Nature Of Airway Obstructon Flashcards
How can airways become obstructed?
Hypertrophy of the muscle in the structure
Narrowing of the lumen of the airways due to mucus or foreign bodies
Destruction of surrounding or supporting structures
How do the airways change from central to peripheral?
What are the obstructive conditions of the airways?
Bronchieactasis
Emphysema
Asthma
What is the most common obstructive airway disease?
Asthma
What is asthma?
Exposure to allergen which is taken up by dendritic cells that presents to Th2 cells. Chronic inflammation of the airways characterised by a Th2 immune response that increases IL-4, IL-5, IL-13 which initiates eosinophil activation and mast cell degranulation for bronchoconstriction of the airways.
It causes wheeze, shortness of breath, chest tightness, and cough with limitation of expiratory flow.
What are the acute changes in asthma?
Inflammatory mediators act on airway structures such as tissue and blood vessels for:
Vasodilation, plasma leakage and oedema
Mucus hypersecretion
Sensory nerve activation due to exposure to triggers results in reflex bronchoconstriction, by cholinergic receptors.
What are the chronic changes in asthma?
Subepithelial fibrosis and smooth muscle hypertrophy.
How is asthma diagnosed?
Performing reversibility testing. This is done by using spirometry for testing lung function before medication and after medication of a bronchodilator. If lung function improves, it indicates obstructive lung disease.
What patient signs and symptoms are used for asthma diagnosis?
History of a wheeze and variable PEF or FEV1.
History of atopy
Recurrent episodes of symptoms with variability.
Absence of symptoms of alternative diagnosis
How can peak expiratory flow rate be used?
Peak expiratory flow meter is used to measure flow rate of air in a forceful expiration which provides an indication of ventilation adequacy and airflow obstructive diseases only. PEFR is typically higher in male patients and taller patients.
The measures are effort dependent and vary depending on the meter used. It is important that patients report it twice daily for 2-4 weeks.
How can the peak expiratory flow rate variability be measured?
Difference between Highest reading - lowest reading/ mean of the highest and lowest days.
What is significant PEFR variability?
10-20% variability is the upper limit of normal PEFR range. Any greater is considered concerning.
How is bronchoconstriction assessed in diagnostic testing?
Administration of mannitol via inhalation results in the release of inflammatory mediators such as histamine and prostaglandins. For those with hyperreactivity in asthma, this results in bronchoconstriciton.
Bronchoconstriction is a key feature in asthma triggered by an allergen or exertion such as exercise. This causes an increase in osmolarity and dehydration that mannitol mimics.
How is eosinophilic inflammation assessed in diagnostic testing?
Fractional exhaled nitric oxide, a value for the level of inflammation in the lungs by the levels of the inflammatory mediator nitric oxide present in breath.
What is mannitol?
An osmotic diuretic used to decrease intracranial pressure. It acts on the PCT and Loop of Henle to reduce water re-absorption, with a loss of Na+. Due to a loss of water, there are more solute particles per litre, which results in an increase of osmolarity.
Which are the tests for atopy?
Blood test for total IgE levels and radioallergosorbent test
Skin prick test
What are the types of asthma?
Atopic asthma
Non-allergic asthma
Persistent limitation asthma
Asthma and obesity
Atopic asthma is the most common type.
What are the features of atopic asthma?
Identifiable triggers with childhood onset and driven by eosinophilic inflammation. It is the most common form of asthma
What are the features of non-atopic asthma?
Less common form of asthma triggered by exertion or infection. There is an absence of an eosinophilic response and is driven by neutrophil influx
What is persistent limitation asthma?
Asthma with persistent airflow obstruction is when treatment fails to reverse or only incompletely reverses airflow obstricton that has an unknown cause. This is a feature also present in COPD.
What is the link between asthma and obesity?
Obesity results in systemic inflammation and mechanically results in airway narrowing and resistance, with little presence of eosinophilic inflammation.
What is COPD?
Irreversible expiratory airflow obstruction in the lungs which limits expiration and results in hyper expansion of the lungs due to loss of elastic recoil and airway narrowing from inflammation. There is a severely reduced FEV1, with a low FEV that results in a FEV1/FVC ratio of less than 0.7.
Over time, the chronic hypoxia can lead to pulmonary hypertension.
What is the presentation of COPD?
It is characterised by dyspnoea, chronic cough, that may be productive, recurrent wheeze, weight loss, fatigue and chest tightness.
What are the risk factors for COPD?
Smoking
Abnormal lung development
Genetic predisposition
->These result in acute exacerbations of respiratory symptoms and COPD is linked to chronic comorbidities such as cor pulmonale, which is right sided heart failure due to hypoxaemia inducing vasoconstriction.