Asthma Flashcards
What are the common effects of asthma?
Muscle oedema - excess mucous production + thickening of sub mucosal layer leading to substantial narrowing of airways.
Smooth muscle hypertrophy and overactive, increasing sensitivity to stimuli (exercise, temperature, allergen)
What is asthma?
Chronic inflammatory disorder of the airways leading to variable airflow obstruction.
This is a reversible condition (often spontaneous reversibility, or reversible with treatment)
What are the two main types of asthma?
Extrinsic: common in children
Intrinsic: usually develops in adulthood
How does asthma differ from other respiratory diseases like COPD?
In the reversibility nature. COPD is not reversible
What can reduce incidence of exercise induced asthma?
Proper warm up and cool down
What is extrinsic asthma..
A type of asthma, common in children and is associated with a genetic disposition.
This is precipitated by a known allergen like mould or pollen.
What is intrinsic asthma?
Usually develops in adulthood.
This is triggered by non-allergenic factors like viral infections/irritants, exercise, or emotional upset.
What is the pathophysiology of acute inflammation asthma?
Acute inflammation is caused by an inhaled allergen in allergic patients leading to an early phase allergic reaction which may be followed by a late phase reaction.
What happens in the early phase of acute asthma inflammation?
There is an activation of cells bearing IgE antibodies in response to an allergen.
This causes rapid activation of airway mast cells + macrophages.
These release pro inflammatory mediators (histamines + eicosanoids), inducing contraction of airway smooth muscle.
Mast cells also secrete mediators (PAF + LTB4) leading to narrowing of airways,
There is also plasma protein leakage which induces a thickened airway wall and narrowing of airway lumen with reduced mucous clearance.
This results in narrowing of lumen of the airways and airflow obstruction
What happens in the late phase of acute asthma inflammation?
This late phase usually occurs 6-9 hours post allergen aggravation. Antigen presenting cells (macrophages) engulf the antigen and present it to CD4+ T lymphocytes, thus activating them.
The CD4+ T lymphocytes in turn activate monocytes, eosinophils, basophils, neutrophils which secrete various chemicals to stimulate submucosal oedema leading to airway narrowing
What is the pathophysiology of chronic asthma inflammation?
Lymphocytes secrete mediators which initiate eosinophilopoesis.
Lymphocytes also secrete chemicals which damage epithelial cells
Eosinophils secrete cytokines and various mediators thus also damaging epithelial cell wall, resulting in damaged epithelium, mucous overproduction, and hyper responsiveness
What is PAF and LTB4?
Platelet activating factor and Leukotriene B4
These mediators are secreted by mast cells in the early phase of acute asthma inflammation and result in narrowing of the airways
What are IgE antibodies?
Allergen specific immunoglobulin E antibody
What is eosinophilopoesis?
An increase in eosinophil production in bone marrow
This is initiated by mediators secreted by lymphocytes in chronic asthma inflammation
What do eosinophils do?
In asthma they migrate to the airways to release inflammatory mediators (LTs, granule proteins) cytotoxic mediators and cytokines
What do T lymphocytes do?
In asthma, these are activated by antigen presenting cells.
Their activation leads to the release of cytokines
What happens in mast cell degranulation?
This results in the release of mediators (histamine, eosinophil and neutrophil chemotactic factors) in response to allergens
What do alveolar macrophages do in asthma?
Release inflammatory mediators (platelet deriving factor and leukotrienes)
What do neutrophils do in asthma?
They are a source of mediators (including thromboxanes, leukotrienes, and platelet activating factors)
What are common triggers of asthma?
Respiratory infection: cold, flu
Allergens: airborne pollens, dust mites, animal dander, fungal spores, moulds,
Environment: cold air, fog, tobacco smoke
Emotions: anxiety, stress, laughing, pre-menstrual changes
Medications: NSAIDs, β-blockers, aspirin (if patient allergic, do not give nurofen as they are from same family.)
Food additives: food colouring, preservatives, strong smells
Occupational stimuli: fumes, chemicals, dust
How is asthma typically presented clinically?
Wheezing, breathlessness, chest tightness, increased night time cough
Tiredness with activities you would normally complete easily
Decrease in PEFR (<350-400 )
Worsening allergy symptoms (persistent runny nose, dark circles under eyes, itchy inflammed skin)
Ronchi
What is ronchi?
The coarse rattling sound somewhat like snoring
This is usually caused by secretion in bronchial airways
What happens in exercise induced bronchospasm?
During exercise, pulmonary functions FEV1 and PEFR increase during the first few minutes, but begin to decrease after 7 mins
There is a refractory period lasting up to 3 hours after exercise (which will fail to produce EIB or will produce a lesser reaction)
Patients will respond to histamine hence acute hypo responsiveness of airway smooth muscle does not appear to be a factor
How is EIB defined?
Exercise induced bronchospasm:
A drop in FEV1 greater than 15% of baseline
What factors should be considered in the differential diagnosis of asthma?
Chest X-rays can be used to exclude other things (infections like pneumonia)
Airway obstruction showing reversibility requires administration of treatment if FEV1 improves by 15% or PEFR increases by 200mL. This confirms asthma
If person is smoker and does not show reversible airway obstruction, assess them for COPD
What are the drug classes involved in the treatment of asthma?
β adrenergic bronchodilators Antimuscarinics bronchodilators Inhaled corticosteroids Oral corticosteroids Leukotriene receptor antagonists Sodium cromoglycate
What is the mechanism of action of β2 agonists?
Dilate bronchi by direction action on β2 adrenoreceptors of smooth muscle.
Stimulation activates cytoplasmic G proteins, -> production of cAMP
This decreases unbound intracellular Ca producing smooth muscle relaxation, mast cell membrane stabilisation and skeletal muscle stimulation
There is a need to monitor serum potassium due to hyperkalaemia
This class of drugs is further divided into short acting and long acting