ASTHMA Flashcards
What is asthma characterised by?
Chronic inflammatory condition of lung airways characterised by reversible airflow obstruction and bronchospasm
What 3 characteristic physiology happen?
- Reversible airflow limitation (spontaneously or with treatment)
- Airway hyper-responsiveness
- Inflammation of the bronchi with T cells, mast cells, eosinophils and smooth muscle hypertrophy, mucus plugging and epithelial damage
What is intrinsic asthma?
o definite external cause
o often starts in middle-age (late onset) though these pts often have a Hx of respiratory problems indicative of asthma
What is extrinsic/ atopic asthma?
o no causative agent found
o frequent in atopic individuals
o late onset in adults causes may be via sensitization of chemicals at work
What % of population?
5-8%
How many adults/ children receiving treatment in UK?
1 in 12 children and 1 in 10 adults are receiving treatment for asthma in UK
What causes intrinsic asthma?
no causative agent
Starts middle age (late onset)
What causes extrinsic asthma?
definite cause identified
• More common atopic individuals
• Positive skin prick for common inhaled antigens
• 90% children and 50% adults with asthma
What are the causes of asthma?
- Atopy – atopic triad of hayfever (allergic rhinitis), atopic eczema and asthma
- Genetic
- Environment
o Allergen exposure – especially in early childhood
o Air pollution exposure
o Maternal smoking
o Viral respiratory infections e.g. RSV, rhinovirus
o Occupational sensitizers eg isocyanates
o Extreme exertion – exercise
Hygiene hypothesis
Describe the Type I (IgE mediated) Hypersensitivity Reaction
• Bronchoconstriction/bronchospasm (SM spasm narrowing airway)
• Inflammation
o Caused by mast cells, eosinophils, dendritic cells and lymphocytes
• Mast cells increased in epithelium and surface secretions
• Histamine, prostaglandin D2 and leukotriene C4 released
• Eosinophils found large numbers in bronchial walls and secretions – attracted to region by cytokines (IL3, IL5) and chemokines
o Combined with bronchial hyper responsiveness
• Hyperresponsive – incr in IgE leads to increased responsiveness of the airway
• Increased mucous production (plugging airways)
• Airway remodelling
o Loss of ciliated cells due to epithelial damage
o Increase in mucous-secreting goblet cells due to metaplasia in response to epithelial damage
o Thickened basement membrane due to deposition of repair collagens
o Smooth muscle hyperplasia causes more sustained contraction
o Nerves contribute to irritability of asthmatic airways
• Paroxysmal and reversible obstruction of the airways
Risk factors
Anti-inflamm drugs Hx of atopy Obesity Air pollutant Beta-blockers Early exposure to broad-spectrum antibiotics Smoking Childhood viral infections Premature and low birth weight
Symptoms
- Recurrent episodes
- Wheezing
- Coughing (often nocturnal)
- Sputum – can appear pus-like due to white cells; can be hard to bring up
- SOB
- Chest tightness
- Triggered by cold air, URTIs, exercise, pollution, allergens, occupation
- Intermittent/ Nocturnal dyspnoea – diurnal variation; morning dipping
Signs
- Tachypnoea
- Wheeze - widespread polyphonic (audible)
- Hyperinflated chest
- Hyper-resonant to percussion
- Decreased air entry
- Severe attack: inability to complete sentences, pulse >110, RR >25, PEFR (peak expiratory flow rate) 33-55% predicted
- Life-threatening attack: silent chest, cyanosis, bradycardia, exhaustion, confusion, feeble respiratory effort, PEFR <33%
Signs of severe attack
Inability to complete sentences
Pulse >110
RR >25
PEF 33-50% of predicted
Signs of life-threatening attack
Silent chest Cyanosis Bradycardia Exhaustion PEF <33%predicted Confusion Feeble resp effort
Investigations of acute asthma
PEF Sputum culture Bloods: FBC, U&Es, CRP, cultures ABG – normal or slightly red PaO2 and low PaCO2 (hyperventilating). If PaCO2 raised – refer ICU CXR – exclude infection or pneumothorax
Investigations of chronic asthma
PEF monitoring: diurnal variation of >20%on >3d a week for 2 weeks
Spirometry: obstructive defect (decr FEV1/FVC – FEV1 more decr than FVC. Usually improvement in FEV1 >15%following B2 agonists or steroid trial
CXR: hyperinflation
Skin prick tests – allergens
Histamine or methacholine challenge
Ạspergillus serology
What steps are there in investigating?
- Peak Flow
- Spirometry – measures volume of air pt able to expel after full inspiration; differentiates between obstructive and restrictive disease; can give indication of severity; shows reversibility
- Exercise tests
- Prednisolone trial
- CXR
- Skin prick tests – help identify allergic cause
- Allergen provocation tests
What results would you see in peak flow?
o Not a definitive test
o Useful for monitoring and management
o Best done with patient standing
o Peak flow reduced
What results would you see in spirometry?
o Patient sat down, breathes in fully, then breathes out as fast and hard as possible and keeps going until nothing left
o If FEV1 improves more than 12% following bronchodilator therapy then asthma likely
o Can be normal when asymptomatic so does not exclude
o If normal while symptomatic then asthma is unlikely
What results would you see in exercise tests?
o Widely used for diagnosis in children
o Run for 6mins on a treadmill so HR >160bpm
o Or cold air challenge but a –ve result doesn’t rule out asthma.
What results would you see in prednisone trial?
o Prednisolone 30mg daily for 2wks with lung function measured before and immediately after the course
o >15% improvement diagnostic
