Asthma Flashcards
What is asthma?
A reversible increase in airway resistance involving bronchoconstriction and inflammation
What is asthma characterised by?
A reversible decrease in FEV1:FVC (less than 70%)
Variations in PEF
What does COPD encompasses? And what is it characterised by?
Chronic bronchitis (increased mucus, airway obstructions intercurrent infection)and emphysema (destruction of alveoli)
Characterised by reduced FEV1?, and little variation in PEV
How are airway SM controlled by the ANS?
The parasympathetic system via the vagus nerve causes mucus secretion and bronchoconstriction of the airways by secreting Ach at muscarinic M3 receptors
The sympathetic system produces dilation of the airway by release of NA/A at b2 adrenoceptors. Also, its fibres release NA that act on adrenoceptors of parasympathetic system to inhibit its transmission. In addition,b2 adrenoceptors are present in mucus glands to inhibit its secretion
What is an asthmatic attack caused by?
Exercise, allergens, cold air, smoking, viral infection
What are the clinical features of athsma?
Tight chest Wheezing Cough (worst at night) Breathlessness Decrease FEV1 (reversed by b2 agonists)
How do you diagnose asthma?
Lung function test showing reduction in FEV1 that is reversible with b2 agonists.
What is asthma triggered by?
Stimulus that causes activation of mast cells and mononuclear cells to produce spasmogens and chemotaxins
Name some spasmogens and state where they originate
Histamine (originate from mast cell degranulation) Leukotrienes C4 and D4 (from arachidonic acid acted upon by LOX to form LKT) Prostaglandins D2 (from AA acted upon by COX) both spasmogen and bronchoconstrictor
Name some chemotaxins
PAF platelet activating factor
Leukotriene B4
Why Are b2 agonist first choice from asthmas management? Give examples
Eg: salbutamol, salmeterol (long acting, both reliever and preventer)
It increases FEV1
Act on adrenoceptors of the airways SM to increase cAMP that phosphorylate MLCK (causing its inhibition) and therefore relaxation occurs (action Switched off by PDE which degrade cAMP). It also decreases intracellular calcium and inhibits inflammatory mediators
What other drugs are used for asthma management?
Xanthines, adenosine receptor antagonist (eg: theophylline): used as second line for bronchodilation. Given orally or i.v. in emergency. It is a phosphodiesterase inhibitor hence prevent the breakdown of cAMP to prolong relaxation
Corticosteroids (eg: beclometasone inhale, prednisolone oral): anti-inflammation, act on intracellular receptors to alter gene expression to decrease production of cytokines and increase production of lipocortin/annexin1 (which inhibit PLA2 and therefore production of free AA)
Steroids reduce receptor downregulation when given with b2
Leukotriene receptor antagonist (eg: montelukast): acts as preventive and bronchodilator, antagonise action of LTs.
Omalizumab: monoclonal antibody directed against free IgE. Prevent it from binding to immune cells and triggering the allergic asthma.
What is the step by step guideline for asthma management?
- Beta 2 + regular inhaled steroid
- LABA, LTRA or xanthines
- Increase dose of inhaled steroid
- Add oral steroid
What drugs are used for COPD management?
Roflumilast: selective PDE IV inhibitor
Muscarinic receptor antagonists (eg: ipratropium, tiotropium): block parasympathetic bronchoconstriction and mucus secretion
Describe the Pathophysiology of asthma
- Bronchospasm which causes narrowing of the lumen.
- Mucous layer swells up
- Increase secretion of mucus that gets into the narrow lumen and creates bubbles (responsible for the popping and wheezing during asthmatic attack)
All the above are due to pairs of IgE that bind to the mast cells and cause their degranulation nad release of histamines
