Asthma L18 Flashcards
What are the 2 main pathological components of asthma?
- Smooth muscle contraction
- Airway inflammation
IgE mast cell interaction
What is the mechanism here? (2)
- IgE binds to mast cells
- When in contact with the specific allergen causes mast cell degranulation
Name the 2 targets for asthma treatment.
- Smooth muscle
- Inflammation
Smooth muscle is under both sympathetic and parasympathetic control. ____1____ control (through the Vagus nerve) causes constriction, so blocking this is a target for muscle relaxation.
Another key controller of the smooth muscle is circulating ____2____ which binds to the B2 adrenergic receptors on the surface of the muscle cells. Both ____1____ and adrenergic control cause the release of cyclic AMP (cAMP) within the cell which causes relaxation of the smooth muscle.
- Parasympathetic
- Adrenaline
Treatments based on targeting airway smooth muscle
Aim is to:
- Increase cAMP levels in muscle cell
- Decrease intracellular calcium
- Muscle relaxation
What can we do to achieve this? (4)
- Block Vagus nerve
- Increase stimulation of B2 receptors
- Theophylline reduces break down of cAMP thus increasing intracellular levels
- Displace calcium with magnesium to lower calcium levels, leading to relaxation
Asthma treatments
Describe the difference in effect between bronchodilators and anti-inflammatory agents.
Bronchodilators have an immediate effect. Anti-inflammatory agents have a less immediate effect due to the time it takes for the inflammatory response to die down. But the effects are more long lasting.
BTS/SIGN guidelines for asthma management
List the methods of diagnosing asthma. (6)
- Symptoms
- Presence of airflow obstruction
- Variability of airway calibre
- Response to bronchodilator
- Response to bronchoconstrictor
- Airway inflammation
- Blood eosinophilia
- Sputum eosinophilia
- Exhaled air nitric oxide
- Airway biopsy
Read
One of the key features of asthma = variability of symptoms.
Exercise and cold air tend to dry out the airways. This drying out is a stimulus for contraction of the smooth muscle.
Important hormones = growth hormone, cortisol and adrenaline. All are bronchodilators and work by relaxing smooth muscles. There is little of the hormones circulating in the early hours of the morning which leads to asthma attacks being a distinct problem during sleep.
Spirometry is an important tool in diagnosing and quantifying asthma.
Why is the reliability of spirometry dependent on when the measurement is taken though?
As most asthmatics breath normally throughout the day and would therefore be negatively diagnosed if they were tested at this time.
If FEV1:FVC <__% = airway obstruction
70
Define FEV1.
The volume of air that can forcibly be blown out in one second, after full inspiration.
Define FVC.
Forced vital capacity (FVC) is the volume of air that can forcibly be blown out after full inspiration, measured in litres.
Define peak expiratory flow.
A person’s maximum speed of expiration.
Read
FEV1/FVC ratio (FEV1%)
FEV1/FVC (FEV1%) is the ratio of FEV1 to FVC. In healthy adults this should be approximately 70–85% (declining with age). In obstructive diseases (asthma, COPD, chronic bronchitis, emphysema) FEV1 is diminished because of increased airway resistance to expiratory flow; the FVC may be decreased as well, due to the premature closure of airway in expiration, just not in the same proportion as FEV1 (for instance, both FEV1 and FVC are reduced, but the former is more affected because of the increased airway resistance). This generates a reduced value.