Asthma Flashcards
define asthma
chronic inflammatory condition of the airways
three main characteristics of asthma
- airflow limitation
- airway hyper responsiveness to various stimuli
- bronchial inflammation with T lymphocytes, mast cells and eosinophils
main causes/ triggers of asthma
- environmental exposure
- viral infections
- cold air
- emotion
- irritant dusts
- drugs
- genetic factors
examples of environmental stimulants that can cause an asthma attack
- grass pollen
- pets
- pollution
examples of viral infections that can cause an asthma attack
- rhinovirus
- parainfluenza virus
- RSV
examples of irritant dusts that can induce an asthma attack
- perfume
- cigarette smoke
- airborne dust
examples of drugs that can induce an asthma attack
- NSAIDs (aspirin, ibuprofen and indometacin)
- beta blockers (propranolol)
how does NSAIDs induce asthma?
inhibit the COX pathway so production of thromboxane and some anti-inflammatory prostaglandins is decreased leading to over-production of pro-inflammatory leukotrienes
how does the beta blocker propranolol lead to an asthma attack?
block the effects of adrenaline on beta2-adrenoceptors on smooth muscle causing bronchoconstriction
what is the exercise induced wheeze driven by?
release of histamine, prostaglandins and leukotrienes from mast cells
what causes pathological changes in chronic asthma?
inflammatory cells affecting the bronchioles
pathological changes in chronic asthma
- smooth muscle hypertrophy and hyperplasia
- leakage of interstitial fluid
- increased mucous secretion
- epithelial damage making the bronchi more sensitive as nerve endings are exposed
what do the pathological changes in chronic asthma cause?
narrowing of the diameter of the lumen, constricting the airways
characteristic spirometry in asthma
- reduced FEV1
- reduced FEV1/FVC ratio
characteristics peak expiratory flow rate (PEFR) in asthma
decreased
two stages in the asthmatic reaction when an allergen is inhaled
- immediate
2. delayed/ late-phase
describe the immediate reaction
airflow restriction and bronchoconstriction within minutes of contact with allergen
when does the delayed/late-phase of the asthma attack often occur
6 hours after inhalation of the allergen
in the delayed/late-phase what inflammatory mediators are released
- mast cells (histamine, PGD2 and cysteinyl leukotrienes)
- eosinophils (IL-3, IL-5 and LTC4)
- dendritic cells and lymphocytes (Th2 response)
describe the Th2 response in asthmatic individuals (what cells do the T helper lymphocytes activate)
- mast cells via IL-3, IL-4, IL-9 and IL-13
- eosinophils via IL-3 and IL-5
- IgE
what happens if the allergen is introduced into a healthy individual?
- allergen is phagocytosed by an antigen-presenting cell (dendritic, mast, macrophage) and ingested
- Th1 response (IgG and macrophages)
clinical features of asthma
- wheeze
- episodic SOB (worse at night due to more cytokine release at night)
- non-productive cough (nocturnal cough in young children)
- chest tightness
signs in asthma
- tachypnoea
- wheeze
- hyperinflated chest
- hyper resonated percussion note
- high RR and pulse and inability to complete sentences (in acute)
- cyanosis (severe acute)
investigations for asthma
- peak flow
- spirometry
- skin prick test
