Asthma Flashcards
What type of disease is asthma?
Obstructive, inflammatory disease - either acute or chronic (autoimmune response to irritants, since the airways are hypersensitive
What is an obstructive disease?
Resistance to airflow - e.g. due to bronchospasm, inflammation, airway fibrosis or loss of elastic recoil
How is asthma characterised?
hyperactive airway response to various stimuli which results in wide spread inflammation and airway narrowing
What are the risk factors for asthma? (7)
Genetically susceptible individuals are exposed to environmental factors
- Family history of asthma or atopic symptoms (too much IgE)
- Occupational exposures - e.g. to dust, fumes, mould
- Smoking
- Obesity
- Stress
- High temperature and humidity
- Exercise
What are the main changes that occur in the airways in asthma?
- bronchospasm in bronchi and bronchioles
- oedema in the mucous membrane of the bronchi and bronchioles
- excessive mucus production by goblet cells
What causes bronchospasm in asthma?
Allergen inhaled (or predisposing factor released) –> binds with 2x IgE on mast cell –> forms antigen-antibody complex –> presented to the bronchial lining –> release of inflammatory cytokines (histamine and prostoglandins) –> trigger actication of eosinophils, basophils and neutrophils –> decrease in AMP in bronchial smooth muscle –> bronchoconstriction
What causes oedema of the mucous membranes in asthma?
Release of inflammatory cytokines by antibody-antigen complex –> increases capillary permeability –> plasma cells cross into the interstitial fluid –> increased interstitial colloid osmotic pressure –> increased filtration –> allows increased immune cells to enter the airway –> increased interstitial fluid
What causes mucus plugging in asthma?
Inflammatory mediators release mucin –> acts on the goblet cells in gel layer of submucosa –> Goblet cells produce more mucus - which is released into the already swollen and constricted lumen –> mucus is thicker and so less easy to move via MCE
Reduced lumen patency increases turbulence of the air as it moves out - far less effective
What occurs during chronic asthma?
Prolonged exposure to an irritant causes increase IgE in the blood –> increased airway hyperresponsiveness –> continual inflammation over time:
Contraction of the smooth muscle leads to hypertrophy - which causes it to take up more space in the lumen = narrowing
Fibrosis of the away walls - remodelling and scarring, means they are less able change caliber
Enlargement of the goblet cells resulting in increased sputum production
angiogenisis - due to increased demand for inflammatory mediators = increased oedema formation = smaller caliber of airway
Continued use of medications reduces their efficiency so the cycle continues
What causes wheezing during asthma, and when does it occur??
Due to reduced airway calliper (bronchospasm, mucus in the airway, submucosal oedema
- In mild exacerbations: end of expiration
- In severe exacerbations: throughout expiration
- In chronic asthma: during both inspiration and expiration
What causes coughing in asthma?
Increased mucus in the airway
Eosinophils can trigger the cough reflex
What causes Shortness of breath (dysponea)
Reduced ability to effectively exhale = feeling of chest tightness - results in hyperinflation of the lungs (air becomes trapped)
Why is there reduced PEFR in asthma?
If airways are constricted then less able to get air out effectively –> reduced PEFR
Can help to predict attacks
Why is asthma worse in the morning?
Because overnight you are supine, allowing mucus and oedema to sit in the airway and increase constriction
Why might a patient have reduced SpO2 and increased SpCO2 in asthma?
Mucus plugging means the patient is less able to exhale CO2
Retention of CO2 increases RR to try and blow off excess CO2
Results in a viscous cycle where more CO2 is retained and O2 is less able to reach the small airways
