What are the 3 main characterisations of asthma?
Reversible airflow limitation
Airway hyperresponsiveness
Inflammation of the bronchi
What is the meaning of the term Atopy? What are atopic individuals prone to?
A genetic predisposition to IgE-mediated allergen sensitivity -
People are prone
- Allergic asthma
- Atopic dermatitis
- Allergic rhinitis
What is the Hygiene hypothesis?
Reduced exposure to infectious pathogens at a young age predisposes individuals to autoimmune and allergic disease in western countries.
What is aspirin induced asthma? What triad condition do individuals present with?
When asthma attacks can be triggered by aspirin due to a sensitivity - People have SAMTERS TRIAD
- Asthma
- Aspirin sensitivity
- Nasal polyps
What is occupational asthma?
When asthma is triggered by occupational exposures
High molecular weight
- Compounds trigger on a IgE response
- Effects are immediate as soon as person is exposed
- Flour
- Latex
Low molecular weight
- a complex immune response develops after repeated and long-term exposure
- wood dust
- isocyanates
To aid in diagnosing occupational asthma, the patient should keep a diary of what?
Peak expiratory flow diaries during periods of work and holiday
What is exercise induced asthma?
triggered by strenuous physical activity
What are key concepts in the early phase of asthma?
Inhalation of allergens causes type 1 hypersensitivity reaction in the airways
Sensitisation begins to develop causing the release of IgE antibodies
The IgE binds to mast cells
Subsequent exposure to antigen cases mast cells to degranulate and histamines to be released.
This causes smooth muscle contraction and bronchoconstriction (bronchospasm’s) whilst inflammation contributes to airway obstruction, oedema and mucous
late phase - Th2 helper cells -> B cells -> IgE & eosinophils -> • Constriction • Muco-secretion
What are key concepts in the late phase of asthma?
Early phase may be followed by late phase hours later
Inflammatory mediators are recruited (e.g. polymorphonuclear cells, T-cells)
Do beta beta agonists cause complete reversal of the late phase?
No - it is more complex
In asthma chronic inflammation occurs. How does the airway change/ respond to this?
- Fibrous tissue develops
- Airway remodelling causes airway obstruction which manifests as airway narrowing which is irreversible
What are the signs and symptoms of asthma?
Symptoms
- Cough (may be worse at night)
- Dyspnoea (SOB)
- Chest tightness
- Poor sleep
Signs
- Expiratory polyphonic wheeze
- Prolonged expiratory phase
- Tachypnoea
- Harrisons sulcus ( a groove at the inferior border of the rib cage that may be seen in children with chronic severe asthma. Also seen in rickets.)
What are the characterisation and symptoms of an asthma attack?
- Worsening of normal symptoms
- Reduction in PEF
In more severe attacks patients have signs of respiratory failure -
- Tachypnoea
- Tachycardia
- Inability to complete sentences
- Exhaustion
- Reduced respiratory effort
- Silent chest
- Altered conscious level
There are 2 main types of receptors in the airways. What are the names and what does activation of them do?
Sympathetic -> β2 receptors -> bronchodilation & mucociliary clearance
Parasympathetic -> muscarinic receptors
-> bronchoconstriction
What is the formula for flow?
Pressure change/Resistance
What is (Pouseille’s law?
resistance = 1/r4
List 5 extrinsic causes of asthma
Air pollution • Allergen exposure • Maternal smoking • Hygiene hypothesis • Genetics
List 2 key features of intrinsic asthma
Intrinsic -
- non allergic
- less responsive
Which drugs are known to trigger asthma?
Aspirin and beta blockers
Which of the many features of asthma if present make it more likely? (6)
More than one of:
- wheeze
- breathlessness
- chest tightness
- cough
variability - worse at night and in the morning
Triggered by allergies, exercise, drugs cold air
Atopic features
Family history
Low PEFR AND FEV
Features/ symptoms make asthma less likely? (8)
- Dizziness
- Peripheral tingling
- Productive cough in the absence of wheeze of breathlessness
- Consistent normal examination with breathless
- Voice disturbances
- Symptoms only with colds
Significant smoking history (>20 pack years ) - Cardiac disease
- Normal PEF or FEV1 when symptomatic
List 5 possible differential diagnosis for a wheeze
Asthma
COPD
Obstruction e.g. foreign body
Anaphylaxis
Pulmonary oedema
List the main differences between asthma and COPD
Asthma -
- Daily FEV1 variation
- Reversibility
COPD
- Older >35
- Smoking history
- Sputum production (chronic productive cough)
- Persistent/progressive breathlessness
- Variability uncommon
Which diagnostic investigations are conducted to diagnose asthma and what would the results show? (5)
Spirometry - FEV1/FVC <70% ratio
Bronchodilator reversibility -
- FEV1 pre and post beta agonist inhibition
- > 12% or 200ml improvement in FEV1
Fraction exhaled nitric oxide
normal is >25
Asthma is >40ppd
Direct challenge testing (eg
methacholine)
drop in FEV1 when exposed to provoking substance e.g. histamineor methacholine concentration required to cause 20% fall in FEV1 (PC20) OF 8mg/ml or less
Low false negative rate
Peak flow variability
