asthma - pathophysiology

Question 1

pathophysiology of asthma?

Answer 1

chronic inflammatory process by TH2 cells
macrophages process & present antigens to T lymph
activates TH2 cells - release cytokines (interferons etc.)
cytokines attract & activate inflammatory cells (mast cells & eosinophils)

Question 2

what do TH2 cells activate in asthma pathophysiology?

Answer 2

TH2 cells activate B cells to produce IgE
eosinophils release leukotriene C4 - toxic to epithelial cells, causing it to shed (eosinophils sensitive to steroid therapy)

Question 3

2 phase response of asthma?

Answer 3

1. immediate (20mins)

2. late phase (3-12 hrs)

Question 4

immediate response of asthma?

Answer 4

type 1 hypersensitivity reaction
caused by interaction of allergen (antigen) with IgE
mast cell degranulation - release mediators (histamine - bronchoconstriction, prostaglandin (vasodilate), leukotriene)
cause bronchial SM contract - bronchoconstriction (histamine)

Question 5

late phase response of asthma?

Answer 5

3-12 hours, type IV hypersensitivity
involves full spectrum of inflammatory cells (eosinophils, mast cells, lymphocytes, neutrophils) - release lots of mediator & cytokines
cause airway inflammation

Question 6

signs and symptoms of asthma?

Answer 6

wheeze - airways compressed
breathlessness (RR, tracheal tug, IC & subcostal recession, nasal flaring, accessory muscles)
chest tightness
dry cough - worse at night, exercise induced

Question 7

the airway inflammation causes reduced airway calibre (airway narrowing) due to what?

Answer 7

1. mucosal swelling (oedema) - vascular leak (histamine)
   thickening of bronchial walls - infiltration of inflammatory cells
2. mucous over production & abnormal mucous produced (thick), airways occluded by mucous plugs if severe
3. SM contraction (histamine H1 receptors)
4. epithelium shed (leukotriene C4 from eosinophils) - into thick mucus

Question 8

functions of histamine?

Answer 8

vasodilation
leaky capillaries
bronchoconstriction via H1 receptors on SM

Question 9

what are the effects of asthma on gas exchange?

Answer 9

airway narrowing: reduced ventilation of affected alveoli (V/Q mismatch in affected area)
hyperventilation of well ventilated areas can’t compensate for hypoxia, but can compensate for CO2 retention by increased breathing out of CO2

Question 10

what does a flow volume loop look like in asthma?

Answer 10

low PEFR, early scalloping
air trapped - increased residual volume
obstructive pattern on spirometry (FEV1:FVC <70%)