What is Asthma?

  • Most common childhood disease.
  • Chronic inflammatory disorder of the bronchi.
  • Characterized by episodic, reversible bronchospasm, caused by a bronchoconstrictor response to various stimuli.
  • Triggers differ dependent on the person.
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What is Bronchoconstriction?

  • The lining of the bronchioles become swollen and inflamed.
  • The lumen narrows due to inflammation causing airway oedema.
  • Bronchioles produce excess mucus to trap the antigen - this can cause mucus plugs.
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What is the Pathophysiology of Asthma?

  • Inhaled antigen causes an immune response.
  • The blood vessels become leaky, allowing IgE and eosinophils to travel to the tissues.
  • Antigen activates dendritic cells and macrophages.  These are antigen-presenting cells (APC), they present the antigen to T helper cells.
  • Macrophages begin to engulf and eliminate the antigen.
  • Th1 cells activate lymphocytes (T cells, B cells and natural killer cells).  They also contribute to bronchoconstriction.
  • Th2 cells activate IgE cells and eosinophils.  They are also needed for the proliferation and differentiation of B cells.
  • Eosinophils release neuropeptides which cause tissue injury and airway hyperresponsiveness.
  • IgE cells bind to an antigen and then bind to mast cells causing the mast cells to release histamine.
  • Histamine causes inflammation and contributes to bronchoconstriction.
  • Airway obstruction via inflammation increases airflow resistance and decreases flow rate.  This can trap air.
  • Trapped air leads to decreased diffusion in the alveoli.  This causes VQ mismatch.
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What are the Risk Factors for Asthma?

  • Exposure to allergens/irritants
  • Genetics - If a parent has asthma, the child will be more susceptible to it.
  • Exercise - During exercise breathing is fast and through the mouth.  This causes cold, dry air to reach the lungs which can irritate the airway.
  • Stress - Makes inflammatory response more prominent to environmental triggers.
  • Recurrent Respiratory Infections -
    • Recurrent infections with episodes of wheezing during early life are a risk factor for later asthma diagnosis.  
    • Damage to epithelial barrier causes a risk of severe infections.
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What are the Symptoms of Asthma?

  • Cough - An irritant causes the bronchial tubes to constrict, prompting a non-productive cough.
  • Wheezing - Narrowing of the lumen and excess mucus production can cause mucus obstructions in the airway.  These causing a 'wheeze' sound as air is inspired/expired.
  • Tachycardia - Heart rate increases to compensate for lack of oxygen being transported to the blood.
  • Tachypnoea -  As the airway narrows, less oxygen is inspired.  When CO2 levels rise, the pH of the blood drops.  This sends a message to the medulla to increase the respiratory rate to get a higher level of oxygen into the body.
  • Shortness of Breath - The lungs can't hold as much air due to inflammation and mucus build-up.
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What are the Treatments for Asthma?

  • Respiratory Assessment - Chest observed for pattern of breathing, symmetry of movement and accessory muscle usage.  A doctor will listen to chest for wheezing, stridor and air entry/exit.
  • Monitoring
    • ECG - monitor heart rate (side effect of salbutamol is tachycardia).
    • Blood gasses - monitor oxygen and carbon dioxide levels in the blood.
    • Peak flow - measure how quickly air can be expelled from the lungs (indicates a narrowing of the bronchioles).
  • Inhaled Corticosteroids - taken daily to reverse inflammation of the airway.
  • Salbutamol Inhaler - taken PRN (as needed).  Opens the airway during symptomatic episodes.
  • Oxygen - given during asthma exacerbation.  Reverses hypoxia.
  • Magnesium Sulfate - given during asthma exacerbation.  Relaxes bronchiole muscles and expands the airway.
  • Education - Children and parents taught correct inhaler technique and receive advice on avoiding triggers.
  • Follow Up - Follow up with GP who continues to monitor the patient and prescribe medications.  Asthma clinic review to check symptom management.
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