W5 Molecular Pathophysiology of Asthma Flashcards
What is Asthma?
What does the degree of resistance depend on? (2)
Asthma is an obstructive disease (Affects expiration more than inspiration)
* There is resistance to the flow of air through the airways during inspiration and expiration.
- The degree of resistance depends on:
– Airway diameter
– Laminar or turbulent flow
What are the FEV % when a patient has an obstructive disease?
FEV1/FVC ratio reduced in comparison to normal
FEV1 < 80% and FEV1/FVC <70%
What is FEV1?
Forced Expiratory Volume in 1 second
(amount of air you can blow out in one breath)
What are the symptoms of Asthma:
Recurrent episodes of: (4)
More symptoms?
- Dyspnoea (SOB/laboured breathing)
- Wheezing
- Tight chest
- Cough (sometimes)
- Shortness of breath
- Chest tightness or pain
- Wheezing during exhalation
- Coughing or wheezing attacks that are worsened by a respiratory virus
- Chronic unproductive cough
- Significantly variable breathlessness
- Night-time wakening with breathlessness and/or wheeze
- Significant diurnal or day-to-day variability of symptoms
- Acute Sever Asthma: (status asthmaticus) not easily reversed, causes
hypoxaemia, may require hospital treatment
Asthma facts (for info)
- UK prevalence: approx. 4% population
- Half are children
- Prevalence is increasing (since 70s)
- In children, more common in boys
- In adults, more common in women
- Diagnosis of asthma is a clinical one;
– there is no standardised definition of the
type, severity or frequency of symptoms, nor of the findings on investigation
What type of disorder is asthma?
What are the 3 main factors?
A chronic inflammatory disorder of the airways
* Airflow limitation is widespread, variable, and reversible
* In response to variety of stimuli
* Obstructive disorder
3 main factors:
* airway constriction
* airway hypersensitivity and responsiveness
* mucous hyper-secretion
What are the causes of asthma?
Host factors and environmental
exposures
Genetic factors:
Cytokine response profiles
Age
Environment:
Allergens
Pollutants
Infection
Stress
What does inflammation (in asthma) lead to? (3)
- Airway Obstruction
- AHR/bronchospasm (airway hyper responsiveness)
- Airway remodelling
What are the trigger factors for Asthma? (7)
- Allergens - house dust mite, pollen,
moulds, animals - Chemicals - paints, hair sprays
- Drugs - aspirin, ß-blockers, NSAIDs,
- Foods - colourings, nuts, preservatives
- Environmental chemicals - cigarette smoke, wood dust
- Infections - LRTI
- Miscellaneous - cold air, exercise, stress, workplace
Asthma can be categorised into Extrinsic or Intrinsic Asthma:
What is extrinsic also known as?
=Allergic asthma
Specific trigger causes EXTRINSIC asthma
Non-specific trigger causes INTRINSIC asthma
e.g. allergens = specific= extrinsic
so2/smoke/cigarete smoke= both
cold dry air, exercise, virus, drugs= non-specific= intrinsic
What is Atopy?
- The propensity to develop IgE antibodies to common antigens
- Associated to susceptibility to develop asthma, allergic rhinitis, eczema
- 1/3 of population have +ve skin tests
– 1/3 of these will develop asthma
– House dust mite, grass pollens, animal dander are commonest - Early onset asthma
– 98% have +ve skin tests
– more likely to have a history of eczema or family history of asthma - Late onset asthma
– 76% have +ve skin tests
dendritic cell=antigen-presenting cell
T helper cell stimulates immune response by
Asthma Attack: Biphasic
What are released in the early/symptomless phase?
What is the late phase driven by?
Early phase
* Increase in resistance to airflow
– peaks 30-60 min after allergen exposure
– subsides 30-90 min later (due to bronchoconstriction)
* Immediate response to release of
inflammatory mediators from MAST CELLS
Late phase
* Can occur a long time after allergen exposure
– 6+ hours
– night time asthma.
* Driven by a continuation of inflammation
characterised by an influx of EOSINOPHILS into the lungs
What is mucous plugging and hyperinflation?
Mucous blocking bronchus
- Inspiration air is allowed into alveolus
Inflammation causes swelling of tissue due to Oedema. What does this lead to?
Wall of bronchus swells so diameter of lumen decreases
