CR: PBL 5 (Asthma) Flashcards
What is asthma?
Spasm in bronchi of lungs, causing difficulty in breathing, resulting from an allergic reaction or hypersensitivity
What is peak flow?
Device measures maximum air flow out of lungs during forced expiration
What does salbutamol do?
Causes bronchodilation
Describe the pathophysiology of asthma
Allergen exposure –> antigen moves through epithelia of bronchi –> antigen binds to IgE-mast cell complex –> degranulation of mast cell –> release of histamine, proteases and chemotactic factors –> bronchoconstriction, vasodilation and increased vascular permeability –> eosinophils and neutrophils drawn in from the blood –> inflammation and redness
What is status asthmaticus?
Asthma attacks follow one another without pause
How can asthma be diagnosed with peak flow tests?
When the volume of air that can be forced out of the lungs in one breath is reduced
How can asthma be diagnosed with spirometry tests?
Measures FEV1 and FVC and compares them to averages measurements for people of same age, sex and height
How is asthma treated?
Reliever inhalers and preventer inhalers predominantly (can use oral steroids)
Describe how ‘reliever inhalers’ work
Contain short-acting beta 2 agonist
Describe how ‘preventer inhalers’ work
Reduce inflammation and sensitivity of airways to prevent asthma attack by containing an inhaled corticosteroid
Why may oral steroids be given in the treatment of asthma?
To regain control of asthma when it’s temporarily upset or when long-term control of asthma remains a problem despite maximal doses of inhalers
Why are steroids not commonly used as a long-term treatment of asthma?
Have serious possible side effects
What are some of the potential side effects of oral steroids taken for more than 3 months?
Osteoporosis, hypertension, diabetes, increased appetite, cataracts, glaucoma, skin thinning, muscle weakness
Describe the mechanism of action of salbutamol
Bind to b2 adrenoreceptors on bronchial smooth muscle –> activation of adenyl cyclase –> catalyses ATP to cAMP –> cAMP lowers intracellular Ca2+ concentration –> smooth muscle relaxation and high cAMP levels inhibit bronchoconstrictor mediators e.g. histamine and leukotriene from mast cells
Describe how corticosteroids work
Inhibit the recruitment of inflammatory cells (T cells, mast cells, eosinophils and dendritic cells) by suppression of chemotactic factors and adhesion molecules
Why was the patient in status asthmaticus suffering from alkalaemia?
Tachypnea/hyperventilation removed more CO2 than normal so there is less CO2 to combine with water and form H2CO3 and therefore H+ ions are used to buffer this change, and therefore the pH increases
What is involved in a long-term asthma plan
Proactive monitoring and managing of symptoms, reducing exposure to allergens,
What controls respiration?
Respiratory centres in the brainstem
How do higher centres of the brain contribute to respiratory control?
Involved in voluntary control (pain, emotion, temperature) and changes the impulses from the pontine respiratory centre to the medullary respiratory centre to affect the lungs
How do peripheral chemoreceptors contribute to respiratory control?
Carotid and aortic bodies detect changes in blood composition, and if there is more CO2, less O2 and decreased pH –> stimulates increased breathing rate
Do chemoreceptors respond more quickly to CO2 or O2 changes?
CO2 accumulation
How do central chemoreceptors contribute to respiratory control?
Medullary chemoreceptors and respond to increase in CO2 –> increased breathing rate
How do receptors in muscles and joints contribute to respiratory control?
Respond to contraction/exercise to increase the breathing rate
How do irritant receptors in the lungs contribute to respiratory control?
Aim to help exhale irritant –> supress inhalation in medullary respiratory centre –> blowing off substance
How do stretch receptors in the lungs contribute to respiratory control?
Prevent extreme over-inflation of the lungs (Hering-Brever reflex) –> reduces inspiration size
What is the role of the pontine respiratory centre?
Interacts with the medullary respiratory centre to smooth/coordinate res
What is the role of the medullary respiratory centre?
To control inspiration of diaphragm and breathing rhythm
What are the two aspects of the medullary respiratory centre?
Dorsal - inspiration of diaphragm
Ventral - breathing rhythm
What is the normal oxygen saturation for a healthy adult?
95-100%
How can asthma be distinguished from COPD during lung function tests?
Peak flow wouldn’t improve after salbutamol use in COPD
Describe the symptoms of a severe asthma attack
SaO2 25/min, Inability to complete sentences in one breath
Define hypocapnia
Having an abnormally low arterial carbon dioxide level
Why may an asthmatic have hypocapnia?
Hyperventilation leads to excess CO2 removal leading to less than normal –> hypocapnia
How can beta 2 adrenoreceptor agonists be used in the treatment of asthma?
Mimics sympathetic bronchodilator action and acts as a bronchodilator. Activates adenylate cyclase to increase cAMP and may also reduce mediator release from inflammatory cells and airway nerves.
What is FVC?
Functional vital capacity (volume of hair that can be maximally exhaled)
What is FEV1?
Forced expiratory volume in one second (amount of air you can breathe out in 1 second)
Why may reliever inhalers be insufficient in status asthmaticus?
There is often smooth muscle hypertrophy and basement membrane thickening, so smooth muscle relaxation still may not notably improve the flow impedence in the airways (remain largely obstructed)
Which receptors can contribute to increasing respiratory rate?
Higher centres of brain, peripheral and central chemoreceptors, receptors in muscle and joints
Which receptors can contribute to decreasing respiratory rate?
Higher centres of brain, irritant and stretch receptors in the lungs
What is the Hering-Brever reflex?
reflex triggered to prevent over-inflation of the lung. Pulmonary stretch receptors present in the smooth muscle of the airways respond to excessive stretching of the lung during large inspiration –> reduces inspiration size
