Cardio - Asthma and Respiratory Immunology Flashcards
Describe the epidemiology of asthma
Affects 5.4 million people in the UK
1 million children affected
3 people die every day in UK
£1 billion spent by NHS annually
What are the 4 cardinal features of asthma
- Wheeze ± dry cough (+ shortness of breath or dyspnoea)
- Allergen sensitisation/atopy
- Reversible airway obstruction
- Airway inflammation
What may be associated with the dry cough along with the wheeze
Worse on exertion, with colds or with allergen exposure
What is associated with airway inflammation
Eosinophilia
Type 2 lymphocytes
What are the 3 objective things we use for the diagnosis of asthma
Allergen sensitisation/ atopy
Reversible airway obstruction
Airway inflammation
What does a patent airway allow for?
Laminar flow of air
What type of airway does an asthmatic have even if they are well without treatment
Thickened airway due to wall inflammation and tightened smooth muscles
What causes the wheeze in asthma
Turbulent flow
How do we check for reversible airway obstruction
Spirometry with the use of bronchodilators
Describe the flow vol loop of an asthmatic
We see coving when they patient is breathing out indicating airway obstruction. This is because of an increased resistance in the airway reducing flow rate
What should we see happen in the loop if an asthmatic is given bronchodilators
We should see the coving turn into a more straight laminar flow on the FVL
What does the patient need to do when doing spirometry
Wear nose clips and do a forced expiratory manoeuvre
What do children need in spirometry
Incentive device for cooperation
What do we look for in terms of airway inflammation?
Eosinophilia
What is a local allergen challenge?
When we inject an allergen directly into the airway of a sensitised asthma patient, we see inflammation, swelling and narrowing of the airway after around 10 minutes
What are the 2 stages of allergic asthma pathogenesis
- Sensitisation and exposure to allergens
2. Parallel inflammation and remodelling of the airway
With airway remodelling what do we see
- Increased size and number of smooth muscle cells in airway.
- Increase in matrix size
- Increase in goblet cells in the epithelium to increase mucus production
In airway inflammation what do we see
Recruitment of inflammatory cells, mainly eosinophils
Why do only some people who are sensitised develop asthma?
There is genetic susceptibility combined with environmental exposures (allergen, infection, pollution)
What genes may be associated with susceptibility to asthma
IL33 and GSDMB - patients have multiple mutations
What type of immunity is associated with allergic asthma?
Type 2
How does sensitisation happen in allergic asthma?
Inhaled allergen acts as an antigen which is presented to the DCs of the lungs (APC). DCs then carry them to mediastinal lymph nodes where naive Th0 cells differentiate to Th2 to secrete IL4 IL5 IL13.
What does IL5 do
Recruits eosinophils and promotes their survival
What does IL4 do
Helps the conversion of plasma cells to secrete IgE
What does IL13 do
Promotes mucin secretion
After sensitisation, what happens if antigen exposure happens again?
Antigen is recognised by specific IgE. These then bind to mast cells to degranulate them and give an allergic reaction
What do mast cells release when degranulated
Histamines, eicosanoids, cytokines, chemokines, enzymes, growth factors
What are the 2 main tests for allergic asthma?
Skin prick test
IgE test
What is the skin prick test?
Intradermal injection of positive control (histamine) and negative control (saline), and then house dust mites, dander etc. We then measure response with wheel and flare
What is the IgE test?
We test the blood for specific IgE antibodies
What tests can we use for eosinophilia?
Stable blood eosinophil count
Induced sputum eosinophil count
Exhaled nitric oxide
What is an abnormal blood eosinophil count when normal
≥300 cells/mcl
What is an abnormal induced sputum eosinophil count
≥2.5% eosinophil
What is a contraindication to using exhaled nitric oxide test
If they are using steroids
What else can FeNO be used for?
Measuring compliance of ICS
What are the NICE steps for asthma diagnosis?
Clinical assessment
Objective tests
What do we do in our clinical assessment?
History
Examination
Assess/confirm wheeze when they are acutely unwell
What are our objective tests?
Obstruction - FEv1/FVC
Reversible obstruction- bronchodilator reversibility (BDR)
FeNO
What is the diagnosis for FEV1/FVC
<0.7
What is the diagnosis for Bronchodilator reversibility on obstruction?
