatment (higher doses of steroid required)
    • Investigations
      • PEFR
        • Influenced by gender, age, height and co-morbidities
        • 15% variability between days
        • Will be reduced
      • Spirometry
        • FEV1 - voume of air forcefully expired from full inflation in the first second. mesaured in litres.
        • FEV1/FVC ratio should be over 75%.
        • FVC - total volume of air that can be forcefully expired from total lung capacity. If the majority of FVC exhalation takes over three seconds --> obstructive lung disease.
    • Immunology
      • Allergen is inhaled
        • Mast cell degranulation
          • Release of mediators
            • Preformed e.g. histamine
            • Newly formed e.g. leukotrienes & prostaglandins
        • Activation of dendritic cells
          • Antigen fragment is presented along with MHCII on cell-surface membrane
            • Interacts with TH2 cell receptor
              • interaction between  CD80/CD86 & CD28 triggers co-simulatory signal that activates TH2 cell
                • Activated TH2 cell secretes cytokines
                  • IL5 - Activates eosinophilic inflammatory process
                  • IL13 & IL4 activate B cells, which secrete antibodies and promote IgE class switch
                    • IgE released
                      • IgE activates FC epsilon R1 receptor on mast cells
                        • Mast cell degranulation
                          • Release of mediators
                            • Preformed e.g. histamine
                            • Newly formed e.g. leukotrienes & prostaglandins
    • Treatment
      • 1.Short acting B2 agonist e.g. Salbutamol
      • 2. Add an inhaled corticosteroid e.g. Beclometasone/ Fluticasone (200-800mcg)
      • 3. Add a long-acting B2 agonist e.g. Salmeterol
      • 4. Increase steroid dose (up to 20000mcg daily), or add a leukotriene receptor antagonist (e.g.montelukast), methylxanthine (e.g.theophylline) or anti-IgE drug (e.g. omalizumab)
      • 5. Move to an oral steroid e.g. Prednisolone
    • Airway smooth muscle contraction
      • Bronchodilation: Circulating adrenalineacts on B2 adrenoceptors
      • Bronchoconstriction: ACh acts on M3 receptors
      • Parasympathetic

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