23. Asthma Flashcards
Define ‘asthma’
Long term inflammatory disease of the airways
Results in airflow obstruction that is reversible
Characterised by spasms of the bronchi
Describe asthma
Decrease in the lumen of the airways due to inflammation
There is hypertrophy of the airway muscle wall, increased mucous production and inflammatory cell infiltration
Produces wheezing - cough and get breathless
Is generally atopic
Give the pathogenesis of asthma
Allergens activate Th2 cells which release IL4
IL4 (and 13) activates B cells - the B cells produce IgE - the IgE activates mast cells
IL4 also activates mast cells
The mast cells (also activated by IL4, 6, 9, IgE) release mediators of inflammation - histamine, kinins, PGD3 and LTC4
These mediators activate nerve endings, produce mucous, produce airway wall oedema and cause bronchoconstriction
What different components can cause asthma?
Genetics
Allergens
Irritants e.g. dust
Infection - e.g. chest infection inflames the airways and they are then more likely to get irritated
Exercise - exercise induced asthma i.e. this is the only time they get their symptoms and their wheezing
Changing hormone levels - worse symptoms in a woman during her period
Why else may a patient be wheezing? (not asthma)
Bronchilitis - in children
Upper airway obstruction e.g. epiglotitis
Upper airway dysfunction
COPD
How would asthma present on a spirometer? (physiology of asthma)
During an asthma attack, all indices of expiratory flow are reduced - peak flow, FEV1, FEV1/VC (these then increase following treatment with a bronchodilator)
The vital capacity is also reduced due to closure of the airways
What is peak flow?
The person’s maximum speed of expiration
This is the best way to analyse obstructive diseases - measured morning and evening and measurements vary between the two - the worse the asthma is, the greater the difference
How can you measure flow through the airways easily to be able to diagnose a patinet?
Can use flow volume loops - these show the maximum inspiratory and expiratory flow
You can then see if this matches a flow loop of someone with restrictive or obstructive respiratory disease
Define asthma, relating to peak flow
20% variation of peak flow for three days a week, for two weeks on their PEFR diary
Airflow through a tube - what components can impact the flow?
Radius of the tube (raised to the fourth power)
Viscosity of the gas
Pressure difference across the tube
Length of the tube
What is ‘challenge testing’ and how is it used in asthma diagnosis?
Monitor the peak flow (PEFR) over time and see what happens when the patient comes into contact with an allergen e.g. pets
What stimuli can be used in challenge testing?
Histamine
Metacholine
Allergens (may be a bit risky)
Cold air - this is cheap and easy
What is ‘bronchial hyper reactivity’ and how does this differ to asthma?
This is a bronchial spasm due to an irritant only - there is no involvement of allergens
The person experiences coughing, wheezing and breathlessness in response to an irritant
Aka. Reactive Airways Dysfunction Syndrome (RADS)
What is the lung function of an asthma patient between asthma attacks?
In some instances this will be reduced but in many patients, lung function may be normal between attacks - normal PEFR, FEV1, FEV1/VC, VC
What are common allergens causing asthma?
Dust, dust mite, grasses, tree pollen, pet fur, urine