≥12%
What is the diagnosis for FeNO in adults
> 40 ppb
What is the diagnosis for FeNO in children
> 35 ppb
How many tests do we need to confirm our diagnosis
2
When do we need to test spirometry or peak expiratory flow?
We need to test these over 2 weeks to show variability
What are the preferred tests for asthma
Spirometry
Consider BDR if spirometry shows obstruction
If we can’t do BDR or spirometry, what should we do.
If child - treat based on prior findings and try again in 6-12 months
If not - consider FeNO
If FeNO doesn’t help with diagnosis, what do we do
Monitor peak flow variability for 2-4 weeks
What is the aim of basic maintenance therapy?
Reduce airway inflammation
What do we include in basic maintenance therapy?
- Inhaled corticosteroids (ICS - reduce eosinophils)
2. Leukotriene receptor antagonist - reduces type 2 inflammation
What is the aim of acute symptomatic relief?
Smooth muscle relaxation
What do we include in acute symptomatic relief?
- Beta-2 agonist
2. Anticholinergic therapies
What steroid sparing therapies can we use for severe asthma?
Biologics to target IgE or for airway eosinophils
What biologics do we have for targeting airway eosinophils
Anti IL5 antibody
Anti IL5 receptor antibody
What is the prime function of inhaled corticosteroids?
Induce apoptosis of eosinophils to reduce inflammation
How do ICS affect Th2?
Reduce the release of cytokines and mediators
How do ICS affect mast cells?
Reduce numbers
How do ICS affect epithelial cells
Reduce cytokines and mediators
How do ICS affect endothelial cells
Reduce leaking
How do ICS affect airway SMC?
Reduce cytokines and increase beta receptors
How do ICS affect mucus glands
Decrease mucus secretion
How can we assess adherence accurately?
Ensure optimal device and technique, and we can attach an electronic device to their ICC inhaler to measure how often they’re taking the dose
What is the threshold for giving ICS ± leukotriene receptor antagonist
Even if an adult of child has mild asthma, they are still given maintenance therapy
What is a common scenario whereby someone with asthma dies?
Someone people fine therefore don’t take their maintenance therapy and suddenly they become exposed to an allergens causing an acute lung attack and thus death in some cases
What is the altered immune response underlying an acute lung attack?
- Increased inflammation, especially alarming (e.g. IL33)
- Decreased IFN-1/3 release and response
- Increased mast cell degranulation
- Increased eosinophil recruitment
- Increased mucus production
- Decreased CD8 and Th1 responses
- Increased Th2 response
- Increased viral replication and slower clearance
What is the effect of an acute lung attack in school age children
Severity of illness is worse:
- Acute wheeze
- Eosinophilia is worse
How do we treat an acute lung attack
High dose of systemic steroids
When do we start anti-IgE therapy
When there is severe asthma that doesn’t respond to ICS or maintenance therapy
What is anti-IgE therapy?
Humanised monoclonal anti-IgE antibody that binds to circulating IgE to prevent interaction with mast cells thus preventing the allergic cascade
Why may anti-IgE therapy not be used indefinitely?
IgE production may decrease over time with biologic therapy therefore there is less need for it
What is the criteria for starting someone on Omalizumab?
- Severe persistent IgE mediated asthma
- 6+ years old
- Optimised standard therapy w/ no response despite good adherence
- Frequent exacerbations
What are the limitations of omalizumab?
- Need a specific IgE range to start - most people don’t have this (30-1500)
- Very expensive treatment
What is the dosage of omalizumab?
Based on weight and serum IgE but normally 2-4 weekly subcutaneous injections
What is Mepolizumab?
Anti-IL5 antibody that regulates the growth, survival, activation and recruitment of eosinophils.
What is mepolizumab used for?
It is used for severe eosinophilic asthma
What is the criteria for mepolizumab?
- ≥300 eosinophils/mcl in the last year
- 4 exacerbations in the last 12 months requiring oral steroids
- After an oral trial for 12 months - you need at least 50% reduction in attacks for continuation
How do we know Anti-IL5 antibodies are effective in asthma?
DREAm trial showed efficacy of anti IL5 antibodies for severe asthma