ASTHMA PATHOPHYSIOLOGY, CAUSES, SIGNS AND SYMTOMS WORK BY: MEGAN, ELIZABETH, JO,GRACE
What makes up the Respiratory System? (http://www.ama-assn.org/ama1/pub/upload/images/446/respiratorydetail.gif
What is the main function? A route for the supply of oxygen to the body and its cells and for the expiration of carbon dioxide. • External respiration – the exchange of gases between the blood and the lungs • Internal respiration – the exchange of gases between the blood and the cells
Control of respiration The respiratory centre is located in the medulla oblongata and the pons (in the brain stem). Chemoreceptors respond to the changes in the partial pressure of oxygen and carbon dioxide in the blood and the cerebrospinal fluid. • Central chemoreceptors – located in the medulla oblongata – when PCO2 rises, they respond by stimulating the respiratory centre to increase ventilation. • Peripheral chemoreceptors – located in the aorta and carotid bodies (in the neck) – more sensitive to small rises in PCO2 and respond by increasing the rate and depth of breathing. Also an increase in blood acidity levels are addressed through increased ventilation.
PATHOPYHSIOLOGY The pathophysiology of asthma is complex and involves the following components: • airway inflammation • intermittent airflow obstruction • bronchial hyperresponsiveness.
AIRWAY INFLAMMATION Airway inflammation in asthma is: • a direct response of the immune system to a trigger • a cascade of immunologic events that includes inflammatory cells and mediators • an immune-mediated process that leads to inflammatory changes in the airway, including eosinophil recruitment and airway oedema.
To understand let’s look at the Immune System The three main components of the immune system are • antibodies • inflammatory cells • inflammatory mediators
ANTIBODIES • An antibody, or an immunoglobulin (Ig), is a small protein molecule created by the immune system to have a close structural "fit" to the surface of a foreign substance. • The foreign substance is an antigen. • The primary job of antibodies is to bind to an infectious agent (a virus, bacteria, or parasite) and, in so doing, to notify and trigger the rest of the immune system to fight off this invader.
INFLAMMATORY CELLS • Inflammatory cells circulate in the bloodstream and can "sense" the body's surroundings or exposures to create immune responses directed against those exposures.
INFLAMMATORY MEDIATORS • Inflammatory mediators are chemical substances that are secreted by immune cells to induce (or respond to) an ongoing immune response generated against a specific exposure to the body e.g. histamine, mast cell tryptase, leukotrienes, prostaglandins, eosinophil cationic protein, and cytokines.
OK!. Relate that to asthma……. • Antibodies (IgE) bind to mast cells and basophils around the bronchial blood vessels recruiting inflammatory cells(notably eosinophils) to the site • If allergen encountered again, reaction releases histamine and bradykinin leading to bronchospasm, oedema,and excessive secretion of thick mucus
BRONCHIAL HYPERSENSITIVENESS • The fundamental defect in asthma is that, for reasons that are unclear, these inflammatory actions occur in the bronchioles when no serious infection, toxin, or other inhaled threat to the body exists.
Controlling airway caliber • Smooth muscle in the bronchial wall can contract or relax, without conscious control, to result in constriction or dilation of the airway. • The airway smooth muscle allows the body to change airway diameter for different environmental conditions. • The body may respond to an inhaled noxious stimulus — such as smoke or another toxic irritant — by causing the airways to constrict. • This "clamp down" of the airway smooth muscle, sometimes termed bronchospasm, can serve to protect the delicate alveoli from toxic damage.
CONT…. • During an asthma attack, the lining of the bronchial tubes swell, causing the airways to narrow and reducing the flow of air into and out of the lungs.
GOT THE 3 PROBLEMS! SO WHAT ARE THE REPERCUSSIONS…….. • Bronchi and bronchioles are chronically inflamed • Oedema formation • Production of thick tenacious mucus • Bronchial smooth muscle spasms • Impaired mucocilliary function • Thickening of airway walls
MORE……….. • Increased contractile response of bronchial smooth muscles • Cell damage caused by eosinophil infiltration
Mmmhhhhh…… • Airway obstruction increases resistance to airflow and decreases flow rate, primarily expiratory flow • The differences in air resistance leads to uneven distribution of inspired air as more air flows to the less resistant areas • Hyperventilation triggered by increased lung volume • Interpleural and alveolar gas pressure rises causing decreased perfusion of alveolar
Mmmmhhhhh…… • Leads to variable and un-even ventilation-perfusion variable within different lung segments
WHAT COULD BE THE CAUSES OF SIMON’S ASTHMA THEN? Allergens • Animal dander (from the skin, hair, fur or feathers of animals) • Dust mites (contained in house dust) • Cockroaches • Pollen from trees and grass • Mould (indoor and outdoor) • Fungal spores
CONT….. Irritants • Air pollution - Passive smoking from tobacco smoke, or vehicle exhaust fumes • Fumes given off by cleaning products and solvents in the home including floor cleaners, room fresheners and polish • Cold air • Strong odours from painting or cooking • Scented products • Strong emotional expression (including crying or laughing hard) worry and stress • Chemical irritants in the workplace
However, there are other causes • Medicines such as aspirin and beta-blockers • Sulphites in food (dried fruit) or beverages (wine) • A condition called gastroesophageal reflux disease that causes heartburn and can worsen asthma symptoms, especially at night • Diet - Foods such as nuts and shellfish • Genetic - A family history of asthma, eczema or allergies • Exercise – Especially when cold. • Changes in the weather • Urbanization has also been associated with an increase in asthma
More trouble…………. • Many aspects of modern lifestyles – such as changes in housing and diet and a more hygienic environment – may have contributed to the rise in asthma over the last few decades • Latex gloves - wood dust - flour dust • Research has shown that smoking during pregnancy significantly increases the risk of a child developing asthma • Children whose parents smoke are more likely to develop asthma • Viral and bacterial chest infections.
Therefore……. • Any of these causes could explain Simon’s asthma symptoms • To help identify triggers and to confirm sensitisation Simon could have a skin prick test. • This is a specific IgE blood test for the suspected allergen. • Simon then could have perhaps been given avoidance advice.
SIGNS AND SYMPTOMS OF ASTHMA Classified according to levels of severity: Moderate asthma • expiratory wheeze • dry non-productive cough • dyspnoea • chest tightness • PEFR of 50% or more
SIGNS AND SYMPTOMS OF ASTHMA Acute severe asthma • PEFR of 33% - 50% • respiratory rate of 25 / minute or more • severe dyspnoea • inability to complete sentence in one breath
SIGNS AND SYMPTOMS OF ASTHMA Life threatening asthma • PEFR of 33% or less • bradycardia • oxygen saturation levels of 92% or less, • PaO2 of 8kPa or less • dysrhythmia, • hypotension • chest silent - exhaustion • cyanosis • confusion
SIGNS AND SYMPTOMS OF ASTHMA Near fatal asthma • symptoms similar to life - threatening asthma (above) • raised PaCO2, and / or requiring ventilation.
References • Alexander, M. F., Fawcett, J.N. and Runciman, P. J. (2005) Nursing practice, hospital and home: The adult. 3nd ed. Edinburgh: Churchill Livingston. • Brooker, C and Nicol, M (eds) (2003) Nursing Adults The Practice of Caring, London: Mosby • www.asthma.org.uk • www.nhs.direct.uk • www.who.int/respiratory/asthma/causes • www.amaassn.org/ama1/pub/upload/images/446/respiratorydetail.gif