Asthma Flashcards
Define Asthma
A chronic lung condition that exhibits symptoms of coughing, wheezing and chest tightness.
It involves chronic airway inflammation, airway hypersensitivity & Variable airflow limitation
Describe asthma phenotypes
Extrinsic phenotypes (allergic)
Occurs in atopic individuals who have an overactive immune system
EP has a genetic component e.g. ADAM33
Produces IgE antibodies to many common allergens, IgE production mediates inflammation
Intrinsic (non-allergic)
Has no identifiable triggers and presents itself in middle age, it involves local inflammation.
It can be induced by occupation, aspirin induced or food induced
Describe the cellular mechanisms involved in asthma
The main immune cells involved are T-helper 2, mast cells and eosinophils
Inflammatory cells, such as T-helper 2 (Th2) lymphocytes, mast cells, eosinophils, and neutrophils, are activated in the airway. Th2 cells, in particular, release cytokines (e.g., interleukins IL-4, IL-5, IL-13) that drive the inflammatory process.
Mast cells produce mediators such as histamine which has a direct effect on the bronchioles smooth muscle, causing bronchospasm as well as increased mucus production & vascular leakage.
Eosinophils are recruited to the airways in response to IL-5. These cells release toxic proteins and inflammatory mediators that contribute to airway damage and remodeling.
Describe the pathophysiology of asthma
An inhaled allergen is engulfed by dendritic cells, T helper 2 cells become activated, which then release cytokines and interlukins.
- IL3/4 produce IgE antibodies from B cells which bind to mast cells
- IL9 produces mast cells & activates them
- IL5 promotes esinophil production from bone marrow
Inhaled allergen binds to mast cells/IgE which releases inflammatory mediators e.g., histamine, leukotrienes
Smooth muscle contraction: In response to mediators like histamine and leukotrienes, the smooth muscle surrounding the bronchi contracts, causing the airways to narrow.
Mucus hypersecretion: The inflammatory process also triggers excessive mucus production from goblet cells, which can further obstruct the airway.
A late reaction will occur 6-8 hours after exposure, it will result in long-lasting inflammation
Describe airway hyperresponsiveness
Asthmatics have hypersensitive airways that can become easily triggered & react to otherwise harmless susbtances. Asthmatics react to irritants at lower levels.
It causes airway inflammation, high levels of esinophils, bronchospasm & bronchoconstriction & mucus hypersecretion
Describe airway remodelling in asthma
Chronic inflammation can lead to structural changes in the airways.
Thickening of the basement membrane: The epithelial layer of the airway becomes thicker due to fibrosis (scar tissue formation).
Smooth muscle hypertrophy: The smooth muscle surrounding the bronchi may increase in size and number, contributing to increased airway tone.
Mucus gland hyperplasia: There is an increase in the number of goblet cells, which further contributes to mucus obstruction.
Bronchial hyperresponsiveness, Airways become more easily triggered over time
These changes can lead to irreversible airflow obstruction over time & cause a worse clinical outcome, so early diagnosis & treatment is important to reduce inflammation
Describe lung function in asthmatics
Spirometry may be normal if a person is asymptomatic.
After the patient inhales a bronchodilator spirometry is repeated to measure how much FEV1 improves. A significant improvement ( more than a 12% increase in FEV1) is considered indicative of asthma, as it shows that the airway obstruction is reversible.
In asthma, FEV1 is often reduced due to airflow limitation. A significant reduction in FEV1 indicates the degree of obstruction.
In asthma, FVC may be normal or reduced depending on the severity of the condition.
In asthma, this ratio is typically reduced because FEV1 is reduced more significantly than FVC, indicating airflow obstruction.
A ratio less than 70% of the predicted value (depending on age, height, and gender) is generally considered indicative of obstructive lung disease.
Asthmatic tend to have a normal/ increased total lung capacity, with increased airway resistance.
They have a raised residual volume and abnormal blood gases during an asthma attack
Describe the aims in treatment of asthma
- To relieve daytime & nighttime symptoms
- no need for emergency medication
- To prevent limitations on physical activity & flare-ups
- To enable normal lung function e.g., FEV1/FVC % greater than 80%
- To treat asthma with minimal side effects
Describe the use of inhalers in asthma treatment
There are 2 main groups:
Beta2-agonists (salbutamol) and antimuscarinic (anticholinergic) e.g., ipratropium bromide
These can be short or long lasting
SAMA
SABA
LAMA
LABA
Describe Beta2-agonists and their side effects
Beta2-agonists (B2 adrenergic receptor agonists) act on B2 adrenergic receptors and allow smooth muscle relaxation of bronchioles by enabling dilation of bronchi and vasodilation of BV’s
Side effects:
1. Headaches
2. Anxiety
3. Nausea
4. muscle tremors
5. Nervousness
6. Tachycarida or palpitations
Describe glucocorticosteriods & their side effects
GCS are taken via inhalation everyday e.g., betamethasone.
It can also be given orally e.g., in tablet form
In severe cases, it can be given intravenously
side effects:
Severe asthmatics may need large oral doses for a long period, this could cause Cushioned symptoms causing a change in their metabolism of fats, proteins and carbs.
This may cause patients to not take their steroid meds out of fear of developing cushingoid symptoms.
What are the side effects of inhaled steroids
- Thrush (yeast infection) on the tongue, mouth or throat, which can cause discomfort
This can be prevented by rinsing the mouth with water after use.
Typically inhaled steroids at low doses have few side effects
Describe the differences between asthma & COPD
COPD is irreversible progressive obstruction normally caused by smoking, poor bronchodilator response and low gas transfer in emphysema.
It involves inflammatory cells such as neutrophils, macrophages and t-helper lymphocytes. The obstruction caused to the airway is irreversible.
Asthma is an intermittent reversible obstruction triggered by allergens such as pollen, it has a normal gas transfer and a strong response to bronchodilators. It involves inflammatory cells such as Eosinophils that produce IgE, Mast cells, CD4 cells & t-lymphocytes.
The limitation to airways may be fully reversible due to treatment using bronchodilators.
